Thermophilic anaerobic digestion of mixed sludge and primary sludge pretreated by short time and low temperature thermal condition

Thermophilic anaerobic digestion of thermal pretreated sludge was investigated using completely stirred tank reactors (CSTRs) at (55±1)℃. Two kinds of concentrated sludge, mixed sludge and primary sludge, both with a TS concentration of 35 g·L^-1, were thermally pretreated at 90℃ for 30 minutes, respectively. The performance and stability of thermophilic anaerobic digestion were investigated at a hydraulic retention time (HRT) of 20 days, including biogas production rate, removal efficiency of organic matter, and COD mass balance. The results showed that the biogas production rate of the mixed and primary sludge were (343.00±9.86) mL·g^-1, and (365.00±7.61) mL·g^-1, respectively; and VS removal efficiencies of those two kinds of sludge were 38.9% and 45.8% in the thermophilic anaerobic digestion. The results of COD mass balance of mixed and primary sludge showed that over 33.6% and 43.9% of the influent organic matters were transformed to biogas with a methane content about 70%.