[The use of chemical uncoupler to reduce sludge yield in activated sludge process]

To determine whether chemical additions can be used to reduce sludge production in biological wastewater treatment, 3,3',4',5-tetrachlorosalicylanilide (TCS), served as a metabolic uncoupler was added to activated sludge cultures. The batch tests have confirmed that TCS is an effective chemical uncoupler in reducing the sludge yield when its concentration is higher than 1.0 mg/L. It was showed that TCS was able to reduce sludge yield by approximately 50% when the TCS concentration was 6.0 mg/L. It was also revealed that substrate removal capability and effluent nitrogen concentration were not affected adversely by the presence of TCS when TCS was dosed every other day in a range of 2.0-3.6 mg/L during the 40 d operation of activated sludge batch cultures. Such a sludge growth reduction is associated with the enhancement of microbial activities in terms of the SOUR and dehydrogenase activity. Sludge settleability from the treated and control samplers was comparable and not significantly different. Meanwhile, there was a finding that the filamentous bacteria still grow in sludge floc in the control reactor after 40 d operation. These results suggested that it might be possible to apply TCS in activated sludge systems to reduce the excess sludge yield.