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Organic loading — Unit amounts of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total <br /> organic carbon (TOC), entering the plant each 24-hour period. <br /> Outfall—The outlet or channel through which sewage effluent is discharged. <br /> Oxidation —A process of breaking down that occurs when oxygen is added to a compound. <br /> Oxygen deficiency — The additional quantity of oxygen required to satisfy the oxygen requirements in a given <br /> liquid. Usually expressed in milligrams per liter or parts per million. <br /> Oxygen uptake—The amount of oxygen being used by an activated sludge system during a specific period of time. <br /> Percolation —The flow or trickling of a liquid through a contact or filtering medium. <br /> pH — A chemical term for measuring the amount of acid or alkali in a solution. On a scale of 0 to 14 pH, 7.0 is <br /> neutral; pH less than 7.0 indicates increasing acidity; pH greater than 7.0 indicates increasing alkalinity. <br /> Quiescent—Characterized by a lack of or negligible movement of the suspending media, such as liquid or gas. <br /> Rate, filtration —The rate of application of wastewater to a filter, usually expressed in gallons per minute per square <br /> foot of filter media surface area. <br /> Reaeration—The absorption of oxygen into waters having an oxygen deficiency. <br /> Sanitary sewer—A sewer intended to carry wastewater from homes, businesses, and industries. <br /> Screening —The removal of coarse suspended solids (SS) and floating solids by straining through racks or mesh <br /> screens. <br /> Scum—Generally organic matter that floats on the surface of wastewater. <br /> Skimming—The process of removing floating grease or scum from the surface of wastewater. <br /> Sloughings— Filter slimes that have been removed from the filter media by the backwash process. <br /> Sludge—Accumulated or concentrated solids from sedimentation or clarification of wastewater. <br /> Sludge age — A measure of the length of time particles of suspended solids (SS) are retained in the treatment <br /> process, expressed in days. <br /> Sludge bed—An area where digested sludge is dried by drainage and evaporation. <br /> Sludge bulking — A phenomenon that occurs in which the sludge occupies excessive volumes and will not <br /> concentrate readily. <br /> Sludge dewatering—The process of removing all or part of the water in sludge to form a semisolid mass or cake. <br /> Sludge digestion —The process by which organic or volatile matter in sludge is gasified, liquefied, mineralized, or <br /> converted into more stable organic matter through the activities of either anaerobic or aerobic organisms. <br /> Sludge, raw—Settled sludge removed from sedimentation tanks. <br /> Sludge volume index(SVI) —A numerical expression of the settling characteristics of activated sludge. <br /> Solids, colloidal—Finely divided solids intermediate in size between dissolved and suspended particles. <br />