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Symbols and Acronyms

cake   Wastewater solids that have been sufficiently dewatered to form a semisolid mass.

calcium hypochlorite  [Ca(OCl)2·4H2O] A solid that, when mixed with water, liberates the hypochlorite ion OCl2 and can be used for disinfection.

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 °C by 1 °C.

capacitor (condenser)  A device to provide capacitance, which is the property of a system of conductors and dielectrics that permit the storage of electrically separated charges when potential differences exist between the conductors. A dielectric is an insulator.

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 an electrical apparatus is rated either by the user or manufacturer.

carbon (C)  (1) A chemical element essential for growth. (2) A solid material used for adsorption of ­pollutants.

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 BOD.

carbon adsorption  The use of either granular or powdered carbon to remove organic compounds from wastewater or effluents. Organic molecules in solution are drawn to the highly porous surface of the carbon by intermolecular attraction forces.

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 also 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. See also recarbonation.

carcinogen  A material that induces excessive or abnormal cellular growth in an organism.

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 are placed staggered projections arranged to break up the water and bring it into contact with air.

cathodic protection  An electrical system for prevention of rust, corrosion, and pitting of steel and iron surfaces in contact with water. A low-voltage current is made to flow through a liquid or a soil in contact with the metal in such a manner that the external electromotive force renders the metal structure cathodic and concentrates corrosion on auxiliary anodic parts used for that purpose.

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 also alkalinity.

cavitation  (1) The action, resulting from forcing a flow stream to change direction, in which reduced internal pressure causes dissolved gases to expand, creating negative pressure. Cavitation frequently causes pitting of the hydraulic structure affected. (2) The formation of a cavity between the downstream surface of a moving body (e.g., the blade of a propeller) and a liquid normally in contact with it. (3) Describing the action of an operating centrifugal pump when it is attempting to discharge more water than suction can provide.

Celsius  The international name for the centigrade scale of temperature, on which the freezing point and boiling point of water are 0 °C and 100 °C, respectively, at a barometric pressure of 1.013 3 105 Pa
(760-mm Hg).

centigrade  A thermometer temperature scale in which 0° marks the freezing point and 100° the boiling point of water at 760-mm Hg barometric pressure. Also called Celsius. To convert temperature on this scale to Fahrenheit, multiply by 1.8 and add 32.

centrate  Liquid removed by a centrifuge; typically contains high concentrations of suspended, nonsettling 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.

centrifugal screw pump  A centrifugal pump having a screw-type impeller; may be of axial flow or combined axial and radial flow.

centrifugation  Imposition of a centrifugal force to separate solids from liquids based on density differences. In sludge dewatering, the separated solids commonly are called cake and the liquid is called centrate.

centrifuge  A mechanical device in which centrifugal force is used to separate solids from liquids or to separate liquids of different densities.

certification  A program to substantiate the capabilities of personnel by documentation of experience and learning in a defined area of endeavor.

cfs (cu ft/sec)  The rate of flow of a material in cubic feet per second; used for measurement of water, wastewater, or gas; equals 2.832 3 1022 m3/s.

chain bucket  A continuous chain equipped with buckets and mounted on a scow. Also called a ladder dredge.

chamber  Any space enclosed by walls or a compartment; often prefixed by a descriptive word indicating its function, such as grit chamber, screen chamber, discharge chamber, or flushing chamber.

change of state  The process by which a substance passes from one to another of the solid, the liquid, and the 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. (3) The part of a body of water deep enough to be used for navigation through an area otherwise too shallow for navigation. (4) Informally, a more or less linear conduit of substantial size in cavernous limestones or lava rocks. See also open channel.

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  Commonly, any substance used in or produced by a chemical process. Certain chemicals may be added to water or wastewater to improve treatment efficiency; others are pollutants that require removal.

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 also 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 flowrate 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 usually graduated in gravimetric terms. Such devices may have proprietary names.

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 using inorganic dichromate or permanganate salts as oxidants in a 2-hour test.

chemical precipitation  (1) Formation of particulates by the addition of chemicals. (2) The process of softening water by the addition of lime or lime and soda to form insoluble compounds; usually 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 sludge  Sludge obtained by treatment of water or wastewater with inorganic coagulants.

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.

chloramines  Compounds of organic or inorganic nitrogen formed during the addition of chlorine to wastewater. See breakpoint chlorination.

chlorination  The application of chlorine or chlorine compounds to water or wastewater, generally 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 (Cl2)  An element ordinarily existing as a greenish-yellow gas about 2.5 times heavier than air. At atmospheric pressure and a temperature of 230.1 °F (248 °C), the gas becomes an amber liquid about 1.5 times heavier than water. Its atomic weight is 35.457, and its molecular weight is 70.914.

chlorine contact chamber  A detention basin provided to diffuse chlorine through water or wastewater and to provide adequate contact time for disinfection. Also called a chlorination chamber or chlorination basin.

chlorine demand  The difference between the amount of chlorine added to a wastewater and the amount of chlorine remaining after a given contact time. Chlorine dosage is a function of the substances present in the water, temperature, and contact time.

chlorine dose  The amount of chlorine applied to a wastewater, usually 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 49 °F (9 °C) or lower. Chlorine ice is frequently 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 residual  The amount of chlorine in all forms remaining in water after treatment to ensure disinfection for a period of time.

chlorine room  A separate room or building for housing chlorine and chlorination equipment, with arrangements for protecting personnel and plant equipment.

chlorine toxicity  The 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. The types of chromatography are adsorption, column, gas, gel, liquid, thin-layer, and paper.

ciliated protozoa  Protozoans with cilia (hair-like appendages) that assist in movement; 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.

circuit  A conductor or a system of conductors through which an electrical current flows or is intended to flow.

circuit breaker  A device designed to open or close a circuit by nonautomatic means and open the circuit automatically on a predetermined overload of current without injury to itself.

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 preferable when describing 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.

clear-water basin  A reservoir for the storage of filtered water of sufficient capacity to prevent the necessity of frequent variations in the rate of filtration with variations in demands. Also called filtered-water reservoir, clear-water reservoir, clear well.

closed centrifugal pump  A centrifugal pump having its impeller built with the vanes enclosed within circular disks.

closed conduit  Any closed artificial or natural duct for conveying fluids.

closed impeller  An impeller having the side walls extended from the outer circumference of the suction opening to the vane tips.

coagulant  A simple electrolyte, usually an inorganic salt containing a multivalent cation of iron, aluminum, or calcium [for example, FeCl3, FeCl2, Al2(SO4)3, and CaO]. Also, an inorganic acid or base that induces coagulation of suspended solids. See also 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 flocculents in water 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 also 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. Coatings may be of various materials.

Cocci  Sphere-shaped bacteria.

codisposal  Joint disposal of wastewater sludge and municipal refuse in one process or facility. Disposal can be intermediate, as with incineration or composting, or final, as with placement in a sanitary landfill.

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.

coil  A set of windings with or without an iron core, shaped to produce a magnetic force when current flows through the windings. This force is used in relays and other electrical equipment to pull contacts together or to separate them.

coliform-group bacteria  A group of bacteria predominantly inhabiting the intestines of man or animal, but also occasionally found elsewhere. It includes all aerobic and facultative anaerobic, Gram-negative, non-spore-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. The two groups are not always identified, but they are generally of equal sanitary significance.

collection system  In wastewater, a system of conduits, generally underground pipes, that receives and conveys sanitary wastewater or stormwater; in 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 0.002 mm and greater than 0.000 001 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 clump 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 available chlorine  The concentration of chlorine that is combined with ammonia as chloramine or as other chloro derivatives, yet is still available to oxidize organic matter.

combined available residual chlorine  That portion of the total residual chlorine remaining in water or wastewater at the end of a specified contact period that will react chemically and biologically as chloramines.

combined residual chlorination  The application of chlorine to water or wastewater to produce, with natural or added ammonia or with certain organic nitrogen compounds, a combined chlorine residual.

combined sewer  A sewer intended to receive both wastewater and storm or surface water.

combustible-gas indicator  An explosimeter; 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.

commercially dry sludge  Sludge containing not more than 10% moisture by weight; the limit is 5% in the fertilizer trade.

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 aeration tank.

composite sample  A combination of individual samples of water or wastewater taken at preselected 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 the time of sampling.

compost  The product of the thermophilic biological oxidation of sludge or other materials.

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, usually 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.

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. Water that falls as precipitation from the atmosphere has condensed from the vapor state to rain or snow. Dew and frost are also forms of condensation.

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.

conductor  A material that offers very little resistance to the flow of current and is, therefore, used to carry current or conduct electricity.

conduit (duct) bank  A length of one or more conduits or ducts (which may be enclosed in concrete) that is designed to contain cables.

contacts  Any set of points that may be joined manually or automatically to complete a circuit. Contacts are found in breakers, switches, relays, and starters.

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 between treatment chemicals or other materials and the liquid treated.

contact time  The time that the material processed is exposed to another substance (such as activated sludge or activated carbon) for completion of the desired reaction. See also 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 pump  A displacement pump within which the direction of flow of the water is not changed or reversed.

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.

continuous load  A load where the maximum current is expected to continue for 3 hours or more.

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 flowrates to correspond with flow variations in receiving waters to maintain established water quality.

controller  A device or group of devices, that serve to govern, in some predetermined measure, the electrical power delivered to the apparatus to which it is connected.

convection  (1) 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. (2) In meteorology, atmospheric motions that are predominantly vertical, resulting in vertical transport and mixing of atmospheric properties; sometimes caused when large masses of air are heated by contact with a warm land surface.

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 generally 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.

cooling coil  A coil of pipe or tubing containing a stream of hot fluid that is cooled by heat transfer to a cold fluid outside. Conversely, the coil may contain a cold fluid to cool a hot fluid in which the coil is immersed.

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. Sometimes called a sludge judge.

correlation  (1) A mutual relationship or connection. (2) 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.

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. (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.

culture  Any organic growth that has been developed intentionally by providing suitable nutrients and environment.

culture media  Substances used to support the growth of microorganisms in analytical procedures.
cyclone separator  A conical unit used for separating particles by centrifugal force.