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but rotifers would start to increase.Rotifers eat small particles of the floc and do not depend upon individual cells,as do protozoa. NOTES Too long an aeration period would result in death of all biological forms; only the inert fraction of the cells would remain. Activated sludge is never allowed to go this far in the aeration cycle of a well- designed system. During the endogenous phase, the floc colonies are separated from the liquid before clarification. This concentrated floc is fed by fresh batches of organic matter entering the treatment system. Since the quality of microorganisms is higher than the first time around, the initial F:M ratio is lower and the bacteria start at a higher level in the growth cycle. A constant time period of aeration allows the system to progress further into the endogenous phase with each cycle. This results in better flocculation and a clearer effluent. Thus, the rate of organic removal is most rapid in the growth phase, while floc formation is best in the endogenous phase. EXTENDED AERATION In theory, the rate of sludge buildup is balanced in the extended aeration process by the rate of sludge destruction, but in practice the effluent discharge quality will ultimately be degraded due to the loss of some suspended solids over the weir, thus requiring periodic wast- ing of sludge. This is especially true where a highly polished effluent is required. The surplus sludge has no odor and may be discharged for direct drying on open beds, diverted to an optional sludge digester, accu- mulated for disposal in designated areas, or simply removed as a batch, on a predetermined schedule, from the clarifier. The interval for sludge wasting or removal depends upon the plant design,the system operator's skill, and the influent characteristics. The AquaClear batch-reactor process is a modified version of the activated-sludge process. Known as a complete mix system, it treats wastewater in batches, sequentially controlled by a microprocessor timing system. This unique feature makes possible effective, quality treatment of sewage, regardless of surge flow patterns. The principal steps are: 1. Raw sewage is pretreated prior to entering the aeration chamber(s) by either of the following two methods: a. Mechanical, basic disintegration and separation (BOD and SS removal). b. Physical, separation and nitrification initiation (BOD, SS, and basic NOD removal). NOTE: The above are not always required, especially in the case of small flows, in which case waste is directly entered into the aeration chamber from the collection system. 9