Comparation of mesophilic and thermophilic anaerobic co-digestion of food waste and waste activated sludge driven by biochar derived from kitchen waste

Anaerobic co-digestion of food waste and wasted sludge is a promising practice to integrate waste management and improve energy balance. In this study, the effects of kitchen waste biochar on the mesophilic and the thermophilic co-digestion were compared. Biochar showed a better performance in thermophilic treatments, and the highest methane production was obtained at 15 g L−1 biochar, while the time for complete digestion was shortened from 20 days in the controls without biochar to 13 days in the 15 g L−1 biochar-assisted treatments. Compared to the mesophilic treatments, thermophilic treatments demonstrated fast pH drop and volatile fatty acids accumulation. Based on the Gompertz model, 15 g L−1 biochar increased the maximum specific methane production rate by 2-fold and reduced the lag time by 31.6%, which was attributed to fast volatile fatty acids consumption and recovery from pH drop. pH, temperature and volatile fatty acids were significant factors shaping the distinct microbial dynamics. Methanosaeta dominated in archaeal community in mesophilic treatments, while Methanosarcina and Methanothermobacter were favored in thermophilic treatments. The higher acetogenesis rate integrated with enriched acetoclastic methanogenesis led to its better performance in biochar-assisted thermophilic co-digestion.