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2. Sewage, while exposed to aeration and mixing, is allowed to accumulate within the aeration chamber until enough volume is NOTES present to initiate a batch cycle. 3. After the mixed liquor has reached a predetermined level, a portion, or batch, is transferred to the clarifier for a programmed period of quiescent settling. 4. Upon completion of the quiescent settling period, the superna- tant is transferred through a chlorination cycle in the chlorine contact chamber, then through tertiary filters, and finally the tertiaried effluent may be dechlorinated and further sterilized by optional ultraviolet light prior to discharge. Settled sludge from each stage, and filter backwash, are returned to the aeration chamber and recycled.If physical pretreatment is incor- porated, settled sludge and backwash may be returned to the pre- treatment chamber. MECHANICAL PRETREATMENT DISINTEGRATION. If required, influent may be disintegrated by pretreatment prior to entering the aeration chamber by one of three methods: 1. A receiving basket, partially submerged in the mixed liquor in the aeration chamber. Sewage solids are contained and exposed to aerated mixed liquor for particle size reduction and mixed- liquor absorption. 2. A static fine screen is mounted outside the aeration chamber. As the raw waste stream flows across the metal grating, foreign articles are captured and fall into a dropbox.Sewage waste passes through the screen directly into the aeration chamber. 3. A comminutor, mounted outside the aeration chamber, reduces the size of all incoming matter by high-speed cutting.After pass- ing through the comminutor,waste enters the aeration chamber. PHYSICAL PRETREATMENT SEPARATION AND NITRIFICATION INITIATION. (NOTE: The following may not be required for nitrification where detention peri- ods of 14 hours or more are anticipated. With reduced solids con- centration, the normal calculated aeration demand for the batch process is sufficient for nitrification supplementation. Should exter- nal nitrification be deemed necessary, the following procedure is used.) Prior to entering the treatment plant, raw sewage may be collected in a baffled buffer tank. The buffer tank is anaerobic and sized for a detention period which will allow solid/liquid separation, retention of solids and floatable materials, and promotion of facultative anaer- obes by degeneration of natural dissolved oxygen levels. 10