The effects of biological co-pretreatment on biogas production from anaerobic co-digestion of food waste (FW) and waste activated sludge (WAS) were investigated. FW and WAS underwent anaerobic co-pretreatment to improve hydrolysis efficiency followed by co-digestion. Results showed that the methane yield from co-digestion of co-pretreated FW and WAS was 24.6% higher than that of control substrates without pretreatment. An increase of 10.1% in solids reduction was achieved in the anaerobic digester under the optimum pretreatment time of 24 h. Compared to mono-digestion of FW with pre-treatment, the combination of anaerobk co-digestion and co-pretreatment of FW and WAS resulted in a higher treatment performance and methane production due to synergistic effects of pH amendment and enhancement of WAS particles solubilization. Pyrosequencing analysis indicated that anaerobic co-pretreatment reduced the abundance of filamentous bacteria of genus Levilinea in the subsequent co-digestion, which was liable to cause a decrease in anaerobic digestion performance. (C) 2017 Elsevier Ltd. All rights reserved.