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The WQA Glossary of Terms

This Glossary is published by the Water Quality Association (WQA) as a service to members and leaders in education, government, and industry.

© Copyright 2010 by Water Quality Association

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Absolute Filter Rating: Filter rating meaning that 99.9 percent (or essentially all) of the particles larger than a specified micron rating will be trapped on or within the filter.

Absorption: The process of one substance actually penetrating into the structure of another substance.

This is different from adsorption, in which case one substance adheres to the surface of another.

Acid: A substance which releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with a base to form a neutral salt and water.

An acid is the opposite of an alkali, has a pH rating lower than 7.0, will turn litmus paper red, and has a sour taste.

Acid Rain: Precipitation which has been rendered (made) acidic by airborne pollutants.

Acidity: The quantitative capacity of a water or solution to neutralize an alkali. Acidity is usually measured by titration with a standard solution of sodium hydroxide and expressed in ppm or mg/L of calcium carbonate equivalent.

Acidity is usually measured by titration with a standard solution of sodium hydroxide and expressed in ppm or mg/L of calcium carbonate equivalent

Activated Alumina: A medium made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove several contaminants including fluoride, arsenic, and selenium.

This activated carbon medium requires periodic cleaning with an appropriate regenerant such as alum, acid, and/or caustic.

Activated Carbon: A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous substances (bituminous coal or cellulose-based substances such as wood or coconut shell) to 700 degrees C or less in the absence of air to form a carbonized char, and then activating (oxidizing) at 800 to 1000 degrees C with oxidizing gases such as steam and carbon dioxide (oxygen is never used as the oxidizing gas because its reaction with the carbon surface is too rapid and violent) to form pores, thus creating a highly porous adsorbent material.

Activated carbon is commonly used for dechlorination and for reducing trace and soluble materials such as organic chemicals and radon from water.

Activated Carbon Block Filter: Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants.

The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon. Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon.

Activated carbon block filters typically have a 0.5 to 1 micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of Giardia and Cryptosporidium.

Adsorbent: A water treatment medium, usually solid, capable of the adsorption of liquids, gases, and/or suspended matter. Activated alumina and activated carbon are common adsorbents used in water processing.

Adsorption: The physical process occurring when liquids, gases, or suspended matter adhere to the surfaces of, or in the pores of, an adsorbent medium.

Adsorption is a physical process which occurs without chemical reaction.

Aeration: The process whereby water is brought into intimate contact with air by spraying or cascading, or air is brought into intimate contact with water by an air aspirator or by bubbling compressed air through the body of water.

Both pressure (closed) aerators and open (gravity) aerators are used. Closed aeration is used chiefly for oxidation; open aeration for degassing.

Aesthetic Contaminants: Characteristics of water which affect its taste, odor, color, and appearance (and may affect the objects touched by the water) but which do not in themselves have any adverse health effects in otherwise potable water.

Suggested Maximum Contaminant Levels (MCLs) for various aesthetic contaminants in drinking water are part of the National Secondary Drinking Water Regulations issued by the USEPA. These aesthetic standards are advisory only, not enforceable by the USEPA.

Air Gap: A clear vertical space between the end of the water treatment device's drainline and the flood level rim of a receptacle which holds water.

An air gap is used to prevent cross connection between the water treatment device and a possible source of waste water thereby preventing a reverse flow of water from the sewer into the water supply system. Without an air gap, such reverse flow could occur due to an increase in the pressure in the sewer system or the creation of a negative pressure in the water supply line.

Local plumbing codes indicate how wide the air gap needs to be.

Algae: Single-celled or simple multicelled organisms, commonly found in surface water, which produce their own food through photosynthesis.

Excessive algae growth may cause the water to have undesirable odors or tastes, and decay of algae can deplete the oxygen in the water.

Algal Bloom: Sudden, massive growths of microscopic and macroscopic plant life, such as green or blue-green algae, which develop in lakes and reservoirs.

Algicide: Any substance or chemical specifically formulated to kill or control algae.

Alkali: A substance which creates a bitter taste and a slippery feel when dissolved in water and will turn litmus paper blue. An alkali has a pH greater than seven and is the opposite of an acid. Highly alkaline waters tend to cause drying of the skin.

Alkalis may include the soluble hydroxide, carbonate and bicarbonate salts of calcium, magnesium, potassium, and sodium.

A hydroxide alkali may be called a base.

Alkaline: The condition of water or soil which contains a sufficient amount of alkali substances to raise the pH above 7.0.

Alkalinity: The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH.

Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity.

In the water industry, alkalinity is expressed in mg/L of equivalent calcium carbonate.

The following chemical equilibrium equations show the relationships among the three kinds of alkalinity: carbonate (CO32-), bicarbonate (HCO3-), and hydroxide alkalinity (OH-). Total alkalinity is the sum of all three kinds of alkalinity.

CO2 + H2O <===> H2CO3 <===> H+ + HCO3- <===> pH 4.5 pH 8.3 2H+ + CO32-

Above pH 9.5 (usually well above pH 10), OH- alkalinity can exist or CO32- and OH- alkalinities can coexist together. Different tests are used to determine the quantity of the different kinds of alkalinities present in water.

2. A property of water soluble substances (or mixtures) causing the concentration of hydroxyl ions (OH-) in water solutions to be higher than the concentration of hydrogen ions (H+). Alkalinity is exhibited in solution by alkalies such as sodium hydroxide and by alkaline salts such as sodium carbonate.

Soap and soap-based products are alkaline, since soap is a moderately alkaline salt and performs well only in an alkaline medium. Detergent products can be formulated with any desired level of alkalinity as dictated by the needs of the cleaning tasks to be performed.

Since the alkalinity is useful in removing acidic, fatty, and oily soils, most detergents are more effective on laundry soils when on the alkaline side. Generally, alkalinity is supplied to laundry detergents by builders.

All automatic dishwasher detergents utilize alkalinity, as do most cleansers and hard surface cleaners. In contrast, most hand dishwashing detergents are close to neutrality, performing efficiently without alkalinity because of the mechanical action of hand rubbing with sponge or dishcloth.

Ambient: Environmental or surrounding conditions.

Ambient Temperature: Temperature of the surrounding air (or other medium). For example, temperature of the room where a gas chlorinator is installed.

Ammonia: An alkaline gas composed of nitrogen and hydrogen (NH3).

Ammonium: The ionic form of ammonia nitrogen that is usable by plants. See Also ammonia.

Amoeba: A single-celled protozoan that is widely found in fresh and salt water. Some types of amoebas cause diseases such as amoebic dysentery.

Anion: (AN-EYE-on) An ion with a negative charge. An anion [such as chloride (Cl-), nitrate (NO3-), bicarbonate (HCO3-), or sulfate (SO42-)] may result from the dissociation of a salt, acid, or alkali.

An anion [such as chloride (Cl-), nitrate (NO3-), bicarbonate (HCO3->/sup>), or sulfate (SO42-)] may result from the dissociation of a salt, acid, or alkali.

Anion Exchange: An ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger.

Anion Membrane: See Ion Exchange Membrane.

Anode: The positive pole of an electrolytic system; also the metal which goes into solution in a galvanic cell.

Sacrificial anodes of metals such as magnesium, aluminum, or zinc are sometimes installed in water heaters or other tanks to deliberately establish galvanic cells to control corrosion of the tank through the sacrifice of the anode.

Aqueous: (A-kwee-us) Something made up of, similar to, or containing water; watery.

Aquifer: A natural water-bearing geological formation (e.g., sand, gravel, sandstone) which is found below the surface of the earth.

Aromatic: A type of organic compound in which the characteristic chemical groups are linked to a particular type of six-member hexagonal carbon ring which contains three double bonds, typified by benzene. Such rings have peculiar stability and chemical character, and are present in the rather reactive and highly versatile compounds derived from petroleum and coal tar.

The name refers to the strong and not unpleasant odor characteristic of most substances of this nature.

Artesian: (are-TEE-zhun) Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free flowing.

Aseptic: a, not + sepsis, decay

1. Free or freed from pathogenic organisms and their toxins.

2. A sterile condition, free from germs, infection, and any form of life.

Atom: The smallest possible component of an element. An atom is comprised of a nucleus (made up of one or more protons and two or more neutrons except for hydrogen which may have no neutrons) and one or more electrons which revolve around the nucleus.

Atoms come together to form molecules.

Atomic Absorption Spectroscopy: A spectroscopy chemical analytical technique used for determining the metal elements in water by measuring the well-defined characteristic light wave lengths absorbed by each respective element when the element has been thermally excited into an atomic vapor.

The sample to be analyzed is atomized into an atomic vapor by either aspirating the sample into a specific flame (in flame AA) or by vaporization with a tube of graphite that is electrically heated to a temperature between 1500 and 2800 degrees C (in flameless AA). A light beam of specific characteristic wave lengths is directed through the vapor, into a monochromator that further defines the very small range of wave lengths to be analyzed, and into a detector that measures the amount of light absorbed by the atomized element.

Identification of the element is possible because each element has its own well-defined characteristic absorption wave length. The amount of absorbance measured is proportional to the concentration of the element in the sample.

Attrition: The gradual lessening of the capacity or effectiveness of a medium. This may occur due to friction, sacrificial properties of the medium, chemical attack on the medium, or contaminant saturation of the medium.

Automatic Water Softener (or Automatic Filter): A water softener (or filter) that is equipped with a clock timer which automatically initiates the backwash and/or regeneration process at certain preset intervals of time.

All operations, including bypass of treated or untreated water (depending upon design), backwashing, brining, rinsing, and returning the unit to service are performed automatically.

Autotrophic: auto, self + trophe, nourishment

Capable of obtaining food or nourishment from simple raw materials.

Autotrophic organisms or autotrophs are organic compound producers such as algae, plants, and certain bacteria that use carbon dioxide or carbonates, inorganic nitrogen, water, and an energy source such as photosynthesis from sunlight to make (or synthesize) complex molecules.

Opposite of heterotrophic.

Available Chlorine: A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials that are used as a source of chlorine when compared with that of elemental (liquid or gaseous) chlorine.

Axial Flow: See Longitudinal Flow

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Back Pressure: Pressure which creates resistance against a flow of water.

Back Siphonage: A form of backflow which occurs due to negative pressure.

Backflow: The flow of water in a pipe or line in a direction opposite to the normal flow.

Backflow is a problem if there is back siphonage or back pressure causing reverse flow from a cross connection.

Backflow Preventer: A device or system installed in a water line to stop backflow from a nonpotable source.

Backwash: A form of backflow which occurs due to negative pressure.

Bacteria: Single-celled organisms (singular form=bacterium) which lack well-defined nuclear membranes and other specialized functional cell parts and reproduce by cell division or spores.

Bacteria may be free-living organisms or parasites. Bacteria (along with fungi) are decomposers that break down the wastes and bodies of dead organisms, making their components available for reuse.

Bacterial cells range from about 1 to 10 microns in length and from 0.2 to 1 micron in width. They exist almost everywhere on earth. Despite their small size, the total weight of all bacteria in the world likely exceeds that of all other organisms combined.

Some bacteria are helpful to man, others harmful.

Bactericide: Any substance or agent which kills bacteria, both disease causing and nondisease causing.

Spores and nonbacterial microorganisms (e.g., algae, fungi, and viruses) are not necessarily killed by a bactericide.

Bacteriostatic: Having the ability to inhibit the growth of bacteria without destroying the bacteria.

For example, silver-impregnated activated carbon will reduce bacterial colonization in a bed but not eliminate it.

Baffle: A deflecting barrier to affect the flow pattern of water.

Bar: A unit of pressure. One bar equals 14.5 pounds per square inch (psi), or about 0.987 standard atmospheres.

Base: An alkali which releases hydroxyl ions when dissolved in water.

Bead (Resin Bead): In water processing, refers to the spherical shape of individual particles of ion exchange resin products, as compared to the irregular shaped particles of most other granular media products.

Bead Count: A method of evaluating the physical condition (quality) of the resin in a bed by determining the percent of whole, cracked, or broken beads in a wet sample of the resin.

Bed: The mass or volume of ion exchange resin or other media through which the water passes in the process of water treatment.

Bed Depth: The height of the resin or other media (excluding support material) in a bed, usually expressed in inches or centimeters.

Bed Volume (BV): A term used as a measurement of a volume of incoming (feedwater) in gallons or liters, equal to (in cubic feet or liters) the volume of ion exchange or filter media product in a tank-including voids. Example: one bed volume for a cubic foot bed would be equal to 7.48 U.S. gallons or 28.3 liters. This term is used mainly in laboratory and in experimental testing rather than in equipment capacity ratings.

Biodegradable: Subject to degradation (breakdown) into simpler substances by biological action.

For example: the breakdown of detergents, sewage wastes, and other organic matter by bacteria.

Biofilm: An accumulation of sessile microbial growth imbedded in a film of adhesive polymer and attached on the surface of a support material, such as the interior surface of water pipe or water storage vessels.

Bacteria within the film may be protected from the action of disinfectants and sanitizers.

Biogas (Methane): A colorless, odorless, flammable gas consisting of the hydrocarbon (CH4) and resulting from the decay of vegetable matter or manure due to the action of anaerobic bacteria in swampy land, closed landfills, or sewage disposal plants.

Methane is also known as biogas and it is called swamp gas when produced in marshy land. Coal miners know methane as one of the main components of fire-damp and also of coal-gas.

Methane dissolved in water gives the water a milky cast, and since it is flammable, methane must be safely aerated and vented to the atmosphere during removal.

Biological Growth: The activity and growth of any and all living organisms.

Biologically Activated Carbon: Activated carbon which maintains active microbiological growth to aid in the degradation and reduction of organics that have been adsorbed on the surface and in the pores of activated carbon.

Biological activation of carbon can be enhanced by enriching the feedwater with air or ozone.

Bleach: A strong oxidizing agent and disinfectant formulated to break down organic matter and destroy biological organisms.

Commonly refers to a 5.25 percent nominal solution of sodium hypochlorite (household bleach) which is equivalent to 3 percent to 5 percent available free chlorine (strength varies with shelf life).

Sodium hypochlorite is also available commercially in concentrations of between 5 percent and 15 percent available chlorine. Dry bleach is a dry calcium hypochlorite with 70 percent available chlorine.

Blind Spots:Places in the filter medium or membrane where no filtration takes place.

Blinding: The reduction or shutting off of flow due to filter medium or membrane fouling.

Block Carbon (Activated Carbon Block Filter): Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants.

The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon. Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon.

Activated carbon block filters typically have a 0.5 to 1 micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of Giardia and Cryptosporidium.

Blowby: 1. The technique sometimes used for recycling concentrate back to the feed.

2. Contaminant leakage through or by the water treatment device.

Blue-Green Algae (Cyanobacteria): Single-celled organisms (singular=cyanobacterium) similar to bacteria, except cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis.

Cyanobacteria are autotrophic producers of their own food from simple raw materials, whereas bacteria are heterotrophic decomposers of the wastes and bodies of other organisms. Cyanobacteria were formerly known as blue-green algae.

Blooms or population explosions of cyanobacteria cause water pollution. Some cyanobacteria-like bodies (CLBs) have been associated with causing waterborne diarrheal illnesses.

Bone Char: 1999 A black pigment substance, with a carbon content of about 10 percent, made by carbonizing animal bones.

Bone char is used for decolorizing sugar and water treatment. It has been used as a selective anion exchanger for fluoride and arsenic reduction.

Bored Well: A shallow (10 to 100 feet or 3 to 30 meters) large-diameter well (8 to 36 inches or 20 to 90 cm.) constructed by hand-operated or power-driven augers.

Bottled Artesian Water: Bottled water from a well tapping a confined aquifer in which the water level stands above the water table. Bottled artesian water shall meet the requirements of bottled natural water.

Bottled Distilled Water: Bottled water which has been produced by a process of distillation and meets the definition of purified water in the most recent edition of the United States Pharmacopeia.

Bottled Fluoridated Water: Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).

Bottled Mineral Water: Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).

Bottled Natural Water: Bottled spring, mineral, artesian, or well water which is derived from an underground formation, and is not derived from a municipal system or public water supply.

Bottled Spring Water: Bottled water derived from an underground formation from which water flows naturally to the surface of the earth, or is pumped through a borehole from a spring source. Bottled spring water shall meet the requirements of bottled natural water.

Bottled Water: Water that is placed in a sealed container or package, and is offered for sale for human consumption or other consumer uses.

Bottled water may be with or without natural or added carbonation, and may be prepared with added flavors, extracts, and/or essences derived from a spice or fruit and comprising less than one percent by weight of the final product.

Said products shall contain no sweeteners, acidulants, or additives other than said flavors, extracts, or essences.

Bottled Water Plant: Any place or establishment in which bottled water is prepared for sale.

Brackish Water: Water containing dissolved solids in the range of 1,000 to less than 15,000 parts per million.

Brass: A metal alloy of copper, zinc, and usually some lead. Brass is harder and stronger than copper because of its zinc content; lead contributes malleability and ductility.

Machined brass plumbing products are often made from Copper Development Association (CDA) 360 series brass which contains about 65 percent copper, 32 percent zinc, and 3 percent lead.

Breakpoint Chlorination: A chlorination procedure in which the chlorine is added until the chlorine demand is satisfied and a chlorine residual occurs.

The breakpoint is reached when a free chlorine residual is achieved. Further additions of chlorine produce a free chlorine residual proportional to the amount added.

Breakthrough:  The first appearance in the product water of an amount of the contaminant which exceeds the design performance criteria.

Bridging: 1. Bridging occurs in water softening when salt sticks together to form one large solid mass of pellets, or by the salt caking in a dry-salt brine tank which causes failure of the liquid or brine beneath the dry salt to become saturated. The result of bridging is insufficient salt in the regenerant solution to properly regenerate the cation resin.

2. The ability of particles to form a crustlike film over void spaces within a filter medium or membrane.

Brine: A strong solution of salt(s) (usually sodium chloride and other salts too) with total dissolved solids concentrations in the range of 40,000 to 300,000 or more milligrams per liter. Potassium or sodium chloride brine is used in the regeneration stage of cation and/or anion exchange water treatment equipment.

Sodium chloride brine saturation in an ion exchange softening brine tank is about 26 percent NaCl by weight at 60 degrees Fahrenheit.

Bromine (Br): A nonmetallic usually univalent or pentavalent element that lies between chlorine and iodine in the halogen group of the periodic table.

Bromine has been used in swimming pools for disinfection and in cooling towers as a biocide, but its use in drinking water as a primary disinfectant has been limited because of uncertain effectiveness in the presence of organic material, ammonia, and other amines.

Buffer: A chemical substance which stabilizes pH values in solutions.

Buffer Capacity: A measure of the capacity of a solution or liquid to neutralize acids or bases.

This is a measure of the capacity of water for offering a resistance to changes in pH.

-C-

Calcite: 1. Calcium carbonate (CaCO3).

2. A trade name for finely ground grades of marble or limestone, very high in calcium carbonate, which are used to raise the pH reading (reduce the acidity) of low pH (acidic) water or to filter out sediment.

Calcium (Ca): One of the principal elements making up the earth's crust.

Calcium compounds, when dissolved, make water hard. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are a means of clearly identifying hard water.

Calcium Carbonate: [CaCO3] A chemical compound found in nature as calcite (in limestone, marble, and chalk) and aragonite (in pearls) and in plant ashes, bones, and many shells.

Calcium Chloride: [CaCl2] A soluble salt, some uses of which are similar to those of sodium chloride.

Since its most striking property is its ability to draw moisture from the air and so dissolve itself, it is often used as an air dryer and as a de-icing salt.

Calorie: The amount of heat required to raise the temperature of one gram of water one degree Celsius (Centigrade).

Capillary Action: A phenomenon in which water or other liquids will rise above the normal liquid level in a tiny tube or capillary due to the attraction of the molecules in the liquid for each other and for the walls of the tube.

Carbon (C): An element which is found in almost all living or formerly living matter including plants, proteins, organics, and hydrocarbons.

Carbon combines readily with oxygen to form carbon dioxide (CO2). In water treatment applications, the term "carbon" is sometimes used as a short reference for activated carbon.

Carbon Block: SEE Activated Carbon Block Filter

Carbon Dioxide: A naturally-occurring gas (CO2) present in the atmosphere and formed by the decay of organic matter. Carbon dioxide is naturally present in air to the extent of 0.03 percent by volume and 0.05 percent by weight, in rainwater at 2 to 6 ppm, and in most water supplies from zero to 50 ppm. Carbon dioxide is the gas in carbonated beverages. Dissolved in water, it can form carbonic acid (H2CO3).

Carbonaceous: Containing carbon and derived from organic substances such as coal, coconut shells, and wood.

Carcinogen: Any substance which tends to produce cancer in an organism.

Cartridge: Any removable preformed or prepackaged component containing a filtering medium, ion exchanger, membrane, or other treatment material which fits inside a housing to make up a cartridge filter. Also called an element.

Cartridge Filter: A device often used for single faucet water treatment, made up of a housing and a removable cartridge (element).

In high flow rate commercial applications, the elements are clustered in a large housing, and the elements are cleanable and reusable. In residential use, disposable elements are used.

Catalyst: A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction.

Catalyst Media: Those filter media which can cause certain reactions to occur in water treatment, such as activated carbon, calcite, manganese greensand, magnesium oxides, and dissimilar metal alloys.

Catalyst/Oxidizing Filters: A class of media bed filters which contain manganese treated greensand, zeolites, or pumicites.

Catalytic Activated Carbon: Activated carbon with modified surface properties that enhance the functionality of the activated carbon in converting the oxidation state of various elements.

For example, with hydrogen sulfide (H2S), the sulfide ion (S-) is adsorbed and then converted on the catalytic carbon to elemental sulfur (S0) and sulfate ion (SO4 --). Once the sulfide is adsorbed and converted, it is desorbed and the site is restored.

For these reactions to occur, excess dissolved oxygen is required in the water and a minimum empty bed contact time (EBCT) of five minutes may be necessary.

Catalyze: To act as a catalyst. Or, to speed up a chemical reaction.

Cation: A positively charged ion in an electrolyte solution, attracted to the cathode under the influence of a difference in electrical potential.

Sodium ion (Na+) is a cation.

Cation Exchange: The ion exchange process in which cations in solution are exchanged for other cations available from an ion exchange product. Formerly called base exchange.

Cation Exchange Resin: An ion exchange material possessing reverse exchange ability for cations.

Sulfonated polystyrene copolymer divinylbenzene exchange resin is used almost exclusively today in ion exchange water softeners.

A cation exchange resin may be called a cation exchanger or a base exchanger.

Cation Exchange Water Softener: An equipment unit capable of reducing water hardness by the cation exchange process.

Cation Membrane:  SEE Ion Exchange Membrane

Cationic Polymer: A polymer having positively charged groups of ions; often used as a coagulant aid.

Caustic: 1. Caustic soda (NaOH) or any compound chemically similar to caustic soda.

2. Any substance capable of burning or destroying animal flesh or tissue. The term is usually applied to strong bases.

Cavitation: The formation and collapse of a gas pocket or bubble on the blade of an impeller or the gate of a valve. The collapse of this gas pocket or bubble drives water into the impeller or gate with a terrific force that can cause pitting on the impeller or gate surface.

Cavitation is accompanied by loud noises that sound like someone is pounding on the impeller or gate with a hammer.

Cellulose Acetate (CA) & Cellulose Triacetate (CTA): A cellulose ester obtained by introducing the acetyl radical (CH3CO-) of acetic acid into cellulose (as cotton or wood fibers) to produce a tough plastic material which is used to make the cellulosic-type of semipermeable reverse osmosis membranes.

Cellulose triacetate (CTA): SEE Cellulose Acetate

Celsius: SEE Centigrade

Centigrade: A temperature scale in which 100 degrees is the boiling point and zero degrees the freezing point for water at sea level.

Centimeter: One one-hundredth (1/100) of a meter (m).

Challenge Water: Water specifically prepared for testing the performance of water treatment equipment products.

Challenge water for each type of equipment is specifically defined in the individual equipment testing standards such as those established by the Water Quality Association and the National Sanitation Foundation International.

Channeling: The higher and unbalanced flow of water or regenerant through a limited number of passages in a filter or ion exchanger bed, as opposed to an evenly distributed flow through all passages in the bed. Channeling results in the greater flow of liquid through passages of lower resistance which can occur in fixed beds or columns of media particles due to nonuniform packing, irregular sizes and shapes of the particles, gas pockets, wall effects, fouling of the bed and resulting plugging of many passages, poor distributor design, low flow rates, faulty operations procedures, insufficient backwash, and other causes.

Charcoal: An adsorbent carbon product which has about one-third the surface area of activated carbon.

Charged Polysulfone Membrane: Normal (uncharged) polysulfone (PS) membranes contain physical pores that can pass salts; they are used in ultrafiltration water treatment. Charged PS membranes have been chemically sulfonated to create the ability to reject dissolved salts.

The sulfonation process permanently affixes sulfonate (SO3-) groups on the membrane surface, in a process similar to that used to give cation exchange resins their charge characteristics. These negatively charged sites repel anions, and indirectly repel the cations also due to the cations' attraction to anions in the concentrate solution. Charged PS membranes have salt rejection and chlorine tolerance characteristics similar to cellulosic membranes, and offer a permeate flux rate comparable to thin-film composite membranes.

However, charged PS membranes are more easily fouled by any divalent or trivalent cations, such as calcium, magnesium, or iron existing in the feedwater.

Check Valve: A valve which will allow water to pass in one direction but will close and prevent flow (backflow) in the opposite direction.

Chemical Stability: Resistance to attack by chemical action.

This term is often applied to the resistance of ion exchange resins to breakdown due to contact with aggressive solutions.

Chloramines: Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Unlike chlorine, chloramines do not combine with organics in the water to form potentially dangerous trihalomethanes (THMs).

Chloramines can exist in three forms: 1. monochloramine (NH2Cl) 2. dichloramine (NHCl2) 3. nitrogen trichloride (NCl3).

The proportions of the chloramines depend on the physical and chemical properties of the water. Water containing chloramines may not be used for fish or for kidney dialysis applications.

Chlorinated Polyvinyl Chloride (CPVC): A rigid, high-strength thermo-plastic polymer (polyvinyl dichloride) that is practically inert toward water, inorganic reagents, hydrocarbons, and alcohols over a broad temperature range, used for pipe and pipe fittings.

Chlorination: The treatment process in which chlorine gas or a chlorine solution is added to water for disinfection and control of microorganisms. Chlorination is also used in the oxidation of dissolved iron, manganese, and hydrogen sulfide impurities.

Chlorine: (Cl2) A gas widely used in the disinfection of water and as an oxidizing agent for organic matter, manganese, iron, and hydrogen sulfide.

Chlorine is known to react with organic matter in the water to form trihalomethanes (THMs), a suspected carcinogen.

Chlorine Contact Chamber: That part of a water treatment plant where effluent is disinfected by chlorine.

Chlorine Demand: A measure of the amount of chlorine which will be consumed by organic matter and other oxidizable substances in a water before a chlorine residual will be found.

Chlorine demand represents the difference between the total chlorine fed and the chlorine residual.

Chlorine Requirement: The amount of chlorine which is needed for a particular purpose.

Some reasons for adding chlorine are reducing the number of coliform bacteria (Most Probable Number), obtaining a particular chlorine residual, or oxidizing some substance in the water. In each case, a definite dosage of chlorine will be necessary. This dosage is the chlorine requirement.

Chlorine residual: SEE residual chlorine; total chlorine residual

Chlorine, combined: SEE combined available residual chlorine

Chlorine, free: SEE free available residual chlorine

Chronic Exposure: Long-term, low-level exposure to a toxic chemical.

Cistern: A small tank (usually covered) or a storage facility used to store water for a home or farm. Often used to store rainwater.

Clarifier: A large circular or rectangular tank or basin in which water is held for a period of time, during which the heavier suspended solids settle to the bottom.

Clarifiers are also called settling basins and sedimentation basins.

Clay: A type of naturally-occurring hydrated aluminum silicate (Al2O3SiO2 x H2O) soil. Natural clay is activated and used as a coagulant adsorbent filter aid.

Clay particles can have a diameter of less than five microns.

Clear Well: A reservoir for the storage of filtered water of sufficient capacity to prevent the need to vary the filtration rate with variations in demand.

Also used to provide chlorine contact time for disinfection.

Clumping: The formation of media agglomerations or resin clumps within an operating filter or ion exchange bed due to organic fouling or electrostatic charges.

Coagulant: A material, such as alum, which will form a gelatinous precipitate in water and cause the agglomeration of finely divided particles into larger particles which can then be removed by settling and/or filtration.

Coagulation: The clumping together of very fine colloidal (less than 0.1 micron in size) and dispersed (0.1 to 100 microns in size) particles into larger visible agglomerates of these particles (usually between 100 and 1,000 microns in size) caused by the use of chemicals (coagulants).

The chemicals neutralize the electrical charges of the fine particles and cause destabilization of the particles. This clumping together makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.

Coalescence: The union or growing together of colloidal particles into a group or larger unit as a result of molecular attraction on the surfaces of the particles.

Cohesion: Molecular attraction which holds two particles together

Cold Sterilization: The use of submicron filtration to screen out bacteria from a water or fluid.

Coliform Bacteria: A particular group of bacteria primarily found in human and animal intestines and wastes.

These bacteria are widely used as indicator organisms to show the presence of such wastes in water and the possible presence of pathogenic (disease-producing) bacteria. Escherichia coli (E. coli) is one of the fecal coliform bacteria widely used for this purpose.

coliform organism: See colloids

Colloids: Very fine solid particles, typically between 0.1 and 0.001 microns in diameter, which are suspended in a liquid or gas and will not settle out of a solution and cannot be removed by conventional filtration alone.

When in sufficient concentrations, colloidal matter may give a grayish cast to a standing water sample.

The removal of colloidal particles usually requires coagulation to form larger particles which may then be removed by sedimentation and/or filtration.

Color: A shade or tint which is imparted to water by substances which are in true solution and thus cannot be removed by mechanical filtration.

Color is most commonly caused by dissolved organic matter, but it may be produced by dissolved mineral matter.

Color Throw: The discharge of color into the effluent of an ion exchange or filter media system by any component.

Usually occurs after an extended "standing" period which allows slowly-soluble colored matter to accumulate in the water. A color throw may result from the leaching of color bodies from an ion exchange resin into the water.

Column: A vessel, usually a cylindrical and vertical tank, with an inlet at one end and an outlet at the other end, with some means of holding the medium in place so that a stream of water passing through it is processed.

Also known as a bed of filter or catalyst medium, or ion exchange resin.

Combined Available Residual Chlorine: The concentration of residual chlorine which is combined with ammonia (NH3) and/or organic nitrogen in water as chloramine (or other chloro derivative) yet is still available to oxidize organic matter and utilize its bactericidal properties.

The combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in reactions.

Combined Residual Chlorination: The application of chlorine to water to produce combined available residual chlorine.

This residual can be made up of monochloramines, dichloramines, and nitrogen trichloride.

Common Salt: Sodium chloride (NaCl). A white or colorless crystalline compound that occurs abundantly in nature (present as 2.6 percent of seawater) and in animal fluids.

Sodium chloride is used in water treatment to regenerate cation exchange water softeners and some dealkalizer systems. Also called table salt or common table salt.

Community Water System: A public water system which serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents.

Compensated Hardness: A calculated value based upon the total hardness, the magnesium-to-calcium ratio, and the sodium, iron, and manganese concentrations in a water.

This value is used to correct for the reduction in hardness removal capacity of a cation exchange water softener which is caused by the presence of these substances. No single method of calculation has been uniformly accurate.

Complete Treatment: In municipal water treatment, a method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation - flocculation, sedimentation, and filtration.

Also called conventional filtration.

Composite Membrane: A semipermeable membrane used in water treatment, consisting of a rejecting barrier layer of one chemical composition (usually a type of polymer) supported by one or more layers of porous materials with different composition(s).

Compound: A substance composed of two or more elements whose composition is constant.

For example, table salt (sodium chloride - NaCl) is a compound.

Concentrate Stream: In reverse osmosis applications, the stream into which rejected ions and materials are concentrated.

Concentrated Solution: A solution which contains a relatively high quantity of the solute.

Concentration: 1. The process of increasing the dissolved solids per unit volume of solution, usually by evaporation of the liquid or separation of the liquid by passage through a semipermeable membrane.

2. The amount of the material dissolved in a unit volume of a solution.

Condensate: Water obtained by condensation of steam or water vapor.

Conditioned Water: Any water which has been treated by one or more processes (adsorption, deionization, filtration, softening, reverse osmosis, etc.) to improve the water's usefulness and/or aesthetic quality by reducing undesirable substances (iron, hardness etc.) or undesirable conditions (color, taste, odor, etc.).

Conductance: A measure of the ability of a solution to allow an electric current to flow through it; the reciprocal of resistance. The unit of measure for conductance is the siemens (formerly called mho), which is the reciprocal of the ohm (the unit of measure for resistance).

In electrolytic or ionic solutions, the current is carried by ions; liquids such as pure water, glass, and high polymers (such as rubber and cellulose) exhibit poor conductance.

Conductivity: The property of a substance to conduct (carry) heat or electricity; the unit of measure is the siemens (formerly called mho), which is the reciprocal of resistivity (1 divided by resistivity).

Confluent Growth: A continuous bacterial growth covering the entire filtration area of a membrane filter, or a portion thereof, in which bacterial colonies are not discrete.

Contact Time: 1. The time in minutes the water is in contact with an ion exchange medium or filter medium.

2. The time the brine or other ion exchange regenerant is in intimate contact with the resin.

3. As relates to disinfection, the time the water is allowed to contain the disinfectant to assure potability.

Contact time may also be called retention time.

Contaminant: 1. Any undesirable physical, chemical, or microbiological substance or matter in a given water source or supply. Anything in water which is not H2O may be considered a contaminant.

2. Any foreign component present in another substance.

Contamination: The introduction of any contaminant into a water source or supply.

Continous Flow Operation: The process wherein a continuous and steady flow of water is processed for treatment through the media (as compared to intermittent flow operation).

Convection: The transfer of heat through a fluid by circulating currents.

Conventional Filtration: In municipal water treatment, a method of treating water to remove particulates.

The method consists of the addition of coagulant chemicals, flash mixing, coagulation - flocculation, sedimentation, and filtration. Also called complete treatment.

Conveyance Loss: Water lost in conveyance (pipe, channel, conduit, ditch) by leakage or evaporation.

Corona: An electrical discharge effect which causes ionization of oxygen and the formation of ozone.

Corona Discharge: The discharge of electricity causing a faint glow adjacent to the surface of an electrical conductor and, similarly, adjacent to the dielectrics in an ozone generator during ozone production.

Corona discharge results from electrical discharge and indicates ionization of oxygen and the formation of ozone in the surrounding air. The corona discharge is a violet-blue color with air, but colorless with high purity oxygen.

Corrosion: The gradual decomposition or destruction of a material by oxidation or chemical actions, often due to an electrochemical reaction.

Corrosion may be caused by: 1) stray current electrolysis, 2) galvanic corrosion caused by dissimilar metals, or 3) differential concentration cells.

Corrosion starts at the surface or a material and moves inward. Corrosion of iron or steel is commonly called rusting.

Corrosion Inhibitor: A substance that slows the rate of corrosion of metal plumbing materials by water, especially lead and copper materials, by forming a protective film on the interior surface of those materials.

Corrosivity: An indication of the corrosiveness of a water.

The corrosiveness of a water is described by the water's pH, alkalinity, temperature, total dissolved solids, dissolved oxygen concentration, and the Langelier Index.

Critical Bed Depth: The minimum depth of an ion exchange, adsorbent, or otherwise reactive filter bed that is required to contain the mass transfer zone.

Critical Pressure: The minimum pressure necessary to liquify a gas which is at critical temperature.

Critical Temperature: The temperature above which a gas cannot be liquefied solely by an increase in pressure.

Cross Contamination: 1. Contamination which occurs in a mixed bed deionizer unit when anion and cation resins are mixed together after regeneration due to the malfunction of the system.

2. The intermixing of two water streams which results in unacceptable water quality for a given purpose.

Cross flow filtration: A type of filtration that uses the shear force of tangential flow across the membrane surface (during suspension recirculation) to keep the particle buildup to a minimum. Particle boudary layers cannot be completely eliminated by cross flow, however, due to low fluid velocity that exists at the membrane surface. Ultrafiltration and reverse osmosis are examples of cross flow filtration. Cross flow filtration is also called tangential flow filtration.

Cross-linked Polyethylene (XLPE or PEX): Polyethylene that, by cross-linking via irradiation of linear polyethylene with an electron beam or gamma radiation, or with a chemical cross-linking agent, such as benzoly peroxide, is made to be a non-toxic thermosetting (remaines solid upon heating) white solid with superior strength and durability, high temperature and pressure resistance, and inertness toward chemical attack and corrosion. Cross-linked polyethylene pipe and tubing is accepted by many plumbing codes for potable water distribution with buildings. It is flexible (bend radii of six times or greater the outside pipe/tubing diameter) and can be used in place of polybutylene (PB) water pipe.

Cryptosporidiosis (crip-toe-spor-ID-ee-OH-sis): The illness produced by infection with Cryptosporidium. The most common symptoms of this disease including fever, headache, nausea, vomiting, anorexia, abdominal cramping, and watery diarrhea. These symptoms usually begin two to ten days after infection and generally last two weeks or less. Cryptosporidiosis in individuals with weakened immune systems is a more severe disease.

The most common symptoms of this disease including fever, headache, nausea, vomiting, anorexia, abdominal cramping, and watery diarrhea. These symptoms usually begin two to 10 days after infection and generally last two weeks or less. Cryptosporidiosis in individuals with weakened immune systems is a more severe disease.

Cryptosporidium: (crip-toe-spor-ID-ee-um) A waterbourne protozoan that forms oocysts and causes acute gastrointestinal illness in humans. Several species of cryptosporidium exist, but only one, C. parvum, is known to be infective to humans. In the environment, the organism's fertilized eggs are protected by an outer shell form called an oocyst (OH-oh-cist). Once injested, the organism emerges from the shell and infects the lining of the small intestines. Cryptosporidium is commonly found in unfiltered surface water and is resistant to disinfectants such as chlorine and ultraviolet light, but C. parvum oocysts, generally being three to five microns in diameter, can be removed by filters that capture all particles of one micron and greater in size.

Cumulative Exposure: The summation of exposures of an organism to a chemical over a period of time.

Cyanobacteria: Single-celled organisms (singular = cyanobacterium) similar to bacteria, except cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis.

Cyanobacteria are autotrophic producers of their own food from simple raw materials, whereas bacteria are heterotrophic decomposers of the wastes and bodies of other organisms. Cyanobacteria were formerly known as blue-green algae.

Blooms or population explosions of cyanobacteria cause water pollution. Some cyanobacteria-like bodies (CLBs) have been associated with causing waterborne diarrheal illnesses.

Cyanobacteria-like Bodies (CLBs): Organisms that, upon analysis, appear to be cyanobacteria i.e., 8-10 micrometers in size, staining red with modified acid fast stains, and autofluorescing under ultraviolet (UV) light.

Cyclospora oocysts have been sometimes confused for cyanobacteria-like bodies in microorganism analyses.

Cyanosis: A dusky bluish or purplish discoloration of the skin or mucous membranes due to insufficient oxygen in the blood as could be caused by excessive nitrates in drinking water and methemoglobinemia in infants.

Cyclospora: A genus of protozoa parasites belonging to the order Coccidia and the phylum Apicomplexa.

Cyclospora cayetanensis species are pathogenic to humans causing disease symptoms similar to those caused by Cryptosporidium, except cyclosporiasis does appear responsive to treatment with medicine such as trimethoprim-sulfamethoxazole (TMP-SMX).

Cyclospora reproduce with environmentally resistant oocysts (about 8-10 micrometers in size) that can be carried viably in unfiltered water supplies.

Cyst: A capsule or protective sac produced about themselves by many protozoans (as well as some bacteria and algae) as preparation for entering a resting or a specialized reproductive stage.

Similar to spores, cysts tend to be more resistant to destruction by disinfection. Fortunately, protozoan cysts are typically 2 to 50 microns in diameter and can be removed from water by fine filtration.

-D-

Dead End Filtration: A flow pattern in which all water flows through the medium or membrane (as opposed to cross flow filtration) thus allowing a buildup of a particulate layer on or near the surface of the medium and requiring periodic backwashing, repeated cleaning, or cartridge replacement.

Dechlorination: The deliberate removal of chlorine from water. The partial or complete reduction of residual chlorine by any chemical or physical process.

Decomposition: The conversion of chemically unstable materials to more stable forms by chemical or biological action.

If organic matter decays when there is no oxygen present (anaerobic conditions or putrefaction), undesirable tastes and odors are produced. Decay of organic matter when oxygen is present (aerobic conditions) tends to produce much less objectionable tastes and odors.

Defluoridation: The removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.

Degassing, Degasify, Degasification: The removal of dissolved gases such as carbon dioxide, methane, hydrogen sulfide, and oxygen by:

1. subjecting the water to a pressure below atmospheric pressure (vacuum degassing) or

2. passing large amounts of air thoroughly through the water at atmospheric pressure (air stripping).

Degradation: As relates to ion exchange, the loss of capacity, reduction of resin particle size, excessive swelling of resin particles, or any combination of these factors resulting in a lessening of the ion exchange capabilities of the resin.

This may occur as a result of the type of service for which the resin was used, the solution concentrations used, heat, or aggressive operating conditions.

Deionization: The removal of all ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure: First, positively-charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. Second, negatively-charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions.

The hydrogen and hydroxide ions introduced in this process unite to form water molecules. This process is also called demineralization by ion exchange.

Delivered Water: The finished product water from a public or private utility water plant which is carried through a water main network of pipes and arrives at the point-of-use (homes, institutions, and business facilities).

Delta P: The pressure drop or loss (in psi) by flowing water in a pressurized system as the result of the velocity and turbulence of the flowing water, restrictions the water flows through, and roughness of surfaces the water flows past. The symbol for Delta P is P.

Demand Initiated Regeneration (DIR): A method of automatically initiating regeneration or recycling in filters, deionizers, or softeners after a pre-determined metered volume of water has been processed.

In a softener or deionizer, regeneration may be triggered automatically based upon an electrical or mechanical signal. All operations including bypass (of hard or soft water depending upon design), backwashing, brining, rinsing, and returning the unit to service are initiated and performed automatically in response to the demand for treated water.

Demineralization by Ion Exchange: See deionization.

Density: The mass of a substance per specified unit of volume; for example, pounds per cubic foot. True density is the mass per unit volume excluding pores; apparent density is the mass per unit volume including pores.

The density of water is 1.0 gram per cubic centimeter or about 62.4 pounds per cubic foot.

Deposits: See Water Spotting.

Depth Filtration: A filtration process in which water flows through progressively smaller pore spaces in a filter media bed.

Depth filters are designed to entrap particles throughout the mass of filter media, as opposed to a surface filter where only the surface layer does the actual filtering.

Depth filtration can be accomplished with a multilayered bed or multimedia filtration.String-wound fiber cartridge elements can also function as depth filters.

Dermal Exposure: Contact between a chemical and the skin.

Desalination: The removal of dissolved inorganic solids (salts) from a solution such as water to produce a liquid which is free of dissolved salts.

Desalination is typically accomplished by distillation, reverse osmosis, or electrodialysis.

Desiccant: [DES-uh-kant] A hygroscopic substance such as activated alumina, calcium chloride, silica gel, or zinc chloride that draws water vapor from the air. Desiccants are used to maintain a dry environment for equipment and materials.

Desorption: The opposite of adsorption.

The process of removing an adsorbed material from the medium or resin on which it has been adsorbed. Desorption is usually accomplished by heating, a reduction of pressure, by the presence of another more strongly adsorbed substance, or a combination of these means.

Dessication: A process used to thoroughly dry air; to remove virtually all moisture from air.

Destratification: The development of vertical mining within a lake or reservoir to eliminate (either totally or partially) separate layers of temperature, plant, or animal life.

This vertical mixing can be caused by mechanical means (pump) or through the use of forced air diffusers which release air into the lower layers of the reservoir.

Detention Lag: The time period between the moment a change is made and the moment when such a change is finally sensed by the associated measuring instrument.

Detention Time: 1. The theoretical (calculated) time required for a small amount of water to pass through a tank at a given rate of flow.

2. The actual time in hours, minutes, or seconds that a small amount of water is in a settling basin, flocculating basin, or rapid-mix chamber. In storage reservoirs, detention time is the length of time entering water will be held before being drafted for use (several weeks to years, several months being typical).

Detention Time (hr) = Basin Volume (gal.)(24 hr/day)/Flow (gal/day)

Detergent: Any material with cleansing powers: soaps, synthetic detergents, man-made alkaline materials, solvents, and abrasives. In common domestic usage, the term is often used to refer to synthetic detergents.

Dew Point: The temperature to which air must be cooled to cause condensation of the water vapor it contains.

Dialysis: The separation of components of a solution by diffusion through a semipermeable membrane which is capable of passing certain ions or molecules while rejecting others.

Diaphragm Pump: A positive-displacement pump in which the reciprocating piston is separated from the solution by a flexible diaphragm, thus protecting the piston from corrosion and erosion and avoiding related problems with packing and seals.

Diatomaceous Earth: A fine, siliceous (made of silica) "earth" composed mainly of the skeletal remains of diatoms, a type of free-floating, microscopic plant found in the ocean.

Diatomaceous earth is used as a water filtration medium.

Diatomaceous Earth Filtration: A filtration method resulting in substantial particulate removal, that uses a process in which:

1. A "precoat" cake of diatomaceous earth filter media is deposited on a support membrane (septum); and

2. While the water if filtered by passing through the cake of the septum, additional filter media, known as "body feed," is continuously added to the feedwater to maintain the permeability of the filter cake.

Diatomic Molecule: A molecule containing only two atoms, such as hydrogen as H2 or oxygen as O2.

Differential Pressure: The difference in pressures at two points in a water system. Differences may be due to variations in elevation, or to friction losses, or to pressure drops caused by resistance to water flow through pipes, softeners, filters, or other devices.

Diffuser: See Distributor.

Diffusion: The movement of suspended or dissolved particles from a more concentrated to a less concentrated region as a result of the random movement of individual particles; the process tends to distribute them uniformly throughout the available volume.

Digestion: The process by which complex organic materials are broken down and decomposed into simpler substances as a result of a chemical or biological reaction or a combination of reactions.

Aerobic digestion takes place in the presence of air; anaerobic digestion takes place in the absence of air.

Dilute Solution: A solution that has been made weaker, usually by the addition of water.

Dilution: The act of adding more solvent or water to a given solution to make it less concentrated.

Sometimes this is done to attain the proper concentration; sometimes to make the solution easier to handle.

Dimictic: Lakes and reservoirs which freeze over and normally go through two stratification and two mixing cycles within a year.

Direct Filtration: A filtration method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration.

The flocculation facilities may be omitted, but the physical/chemical reactions will occur to some extent. The sedimentation process is omitted.

Direct Runoff: Water that flows over the ground surface or through the ground directly into streams, rivers, or lakes.

Disinfect: To free from infection by either a chemical or physical means; causing the absence of pathogenic or indicator coliform bacteria in drinking water.

Disinfectants kill or inactivate 99.9 to 99.9999 percent (but not 100%) of microorganisms under controlled conditions. Some common disinfectants are the halogens: chlorine, iodine, bromine, and hypochlorites; ozone, potassium permanganate, hydrogen peroxide, peracetic acid; formaldehyde, glutaraldehyde, phenol (carbolic acid), organic acids, benzoic and salicylic acids and their sodium salts, high pH, heat, ionizing radiation, and electromagnetic waves such as those of ultraviolet light.

The USEPA requires that a disinfection claim must show killing or inactivation of all vegetative microbes in 10 minutes.

Disinfection: The treatment of water to inactivate, destroy, and/or remove pathogenic (disease-producing) bacteria, viruses, cysts, and other microorganisms (but not completely eliminating all microorganisms) for the purpose of making the water microbiologically safe for human consumption.

A disinfection operation should reduce the total viable microorganism population by 99.9 to 99.9999 percent. Disinfection may involve the use of disinfecting chemicals such as chlorine, iodine, ozone, or hydrogen peroxide; or it may involve physical processes such as distillation, microfiltration, ultrafiltration, boiling, or ultraviolet radiation.

Disinfection Byproduct: A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply.

Dispersant: A chemical (such as a polyphosphate) added to water which causes particulates in water to remain in suspension.

 

Dispersing Agent: A material that increases the stability of particles in a liquid.

Disposable Component: Any component of a piece of water treatment equipment or water treatment system which is manufactured to be disposed of instead of repaired or reused.

Example: A cartridge filter element.

Dissociation: The process by which a chemical combination breaks up into simpler constituents such as atoms, groups of atoms, ions, or multiple different molecules.

Often this breakdown is reversible, as in the case of ionization.

Dissolved Inorganic Carbon: The fraction of inorganic carbon (the carbonate, bicarbonate, and dissolved CO2) in water that passes through a 0.45 micron pore-diameter filter.

Dissolved Matter: That portion of matter or solids, exclusive of gases, which is dispersed in water to produce a homogenous liquid.

According to the definition used in the water treatment industry, "dissolved matter" is that portion of the total matter that will pass through a 0.45 micron pore-diameter membrane filter.

Dissolved Organic Carbon: The fraction of total organic carbon (all carbon atoms covalently bonded in organic molecules) in water that passes through a 0.45 micron pore-diameter filter.

Dissolved Oxygen: Measure of water quality indicating free oxygen dissolved in water.

Dissolved Solids: The weight of matter, including both organic and inorganic matter, in true solution in a stated volume of water.

The amount of dissolved solids is usually determined by filtering water through a 0.45 pore-diameter micron filter and weighing the filtrate residue left after the evaporation of the water at 180 degrees Celcius.

Distillate: The product water or condensate, which is mineral-free and potable, from a distiller unit.

Distillation: The process of separating the water from the organic and inorganic contaminants through a combination of evaporation (or vaporization), cooling, and condensation.

Distilled Water: Water which has been cleansed by passing through one or more evaporation-condensation cycles until it contains a very low amount of dissolved solids (usually less than 5.0 ppm TDS).

Distributor: Distributor

A fitting, usually installed at the top and bottom of the tank in a loose media system, which is designed to produce even flow through all sections of an ion exchanger or filter media bed and to function as a retainer of the media in the tank.

May also be called a diffuser.

Divalent: [die-VAY-lent] Having a valence of two, such as the ferrous ion, Fe2+.

Also called bivalent.

Diversion: 1. Use of part of a stream flow as a water supply.

2. A structural conveyance (or ditch) constructed across a slope to intercept runoff flowing down a hillside, and diverting it to some convenient discharge point.

DOC: Dissolved Organic Carbon.

Dosage: The quantity of a chemical administered to an organism.

Dose: The actual quantity of a chemical to which an organism is exposed.

Dose Equivalent: The product of the absorbed dose from ionizing radiation and such factors as account for differences in biological effectiveness due to the type of radiation and its distribution in the body as specified by the International Commission on Radiological Units and Measurements (ICRU).

Dose-Response: A quantitative relationship between the dose of a chemical and an effect caused by the chemical.

Dose-Response Curve: A graphical presentation of the relationship between degree of exposure to a chemical (dose) and observed biological effect or response.

Dose-Response Relationship: The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury produced.

Down Gradients: The direction that groundwater flows; similar in concept to downstream for surface water, such as down river.

Downflow: The term used to designate the direction (downward) in which water or a regenerant flows through an ion exchange or filter media bed during any phase of the operating cycle.

This is the flow pattern found in conventional column operation: in at the top, out at the bottom of the column.

The pattern may also be called cocurrent flow in ion exchange systems.

Downflow Softening: The softening process in which raw water enters at the top of the softener bed column and passes downward through the cation resin and out the bottom.

In this process, the brining would also be in this same cocurrent direction.

DPD: A method of measuring the chlorine residual in water. The residual may be determined by either titrating or comparing a developed color with color standards.

DPD stands for N,N-diethyl-p-phenylene-diamine.

Draft: 1. The act of drawing or removing water from a tank or reservoir.

2. The water which is drawn or removed from a tank or reservoir.

Drain: A pipe, conduit, or receptacle in a building which carries liquids by gravity to waste.

The term is sometimes limited to refer to disposal of liquids other than sewage.

Drain Line: A pipeline which is used to carry backwash water, regeneration wastes, and/or rinse water from a water treatment system to a drainage receptacle or waste system.

Drainage: A technique to improve the productivity of some agricultural land by removing excess water from the soil; surface drainage is accomplished with open ditches; subsurface drainage uses porous conduits (drain tile) buried beneath the soil surface.

Drawdown: 1. The drop in the water table or level of water in the ground when water is being pumped from a well.

2. The amount of water used from a tank or reservoir.

3. The drop in the water level of a tank or reservoir.

Drilled Well: A well constructed by either cable tool or rotary methods which operates by cutting or abrasion; materials are brought to the surface by means of a hollow drill tool, a boiler, a sand pump, or by another hydraulic and/or self-cleaning method.

Drinking Water: 1. A water, treated or untreated, which is intended for human use and consumption and considered to be free of harmful chemicals and disease-causing bacteria, cysts, viruses, or other microorganisms.

2. Safe water that has been further treated to enhance aesthetic quality and/or reduce mineral content by one or more point-of-use processing devices.

Drinking Water Standards: Standards that define allowable water quality limits for potable and domestic water supplies.

The U.S. Environmental Protection Agency (EPA) is responsible for the National Primary Drinking Water Regulations, which are health-related standards that establish the Maximum Contaminant Levels (MCLs) for regulated substances in drinking water.

An MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer's tap. MCLs are enforceable at public water systems under the Safe Drinking Water Act.

The EPA also has set Maximum Contaminant Level Goals (MCLGs) at levels which no known or anticipated adverse effects on the health of persons occur and which allow an adequate margin of safety. The enforceable MCL is set as close to the MCLG as reasonable, taking into consideration the costs and treatment techniques available to public water systems.

National Secondary Drinking Water Regulations, also issued by the EPA, pertain to aesthetic characteristics of water and are advised, but not enforceable, by the Federal government.

Driven Well: A shallow, usually small well (having a diameter of 1.5 inches to 3 inches or 4 to 10 cm) constructed without the aid of any drilling, boring, or jetting device, by driving a series of connected pipe lengths into unconsolidated material to a water-bearing stratum.

Dual-Function Media: Any filter or ion exchange media which is used to perform two treatment steps in an application.

Example: activated carbon filtration and adsorption; or cation resin softening and dissolved iron removal.

Dug Well: A shallow, large diameter well constructed by excavating with power machinery or hand tools instead of drilling or driving.

Typically a dug well is constructed for an individual residential water supply and yields considerably less than 100 U.S. gallons per minute (380 L/min.)

DVB: Divinylbenzene.

Dynamic Pressure: When a pump is operating, the vertical distance (in feet) from a reference point (such as a pump center line) to the hydraulic grade line is the dynamic head.

Dynamic System: A process or system in which motion occurs as compared to static conditions with no motion.

For example: an ion exchange system is considered a dynamic system because the continuous flow of the water to be treated creates continuous motion, as opposed to a static batch system in which the water does not move during the reaction process.

Dynamic Water Pressure: The water pressure at the inlet to a -dynamic water processing system.

-E-

Ecosystem: A system made up of the community of living things (animals, plants, and microorganisms) which are interrelated to each other and the physical and chemical environment in which they live.

Eddy: A circular movement or whirlpool occurring in flowing water due to currents created by various obstructions or dynamic forces in the water.

Eduction: The process of bringing something out, sucking it out, or separating it out from something else, as in drawing soda pop out of a can with a straw.

Eductor: A venturi with an opening at the throat which will educt (suck in) air or liquid.

Eduction is accomplished by joining the fluids just after the constriction in the tube where a vacuum is created, thus sucking the incoming fluid into the flowing water stream. This device is commonly used to introduce (through both eduction and ejection) a gas or liquid into a flowing stream.

For example, when feeding a chemical to a water supply, the venturi serves to educt the chemical from its solution container and to eject it into the water stream.

Also called an ejector.

Effective Range: That portion of the design range (usually upper 90 percent) in which an instrument has acceptable accuracy.

Effective Size: A measure of the diameter of particles in a media bed or resin bed. Effective size is that mesh size which will permit 10 percent of the bed's particles to pass and will retain the remaining 90 percent; in other words, that size for which 10 percent of the media grains or particles are smaller and 90 percent are larger.

Efficiency: As relates to ion exchange, a measure of the effectiveness of the operational performance of an ion exchanger, usually based on the ratio of output per unit of input. This ratio is often expressed as the amount of regenerant required to produce a unit of contaminant reduction capacity. For example: pounds of salt per kilograins of hardness removed or pounds of acid per kilogram of salt removed. SEE A:LSO salt efficiency.

In media filtration, efficiency is the percent of contaminant reduction which occurs with a specified medium volume and specified water contact time.

In membrane filtration, the figure obtained (expressed as a percent) by dividing the volume (gallons or liters) of product water produced by the total volume (gallons or liters) of feedwater fed to the particular unit or system.

Effluent: The outflow from any water processing system or device. Sometimes used to mean the product water of a given device or system.

Ejection: The process of forcing something out, expelling it.

Ejector: A device used to disperse a chemical solution into water being treated.

Ejector Pump: A shallow or deep well pump operating on the venturi principle.

Commonly referred to as a jet pump.

Electrical Conductivity: The property of a substance to conduct (carry) heat or electricity; the unit of measure is the siemens (formerly called mho), which is the reciprocal of resistivity (1 divided by resistivity).

Electrochemical Reaction: Chemical changes produced by electricity (electrolysis) or the production of electricity by chemical changes (galvanic action).

In corrosion, a chemical reaction is accompanied by the flow of electrons through a metallic path. The electron flow may come from an external force and cause the reaction, such as electrolysis caused by a DC (direct current) electric railway or the electron flow may be caused by a chemical reaction as in the galvanic action of a flashlight dry cell.

Electrode: A conductive, usually metallic, substance used to establish electrical contact with nonmetallic parts of a circuit.

Electrodialysis: A dialysis process using semipermeable membranes in which ions migrate through the membranes from a less concentrated to a more concentrated solution as a result of the ions' respective attractions to a positive electrode (anode) and a negative electrode (cathode) created by direct electric current.

Electrolysis: The decomposition of material by an outside elecrical current.

Electrolyte: 1. A substance which when dissolved in water separates into two or more ions which can carry an electric current.

2. A nonmetallic substance which can carry an electric current by movement of ions instead of electrons.

Electrolytic Cell: A device in which the chemical decomposition of material causes an electric current to flow. Also, a device in which a chemical reaction occurs as a result of the flow of electric current.

Chlorine and caustic (NaOH) are made from salt (NaCl) in electrolytic cells.

Electron: A negatively-charged particle that revolves around the nucleus of an atom. In a neutral (without electrical charge) atom, the negative charges of the electrons are balanced by the positive charges of the protons in the nucleus. When an atom loses or gains one or more electrons, resulting in the atom carrying a negative or positive charge, the atom has become an ion.

Element: A substance that consists of only one kind of atom and which cannot be decomposed into simpler substances by ordinary chemical means.

Examples: iron, calcium, carbon, magnesium. There are more than 100 elements, some found in nature, some man-made. Several elements may combine into more chemically complex substances such as compounds.

Elution: The process of separating or washing out adsorbed material, especially by use of a solvent.

In ion exchange, the stripping of ions from the medium by passing a more highly concentrated ionized solution through the ion exchanger bed.

Emission Spectroscopy: A chemical analytical technique used to determine metal elements in water by measuring the well-defined characteristic radiation given off by each respective element as the thermally-excited element returns from an atomic vapor state to its fundamental state.

Emollient: An ingredient for making skin soft or supple, or soothing the skin.

Materials such as fatty acids and lanolin are included in some toilet bars and skin preparation products to provide emollient properties.

Emulsification: The dispersion or suspension of fine particles or globules of one or more liquids in another liquid.

The emulsification process is important in all types of cleaning where oily or fatty soils are encountered. The principal agent in emulsification is the surfactant, with aid from a builder that ties up hardness minerals.

Endangerment Assessment: A site-specific risk assessment of the actual or potential danger to human health or welfare and the environment from the release of hazardous substances or waste.

The endangerment assessment document is prepared in support of enforcement actions under U.S. environmental laws such as CERCLA or RCRA.

Endemic: Something peculiar to a particular people or locality, such as a disease which is always present in the population.

Endocarditis: Infection of the heart valves.

Endothermic: A term used to describe a process or change in which heat is absorbed and that requires high temperature for the initiation and maintenance. For example, melting ice absorbs heat and is, therefore, an endothermic process.

Endpoint: The point at which a process or cycle is completed because a predetermined measurable value has been reached.

Example: When the hardness in the product water reaches a set endpoint showing excessive hardness leakage, the resin bed is considered to be exhausted and in need of regeneration; when a certain predetermined color endpoint is reached during chemical titration, the process is complete.

Endrin: A pesticide toxic to freshwater and marine aquatic life that produces adverse health effects in domestic water supplies.

Enteric: Of intestinal origin, especially applied to wastes or bacteria.

Entrain: To trap bubbles in water either mechanically through turbulence or chemically through a reaction.

Entropy: The capacity of a system or a body to hold energy that is not available for changing the temperature of the system (or body) or for doing work.

Enzymes: A large class of complex proteinaceous molecules, which act as catalysts in biochemical reactions, and as produced by living cells can bring about digestion (breakdown) of organic molecules into smaller units that can be used by living cells.

Selected types of enzymes are useful in laundering, particularly in presoaking, where they break down certain soils and stains to simpler forms, which are then more readily and completely removed by the laundry soap or detergent. Reasons for their primary use in presoaking are: they need more than the usual wash period of 10-15 minutes to be effective, especially on stubborn stains and soil; also, their effectiveness is deactivated by liquid chlorine bleach, so the two must be used separately to obtain the full benefit of each.

EPA: See USEPA

Epidemic: Widespread outbreak of a disease, or a large number of cases of a disease, in a single community or relatively small area.

Disease may spread from person to person, and/or by the exposure of many persons to a single source, such as a water supply.

Epidemiologic Study: Study of human populations to identify causes of disease. Such studies often compare the health status of a group of persons who have been exposed to a suspect agent with that of a comparable non-exposed group.

Epidemiology: A branch of medicine which studies epidemics (diseases which affect significant number of people during the same time period in the same locality).

The objective of epidemiology is to determine the factors that cause epidemic diseases and how to prevent them.

Equalization: A means of providing more uniform flow rate and composition of a water supply by use of a reservoir that receives water from a pump or treatment system, evens out the incoming flow variation, and permits temporary water withdrawal in excess of the pump or treatment system capacity.

Equilibrium: In chemistry, a condition in which reversible chemical reactions are taking place at the same time in such a manner (equivalent rate) that there is no change in the net concentration of the substances involved in the chemical processes. As a result of these simultaneous reactions, the substances involved in the reactions can be shown to be in a constant ratio to each other.

In physics, the state in which the action of multiple forces produces a steady balance or seeming lack of change. This may be due to a true stop in action or to continuing actions which neutralize each other, resulting in no net change.

Equilibrium Shift: A change in the relative concentrations of reacting substances such that a different reaction or reaction rate is caused.

For example, a change in the relative concentrations of sodium and calcium ions will dictate both the exchange rate and the selection of which ions will be adsorbed to and released from the ion exchange resin beads.

Erosion: The process in which a material is worn away by a stream of liquid (water) or air, often due to the presence of abrasive particles in the stream.

Erosion is a physical or mechanical wearing away process rather than a chemical or electrochemical wearing away process (corrosion).

Etching: The deterioration by chemical change on the surface of glassware caused by the action of high temperatures and detergents, and that is more prevalent or intensified in soft or softened water supplies.

Very high water temperatures in automatic dishwashers can cause detergent phosphate compounds to change into even more aggressive forms. If enough dish soil or water hardness is available, it will react with the most aggressive of these sequestering phosphates. Otherwise, however, the excessive detergent agents can actually extract elements directly from the glassware composition.

In early stages, incipient etching appears as a rainbow-colored film similar to an oil-on-water film. As etching progresses, this changes to opaqueness, which appears similar to filming except that it cannot be removed or repaired since etching is an actual eating away of the glass. It is sometimes called "soft water filming."

The solution to chemical etching is to use less detergent, water temperatures below 140 degrees F, and sufficient amounts of water during the rinse cycle. (Poor rinsing can also be caused by overloading the dishwasher.)

Mechanical etching can occur when two glasses rub against each other in the dishwasher.

Etiology: The cause of a disease.

Eutrophic: Reservoirs and lakes which are rich in nutrients and very productive in terms of aquatic animal and plant life.

Eutrophication: The increase in the nutrient levels of a lake or other body of water; this usually causes an increase in the growth of aquatic animal and plant life.

Evaporite: A mineral precipitated as a result of evaporation, such as the solids left behind in the distillation process.

Exchange Capacity: See Rated Capacity

Exchange Sites: Locations on each bead of ion exchange resin which hold mobile ions that are available for exchange with other ions in the solution that passes through the resin bed.

In cation water softening, for example, mobile sodium ions located at the various exchange sites are exchanged for calcium, magnesium, iron, or other polyvalvent cations in the water being softened.

Exchange sites are also called functional groups.

Exchange Velocity: The rate at which one ion is displaced in favor of another in an ion exchanger.

Exchanger: See Ion Exchanger

Exemption: A state with primary enforcement responsibility under the U.S. Safe Drinking Water Act may relieve a public water system from a requirement respecting an MCL, treatment technique, or both, by granting an exemption if certain conditions exist.

These are:

1. The system cannot comply with an MCL or treatment technique due to compelling factors which may include economic factors; 2. The system was in operation on the effective date of the MCL or treatment technique requirement; 3. The exemption will not result in an unreasonable public health risk.

Exhaustion: The state of an ion exchanger or other adsorbent that is no longer capable of useful ion exchange due to the depletion of the initial supply of available exchangeable ions.

A unit that is "exhausted" requires regeneration to restore its capacity to treat water.

Exhaustion Wave Front: The boundary between the absence and presence of a contaminant as it passes through a media bed.

Exothermic: A term used to describe a chemical process in which heat is released. For example, combustion is an exothermic process because heat is released.

Exposure: Contact with a chemical or physical agent.

Exposure Assessment: The determination or estimation (qualitative or quantitative) of the magnitude, frequency, duration, route, and extent (number of people) of exposure to a chemical.

Exposure Level: The amount (concentration) of a chemical at the absorptive surfaces of an organism.

External Water Treatment: A term used in boiler water treatment referring to the "outside" (that is, not inside the boiler) preparation of the source water to be used for boiler feedwater or boiler makeup water.

This preparation may include such steps as cation exchange softening, pH modification, or dealkalization.

Extrapolation: Estimation of unknown values by extending or projecting from known value.

-F-

Fabric Softener: A laundry additive that gives fabrics a soft feel and smooth surface, reduces static electricity and wrinkling, and makes ironing easier. Most fabric softeners are designed for addition to the wash, rinse, or drying cycles.

Wash- and rinse-added types are liquids; dryer-added fabric softeners come as sprays, impregnated tear-off sheets, and impregnated foam (porous) sheets, or as a slow-dispensing solid bar that attaches to the fin of a dryer.

The softening agent most commonly used is a cationic quaternary ammonium compound. A fluorescent whitening agent or bluing is frequently included, as well as fragrance. Infrequently, antimicrobial ingredients are added.

Fabric softening ingredients also are incorporated in some laundry detergent products.

FAC: Free Available (residual) Chlorine

Facultative Organisms: Facultative microbes can use either molecular (dissolved) oxygen or oxygen obtained from food material such as sulfate or nitrate ions. In other words, facultative organisms can live under aerobic or anaerobic conditions.

Fahrenheit: A temperature scale in which water freezes at 32 degrees and boils at 212 degrees at atmospheric pressure.

Fast Rinse: at a faster rate of flow than that for which the brine was applied.

Because of the greater density of the brine, it moves down through the bed in a piston-like fashion. If rinsing were to continue at this rate until the chlorides had dropped to the acceptable level at which the unit could be returned to service, the time required would be excessive. After the higher concentrations of brine have passed from the unit, little is gained by prolonging the rinse time.

The rinse rate during the last few minutes is increased approximately fivefold to complete the rinse cycle. This fast rinse quickly removes the last traces of chlorides and significantly reduces the regeneration time.

Fatty Acids: The principal components in the molecular structure of natural fats, vegetable oils, fish oils, waxes, rosin, and essential oils, where they are bound chemically with glycerin; this combination is termed a glyceride.

Fatty Alcohol: Primary alcohols from C6 to C22, usually straight chain, which is the type used by the detergent industry.

Fecal Coliform Bacteria: Bacteria found in the intestinal tracts of mammals and, therefore in, fecal matter. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens.

Fecal Streptococcus: Streptococcus bacteria found in fecal matter

Feed Pressure: The pressure at which water is suppled to a water trestment device

Feed-and-Bleed: An ultrafiltration term borrowed from old-fashioned boiler operators. When applied to an ultrafilter design, it means multiple stages of ultrafilter units where the feedwater is controlled at a rate equal to the permeate plus concentrate flow rates and the reject water from the initial ultrafiltration stages is recirculated to subsequent stages.

Feedback: The circulating action between a sensor measuring a process variable and the controller which controls or adjusts the process variable.

Feedwater: The water to be treated that is fed into a given water treatment system.

Fermentation: The conversion/breakdown of organic matter by anaerobic bacteria into carbon dioxide, methane, and similar compounds of low-molecular weight.

Ferric Iron: Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide [Fe(OH)3] or ferric oxide (Fe2O3), which are suspended in water and visible as "rusty water." Ferric iron can normally be removed by filtration.

Also called precipitated iron.

Ferrous Iron: A divalent iron ion, usually as ferrous bicarbonate [Fe(HCO3)2] which, when dissolved in water, produces a clear solution. It is usually removed by cation exchange water softening.

Also called clear water iron.

Ficks Law of Diffusion: A law of chemistry and physics: the rate of diffusion of one substance in another is proportional to the negative gradient of the concentration of the first substance.

Filming: See Water Spotting

Filter: A device installed as part of the water system through which water flows for the purpose of removing turbidity, taste, color, iron, or odor.

Filters can be loose media beds in tanks or cartridge-type devices (either packed-medium cartridges or membrane cartridges) and filter media may be used for mechanical, adsorptive, neutralizing, or catalyst/oxidation filtration processes.

Filter Aid: An agent (such as diatomite) that improves filtering effectiveness in some way, such as enhancing the retention of particles or increasing the permeability of the filter to water flow.

A filter aid is either added to the suspensions to be filtered or placed on the filter as a layer through which the liquid must pass.

Filter Area: The effective area, expressed in square feet, through which water approaches the filter media.

Also called surface area.

Filter Cake: 1. Solids deposited on top of a filter media bed, often by use of chemically feeding a coagulant or filter aid. 2. The dewatered residue from a filter, centrifuge, or other dewatering device.

Filter Media: The selected materials in a filter that form the barrier to the passage of filterable suspended solids or dissolved molecules. Filter media are used to remove undesirable materials, tastes, and odors from a water supply and to adjust the pH in a water supply.

Filter designs include: 1)loose media filters with grains, resin, or other particles lying in beds or loosely packed in column-form in tank-type filters; or 2)cartridge-type filters which may contain membranes, fabric, fiber, bonded-ceramic, precoat, or cast solid-block filter media. The media used in some filters are chemically inert, such as sand, which performs only a mechanical filtration. Other filter media are multifunctional, chemically-reactive media such as calcite, activated carbon, magnesia, manganese dioxide, and manganese greensand.

Filter Rating: See Micron Rating

Filter-Ag: The trade name for an aluminum silicate (pumicite) granular product used as a general purpose filter medium.

Filtrate: 1. The effluent liquid from a filter system; that part of the feed stream which has passed through the filter. 2. The liquid remaining after removal of solids, as the liquid extracted in the formation of a filter cake.

Filtration: The process of separating solids from a liquid by means of a porous substance such as a permeable fabric or membrane or layers of inert media.

Fines: Extremely small particles which are smaller than the specified size (in millimeters) for the medium. Fines may be formed in the manufacturing process, may result from breakdown of medium particles (ion exchange resins or activated carbon) during service, or may result from the dissolving of a medium such as calcite.

An excess of fines in a filter, softener, or deionizer can create undesirable pressure drop in the system, cause sloughing of particles, or create undesirable qualities in the filter effluent.

Finished Water: Product water as it leaves the municipal treatment plant for delivery to consumers. When it arrives at the point-of-use, it has become delivered water. Also called product water.

First Draw Sample: A one-liter sample of tap water, collected in accordance with CFR Section 141.86(b)(2), that has been standing in plumbing pipes at least six hours and is collected without flushing the tap.

Fission:  As relates to biology, reproduction by cell division.

Fixed Bed: 1. The filter or ion exchange medium retained in a vessel. 2. Also refers to media beds which are "contained". That is, filled to the top or to the restraining barrier with filter media and not capable of being expanded during backwashing.

Fixed Matter: The residue (particulate and/or dissolved material) that remains behind (immovable or fixed) despite action to expel it, such as the residue remaining after heating or burning a substance to drive off the volatile solids.

Fixed Solids: The term used in the laboratory analysis of the solid's content of water to define the residue of total suspended and/or dissolved solids after ignition (burning) or heating for a specified time at a specified temperature.

Fixture: As relates to plumbing, any permanently-installed receptacle that will hold water, such as a sink, lavatory, or water closet (toilet).

Flagellates: Microorganisms that move by the action of tail-like projections.

Flash: The portion of a superheated fluid that is converted to vapor when its pressure is reduced as in flash distillation.

Flash Distillation: A distillation process in which hot incoming water flows into a chamber in which pressure is low, causing some of the water to flash (turn quickly into steam.)

Floc: As relates to water treatment, avery fine, fluffy-type mass formed by the coming together of a number of fine suspended particles. A floc can occur naturally, but most frequently it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity or color.

In wastewater treatment, a clump of solids formed in sewage by biological or chemical action.

Floc (Water Treatment): A very fine, fluffy-type mass formed by the coming together of a number of fine suspended particles. A floc can occur naturally, but most frequesntly it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity of color.

Flocculation: The process of bringing together destabilized or coagulated particles to form larger masses or flocs (usually gelatinous in nature) which can be settled and/or filtered out of the water being treated.

Flocculents: Materials which when added to water cause suspended particles to coagulate into larger groupings and form gelatinous clouds of precipitate which enclose additional fine particles of suspended dirt.

The precipitate and the dirt can then be settled or filtered out of the water being treated.

Flood Plain: The flat or nearly flat land on the floor of a stream valley or tidal area that is covered by water during floods.

Flood Rim: The edge of a receptacle (such as a plumbing fixture) from which water will overflow.

Flow Control Valve: A cylindrical pressure-compensating valve installed to regulate the flow of water. Rated in gpm or gpd.

Flow Controller: An in-line device or orifice fitting which will regulate and control flow of water or regenerant over a broad range of inlet water pressures. Some types are manually adjustable.

Flow Meter: An instrument, mechanical or electronic, used for recording (in gallons, cubic feet, or cubic meters) the quantity of water passing through a particular pipe line or outlet.

In water processing systems, meters may initiate certain functions such as automatically starting the regeneration cycle in an ion exchange system.

Flow Rate: The quantity of water or regenerant which passes a given point in a specified unit of time, often expressed in U.S. gpm (or L/min).

In filters, flow rate is usually measured in gpm/sq.ft. of bed area. In ion exchangers, it is expressed in gpm/cu.ft. of resin.

Flow rate is a critical design parameter by which the effectiveness of the water treatment unit is measured.

Flow Sensor: A device that measures flow rate and can control or measure an action (such as chemical feed) in proportion to the flow rate of the fluid.

Flow Switch: A device which, according to a preset flow rate condition, causes an action when the actual flow rate falls outside the preset limit(s).

Fluidized: A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized.

In water treatment, a bed of filter media is fluidized by backwashing water through the filter.

Fluidized Bed: A medium bed which has become expanded during the backwash step or during "upflow" regeneration of an ion exchanger.

Flume: A raceway or channel constructed to carry water or to permit the measuring of its flow.

Fluorescein: An orange-red compound that exhibits intense fluorescence in alkaline solutions and is used to dye water in order to trace its course and movement.

Fluoridation: The addition of a chemical to increase the concentration of fluoride ions in drinking water to a predetermined optimum limit to reduce the incidence (number) of dental caries (tooth decay) in children.

Defluoridation is the removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.

Fluoride: A naturally-occurring constituent of some water supplies, an excess of which (over 2.0 ppm) can cause discolored teeth (mottling).

Skeletal fluorosis, a serious crippling bone disorder resembling osteoporosis, can develop from many years of exposure to drinking water with more than 4.0 ppm of fluoride.

Fluorosis: An abnormal condition caused by excessive intake of fluorine, characterized chiefly by mottling of the teeth.

Flush: 1. To open a cold-water tap to clear out all the water which may have been sitting for a long time in the pipes. In new homes, to flush a system means to send large volumes of water gushing through the unused pipes to remove loose particles of solder and flux.

2. To force a cleansing liquid rapidly through piping, tubing, storage vessels, process tanks, or other plumbing items to clean them out.

Flush Tank: The chamber of the toilet in which the water is stored for rapid release to flush the toilet. The size of the flush tank is to be accounted for in proper sizing of any plumbing system or water treatment system.

Flush Valve (Flushometer): A self-closing valve used for flushing urinals and toilets in public buildings. This type of valve allows very high flow rates (15-20 gpm) for a few seconds.

Flushing: In municipal water systems, a method used to clean water distribution lines. Hydrants are opened and water with a high velocity flows through the pipes, removes deposits from pipes, and flows out the hydrants.

Flux: In cross flow filtration, the flow rate of product water through a reverse osmosis, electrodialysis, or ultrafiltration membrane.

The flow rate is usually given in terms of volume unit per time per membrane area, such as gallons per day per square foot or liters per hour per square meter.

FMA: Free mineral acidity

Foam: A mass of bubbles formed on liquids by agitation.

Foot Valve: A water softener valve, controlled by a float, which controls the amount of water entering or brine solution leaving the brine tank. A special type of check valve located at the bottom end of the suction pipe on a pump. This valve opens when the pump operates to allow water to enter the suction pipe but closes when the pump shuts off to prevent water from flowing out of the suction pipe.

Formaldehyde: Formic aldehyde methanol, HCHO3, made by oxidation of synthetic methanol or low-boiling petroleum gases such as propane or butane. Available commercially as a 37-50 percent aqueous solution which may contain up to 15 percent methanol to inhibit polymerization.

Commercial grades are called formalin. An effective preservative, disinfectant, and sanitizing agent, although it is not a sterilizer, because formaldehyde does not kill completely all microorganisms. Is not typically used to sanitize drinking water treatment equipment because of personal hazards associated with it i.e., toxic by inhalation, strong irritant, and a carcinogen.

Formation: A group of similar consolidation (that is, relatively solid) rocks of unconsolidated (that is, relatively loose) minerals.

Fouling: In electrodialysis applications, the deposit of organic or other materials on the surface of the electrodialysis membrane surface, causing membrane inefficiencies.

As relates to filtration or ion exchange, the accumulation of undesirable foreign matter in a filter or ion exchange media bed causing clogging of pores or coating of surfaces and inhibiting or limiting the proper operation of the bed and the treatment system.

In reverse osmosis or ultrafiltration applications. a phenomenon in which a reverse osmosis or ultrafiltration membrane adsorbs, interacts with, or becomes coated by solutes and/or precipitates in the feed stream resulting in a decrease in membrane performance by lowering the flux and/or affecting the rejection of solutes.

Fouling (filtration/ion exchange): The accumulation of undesirable foreign matter in a filter or ion exchange media bed causing clogging of pores or coating of surfaces and inhibiting or limiting the proper operation of the bed and the treatment system.

Fouling (reverse osmosis/ultrafiltration): A phenomenon in which a reverse osmosis or ultrafiltration membrane absorbs, interacts with, or becomes coated by solutes and/or precipitates in the feed stream resulting in a decrease in membrane performance by lowering the flux and/or affecting the rejection of solutes.

FPS: Feet (foot) per second

Fractionate: To separate into fractions or parts.

Free Available (Residual) Chlorine (FAC): That portion of the total available residual chlorine composed of dissolved chlorine gas (Cl2), hypochlorous acid (HOCl), and/or hypochlorite ion (OCl-) remaining in water after chlorination.

This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.

Free Residual Chlorination: The application of chlorine to water to produce a free available chlorine residual equal to at least 80 percent of the total residual chlorine (sum of free and combined available chlorine residual).

Freeboard: The vertical distance between the top of a filter media bed (or ion exchange resin bed) and the overflow or collector. This space allows for bed expansion during backwashing.

The distance may be expressed in linear measurement or as a percent of the bed depth.

Fresh Water: Water having less than approximately 1,000 mg/L (ppm) of total dissolved solids (TDS).

Friability: An expression of the ability of ion exchange beads to resist cracking under hydrostatic operation.

Friction Losses: The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, and restrictions caused by fittings.

Water flowing in a pipe loses pressure or energy as a result of friction losses.

Fulvic Acid: A water-soluble, natural organic substance of low molecular weight which is derived from humus often found in surface water.

Fulvic acid contributes to the formation of trihalomethanes in chlorinated water supplies and can contribute to organic fouling of ion exchange resin beds. Fulvic acids are chelating agents that can bind and hold metal ions in solution, and are particularily involved in the solubilization and transport of iron in water.

Fulvic acid compounds are associated with color in water. These yellow-brown materials frequently are encountered along with soluble iron.

Functional Groups: See Exchange Sites

Fungi: (singular = fungus) Mushrooms, molds, mildews, rusts, and smuts that are small nonchlorophyll-bearing plantlike organisms lacking roots, stems, and leaves. They have distinct nuclei surrounded by nuclear membranes as well as other specialized functional cell parts but cannot carry on photosynthesis. They occur in natural waters and grow best in the absence of light.

Their decomposition may cause objectionable tastes and odors in water.

-G-

 

Gallionella Ferruginea: One of several types of bacteria that use iron in their metabolism and are capable of depositing gelatinous ferric hydroxide.

Gallon: The common U.S. unit of measurement of liquid volume. (The international unit of volume measurement is the liter.)

One U.S. gallon has a volume of 231 cubic inches or 3.785 liters. The Imperial (British) gallon equals 277.418 cubic inches or 4.546 liters.

Galvanic Corrosion: A form of corrosion which occurs in a galvanic cell in which one of the metals dissolves and goes into solution.

This form of corrosion is accelerated by high concentrations of dissolved minerals in water that increase electrical conductivity.

Galvanic corrosion may occur if two pipes of dissimilar metals are joined directly--without the use of a pipe fitting designed to insulate different metals from one another and prevent such corrosion of the pipes.

Galvanize: To coat a metal (especially iron or steel) with zinc.

Galvanization is the process of coating a metal with zinc.

Gamma decay: A type of radiation, gamma radiation, where gamma rays are emitted and that usually accompanies alpha or beta decay. Gamma rays are photons, and are without rest mass or charge. Alpha or beta decay may simply proceed directly to the ground (lowest energy) state of the daughter nucleus without gamma emission, but the decay may also proceed wholly or partly to higher energy states (excited states) of the daughter. In the latter case, gamma emission may occur as the excited states transform to lower energy states of the same nucleus may transform to a lower energy state by ejecting an electron from the cloud surrounding the nucleus. This orbital electron ejection is known as internal conversion and gives rise to an energetic electron and often an x-ray as the atomic cloud fills in the empty orbital of the ejected electron. SEE ALSO alpha decay; beta-minus decay; beta-plus decay; photon; radioactivity.

Garnet: A group of hard, reddish, glassy, mineral sands made up of silicates of base metals (calcium, magnesium, iron, and manganese).

Garnet has a higher density than sand.

Gas Chromatograph (GC): A chemical analytical instrument used to separate a sample into components during gas chromatography.

Gas Chromatography (GC): Chromatography in which the sample mixture is vaporized and injected into a stream of carrier gas such as helium or nitrogen (mobile phase) which is moving through a column containing solid medium or medium coated with a relatively nonvolatile liquid (stationary phase).

The mobile phase sample is, thereby, separated into its component compounds according to the unique affinity of each compound for the stationary phase.

The components appear separately at the effluent end of the column where they can be detected and measured by density differences, thermal conductivity changes, or ionization detectors.

The detector gives a signal (in peak form) for each separated component compound; the intensity of the signal is proportional to the quantity of the compound injected, making it possible to provide a quantitative analysis by calibration.

Gastroenteritis: An inflammation of the stomach and intestine resulting in diarrhea, with vomiting and cramps when irritation is excessive.

When caused by an infectious agent, it is often associated with fever.

Gate Valve: A type of valve in which the closing element (the gate) is a disc that moves across the stream in a groove or slot for support against pressure.

A gate valve has relatively large full ports and a straight line flow pattern.

A gate valve creates very little pressure drop; this valve is, however, subject to leakage if the sealing surfaces are scored or marred or if debris becomes lodged in the groove.

Gauge Pressure: The pressure within a closed container or pipe as measured with a gauge.

In contrast, absolute pressure is the sum of atmospheric pressure (14.7 lbs/sq in) PLUS pressure within a vessel (as measured by a gauge).

Most pressure gauges read in gauge pressure or psig (pounds per square inch gauge pressure).

Gel Zeolite: A synthetic sodium alumina silicate cation exchange product that was very widely used in residential water softeners prior to the development of DVB/styrene cation resin.

Also called siliceous gel zeolite.

Geological Log: A detailed description of all underground features discovered during the drilling of a well (depth, thickness, and type of formations).

Geophysical Log: A record of the structure and composition of the earth encountered when drilling a well or similar type of test hole or boring.

Germicidal Ultraviolet: An ultraviolet light that peaks at a 2,537-angstrom wavelength and is in a wavelength that lies between 200 and 300 nanometers.

This is known as the germicidal or short-wave ultraviolet band.

Giardia: A common waterborne protozoan that forms cysts and is resistant to disinfectants such as chlorine and ultraviolet light.

Giardia can be removed by filters that capture all particles of four microns and greater in size.

Giardia Lamblia: Flagellate protozoan which is shed during its cyst stage into the feces of man and animals.

When water containing these cysts is ingested, the protozoan causes a severe gastrointestinal disease called giardiasis.

Giardiasis: Intestinal disease caused by an infestation of Giardia flagellates.

Glauconite: A natural dull-green iron potassium silicate mineral occurring abundantly in greensand.

The approximate formula for glauconite is K15(Fe, Mg, Al)4-6(Si,Al)3O20(OH)4.

Globe Valve: A type of valve in which the closing element is a segment of a sphere or a flat or rounded gasket which is moved into or onto a round port.

The globe valve usually has small ports, an "S" flow pattern and relatively high pressure drop.

Globe valves provide tight dependable seals with minimum maintenance.

Glutaraldehyde: [OCH(CH2)3CHO] A general disinfectant for drinking water treatment equipment, including reverse osmosis membranes. Available as sporicidin and cidex, for example; requires full strength use for disinfection.

A general disinfectant for drinking water treatment equipment, including reverse osmosis membranes. Available as sporicidin and cidex, for example; requires full strength use for disinfection.

Glycerin: A trihydroxy alcohol with sweet tast and syrup-like consistency; the "gylcerine" spelling has come into general use, but it is chemically incorrect.

Grab Sample: A single sample collected at a particular time and place which represents the composition of the water only at that time and place.

Grade: The elevation of the invert of the bottom of a pipeline, canal, culvert, or similar conduit. The inclination or slope of a pipeline, conduit, stream channel, or natural ground surface usually expressed in terms of the ratio or percentage of number of units of vertical rise or fall per unit of horizontal distance. A 0.5 percent grade would be a drop of one-half foot per hundred feet of pipe.

Grain: A unit of weight equal to 0.0648 grams or 0.000143 pounds or 1/7000th of a pound.

Grains Per Gallon (gpg): A common method of reporting water analysis results in the United States and Canada.

One grain per gallon equals 17.1 parts per million (ppm) or 17.1 milligrams per liter. Grains per Imperial gallon equals 14.3 mg/L (or ppm).

Gram: The basic unit of weight measurement in the metric system.

One gram equals 0.0022 pounds or 15.432 grains. The gram was originally devised as the weight of one cubic centimeter or one milliliter of water at 4 degrees Centigrade.

Gram-milliequivalent: The equivalent weight (in grams) divided by 1,000.

GRAS: Designation for materials listed by the U.S. Food and Drug Administration (FDA) as "generally regarded as safe."

Gravel Support Bed: Various layers of different sized gravel and coarse sand placed above the underdrain network to support filter or ion exchange media beds.

The gravel support bed contributes greatly to the distribution and collection of product water and the even dispersal of the backwash water flow.

Gravimetric Measurement: Measurement on the basis of weight.

Gray (Gy): The SI unit of absorbed dose of ionizing radiation.

One gray (Gy) equals 100 rads.

Greensand: A naturally-occurring mineral that consists largely of dark greenish grains of glauconite and which possesses ion exchange properties.

Greensand was the original product used in commercial and home cation exchange water softening units and was the base product for manufacturing manganese greensand zeolite products.

Grey Water: Waste water other than sewage, such as sink drainage or washing machine discharge.

Groundwater: Water found beneath the surface of the ground.

Groundwater is primarily water which has seeped down from the surface by migrating through the interstitial spaces in soils and geologic formations.

Grouting: Cement-like fluid which is poured or injected into the bore hole during well drilling to seal crevices and to prevent contamination or loss of drilling mud.

Grouting provides protection around the metal well casing and helps prevent corrosion and infiltration into the well bore hole from surface water and shallow groundwater.

Grouting can sometimes improve the strength and elasticity of the rock formation itself.

Gypsum: (CaSO4 2H2O) A moderately insoluable calcium sulfate, containing 20.9 percent water, which is often used as a soil amendment to aid in building soil structure and permeability.

A moderately insoluble calcium sulfate, containing 20.9 percent water, which is often used as a soil amendment to aid in building soil structure and permeability.

-H-

H2O: The chemical formula for water (dihydrogen oxide).

Half-life: The time required for half of the substance present at the beginning to dissipate or disintegrate.

Halite: A geological term for rock salt, a mineral which is more than 95 percent sodium chloride (NaCl).

Also called native salt or fossil salt.

Halogens: A family group of elements, including bromine, chlorine, fluorine, astatine, and iodine, which are extremely active chemically. These elements exist in the free state normally as diatomic

molecules, but more commonly are found as the ionic component in compounds with various other elements.

Halophilic: Thriving in a salt environment.

Halophilic Bacteria: Salt-tolerant bacteria often found in solar salt which has not been fully kiln dried or in salt which may have been exposed to unsanitary conditions over a long period of time.

Hard Water: Water containing total hardness in the amount of one grain per U.S. gallon (or more) measured as calcium carbonate equivalent.

Hardness: A common quality of water which contains dissolved compounds of calcium and magnesium and, sometimes, other divalent and trivalent metallic elements. The term hardness was originally applied to waters that were hard to wash in, referring to the soap wasting properties of hard water. Hardness prevents soap from lathering by causing the development of an insoluble curdy precipitate in the water; hardness typically causes the buildup of hardness scale (such as seen in cooking pans). Dissolved calcium and magnesium salts are primarily responsible for most scaling in pipes and water heaters and cause numerous problems in laundry, kitchen, and bath. Hardness is usually expressed in grains per gallon (or ppm) as calcium carbonate equivalent.

The degree of hardness standard as established by the American Society of Agricultural Engineers (S-339) and the Water Quality Association (WQA) is:

Term grains/gallon mg/Liter(ppm) Soft = less than 1.0 less than 17.1 Slightly Hard = 1.0 to 3.5 17.1 to 60 Moderately Hard = 3.5 to 7.0 60 to 120 Hard = 7.0 to 10.5 120 to 180 Very Hard = 10.5 and above 180 and above

Hardness as Calcium Carbonate: The value obtained when the hardness-forming salts are calculated in terms of equivalent quantities of calcium carbonate.

This method of water analysis provides a common basis for comparison of different salts and compounds.

Hazard Evaluation: A component of risk assessment that involves gathering and evaluating data on the types of health injury or disease (e.g., cancer) that may be produced by a chemical and on the conditions of exposure under which injury or disease is produced.

Head: The pressure at any given point in a water system, generally expressed in pounds per square inch (psi).

May also be called pressure head or velocity head. Head is calculated as the pressure exerted by a hypothetical column of water standing at the height to which the free surface of water would rise above any point in a hydraulic system.

For this reason, head is sometimes expressed as the height of a column of water which would produce a given pressure; this measurement may be called hydrostatic head.

The pressure head in feet of water is equal to the pressure in psi times 2.31 ft/psi.

Head Loss: The reduction of water pressure (head), measured in psi, in a hydraulic or plumbing system.

Head loss is a measure of the resistance of the medium bed (or other water treatment system) and/or plumbing system to the flow of the water through it. In water treatment technology, head loss is basically the same as pressure drop.

Health Effects Concern: Exposure to contaminant at a toxicologically significant level as defined by the maximum contaminant levels (MCLs) for regulated contaminants or action for nonregulated contaminants.

Heat Exchanger: An apparatus used to transfer heat from one medium to another or used to remove heat from or add heat to a fluid.

Heat of Vaporization: The amount of additional (latent) heat needed to change a given amount of liquid existing at its boiling point temperature into a vapor.

Heavy Metals: Metallic elements with high atomic weights, e.g., mercury, chromium, cadmium, arsenic, and lead.

They can damage living things at low concentrations and tend to accumulate in the food chain.

Hectare: A measure of area in the metric system similar to an acre.

One hectare is equal to 10,000 square meters and 2.4711 acres.

Heel: In ion exchange applications, the lower zone of the ion exchange bed that is "passed by" in either the softening, deionization, or dealkalization mode or during the application of regenerants.

This condition is usually due to the configuration of the vessel or the lack of a good underdrain distribution system.

Heme: A deep red pigment (C34H32N4O4Fe) which contains reduced (ferrous) iron.

Heme is found in red blood cells (hemoglobin). It is also found outside the body in the nonprotein portions of some organic molecules called hemoproteins. In water quality treatment, it may be referred to as heme iron, which is organically-bound iron that can cause water to have a pinkish cast to it.

Hemodialysis: The process of purifying a kidney patient's blood by means of a dialysis membrane.

Hemodialysis Grade Water: Water which meets the requirements set forth by the American National Standards for Hemodialysis Systems and covered in the Association for the Advancement of Medical Instrumentation (AAMI) standards.

Hemolysis: The rupturing of red blood cells which sometimes occurs during hemodialysis.

Hemolysis may be caused by the presence of chloramines in dialysis water.

Henrys Law: A law of chemistry that states that the weight of a gas dissolved (at a given temperature) in a liquid is proportional to the pressure of the gas above the liquid.

Hepatic: Pertaining to the liver.

Hepatitis: Hepatitis is an inflammation of the liver usually caused by an acute viral infection.

Yellow jaundice is one symptom of hepatitis.

Herbicide: A compound, usually a man-made organic chemical, used to kill or control plant growth.

Hertz (Hz): The number of complete electromagnetic cycles or waves in one second of an electrical or electronic circuit. Also called the frequency of the current. Abbreviated Hz.

Heterocyclic: A type of organic compound in which the characteristic chemical groups are linked in a closed ring structure and in which one or more atoms in the ring is an element other than carbon, e.g., silica, sulfur, nitrogen, etc.

Heterotrophic: heteros, other + trophe, nourishment.

Obtaining food or nourishment from other organisms.

Heterotrophic organisms or heterotrophs are consumers such as man or decomposers such as bacteria that obtain their nourishment and energy from the organic molecules manufactured by the autotrophic organisms (the producers). All animals, for example, are consumers and heterotrophs that depend on complex organic molecules produced by autotrophs for their food and energy.

Heterotrophic Microorganisms: Bacteria and other microorganisms that use organic matter synthesized by other organisms for energy and growth.

Heterotrophic Plate Count (HPC): A procedure for estimating the total number of live nonphotosynthetic bacteria in water.

Colony-forming units (CFU) are counted after spreading an aliquot portion of a sample over a membrane or pour plate and incubating in an amiable growth medium (agar) and at an amiable temperature.

(These generally are not considered to be disease-causing bacteria.)

High Frequency Ozonation: Operation of an ozone generator at frequencues equal to or greater than 1,000 cycles per second or 1,000 hertz.

High Performance Liquid Chromatography (HPLC): A general term applied to modern instrumental techniques adopted to greatly increase the scope and precision of the liquid chromatography analytical method.

Among the varied HPLC techniques are:

Reversed phase chromatography, which uses a polar liquid phase for elution of a column containing a nonpolar phase. This technique is used, for example, to analyze the polynuclear aromatic hydrocarbon category (pyrenes, naphthalenes, etc.) of synthetic organic compounds; Ion exchange chromatography, which makes it possible to separate large numbers of cations and anions; Exclusion chromatography, which separates, on a porous gel, compounds according to their size and makes it possible to determine their apparent molecular weights and to separate fractions of different molecular weights for further analyses.

High Salting: The use of 15 pounds or more of salt (NaCl or KCl) to regenerate each cubic foot of cation resin.

High salting is generally recommended for high total hardness water and water containing high concentrations of dissolved heavy metals.

Histology: The study of the structure of cells and tissues; usually involves microscopic examination of tissue slices.

Homogenous: Having the same composition throughout.

Homogenized milk is homogeneous because the fat globules have been broken into smaller colloid-sized particles that remain distributed throughout the liquid milk. In nonhomogenized milk, the fat globules rise to the top of the container as cream.

Hose Bib: Faucet.

A location in a water line where a hose is connected.

Hot Lime-Soda Softening: A method of partially softening water by adding lime and soda ash to chemically precipitate the calcium, magnesium, iron, and silica at a water temperature of about 212 degrees Fahrenheit. This process also drives off carbon dioxide.

Hot Process Softening: A term used to encompass several softening/clarifying processes using lime, lime and soda ash, or lime and cation softening to treat water which is at or near the boiling point.

Hot process softening can remove carbon dioxide, silica, and precipitated magnesium and is used mainly for boiler feedwater preparation and sulfur mining.

Hot-Lime Softening: A partial softening method which requires adding a lime slurry to water which is at about 212 degrees Fahrenheit and then chemically precipitating and removing the calcium and magnesium hardness via sedimentation and filtering.

HPC: Heterotrophic Plate Count

HPLC:  High Performance Liquid Chromatography (same as high pressure liquid chromatography)

HTH: (pronounce as separate letters): High Test Hypochlorite. Calcium hypochlorite or Ca(OCl)2. "HTH" is a trademark (Olin) for a high-test calcium hypochlorite product containing 70 percent available chlorine that is commercially available in both water-soluble granular and tablet form.

Human Equivalent Dose: A dose which, when administered to humans, produces an effect equal to that produced by a dose in animals.

Human Exposure Evaluation: A component of risk assessment that involves describing the nature and size of the population exposed to a substance and the magnitude and duration of their exposure.

The evaluation could concern past exposures, current exposures, or anticipated exposures.

Human Health Risk: The likelihood (or probability) that a given exposure or series of exposures may have or will damage the health of individuals experiencing the exposures.

Humic Acid: Humic substances that are soluble in strong base solutions but insoluble in acidified (to pH < 2) water, and that affect water quality through exchange of species, such as cations or organic materials.

Humic Substances: The organic portion of soil that remains after prolonged microbial decomposition, and that is formed by the decay of leaves, wood, and other vegetable matter. Humic substances can impart a yellowish-brown to brownish-black color to water; dectectable to 0.1 ppm in water.

Humic substances are commonly classified on the basis of solubility.

If a material containing humic substances or humus is extracted with a strong base and the resulting solution is then acidified, the products are a) a nonextractable plant residue called humin, b) a material called humic acid that precipitates from the acidified (pH < 2) solution, and c) an organic material called fulvic acid that remains dissolved in the acidified solution.

The high molecular weight and polyelectrolytic humic substance macromolecules range from a molecular weight of a few hundred for fulvic acid to tens of thousands for the humic acid and humin fractions.

Humic substances form suspected-carcinogenic trihalomethanes (THMs, such as chloroform, dibromochloromethane, bromodichloromethane, and bromoform) by reaction with chlorine. Humic substances are excellent chelating agents that bind with and hold metal ions in water, and they also effectively exchange cations with water.

Humidification: The process of increasing the water vapor or moisture content.

Humin: Humic substances that remain insoluble in both strong base solutions and in water.

Humins can effectively exchange cations with water and may accumulate quantities of metals. Lignite coal, for example, is largely a humin and humic-acid material, which, through ion exchange, tends to remove some metal ions from water.

Hydrate: A substance formed by combining water with a compound.

Hydration: The chemical combination of water into another substance.

Hydraulic: Referring to water or other fluids in motion.

Hydraulic Classification The rearrangement, during backwashing, of ion exchange or other media particles according to size.

As the result of classification, the smallest particles tend to rise to the top of the bed while the largest tend to sink to the bottom because of weight or surface area ratio.

Hydraulic Conductivity: The capacity of rock or soil formations to transmit water to a pumping well. Capacity is related to the amount and size of interconnecting pore spaces in the rock.

Hydraulic Staging: Multiple passes of water between electrodes used in an electrodialysis or through a sequence of subsequent membranes or filters used in a reverse osmosis or filtration system to achieve further treatment.

Hydrocarbon: An organic compound containing only carbon and hydrogen.

Hydrocarbons often occur in petroleum products, natural gas, and coals.

Hydrochloric Acid (HCl): A water-based solution of hydrogen chloride which is a strong, highly corrosive acid. HCl may be used as a regenerant for cation resin deionization systems operated in the hydrogen (H+) cycle.

HCl may be used as a regenerant for cation resin deionization systems operated in the hydrogen (H+) cycle.

Hydrocyclone: The basic form of most separators which act on the principle of centrifugal force and are used to remove sand and abrasives from well water.

Hydrogen Bond: The weak attraction between a hydrogen atom carrying a partial positive charge and some other atom with a partial negative charge.

Hydrogen bonds occur in polar compounds such as water by the attraction of a hydrogen atom of one molecule to two unshared electrons of another molecule.

Hydrogen bonds are less than one-tenth as strong as covalent bonds where electrons are actually shared by a pair of atoms, but they significantly affect properties such as the melting point, boiling point, and crystalline structure of substances.

Hydrogen Cycle: A cation exchange cycle (H+ form) in which the cation medium is regenerated with acid and all cations in the water are removed by exchange with hydrogen ions.

Hydrogen Peroxide: H2O2  A strong disinfectant and oxidizing agent used mostly in dilute water-based solutions. Hydrogen peroxide can be formed in water with a 1948-angstrom mercury-vapor ultraviolet lamp.

Hydrogen peroxide may be used in advanced oxidation processes in combination with ozone to encourage the formation of highly reactive hydroxyl radicals; this process is then called the Peroxone process.

Also called peroxide.

Hydrogen Sulfide (H2S): A corrosive and flammable gas often found dissolved in well water and often accompanied by iron and low pH values. Hydrogen sulfide develops from decaying organic matter, from sulfate-reducing bacteria, and from petroleum refining. H2S formation can be catalyzed by a magnesium anode rod in a hot water heater; anaerobic sulfate-reducing bacteria can live in a hot water heater so long as water temperatures are below 140° Fahrenheit, and to produce H2S the SRB need only a ready source of sulfate ions in the incoming water supply and a ready source of electrons as provided by the water heater's anode rod.

The odor of water with as little as 0.5 milligrams per liter (mg/L) of hydrogen sulfide concentration is detectable by most people. Concentrations less than one mg/L give the water a "musty" or "swampy" odor. Over one mg/L hydrogen sulfide concentration gives water a very disagreeable "rotten egg" odor and makes the water corrosive to plumbing. Generally, hydrogen sulfide levels are less than 10 mg/L, but occasionally amounts of 50 to 75 mg/L are found. At higher pH levels hydrogen sulfides present in the ionized alkaline sulfide (HS- and S2-) forms, and at low pH levels it is present in the H2S gaseous form. At pH 5.0 about 90 percent is present as gaseous H2S and 10 percent as sulfide. At pH 8 only six percent is present as a gas.

Hydrogen sulfide concentrations up to about six mg/L can be removed from water using an oxidizing filter (same as an iron filter). Hydrogen sulfide concentrations exceeding six mg/L can be removed by injecting an oxidizing chemical such as household bleach or potassium permanganate and using a filter. The oxidizing chemical should be thoroughly mixed into the water upstream from a retention tank to provide at least 20 minutes of contact time between the chemical and water. Sulfur particles can then be removed by activated carbon filtration. When potassium permangante is used a manganese greensand filter is recommended. Other oxidants such as ozone and hydrogen peroxide are also excellent for oxidizing hydrogen sulfide to precipitate sulfur and even to innocuous sulfate.

Hydrogeologic Conditions: Conditions stemming from the interaction of groundwater and the surrounding soil and rock.

Hydrogeology: The geology of groundwater, with particular emphasis on the chemistry and movement of water.

Hydrologic Cycle: The complete circuit pursued by water in nature, including 1. falling of precipitation (rain, hail, sleet, snow, dew); 2. the journal of fallen water over and through the earth's surfave formations; and 3. eventual evapoation of the water and its return to the atmosphere to again fall as precipitation.

Hydrology: The study of the occurrence, distribution, and circulation of the natural waters of the earth.

Hydrolysate: The product of hydrolysis.

 

Hydrolysis: A chemical reaction in which a substance reacts with water and becomes a different substance. This involves the ionization of the water molecule as well as splitting of the compound hydrolyzed.

An example is the chemical reaction of salt with water which then forms an acid and a base: (NaCl + H2O hydrolyzes to HCl + NaOH).

Hydrometallurgy: The treatment of ores by wet processes as in leaching and accompanying operations, and the technology of separation or recovery of heavy or noble metals from liquid solutions by ion exchange methods.

Hydrometer: A device for measuriing the density or specific gravity of liquids.

Hydrometers commonly consist of a thin glass or metal tube graduated to indicate either specific gravities or percentages of solution constituents and weighted so that they float upright.

Hydrophilic: Having a strong affinity (liking) for water, and thereby exhibiting the characteristic of absorbing water.

Example: Cotton is a hydrophilic fiber. The opposite of hydrophobic.

Hydrophobic: Having a strong aversion (dislike) for water, and thereby exhibiting the characteristic of repelling water.

Example: Nylon is a hydrophobic fiber. The opposite of hydrophilic.

Hydropneumatic System: A system that uses both air and water in its operation.

An example is the pressure tank which uses an air chamber to maintain pressure in a well system even when the pump is not operating.

Hydrosphere: The water of the earth, including surface lakes, streams and oceans, underground water, and water in the atmosphere.

Hydrostatic Pressure: The pressure at a specific elevation exerted by a body of water at rest or, In the case of groundwater, the pressure at a specific elevation due to the weight of water at higher levels in the same zone of saturation.

Hydroxide: The ion formed by an oxygen and a hydrogen atom.

This term is used to describe the anionic hydroxyl radical (OH-) which is responsible for the alkalinity of a solution.

Hydroxyl: The univalent group or radical (OH-), consisting of one atom of oxygen and one of hydrogen, that is characteristic of hydroxides such as sodium hydroxide (NaOH), which is used as a regenerant for anion exchange resins.

Hygroscopic: Having the characteristic of drawing moisture in from the atmosphere such as silica gel, calcium chloride, or zinc chloride.

Sodium chloride (NaCl) is also a hygroscopic substance.

Hyperfiltration: A water treatment process in which desalination of water is achieved by forcing salt solutions, under pressure, through a membrane which generally passes water more readily than salts.

An early term for reverse osmosis technology.

Hypochlorination: The application of hypochlorite compounds to water for the purpose of disinfection.

Hypochlorite: The Ocl- anion, which is the dominant reaction product of chlorine in water at pH greater than 8.

Calcium and sodium hypochlorites are commonly used as disinfecting and bleaching agents.

High-test hypochlorite is a dry solid, largely calcium hypochlorite, which has excellent stability when kept in dry storage and is used as a disinfectant.

-I-

ICAP: Inductive Coupling Argon Plasma Spectroscopy

ICP: Inductive Coupling Plasma Spectroscopy

Immiscible: Not capable of being mixed.

For example, oil and water are said to be immiscible.

Impeller: A rotating set of vanes in a pump designed to pump or lift water.

Impermeable: Not easily penetrated.

The property of a material or soil that does not allow, or allows only with great difficulty, the movement or passage of water.

Impounded Water: Water which is stored in an artificial man-made basin or dammed ravine by diverting flowing streams or collecting rainfall runoff, as in a reservoir.

Inactivate: To make inactive or inert, esp. the alteration or destruction of a biologically active agent such as pathogenic microorganisms or antigens so as to render them harmless.

Incubation Period: The time between initial contact with an infectious agent and the appearance of the first sign or symptom of disease.

Indicator:(Chemical) A chemical material or solution which can be used to show (usually by color change or depth of color) the endpoint of a chemical reaction or chemical concentration.

Examples are litmus; orthotolidine reagent.

(Instrument) A device which indicates the result of a measurement.

Most indicators in the water treatment field use either a fixed scale and movable indicator (pointer), such as a pressure gauge, or a movable scale and movable indicator like those used on a circular-flow recording chart.

Also called a receiver.

 

Induced Infiltration: An emission spectroscopy technique for chemical analysis in which the elements that are to be measured are introduced into a high temperature (6,000 to 8,000 degrees C) argon plasma and, thereby, converted into atomic vapor.

Emission spectroscopy is used to identify and quantify the elements. The high temperature of the plasma limits interferences and ICP has broader application (e.g., for waste water analyses) than atomic absorption (AA) spectroscopy for metals analyses, but it has lower detection power.

Inert Media: Synthetic resin beads or water treatment materials that are nonreactive.

Inert media are used as a neutral nonreactive layer to more effectively separate the cation resin from the anion resin in mixed bed deionizers in order to regenerate each separately.

Infiltration: The movement of water into rocks or soil through interstitial pores, small cracks, or crevices in the soil or rock.

Infiltration Rate: Quantity of water (usually measured in inches) that will enter a particular type of soil per unit time (usually one hour).

Influent: The stream of water to be treated as it flows into any kind of water treatment unit or device, such as hard water into a softener or turbid water into a filter.

Ingestion: Type of exposure in which a substance is introduced through the mouth.

Inhalation: Type of exposure in which a substance is introduced through the lungs.

Inhibitor: Any chemical substance that is added to a water supply (or solution of any kind) which interferes with ("inhibits") a chemical reaction.

For example, inhibitors are sometimes used to help prevent precipitation or corrosion.

In-line Filtration: The addition of chemical coagulants directly to the filter inlet pipe.

The chemicals are mixed by the flowing water. Flocculation and sedimentation facilities are eliminated. This pretreatment method is commonly used in pressure filter installation.

Inorganic Matter: Chemical substances which do not arise from the process of living growth, are composed of matter other than plant or animal matter, and don't contain hydrocarbons or compounds of basically carbon structure.

In-parallel Flow: A piping arrangement which directs separate streams through two or more units of a treatment system in a balanced manner, with equal flow to each device, so that a higher total flow rate than that from a single unit can be achieved.

Input Horsepower: The total power used in operating a pump and motor.

Input HP = (brake HP)(100%) / motor efficiency, %

Insecticide: Any substance or chemical formulated to kill or control insects.

In-series Flow: A piping arrangement in which the entire effluent flow from one unit of a water treatment system is fed to a second succeeding unit.

This arrangement forces the water through multiple treatment units and achieves greater reduction of contaminants than can be achieved by a single pass of water through a single unit.

Installation: The connecting or setting up and startup operations of any water treatment system. The term also refers to complete assembly of piping, valves, drain line, pumps, meters, and controls by which the equipment is connected into the water supply system.

In-Stream Uses: Water uses that can be carried out without removing the water from its source, as in navigation and recreation.

Integrated Exposure Assessment: A summation over time, in all media, of the magnitude of exposure to a toxic chemical.

Interface: The surface which forms a common boundary between two spaces or two parts of matter, such as the surface boundary formed between oil and water.

The term "interface" is often used to refer to the space between two different ion exchange resins in a mixed bed or to the resin surface at the regeneration grid in a mixed bed deionization system.

Interflow: Lateral movement of water in the upper layer of soil.

Intermittent Flow: The interrupted patterns of water usage which occur in the home or in commercial businesses opposed to the steady constant flow patterns common in industry, such as in factories.

This term may also be used to refer to "on-off" flow patterns of water through treatment units specified in testing standards to simulate customer water use patterns.

Internal Friction: Friction within a fluid (water) due to cohesive forces.

Interspecies Extrapolation Model: Model used to extrapolate from results observed in laboratory animals to humans.

Interstices: The pores or other spaces which are not occupied by solid matter and may be found between filter medium particles, ion exchange resin beads, or other similar treatment media.

Interstices may be occupied by air, water, or other gaseous or liquid material.

This term is also used to refer to similar spaces between natural soil or rock particles; and spaces between atoms or molecules in solids.

Invert: The lowest point of the channel inside a pipe, conduit, or canal.

Iodine: (I2) A nonmetallic element which is the heaviest and least reactive of the naturally-occurring halogens.

It may be used for disinfection. In both its liquid and vapor forms, iodine is readily adsorbed by activated carbon.

Iodine Number: A measure of the ability of an activated carbon product to adsorb substances with low molecular weights.

The iodine number of a carbon is equal to the milligrams (mg) of iodine that can be adsorbed on one gram of activated carbon.

Ion: An atom or radical group of atoms such as SO42-. Positively-charged ions are called cations; negatively charged ions are called anions. An ion often has entirely different properties than the element (atom) from which it was formed.

 

Ion Exchange: A reversible chemical process in which ions from an insoluble permanent solid medium (the "ion exchanger"--usually a resin) are exchanged for ions in a solution or fluid mixture surrounding the insoluble medium.

The superficial physical structure of the solid is not affected. The direction of the exchange depends upon the selective attraction of the ion exchanger resin for the certain ions present and the concentrations of the ions in the solution.

Both cation and anion exchange are used in water conditioning. Cation exchange is commonly used for water softening.

Ion Exchange Membrane: A water-tight and electrically-conductive membrane which is either ion exchange resin cast in sheet form or powdered ion exchange resin laminated to a membrane fabric.

Both anion and cation ion exchange membranes are used in electrodialysis treatment systems.

Ion Exchanger: A permanent insoluble material (usually a synthetic resin) which contains ions that will exchange reversibly with other ions in a surrounding solution.

Both cation and anion exchangers are used in water conditioning. The volume of an ion exchanger is measured in cubic feet (or cubic liters) of exchanger after the exchanger bed has been backwashed and drained and has settled into place.

Ionic Concentration: A measure of the concentration of any ion in solution, usually expressed in moles per liter.

Ionic Constant: A measure in absolute units of the extent to which a chemical compound or substance in solution will dissociate into ions.

Ionic Weight: The weight of an ion as determined by the sum of the atomic weights of its components.

Ionization Wednesday,Aug 25, 1999 The process in which a chemical combination breaks up into simpler electrically-charged components (individual atoms or groups of atoms) called ions.

The ionization process is related to the gaining or losing of electrons causing the atoms or group of atoms to become electrically charged.

The term "ionization" is sometimes used as if it had the same meaning as dissociation.

Iron (Fe): A very common element often present in groundwater in amounts ranging from 0.01 to 10.0 ppm (mg/L).

Iron may be found in three forms:

In soluble form such as in ferrous bicarbonate; Bound with a soluble organic compound; and As suspended ferric iron particles. Iron above 0.3 mg/L is objectionable in water because of staining of laundry and plumbing fixtures caused by the oxidation and precipitation of ferric hydroxide and/or ferric oxide (ferric iron) into small solid iron particles. Iron can also give a metallic or distorted flavor to beverages.

Iron also occurs in water as ferric iron.

Iron Bacteria: Bacteria which thrive on iron and are able to actually use ferrous iron (as found in water or steel pipes) in their metabolic processes, to incorporate ferric iron in their cell structure, and to deposit gelatinous ferric hydroxide iron compounds in their life processes.

Iron bacteria are found in several varieties including Crenothrix, Lepothrix, and Gallionella.

Iron bacteria can cause staining, plugging, and taste and odor problems in a water system.

Iron Fouling: The accumulation of iron on or within an ion exchange resin bed or filter medium in such amounts that the capacity of the medium is reduced.

Irreversible Effect: Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent.

Isotherm: The measurement which represents the relationship between the mass of the substance adsorbed (adsorbate) at a given temperature and the mass of the adsorbent.

Isotope: One of two or more atoms or elements which have the same atomic number (occupy the same position in the periodic table) but which differ in other respects such as atomic weight and number of neutrons in the nucleus.

-J-

Jackson Turbidity Unit (JTU): A formerly-used measurement of the turbidity in a water sample. This has been replaced by the nephelometric turbidity unit.

Jet (Ejector) Pump: A combined centrifugal and ejector pump.

In a jet pump, a portion of the discharge water from the centrifugal pump is diverted through a nozzle and venturi tube. A pressure zone lower than that of the surrounding area is created by the velocity of water flowing through the venturi tube; therefore, water from the source (the well) flows into this area of reduced pressure. The velocity of the water from the nozzle pushes the water through the pipe toward the surface where the centrifugal pump can lift it by suction. The centrifugal pump then forces the water into the water plumbing system.

Jetted Well: A shallow well constructed by a high-velocity stream of water directed downward into the ground.

Jogging: The frequent starting and stopping of an electric motor.

Joule: A measure of energy, work, or quantity of heat. One joule is the work done when the point of application of a force of one newton is displaced a distance of one meter in the direction of force. The absolute unit of work-energy equal to 107 ergs or about 0.7736 foot-pounds or 0.2389 calories.

One joule is the work done when the point of application of a force of one newton is displaced a distance of one meter in the direction of force.

The absolute unit of work-energy equal to 107 ergs or about 0.7736 foot-pounds or 0.2389 calories.

-K-

KDF: (Kinetic Degredation Fluxion) The trade name for a patened medium composed of high purity copper and zinc granules. KDF is capable of removing chlorine, soluble heavy metals, and other inorganic contaminents from water through the chemical reduction/oxidation (redox) process.

Kelvin Scale: A temperature scale which measures from absolute zero (-273.15 degrees Celsius) in Kelvins which are equivalent to Celsius degrees in magnitude.

Kelvins = Celsius degrees + 273.15.

Kilo: The metric prefix used to mean "1000" of some unit of measure: a kilometer is 1,000 meters; a kilogram is 1,000 grams.

The term kilo is sometimes used to mean kilogram.

Kilograin: 1,000 grains

Kilogram: 1,000 grams

Kiloliter: 1,000 liters (264.18 U.S. gallons) or one cubic meter.

Kilowatt-Hour: The unit of electric energy or work equal to that done by one kilowatt in one hour.

Equal to 1,000 watt-hours.

Kinetic Energy: Energy possessed by a moving body of matter, such as water, as a result of its motion.

Kinetics: The study of the relationships between temperature and the motion and velocity of very small particles.

Kinetic relationships influence the rate of change in a chemical or physical system and are used particularly to describe the dynamics and rate of ion exchange reactions.

KPa: Kilopascal

KYNAR: Trade name for polyvinylidene fluoride.

-L-

L/d: liters per day.

L/min.: liters per minute.

Laminar Flow: The movement of fluid in a particular direction in smooth, continuous, nonturbulent parallel layers which do not mix with each other.

Landfill: Facility in which solid waste from municipal and/or industrial sources is disposed; sanitary landfills are those that are operated in accordance with environmental protection standards.

Langelier Saturation Index: A calculated number used to predict the calcium carbonate (CaCO3) stability of a water; that is, whether a water will precipitate, dissolve, or be in equilibrium with, calcium carbonate.

It is sometimes erroneously assumed that any water that tends to dissolve CaCO3 is automatically corrosive.

Langelier saturation index = pH - pHs where pH = actual pH of the water, and pHs = pH at which the water having the same alkalinity and calcium content is just saturated with calcium carbonate.

Large Public Water System: A public water system that serves more than 50,000 persons.

Latency: Time from the first exposure to a chemical until the appearance of a toxic effect.

Latent Heat: The amount of heat released or absorbed when a substance changes its physical phase with no change in temperature.

For example, the heat absorbed from surroundings when ice melts into liquid water at the freezing point or the heat released when a gas (steam) condenses into liquid water.

The loss or gain of latent heat is not reflected in the temperature of the melting ice or the condensing water.

Laundry Detergent: A product containing a surfactant and other ingredients, formulated to clean and care for the many different fabrics in the family wash.

Next to the surfactant, a builder is an important ingredient in formulated laundry detergents. Builders have a number of functions, principally inactivation of water hardness, which interferes with good cleaning. Built detergent types include granules and liquids.

Some liquid detergents are unbuilt, containing surfactants that are relatively insensitive to water hardness.

Other customary ingredients of laundry detergents include antiredeposition agents, corrosion inhibitors, fluorescent whitening agents, colorants, fragrance, and processing aids.

Optional ingredients include suds control agents, bleach, borax, enzymes, bluing, fabric softener, and soil release agent.

Some laundry detergents are denser or more concentrated than others. Density or concentration influences the amount of product recommended for the wash. Detergents also vary in sudsing characteristics, ranging from high to low suds levels.

Different suds levels are provided for reasons of compatibility with machine design and to satisfy consumer preferences.

Depending on the presence of other ingredients in the laundry detergent formulation, some products offer special benefits in addition to the expected cleaning. Thus, certain laundry detergents are especially effective at lower washing temperatures; others provide additional fabric care benefits, such as softening, static control, and wrinkle reduction.

Layered Bed: As relates to filtration, a multimedia filter bed containing, in the same vessel, several different filter media (such as anthracite, sand, and garnet) with specific gravities which differ enough to maintain different layers even after backwashing. layered bed

In ion exchange, a single exchange bed made up of two or more resins which have bead sizes and densities different enough to maintain layers after backwashing and which can be regenerated with the same regenerant. For example, a layered bed may have a mixed bed of anion resin on top and cation resin below that is regenerated by salt brine solution.

Leach: To dissolve out by the action of a percolating liquid.

Leach Field: The area where the effluent from a septic tank system is distributed by horizontal underground piping designed to aid in the process of natural leaching and percolation through the soil.

Leachate: Water which has percolated or filtered through soil, a filter medium, or other substance containing soluble substances so that it now contains certain amounts of these substances in solution.

Leaching: The process by which soluble substances are dissolved and transported down through the soil by recharge.

Lead (Pb): A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

Lead Service Line: A service line made of lead which connects the water main to the building inlet and any lead pigtail, gooseneck, or other fitting which is connected to such lead line.

Leakage: As relates to ion exchange, the presence in the effluent of the type of ions, present in the feedwater to be treated, which the ion exchange process was supposed to remove.

Incomplete removal of the ions may be caused by incomplete regeneration, excessive service rates, low temperatures, high concentrations of sodium, or interfering TDS in the water being treated, and other factors.

Leakage is also referred to as slippage.

Legionella: Over 26 species of bacteria, such as Legionella pneumophila, which can cause the pneumonia-like illness called "Legionnaires' Disease" (after the American Legion convention at which the disease first drew attention).

These bacteria are known to thrive at about 100 degrees F and are believed to live in infected humidifiers, cooling tower water, and shower rooms.

Infection is by inhalation.

Lesion: A pathological or traumatic discontinuity of tissue or loss of function of a part.

Lethal: Deadly; fatal.

Lifetime Exposure: Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years).

Lime (CaO): A calcined chemical material, calcium oxide.

Lime is used in lime and in lime and soda ash water treatment, but must first be slaked to calcium hydroxide [Ca(OH)2]. Lime is also called burnt lime; calyx; fluxing lime; quicklime; unslaked lime.

Lime Scale: Hard water scale formed in pipes and vessels (generally more severe on the hot water side) containing a high percentage of calcium carbonate (CaCO3) or magnesium carbonate (MgCO3).

Lime Soap: The insoluble calcium and magnesium salts formed from the fatty acid portion of soap when it combines with minerals in hard water; it is commonly referred to as soap curd.

The use of the word lime in this term may come from the fact that limestone areas generally foster hard water, or from the fact that the words lime and calcium are closely associated. Calcium and magnesium fatty acid salts are highly insoluble and precipitate immediately on formation. Since they tend to agglomerate (cluster together), they form curd-like masses. They also tend to adhere to surfaces, thus causing filming or deposits, such as bathtub ring.

The problems lime soap causes spurred the development of mechanical water softeners, packaged water softeners, and the technology leading to new surfactants and builders and detergent products based on them.

Lime Soda Ash Softening: A water treatment which makes use of lime softening followed by the reduction of noncarbonate hardness by addition of soda ash (Na2CO3) to form an insoluble precipitate which is removed by filtration.

This method of removing hardness by filtration is sometimes used by municipalities, but it will leave five or more grains per gallon of residual hardness.

Lime Softening: A water treatment, often used by municipalities, for partial reduction of water hardness. Controlled amounts of slaked lime [Ca(OH)2] are added to a hard water supply to remove the carbonate hardness by precipitation after which the precipitate is filtered out.

Limestone: A sedimentary rock composed mostly of calcium carbonate (CaCO3) and usually some magnesium carbonate (MgCO3).

Limnetic Community: The area of open water in a fresh water lake providing the habitat for fish, phytoplankton, and zooplankton.

Limnology: The scientific study of conditions in freshwater lakes, ponds, and streams.

Lindane: A pesticide that causes adverse health effects in domestic water supplies and also is toxic to freshwater and marine aquatic life.

Linear Alkyl Sulfonate (LAS): Readily biodegradable form of alkylbenzene sulfonate surfactant.

This is the workhorse of the detergent industry, with sodium dodecylbenzene sulfonate being the most important single type. It is distinguished from an earlier form of alkylbenzene sulfonate, termed ABS, but is a linear (straight chain) structure, which provides its good biodegradation properties.

All LAS surfactants are anionic and high sudsing, but their sudsing may be controlled by formulation.

Linearity: How closely an instrument measures actual values of a variable through its effective range; a measure used to determine the accuracy of an instrument.

Liquefication: The transformation to the liquid state. This term is more commonly used to refer to the changing of gases to liquids than to refer to the melting of solids to liquids.

Liquid Chromatography: Chromatography in which the mobile phase is a liquid (i.e., the sample is introduced into a liquid solvent which then flows through a fractionating column and to a detector). Separation of the sample components is accomplished via three different modes: 1. liquid/ liquid, in which the relative solubilities of sample components in two immiscible fluids (one of which is usually water) create separation; 2. liquid/solid, in which the relative adsorption of sample components on a solid adsorptive medium surface creates separation; and 3. molecular-size, in which separations are created because of the variations in effective molecular dimensions of the sample components in solution.

Liquor: A solution of one or more chemical substances (gas, solid, or liquid) in water.

Liter: The basic international metric unit of volume measure.

One liter equals 33.82 fluid ounces; 3.785 liters equals one U.S. gallon. One liter of water weighs 1,000 grams at 4 degrees Celsius at standard atmospheric pressure.

Littoral Zone: 1. That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. 2. The strip of land along the shoreline between the high and low water levels.

Loading: The quantity of a substance entering the environment (soil, water, or air).

LOAEL: Lowest-observed-adverse-effect level; the lowest dose in an experiment which produced an observable adverse effect.

Lodestone: SEE magnetite

Logarithm: The exponent that indicates the power to which a number must be raised to produce a given number.

Also abbreviated to "log."

Longitudinal Flow: A flow pattern in which water travels from the bottom to top (or vice versa) in either a cartridge-type or loose media tank-type filtration system.

The advantages are greater contact time, higher unit capacity, more complete utilization of medium, and more uniform water quality.

Also called axial flow.

Loop: 1. The plumbing network designed to continuously circulate ultrapure grade water in high purity water systems between storage and disinfection modes to maintain microbiological cleanliness. 2. A plumbing connection used to bypass water around a location designed for installation of a water treatment system or used when the treatment system is out of service for any reason.

Loose Media Filters: Those filter units which have medium products positioned in a filter bed such that the individual medium grains or particles can be repositioned or lifted relative to each other with the flow of water or backwash water; as compared to permanently fixed bed media filter or a fixed solid block of filter media.

Loose medium (media): Filter or ion exchange media (in a tank or bed) which can be expanded during backwashing and rinsing. "Loose" is used to differentiate froma contained or "fixed medium" in a tank or the fixed or compressed media layer in a cartridge filter.

Lye: SEE sodium hydroxide

Lyse: To undergo lysis

Lysimeter: A device for measuring the percolation and drainage of water through soils.

Lysis: A process of disintegration or destruction of bacteria or microbiological cells by chemically breaking them down into their component parts.

-K-

KDF: (Kinetic Degredation Fluxion) The trade name for a patened medium composed of high purity copper and zinc granules. KDF is capable of removing chlorine, soluble heavy metals, and other inorganic contaminents from water through the chemical reduction/oxidation (redox) process.

Kelvin Scale: A temperature scale which measures from absolute zero (-273.15 degrees Celsius) in Kelvins which are equivalent to Celsius degrees in magnitude.

Kelvins = Celsius degrees + 273.15.

Kilo: The metric prefix used to mean "1000" of some unit of measure: a kilometer is 1,000 meters; a kilogram is 1,000 grams.

The term kilo is sometimes used to mean kilogram.

Kilograin: 1,000 grains

Kilogram: 1,000 grams

Kiloliter: 1,000 liters (264.18 U.S. gallons) or one cubic meter.

Kilowatt-Hour: The unit of electric energy or work equal to that done by one kilowatt in one hour.

Equal to 1,000 watt-hours.

Kinetic Energy: Energy possessed by a moving body of matter, such as water, as a result of its motion.

Kinetics: The study of the relationships between temperature and the motion and velocity of very small particles.

Kinetic relationships influence the rate of change in a chemical or physical system and are used particularly to describe the dynamics and rate of ion exchange reactions.

kPa: Kilopascal

KYNAR: Trade name for polyvinylidene fluoride.

-L-

L/d: liters per day.

L/min.: liters per minute.

Laminar Flow: The movement of fluid in a particular direction in smooth, continuous, nonturbulent parallel layers which do not mix with each other.

Landfill: Facility in which solid waste from municipal and/or industrial sources is disposed; sanitary landfills are those that are operated in accordance with environmental protection standards.

Langelier Saturation Index: A calculated number used to predict the calcium carbonate (CaCO3) stability of a water; that is, whether a water will precipitate, dissolve, or be in equilibrium with, calcium carbonate.

It is sometimes erroneously assumed that any water that tends to dissolve CaCO3 is automatically corrosive.

Langelier saturation index = pH - pHs where pH = actual pH of the water, and pHs = pH at which the water having the same alkalinity and calcium content is just saturated with calcium carbonate.

Large Public Water System: A public water system that serves more than 50,000 persons.

Latency: Time from the first exposure to a chemical until the appearance of a toxic effect.

Latent Heat: The amount of heat released or absorbed when a substance changes its physical phase with no change in temperature.

For example, the heat absorbed from surroundings when ice melts into liquid water at the freezing point or the heat released when a gas (steam) condenses into liquid water.

The loss or gain of latent heat is not reflected in the temperature of the melting ice or the condensing water.

Laundry Detergent:  A product containing a surfactant and other ingredients, formulated to clean and care for the many different fabrics in the family wash.

Next to the surfactant, a builder is an important ingredient in formulated laundry detergents. Builders have a number of functions, principally inactivation of water hardness, which interferes with good cleaning. Built detergent types include granules and liquids.

Some liquid detergents are unbuilt, containing surfactants that are relatively insensitive to water hardness.

Other customary ingredients of laundry detergents include antiredeposition agents, corrosion inhibitors, fluorescent whitening agents, colorants, fragrance, and processing aids.

Optional ingredients include suds control agents, bleach, borax, enzymes, bluing, fabric softener, and soil release agent.

Some laundry detergents are denser or more concentrated than others. Density or concentration influences the amount of product recommended for the wash. Detergents also vary in sudsing characteristics, ranging from high to low suds levels.

Different suds levels are provided for reasons of compatibility with machine design and to satisfy consumer preferences.

Depending on the presence of other ingredients in the laundry detergent formulation, some products offer special benefits in addition to the expected cleaning. Thus, certain laundry detergents are especially effective at lower washing temperatures; others provide additional fabric care benefits, such as softening, static control, and wrinkle reduction.

Layered Bed: As relates to filtration, a multimedia filter bed containing, in the same vessel, several different filter media (such as anthracite, sand, and garnet) with specific gravities which differ enough to maintain different layers even after backwashing. layered bed

In ion exchange, a single exchange bed made up of two or more resins which have bead sizes and densities different enough to maintain layers after backwashing and which can be regenerated with the same regenerant. For example, a layered bed may have a mixed bed of anion resin on top and cation resin below that is regenerated by salt brine solution.

Leach: To dissolve out by the action of a percolating liquid.

Leach Field: The area where the effluent from a septic tank system is distributed by horizontal underground piping designed to aid in the process of natural leaching and percolation through the soil.

Leachate: Water which has percolated or filtered through soil, a filter medium, or other substance containing soluble substances so that it now contains certain amounts of these substances in solution.

Leaching: The process by which soluble substances are dissolved and transported down through the soil by recharge.

Lead (Pb): A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

Leakage: As relates to ion exchange, the presence in the effluent of the type of ions, present in the feedwater to be treated, which the ion exchange process was supposed to remove.

Incomplete removal of the ions may be caused by incomplete regeneration, excessive service rates, low temperatures, high concentrations of sodium, or interfering TDS in the water being treated, and other factors.

Leakage is also referred to as slippage.

Legionella: Over 26 species of bacteria, such as Legionella pneumophila, which can cause the pneumonia-like illness called "Legionnaires' Disease" (after the American Legion convention at which the disease first drew attention).

These bacteria are known to thrive at about 100 degrees F and are believed to live in infected humidifiers, cooling tower water, and shower rooms.

Infection is by inhalation.

Lesion: A pathological or traumatic discontinuity of tissue or loss of function of a part.

Lethal: Deadly; fatal.

Lifetime Exposure: Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years).

Lime (CaO): A calcined chemical material, calcium oxide.

Lime is used in lime and in lime and soda ash water treatment, but must first be slaked to calcium hydroxide [Ca(OH)2]. Lime is also called burnt lime; calyx; fluxing lime; quicklime; unslaked lime.

Lime Scale: Hard water scale formed in pipes and vessels (generally more severe on the hot water side) containing a high percentage of calcium carbonate (CaCO3) or magnesium carbonate (MgCO3).

Lime Soap: The insoluble calcium and magnesium salts formed from the fatty acid portion of soap when it combines with minerals in hard water; it is commonly referred to as soap curd.

The use of the word lime in this term may come from the fact that limestone areas generally foster hard water, or from the fact that the words lime and calcium are closely associated. Calcium and magnesium fatty acid salts are highly insoluble and precipitate immediately on formation. Since they tend to agglomerate (cluster together), they form curd-like masses. They also tend to adhere to surfaces, thus causing filming or deposits, such as bathtub ring.

The problems lime soap causes spurred the development of mechanical water softeners, packaged water softeners, and the technology leading to new surfactants and builders and detergent products based on them.

Lime Soda Ash Softening: A water treatment which makes use of lime softening followed by the reduction of noncarbonate hardness by addition of soda ash (Na2CO3) to form an insoluble precipitate which is removed by filtration.

This method of removing hardness by filtration is sometimes used by municipalities, but it will leave five or more grains per gallon of residual hardness.

Lime Softening: A water treatment, often used by municipalities, for partial reduction of water hardness. Controlled amounts of slaked lime [Ca(OH)2] are added to a hard water supply to remove the carbonate hardness by precipitation after which the precipitate is filtered out.

Limestone: A sedimentary rock composed mostly of calcium carbonate (CaCO3) and usually some magnesium carbonate (MgCO3).

Limnetic Community: The area of open water in a fresh water lake providing the habitat for fish, phytoplankton, and zooplankton.

Limnology: The scientific study of conditions in freshwater lakes, ponds, and streams.

Lindane: A pesticide that causes adverse health effects in domestic water supplies and also is toxic to freshwater and marine aquatic life.

Linearity: How closely an instrument measures actual values of a variable through its effective range; a measure used to determine the accuracy of an instrument.

Liquefication: The transformation to the liquid state. This term is more commonly used to refer to the changing of gases to liquids than to refer to the melting of solids to liquids.

Liquid Chromatography: Chromatography in which the mobile phase is a liquid (i.e., the sample is introduced into a liquid solvent which then flows through a fractionating column and to a detector). Separation of the sample components is accomplished via three different modes: 1. liquid/ liquid, in which the relative solubilities of sample components in two immiscible fluids (one of which is usually water) create separation; 2. liquid/solid, in which the relative adsorption of sample components on a solid adsorptive medium surface creates separation; and 3. molecular-size, in which separations are created because of the variations in effective molecular dimensions of the sample components in solution.

Liquor: A solution of one or more chemical substances (gas, solid, or liquid) in water.

Liter: The basic international metric unit of volume measure.

One liter equals 33.82 fluid ounces; 3.785 liters equals one U.S. gallon. One liter of water weighs 1,000 grams at 4 degrees Celsius at standard atmospheric pressure.

Littoral Zone: 1. That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. 2. The strip of land along the shoreline between the high and low water levels.

Loading: The quantity of a substance entering the environment (soil, water, or air).

LOAEL: Lowest-observed-adverse-effect level; the lowest dose in an experiment which produced an observable adverse effect.

Logarithm: The exponent that indicates the power to which a number must be raised to produce a given number.

Also abbreviated to "log."

Longitudinal Flow: A flow pattern in which water travels from the bottom to top (or vice versa) in either a cartridge-type or loose media tank-type filtration system.

The advantages are greater contact time, higher unit capacity, more complete utilization of medium, and more uniform water quality.

Also called axial flow.

Loop: 1. The plumbing network designed to continuously circulate ultrapure grade water in high purity water systems between storage and disinfection modes to maintain microbiological cleanliness. 2. A plumbing connection used to bypass water around a location designed for installation of a water treatment system or used when the treatment system is out of service for any reason.

Loose Media Filters: Those filter units which have medium products positioned in a filter bed such that the individual medium grains or particles can be repositioned or lifted relative to each other with the flow of water or backwash water; as compared to permanently fixed bed media filter or a fixed solid block of filter media.

Loose medium (media): Filter or ion exchange media (in a tank or bed) which can be expanded during backwashing and rinsing. "Loose" is used to differentiate froma contained or "fixed medium" in a tank or the fixed or compressed media layer in a cartridge filter.

Lye: SEE sodium hydroxide

Lyse: To undergo lysis

Lysis: A process of disintegration or destruction of bacteria or microbiological cells by chemically breaking them down into their component parts.

-M-

Macroporous Resin: A special grade of ion exchange resins which have large pores and a higher resistance to oxidation and organic fouling.

They were developed to provide increased surface area for reactions with organic matter with large molecular weights.

Macroporous resins are manufactured with a third ingredient that is soluble in the styrene and divinylbenzene monomers but becomes insoluble in the polymer structure as it is formed. The third ingredient is then removed from the resin structure by a solvent leaving a resin bead that has both a continuous resin phase and a continuous pore phase, resulting in considerable net porosity and internal surface area.

Macroporous resins, which are produced in both anion and cation versions, contain higher levels (12% or more) of divinylbenzene cross-linking, which reduces the swelling of the polymer resin in water.

Also called macroreticular resin.

Macroscopic Organisms: Organisms big enough to be seen by the eye without the aid of a microscope.

Magnesia: Magnesium oxide (MgO) that has been specially processed.

Magnesia water treatment can be used for pH modification of water.

Magnesium (Mg): One of the elements that make up the earth's crust as part of many rock-forming minerals such as dolomite.

Magnesium and calcium dissolved in water constitute hardness. The presence of magnesium in water contributes to the formation of scale and the insoluble soap curds which identify hard water.

Magnetite: (Fe3O4) A black magnetic oxide of iron that is extremely dense and used as a coagulant and filter medium in water treatment.

Magnetite is readily recognized by its strong attraction to magnets.

Also called lodestone.

Malignant: Very dangerous or virulent, causing or likely to cause death.

Manganese (Mn): An element sometimes found dissolved in groundwater, usually in combination with--but in lower concentrations than--iron.

Manganese is noticeable because in concentrations above 0.05 mg/L it causes black staining of laundry and plumbing fixtures.

Important ores of manganese are pyrolusite, manganite, psilomelane, and rhodochrosite.

Manganese Greensand: Greensand which has been processed to incorporate the higher oxides of manganese into its pores and onto its surface.

Manganese greensand has a mild oxidizing power and is often used in the oxidation, precipitation, and removal of iron, manganese, and/or hydrogen sulfide.

It is regenerated by solutions of potassium permanganate (KMnO4).

Manganite [MnO(OH)]: A form of manganese ore, consisting of manganic hydroxide, which is used in filters designed to reduce iron, manganese, and/or hydrogen sulfide and requires a very high backwash rate because of its very high density (specific gravity 4.3).

Similar to pyrolusite.

Manometer: An instrument for measuring pressure.

Usually, a manometer is a glass tube filled with a liquid that is used to measure the difference in pressure across a flow-measuring device such as an orifice or Venturi meter.

The instrument used to measure blood pressure is a type of manometer.

Mass Spectrometry (MS): A method of chemical analysis, used as a detector in gas chromatography, for example, in which the compounds emerging from the chromatograph are fragmented and ionized by bombardment with a beam of electrons.

An electromagnetic field separates the ions according to their individual mass-to-charge ratios into a characteristic mass spectrum of the molecule.

An analog computer analyzes the spectra and makes it possible to identify molecules even in cases of poor separation on the chromatography column, hence the advantage of mass spectrometry compared to selective chromatograph detectors.

Mass Transfer: The movement of molecules of a substance to and across an interface from one phase to another. For example, the amount (mass) of ozone that transfers from air, across the air-water interface and into water; or the amount of organic material that transfers from water to a solid adsorption surface.

The rate and amount of mass transfer can be increased by:

1. enlarging the interface boundary by increasing the area of the interface or by rapid renewal or clearance of the interface; 2. increasing the concentration difference (which is the driving force) across the interface boundary, and/or; 3. increasing the length of time (contact time) the interface boundary exists.

Mass Transfer Zone: The region in a treatment unit where the concentration of the contaminant(s) of interest in the water or fluid decreases from influent concentration(s) to the lowest detectable concentration(s). For example, the region of an adsorption column in which adsorption is taking place.

Maximim containment level (MCLs): SEE drinking water standards

Maximum containment level goals (MCLGs): SEE drinking water standards

Maximum Total Trihalomethane Potential (MTTP): The maximum concentration of total trihalomethanes produced in a given water containing a disinfectant residual, after seven days at 25 degrees C or above.

MCL: maximum contaminant level.

MCLG: maximum contaminant level goal.

Mean Particle Diameter: The weighed average particle size, in millimeters, of the media particles or beads in a filter or ion exchange bed. Mean particle diameter is computed by multiplying the percent retained in a size fraction by the respective mean sieve openings, summing these values and dividing by 100.

Mechanical Filter: A pressure or gravity filter designed to physically separate and remove suspended solids from a liquid by mechanical (physical) means rather than by the chemical means.

Media: A selected group of materials used in filters and filter devices to form barriers to the passage of certain solids or molecules which are suspended or dissolved in water. It is also common to use the term media to refer to ion exchange resin products.

Media is the plural form of medium and refers to more than one type of barrier material.

Median: A statistical term representing the middle value of a series of numbers when the numbers are arranged in order of their numerical quantity or value. Equal numbers of data points can be found that are greater than or less than the median. For example, in the sequence 1,3,4,7,8,10,12, the median is 7.

Medium: The singular form of media.

Medium Size Public Water System: A public water system that serves greater than 3,300 and less than or equal to 50,000 persons.

Meg: Abbreviation for megohm. Meg means one million.

Mega: 1. A prefix meaning large; 2. A million of; or multiplied by one million.

2. a million of, or multiplied by one million.

Megohm: A unit of electrical resistance equal to one million ohms.

Membrane: A thin sheet or surface film, either natural or man-made, of microporous structure that performs as an efficient filter of particles down to the size range of chemical molecules and ions.

Such membranes are termed "semipermeable" because some substances will pass through but others will not. Usually small ions, water, solvents, gases, and other very small molecules can pass through a membrane, but other ions and macromolecules such as proteins and colloids are barred from passage.

Man-made (synthetic) membranes are highly engineered polymer films about 100 angstroms thick and with controlled distributions of pores ranging from 5 to 5,000 angstroms in diameter.

Membranes are used in reverse osmosis, electrodialysis, nanofiltration, ultrafiltration, and as pleated final filter cartridges in water treatment.

SEE ALSO cellulose acetate (CA); cellulose triacetate (CTA); charged polysulfone membrane.

Membrane Filtration: A laboratory analytical technique for the quantitative and qualitative analysis of bacterial or particulate matter in a water sample.

Upon filtering through a membrane of specified pore size (e.g., 0.45 micron), bacteria and particles of larger size are separated from the water sample and are retained on the filter. Then by incubation with a suitable nutrient and temperature, the captured bacteria will grow to visible colonies that can be counted; or by careful weighing, the amount of suspended particulate solids can be determined in the water sample.

Membrane softening: SEE nanofiltration

Meniscus: The curved top of a column of liquid (water, oil, mercury) in a small tube.

When the liquid wets the sides of the container (as with water), the curve forms a valley. When the confining sides are not wetted (as with mercury), the curve forms a hill or upward bulge.

Mercury vapor ultraviolet light: The ultraviolet light given off as the result of an electron flow through an ionized mercury vapor between electrodes in an ultraviolet lamp. The mercury vapor UV wavelength, which is most destructive to microorganisms in water, is 254 nanometers.

Mesh Size: Mesh is the number of openings in a square inch of a screen or sieve.

It is equal to the square of the number of strands of metal or plastic screening per lineal inch. Ion exchange and filter media are graded by U.S. mesh or screen sizes according to the percent of the medium's particles that will pass through or be retained on certain mesh screens.

Standard U.S. mesh screen #16 equates to a 1.19 millimeter particle diameter; mesh size #40 is 0.42 millimeters. Therefore, media rated as 95 percent -16+40 U.S. mesh would have 95 percent or more of the media particles with sizes between 0.42 and 1.19 mm in diameter.

Mesotrophic: Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.

Metabolism: The sum of the chemical reactions occurring within a cell or a whole organism; includes the energy-releasing breakdown of molecules (catabolism) and the synthesis of new molecules (anabolism).

Metabolite: Any product of metabolism, especially a transformed chemical.

Metalimnion: The middle layer in a thermally stratified lake or reservoir. In this layer, there is a rapid decrease in temperatures with depth.

Also called the thermocline.

Metastatic: Pertaining to the transfer of disease from one organ or part to another not directly connected with it.

Methane: A colorless, odorless, flammable gas consisting of the hydrocarbon (CH4) and resulting from the decay of vegetable matter or manure due to the action of anaerobic bacteria in swampy land, closed landfills, or sewage disposal plants.

Methane is also known as biogas and it is called swamp gas when produced in marshy land. Coal miners know methane as one of the main components of fire-damp and also of coal-gas.

Methane dissolved in water gives the water a milky cast, and since it is flammable, methane must be safely aerated and vented to the atmosphere during removal.

Methoxychlor: A pesticide which causes adverse health effects in domestic water supplies and is also toxic to freshwater and marine aquatic life.

The chemical name for methoxychlor is 2,2-bis (p-methoxyphenol)-1,1,1-trichloroethane.

Methyl Orange: An acid-base indicator that turns red in a solution below three on the pH scale and yellow between pH of 4.4 and 7.0.

Methyl Tertiary Butyl Ether (MTBE): Since MTBE was incorporated in the mid-1980s into gasoline mixtures as an antiknock replacement for aromatics and as an "oxygenator" to reduce carbon monoxide emissions, it has increasingly appeared in groundwater due to spills of reformulated gasoline and leaking underground storage tanks at gasoline stations. It is highly water soluble and its appearance typically marks the leading front of a contamination plume. The molecular weight of MTBE (C5H12O) is 88.15.

In terms of noncarcinogenic effects, it has low oral toxicity, but at the gasoline pump and in the automobile, symptoms such as airway and eye irritation have been reported. In water, MTBE has a noticeable odor at 20 to 40 µg/L (U.S. Environmental Protection Agency, 1997). Though MTBE is not mutagenic/genotoxic, exposure to high levels by inhalation (8000 ppm) or by ingestion (1000 mg/kg) was associated with the development of lymphoma and leukemia, as well as liver, renal, and testicular cancers in rodents (Burleigh-Flayer et al., 1992; Belpoggi et al., 1995).

The relevance of these cancers to human health is not clear, but "weight of evidence suggests that MTBE is an animal carcinogen." "Concentrations in the range of 20 to 40 µg/L are about 20,000 to 100,000 (or more) times lower than the range of exposure levels in which cancer or non-cancer effects were observed in rodent tests." (U.S. Environmental Protection Agency, 1997). Thus, the USEPA says "protection of the water source from unpleasant taste and odor will also protect consumers from potential (MTBE) health effects."

MTBE is adsorbed onto activated carbon similar to chloroform, but with a use rate of 2-3 times that of chloroform, i.e., the life of the activated carbon may be only 1/2 to 1/3 of that for chloroform when MTBE will begin to break through. For concentrations of MTBE greater than 100 µg/L or parts per billion, pretreatment with an atmospheric air stripping system with repressurization is recommended prior to activated carbon adsorption.

Mg/L: Milligrams per liter.

Mho: (Backward spelling of ohm)

A unit of conductance equal to the reciprocal of the ohm. Also called siemens.

Microbial Growth: The activity and growth of microorganisms such as bacteria, algae, diatoms, plankton, and fungi.

Microbiocide: Similar to biocide but does not necessarily kill macroscopic and multicelled organisms.

Microbiologically unsafe water: Water that (1) is known to contain disease-causing bacteria, viruses, protozoa or other disease-causing microbiological agents, or (2) shows a positive test for an indicator orgaism such as coliform, fecal coliform, or E. coli bacteria, or (3) is determined unsafe by an appropriate health or regulatory agency.

Microfiltration: The separation or removal from a liquid of particulates and microorganisms in the size range of 0.1 to 2 microns in diameter.

Microgram: One-millionth of a gram (3.5 X 10E-8 oz. = 0.000000035 oz.).

Micrograms Per Liter: One microgram of a substance dissolved in each liter of water.

This unit is equal to parts per billion (ppb) since one liter of water is equal in weight to one billion micrograms.

Microhm: One millionth of an ohm.

The unit of measurement for testing the electrical resistance of water to determine its purity. The closer water comes to absolute purity, the greater its resistance to conducting an electric current.

Absolutely pure water has a specific resistance over 18 million ohms across one centimeter at a temperature of 78 degrees F (25 degrees C).

Micron: A metric unit of length equal to one millionth of a meter or one thousandth of a millimeter or about 0.00003937 inches.

Micron Rating: A measurement applied to filters or filter media to indicate the particle size at which suspended solids above that size will be removed.

As used in the water treatment industry standards, this may be an absolute rating or a nominal rating.

Microorganism: A living organism invisible or barely visible to the naked eye and generally observable only through a microscope. Also called a microbe. Microorganisms are generally considered to include algae, bacteria, fungi, protozoa, and viruses.

Microorganisms are generally considered to include algae, bacteria, fungi, protozoa, and viruses.

Microporous Resin: Ion exchange resin with low porosity, usually polystyrene cross-linked typically with about three percent divinylbenzene.

The lower cross-linking means microporous resins also have less strength and less resistance to degradation, swelling, and mushing.

Microsiemens: One-millionth of a siemens (formerly called mho).

The microsiemens is the practical unit of measurement for conductivity and is used to approximate the total dissolved solids content of water. Water with 100 mg/L (ppm) of sodium chloride will have a specific resistance of 4,716 ohms-centimeter and a conductance of 212 microsiemens per centimeter.

Absolute pure water, from a mineral content standpoint, has a conductivity of 0.03 microsiemens per centimeter at 25 degrees C (78 degrees F).

Also called micromhos.

Microwatt: One millionth of a watt.

Midpoint: The point at or near the middle of a scale or set of experimental results data in scientific analyses.

Mil: A unit of length equal to 0.001 of an inch.

The diameter of wires and tubing is measured in mils, as is thickness of plastic sheeting.

Milligram (mg): One-thousandth of a gram (3.5 X 10-5 oz. = 0.000035 oz.).

Milligrams per Liter (mg/L): A measure of concentration of a dissolved substance.

A concentration of one mg/L means that one milligram of a substance is dissolved in each liter of water.

For practical purposes, this unit is equal to parts per million (ppm) since one liter of water is equal in weight to one million milligrams. Thus, a liter of water containing 10 milligrams of calcium has 10 parts of calcium per one million parts of water, or 10 parts per million (10 ppm).

Millilimicron: A unit of length equal to 10E-3 microns (one thousandth of a micron), 10E-6 millimeters, or 10E-9 meters; correctly called a nanometer (nm).

Milliliter (ml): A unit of volume measure equal to 1/1000 liter (or one cubic centimeter); the volume occupied by one gram of pure water at 4 degrees C at 760 mm of pressure or standard atmospheric pressure.

Mineral (1): An inorganic (nonliving) substance which occurs naturally in the earth and has a composition that can be expressed as a chemical formula and a set of characteristics (crystalline structure, hardness, etc.) common to all minerals. Examples of minerals are sulfur, salt, and stone. Certain organic substances, such as coal, are also sometimes referred to as minerals. The word mineral is also used to refer to matter derived from minerals, such as inorganic ions found in water and reported as mineral content.

Mineral (2): Term used in the water treatment industry to refer to naturally-occurring inorganic cation exchangers formerly used in water softeners - as opposed to the synthetic organic resins used today for water softening.

Mineral Acidity: Acidity in water due to the presence of strong inorganic acids such as hydrochloric, nitric, and sulfuric acids as opposed to weak acidity due to such acids as carbonic acid or acetic acid.

Mineral acidity is usually expressed in water analysis as FMA (free mineral acidity).

Mineral Salt: A chemical compound formed by the combination of a mineral acid and a base.

Minerals from dissolved rock exist in water in the form of dissolved mineral salts. An excess of mineral salts can give water a disagreeable taste or even be harmful to human health.

Mineral Water: Water which is naturally or artificially impregnated with mineral salts or gases (carbon dioxide).

The term is also used to designate bottled water that contains no less than 250 ppm total dissolved solids (TDS) and originates from a protected groundwater source.

Mineral-Free Water: Water produced by either distillation or deionization.

This term is sometimes found on labels of bottled water as a substitute term for distilled or deionized water.

Mineralization: The microbial conversion of an element from an organic to an inorganic state.

Miscible: Able to be mixed together or dissolved into each other to produce a homogenous substance.

Mixed Bed: The intermix of two or more filter or ion exchange products in the same vessel during a service run.

The most common use is in ion exchange systems having a 40/60 percent cation to anion resin bed such as that for a deionization polisher unit. In filtration, there may be an intermix of two or more media in a single tank with each stratified into separate layers.

Mixed Media: The use of two or more media products in a single filtration loose media bed where the products are intermixed--rather than in stratified layers.

For example, the intermix use of calcite and magnesia in pH modification.

Mode: In statistics, the most frequently occurring number in a set of numbers. For example, in the set 1,2,4,4,4,4,6,8,10, the number 4 is the mode.

Modeling: Use of mathematical equations to simulate and predict real events and processes.

Module: The membrane element and its housing in a reverse osmosis unit.

Mole: The molecular weight of a substance, usually expressed in grams.

Molecular Weight (MW or mw): The molecular weight of a compound in grams is the sum of the atomic weights of the elements in the compound.

For example, the molecular weight of sulfuric acid (H2SO) in grams is 98.

Molecule: The smallest particle of an element or compound that retains all of the characteristics of the element or compound.

A molecule is made up of one or more atoms.

The helium molecule, for example, has only one atom per molecule. Oxygen molecules (O2) have two atoms; ozone molecules (O3) have three atoms. Molecules found in chemical compounds often have many atoms of various kinds.

Monitoring: Measuring concentrations of substances in environmental media or in human or other biological tissues.

Monitoring Wells: Wells used to collect groundwater samples for analysis to determine the amount, type, and spread of contaminants in groundwater.

Monochromatic: Consisting of radiation or rays, such as ultraviolet rays, of a single wave length or of a very small range of wave lengths.

Monomer: A molecule of low molecular weight capable of reacting with identical or different monomers to form polymers.

Monomictic: Lakes and reservoirs which are relatively deep, do not freeze over during the winter months, and undergo a single stratification and mixing cycle during the year.

These lakes and reservoirs usually become destratified during the mixing cycle, usually in the fall of the year.

Monovalent: Having a valence of one, such as the cuprous (copper) ion, Cu+.

Also called univalent.

Motile: Capable of self-propelled movement.

A term that is sometimes used to distinguish between certain types of organisms found in water.

Motive Flow: The water flow rate (e.g., gallons per minute) through a venturi injector that provides the suction at the injection port of the injector to induce the flow of another liquid (such as a regenerant) or gas (such as air or ozone) into the flow of water.

MTD: Maximum tolerated dose, the dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity.

Mulch: Any substance spread or allowed to remain on the soil surface to conserve soil moisture and shield soil particles from the erosive forces of raindrops and runoff.

Multifunctional Medium: A single filter or ion exchange medium used to treat water for the removal of more than one constituent. Examples are activated carbon for chlorine removal and sediment filtration, calcite for pH modification and filtering of precipitated iron, or cation resin for reduction of dissolved iron as well as hardness removal.

Multilayered Bed: A media bed in which more than one filter or ion exchange medium is used in the same vessel, with each medium retaining its stratified position as a layer - even after specified backwashing is performed - due to differences in media densities.

Municipal Sewage: Wastes (mostly liquid) originating from a community; may be composed of domestic waste waters and/or industrial waste waters.

Municipal Softening: A hardness reduction process performed at municipal central treatment plants to deliver water in the range of 5 to 12 grains per gallon total hardness.

Municipal Water: Water that has been processed at a central plant to make it potable or "safe to drink" and which is then distributed to homes and businesses via water mains.

Either public agencies or private companies can be involved in providing "municipal water". The term is a general one used to refer to the common source of water in most urban and suburban areas--as opposed to water obtained from separate proprietary sources such as private wells.

Mushing: Mushing of water softener salt occurs when salt pellets break down into their crystallized form.

If a water softener brine tank is caked with salt or if a ridge of salt appears in the unit, the salt has either mushed or bridged, or both. Both salt mushing and salt bridging conditions prevent proper circulation of salt in the unit and require that the brine system be cleaned.

Mutagenicity: The capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cell.

-N-

Nanofiltration: A membrane treatment process which falls between reverse osmosis and ultrafiltration on the filtration/separation spectrum.

The nanofiltration process can pass more water at lower pressure operations than reverse osmosis, can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color bodies present in water, and can reject selected (typically polyvalent) salts.

Nanofiltration may be used for selective removal of hardness ions in a process known as membrane softening.

Nanometer (nm): One billionth (10-9) of a meter, and equal to one millimicron or 10 angstroms.

Natural Softening: The replacement of hardness-causing minerals by sodium and/or potassium as the result of the normal flow of water in the ground.

Natural Sparkling Water: Carbonated water whose carbon dioxide content is from the same source as the water itself.

Naturally Soft Water: Ground, surface, or rain water sufficiently free of calcium and magnesium salts so that no curd will form when soap is used and no calcium- or magnesium-based scale will form when the water is heated.

Necrosis: Death of cells or tissue.

Negative Charge: The electrical potential of an atom which gains one or more electrons, therefore leaving it with more electrons than protons.

Anions carry negative charges.

Negative Head: A condition of negative pressure or of partial vacuum.

Negative Pressure: A pressure below that of the existing atmospheric pressure taken as a zero reference.

Neoplasm: An abnormal growth or tissue, as a tumor.

Nephelometric: A means of measuring turbidity in a sample by using an instrument called a nephelometer.

A nephelometer passes light through a sample, and the amount of light deflected (usually at a 90-degree angle) is than measured.

Nephelometric Turbidity Unit (NTU): The standard unit of measurement used in the water analysis process to measure turbidity in a water sample.

The NTU has replaced the formerly used Jackson turbidity unit (JTU).

Neurotoxicity: Exerting a destructive or poisonous effect on nerve tissue.

Neutral: In water chemistry, the midpoint (neutral) reading of 7.0 on the pH scale, indicating that the solution (water) producing the neutral reading will produce neither an acid nor alkaline reaction. A 7.0 reading on the pH scale means that there are an equal number of free hydrogen (acidic) ions and hydroxide (basic) ions.

As relates to electricity, a condition of being uncharged because of a balance between negative and positive charges. The condition of neutrality means that there is neither an excess nor a lack of electrons.

Neutralization: The addition of either an acid to a base or a base to an acid to produce a more nearly neutral solution.

The use of alkaline or basic materials to neutralize acidity of some water is common practice in water processing.

Neutralization does not always mean the attaining of pH 7.0. When a strong acid reacts (is neutralized) with a weak base, the resulting pH may remain less than 7.0; when a strong base reacts with a weak acid, the pH may remain greater than 7.0.

Neutralizer: 1. An alkaline substance such as calcium carbonate (calcite) or magnesium oxide (magnesia) used to neutralize acidic waters or an acidic substance such as acetic acid or dilute hydrochloric acid used to neutralize alkaline waters.

2. The term "neutralizer" is commonly used to refer to calcite or magnesia acid-neutralizing filters used to neutralize acidity and/or reduce free carbon dioxide in water and thereby raise the pH of acidic water.

Neutron: A fundamental particle found in the nucleus of an atom.

A neutron has a mass equal to that of a proton but carries no charge.

Newton: The force necessary to give acceleration of one meter per second to one kilogram of mass.

Nitrate: A natural nitrogen compound (NO3-) sometimes found in well or surface waters.

In high concentrations, nitrates can be harmful to young infants or young livestock.

Nitrogen Fixation: The biological or chemical process by which elemental nitrogen, from the air, is converted to organic or available nitrogen.

NOAEL - No observed adverse effect level: The highest dose in a toxicity experiment which did not produce an observable adverse effect.

Noble: Chemically unreactive, especially toward oxygen or resists chemical action such as corrosion caused by air, water, or (to a lesser degree) acids.

Gold, silver, platinum, palladium, and mercury are said to be "noble metals" because they don't rust and are resistant to acid damage.

Certain gases are called "noble gases" because they are inert (chemically inactive and stable.)

Noble Metal: Chemically inactive metal (such as gold).

A metal that does not corrode easily and is much scarcer (and more valuable) than the so-called useful or base metals.

Noble Metal: Chemically inactive metal (such as gold).

A metal that does not corrode easily and is much scarcer (and more valuable) than the so-called useful or base metals.

Nominal Diameter: An approximate measurement of the diameter of a pipe.

Although the nominal diameter is used to describe the size or diameter of a pipe, it is usually not the exact inside diameter of the pipe.

Nominal Filter Rating: Filter rating indicating the approximate size particle, the majority of which will not pass through the filter.

It is generally interpreted as meaning that 85 percent of the particles of the size equal to the nominal filter rating will be retained by the filter.

Noncarbonate Hardness: Hardness caused by calcium or magnesium existing in compound form with chloride, sulfate, and nitrate anions rather than with the more common carbonate or bicarbonate anions.

Noncarbonate hardness will not be precipitated by boiling. Noncarbonate hardness is the excess of total hardness over total alkalinity. High concentration (e.g. as caused by evaporation) of noncarbonate hardness anions can make the water more corrosive.

The term noncarbonate hardness has largely replaced the term permanent hardness, which has the same meaning.

Noncommunity Water System (NCWS): A public water system that is not a community water system.

There are two types of NCWSs: transient and nontransient.

Nonconventional Pollutant: Any pollutant which is not statutorily listed or which is poorly understood by the scientific community.

Nondegradable: Resistant to decomposition or decay by biological means such as bacterial action or from chemical or physical causes such as oxidation, heat, sunlight, or solvents.

Nonpathogenic: Not disease-producing.

Nonpoint Source: Pollution sources which are diffuse and do not have a single point of origin or are not introduced into a receiving stream from a specific outlet.

The pollutants are generally carried off the land by stormwater runoff. the commonly used categories for non-point sources are; agriculture, forestry, urban, mining, construction, dams and channels, land disposal, and saltwater intrusion.

Nonpotable: Water that may contain objectionable pollution, contamination, minerals, or infective agents and is considered unsafe and/or unpalatable for drinking.

Nonsettleable Solids: Very small, fine suspended solids, typically colloidal particles of less than 0.1 microns in diameter, which will not settle out of calm nonturbulent water, sewage, or other liquids in what is considered a reasonable time of about two hours.

Normal Flow Filtration: The flow of the entire feedwater stream in one direction directly through the filter media. The flow is usually "normal" or perpendicular to the media surface area.

North American Industry Classification System (NAICS): The standard statistical classification system, adopted in 1997 by the United States Office of Management and Budget (OMB), that assigns an industry number to businesses and business units by type of economic activity. The NAICS has been harmonized with and also adopted by Mexico and Canada. It replaces the Standard Industrial Classification (SIC) system used in the U.S. from 1938 and until 1997. The NAICS is a standard industry classification system that facilities the collection, tabulation, presentation, and analysis of data relating to establishments and ensures that data about the U.S. economy published by U.S. statistical agencies are uniform and comparable among the North American countries. The NAICS uses a six-digit numerical coding system to identify particular industries and their placement in the hierarchical structure of the classification system. The first two digits group establishments (or locations at which an economic activity occurs) into one of 20 sectors, such as for example, Agriculture, Mining, Construction, Manufacturing, Wholesale Trade, Retail Trade, and Administration and Support Services. The remaining digits designate one of the 1,170 industries identified in NAICS. When any employer applies for an Employer Indentification Number (EIN), information about the type of activity in which that business is engaged is requested in order to assign a NAICS code.

In addition statistical agencies such as the Census Bureau and the Bureau of Labor Statistics assign NAICS codes based on information reported to them. Water treatment equipment manufacturing, for example, is in NAICS 333319, water softener and water conditioning direct selling and service providers are in NAICS 454390, water softening and conditioning equipment wholesaling is in 421720, water softening and conditioning compounds and materials wholesaling is in 422690, and water softening and conditioning support services are in 561990. Bottled water manufacturing (purifying and bottling) is in NAICS 312112, bottled water stores are in NAICS 445299, bottled water wholesaling is in NAICS 422490, and other water treatment and distribution is in NAICS 221310.

Nosocomial: Acquired after admittance to a hospital.

Not Detectable: A term used in reporting test results to mean that the substance being tested cannot be detected by the equipment or method being used for this particular test.

This term implies that it is possible that trace amounts may be present in quantities too small to be detected by the test equipment or method.

NSDWR: National Secondary Drinking Water Regulations.

NTU: Nephelometric turbidity unit.

Nutrient: Any substance that is assimilated (taken in) on organisms and promotes growth.

For example, carbon dioxide, nitrogen, phosphorous, potassium, and numerous mineral elements are essential nutrients which promote the growth of plants.

Water and oxygen are also included in this definition.

Nutrient Pollution: Contamination of water resources by excessive inputs of nutrients: in surface waters, excess algae production is a major concern.

-O-

Occlusion: An absorption process by which one substance is taken in and retained in the interior rather than on the external surface of another, sometimes occurring by coprecipitation.

Odor Threshold: The minimum odor of a water sample that can just be detected after successive dilutions with odorless water. Also called threshold odor.

Off-Gas: Air or vapor given off or expelled as a byproduct or result of an operation or treatment process.

Offstream Uses: Water withdrawn from surface or groundwater sources for use at another place.

Ohm: The standard unit for measuring resistance to the passage of an electrical current.

One ohm is equal to the resistance created between two points on a conductor when a potential difference of one volt creates a current of one ampere.

An ohm is also equal to the resistance offered by a column of mercury which is 1.02mm in cross sectional area and 106.3 cm long at 0 degrees C.

Electrical resistance in a solution is often related to the electrolyte concentration in the solution.

Oleophilic: Having a strong affinity (liking) for oil, and thereby exhibiting the characteristic of adsorbing oily-type substances.

Activated carbon is an oleophilic material. The opposite of oleophobic.

Oleophobic: Having a strong aversion (dislike) for oil, and thereby exhibiting the characteristic of repelling oily-type substances.

Water is oleophobic. The opposite of oleophilic.

Oleum: (H2SO4 + SO3) The Latin word for oil.

Oleum is a solution of sulfuric acid and sulfur trioxide that is a form of fuming sulfuric acid.

The term is used to describe a stage in the production of sulfuric acid.

Olfactory Fatigue: A condition in which a person's nose, after exposure to certain odors, is no longer able to detect the odor.

Oligo-dynamic Action: The bacteriostatic action exerted by very small amounts of heavy metals such as copper, silver, and zinc which deactivates bacteria and creates a hostile environment for the growth of bacterial colonies.

Oligotrophic: Reservoirs and lakes which are nutrient poor and contain little aquatic plant or animal life.

Oncology: Study of cancer.

Oocyst: The fertilized egg form of parasitic sporozoa protozoa such as Giardia, Cryptosporidium, and Cyclospora that is encapsulated in a tough shell.

The oocyst is an environmentally resistant transmissible form of certain protozoan parasites that is excreted in the feces of an infected host and carried viably in unfiltered water supplies.

Opacity: The capacity of matter to block the passage of light or other radiant energy such as heat.

A measure of opacity might be the percentage of light transmission through a plume. Opacity is the opposite of transparency, and an object with a high degree of opacity is said to be opaque.

Operating Cycle: In filtration applications, the complete filtration process consisting of filter service, backwash and rinse, and return to service.

As relates to ion exchange, the cycle of service run, backwash and regeneration, slow rinse, fast rinse, and return to service.

Operating Pressure: The manufacturer's specified range of pressure expressed in pounds per square inch (psi) within which a water processing device or water system is designed to function.

A range of 30 to 100 psi is often indicated.

Also called working pressure.

Operating Temperature: The manufacturer's recommended feedwater or inlet water temperature for a water treatment system.

Operation and Maintenance Costs: The ongoing, repetitive costs of operating a water system; for example, employee wages and costs for treatment chemicals and periodic equipment repairs.

Oral: Of the mouth; through or by the mouth.

Organic: 1. Having the characteristics of, or being derived from, a living organism, plant, or animal. 2. Containing carbon (although a few very simple carbon compounds such as the carbon oxides, the carbides, carbon disulfide, and metallic carbonyls and carbonates are considered inorganic).

Over 6,000,000 carbon-containing organic compounds have been identified and named.

Organic Chemical: A chemical having a carbon-hydrogen structure.

Organic Iron: Iron that is bound or complexed with organic compounds, such as naturally occurring humic and fulvic acids.

In waters laden with a high level of these vegetation decay products, iron is sometimes present in an organic form. The decaying process of vegetation produces humic and fulvic acids. Iron will react with these natural complexation or chelating agents to form either an insoluble colloid with humic acid and humin, or a soluble complex chelate with fulvic acid and tannin.

Organic iron can be present in a colorless form, but most often occurs as a yellow, yellowish- brown, or pink color. The humic acid and humin colloids developing the color seem to be permanently suspended in the water due to their particle size, normally less than 0.1 micron.

Organic iron can also be referred to as tannin, heme iron, complexed iron, or pink iron.

Organic Matter: Substances consisting of, or derived from, plant or animal matter as opposed to inorganic matter which is derived from rocks, ores, and minerals.

Organic matter is characterized by its carbon-hydrogen structure.

Organics: Term often used to describe any (or all) of the compounds, natural or man-made, with chemical structures based upon carbon.

Examples are hydrocarbons, wood, sugars, proteins, methane, plastics, petroleum-based compounds, solvents, pesticides, herbicides, trihalomethane (THM), and trichlorethylene (TCE).

Organism: Any form of animal or plant life.

Organoleptic: Affecting perceptions that are stimulated by senses in the eye, ear, skin, nose, or mouth.

Used to describe subjective characteristics such as flavor, odor, color, appearance, and related factors of food and water.

Orifice: 1. An opening, such as a hole or vent in something

2. In water treatment, usually an opening through which water can pass or a restricted opening placed in a pipe line to provide a means of controlling or measuring flow. For example, a flow controller.

ORP (Oxidation-Reduction Potential): The electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element (the reductant): used as a qualitative measure of the state of oxidation in water treatment systems.

OSHA: The Williams-Steiger Occupational Safety and Health Act of 1970 (OSHA) is a law designed to protect the health and safety of industrial workers and also the operators of water supply systems and treatment plants.

OSHA also refers to the federal and state agencies which administrator the OSHA regulations.

Osmosis: The natural tendency for water to spontaneously pass through a semipermeable membrane separating two solutions of different concentrations (strengths).

The water will naturally pass from the weaker (less concentrated) solution containing fewer particles of dissolved substance to the stronger (more concentrated) solution containing more particles of a dissolved substance. Thus, natural osmosis causes the stronger solution to become more diluted and tends to equalize the strength of the solutions on both sides of the membrane.

Osmotic Pressure: The pressure and potential energy difference which exists between two solutions on either side of a semipermeable membrane because of the tendency of water to flow in osmosis.

Every 100 ppm (mg/L) of TDS generates about one pound per square inch of osmotic pressure.

This osmotic pressure must first be overcome by water pressure for a reverse osmosis membrane to become effective.

Osmotic Stability: An expression of the ability of an ion exchange resin to resist physical degradation due to volume changes (shrinkage and swelling) imposed by repeated applications of dilute and concentrated solutions.

Overrun: Operating a filter or ion exchange system beyond its predetermined exhaustion point.

This means the filter or system is unlikely to be as effective as it should be, and it probably needs some regeneration to restore capacity (ion exchange), or a cleansing, backwashing, or media/element replacement to reduce headloss and restore capacity (mechanical, adsorption, or neutralization filter).

Overturn: The almost spontaneous mixing of all layers of water in a reservoir or lake when the water temperature becomes similar from top to bottom.

This may occur in the fall/winter when the surface waters cools to the same temperature as the bottom waters and also in the spring when the surface waters warm after the ice melts.

Also called turnover.

Oxidation: The process in which a molecule, atom, or ion loses electrons to an oxidant. The oxidized substance (which lost the electrons) increases in positive valence. Oxidation never occurs alone, but always occurs as part of the oxidation-reduction (redox) reaction. The reduced substance gains electrons and thereby decreases in positive valence.

Oxidation (ion exchange): Specific attack on the cross linking of the co-polymer of ion exchange resins by an oxidant (chlorine, peroxide, ozone, or others) leading to degradation (loss of structure of resin beads) and shortening of the resin life.

Oxidation-Reduction (Redox) Reaction: The combination of the processes involved in the flow of electrons from a reducing agent (reducer) to an oxidizing agent (oxidant). The total number of electrons lost by one substance is the same as the total number of electrons gained by another substance. Oxidation and reduction always occur together simultaneously and are really opposite sides of the same reaction, often called the redox reaction.

In earlier years, oxidation referred to the combining of a substance with, or addition of, oxygen, and reduction meant the loss or reduction of oxygen. However, as chemistry became more advanced, it was seen that the real key to what was happening was the loss or gain of electrons.

Now, the definitions accepted are as follows:

Oxidation is the loss of electrons from the reducing agent (which is said to have "been oxidized" in the process). Since electrons carry negative charges, oxidation results in an increase of positive valence. Reduction is the acquiring of electrons (the ones lost in the oxidation process) by the oxidizing agent (which is said to have "been reduced" in the process). Because electrons (carrying negative charges) have been acquired, reduction results in a lowering (a reduction) of positive valence. It may be helpful to remember that the word "agent" refers to an active substance that produces or brings about some effect. Therefore, the oxidizing agent is the substance that brings about oxidation; the reducing agent is the substance that brings about reduction.

Oxidation-Reduction Potential (ORP): The electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element (the reductant); used as a qualitative measure of the state of oxidation in water treatment systems.

Oxidize: To increase a molecule or ion in positive valence; to lose electrons to an oxidizing agent.

Oxidizing Agent: A chemical substance that gains electrons (i.e., is reduced) and brings about the oxidation of other substances in chemical oxidation and reduction (redox) reactions.

Examples of oxidizing agents include oxygen, ozone, chlorine, peroxide.

Oxidizing Filter: A type of filter used to change the valence state of dissolved molecules, making them insoluble and, therefore, filterable.

For example, a filter that oxidizes ferrous iron, manganous manganese, and/or anionic sulfur by use of catalytic media such as manganic oxides and then filters the oxidized precipitates out of the water.

Oxygenate: To impregnate or combine with oxygen such as the forced draft step in aeration.

Maximum oxygen exposure.

Ozonation: The process of feeding ozone into a water supply for the purpose of decolorization, deodorization, disinfection, or oxidation.

Ozone Destruction: The step by which a component unit of an ozonation system destroys all or some of the ozone present in the off-gas being vented.

Ozone Enrichment: A step in the ozonation process in which more ozone is added to a gas which previously contained ozone.

Ozone Half-Life: The period of time required for 50 percent of a given quantity of ozone to decompose at a specific temperature and pressure.

Ozone-(O3): A very strong oxidizing agent which is unstable and must be generated on site.

Ozone is a highly reactive form of oxygen and can be produced by sending a high voltage electrical discharge through air or oxygen (such as occurs in a lightning storm). Some degree of ozone can also be produced by certain types of ultraviolet lamps.

Ozone is an excellent oxidizing agent and bactericide.

Ozonide: A compound which occurs as a byproduct of ozonation.

Ozonolysis: 1. The oxidation of an organic material by ozone.

2. The use of ozone as a tool in analytical chemistry to locate double bonds in organic compounds.

Ozonosphere: A region in the upper atmosphere containing a relatively high concentration of ozone which absorbs certain wavelengths of solar ultraviolet radiation that are not screened out by other substances in the atmosphere.

-P-

Pa: Pascal.

Packed Bed: A bed of filter or ion exchange medium which is completely retained so that no bed expansion can occur and no backwash step is used to reclassify the filter or resin.

Packed beds are usually part of the design features in ion exchange water softeners used to obtain high capacity and increased regeneration efficiency.

Palatable: Water at a desirable temperature that is free from objectionable tastes, odors, colors, and turbidity. Pleasing to the senses.

Particle: A very tiny, separate subdivision of matter.

Particle Count: The results of a microscopic examination of treated water with a special "particle counter" which classifies suspended particles by number and size.

Particle Filtration: Filtration of particles in the size range of two microns or larger in diameter.

Particle filtration is typically handled by cartridge filters and media filters.

Particle Size: As used in water industry standards, this term refers to the size, expressed in microns, of a particle suspended in water as determined by the smallest dimension.

Particulate: A very small solid suspended in water which can vary widely in size, shape, density, and electrical charge.

Colloidal and dispersed particulates are artificially gathered together by the processes of coagulation and flocculation.

Parts Per Billion (ppb): A measure of proportion by weight which is equivalent to one unit weight of solute (dissolved substance) per billion unit weights of the solution.

This measurement is often used as a measure of concentration when analyzing water for contaminants. Since one liter of water weighs one billion micrograms, one ppb is the equivalent of one microgram per liter when used in water analysis.

Parts Per Million (ppm): A measure of proportion by weight which is equivalent to one unit of weight of solute (dissolved substance) per million weights of solution.

Since one liter of water weighs one million milligrams, one ppm is equal to one milligram per liter (mg/L).

Milligram per liter is the preferred unit of measure in water or waste water analysis.

Pascal (Pa): A unit of pressure equal to one newton of force per square meter.

One thousand pascals equal one kilopascal (KPa); a kilopascal equals 0.145 pounds per square inch.

1 psi = 6895 Pa = 6.895 kN/sq.m = 0.0703 kg/sq.cm

Pasteurization: A process for the partial sterilization (disinfection) of a substance, usually a liquid, by heating it to a critical temperature for a specified period of time.

Pasteurization does not greatly change the chemical composition of the sterilized substance.

Pathogenic: Capable of causing disease.

Pathogenic Organisms: Organisms, including bacteria, viruses, or cysts, capable of causing diseases (typhoid, cholera, dysentery) in a host (such as a person).

There are many types of organisms which do NOT cause disease. These organisms are called nonpathogenic

Pathogens: Microorganisms that can cause disease in other organisms or in humans, animals, and plants.

They may be bacteria, viruses, or parasites and are found in sewage, in runoff from animal farms or rural areas populated with domestic and/or wild animals, and in water used for swimming.

Fish and shellfish contaminated by pathogens, or the contaminated water itself, can cause serious illnesses.

Pathology: The study of disease.

Peak Operating Flow: The maximum rate of flow under which a treatment unit is designed to properly function and produce a certain quality product water.

Percent Recovery: The percentage of the feedwater which becomes product water.

Determined by the number of gallons (or liters) of product water divided by the total gallons (or liters) of feedwater and multiplied by 100.

The percent recovery is called recovery rate in reverse osmosis and ultrafiltration.

Percent Rejection: (reverse osmosis/ultrafiltration) The percentage of TDS in the feedwater that is prevented from passing the membrane with the permeate.

The formula used is: the difference obtained from the TDS in feedwater minus TDS in permeate divided by TDS in feedwater; then multiply the answer obtained by 100 to obtain a percent.

Percent Saturation: The amount of a substance that is dissolved in a solution compared with the amount that could be dissolved in the solution, expressed as a percent.

Amount of substance that is dissolved divided by the amount that could be dissolved in solution X 100 percent.

Percolating: Water that passes through soil or rocks under the force of gravity.

Percolation: 1. The slow seepage of water into and through the ground.

2. The slow passage of water through a filter medium.

Performance Evaluation Sample: A reference sample provided to a laboratory for the purpose of demonstrating that the laboratory can successfully analyze the sample within limits of performance specified by the Agency.

The true value of the concentration of the reference material is unknown to the laboratory at the time of the analysis.

Periphyton: Microscopic plants and animals that are firmly attached to solid surfaces under water such as rocks, logs, pilings, and other structures.

Peristaltic Pump: A self-priming pump that achieves pumping action by moving a system of rollers against a flexible tube.

The pumped fluids (e.g., chemical feeds) are never exposed to the air or to the mechanical moving parts. The roller design prevents siphoning by providing a constant seal on the pumping tube.

Permeability: 1. The ability of a body, such as a reverse osmosis or ultrafiltration membrane, to pass a liquid under pressure or to pass ions under the influence of an electric current as an ion exchange membrane in electrodialysis.

2. The ability of rock or soil to transmit water.

Permeate: 1. To penetrate and pass through, as water penetrates and passes through soil and other porous materials.

2. That portion of the feedwater which passes through a membrane to become product water.

Permissible Dose: The dose of a chemical that may be received by an individual without the expectation of a significantly harmful result.

Permselectivity: The ability of a semipermeable membrane to also be an ion exchanger and to allow selective passage of anions or cations under the influence of an electric current.

Permselectivity is a term often used in relation to electrodialysis.

Permutit Process: An older term for the cation exchange method of water softening.

Peroxide: 1. Any compound containing the two oxygen atoms united together into a bivalent -O-O- group. Readily releases abnormally active atomic oxygen, and therefore any peroxide is a strong oxidizing agent.

2. Hydrogen peroxide.

Peroxone Process: A water treatment process in which ozone is exposed to ultraviolet light or hydrogen peroxide as it is being applied to the water. This avanced oxidation process (AOP) initiates the formation of highly reactive hydroxy radicals to achieve a higher level and range of oxidations.

Persistence: The resistance to degradation as measured by the period of time required for complete decomposition of a material.

Pesticide: Any substance or chemical designed or formulated to kill or control weeds or animal pests.

Petroleum Derivatives: Chemicals formed when gasoline breaks down in contact with groundwater.

PEX: cross-linked polyethylene.

pH: A measure of the degree of the acidity or the alkalinity of a solution as measured on a scale ("pH scale") of 0 to 14.

The midpoint of 7.0 on the pH scale represents neutrality--that is, a "neutral" solution is neither acid nor alkaline. Numbers below 7.0 indicate acidity; numbers above 7.0 indicate alkalinity.

It is important to understand that pH is a measure of intensity, not of capacity. That is, pH indicates the intensity of alkalinity or acidity in the same way temperature tells how hot something is but not how much heat the substance carries.

More specifically, pH is the negative of the logarithm of the hydrogen ion concentration of a solution. The hydrogen ion concentration is the weight of hydrogen ions, in grams, per liter of solution. In neutral water, for example, the hydrogen ion concentration is 107- grams per liter; the pH is therefore 7.

Since it is hydrogen that is responsible for acidity and alkalinity, the abbreviation "pH" stands for "potential of hydrogen." The neutral point of 7.0 actually indicates the presence of equal concentrations of free hydrogen and hydroxide ions.

Pharmaceutical Grade Water: The collective term for six types of water as defined by the U.S. Pharmacopeia:

1. purified water; 2. water for injection; 3. bacteriostatic water for injection; 4. sterile water for inhalation; 5. sterile water for injection; and 6. sterile water for irrigation.

Phase: A term used in general chemistry to refer to a particular homogeneous form (solid, liquid, or gaseous) of a substance which might exist in other forms or phases.

For example, ice is the solid phase of water.

Phenolic Compounds: Organic compounds that are derivatives of benzene.

Phosphate: A salt of phosphoric acid. In the water industry, polyphosphates are used as sequestering agents to control iron and hardness, and as coating agents to control corrosion by formation of a thin passivating film on metal surfaces.

The complex phosphates also are a group of sequestering agents widely used in detergent formulations (except where phosphates are banned by law) because of their superiority in chemical water softening, sequestering, and other builder functions.

Sodium tripolyphosphate was the original builder upon which modern laundry detergent technology developed, and is used in laundry granules, automatic dishwasher detergents, and cleansers. It is adaptable to the spray drying process by which granules are made.

Tetrasodium pyrophosphate is also used in detergent granules, but since it does not rank as high in overall performance as sodium tripolyphosphate, its application is more limited.

Highly soluble tetrapotassium pyrophosphate is used in liquid laundry detergents and in hard surface cleaners, where it serves as a builder, water softener, and source of alkalinity.

Another complex phosphate, sodium metaphosphate, is marketed as a packaged water softener. The most widely used sodium metaphosphate is sodium hexametaphosphate (SHMP), which softens by sequestering.

The orthophosphate form of phosphates, trisodium phosphate (also called sodium orthophosphate), is a water softener that inactivates hardness minerals by precipitation. It is used to a limited extent in soap and detergent formulations as a builder, as a source of alkalinity, and for its water-softening properties. It is also used in powdered hard surface cleaners and cleansers to supply alkaline cleaning power.

Chlorinated trisodium phosphate is a dry chlorine bleach which, in water, acts much like sodium hypochlorite (liquid chlorine bleach). It provides a means of incorporating chlorine bleach effectively in dry products, and for this reason is used in cleansers and automatic dishwasher detergents. It also provides alkalinity that aids in cleaning.

Waters containing concentrations of iron, manganese, calcium, or magnesium sometimes can be treated with a sequestrant such as polyphosphate and kept from depositing these mineral precipitates or scales for a period of time. However, polyphosphate sequestering is not permanent, and therefore may not be as effective as actually removing the iron, manganese, and hardness minerals, as is done with iron filters and ion exchange water softening, for example. The sequestering value of polyphosphates is destroyed when they revert (hydrate) to orthophosphate. Polyphosphate reversion or hydration to orthophosphate occurs naturally in water with time. Intentions would be for this reversion not to happen and not to drop the sequestered water hardness, iron, and manganese out until after it reaches the waste water. But, the polyphosphate reversion process can be accelerated by various uncontrolled conditions, such as low pH, high temperature, and the presence of the oxides of certain heavy metals, including iron, calcium, copper, and zinc in water. It is important in phosphate feed water treatment operations to: 1)maintain a stable pH within the phosphate product's performance rage. 2) determine the polyphosphate composition or blend that is most compatible with the specific water quality objectives and conditions, and 3) apply the appropriate dosage of phosphate to accomodate the system demand. Because of the difficulty in maintaining phosphate stabilities in the presence of varying pH, time, temperature, and metal oxides in most natural water supplies, the actual removal of iron, manganese, and water hardness is generally a more assuredly effective water treatment method.

Municipal applications of polyphosphates to water supplies can interfere with home water treatment technologies. A portion of any water hardness, iron,

Phosphorus (P): A nonmetallic element which is essential to life.

However, too much phosphorus in a body of water can cause excessive growth of plant life, which can create a lack of oxygen as the plants die and decay.

Photon: The basic unit (quantum) of electromagnetic radiation. Light waves, gamma rays, x-rays, and so on consist of photons. Photons are discrete concentrations of energy that seem to have no rest mass and move at the speed of light. Their nature can be described only in mathematical terms. Photons are emitted when electrons move from one energy state to another, as in an excited atom. SEE ALSO gamma decay; radiation.

Photosynthesis: The chemical process by which green plants make carbohydrates (which the plants use as food) from carbon dioxide and water in the presence of sunlight and chlorophyll.

Oxygen is released as a byproduct of photosynthesis.

Phreatophyte: A type of plant with very long roots and extensive root systems which draws its water from the water table or other permanent groundwater supplies.

Examples of phreatophytes are willow and salt cedar. Excessive growths of phreatophytes are undesirable in areas where water is scarce since they can consume large quantities of water.

Physical Stability: A measure of the ability of an ion exchanger or a filter medium to resist breakdown caused by the physical forces such as crushing, attrition, or high temperatures to which it is subjected during use.

Phytoplankton: Small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water.

Pico (p): A prefix used in the metric system to mean one-trillionth or 10-12 or 0.000000000001.

Picocurie (pCi): A measure of radioactivity.

One picocurie of radioactivity is equivalent to 0.037 nuclear disintegrations per second, or to 0.037 becquerels (Bqs).

pK: A measure of the completeness of an incomplete chemical reaction, using a logarithmic scale. Also used to express the extent of dissociation of weak acids and complex ions. The weaker the electrolyte, the larger is its pK. The strengths of different acids may be compared by using pK values. Mathematically speaking, pK is the negative of the logarithm of the ionization (dissociation) constant (pKeq) of a chemical compound.

Plankton: 1. Small, usually microscopic, free-floating plants (phytoplankton) and animals (zooplankton) in aquatic systems.

2. All of the smaller free-floating, suspended, or self-propelled organisms in a body of water.

Plastic: Any high polymer, usually synthetic, material that during its manufacture or processing can be extruded, molded, cast, drawn, or laminated into objects of all sizes and shapes by application of heat or pressure, by chemical condensation, or by casting during polymerization of monomers, and that can retain the new shape under conditions of use.

Plastic Pipe: Tubing or pipe made from unreinforced thermoplastic polymers such as polyethylene, polybutylene, polyvinyl chloride, chlorinated polyvinyl chloride, and polypropylenes, and from reinforced thermosetting polymers such as epoxides and polyesters with glass fibers as reinforcing to increase strength.

Plastic pipe is characteristically flexible to rigid, lightweight, and strong; it resists attack by chemicals, corrosion, and weathering.

Plug Flow: A flow pattern in which the water being processed passes through the medium (such as a granular filter or an ion exchange bed) in a "piston-like" fashion instead of in turbulent or mixed flow patterns such as are found in other processes like ultraviolet light disinfection and electrodialysis.

Plumes: The way polluted water extends downstream from the pollution source (analogous to smoke from a smokestack as it drifts downwind in the atmosphere).

Pneumatic: Powered or moved by air pressure or compressed air.

POE: Point of entry.

Point-of-Entry (POE) Treatment: Full service water treatment applied to the water entering a house or building for the purpose of reducing contaminants in the water distributed throughout the house or building (outside faucets may be excepted from treatment).

Point-of-Use(POU) Treatment: Water treatment applied to a single tap used for the purpose of reducing contaminants in water at that one outlet.

POU treatment is often used to treat water for drinking and cooking only.

Polarize: As relates to electricity and corrosion control, to disrupt the corrosion process by developing a barrier on an anodic or cathodic surface.

Polisher: A treatment stage placed at the end of other treatment to bring the water to a more highly conditioned and more perfect state. For example, a mixed bed of ion exchange media installed as the final treatment step in the deionization process to remove last traces of undesirable ions.

Polishing Filter: A filter installed for use after the primary water treatment stage to remove any traces of undesirable matter or to polish the water.

Pollutant: A contaminant existing at a concentration high enough to endanger the environment or the public health or to be otherwise objectionable.

Pollution: Generally, the presence of matter or energy whose nature, location, or quantity produces undesired environmental effects.

Under the Clean Water Act, for example, the term is defined as the man-made or man-induced alteration of the physical, biological, and radiological integrity of water.

Polycarbonate: A thermoplastic polymer resin that is a linear polyester of carbonic acid. Polycarbonate is a transparent, nontoxic, noncorrosive, heat resistant, high impact strength plastic; it is generally stable, but may be subject to attack by strong alkalies and some organic hydrocarbons. It can be molded, extruded, or thermoformed, and is commonly used for numerous services, such as nonbreakable windows, household appliances, tubing, piping, and cartridge filter sumps.

Polyethylene: A tough thermoplastic polymer (-CH2CH2-) of ethylene that resists chemicals and absorbs very little moisture.

Polyethylene can vary from soft and flexible to hard and rigid depending on the pressures and catalysts used during manufacturing.

Low density polyethylene has its melting point at about 240 degrees Fahrenheit and tensile strength of 1500 psi; high density polyethylene melts at 275 degrees Fahrenheit and has tensile strength of 4000 psi.

Among services, polyethylene is commonly used for tubing and piping, food packaging, garment bags, and molded plastic products.

Polymer: A chemical formed by the union of many monomers (a molecule of low molecular weight).

Polymers are used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water.

All polyelectrolytes are polymers, but not all polymers are polyelectrolytes.

Polyphosphate: Any of a broad familiy of inorganic phosphorus compounds that are commonly referred to as molecularly dehydrated phosphates or condensed phosphates, including hexametphosphate, tripolyphosphate (P3O105-), and pyrophosphate <(P2O7<5-), among others. Unlike orthophosphate (PO43-), for which four oxygen atoms always surround a single central phosphate, polyphosphates are arranged as polymeric chains or occasionally rings that vary in their phosphorus-to-oxygen ratio and chain length with different commercial formulations. Polyphosphate is used as a sequestering agent to control iron and hardness, and as a coating agent that forms a thin passivating film on metal surfaces to control corrosion. Polyphosphates in solution are anionic and may be removed from water with anion exchange resins. However, polyphosphates that have reacted with a metal (e.g., iron) can form a sticky colloidal precipitate that must be filtered to be removed from water. Inorganic polyphosphates may tend to breakdown (hydrolyze) into orthophosphate groups plus molecules of shortened chain length over time and under extreme temperature and pH conditions. Upon breakdown these phosphate compounds can drop out any sequestered metal ions, such as iron and hardness, allowing them to precipitate from the water.

Polypropylene: A thermoplastic polymer of propylene resembling polyethylene, and used for making molded and extruded plastic products such as water pipe, tubing, and fittings.

Polystyrene: Polymerized styrene.

Polystyrene forms the skeletal structure of most common ion exchange resin beads.

Polysulfone: A synthetic thermoplastic polymer. Used in the manufacture of ultrafiltration membranes and in thin-film composite and charged polysulfone reverse osmosis membranes.

Polyvinyl Chloride (PVC): A thermoplastic polymer resin material (-CH2CHCl-) that is rigid and practically chemically inert.

Commonly used for water pipes and fittings, as well as numerous other services such as siding, gutters, raincoats, chemical containers, flooring, toys, tennis court surfaces, and films and package coatings for food containers.

Polyvinylidene Fluoride (PVDF): A thermoplastic fluorocarbon polymer that can be used for injection molded or extruded products.

More highly inert and resistant to oxidative degradation than polypropylene plastic, for example, but not as inert as the tetrafluoroethylene (TFE) fluorocarbon polymers (Teflon).

Pore Volume: The volume of pores in a unit weight of media particles or filter bed.

Pores: Very small open spaces in a rock or granular material, including the complex network of channels in the interior of a particle, such as those within an ion exchange resin bead or an activated carbon granule.

Porosity: A measure of the volume of pores in a material.

Porosity is calculated as a ratio of the interstices of a material (e.g., the volume of spaces between the media particles in a filter bed) to the volume of its mass, and is expressed as a percentage.

Porous: Full of pores through which water, light, etc. may pass.

Positive Charge: The electrical potential of an atom which has lost one or more electrons, therefore leaving it with more protons than electrons.

Cations carry positive charges.

Positive Displacement Pump: A type of piston, diaphragm, gear, or screw pump that delivers a constant volume with each stroke.

Positive displacement pumps are used as chemical solution feeders.

Postchlorination: The application of chlorine to a water following other water treatment processes.

Potable (Drinking) Water: A water supply which meets USEPA and/or state water quality standards and that is considered safe and fit for human consumption.

Potassium Chloride (KCl): A colorless potassium salt which can be used as a regenerant in cation exchange water softeners and dealkalizers.

Potassium Cycle: The use of potassium chloride salt instead of sodium chloride salt in the regeneration of cation ion exchange water softeners.

The potassium ion (K+) becomes the exchangeable ion rather than the sodium ion (Na+) in the sodium cycle system.

Potency: Amount of material necessary to produce a given level of a deleterious effect.

Potentiation: The effect of one chemical to increase the effect of another chemical.

POU: Point-of-use.

Pounds Per Square Inch (psi): Unit of measure for expressing pressure.

Pounds Per Square Inch Gauge (psig): Pressure measured with respect to that of the atmosphere. This is a pressure gauge reading in which the gauge is adjusted to read zero at the surrounding atmospheric pressure. It is commonly called gauge pressure.

Ppb: Parts per billion.

Ppm: Parts per million.

Ppt: Parts per trillion.

Prechlorination: The application of chlorine to a water supply prior to other water treatment processes which may follow.

Precipitate: 1. As a verb: to cause a dissolved substance to form a solid which comes out of solution and can be removed by settling or filtering. For example, the reduction of dissolved iron by oxidation, precipitation and filtration.

2. As a noun: the solid formed when a dissolved substance comes out of solution in such a way that it can be settled or filtered out.

3. As a verb: to cause moisture to condense and be deposited as rain, sleet, snow, etc.

Precipitation: 1. The process by which atmospheric moisture falls onto a land or water surface as rain, snow, hail, or other forms of moisture.

2. The chemical transformation of a substance in solution into an insoluble form (precipitate).

Precoat: The application, usually by slurry, of a very fine granular filter medium such as diatomaceous earth to a retainingmembrane or fabric surface prior to a service run. Precoating makes the medium unfit for further use. At the end of each service run, the precoat medium is rinsed off and disposed of prior to application of a new precoat to the filter septum.

Precursor: Compounds which lead to other compounds.

For example, natural humic and fulvic acids which, upon combination with chlorine, lead to trihalomethanes.

Preservative: An agent that prevents the deterioration of materials; usually associated with the prevention of biological deterioration.

Pressure Differential: The difference in the pressure between two points in a water system.

The difference may be due to the difference in elevation and/or to pressure drop resulting from water flow.

Pressure Drop: 1. A decrease in the water pressure (in psi) which occurs as the water flows. Pressure drop may occur for several reasons: internal friction between the molecules of water, external friction between the water and the walls of the piping system, or rough areas in the channel through which the water flows.

2. The difference between the inlet and outlet water pressure during water flow through a water treatment device such as a water conditioner. Abbreviated P and measured in pounds per square inch gauge pressure.

Pressure Head: The vertical distance (in feet) equal to the pressure (in psi) at a specific point.

The pressure head is equal to the pressure in psi times 2.31 ft/psi.

Pretreatment: Any water treatment step performed prior to the primary treatment process, such as filtration prior to deionization.

Prevalence Study: An epidemiological study which examines the relationship between diseases and exposures as they exist in a defined population at a particular point in time.

Prime: The action of filling a pump casing with water to remove the air.

Most pumps must be primed before startup or they will not pump any water.

Process Variable: A physical or chemical quantity which is usually measured and controlled in the operation of a water treatment plant or an industrial plant.

Process Water: Water used in a manufacturing or treatment process or in the actual product manufactured.

Examples would be water used for washing, rinsing, direct contact, cooling, solution makeup, chemical reactions, and gas scrubbing in industrial and food processing operations.

In many cases, water is specifically treated to produce the quality of water needed for the process.

Product Staging (reverse osmosis): The practice of using some of the product water from the first stage of RO treatment as feedwater for the second stage.

Product Water: Water that has been through the total treatment process and meets the quality standards required for the use to which the water will be put.

Product water is called by different names, depending upon which treatment process it has gone through:

"Centrate" from a centrifuge "Distillate" from a distiller "Filtrate" from a filter unit "Finished" from a municipal treatment plant "Deionized" from an cation and anion exchange system "Softened" from a softener unit "Permeate" from a reverse osmosis or ultrafiltration unit.

Production Rate: The amount (gallons or liters) of product water the system produces per minute or (especially for reverse osmosis) per 24 hour period.

Protozoa: Microscopic, usually single-celled microorganisms which live in water and are relatively larger in comparison to other microbes.

Protozoa are higher on the food chain than the bacteria that they eat. Many protozoa are parasitic.

Singular form: protozoan or protozoon.

Psi: Pounds per square inch.

Psig: Pounds per square inch gauge.

Public Water System: A system for the provision to the public of piped water for human consumption, if such system has at least 15 service connections or regularly serves an average of at least 25 individuals daily at least 60 days out of the year.

Such term includes: 1. any collection, treatment, storage, and distribution facilities under control of the operator of such system and used primarily in connection with such system; and 2. any collection or pretreatment storage facilities not under such control which are used primarily in connection with such system. A public water system is either a "community water system" or a "noncommunity water system."

Pumping Station: Mechanical devices installed in sewer or water systems or other liquid-carrying pipelines that move the liquids to a higher level.

Pure Water: This term has no real meaning unless the word "pure" is defined by some standard.

The Water Quality Association Promotion Guidelines recommend against the use of the words "Pure Water" in advertising unless the meaning of "pure" is very clearly explained for the consumer. The capacity of the words "pure", "purification," "purifier" and other derivatives of the word "pure" to mislead consumers is considerable.

In an absolute sense, all available water contains an amount of some substances in addition to H2O.

The context that is meant by use of these words should always be clearly and accurately defined.

Purified Water: Water produced from water meeting the USEPA standards for safe drinking water through treatment by distillation, reverse osmosis, deionization, or other processes and which meets United States Pharmacopoeia (USP) purity standards for "purified water" can be labeled as "purified."

These standards regulate pH, chloride, sulfate, ammonia, calcium, carbon dioxide, heavy metals, oxidizable substances, total solids, and bacteria.

If water meeting the USP standard has been distilled, it can alternatively be labeled "distilled water."

Purveyor: An agency or person that supplies water (usually potable water).

Putrefaction: Biological decomposition of organic matter, with the production of ill-smelling and tasting products, associated with anaerobic (no oxygen present) conditions.

PVC: Polyvinyl chloride.

Pyrite: Iron disulfide (FeS2 ). A common mineral that has a bright metallic luster and a brass-yellow color.

Also called iron pyrite or fool's gold.

Pyrogens: Substances (often of unknown origin) that produce fever when introduced into the human body.

Being chemically and physically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria.

-Q-

Qualitative: Descriptive of kind, type, or direction, as opposed to size, magnitude, or degree.

Quantitative: Descriptive of size, magnitude, or degree.

Quartz Jacket: A clear, pure fused quartz tube used to protect the high intensity ultraviolet lamps in ultraviolet systems.

It usually retards less than 10 percent of the ultraviolet radiation dose.

-R-

 

Rad: A unit of absorbed dose of ionizing radiation, corresponding to 100 ergs of energy per gram of absorbing material.

In the International System (SI) of Units, the rad is replaced by the gray (Gy); one gray (Gy) = 100 rads.

Radial Flow: The flow pattern in which water flows from the outside of a filter element to the center core.

For example, a replaceable cartridge filter unit is often designed for radial flow.

Radical: 1. A group of atoms acting as a single atom which go through chemical reactions without being changed.

2. Some examples are bicarbonate (HCO3-); hydroxide (OH-); sulfate (SO4--). Free radicals contain one or more unpaired electrons and are usually short-lived and highly reactive.

Radioactivity: Emissions of radiant atomic energy (alpha, beta, and/or gamma rays) from some elements (radium, radon, uranium, thorium, etc.) caused by the spontaneous disintegration of the nuclei of the atoms of these elements.

Radionuclide: Any man-made or natural element which emits radiation in the form of alpha or beta particles, or as gamma rays.

Radium (Ra): Naturally-occurring radioactive elements (radium 226 and radium 228) created in the decay of the uranium and thorium series.

Radium can be removed from water by cation exchange softening.

Radon (Rn): A colorless, odorless, short-lived radioactive gas which is produced by decay of the uranium/radium series and is soluble in water.

Radon is considered carcinogenic when inhaled by humans.

Radon can be removed from water by aeration or activated carbon.

Range: The spread from minimum to maximum values that an instrument is designed to measure.

Rated Capacity: As relates to softening or ion exchange, rated capacity, as stated by the manufacturer, may refer to any of several figures, all of which are given in relation to the period between regenerations:

1. the expected number of days the equipment will be in service;

2. the expected number of gallons of product water delivered; or

3. the grains of total hardness removed.

The capacity of an ion exchange system will vary, within limits, with the amount of regenerant used.

In filtration or adsorption applications, the manufacturer's statement regarding the expected number of days the equipment will be in service or the expected number of gallons of product water delivered before it is expected that backwashing and rinse down should occur.

Rated Capacity: (filtration or adsorption) The manufacturer's rated service cycle statement regarding the expected number of days the equipment will be in service or the expected number of gallons treated water delivered between servicing of the media (cleaning, regeneration, or replacement), as determined by testing or as specified by the manufacturer.

Rated In-Service Life: The total gallons (as specified by the manufacturer) of treated water delivered, or the length of time (based on water flow rates) the unit will be in operation before servicing (regenerating, cleaning, or replacement) of the treatment unit is expected to be necessary.

Rated Pressure Drop: In softening or filtration applications, rated pressure drop is the expected pressure drop in psi as stated by the equipment manufacturer or obtained under test conditions.

Rated pressure drop is based on rated service flow rate for clean water at 60 degrees Fahrenheit using a freshly regenerated softener or a backwashed filter.

The general limit is 15 psi at the specified service flow rate for the unit.

Rated Service Flow: The manufacturer-specified maximum and minimum flow rates at which a particular piece of water treatment equipment will continuously produce the desired quality of water.

Rated Softening Capacity: The statement by the water softener manufacturer about the expected number of grains per gallon of total hardness (as calcium carbonate equivalent) that will be removed between regenerations at the specified flow rate using the specified amount of regenerant (usually sodium chloride).

The capacity of ion exchanger resin to remove hardness increases, within limits, with higher regeneration salt dosages; therefore, rated softener capacity must be related to the pounds of salt required for each regeneration.

Raw Water: 1. Water, usually from wells or surface sources, which has had no previous treatment and is entering a water processing system or device.

2. Water at the inlet side of any water treatment system or device.

Reaction Tank: A tank or reservoir in which water treatment chemicals are allowed residence time to react with contaminants in the water; hydraulic or mechanical mixing to ensure thorough distribution, and internal piping or baffles to inhibit short-circuiting of the water flow may be provided.

Reaeration: The introduction of air through forced air diffusers into the lower layers of the reservoir.

As the air bubbles form and rise through the water, oxygen from the air dissolves into the water, and replenishes the dissolved oxygen.

The rising bubbles also cause the lower waters to rise to the surface where oxygen from the atmosphere is transferred to the water. This is sometimes called surface reaeration.

Reagent: A pure chemical substance that is used to make new products or is used in chemical tests to measure, detect, or examine other substances.

Recarbonation: A process in which carbon dioxide is bubbled into the water being treated to lower the pH.

The pH may also be lowered by the addition of acid.

Recarbonation is the final stage in the lime-soda ash softening process. This process converts carbonate ions to bicarbonate ions and stabilizes the solution against the precipitation of carbonate compounds.

Receiving Waters: All distinct bodies of water that receive runoff of waste water discharges, such as streams, rivers, ponds, lakes, and estuaries.

Recharge: Process by which rainwater (precipitation) seeps into the groundwater system.

Recharge Area: Generally, an area that is connected with the underground aquifer(s) by a highly porous soil or rock layer.

Water entering a recharge area may travel for miles underground.

Recharge Rate: The quantity of water per unit time that replenishes or refills an aquifer.

Reciprocal: Inversely or oppositely related.

For example, 1,000 ohms of resistance is the reciprocal of 1/1,000 siemens (formerly mhos) of conductance.

Recirculation: 1. In water treatment system design, the continuous operation of the transfer pump to keep water flowing through the system (especially through the disinfection component) at a rate above the water use rate in order to reduce the hazard of bacterial growth.

2. In cross flow membrane filtration systems, the recycling of a portion of the reject stream to maintain a desirable flow across the membrane while the system is in operation.

Reclaimed Brine: That portion of a previously-used brine solution used to regenerate a batch of cation resin for portable exchange softener tanks.

Brine which still measures at least 30 percent saturation and is low in total hardness can be reused in the first stages of the next cation batch regeneration.

Redox: A shortened term for "oxidation-reduction".

Used in terms such as "redox reactions" and "redox conditions".

Reducing Agent: Any substance, such as base metal (iron) or the sulfide ion (S2-), that will readily donate (give up) electrons.

The opposite is an oxidizing agent.

Reduction: Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound.

Under anaerobic conditions (no dissolved oxygen present), sulfur compounds are reduced to odor-producing hydrogen sulfide (H2S) and other compounds.

The opposite of oxidation.

Regenerant: In ion exchange or softening applications, a regenerant is the chemical solution used to restore an exhausted bed of ion exchange resin to the fully ionic (regenerated) form necessary for the desired ion exchange to again take place effectively. Regenerants are also used in a similar fashion to restore catalyst (e.g., iron and manganese removal) media for reuse.

Sodium chloride brine is normally used to regenerate cation exchange water softeners and for some dealkalizer systems. Hydrochloric and sulfuric acids are used for hydrogen-form cation deionizations units. Sodium hydroxide is normally used to regenerate OH- form anion deionizations systems. Potassium permangante regenerant is used to regenerate a manganese greensand iron and manganese removal filter.

Regeneration: In ion exchange applications, the use of a chemical solution (regenerant) to displace the contaminant ions deposited on the ion exchange resin during the service run and replace them with the kind of ions necessary to restore the capacity of the exchange medium for reuse.

This process is also called recharging or rejuvenation.

Catalyst media are recharged similarly.

Regeneration Cycle: The several steps including backwash, application of regenerant, dilution, and fresh or deionized water rinse necessary to accomplish regeneration of an ion exchange bed or oxidizing filter.

Regeneration Level: The quantity of regenerant, usually expressed in pounds per cubic foot of ion exchanger bed or pounds per regeneration, used in the regeneration cycle of an ion exchange system.

Regeneration level may also be called salt dosage.

Regeneration Water: All of the water consumed in the regeneration steps: backwash, regeneration (brining), dilution, and rinse.

Raw water or partially-treated water may be used for the rinse down.

Reject Staging: A method used to raise the production rates of a reverse osmosis system by using the reject water from the first stage as the feedwater for the second or succeeding stage in the RO process.

Reject Water: A term used in distillation, electrodialysis, reverse osmosis, and ultrafiltration to describe that portion of the incoming feedwater that has passed across the membrane but has not been converted to product water and is being sent to the drain.

Also called brine, concentrate, or retentate.

Rejection: In cross flow (membrane) filtration and distillation applications, the prevention by the membrane of the passage of total dissolved solids and other contaminants into the product water.

Rejection Rate: In a reverse osmosis or ultrafiltration system, rejection rate is

1. the quantity of the feedwater that does not pass through the membrane expressed as a percent of the total quantity of incoming feedwater; or

2. the concentration of contaminants that do not pass through the membrane as a percent of the total concentration of those particular contaminants in the feedwater.

Relative Density: The ratio of the density of a specific substance to the density of another substance which is used as a standard.

The standard for comparison with liquids is pure water at 4 degrees Celsius. The standard for gases is air at normal temperature and pressure.

Relative density was formerly called specific gravity.

Rem: The unit of dose equivalent from ionizing radiation to the total body or any internal organ or organ system.

Equivalent dose (or the rem value) gives a measure of the biological harm caused by radiation exposure.

A millirem (mrem) is 1/1000 of a rem.

In the International System (SI) of Units, the rem is replaced by the sievert (Sv); one sievert (Sv) equals 100 rems.

Removable: Capable of being taken away from a water treatment equipment unit using only simple tools such as a screwdriver, pliers, or open-end wrench.

Readily removable indicates capable of being taken away from a water treatment unit without the use of tools.

Renal: Pertaining to the kidney.

Representative Sample: 1. A portion of water or material that is, as nearly as possible, identical in content and consistency to that in the larger body of water or material being sampled.

2. In water treatment equipment manufacturing and testing, a typical production line sample that exhibits the essential features corresponding to and equivalent to (within plus or minus 10 percent) the other production units of that model.

Reserve Capacity: The amount of further contaminant reduction or length of time a device can continue to operate at a high level of performance after a signal of upcoming exhaustion is triggered.

Reservoir: Any natural or artificial holding area used to store, regulate, or control water.

Residential Equipment: The term sometimes used to denote smaller-sized water processing equipment which has been designed primarily for home use and intermittent household water flow rates up to 12 gallons per minute.

Water Quality Association equipment performance standards define residential equipment as that having an inlet designed to accommodate pipe size of no greater than one inch internal pipe size (IPS) diameter.

May also be referred to as domestic equipment or household equipment.

Residual: The amount of a specific material which remains in the water after the water has been through a water treatment step.

Residual may refer to undesirable material remaining as the result of incomplete removal (called leakage) or to material that is meant to remain in the treated water, such as "residual chlorine."

Residual Chlorine: Chlorine allowed to remain in a treated water after a specified period of contact time and to provide disinfection protection throughout the distribution system.

The amount of residual chlorine is the difference between the total chlorine added and that consumed by the oxidizable matter.

Residual Disinfectant Concentration: C in CT calculations.

The concentration of disinfectant measured in mg/L in a representative sample of water.

Residue: The dry solids remaining after the evaporation of a sample of water or sludge.

Resin: As used in the water processing industry, this term refers to ion exchange resin products which are usually specifically-manufactured organic polymer beads used in softening and other ion exchange processes to remove dissolved salts from water.

Resin Bead: In water processing, refers to the spherical shape of individual particles of ion exchange resin products, as compared to the irregular shaped particles of most other granular media products.

Resin Cleaner: One of several different chemical compounds used to cleanse ion exchange resin products of dissolved iron, aluminum, and various organics attracted to or bonded to the resin beads.

Resistance: That property of a material that resists the flow of an electric current.

The standard unit of resistance is the ohm.

Respiration: The process in which an organism uses oxygen for its life processes and gives off carbon dioxide.

Retention: In membrane filtration, retention describes the minimum particle or molecule size retained by the membrane under a given set of conditions, namely, pressure, flux recovery, and temperature.

Reverse Deionization: The use of the anion exchange resin ahead of the cation exchange resin (the reverse of the usual order) in a deionization system.

Reverse Osmosis: A water treatment process that removes undesirable materials from water by using pressure to force the water molecules through a semipermeable membrane.

This process is called "reverse" osmosis because the pressure forces the water to flow in the reverse direction (from the concentrated solution to the dilute solution) to the flow direction (from the dilute to the concentrated) in the process of natural osmosis.

RO removes ionized salts, colloids, and organic molecules down to a molecular weight of 100.

May be called hyperfiltration.

Reversible Effect: An effect which is not permanent, especially adverse effects which diminish when exposure to a toxic chemical is ceased.

RfD (Reference dose): The daily exposure level which, during an entire lifetime of a human, appears to be without appreciable risk on the basis of all facts know at the time. Same as ADI.

Rill: A small channel eroded into the soil surface by runoff; rills easily can be smoothed out (obliterated) by normal tillage.

Rinse:  In softening or ion exchange applications, the step in the regeneration process in which fresh water is passed through the bed of resin to remove any excess or spent regenerant prior to placing the softener into service.

Risk: The potential for realization of unwanted adverse consequences or events.

Risk Assessment: A qualitative or quantitative evaluation of the environmental and/or health risk resulting from exposure to a chemical or physical agent (pollutant); combines exposure assessment results with toxicity assessment results to estimate risk.

Risk Factor: Characteristic (e.g., race, sex, age, obesity) or variable (e.g., smoking, occupational exposure level) associated with increased probability of a toxic effect.

Risk Management: Decisions about whether an assessed risk is sufficiently high to present a public health concern and about the appropriate means for control of a risk judged to be significant.

Risk Specific Dose: The dose associated with a specified risk level.

RO: Reverse Osmosis

Rotary Drilling: A common hydraulic well-drilling method which uses a rotating drill pipe with a hard-tooled drill bit attached at the bottom.

A fluid (drilling mud) is forced down through the drill pipe and then forced up again between the drill pipe and the well hole, carrying rock chippings (cuttings) up with the mud.

Route of Exposure: The avenue by which a chemical comes into contact with an organism (e.g., inhalation, ingestion, dermal contact, injection).

Runoff: That part of precipitation, snow melt, or irrigation water that runs off the land into streams or other surface water.

It can carry pollutants from the air and land into the receiving waters.

Rust (Ferric Oxide): A reddish corrosion product occasionally found in water.

Rust is formed as a result of electrochemical interaction between iron and atmospheric oxygen in the presence of moisture.

Rust Remover: A product that removes rust stains from fabrics, dishwashers, and other washable surfaces, such as bathrooms, kitchens, tea kettles, dishes and glassware, and wherever water comes in contact.

Most commonly, these materials are composed of reducing agents (such as sodium hydrosulfite) or acid products, and may be in liquid, powder, or gel form.

During laundering, some rust removers may be used in the regular laundry cycle or for presoaking. They may also be useful for miscellaneous stain removal, such as removal of dyebleeding.

Rust removers made to remove rust, scale, and lime deposits from the inside of dishwashers are a combination of acids. Used periodically as needed, they are added at the beginning of the main wash cycle (no dishes or other cleanser present) and are allowed to remain through the balance of the cycles.

-S-

Sacrificial Anode: An anode made of suitable metal placed in a water heater tank to protect the tank from corrosion. Anodes of metals such as aluminum, magnesium, or zinc are sometimes installed in water heaters and other tanks to control corrosion of the tank. The introduction of the anode creates a galvanic cell in which the magnesium or zinc will go into solution (be corroded) more quickly than the metal of the tank, thereby imparting a cathodic (negative) charge to the tank metal(s) and thus preventing tank corrosion.

This corroding of the anode metal is called "the sacrifice of the anode".

Safe: Condition of exposure under which there is a "practical certainty" that no harm will result in exposed individuals.

Safe Drinking Water Act (SDWA): The national legislation first passed by the U.S. Congress and signed into law by the President in 1974 and amended in 1986.

The SDWA directs the U.S. Environmental Protection Agency to promulgate and enforce standards for safe drinking water necessary to protect public health at public water systems serving 25 or more people for an average of 60 days per year.

The law also contains provision for delegating primary enforcement responsibility to states and for protecting underground sources of drinking water.

Safe Water: Water that does not contain harmful bacteria, or toxic materials or chemicals. Water may have taste and odor problems, color and certain mineral problems and still be considered safe for drinking.

Safe Yield: The annual quantity of water that can be taken from a source of supply over a period of years without depleting the source beyond its ability to be replenished naturally in "wet years."

Salimeter: A hydrometer which measures the percent of salt as NaCl in brine or other salt solutions. A 100 percent reading on a salimeter is about 26.4 percent salt by weight at 60 degrees F. Some people use the term "salinometer" to refer to a salimeter.

Saline: Consisting of, or containing, salt.

Salinity: The relative concentration of dissolved salts, usually sodium chloride, in a given water. A measure of the concentration of dissolved mineral substances in water.

Salt: 1. Chemistry A chemical compound formed by the neutralization of an acid with a base. For example, H2SO4 (acid) + 2NaOH (base) = Na2SO4 (salt) + 2H2O (water). 2. Water Treatment Sodium chloride (NaCl) or potassium chloride (KCl), both of which are used in solution form to regenerate cation exchange water softeners and some dealkalizers. 3. Common table salt, which is sodium chloride (NaCl).

Salt Dosage: See Regeneration Level.

Salt Efficiency: In an ion exchange water softener, the hardness removal capacity calculated as grains of hardness removed divided by the weight of salt in pounds that is used to achieve that amount of hardness reduction.

Operational salt efficiency refers to the salt efficiency performance of a water softener under conditions of actual or simulated long term use (six months or more) in a household where gallons of water usage typically varies from day to day.

Salt Water: The general term for all water over 1,000 ppm (mg/L) total dissolved solids.

  • Fresh Water - <1,000 TDS
  • Brackish - 1,000-5,000 TDS
  • Highly Brackish - 5,000-15,000 TDS
  • Saline - 15,000-30,000 TDS
  • Sea Water - 30,000-40,000 TDS
  • Brine - 40,000-300,000+ TDS

Sand: Soil particles between 0.05 and 2.0 mm in diameter.

Sand Filter: The oldest and most basic filtration process, which generally uses two grades of sand (coarse and fine) for turbidity removal or as a first stage roughing filter or prefilter in more complex processing systems.

Municipal water treatment systems often used gravity rapid-rate sand filters. Pressure-type sand filters plus coagulants are used for commercial applications.

For home use or for small swimming pools, a pressure sand filter is also used.

Sanitary Survey: An on-site review of the water source, facilities, equipment, operation, and maintenance of a public water system for the purpose of evaluating the adequacy of the facilities for producing and distributing safe drinking water.

Sanitization: The act of sanitizing. Sanitization is not an absolute phenomenon; it is a partial removal or inactivation of microorganisms. Depending on the system, a sanitization operation should reduce the viable organism population by 50 to 99.9 percent, but it should completely eliminate enteric pathogen-related organisms such as Salmonella and E. coli.

(Disinfection by comparison, should reduce 99.9 to 99.9999 percent of viable microorganisms.)

Sanitize: To reduce the number of bacterial contaminants to safe levels as judged by public health requirements. To make clean and free or inactivation of dirt, filth, and conditions injurious to health.

Generally considered to reduce germ count by 50 to 99.9 percent.

The USEPA requires that sanitizing claims must show a 99.9 percent microbial reduction in five minutes.

Sanitizer: An agent that results in the reduction of bacterial numbers to accepted public health limits by sanitizing. Sanitizers are applied in the cleaning operations of inanimate objects.

Saprophytes: Organisms living on dead or decaying organic matter. They help natural decomposition of organic matter in water.

Saturated Solution: A solution which contains the maximum amount of the dissolved substance (solute) that a solution of this kind can normally hold at this temperature.

Saturated Zone: The area below the water table where all open spaces are filled with water.

Saturation: In water chemistry, means the state of a solution (water) when it holds the maximum equilibrium quantity of dissolved matter at a given temperature and pressure. The limit when no more of a given substance will dissolve.

Saturation Index: A scale showing the relationship of calcium carbonate to the pH and hardness of a given water. The saturation index is commonly used to determine the scale-forming tendency of a particular water.

Scale: A coating or precipitate deposited on surfaces such as kettles, water pipes, or steam boilers that are in contact with hard water.

Waters that contain carbonates or bicarbonates of calcium or magnesium are especially likely to cause scale when heated.

Also called hard water scale.

Scavenger: In water treatment applications, a polymer matrix or ion exchanger that is used specifically to remove organic species from the feedwater before the water is to pass through the deionization process.

SCFM: Cubic feet of air per minute at standard conditions of temperature, pressure, and humidity (0 degrees C/14.7 psia/50% relative humidity).

Schedule, Pipe: A sizing system of arbitrary numbers that specifies the I.D. (inside diameter)and O.D. (outside diameter) for each diameter pipe. This term is used for steel, wrought iron, and some types of plastic pipe. Also used to describe the strength of some types of plastic pipe.

Screen Size: See Mesh Size.

SDI: Silt Density Index.

SDWA: See Safe Drinking Water Act.

Secondary Drinking Water Regulations: See Drinking Water Standards.

Secondary Treatment: As relates to waste water treatment, the process which makes up the second step in treating waste water and removes suspended and dissolved solids and biochemical oxygen demand (BOD) from the waste water which has already undergone primary treatment.

Sediment Yield: The quantity of sediment arriving at a specific location.

Sedimentary Rock: Rock that results from the consolidation of layers of loose sediment made up of various kinds of organic and inorganic matter.

Sedimentation: The process of suspended solid particles settling out (going to the bottom of the vessel) of water that has little or no movement.

Sometimes sedimentation only occurs after the particles have begun to coagulate (either naturally or because of the use of a coagulant aid such as alum) into larger and heavier flocs.

Seepage: The percolation of water through the soil from unlined channels, ditches, water courses, and water storage facilities.

Selective Ion Exchanger: An ion exchange medium which shows selectivity. For example, a chelating ion exchange resin which will remove only gold ions from solution.

Selectivity: The tendency of an ion exchanger to "prefer" (have more attraction for) certain kinds of ions over others, as if the resin were ranking the types of ions in order to be removed: most preferred ion, second most preferred, etc.

Seltzer Water: See Soda Water.

Semiconfined Aquifer: An aquifer that is partially confined by a soil layer (or layers) of low permeability through which recharge and discharge can occur.

Semipermeable Membrane: See Membrane.

Sepralator: A spiral-wound membrane element or cartridge used in cross flow membrane systems.

Sepsis: A diseased state caused by the presence of pathogenic microorganisms in the bloodstream.

Septicemia: Bacteria multiplying in the bloodstream.

Sequential Actions: One action occurring after or followed by others in a given order--as opposed to simultaneous actions.

Sequester: To keep a substance (e.g., iron or manganese) in solution through the addition of a chemical agent (e.g., sodium hexametaphosphate) that forms chemical complexes with the substance. In the sequestered form, the substance cannot be oxidized into a particulate form that will deposit on or stain fixtues. Sequestering chemicals are aggressive compounds with respect to metals, and they may dissolve precipitated metals or corrode metallic pipe materials.

Serial Filtration: The arrangement of two or more filtering steps, one following the other, in order to remove increasingly finer particulates at each stage and provide for filtration of all sizes of suspended solids.

Cartridge-style units often employ this method, using depth prefilters (compressed fibers) followed by surface filtration with a micromembrane cartridge element.

Service Flow: The rate in U.S. gallons per minute (gpm) or liters per minute (L/min) at which a given water processing system can deliver product water. The rating may be for intermittent peak flow or constant flow.

Service Pipe: The pipeline extending from the water main to the building served or to the consumer's system.

Sessile: Attached firmly to a permanent base and not free to move about.

Bacteria grow and multiply faster when attached (sessile) in water systems, than when free-floating (planktonic) in water. Attached sessile cells form a larger colony; their polysaccharide containing glycocalyx slime layer helps adhere other bacteria cells and nutrients which float past and also acts as a protective layer which resists chemical disinfectant penetration.

This sessile microbial colonization is known as biofilm in water systems.

Shallow Well: A well sunk in easily-penetrated ground to a point which is below the water table but usually less than about 30 feet in depth.

Shearing Action: The action of low temperature water flowing at high rates which splits and separates particle agglomerations, and prevents the formation of floc deposits during the coagulant feed/filtration process.

This action may also tear away from the filter any previous deposits or suspended matter.

Shock Load: The arrival at a water treatment system of raw water containing unusual amounts of algae, colloidal matter, color, suspended solids, turbidity, or other pollutants.

SI System of Units: The International System (SI) of units that was adopted and recommended for use in science and technology by the 11th General Conferece on Weights and Measures in 1960.

This coherent system of units is built from the following seven SI base units:

Physical Name of SI Unit Symbol for Quantity SI Unit

length meter m

mass kilogram kg

time second s

electric ampere A current

thermodynamic kelvin K temperature

amount of mole mol substance

luninous candela cd intensity

Siemens (S): Formerly called mho.

The siemens (S) is the SI unit of conductance equal to the reciprocal of the ohm.

Silica Friday,Jun 16, 2000 As used in water chemistry, a collective term encompassing all reactive (dissolved) and inert (nonreactive and undissolved or colloidal) forms of the chemically resistant dioxide SiO2 of silicon, or silicates formed from silicon and oxygen in combination with one or more other minerals or metals. Silica, such as quartz for example, is present in almost all earth's minerals, rocks, soils, sands, and clays. It is found in fresh water in a range of 1 to 100 mg/L. In a laboratory water analysis report, silica is nearly always identified as silicon dioxide (SiO2), however when dissolved in water silica is actually hydrated to silicic acid (SiO2 nH2O) and associated anions. Below a pH of 9, silica is present mostly in the silicic acid form (SiO2 2H2O, also written as H4SiO4. At low pH, silicic acid can polymerize or condense to form uncharged colloid particles (known as colloidal silica) as small as 0.02 microns in size. As the pH of water exceeds 8, silicic acid (H4SiO4) increasingly dissociates into the bisilicate anions H3SiO4- and H2SiO42-. This will increase the solubility of the silica unless divalent and polyvalent cations are available in significant concentrations. These cations of calcium, magnesium, iron, and aluminum, for example, will likely cause precipitation of insoluble silicate salts, especially at higher pH levels. The precipitation of multivalent cations with the silicates tends to occur at a pH value of 1 to 2 points below the point at which the cation hydroxide solubilities would be exceeded. Silicates can interfere with the crystal growths of precipitating metal and mineral cations thereby keeping such silicate complexed particulates in the colloidal size ranges, e.g., silicates are a contributor to formations of colloidal iron and colloidal manganese.

 

Silicates: A group of compounds containing oxygen and silica(SiO2). Silicates are considered anodic corrosion inhibitors combining with the free metal released at the anode site of corrosion activity and forming an insoluble metal-silicate compound. Silicates can also be used to sequester soluble iron and manganese present in source water to help prevent oxidation and the formation of red and black water.

Silt: Soil particles between 0.05 and 0.002 millimeter in approximate diameter.

Silt Density Index (SDI): A test used to measure the level of suspended solids in feedwater for membrane filtration systems. The test consists of the time it takes to filter 500 milliliters of the test water through a 47 millimeter diameter, 0.45 micron rated microporous filter under a constant pressure of 30 psig.

The SDI of feedwater to a reverse osmosis membrane should be maintained at less than 5, preferably less than 3.3.

SDI = 100 (1-t1/t2)/T      where:

t1 = time to filter 500 mL of water initially,

t2 = time to filter 500 mL of water after T minutes (T is usually 15 minutes.)

Simulate: To reproduce the action of some process, usually on a smaller scale.

Single-Stage Pump: A pump that has only one impeller. A multistage pump has more than one impeller.

Single-Stage System: (reverse osmosis) A reverse osmosis system in which the water is passed through the membrane(s) only once by using a single high-pressure pump.

Sink: A place in the environment where a compound or material collects.

Slope: The slope or inclination of a trench bottom or a trench side wall is the ratio of the vertical distance to the horizontal distance or "rise over run."

Sloughing: The action of a medium (filter, ion exchanger, or membrane) casting off into the effluent stream any substance intended for removal from the water.

Sloughing may be caused by shearing action or by ion selectivity.

Slow Rinse: 1. (ion exchange) That portion of the rinsing stage which usually follows the introduction of the regenerant and during which the rinse water (deionized, decationized, softened, or untreated water) passes through the resin at the same flow rate as the regenerant;

2. (filtration) The initial rinse down after application of regenerant for resettling the medium bed. After the bed is resettled, a final fast rinse is used to "purge" the bed.

Slow Sand Filtration: A process involving passage of raw water through a bed of sand at low velocity (generally less than 0.4 m/h) resulting in substantial particulate removal by physical and biological mechanisms.

Sludge: The settleable solids separated from water during processing.

Slug: A temporary abnormally high concentration of an undesirable substance which shows up in the product water.

A slug is generally a symptom of a malfunction of the water processing unit.

For example, a "slug" of iron-rust might appear due to the shearing action of a high-demand flow which loosens a previously deposited iron precipitate.

Slurry: A watery mixture or suspension of insoluble (not dissolved) matter; a thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).

Small Bore Piping: Copper or stainless steel pipe with a small diameter of 0.5 inches or 15 mm.

Such pipe is commonly found in pump-assisted hot water central heating systems.

SMCLs: Secondary Maximum Contaminant Levels. Secondary MCLs for various water quality indicators are established to protect public welfare.

SNARL: Suggested No Adverse Response Level. The concentration of a chemical in water that is expected not to cause an adverse health effect.

Soap: The water-soluble reaction product of a fatty acid ester and an alkali (usually sodium hydroxide) which produces suds when used with water for washing or cleaning purposes.

Some soaps are mild disinfectants. Common soaps such as sodium and potassium soaps are soluble but can be converted to insoluble calcium and magnesium soap "curds" (bathtub rings) by the presence of hardness ions in the water.

Soap Curd: The insoluble precipitate that forms when soap is used in hard water. Soap curd and lime soap are synonymous

SOCs: synthetic organic chemicals.

Soda Ash:  (Na2CO3) A common water treatment chemical, sodium carbonate, which is used for pH modification, as an alkaline builder in some soaps and detergents, and in the lime-soda ash water softening process.

Soda Water: Water which has been impregnated with carbon dioxide (CO2) so that it will be effervescent when not under pressure. Same as carbonated water, seltzer water, and sparkling water.

Sodium: (Na+) A metallic element found abundantly in compounds in nature, but never existing alone.

Sodium compounds are highly soluble and do not form curds when used with soaps or detergents.

Many sodium compounds are used in the water treatment industry. Most notable is the use of sodium chloride as a regenerant in the cation exchange water softening process.

Sodium Bicarbonate: (NaHCO3) A mild alkali, commonly called baking soda.

Sodium bicarbonate is used in powdered hard surface cleaners and some presoak formulations to provide alkaline cleaning at a controlled level.

Sodium Chloride (NaCl): The chemical name for common table salt.

Sodium chloride is also widely used for regeneration of ion exchange water softeners and in some dealkalizer systems.

Sodium Cycle: The cation exchange water softening process in which sodium ions in the resin are exchanged for hardness ions in the water.

Sodium chloride is commonly used for resin regeneration.

Sodium Hypochlorite (NaOCl): Liquid bleach; used as a source of chlorine in water treatment.

Laundry bleach available from grocery stores is 5.25 percent chlorine and commercial strength bleach available from swimming pool suppliers or chemical companies is usually 12.5 percent chlorine.

Soft Water: Any water which naturally contains less than 1.0 grain per gallon (17.1 mg/L or ppm) of total hardness expressed as calcium carbonate equivalent.

Softened Water: Any water which has been processed in some manner to reduce the total hardness to 17.1 mg/L or ppm (1.0 grain per gallon) or less expressed as calcium carbonate equivalent.

Soil Erodibility: A measure of the soil's susceptibility to raindrop impact, runoff, and other erosional processes.

Soil Profile: A vertical section of the earth's highly weathered upper surface often showing several distinct layers or horizons.

Soil Sealant: A chemical or physical agent that plugs porous soils and prevents leaching or percolation.

Soil Structure: The arrangement of soil particles into aggregates.

Soil Texture: The proportions of soil particles (sand, silt, and clay) in a soil profile.

Solar Salt: Common salt which is produced by solar evaporation in shallow ponds or lagoons and used in water softener regeneration.

Solder:A metallic compound used to seal the joints between pipes. Until recently, most solder contained 50 percent lead. The use of lead solder containing more than 0.2 percent lead is now prohibited for pipes carrying potable water.

 

Sole Source Aquifer: An aquifer that supplies 50 percent or more of the drinking water of an area.

Solenoid Shutoff Valve: An electrical device operated by a magnetic coil to make the valve either open for flow or close to shut off water flow.

This type of valve is used extensively for flow control and direction on many water processing systems.

Solids: (In water laboratory analyses) The matter dissolved or suspended in water.

Solute: The substance which is dissolved in the solvent (generally a liquid such as water) to form a solution.

Solution: A mixture in which one or more substances (solutes) are dissolved into another substance (solvent), usually a liquid, in such a way that the solute is equally distributed (homogeneous) throughout the solvent in the form of either molecules (as in a sugar solution) or ions (as in a salt solution).

Solvent: A liquid substance that dissolves another substance (the solute) to form a solution.

Sorption: A surface phenomenon which may be either absorption or adsorption, or a combination of the two; often used when the specific mechanism is not known.

Sparger: A perforated pipe in an aerator or ozone contact compartment through which the air or ozone-containing air is sprayed into the water, and which allows for the diffusion of the air or ozone into the water.

Specific Gravity: Weight of a particle, substance, or chemical solution in relation to the weight of water. Water has a specific gravity of 1.000 at 4 degrees C (39 degrees F). Particulates in raw water may have a specific gravity of 1.005 to 2.5.

 

Spectroscopy: A technique used in chemical analyses which is based on the principle that many substances, when crossed by a beam of light, allow a unique and well-defined fraction of that light to pass or emit a well-defined fraction of radiation when returning from an atomic vapor state to their fundamental state.

The characteristic wave length pattern of the absorbed or emitted light can be used to identify the particular substance with great certainty.

The quantity of the light absorbed or emitted is proportional to the concentration of the substance.

Spectroscopy is one of the most frequently used analytical methods for water analyses. Ultraviolet light (UV) spectroscopy (using light wave lengths between 10 and 390 nanometers) and infrared (IR) spectroscopy (using light wave lengths between 780 and 300,000 nanometers) are used particularly to identify and quantify organic molecules. Atomic absorption spectroscopy (AA) is used to identify and quantify inorganic elements.

Spectroscopy is also called spectrometry and spectrophotometry.

Sphericity: The measure of the bead roundness or "whole bead" count of beads in an ion exchange resin product or other bead form absorbent or filter medium.

Spiral-Wound: A very common construction configuration for one style of reverse osmosis membrane and cartridge filter element.

In RO membranes, the membrane sheets are assembled in layers around a perforated mandrel product water tube, with coarse mesh spacer screens between the layers, to form a complete module element.

In cartridge filter elements, the filtration material, such as fiber cord, is continuously wound around a perforated mandrel core tube.

Split-Stream Treatment: The art of proportionally blending a stream of treated water with a stream of untreated water from the same source to achieve a lower measurement of a given contaminant in the blended stream, thus not removing all of the contaminant but still meeting the water quality desired, such as meeting a maximum contaminant level requirement for delivered water.

Split-stream operation makes it possible to treat less than the full flow of water.

Spore: A small reproductive body, often single-celled, capable of reproducing the organism under favorable conditions.

The spore is sometimes considered the resting stage of the organism. Among the organisms that may produce spores are algae, bacteria, and certain protozoans.

In water, most spores resist adverse conditions which would readily destroy the parent organism.

Sporicide: An agent that destroys microbial spores. By definition, sterilizing agent.

Spring: A place where groundwater flows naturally from the soil or rock formation onto the land surface or into a body of surface water.

A spring is sometimes used as a source of water for a shallow dug well.

Spring Water: Water obtained from an underground formation from which water flows naturally to the surface, or would flow naturally to the surface if it were not collected underground.

Stability: The ability of an ion exchange product or filter medium to withstand physical and chemical degradation in cycle-after-cycle operations.

Stainless Steel (ss): A chromium alloy with substantially 50 percent or more iron and usually with some nickel (typically 12 to 30 percent chromium and zero to 22 percent nickel) that is practically inert toward rusting and corrosion.

The nickel content of ss contributes to improved corrosion resistance. Austenitic stainless steel contains 16 to 26 percent chromium, six to 22 percent nickel, low (less than 0.15 percent) carbon, and cannot be hardend by heat treatment; ferritic ss contains 15 to 30 percent chromium, low (0.1 percent) carbon, and cannot be hardened by heat treatment; martensitic ss contains 12 to 20 percent chromium, controlled carbon and other additives, and can be hardened by heat treatment which increases the tensile strength from 80,000 to 200,000 psi.

Standard: A physical or chemical quantity whose value is known exactly and is used to calibrate or standardize instruments.

Standard Industrial Classification (SIC): The statistical classification standard published by the United States Office of Management and Budget (OMB) that assigns an industry number to businesses and business units by type of economic activity.

It is the classification standard underlying all establishment-based Federal economic statistics classified by industry type.

The system uses from a one-digit to a four-digit classification number depending on how narrowly the business unit is defined. There are 11 one-digit groupings and over 1,000 four-digit groupings.

Household and industrial water treatment equipment manufacturing, for example, is in SIC 3589, water conditioning service is in SIC 7389, distribution of water conditioning equipment is in SIC 5074, manufacturing of fluid power control valves is in SIC 3492, manufacturing of water treatment chemicals is in SIC 2899, manufacturing of distilled water is also in SIC 2899, manufacturing of pharmaceutical water or of water purification tablets is in SIC 2834, manufacturing of carbonated and flavored bottled water is in SIC 2086, bottling natural, spring, or mineral water is in SIC 5149, and retailing bottled water is in SIC 5499.

Standard Methods: A shortened title for the Standard Methods for the Examination of Water and Wastewater, a joint publication of the American Public Health Association, American Water Works Association, and the Water Pollution Control Federation.

This widely-used volume outlines the procedures used to analyze water and waste water impurities and characteristics.

Standardize: To compare with a standard.

In chemistry, to find out the exact strength of a solution by comparing it with a standard of known strength, or to set up an instrument or device to read a standard. This allows you to adjust the instrument so that it reads accurately, or enables you to apply a correction factor to the readings.

Starch: Chemically, starch refers to complex carbohydrates obtained from vegetable sources.

In home laundry usage, the term has been expanded to cover products that perform the same function as starch, i.e., supplying body or stiffness to fabrics, but that are based on synthesized chemicals such as carboxymethylcellulose or polyvinyl acetate. The latter are called synthetic or plastic starches.

State: The agency of the State or Tribal government which has jurisdiction over public water systems.

During any period when a State or Tribal government does not have primary enforcement responsibility pursuant to Section 1413 of the Safe Drinking Water Act, the term "State" means the Regional Administrator, U.S. Environmental Protection Agency.

Static: Fixed in position; resting; without motion.

Static Head: When water is not moving, the vertical distance (in feet) from a specific point to the water surface is the static head.

(The static pressure in psi is the static head in feet times 0.433 psi/ft.)

Static Pressure: The static pressure in psi is the static head in feet times 0.433 psi/ft.

The static pressure in psi is the static head in feet times 0.433 psi/ft.

Static Pressure: The static pressure in psi is the static head in feet times 0.433 psi/ft.

The static pressure in psi is the static head in feet times 0.433 psi/ft.

Static Water Level: The elevation or level of the water table in a well when the pump is not operating. The level or elevation to which water would rise in a tube connected to an artesian aquifer, or basin, or conduit under pressure.

Stator: That portion of a machine which contains the stationary (non-moving) parts that surround the moving parts (rotor).

Steady Operating Flow Rate: The flow in U.S. gallons per minute (or liters per minute) at which a water processing filter or ion exchanger will deliver its rated capacity.

For water softeners, this flow is based upon delivering softened water from an incoming raw water of 20 grains per gallon total hardness as calcium carbonate.

Stepwise Regeneration: The method of regenerating ion exchange resin beds several times with the same regenerant, but at a higher concentration each time.

The method is usually used to avoid calcium sulfate precipitation when sulfuric acid is employed as a regenerant for cation bed units of deionizer systems that are being used to decationize unsoftened feedwater.

Sterilization: The removal or destruction of all (or greater than 99.9999 percent of all) microorganisms, including pathogenic and other bacteria, vegetative forms and spores.

Sterilize: Complete (100 percent or at least greater than 99.9999 percent) destruction or inactivation of all living organisms.

The USEPA requires that sterilization claims must demonstrate killing or inactivation of all microorganisms, including bacterial spores.

Stethoscope: An instrument used to magnify sounds and convey them to the ear.

Stoichiometric: Related to the proportions in which chemicals combine to form compounds and the weight relations in chemical reactions.

Stoichiometry is the mathematical and theoretical study of how chemicals combine.

Stokes Law: A formula for calculating the rate of fall of particles through a liquid medium.

The rate at which a spherical particle will rise or fall when suspended in a liquid medium varies as the square of the particle's radius, as the density of the particle, and as the viscosity of the fluid.

Stratification: The formation of separate layers (of temperature, plant, or animal life) in a lake or reservoir.

Each layer has similar characteristics such as all water in the layer has the same temperature.

Stratified Bed: In ion exchange applications, a bed in which two exchangers of different classes and different densities have been placed in the same column (bed), such as weak base anion resin on top of a strong base anion exchanger, or in cation exchange systems, a weak acid on top of a strong acid resin.

String Wound Element: A cartridge-style filter element constructed by continuous spiral winding of natural or synthetic yarn around a preformed product water tube core and then building it up in layers to form a depth-type filter element.

Styrene: (C8H8) A fragrant, liquid, unsaturated hydrocarbon used chiefly in the manufacture of synthetic rubber, resins, and plastics.

Styrene is the prime ingredient in many cation and anion exchange resins.

Submerged Aquatic Vegetation (SAV): Aquatic vegetation, such as sea grasses, that cannot withstand excessive drying and therefore live with their leaves at or below the water surface.

SAVs provide an important habitat for young fish and other aquatic organisms.

Submergence: The distance between the water surface and the media surface in a filter.

Submersible Pump: A pump designed to fit inside the well casing and to operate below the water level in a drilled well.

Submicron Filter: A cartridge-type membrane filter used in fine particle separation applications to remove particulates of less than one micron in size.

Sulfate Bacteria: Sulfate-reducing bacteria, such as Desulfovibrio, and the single-celled aerobic sulfur-oxidizers of the genus Thiobacillus.

The sulfate-reducing bacteria contribute to tuberculations and galvanic corrosion of water pipes and to hydrogen sulfide taste and odor problems in water. Thiobacillus, by its production of sulfuric acid, has contributed to acid corrosion of metals.

Sulfur (S): A yellowish solid chemical element.

"Sulfur" is also often used to refer to sulfur water.

Sulfur Water: Water containing objectionable amounts of hydrogen sulfide gas which causes an offensive "rotten egg" odor.

Sulfuric Acid: (H2SO4) A very strong, corrosive and hazardous acid used as a regenerant for the cation stage of an ion exchange deionization system.

Sulfuric acid is also used occasionally to lower the pH of highly alkaline water.

When higher concentrations of sulfuric acid are combined with high concentrations of calcium, calcium sulfate crystals precipitate and create tenacious fouling of media particles.

An older name for sulfuric acid is oil of vitriol.

Superchlorination: The addition of excess amounts of chlorine to a water supply to speed chemical reactions or ensure disinfection within a short contact time.

The chlorine residual following superchlorination may be high enough to be unpalatable, and thus dechlorination is commonly employed before the water is used.

Supplier of Water: Any person who owns or operates a public water system.

Support Media Bed: Material of a specific graded particle size (such as gravel) used as a subfill to support the primary medium bed.

In larger diameter systems (tanks), this bed improves the collection of processed water and promotes more uniform distribution of the backwashing water.

Surface Filtration: Filtration that occurs at the surface layer (as opposed to within the body depth) of the filter and is accomplished by passing the material to be filtered over a grating, screen, sieve, or membrane fabric with microsized holes.

The size of the holes in the filter determines what materials will pass through and what will be filtered out (held back).

Surface Runoff: Precipitation, snow melt, or irrigation in excess of what can infiltrate the soil surface and be stored in small surface depressions; runoff is a major transporter of nonpoint source pollutants.

Surface Tension: The tendency of a liquid to form a relatively tough "skin" or film on its surface.

Surface tension is caused by the attraction between the molecules of the liquid, and it is surface tension that causes water molecules to stick together and form drops. Surface tension makes it possible to float a razor blade on the surface of a glass of water even though the blade is much heavier than the water.

The surface tension that holds the drops together makes it difficult for the water to penetrate or "wet" fabrics (or skin). Soaps and detergents contain "wetting agents" to reduce surface tension and increase fabric penetration by water.

Surface Water: All water naturally open to the atmosphere (rivers, lakes, reservoirs, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other collectors which are directly influenced by surface water.

Surfactant: A surface-active substance that when added to water lowers surface tension and increases the "wetting" capabilities of the water. Reduced surface tension allows water to spread and to penetrate fabric or other substances to be washed or cleaned.

There are three categories of surfactants: detergents, wetting agents, and emulsifiers.

"Surfactant" is a contraction for surface-active agent.

Surge Chamber: A chamber or tank connected to a pipe and located at or near a valve that may quickly open or close or a pump that may suddenly start or stop.

When the flow of water in a pipe starts or stops quickly, the surge chamber allows water to flow into or out of the pipe and minimize any sudden positive or negative pressure waves or surges in the pipe.

Suspended Solids: Solids that either float on the surface or are suspended in water or other liquids, and which are largely removable by laboratory filtering. The quantity of material removed from water in a laboratory test, as prescribed in Standard Methods for the Examination of Water and Wastewater.

Sweet Water: Fresh water. Palatable water. Not salt water.

Swelling: The expansion of certain ion exchange resins when converted into a specific ionic state.

This is a reversible expansion, as the resin may well shrink as it becomes exhausted. Some exchangers will expand as they exhaust.

Cation exchange water softening resins will generally swell when exhausted (loaded with hardness ions) and will shrink when regenerated with heavier salt dosages of 10 to 15 pounds of sodium chloride (NaCl) or potassium chloride (KCl) per cubic foot of resin.

Standard cation softening resin (8 percent polystyrene/DVB), in the calcium form, will shrink about 5 percent in volume when treated with a 25 percent salt-brine solution.

Synergism: The combined action of several chemicals which produces a greater effect than would be obtained by simply adding together the effects produced by each chemical separately.

Synergism is also called synergy.

Synthetic Organic Chemicals: Man-made organic substances including herbicides, pesticides, and various industrial chemicals and solvents.

Synthetic organic chemicals are generally considered dangerous in drinking water at concentrations above the USEPA maximum contaminant levels.

Often referred to as SOCs.

System: A complete integrated series consisting of various components and perhaps multiple water treatment processes which can be tested, installed, and operated as a singular unit of equipment.

For example, a single RO treatment system generally consists of two or more stages of media filtration plus cross flow membrane filtration and water storage.

Systemic: Relating to whole body, rather than its individual parts.

Systemic Effects: Effects observed at sites distant from the entry point of a chemical due to its absorption and distribution into the body.

-T-

Tangential Flow Filtration: See Cross Flow Filtration.

Tannin: Any of a group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees andplants, and are part of the degredation-resistant fulvic acid materials formed during the decomposition of vegetation.

Tannins occur in water in almost any location where large quantities of vegetation have decayed. Tannins can impart a faintly yellowish to brown color to water.

Tannin molecules tend to form anions in water above pH 6 and can then be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.

Tansmittancy: The ability of water to trasmit or convey ultraviolet energy

Taste Threshold: The minimum concentration of a chemical or biological substance which can just be tasted.

TDS: Total Dissolved Solids.

TDS Creep: The appearance of salt in RO product water which sometimes occurs as a result of the reduction of differential pressure across the membrane as can occur when the RO unit has been shut down for a period of time.

Water flow will cease to permeate through the membrane when there is insufficient differential water pressure across the membrane.

However TDS permeates through the membrane as a function of the TDS concentration difference across the membrane.

Teflon: Trade name for a high temperature industrial plastic material used in cookware finishes, bearings, lubricating, plumbing sealants, and a practically inert coating on metal and glass surfaces.

Telemetry: The electrical link between the transmitter and the receiver. Telephone lines are commonly used to serve as the electrical line.

Temporary Hardness: See Carbonate Hardness.

Tension: 1. Electric potential or voltage. The term usually is used to mean high voltage, as in "high tension transformer" or "high tension lines."
2. Stretched to stiffness or tautness.

Terrace: A broad channel, bench, or embankment constructed across the slope to intercept runoff and detain or channel it to protected outlets, thereby reducing erosion from agricultural areas.

Tertiary Treatment: The third stage of treatment that brings water to a high degree of refinement or conditioning following the reduction of substances in the primary and secondary stages of treatment.

TFC: Thin-film Composite.

TH: Total Hardness.

Therapeutic Index: The ratio of the dose required to produce toxic or lethal effect to dose required to produce nonadverse or therapeutic response.

Thermal Conductivity: The ability of a substance to conduct heat. Mathematically, the ratio of the rate of heat flow to the rate of temperature change in the particular substance.

Thermal Ozone Destructor: A unit in an ozonation system that employs high temperature to destroy excess ozone.

Thermal Stratification: The formation of layers of different temperatures in a lake or reservoir.

Thermocline: The layer in a lake which divides the warm upper current-mixed zone (epilimnion) from the colder lower deep-water stagnant zone (hypolimnion).

During the warm summertime, the thermocline is the middle layer of the lake. Lying between the two layers, the thermocline loses heat rapidly.

Also called the metalimnion.

Thermocouple: A heat-sensing device made of two conductors of different metals joined at their ends. An electric current is produced when there is a difference in temperature between the ends.

Thermoplastic: Materials such as certain synthetic resins and plastics that soften or fuse when heated and harden and become rigid when cooled, and that can usually be remelted and cooled time after time with no appreciable chemical change.

Thermoset: Certain plastics and synthetic resins that once solidified will not resoften or fuse when heated. Thermoset materials may decompose at high temperature, but will not soften or melt.

Thin-Film Composite Membrane: A class of reverse osmosis membranes made with polyamide-based polymer and fabricated with different materials in the separation and support layers.

Thiobacillus: A genus of bacteria that obtain their energy from oxidation of sulfides, thiosulfates, or sulfur, forming sulfur, persulfates, sulfuric acid, and sulfates.

THMs: See Trihalomethanes.

Threshold: The lowest dose of a chemical at which a specified measurable effect is observed and below which it is not observed.

Threshold Odor: The minimum odor of a water sample that can just be detected after successive dilutions with odorless water.

Also called odor threshold.

Threshold Substance: See Trace Substance.

Throughput Volume: The amount in gallons or liters of water passed through an ion exchange resin bed or water treatment system before exhaustion of the exchanger or system is reached.

Thrust Block: A mass of concrete of similar material appropriately placed around a pipe to prevent movement when the pipe is carrying water. Usually placed at bends and valve structures.

Tissue: A group of similar cells.

Titrate: To titrate a sample, a chemical solution of known strength is added on a drop-by-drop basis until a certain color change, precipitate, or pH change in the sample is observed (endpoint).

Titration is the process of adding the chemical reagent in increments until completion of the reaction, as signaled by the endpoint.

Titration: An analytical technique for determining how much of a certain substance (concentration) is present in a solution (such as a water sample) by measuring how much of another substance (of known concentration) must be added to produce a given reaction (often color change in the solution).

Titration is used for determining the level of concentration of a substance in solution. This procedure is widely used in water testing.

TOC: Total Organic Carbon.

Too Numerous to Count: The total number of bacterial colonies exceeds 200 on a 47mm diameter membrane filter used for coliform detection.

Topography: The arrangement of hills and valleys in a geographic area.

Tortuous Path: Water flow through channels which are constricted and marked by repeated twists, bends and winding turns. In an electrodialysis system, water flow in which spacers, turbulence promoters or cross traps are used to produce turbulence in the flow stream.

Total Acidity: The total of all forms of acidity in a solution, including mineral acidity, carbon dioxide, and acid salts.

Total Alkalinity: See Alkalinity.

Total Capacity: See Rated Capacity.

Total Chlorine: The total concentration of the chlorine in a water, including the combined available chlorine and the free available chlorine.

Total Chlorine Residual: The total amount of chlorine residual present in a water sample, without regard to type.

Total Dissolved Phosphorus: Total phosphorus content of material that will pass through a filter of a specific size.

Total Dissolved Solids (TDS): The total weight of the solids that are dissolved in the water, give in ppm per unit volume of water. TDS is determined by filtering a given volume of water (usually through a 0.45 micron filter), evaporating it at a defined temperature (usually 103-105 degrees Celsius), and then weighing the residue.

Note: A test measuring the electrical conductivity of the water provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.

Total Hardness (TH): The total of the amounts of divalent metallic cations, principally calcium hardness and magnesium hardness, expressed in terms of calcium carbonate equivalent.

Total Matter: