Anaerobic co-digestion of sewage sludge, food waste and yard waste: Synergistic enhancement on process stability and biogas production.

Anaerobic co-digestion (co-AD) could be a more sustainable waste management solution by sharing the existed anaerobic digestion (AD) facilities and generating more biogas energy. In this study, a series of co-AD of different urban derived organic wastes (sewage sludge-SS, food waste-FW, yard waste-YW) were conducted in a semi-continuous mode, and the corresponding dynamic evolutions of microbial community structure were followed by using real-time quantitative polymerase chain reaction (qPCR). As for co-AD of two feedstocks, introduction of SS (25%, VS basis) in FW significantly improved the process stability and archaea/total microbe ratio (from 0.4% to 17.1%), which might be due to the regulating effect of abundant trace metals in SS; co-AD of SS (25%, VS basis) with YW improved the methane yield by 2.04 times than AD of YW only together with higher methane contents (57.4 ± 1.3% vs. 50.9 ± 2.2%); in co-AD of FW and YW, synergistic effects in terms of increased methane production (3.4-19.1%) were observed, which was correlated with more robust growth of both bacteria and archaea. As for co-AD of three feedstocks, high methane yields of 314.9 ± 17.1 mL/g VS were achieved with a reliable stability. These findings could provide some fundamental and technical information for the co-treatment of urban derived organic wastes in centralized AD facilities.