Inhibition of volatile fatty acids on methane production kinetics during dry co-digestion of food waste and pig manure.

Graphical abstract Highlights • The VFAs were main inhibition factors on methane production. • The threshold VFA inhibition concentration on methane production was 16.5–18.0 g/L. • The possible functions of some bacteria were first estimated. • Syntrophic oxidation with hydrogenotrophic methanogenesis was the dominant pathway. • An inoculum rate of 50% & FW/PM ratio of 50:50 was preferable operation conditions. Abstract Compared with wet digestion, dry digestion of organic wastes reduces reactor volume and requires less energy for heating, but it is easily inhibited by high volatile fatty acid (VFA) or ammonia concentration. The inhibition on methane production kinetics during dry co-digestion of food waste and pig manure is rarely reported. The aim of this study was to explore the inhibition mechanisms and the microbial interactions in food waste and pig manure dry co-digestion systems at different inoculum rates (25% and 50% based on volatile solids) and food waste/pig manure ratios (0:100, 25:75, 50:50, 75:25 and 100:0 based on volatile solids). The results showed that the preferable operation conditions were obtained at the inoculum rate of 50% and food waste/pig manure ratio of 50:50, with a specific methane yield of 263 mL/g VS added. High VFA concentration was the main inhibition factor on methane production, and the threshold VFA inhibition concentrations ranged 16.5–18.0 g/L. Syntrophic oxidation with hydrogenotrophic methanogenesis might be the main methane production pathway in dry co-digestion systems due to the dominance of hydrogenotrophic methanogens in the archaeal community. In conclusion, dry co-digestion of food waste and pig manure is feasible for methane production without pH adjustment and can be operated stably by choosing proper operation conditions. [ABSTRACT FROM AUTHOR]