Cake: The solids discharged from a dewatering apparatus.

Calendering: A process by which fabric or wire is passed through a pair of heavy rolls to reduce thickness, to flatten the intersections of the threads/wires and to control air permeability. Rolls are heated when calendering synthetic materials. Carbonized threads: Nylon or polyester therads that have been treated to include varrying degrees of carbon.

Cation exchange capacity: The ability of a soil or other solid to exchange cations (positive ions such as calcium) with a liquid.

Cess Pools: This system is similar to a septic tank, in performance. Sewage water usually seeps through the open bottom and portholes in the sides of the walls. These can also clog up with overuse and the introduction of detergents and other material which slow up the bacterial action.

CFU: Viable micro-organisms (bacteria, yeasts & mould) capable of growth under the prescribed conditions (medium, atmosphere, time and temperature) develop into visible colonies (colony forming units) which are counted. The term colony forming unit (CFU) is used because a colony may result from a single micro-organism or from a clump / cluster of micro-organisms.

Chemoautotroph: An organism that obtains its energy from the oxidation of chemical compounds and uses only organic compounds as a source of carbon. Example: nitrifiers.

Chemotroph: An organism that obtains its energy from the oxidation of chemical compounds.

Chemical precipitation: Precipitation induced by addition of chemicals; the process of softening water by the addition of lime and soda ash as the précipitants. Chloramines: Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia.

Cblorination: The application of chlorine to water or wastewater, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results.

Clarification: A process in which suspended material is removed from a wastewater. This may be accomplished by sedimentation, with or without chemicals, or filtration.

Clarifier: Settling tank, sedimentation basin. A tank or basin in which wastewater is held for a period of time, during which the heavier solids settle to the bottom and the lighter material will float to the water surface.

Coagulants: Chemicals which cause very fine particles to clump (floe) together into larger particles. This makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.

Coliform bacteria: Non-pathogenic microbes found in fecal matter that indicate the presence of water pollution; are thereby a guide to the suitability for potable use. Colloids: Very small, finely divided solids (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge.

Combined available chlorine: The concentration of chlorine which is combined with ammonia (NH3) as chloramine or as other chloro derivatives, yet is still available to oxidize organic matter.

Combined sewer: A sewer designed to carry both sanitary wastewaters and storm or surface-water runoff.

Ciliates: A class of protozoans distinguished by short hairs on all or part of their bodies.

COD: Chemical oxygen demand - the amount of oxygen in mg/1 required to oxidize both organic and oxidizable inorganic compounds.

Commensalism: When two organisms coexist, one organism benefits, the other is not affected.

Comminution: Shredding. A mechanical treatment process which cuts large pieces of waste into smaller pieces so that they won't plug pipes or damage equipment. Contact stabilization: Contact stabilization is a modification of the conventional activated sludge process. In contact stabilization, two aeration tanks are used. One tank is for separate reaeration of the return sludge for at least four hours before it is permitted to flow into the other aeration tank to be mixed with the primary effluent requiring treatment.

Conventional treatment: The preliminary treatment, sedimentation, flotation, trickling filter, rotating biological contactor, activated sludge and chlorination of wastewater.

Conversion: Changing from one substance to another. As food matter is changed to cell growth or to carbon dioxide.

CRT: Cell residence time - the amount of time in days that an average "bug" remains in the process. Also termed "sludge age".

DAF: Dissolved air flotation - one of many designs for waste treatment. Decitex (dtex): The mass in grams of 10,000 meters of fiber or yarn. A direct yarn numbering system used to define size of fiber or yarn. The higher the number, the

Declining growth: A growth phase in which the availability of food begins to limit

Degradation: A growth phase in which the availability of food begins to limit cell

Deionized water: Water that goes through an ion exchange process in which all

Denier: The mass in grams of 9000 meters of fiber or yarn. A direct numbering system used to define size of fiber or yarn. The higher the number, the coarser

Denitrification: An anaerobic biological reduction of nitrate nitrogen to nitrogen gas, the removal of total nitrogen from a system, and/or an anaerobic process that occurs when nitrite ions are reduced to nitrogen gas and bubbles are formed as a result of this process. The bubbles attach to the biological floe in the activated sludge process and float the floe to the surface of the secondary clarifiers. This condition is often the cause of rising sludge observed in secondary clarifiers or

Depth filter: A filter medium consisting of randomly distributed particles or fibers resulting in openings with a non-uniform and tortuous path.

Detritus: Dead plant and animal matter, usually consumed by bacteria, but some

Dew Point: The temperature to which air with a given quantity of water vapor must be cooled to cause condensation of the vapor in the air.

D/I unit: Deionizing unit, frequntly used to maintain water quality in aquariums. Advantages: does not waste water like the R/O unit, is designed to be hooked up to either a faucet or household piping system, the anion & cation resins can be regenerated (with another expensive unit) indefinitely, and these systems allow a larger water flow (up to 2,000 gallons a day), than an R/O system, but cost

Diatomaceous earth: A fine, siliceous (made of silica) "earth" composed mainly of the skeletal remains of diatoms (single cell microscopic algae with rigid internal structure consisting mainly of silica). Tests prove that DE leaches unacceptable amounts of silicate into the water for fish health. If used as a filter substance, a silicone removing resin should be employed afterwards.

Differential pressure: The difference in pressure between two points of a system,

Diffused Air Aeration: A diffused air activated sludge plant takes air, compresses it, and then discharges the air below the water surface of the aerator through some type of air diffusion device.

Digester: A tank in which sludge is placed to allow decomposition by microorganisms. Digestion may occur under anaerobic (most common) or aerobic conditions.

Disinfection: The process designed to kill most microorganisms in wastewater, including essentially all pathogenic (disease-causing) bacteria. There are several ways to disinfect, with chlorine being the most frequently used in water and wastewater treatment plants.

Distribution box: Serves to distribute the flow from the septic tank evenly to the absorption field or seepage pits. It is important that each trench or pit receive an equal amount of flow. This prevents overloading of one part of the system. Dissolved solids: Chemical substances either organic or inorganic that are dissolved in a waste stream and constitute the residue when a sample is evaporated to dryness.

Distributor: The rotating mechanism that distributes the wastewater evenly over the surface of a trickling filter or other process unit.

DO: Dissolved Oxygen - a measure of the oxygen dissolved in water expressed in milligrams per liter.

DOUR: Dissolved Oxygen Uptake Ratio.

Downstream side: The side of a product stream that has already passed through a given filter system; portion located after the filtration unit. Dual chamber test method: Measures near field shielding effectiveness by indicating the signal attenuation caused by passage through test material. Dyeing: The process of adding color to textiles in either fiber, yarn or fabric form.

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