In-situ sludge pretreatment in a single-stage anaerobic digester

This study aimed to develop an in-situ sludge pretreatment method by increasing the temperature from thermophilic to extreme thermophilic condition in a single-stage anaerobic digester. The results revealed that a stable performance was obtained within the temperature range of 55-65 °C, and the maximum methane yield of 208.51 ± 13.66 mL/g VS was obtained at 65 °C. Moreover, the maximum extent of hydrolysis (33%) and acidification (27.1%) was also observed at 65 °C. However, further increase of temperature to 70 °C did not improve the organic conversion efficiency. Microbial community analysis revealed that Coprothermobacter, highly related to acetate oxidisers, appeared to be the abundant bacterial group at higher temperature. A progressive shift in methanogenic members from Methanosarcina to Methanothermobacter was observed upon increasing the temperature. This work demonstrated single-stage sludge digestion system can be successfully established at high temperature (65 °C) with stable performance, which can eliminate the need of conventional thermophilic pretreatment step.