Effect of thermal hydrolysis sludge supernatant as carbon source for biological denitrification with pilot-scale two-stage anoxic/oxic process and nitrogen balance model establishment

To recover carbon source (C-source) from waste activated sludge (WAS) and enhance the nitrogen removal performance, a pilot-scale system consisting of two-stage anoxic/oxic (A/O) process and low-temperature thermal hydrolysis process (THP) was proposed. The C-source recovery parameters for pilot THP were determined by systematically considering the results of orthogonal jar experiment, hydrolyzed sludge biodegradability and actual pilot situation. The results showed that supernatant from WAS treated by pilot-scale THP showed desirable biodegradability (BOD5/SCOD 0.62) and C/N (16) at the condition of heating temperature of 80 °C, heating time of 90 min and sludge water content of 98%. The performances of two-stage A/O process for 35 days indicated that the effluent quality could comply with the preset discharge standard, and hydrolysed sludge supernatant could be utilised as C-source for biological denitrification. A nitrogen balance model was established for two-stage A/O process, which showed high simulation accuracy and could be applied to optimize the operation parameters to meet TN discharge standard.