Oxic-settling-anoxic (OSA) process combined with 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to reduce excess sludge production in the activated sludge system

The potential of oxic-settling-anoxic (OSA) process with addition of 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to reduce excess sludge production was investigated. TCS was dosed into aeration tank with 0.05, 0.10 and 0.15 g every other day in three lab-scale OSA processes, respectively to form the TCS and OSA combined processes. The OSA and TCS combined processes reduced sludge yield by 21–56% under the same sludge retention time (6.75 h) in sludge anoxic holding tank. Substrate removal capability, effluent NH3-N concentrations and total phosphorus removal rates were not adversely affected by the presence of TCS or insertion of sludge anoxic holding tank, but total nitrogen removal rates only decreased significantly in the system with addition of 0.15 g TCS during the 60-day continuous operation. The settleability of sludge in four systems was qualitatively comparable and not significantly different. Microscopic examination and the banding patterns of DGGE profiles demonstrated that microbial population changed after TCS addition and insertion of anoxic sludge holding tank. The results suggest that TCS and OSA combined process is effective in reducing sludge yield, and process performance as well as sludge settleability are not significantly affected by introduction of the chemical uncoupler. The results imply that reduction of excess sludge production is due to uncoupled metabolism at low TCS dosage, but microbial death at high TCS dosage.