Enhanced methanization of sewage sludge using an anaerobic membrane bioreactor integrated with hyperthermophilic biological hydrolysis

Highly efficient methanization of sewage sludge has been a long-standing challenge. Therefore, in this study, hyperthermophilic (70 degrees C) biological hydrolysis pretreatment was investigated as a strategy to improve sludge biodegradability when subsequently combined with an anaerobic membrane bioreactor (AnMBR). Its effects on organics removal, methane yield, microbial community structure and activity were studied at hydraulic retention times (HRTs) ranging from 5 to 20 days. The results obtained from the 170-day continuously fed experiment showed a high methane yield, ranging from 176 to 246 L/kg-VSin the AnMBR by feeding the pretreated sludge at a constant HRT of 5 days. High removal efficiencies of volatile solids ranging from 46% to 63% occurred in the AnMBR. A satisfactory net energy output was also obtained. Methanothermobacter dominated the AnMBR and was robust to the HRT changes. Severe membrane fouling occurred after 140 days under a high solid concentration. Subsequently, chemical cleaning (NaClO and citric acid) successfully recovered the flux and permeability of the membrane. Conclusively, this study lays the foundation for using hyperthermophilic hydrolysis in the mechanization of sludge through integration with AnMBR technology.