Effluent Quality

Activated-sludge process design is based on the desired effluent quality. Successful operation of the activated-sludge process with an F/M ratio of 0.35 lb BOD5 per lb MLSS per day and efficient liquid-solids separation should yield effluent containing an average of 20 mg/l of SS and 20 mg/l of BOD5. For municipal wastewater, activated-sludge treatment removes the following major pollutants in the percentages listed:

90+% BOD5 (biological oxygen demand) 70+% COD (chemical oxygen demand) 90+% SS (suspended solids) 30+% P (phosphorus) 35% N (nitrogen)

represents a large initial capital outlay, with high operation and maintenance costs. Treatment associated with most activated-sludge treatment plants includes primary clarification, sludge handling, and chlorination. Table 7.25.3 shows an estimated cost breakdown for the total activated-sludge treatment facility for plants varying in size from 1 to 100 mgd. The table shows the approximate cost distribution in such a facility together with the approximate cost for various plant sizes and each phase of the total treatment facility.

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