Enhancement of mesophilic anaerobic digestion of waste activated sludge using alkaline-low temperature thermal pretreatment

Disintegration of the waste activated sludge (WAS) of a municipal wastewater treatment plant using alkaline-low temperature thermal pretreatment with different kinds and doses of alkaline at a series of pretreatment temperatures and thermal reaction times were investigated. The effect of alkaline-thermal pretreatment on anaerobic digestion was investigated by mesophilic ((35±1)℃) biochemical methane potential (BMP) test. The results showed that the SCOD release efficiency and the VSS reduction efficiency increased and then decreased with increased alkaline dose and thermal temperature. The optimal pretreatment conditions were 0.05 g NaOH/g TS at 70℃ for 9 h. Under the conditions, the SCOD release efficiency was 52.3%, the VSS reduction efficiency reached 33.3%. The BMP experiment results showed that the TCOD removal efficiency increased to 77.1%, which was significantly higher than the control group. While, the methane production was 2.7 times as many as the control group. The biogas production rate was 354 mL CH₄/g VS under the optimal pretreatment conditions.