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abrasion-resistant material Material that is hard and resistant to physical wear caused by friction.
absorption (1) Taking up of matter in bulk by other matter, as in dissolving of a gas by a liquid. (2) Penetration of substances into the bulk of the solid or liquid. See adsorption.
absorption capacity A measure of the quantity of a soluble substance that can be absorbed by a given quantity of a solid substance.
acclimation (1) The dynamic response of a system to the addition or deletion of a substance until equilibrium is reached. (2) Adjustment to a change in the environment.
accuracy The degree of agreement between the quantity measured and the true quantity.
acid (1) A substance that tends to lose a proton. (2) A substance that dissolves in water with the formation of hydrogen ions.
acid-forming bacteria Microorganisms that can metabolize complex organic compounds under anaerobic conditions. This metabolic activity is the first step in the two-step anaerobic fermentation process leading to the production of methane.
acidity The quantitative capacity of aqueous solutions to neutralize a base. Measured by titration with a standard solution of a base to a specified end point, acidity is typically expressed as milligrams of equivalent calcium carbonate per liter (mg/L CaCO3). See pH.
acre-foot (ac-ft) A volume of water 0.3 m (1 ft) deep and 4047 m2 (1 ac) in area, or 1234 m3 (43 560 cu ft).
activated sludge Sludge particles produced by the growth of organisms in the biological reactor in the presence of dissolved oxygen.
activated sludge loading The unit mass of biological oxygen demand in the applied liquid per unit volume of aeration capacity or per unit mass of activated sludge per day.
activated-sludge process Biological wastewater treatment process that converts nonsettleable (suspended, dissolved, and colloidal solids) organic materials to a settleable product using aerobic and facultative microorganisms.
adsorption The adherence of a gas, liquid, or dissolved material to the surface of a solid or liquid. It should not be confused with absorption.
adsorption water Water held on the surface of solid particles by molecular forces with the emission of heat (heat of wetting).
advanced wastewater treatment Any physical, chemical, or biological treatment process used to accomplish a degree of treatment greater than that achieved by secondary treatment.
aeration (1) The bringing about of intimate contact between air and a liquid by (a) spraying the liquid in the air, (b) bubbling air through the liquid, or (c) agitating the liquid to promote surface absorption of air. (2) The supplying of air to confined spaces under nappes, downstream from gates in conduits, and so on, to relieve low pressures and to replenish air entrained and removed from such confined spaces by flowing water. (3) Relief of the effects of cavitation by admitting air to the affected section.
aeration period (1) The theoretical time, typically expressed in hours, during which mixed liquor is subjected to aeration in a biological reactor while undergoing activated sludge treatment. It is equal to the volume of the tank divided by the volumetric rate of flow of the wastewater and return sludge. (2) The theoretical time during which water is subjected to aeration.
aeration tank A tank in which wastewater or other liquid is aerated. See biological reactor.
aerator A device that brings air and a liquid into intimate contact. See diffuser.
aerobic bacteria (aerobes) Bacteria that require free elemental oxygen to sustain life.
agglomeration Coalescence of dispersed suspended matter into larger flocs or particles.
agitator Mechanical apparatus for mixing or aerating. A device for creating turbulence.
air bound Obstructed, as to the free flow of water, because of air entrapped in a high point. Used to describe a pipeline or pump in such condition.
air chamber A closed pipe chamber installed on the discharge line of a reciprocating pump to adjust for irregular hydraulic conditions and to reduce shocks caused by pulsating flow.
air diffuser Devices of varied design that transfer oxygen from air to a liquid.
air diffusion The transfer of air to a liquid through an oxygen-transfer device. See diffusion.
air injector A component of an air-lift pump made up of an air supply line and diffuser.
air lock A reduction or stoppage of liquid flow caused by entrapped air. See air binding.
air stripping Removal of volatile substances from a solution using the principles of Henry's Law to transfer volatile pollutants from a solution of high concentration into an air stream of lower concentration. The process ordinarily is designed so that the solution containing the volatile pollutant contacts large volumes of air.
air supply valve A valve used to throttle or isolate an air supply line.
air-lift pump A vertical pipe with an air injector submerged in a well. Air bubbles are introduced into the bottom of the well so that the denser water surrounding it lifts or pushes the aerated water up through the discharge pipe. These pumps can be used to pump smaller flows of untreated wastewater or return sludge.
air-powered diaphragm pump A type of reciprocating pump in which compressed air flexes a membrane that is pushed or pulled to contract or enlarge an enclosed cavity. The most common application is to pump sludge from primary sedimentation tanks and gravity thickeners.
algae Photosynthetic microscopic plants that float or are suspended in water. They may also be attached to structures, rocks, etc. In high concentrations, decomposing algae may deplete dissolved oxygen in receiving waters.
algal assay An analytical procedure that uses specified nutrients and algal inoculum to identify the limiting algal nutrient in water bodies.
algal bloom Large masses of microscopic and macroscopic plant life, such as green algae, occurring in bodies of water.
alkali Typically, any substance that has highly basic properties; used particularly with reference to the soluble salts of sodium, potassium, calcium, and magnesium.
alkaline The condition of water, wastewater, or soil that contains a sufficient amount of alkali substances to raise the pH above 7.0.
alkalinity The capacity of water to neutralize acids; a property imparted by carbonates, bicarbonates, hydroxides, and occasionally borates, silicates, and phosphates. It is expressed in milligrams of equivalent calcium carbonate per liter (mg/L CaCO3).
alternating current (AC) An electric current that reverses its direction at regularly recurring intervals.
alum, aluminum sulfate Used as a coagulant in filtration. Dissolved in water, alum hydrolyzes into aluminum hydroxide and sulfuric acid. To precipitate the hydroxide, as needed for coagulation, the water must be alkaline.
ambient Typically refers to the prevailing dynamic environmental conditions in a given area.
ammeter An instrument for measuring electric current, either alternating or direct, in units of amperes.
ammonia (NH3), ammonium (NH4+) Dissolved degradation products of urea and proteins in raw wastewater. Typically, raw wastewater contains 30 to 50 mg/L of NH3. Reactions between chlorine and ammonia are important in disinfection.
ammonia nitrogen Elemental nitrogen present in the form of ammonia (NH3).
ammoniator Apparatus used for applying ammonia or ammonium compounds to water.
ammonification Bacterial decomposition of organic nitrogen to ammonia.
amoeba A group of simple protozoans, some of which produce diseases such as dysentery in humans. See Sarcodina.
ampere Standard unit of electric current measurement. One ampere represents the flow of one coulomb of electricity per second. A flow of one ampere is produced in a resistance of one ohm by a potential difference of one volt.
anaerobic (1) A condition in which free and dissolved oxygen is unavailable. (2) Requiring or not destroyed by the absence of air or free oxygen.
anaerobic bacteria (anaerobes) Microorganisms that grow only in the absence of free and dissolved oxygen.
angular misalignment A type of shaft misalignment that results from a pump shaft and a motor shaft coming together without having parallel axial alignment.
anhydrous ammonia (NH3) Water-soluble colorless gas composed of molecules containing one nitrogen atom and three hydrogen atoms. Typically, ammonia is detectable because of its characteristic pungent and irritating odor. Not to be confused with aqueous ammonia, which is a 15 to 30 percent solution of ammonia in water.
anion A negatively charged ion attracted to the anode under the influence of electrical potential.
anionic flocculant A polyelectrolyte with a net negative electrical charge.
anoxic Condition in which oxygen is available in the combined form only; there is no free oxygen. Anoxic sections in an activated sludge plant may be used for denitrification.
antagonism Detrimental interaction between two entities. See synergism.
antichlors Reagents, such as sulfur dioxide, sodium bisulfite, and sodium thiosulfate, that can be used to remove excess chlorine residuals from water by conversion to an inert salt.
antifoam agent A material having low compatibility with foam and a low surface tension.
anti-siphoning spring A spring added to discharge valves in systems where pumps are located below the liquid level in the suction tank. The spring closes the discharge valve when the pump is off to prevent fluid from moving through the system by siphoning action.
appurtenances Machinery, appliances, or auxiliary structures attached to a main structure enabling it to function, but not considered an integral part of it.
aqueous vapor The gaseous form of water.
armature Rotating member of a brushed direct current motor in which electromotive force is produced by magnetic induction or a stationary component with same function in an alternating current motor.
automatic oiler A type of oiler that automatically regulates the oil reservoir level to keep a bearing properly lubricated.
automatic recording gauge An automatic instrument for measuring and recording graphically and continuously.
automatic sampling Collecting of samples of prescribed volume over a defined time period by an apparatus designed to operate remotely without direct manual control.
autotrophic bacteria Microorganisms that obtain their carbon and energy for growth from inorganic compounds. Most autotrophic bacteria are photosynthetic and use light as a source of energy to assemble the organic molecules they require. Some autotrophic bacteria carry out chemosynthesis, making organic molecules by using energy derived from the oxidation of inorganic compounds in the environment.
average An arithmetic mean obtained by adding quantities and dividing the sum by the number of quantities.
average daily flow The total flow past a point over a period of time divided by the number of days in that period.
average flow Arithmetic average of flows measured at a given point.
average velocity The average velocity of a stream flowing in a channel or conduit at a given cross section or in a given reach is equal to the discharge divided by the cross-sectional area of the section or the average cross-sectional area of the reach. Also called mean velocity.
axial flow impeller Impellers that resemble propellers. Pumps incorporating this type of impeller are used for pumping treated effluent or clean water. They are less useful for raw wastewater or sludge because the tight tolerances of the impellers cannot easily handle solids or stringy material.
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babbitt bearing A type of bearing lined with a soft alloy containing tin, copper, and antimony. The function of the alloy is to reduce friction.
backflow prevention system (1) A system of check valves and pressure relief valves used to prevent the flow of water through a line in a direction opposite to normal or intended flow. A typical system consists of two spring-loaded check valves in series separated by a pressure relief valve. (2) Any effective device, method, or construction used to prevent backflow into a potable water system.
backflushing The action of reversing the flow through a conduit for the purpose of cleaning the conduit of deposits.
back-pressure valve A valve provided with a disk hinged on the edge so that it opens in the direction of normal flow and closes with reverse flow. Also called a check valve.
backwashing The operation of cleaning a filter by reversing the flow of liquid through it and washing out matter previously captured in it. Filters include true filters such as sand and diatomaceous earth, but not other treatment units such as trickling filters.
bacteria A group of globally distributed, rigid, essentially unicellular microscopic organisms lacking chlorophyll. They perform a variety of biological treatment processes including biological oxidation, sludge digestion, nitrification, and denitrification.
bacterial analysis The examination of water and wastewater to determine the presence, number, and identity of bacteria; more commonly called bacterial examination. See bacteriological count.
bacterial slime A polysaccharide slime that is produced by many types of bacteria. This slime helps to hold activated sludge floc together.
bacteriological count A means for quantifying numbers of organisms. See most probable number.
baffles Deflector vanes, guides, grids, gratings, or similar devices constructed or placed in flowing water, wastewater, or slurry systems as a check or to produce a more uniform distribution of velocities; absorb energy; divert, guide, or agitate the liquids; and check eddies.
ball bearing A component in machinery in which the journal turns upon loose hardened steel balls that roll easily in a grooved track so that friction is reduced. Also one of the balls in such a bearing.
ball check valve A non-return valve in which a ball sits within a cylindrical fluid line.
bar screen A screen composed of parallel bars, either vertical or inclined, placed in a waterway to catch debris. Trapped materials (screenings) are raked from it either manually or automatically. Also called bar rack.
barminutor A bar screen of standard design fitted with an electrically operated shredding device that sweeps vertically up and down the screen cutting up material retained on the screen.
base A compound that dissociates in aqueous solution to yield hydroxyl ions. The pH of a base is more than 7.0.
basic data Records of observations and measurements of physical facts, occurrences, and conditions, as they have occurred, excluding any material or information developed by means of computation or estimate. In the strictest sense, basic data include only the recorded notes of observations and measurements, although in general use it is taken to include computations or estimates necessary to present a clear statement of facts, occurrences, and conditions.
bearing A basic machine component designed to reduce friction between moving parts and to support moving loads.
bearing housing A protective outer shell that contains lubricants and prevents contaminants from getting into the bearing.
bearing race The grooved tracks that are fixed to the machine members in ball and roller bearing assemblies that contain the balls or rollers.
Beggiatoa A filamentous organism whose growth is stimulated by hydrogen sulfide.
bell The enlarged (female) end of a pipe into which an adjoining (male) pipe fits.
belt dressing An aerosol product that increases operating efficiency and extends the life of drive belts. Belt dressing can reduce stiffness, restore flexibility, and stop squealing.
belt screen A continuous band or belt of wire mesh, bars, plates, or other screening medium that passes around upper and lower rollers and from which the material caught on the screen is typically removed by gravity, brushes, or other means.
bicarbonate alkalinity Alkalinity caused by bicarbonate ions.
binary fission The division of a single-celled organism into two daughter cells.
bioassay (1) An assay method using a change in biological activity as a qualitative or quantitative means of analyzing a material's response to biological treatment. (2) A method of determining the toxic effects of wastes and wastewaters using viable organisms under controlled conditions.
biochemical (1) Chemical change resulting from biological action. (2) Pertaining to the chemistry of plant and animal life.
biochemical oxidation Oxidation brought about by biological activity resulting in the chemical combination of oxygen with organic matter. See oxidized wastewater.
biochemical oxygen demand (BOD) A measure of the quantity of oxygen used in the biochemical oxidation of organic matter in a specified time, at a specific temperature, and under specified conditions.
biochemical oxygen demand load The biochemical oxygen demand content, typically expressed in kilograms or pounds per unit of time, of wastewater passing into a treatment system or water body.
biodegradation The breakdown of organic materials by microorganisms in soils, bodies of water, and wastewater treatment systems.
biological denitrification The transformation of nitrate nitrogen to inert nitrogen gas by microorganisms in an anoxic environment in the presence of an electron donor.
biological floc A very fine, fluffy mass formed by the aggregation of fine suspended particles, as in a precipitate formed by biological activity.
biological nutrient removal (BNR) An adaptation of the conventional activated-sludge process where anaerobic and anoxic zones are added to biological reactors to create the correct conditions under which bacteria and other microorganisms are able to remove nitrogen and phosphorous from wastewater.
biological oxidation The process by which living organisms, in the presence of oxygen, convert organic matter to a more stable or mineral form.
biological process (1) The metabolic activities of bacteria and other microorganisms, as in during the breakdown of complex organic materials into simple, more stable substances during sludge digestion and secondary wastewater treatment. (2) Any chemical process involving living organisms and their life activities. Also called biochemical process.
biological reactors In wastewater treatment, the tanks where aerobic, anaerobic, or anoxic conditions are created to produce healthy mixed liquor and facilitate biological treatment processes.
biomass The mass of biological material contained in a system.
biosolids The solid organic matter recovered from wastewater treatment processes and used, especially as fertilizer.
bleed (1) To drain a liquid or gas, as to vent accumulated air from a water line or to drain a trap or a container of accumulated water. (2) The exuding, percolation, or seeping of a liquid through a surface.
blinding (1) Clogging of the filter cloth of a vacuum filter, belt press, belt thickener, or pressure filter. (2) Obstruction of the fine media of a sand filter.
blower A compressor designed to provide air to a biological reactor or aerobic digester to provide adequate dissolved oxygen in the fluid to support biological processes.
bottom contraction The reduction in the area of overflowing water caused by the crest of a weir contracting the nappe.
bound water (1) Water held strongly on the surface or in the interior of colloidal particles. (2) Water associated with the hydration of crystalline compounds.
boundary layer viscous drag A force caused by the movement of a body through a fluid. The direction of this force is along the axis parallel to the movement. This force is used to create the pumping action in disc pumps.
breakpoint chlorination Addition of chlorine to water or wastewater until the chlorine demand has been satisfied, with further additions resulting in a residual that is directly proportional to the amount added beyond the breakpoint.
brush aerator A surface aerator that rotates about a horizontal shaft with metal blades attached to it; commonly used in oxidation ditches.
bubbler level measurement A fluid measuring device that operates on the principle that a small constantly regulated air supply bubbling into a liquid will produce a back pressure equal to the static head. Typically, the bubbler pressure is converted to a voltage or current signal that is fed into an electronic network. Variations in the signal level are used to turn pumps on or off, or adjust their speed.
buffer A substance that resists a change in pH.
bulking Inability of activated sludge solids to separate from the liquid under quiescent conditions; may be associated with the growth of filamentous organisms, low DO, or high sludge loading rates. Bulking sludge typically has a sludge volume index greater than 150 mL/g.
buoyancy The upward force exerted on an object immersed in a fluid. The "buoyant force" depends on the object's volume. The greater an object's volume, the greater the amount of fluid it displaces, therefore, the greater the buoyant force.
butt square joints Joints in which the materials being joined butt against each other rather than overlap.
butterfly valve A valve in which the disk, as it opens or closes, rotates about a spindle supported by the frame of the valve. The valve is opened at a stem. At full opening, the disk is in a position parallel to the axis of the conduit.
bypass An arrangement of pipes, conduits, gates, and valves by which the flow may be passed around a hydraulic structure appurtenance or treatment process; a controlled diversion.
bypass line Typically a short segment of piping with isolation valves that allow flow to be diverted around a hydraulic structure, component or treatment unit that may require periodic maintenance. The bypass line allows the main line to stay in service while the unit or component is worked on.
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calcium hypochlorite [(Ca(OCl)2] A solid that, when mixed with water, liberates the hypochlorite ion OCl- and can be used for disinfection. Commercial grades contain 70 percent available chlorine.
calcium oxide (CaO) A calcined chemical material known as lime. Used in lime and soda ash water treatment, but must first be slaked to calcium hydroxide [Ca(OH)2]. Also called burnt lime, quicklime, and unslaked lime.
calibration (1) The determination, checking, or rectifying of the graduation of any instrument giving quantitative measurements. (2) The process of taking measurements or of making observations to establish the relationship between two quantities.
calorie The amount of heat necessary to raise the temperature of 1 g of water at 15 degrees Celsius by 1 degree.
capacitance The ability to store an electric charge, measured in farads. The capacitance of a capacitor is one farad when one coulomb of electricity changes the potential between the plates by one volt.
capacity (1) The quantity that can be contained exactly, or the rate of flow that can be carried out exactly. (2) The load for which a machine, apparatus, station, or system is rated.
capital cost The amount of cash or credit needed initially to complete a project such as the construction of a wastewater treatment plant.
carbon (1) A chemical element essential for growth. (2) A solid material used for adsorption of pollutants.
carbon dioxide A nonflammable, colorless, odorless gas. Its molecules are composed of two oxygen atoms and one carbon atom.
carbonaceous biochemical oxygen demand (CBOD) A quantitative measure of the amount of dissolved oxygen required for the biological oxidation of carbon-containing compounds in a sample. See biochemical oxygen demand.
carbonate hardness Hardness caused by the presence of carbonates and bicarbonates of calcium and magnesium in water. Such hardness may be removed to the limit of solubility by boiling the water. When the hardness is numerically greater than the sum of the carbonate alkalinity and bicarbonate alkalinity, the amount of hardness is equivalent to the total alkalinity and is called carbonate hardness. It is expressed in milligrams of equivalent calcium carbonate per liter (mg/L CaCO3). See hardness.
carbonation The diffusion of carbon dioxide gas through a liquid to render the liquid stable with respect to precipitation or dissolution of alkaline constituents.
carrying capacity The maximum rate of flow that a conduit, channel, or other hydraulic structure is capable of passing.
cascade aerator An aerating device built in the form of steps or an inclined plane on which staggered projections are arranged to break up the water and bring it into contact with air.
cation A positively charged ion attracted to the cathode under the influence of electrical potential.
cationic flocculant A polyelectrolyte with a net positive electrical charge.
caustic alkalinity The alkalinity caused by hydroxyl ions. See alkalinity.
caustic soda (sodium hydroxide) A white crystalline solids that, when dissolved in water, exhibits strong alkalinity and corrosiveness.
cavitation A phenomenon common in centrifugal pumps that occurs when the pump attempts to discharge more flow than it is pulling in through the suction. Reduced internal pressure causes gases to expand and form bubbles around the impeller, which violently implode, potentially causing severe damage to the pump.
Celsius The international name for the centigrade scale of temperature, on which the freezing point and boiling point of water are 0 degrees Celsius and 100 degrees Celsius, respectively, at 101 kPa (1 atm) of pressure. By international agreement, the term Celsius has replaced the term Centigrade.
Centigrade By international agreement, the term Celsius has replaced the term Centigrade.
centrate Liquid removed by a centrifuge typically containing high concentrations of suspended, nonsettling solids.
centrifugal blower A blower that typically is made up of multiple stages to achieve design airflow requirements. Each stage consists of an impeller rotating on a common shaft, enclosed within a casing.
centrifugal non-clog pump A type of centrifugal pump in which the impellers are rounded and free of sharp corners to minimize the chance of collecting rags and stringy objects and the impeller is specially designed to pass larger solids.
centrifugal pump A pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing having an inlet and a discharge connection. The rotating impeller creates pressure in the liquid by the velocity derived from centrifugal force.
certification A program to substantiate the capabilities of personnel by documentation of experience and learning in a defined area of endeavor.
chain and sprocket A device used for the transmission of power where shafts are separated and the use of gears is impractical. Sprockets take the place of gears and drive one another by means of the chain passing over the sprocket teeth. A sprocket is a wheel with teeth shaped to mesh with the chain.
change of state The process by which a substance passes from one to another of the solid, liquid, and gaseous states, and in which marked changes in its physical properties and molecular structure occur.
channel (1) A perceptible natural or artificial waterway that periodically or continuously contains moving water or forms a connecting link between two bodies of water. It has a definite bed and banks that confine the water. (2) The deep portion of a river or waterway where the main current flows.
channel roughness That roughness of a channel including the extra roughness owing to local expansion or contraction and obstacles, as well as the roughness of the stream bed proper; that is, friction offered to the flow by the surface of the bed of the channel in contact with the water. It is expressed as the roughness coefficient in velocity formulas.
check valve A valve with a disk hinged on one edge so that it opens in the direction of normal flow and closes with reverse flow. An approved check valve is of substantial construction and suitable materials, is positive in closing, and permits no leakage in a direction opposite to normal flow.
chemical analysis Analysis by chemical methods to show the composition and concentration of substances.
chemical coagulation The destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of an inorganic coagulant. See flocculation.
chemical conditioning Mixing chemicals with a sludge prior to dewatering to improve the solids separation characteristics. Typical conditioners include polyelectrolytes, iron salts, and lime.
chemical dose A specific quantity of chemical applied to a specific quantity of fluid for a specific purpose.
chemical equilibrium The condition that exists when there is no net transfer of mass or energy between the components of a system. This is the condition in a reversible chemical reaction when the rate of the forward reaction equals the rate of the reverse reaction.
chemical equivalent The weight (in grams) of a substance that combines with or displaces 1 g of hydrogen. It is found by dividing the formula weight by its valence.
chemical feeder A device for dispensing a chemical at a predetermined rate for the treatment of water or wastewater. The change in rate of feed may be effected manually or automatically by flow rate changes. Feeders are designed for solids, liquids, or gases.
chemical gas feeder A feeder for dispensing a chemical in the gaseous state. The rate is typically graduated in gravimetric terms. Such devices may have proprietary names.
chemical metering The use of a variable-speed pump to control the dose of a chemical being used for a particular application.
chemical oxidation The oxidation of compounds in wastewater or water by chemical means. Typical oxidants include ozone, chlorine, and potassium permanganate.
chemical oxygen demand (COD) A quantitative measure of the amount of oxygen required for the chemical oxidation of carbonaceous (organic) material in wastewater.
chemical precipitation (1) Formation of particulates by addition of chemicals. (2) The process of softening water by the addition of lime or lime and soda to form insoluble compounds; typically followed by sedimentation or filtration to remove the newly created suspended solids.
chemical reaction A transformation of one or more chemical species into other species, resulting in the evolution of heat or gas, color formation, or precipitation. It may be initiated by a physical process such as heating, by the addition of a chemical reagent, or it may occur spontaneously.
chemical reagent A chemical added to a system to induce a chemical reaction.
chemical slurry A thin mixture or suspension of fine particles of a chemical in a liquid, typically water.
chemical solution tank A tank in which chemicals are added in solution before they are used in a water or wastewater treatment process.
chemical tank A tank in which chemicals are stored before they are used in a water or wastewater treatment process.
chemical treatment Any treatment process involving the addition of chemicals to obtain a desired result such as precipitation, coagulation, flocculation, sludge conditioning, disinfection, or odor control.
Chezy formula Commonly used during sewer design to predict the minimum velocity required for the sewer to be "self-cleaning."
chlorination The application of chlorine or chlorine compounds to water or wastewater, typically for the purpose of disinfection, but frequently for chemical oxidation and odor control.
chlorinator Any metering device used to add chlorine to water or wastewater.
chlorine (Cl) An element ordinarily existing as a greenish-yellow gas approximately 2.5 times heavier than air. Because of its reactivity, chlorine does not exist in the free elemental state in nature. Chlorine is easily liquefied under pressure. Chlorine is a good bleaching agent because of its oxidizing properties.
chlorine dose The amount of chlorine applied to a wastewater, typically expressed in milligrams per liter (mg/L) or pounds per million gallons (lb/mil. gal).
chlorine ice A yellowish ice formed in a chlorinator when chlorine gas comes in contact with water at 9 degrees Celsius (49 degrees Fahrenheit) or lower. Chlorine ice is detrimental to the performance of a chlorinator if it is formed in quantities sufficient to interfere with the safe operation of float controls or to cause plugging of openings essential to flow indication, control, or rate of application.
chlorine room A separate room or building for housing chlorine and chlorination equipment, with arrangements for protecting personnel and plant equipment.
chlorine toxicity Detrimental effects on biota caused by the inherent properties of chlorine.
chromatography The generic name of a group of separation processes that depend on the redistribution of the molecules of a mixture between a gas or liquid phase in contact with one or more bulk phases. Types of chromatography are adsorption, column, gas, gel, liquid, thin-layer, and paper.
chronic dermatitis Skin disorder characterized by a superficial inflammation of the skin exhibiting erythema, oozing, crushing, scaling, and often vesicular formation. Also known as eczema, the term constitutes at least one-half of all clinical dermatological conditions.
cilia Hairlike projections used by some microorganisms for feeding and locomotion.
ciliated protozoa Microorganisms with cilia; common in trickling filters and healthy activated sludge. Free-swimming ciliates are present in the bulk liquid; stalked ciliates are commonly attached to solids matter in the liquid.
clarification Any process or combination of processes whose primary purpose is to reduce the concentration of suspended matter in a liquid; formerly used as a synonym for settling or sedimentation. In recent years, the latter terms are preferred to describe settling processes.
clarifier Any large circular or rectangular sedimentation tank used to remove settleable solids in water or wastewater. A special type of clarifier, called an upflow clarifier, uses flotation rather than sedimentation to remove solids.
clean-out hole Hole or port that is provided for inspection and maintenance purposes.
close-coupled pump A type of pump in which the pump shaft is integral with the motor shaft.
closed conduit Any closed artificial or natural duct for conveying fluids.
coagulant (1) A simple electrolyte, typically an inorganic salt containing a multivalent cation of iron, aluminum, or calcium [for example, FeCl3, FeCl2, Al2(SO4)3, and CaO]. (2) An inorganic acid or base that induces coagulation of suspended solids. See flocculant.
coagulant or flocculant aid An insoluble particulate used to enhance solid-liquid separation by providing nucleating sites or acting as a weighting agent or sorbent. Also used colloquially to describe the action of flocculants in wastewater treatment.
coagulation The conversion of colloidal (< 0.001 mm) or dispersed (0.001 to 0.1 mm) particles into small visible coagulated particles (0.1 to 1 mm) by the addition of a coagulant, compressing the electrical double layer surrounding each suspended particle, decreasing the magnitude of repulsive electrostatic interactions between particles, and thereby destabilizing the particle. See flocculation.
coagulation basin A basin used for the coagulation of suspended or colloidal matter, with or without the addition of a coagulant, in which the liquid is mixed gently to induce agglomeration with a consequent increase in the settling velocity of particulates.
coating A material applied to the inside or outside of a pipe, valve, or other fixture to protect it primarily against corrosion.
Cocci Sphere-shaped bacteria.
coefficient A numerical quantity, determined by experimental or analytical methods, interposed in a formula that expresses the relationship between two or more variables to include the effect of special conditions or to correct a theoretical relationship to one found by experiment or actual practice.
coefficient of viscosity A numerical factor that is a measure of the internal resistance of a fluid to flow; the greater the resistance to flow, the larger the coefficient. It is equal to the shearing force in dynes per square centimeter (dyne/cm2) transmitted from one fluid plane to another parallel plane 1 cm distant, and is generated by a difference in fluid velocities in the two planes of 1 cm/s in the direction of the force. The coefficient varies with temperature. Also called absolute viscosity. The unit of measure is the poise, a force of 1 dyne/cm2.
cohesion The force of molecular attraction between the particles of any substance that tends to hold them together.
coliform-group bacteria Microorganisms predominantly inhabiting the intestines of humans and other animals, but also occasionally found elsewhere. They include all aerobic and facultative anaerobic, Gram-negative, nonspore-forming, rod-shaped bacteria that ferment lactose with the production of gas. Also included are all bacteria that produce a dark, purplish-green metallic sheen by the membrane filter technique used for coliform identification.
collection system In wastewater, a system of conduits, typically underground pipes, that receive and convey sanitary wastewater or storm water. In a water supply, a system of conduits or canals used to capture a water supply and convey it to a common point.
colloids Finely divided solids (less than 0.012 mm and greater than 0.000001 mm) that will not settle but may be removed by coagulation, biochemical action, or membrane filtration; they are intermediate between true solutions and suspensions.
colony A discrete mass of microorganisms on a surface as opposed to dispersed growth throughout a liquid culture medium.
color Any dissolved solids that impart a visible hue to water.
colorimeter An instrument that quantitatively measures the amount of light of a specific wavelength absorbed by a solution.
combined sewer A sewer intended to receive both wastewater and stormwater.
combustible-gas indicator A device for measuring the concentration of potentially explosive fumes. The measurement is based on the catalytic oxidation of a combustible gas on a heated platinum filament that is part of a Whetstone bridge. Also known as an explosimeter.
comminution An in-stream process of cutting and screening solids contained in wastewater flow.
comminutor A shredding or grinding device that reduces the size of gross suspended materials in wastewater without removing them from the liquid.
complete mix Activated-sludge process whereby wastewater is rapidly and evenly distributed throughout the biological reactor.
composite sample A combination of individual samples of water or wastewater taken at pre-selected intervals to minimize the effect of the variability of the individual sample. Individual samples may be of equal volume or may be proportional to the flow at time of sampling.
compressed air Air that has been reduced in volume thereby exerting a pressure.
compression ring A fitting used in certain kinds of pump seals to maintain pressure against the shaft packing.
concentration (1) The amount of a given substance dissolved in a discrete unit volume of solution or applied to a unit weight of solid. (2) The process of increasing the dissolved solids per unit volume of solution, typically by evaporation of the liquid. (3) The process of increasing the suspended solids per unit volume of sludge as by sedimentation or dewatering.
concentrator A solids contact unit used to decrease the water content of sludge or slurry.
concentric reducer A pipe fitting that has flanges on both ends and that is used to transition between pipes with different sizes. These circular flanges share a common center.
condensate Condensed steam from any heat exchanger.
condensation The process by which a substance changes from the vapor state to the liquid or solid state.
condenser Any device for reducing gases or vapors to liquid or solid form.
conditioning The chemical, physical, or biological treatment of sludges to improve their dewaterability.
connecting rod A plunger pump component that connects the shaft to the plunger.
contact stabilization Modification of the activated-sludge process involving a short period of contact between wastewater and sludge for rapid removal of soluble BOD by adsorption, followed by a longer period of aeration in a separate tank where sludge is oxidized and new sludge synthesized.
contact tank A tank used in water or wastewater treatment to promote contact among treatment chemicals or other materials and the liquid treated.
contact time The period of time that the material being processed is exposed to another substance, such as activated sludge or activated carbon, for completion of the desired reaction. See detention time.
contamination The introduction into water of microorganisms, chemicals, wastes, or wastewater in a concentration that makes the water unfit for its intended use.
continuous-flow tank A tank through which liquid flows continuously at its normal rate of flow, as distinguished from a fill-and-draw or batch system.
contracted weir A rectangular notched weir with a crest width narrower than the channel across which it is installed and with vertical sides extending above the upstream water level producing a contraction in the stream of water as it leaves the notch.
controlled discharge Regulation of effluent flow rates to correspond with flow variations in receiving waters to maintain established water quality.
controller A device or group of devices that govern in some predetermined measure the electrical power delivered to the apparatus to which it is connected.
convection In physics, mass motions within a fluid resulting in the transport and mixing of the properties of that fluid, caused by the force of gravity and by differences in density resulting from nonuniform temperature.
conventional aeration Process design configuration whereby the aeration tank organic loading is higher at the influent end than at the effluent end. Flow passes through a serpentine tank system, typically side-by-side, before passing on to the secondary clarifier. Also called plug flow.
conventional treatment Well-known or well-established water or wastewater treatment processes, excluding advanced or tertiary treatment. It typically consists of primary and secondary treatment.
conversion factor A numerical constant by which a quantity with its value expressed in units of one kind is multiplied to express the value in units of another kind.
conveyance loss The loss of water from a conduit due to leakage, seepage, evaporation, or evapotranspiration.
core sampler A long, slender pole with a foot valve at the bottom end that allows the depth of the sludge blanket to be measured.
correlation The degree of relative correspondence, as between two sets of data.
corrosion The gradual deterioration or destruction of a substance or material by chemical action, frequently induced by electrochemical processes. The action proceeds inward from the surface.
corrosion control (1) In water treatment, any method that keeps the metallic ions of a conduit from going into solution, such as increasing the pH of the water, removing free oxygen from the water, or controlling the carbonate balance of the water. (2) The sequestration of metallic ions and the formation of protective films on metal surfaces by chemical treatment.
corrosive industrial waste Liquid waste that is sufficiently acidic or alkaline to dissolve and wear away metal.
coupling A mechanical device for connecting two adjacent parts together, such as connecting a motor to a shaft of a pump.
crankshaft A shaft for transmitting motion, consisting of a series of cranks and crankpins to which the connecting rods of an engine are attached.
critical depth The depth of water flowing in an open channel or partially filled conduit corresponding to one of the recognized critical velocities.
critical flow (1) A condition of flow in which the mean velocity is at one of the critical values, ordinarily at Belanger's critical depth and velocity. Also used in reference to Reynolds' critical velocities, which define the point at which the flow changes from streamline or nonturbulent flows to turbulent flow. (2) The maximum discharge of a conduit that has a free outlet and has the water ponded at the inlet.
cross connection (1) A physical connection through which a supply of potable water could be contaminated or polluted. (2) A connection between a supervised potable water supply and an unsupervised supply of unknown potability.
cryogenic oxygen generation The production of high-purity liquid oxygen by cooling air to very low temperatures (i.e., 40 K).
cubic foot per second (cfs) The rate of flow equal to one cubic foot of material per second; used for measurement of water, wastewater, or gas. Equals 2.832 x 10-2 m3/s.
cubic meter per second (cms) The rate of flow equal to one cubic meter of material per second; used for measurement of water, wastewater, or gas.
culture Any organic growth that has been developed intentionally by providing suitable nutrients and a suitable environment.
culture media Substances used to support the growth of microorganisms in analytical procedures.
current meter A device used to measure the water velocity or current in a river.
curtain drain A drain constructed at the upper end of the area to be drained, to intercept surface or ground water flowing toward the protected area from higher ground, and carry it away from the area. Also called an intercepting drain.
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data Records of observations and measurements of physical facts, occurrences, and conditions reduced to written, graphical, or tabular form.
day-second foot (dsf) A volume equivalent to a flow of one cubic foot per second maintained for one day.
decant To draw off the upper layer of liquid after the denser material (a solid or another liquid) has settled.
decantation Separation of a liquid from solids or from a liquid of higher density by drawing off the upper layer after the heavier material has settled.
dechlorination The partial or complete reduction of residual chlorine by any chemical or physical process. Sulfur dioxide is frequently used for this purpose.
declining growth phase Period of time between the log growth phase and the endogenous phase, where food is in short supply, leading to ever-slowing bacterial growth rates.
decomposition The breakdown of complex material into simpler substances by chemical or biological processes.
decomposition of wastewater (1) The breakdown of organic matter in wastewater by bacterial action, either aerobic or anaerobic. (2) Chemical or biological transformation of organic or inorganic materials contained in wastewater.
defoamer A material having low compatibility with foam and a low surface tension. Defoamers are used to control, prevent, or destroy various types of foam, the most widely used being silicone defoamers. A valuable property of most defoamers is their effectiveness in extremely low concentration. Defoamers for special purposes are based on polyamides, vegetable oils, and stearic acid. Also referred to as antifoam agent.
degasification (1) The removal of a gas from a liquid medium. (2) In water treatment, the removal of oxygen from water to inhibit corrosion.
degreasing (1) The process of removing greases and oils from waste, wastewater, sludge, or solids. (2) The industrial process of removing grease and oils from machine parts or iron products.
degree (1) On the Celsius thermometer scale 1/100 of the interval from the freezing point to the boiling point of water under standard conditions; on the Fahrenheit scale, 1/180 of this interval. (2) A unit of angular measure; the central angle subtended by 1/360 of the circumference of a circle.
denitrification (1) The anaerobic biological reduction of nitrate nitrogen to nitrogen gas. (2) Removal of total nitrogen from a system. See nitrification.
density current A flow of water through a large body of water that retains its unmixed identity because of a difference in density.
deoxygenation The depletion of dissolved oxygen in a liquid either under natural conditions associated with the biochemical oxidation of the organic matter present or by addition of chemical reducing agents.
deoxygenation constant A constant that expresses the rate of the biochemical oxidation of organic matter under aerobic conditions.
departure The difference between any single observation and the typical.
deposition The act or process of settling solid material from a fluid suspension.
depth of blanket Level of sludge in the bottom of a secondary clarifier.
design criteria (1) Engineering guidelines specifying construction details and materials. (2) Objectives, results, or limits that must be met by a facility, structure, or process in performance of its intended functions.
design flow Engineering guidelines that typically specify the amount of influent flow that can be expected on a daily basis over the course of a year. Other design flows can be set for monthly or peak flows.
design loadings Flow rates and constituent concentrations that determine the design of a process unit or facility necessary for proper operation.
detention time The period of time that a water or wastewater flow is retained in a basin, tank, or reservoir for storage or completion of physical, chemical, or biological reaction. See contact time and retention time.
detergent (1) Any of a group of synthetic, organic, liquid, or water-soluble cleaning agents that are inactivated by hard water and have wetting and emulsifying properties but, unlike soap, are not prepared from fats and oils. (2) A substance that reduces the surface tension of water.
detoxification Physical or chemical treatment to reduce or eliminate the toxicity of a material.
dewater (1) To extract a portion of the water present in a sludge or slurry. (2) To drain or remove water from an enclosure. A structure may be dewatered so that it can be inspected or repaired.
dewpoint The temperature at which air with a given concentration of water vapor must be cooled to cause condensation of the vapor.
diaphragm A dividing membrane or thin flexible partition.
diaphragm pump A positive-displacement pump in which a flexible diaphragm, typically made of rubber or other resilient material, is the operating part. The diaphragm is fastened at the edges in a vertical cylinder. When the diaphragm is raised, suction is exerted, and when it is depressed, the liquid is forced through a discharge valve.
diaphragm-type pressure gauge The measurement from this type of gauge is taken from the movement of the diaphragm, located near the connection to the main line, due to pressure changes in the line. These types of gauges are very useful for measuring the pressure of sludge lines because they are not as prone to clogging as conventional gauges.
diffused aeration Injection of air under pressure through submerged porous plates, perforated pipes, or other devices to form small air bubbles from which oxygen is transferred to the liquid as the bubbles rise to the water surface.
diffused air Small air bubbles formed below the surface of a liquid to transfer oxygen to the liquid.
diffuser A porous plate, tube, or other device through which air is forced and divided into minute bubbles for diffusion in liquids. In the activated-sludge process, it is a device for dissolving air into mixed liquor. It is also used to mix chemicals such as chlorine to process streams.
diffusion (1) The transfer of mass from one fluid phase to another across an interface, for example liquid to solid or gas to liquid. (2) The spatial equalization of one material throughout another.
diffusion aerator An aerator that blows air under low pressure through submerged porous plates, perforated pipes, or other devices so that small air bubbles rise continuously through the water or wastewater.
digester A tank or other vessel for the storage and anaerobic or aerobic decomposition of organic matter in sludge.
digestion (1) The biological decomposition of the organic matter in sludge, resulting in partial liquefaction, mineralization, and volume reduction. (2) The process carried out in a digester.
direct current (dc) An electric current that flows in one direction only and is substantially constant in value.
discharge (1) Flow from a canal, conduit, pump, stack, tank, or treatment process. (2) The volume of the liquid flowing through a cross section per unit of time, often denoted as Q. See effluent.
discharge area The cross-sectional area of a waterway. Used to compute the discharge of a stream, pipe, conduit, or other carrying system.
discharge capacity The maximum rate of flow that a conduit, channel, or other hydraulic structure is capable of passing.
discharge head A measure of the pressure exerted by a fluid at the point of discharge, typically from a pump.
discharge pressure switch A switch used to provide feedback on the operation status of the pump., The switch is mounted on the discharge side of the pump and energized at preset pressures.
discharge rate Determination of the quantity of water flowing per unit of time in a stream channel, conduit, or orifice at a given point by means of a current meter, rod float, weir, pitot tube, or other measuring device or method. The operation includes not only the measurement of velocity of water and the cross-sectional area of the stream of water but also the necessary subsequent computations.
discharge valve A valve located immediately downstream of a pump that can be used for throttling or isolating the discharge piping from the pump.
discrete sedimentation Sedimentation in which removal of suspended solids is a function of terminal settling velocity.
disinfectant A substance used for disinfection and in which disinfection has been accomplished.
disinfected wastewater Wastewater to which a disinfecting agent has been added.
disinfection (1) The killing of waterborne fecal and pathogenic bacteria and viruses in potable water supplies or wastewater effluents with a disinfectant; an operational term that must be defined within limits, such as achieving an effluent with no more than 200 colonies fecal coliform/100 mL. (2) The killing of the larger portion of microorganisms, excluding bacterial spores, in or on a substance with the probability that all pathogenic forms are killed, inactivated, or otherwise rendered nonvirulent.
dispersion (1) Scattering and mixing. (2) The mixing of polluted fluids with a large volume of water in a stream or other body of water. (3) The repelling action of an electric potential on fine particles in suspension in water, as in a stream carrying clay. (4) In a continuous flow treatment unit, the phenomenon of short circuiting.
displacement pump A type of pump in which the water is induced to flow from the source of supply through an inlet pipe and valve and into the pump chamber by a vacuum created therein by the withdrawal of a piston or pistonlike device which, on its return, displaces a certain volume of the water contained in the chamber and forces it to flow through discharge valves and pipes.
disposal Release to the environment.
dissolved oxygen (DO) The oxygen dissolved in water, wastewater, or other liquid-typically expressed in milligrams per liter (mg/L) or percent saturation-available for use by aquatic organisms.
dissolved pollutants Dissolved organic or inorganic material that, at certain concentrations, can render water unfit for potable or nonpotable uses by living organisms.
dissolved solids Solids in solution that cannot be removed by filtration. See total dissolved solids.
distributed control system (DCS) An instrumentation control system of microprocessors located near the equipment they control and linked through a communications network. The overall status of the system can be monitored and operating parameters can be changed from a central operator control station.
diurnal (1) Recurring every day. (2) Occurring during the daytime, but not at night.
domestic wastewater Wastewater derived principally from nonindustrial sources (e.g., dwellings, business buildings, institutions, etc.).
dosing tank Any tank used in applying a dose; specifically used for intermittent application of wastewater to subsequent processes.
double-suction pump An impeller with two suction inlets, one on each side of the impeller.
dowel A pin or stud, with rounded or beveled ends, fastened in one piece to locate it in proper position on a mating part.
drag The resistance offered by a liquid to the settlement or deposition of a suspended particle.
drag coefficient A measure of the resistance to sedimentation or flotation of a suspended particle as influenced by its size, shape, density, and terminal velocity. It is the ratio of the force per unit area to the stagnation pressure and is dimensionless. See friction factor.
drain (1) A conduit or channel constructed to carry off, by gravity, liquids other than wastewater, including surplus underground, storm, or surface water. It may be an open ditch, lined or unlined, or a buried pipe. (2) In plumbing, any pipe that carries water or wastewater in a building drainage system.
drain valve A valve located at a low point on a pump that can be opened when the pump is taken out of service to allow it to drain by gravity.
drawdown (1) The magnitude of the change in surface elevation of a body of water as a result of the withdrawal of water. (2) The magnitude of the lowering of the water surface in a well, and of the water table or piezometric surface adjacent to the well, resulting from the withdrawal of water from the well by pumping. (3) In a continuous water surface with accelerating flow, the difference in elevation between downstream and upstream points.
drip-proof motor A type of squirrel cage motor designed to be open to the atmosphere for cooling the windings. The ventilation openings on these motors are constructed so that water falling on the motor from a vertical angle of no greater than 15 degrees will not enter the motor. These motors are used for indoor or weatherproof and dust-free applications.
dry feeder A feeder for dispensing a chemical or other fine material to water or wastewater at a rate controlled manually or automatically by the rate of flow. The constant rate may be either volumetric or gravimetric.
dry suspended solids The weight of the suspended matter in a sample after drying for a specified time at a specific temperature.
dry weather flow (1) The flow of wastewater in a combined sewer during dry weather. Such flow consists mainly of wastewater, with no stormwater included. (2) The flow of water in a stream during dry weather, typically contributed entirely by groundwater.
dry well A dry compartment in a pumping station, near or below pumping level, where the pumps are located.
dry-bulb temperature The temperature of air measured by a conventional thermometer.
duplex pump A reciprocating pump consisting of two cylinders placed side by side and connected to the same suction and discharge pipe; the pistons move so that one exerts suction while the other exerts pressure resulting in continuous discharge from the pump.
dynamic equilibrium See population dynamics.
dynamic head (1) When there is flow, (a) the head at the top of a waterwheel; (b) the height of the hydraulic grade line above the top of a waterwheel; or (c) the head against which a pump works. (2) That head of fluid that would produce statically the pressure of a moving fluid.
dynamic suction head In systems where the pump is located below the free surface of the liquid to be pumped, it is the vertical distance from the surface of the liquid to the centerline of the suction end of the pump minus the velocity head and entrance and friction losses. Internal pump losses are not subtracted.
dynamic suction lift In systems where the pump is situated at a higher elevation than the free surface of the liquid to be pumped, it is the vertical distance from the surface of the liquid to the center line of the suction end of a pump plus velocity head and entrance and friction losses. Internal pump losses are not added.
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E. coli See Escherichia coli.
eccentric disk A disk with an axis that is offset from its true center so that it is capable of imparting a reciprocating motion when it revolves.
eccentric reducer A pipe fitting with two different sized flanges at each end that is used to join two pipes of different sizes. These circular flanges are offset eccentrically (i.e., they share a common invert).
eductor (1) A device for mixing air with water. (2) A liquid pump operating under a jet principle, using liquid under pressure as the operating medium to entrain air in the liquid. See ejector.
effective size The diameter of the particles of a hypothetical sample of granular material-composed of particles that are spherical in shape, equal in size, and arranged in a given manner-that would have the same transmission constant as the actual material under consideration.
effervescence The vigorous escape of small gas bubbles from a liquid, especially as a result of chemical action.
efficiency The ratio of the useful energy delivered by a dynamic system to the energy supplied to it.
effluent Wastewater or other liquid, partially or completely treated or in its natural state, flowing out of a reservoir, basin, treatment plant, or industrial treatment plant, or part thereof.
effluent quality The physical, biological, and chemical characteristics of a wastewater or other liquid flowing out of a basin, reservoir, pipe, or treatment plant.
ejector A device for moving a fluid or solid by entraining it in a high-velocity stream of air or water.
elbow A pipe fitting that connects two pipes at an angle. The angle is always 90 degrees unless another angle is stated. Also called an ell.
elevation head The energy possessed per unit weight of a fluid because of its elevation above some point. Also called position head or potential head.
emergency lighting Battery-operated lighting units to provide illumination in the event of a power failure.
emission Discharge of a liquid, solid, or gaseous material.
emulsifying agent An agent capable of modifying the surface tension of emulsion droplets to prevent coalescence. Examples are soap and other surface-active agents, certain proteins and gums, water-soluble cellulose derivatives, and polyhydric alcohol esters and ethers.
emulsion A heterogeneous liquid mixture of two or more liquids not typically dissolved in one another, but held in suspension by forceful agitation or by emulsifiers that modify the surface tension of the droplets to prevent coalescence.
end suction pump A type of horizontal centrifugal pump that has an intake located on the side of the pump parallel to the pump shaft.
endogenous respiration Autooxidation by organisms in biological processes.
Enterococci A group of cocci that normally inhabit the intestines of man and animals. No to be confused with fecal Streptococci.
entrainment The trapping of bubbles in a liquid produced either mechanically through turbulence or chemically through a reaction.
enzyme A catalyst produced by living cells. All enzymes are proteins, but not all proteins are enzymes.
epidemic A disease that occurs simultaneously in a large fraction of the community.
equalization In wastewater systems, the storage and controlled release of wastewater to treatment processes at a rate determined by the capacity of the processes, or at a rate proportional to the flow in the receiving stream; used to smooth out variations in temperature and composition, and flow.
equalizing basin A holding basin in which variations in flow and composition of a liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit. Also called balancing reservoir.
equilibrium A condition of balance in which the rate of formation and the rate of consumption or degradation of various constituents are equal. See chemical equilibrium.
equilibrium constant A value that describes the quantitative relationship between chemical species in a system at equilibrium.
equivalent calcium carbonate A common form of expressing the hardness, acidity, total alkalinity, carbon dioxide, carbonate, bicarbonate, noncarbonate, or hydroxide content of water expressed in milligrams per liter (mg/L). It is calculated by multiplying the number of chemical equivalents of any of these constituents present in 1 L by 50, the equivalent weight of calcium carbonate. See chemical equivalent.
Escherichia coli (E. coli) One of the species of bacteria in the fecal coliform group. It is found in large numbers in the gastrointestinal tract and feces of humans and warm-blooded animals. Its presence is considered indicative of fresh fecal contamination, and it is used as an indicator organism for the presence of less easily detected pathogenic bacteria.
essential nutrients Inorganic substances such as nitrogen, phosphorus, and iron that are required in small quantities for biological processes to occur.
euglena A motile unicelluler freshwater autotrophic organism traditionally classified as a plantlike member of the kingdom Protista (algae).
eutrophication Nutrient enrichment of a lake or other water body, typically characterized by increased growth of planktonic algae and rooted plants. It can be accelerated by wastewater discharges and polluted runoff.
evaporation (1) The process by which water becomes a vapor. (2) The concentration of dissolved solids by driving off water through the application of heat.
evaporation opportunity The ratio of the rate of evaporation from a land or water surface in contact with the atmosphere to evaporation under existing atmospheric conditions; that is, the ratio of the actual to the potential rate of evaporation. Also called relative evaporation.
evaporation rate The quantity of water, expressed in terms of depth of liquid water, evaporated from a given water surface per unit of time. It is typically expressed in inches or millimeters per day, month, or year.
evapotranspiration Water withdrawn from soil by evaporation or plant transpiration; considered synonymous with consumptive use.
evapotranspiration potential Water loss that would occur if there was never a deficiency of water in the soil for use by vegetation.
explosimeter A device for measuring the concentration of potentially explosive fumes. Also called a combustible-gas indicator.
explosive gases or vapors Ignitable or flammable gases or vapors (e.g., acetylene, hydrogen, gasoline, and ethylene).
exponential growth phase A phase of microbial population growth rate where the number of cells doubles during a certain period of time. Environmental conditions are ideal (ample food, suitable temperature, etc) for exponential growth to occur.
extended aeration A modification of the activated-sludge process using long aeration periods to promote aerobic digestion of the biological mass by endogenous respiration. The process includes stabilization of organic matter under aerobic conditions and disposal of the gaseous end products into the air. Effluent contains finely divided suspended matter and soluble matter.
extended aeration process A modification of the activated-sludge process. See extended aeration.
extraction The process of dissolving and separating out particular constituents of a liquid by treatment with solvents specific for those constituents.
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facultative Having the ability to live under different conditions, such as with or without free oxygen.
facultative bacteria Bacteria that can grow and metabolize in the presence and absence of dissolved oxygen.
Fahrenheit A temperature scale in which water freezes at 0 degrees Celsius (32 degrees Fahrenheit) and boils at 100 degrees Celsius (212 degrees Fahrenheit) at atmospheric pressure.
fats (wastes) Triglyceride esters of fatty acids. The term is erroneously used as a synonym for grease.
fecal coliform bacteria Aerobic and facultative, Gram-negative, non-spore-forming, rod-shaped bacteria capable of growth at 44.5 degrees Celsius (112 degrees Fahrenheit) and associated with fecal matter of warm-blooded animals. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens.
fecal indicators Fecal coliform, fecal streptococci, and other bacterial groups originating in human or other warm-blooded animals, indicating contamination by fecal matter.
fecal streptococci The subgroup of enterococci that is of particular concern in water and wastewater.
ferric chloride (FeCl3) A soluble iron salt often used as a sludge conditioner to enhance precipitation or bind up sulfur compounds in wastewater treatment. See coagulant.
ferric sulfate (Fe2(SO4)3) A water-soluble iron salt formed by reaction of ferric hydroxide and sulfuric acid or by reaction of iron and hot concentrated sulfuric acid. Also obtainable in solution by reaction of chlorine and ferrous sulfate. Used in conjunction with lime as a sludge conditioner to enhance precipitation.
ferrous chloride (FeCl2) A soluble iron salt used as a sludge conditioner to enhance precipitation or bind up sulfur. See coagulant.
ferrous sulfate (FeSO4 7H2O) A water-soluble iron salt, sometimes called copperas; used in conjunction with lime as a sludge conditioner to enhance precipitation.
filamentous growth Intertwined, threadlike biological growths characteristic of some species of bacteria, fungi, and algae. Such growths reduce sludge settleability and dewaterability.
filamentous organisms Bacterial, fungal, and algal species that grow in thread like colonies resulting in a biological mass that will not settle and may interfere with drainage through a filter.
filter A device or structure for removing solid or colloidal material, typically of a type that cannot be removed by sedimentation, from water, wastewater, or other liquid. The liquid is passed through a filtering medium, typically a granular material but sometimes finely woven cloth, unglazed porcelain, or specially prepared paper.
filter cloth A fabric stretched around the drum of a vacuum filter.
filtered wastewater Wastewater that has passed through a mechanical filtering process.
filtrate The liquid that has passed through a filter.
filtration The process of contacting a dilute liquid suspension with filter media for the removal of suspended or colloidal matter or for the dewatering of concentrated sludge.
final effluent The effluent from the final treatment unit of a wastewater treatment plant.
final sedimentation The separation of solids from wastewater in the last settling tank of a treatment plant.
five-day biochemical oxygen demand (BOD5) A standard test to assess oxygen demand because of biochemical oxidation of carbonaceous material over a period of 5 days under controlled conditions of temperature (20 degrees Celsius).
fixed solids The residue of total suspended or dissolved solids after ignition or heating for a specified time at a specified temperature.
flagellates A varied group of one-celled organisms in the kingdom Protista that possess flagella, which are used for locomotion.
flagellum (pl. flagella) A long cellular whiplike appendage specialized for locomotion and ensheathed in an extension of plasma membrane.
flame arrester (1) A device incorporating a fine-mesh wire screen or tube bundle inserted in a vent or pipe and designed to resist the flashback of flame. (2) Device consisting of multiple number of corrugated stamped sheets in a gas tight housing. As a flame passes through the sheets, it is cooled below the ignition point.
flange A projecting rim, edge, lip, or rib.
flanged coupling A type of rigid coupling consisting of two flanged rigid members with several bolt holes for connecting the two pieces.
flap gate A gate that opens and closes by rotation around a hinge or hinges at the top side of the gate.
flap valve A valve that is hinged at one edge and opens and shuts by rotating about the hinges. See check valve.
flash mixer A device for uniform, quick dispersal of chemicals throughout a liquid.
flash point The temperature at which a gas, volatile liquid, or other substance ignites.
flat-crested weir A weir with a horizontal crest in the direction of flow and of appreciable length when compared with the depth of water passing over it.
flexible coupling A coupling that transmits driving torque as well as accommodates minor misalignments between pump and motor shafts.
flight A scraper in a rectangular sedimentation tank with blades that move sludge along the bottom of the tank to a collection point. As the flights return, scum is collected on the surface of the tank and pushed to an outlet point.
float control A float device-triggered by changing liquid levels-that activates, deactivates, or alternates process equipment operation.
float gauge A device for measuring the elevation of a liquid, the actuating element of which is a buoyant float that rests on the surface of the liquid and rises or falls with it. The elevation of the surface is measured by a chain or tape attached to the float.
float switch An electrical switch operated by a float in a tank or reservoir that typically controls the motor of a pump.
float valve A valve, such as a plug or gate, that is actuated by a float to control the flow into a tank.
floating bushing A bushing that can move radially and thereby center itself around the pump shaft. Used in some mechanical pump seals.
floc Collections of smaller particles agglomerated into larger, more easily settleable particles through chemical, physical, or biological treatment. See flocculation.
flocculant Water-soluble organic polyelectrolytes that are used alone or in conjunction with inorganic coagulants to agglomerate the solids present in water. This process forms large, dense floc particles that settle rapidly.
flocculating tank A tank used for the formation of floc by the gentle agitation of liquid suspensions, with or without the aid of chemicals.
flocculation In water and wastewater treatment, the agglomeration of colloidal and finely divided suspended matter after coagulation by gentle stirring by either mechanical or hydraulic means. For biological wastewater treatment in which coagulation is not used, agglomeration may be accomplished biologically.
flocculation agent A coagulating substance that, when added to water, forms a flocculent precipitate that will entrain suspended matter and expedite sedimentation. Examples are alum, ferrous sulfate, and lime.
flocculator A mechanical device to enhance the formation of floc in a liquid.
flow (1) The movement of a stream of water or other fluid from place to place. The movement of silt, water, sand, or other material. (2) The fluid that is in motion. (3) The quantity or rate of movement of a fluid discharge; the total quantity carried by a stream. (4) To issue forth or discharge. (5) The liquid or amount of liquid per unit time passing a given point.
flow equalization Transient storage of wastewater for release to a sewer system or wastewater treatment plant at a controlled rate to provide a reasonably uniform flow for treatment.
flow meter A device that indicates the flow rate of the pump and verifies that the pump is pumping fluid.
flow rate The volume or mass of a gas, liquid, or solid material that passes through a cross section of conduit in a given time. Flow rates in various wastewater treatment plant streams are measured in order to make process control decisions. Flow rates are expressed in units such as kilograms per hour (kg/h), cubic meters per second (m3/s), liters per day (L/d), or gallons per day (gpd).
flow recording Documentation of the rate of flow of a fluid past a given point. The recording is normally accomplished automatically.
flow regulator A structure installed in a canal, conduit, or channel to control the flow of water or wastewater at the intake or to control the water level in a canal, channel, or treatment unit. See rate-of-flow controller.
flow sensor A device that measures (senses) a parameter, such as depth, velocity, or pressure drop that is related to flow rate.
flow sheet A diagrammatic representation of the progression of steps in a process showing their sequence and interdependence.
flow-control valve A device that controls the rate of flow of a fluid.
flushing The flow of water under pressure in a conduit or well to remove clogged material.
foam (1) A collection of minute bubbles formed on the surface of a liquid by agitation, fermentation, and so on. (2) The frothy substance composed of an aggregation of bubbles on the surface of liquids and created by violent agitation or by the admission of air bubbles to liquid containing surface-active materials, solid particles, or both. Also called froth.
Food-to-microorganism ratio (F:M) In the activated-sludge process, the loading rate expressed as pounds of BOD per kilograms of mixed liquor or mixed liquor volatile suspended solids per second (mg/kgs) or pounds of BOD per pound of mixed liquor or mixed liquor volatile suspended solids per day [lb BOD/d/lb MLSS or MLVSS].
foot valve (1) A valve placed at the bottom of the suction pipe of a pump that opens to allow water to enter the suction pipe, but closes to prevent water from passing out of it at the bottom end. (2) A valve with the reverse action attached to the drainage pipe of a vacuum chamber. It allows water to drain out, but closes to hold the vacuum.
force main A pressure pipe joining the pump discharge at a water or wastewater pumping station with a point of gravity flow.
forced aeration The bringing about of intimate contact between air and liquid where the air, under pressure, is applied below the surface of the liquid through diffusers or other devices that promote the formation of small bubbles.
forced aeration The bringing about of intimate contact between air and liquid where the air, under pressure, is applied below the surface of the liquid through diffusers or other devices that promote the formation of small bubbles.
formazine turbidity unit (FTU) A standard unit of turbidity based on a known chemical reaction that produces insoluble particulates of uniform size. The FTU has largely replaced the JTU. Also known as nephelometric turbidity unit.
fouling A gelatinous, slimy accumulation resulting from the activity of organisms in the water. Fouling may be found on concrete, masonry, or metal surfaces.
free flow A condition of flow through or over a structure where such flow is not affected by submergence or the existence of tailwater.
free oxygen Elemental oxygen (O2).
free-swimming ciliate Mobile, one-celled organisms using cilia (hairlike projections) for movement.
free water Suspended water constituting films covering the surface of solid particles or the walls of fractures, but in excess of pellicular water; mobile water is free to move in any direction under the pull of the force of gravity and unbalanced film pressure.
freeboard The vertical distance between the normal maximum level of the surface of the liquid in a conduit, reservoir, tank, or canal and the top of the sides of an open conduit or the top of a dam or levee that is provided so that waves and other movements of the liquid will not overflow the confining structure.
frequency (1) The time rate of vibration or the number of complex cycles per unit time. (2) The number of occurrences of a certain phenomenon in a given time.
fresh sludge Sludge in which decomposition is little advanced.
fresh wastewater Wastewater of recent origin containing dissolved oxygen.
fresh-air inlet A specially constructed opening typically provided with a perforated cover to facilitate ventilation of a wastewater line.
friction factor A measure of the resistance to flow of fluid in a conduit as influenced by wall roughness.
friction head The head lost by water flowing in a stream or conduit as the result of the disturbances set up by the contact between the moving water and its containing conduit and by intermolecular friction. Strictly speaking, head losses such as those caused by bends, expansions, obstructions, and impact are not included in this term, however, the usual practice is to include all such head losses under this term.
friction loss |