Potential of anaerobic co-digestion of acidic fruit processing waste and waste-activated sludge for biogas production

Abstract

Abstract The potential of acidic fruit processing waste (FPW) and waste-activated sludge (WAS) co-digestion for methane production was investigated using batch and continuous experiments. First, batch experiments showed the co-digestion of FPW and WAS solved acid accumulation and increased cumulative biogas production. When the volatile solid (VS) ratio of FPW to WAS was 2:1, the cumulative biogas production was the highest (4,695.47 mL), which increased by 5.2% and 10.5% compared with the VS ratios of 3:1 and 1:1, respectively. Methane production was the rate-limiting step when the FPW percentage was high, and hydrolysis was the rate-limiting step when the WAS percentage was high. Second, the continuous experiments showed fermentation was the most stable when the VS ratio was 2:1, without acid accumulation or excessive total alkalinity consumption. Additionally, the ammonia nitrogen content in the system was above 138.34 mg·L−1, which solved the slow WAS hydrolysis rate and low nitrogen supply efficiency. Microbial community structure of the reactor was correlated with substrate composition greatly. On the 180th day, the relative abundance levels of Bacteroides, Paludibacter, Litorilinea, Levilinea, and Smithella were higher than those on the 120th day and the 240th day. The enrichment of those bacterial groups was beneficial to improve the substrate hydrolysis rate and reduce the influence of organic acids on the anaerobic system.