Anaerobic stabilization of waste activated sludge at different temperatures and solid retention times: Evaluation by sludge reduction, soluble chemical oxygen demand release and dehydration capability

Anaerobic treatment is the most widely used method of waste activated sludge (WAS) stabilization. Using a semi-continuous stirring tank with condensed WAS, we investigated effects of decreasing the solid retention time (SRT) from 32 days to 6.4 days on sludge reduction, soluble chemical oxygen demand (SCOD) release and dehydration capability, along with anaerobic digestion operated at medium temperature (MT-AD) or anaerobic digestion operated at room temperature (RT-AD). Results showed that effects of temperature on SCOD release were greater at SRT of 32 d and 6.4 d. When SRT was less than 8 d, total solids (TS), volatile solids (VS) and capillary suction time (CST) did not change significantly. CST was lowest at SRT of 10.7 days, indicating best condition for sludge dehydration. Principal component analysis (PCA) showed that the most optimum SRT was higher than 10.7 d both in MT-AD or RT-AD.