AN ACTIVATED-SLUDGE PROCESS WITHOUT EXCESS SLUDGE PRODUCTION

An activated sludge process which produces no excess sludge was develo ped. The process is very simple as a small amount of return sludge is ozonated and then returned to the aeration tank. The ozonation enhance s biodegradability of activated sludge, which is biologically oxidized in the aeration tank. A full-scale plant for treating 450m(3)/d of mu nicipal wastewater was constructed and has been operated successfully for 9 months. The amount of excess sludge eliminated is directly propo rtional to the amount of ozone dosed to the sludge. At the ozone dosin g rate of 0.034 kg/kg-SS, complete elimination of excess sludge has be en achieved when 4 times mote amount of sludge is ozonated than that o f the excess sludge expected in the treatment without ozonation. After 5 months of operation without any withdrawal of excess sludge, small amount of inorganic substances like sand and silt accumulated in the s ludge. On the other hand, inert organic substances does not seem to ac cumulate. As for effluent quality, BOD and nitrogen were kept good. Al though effluent SS was 2-15 mg/l higher compared to a control without ozonation, ii has been well below the discharge limit. (C) 1997 IAWQ. Published by Elsevier Science Ltd.