Effects of digestate recirculation ratios on biogas production and methane yield of continuous dry anaerobic digestion

This study conducted a small scale, push flow, continuous, dry anaerobic digestion experiment using 50% and 60% digestate recirculation ratios to investigate the effects of digestate recirculation ratio on continuous dry anaerobic digestion and to analyze microbial community succession. The results showed that the volumetric biogas production rate could reach 1.6 L/L center dot d during the 60% digestate recirculation ratio. A slight, initial accumulation of volatile fatty acids (VFAs) (maximum concentration 1.6 g/L) was subsequently consumed by the Christensenellaceae R-7 group, and VFA concentrations stabilized at around 20 mg/L. The increased digestate recirculation ratio (60%) promoted both VadinBC27 wastewater-sludge group and Methanobacterium proliferation, and the predominance of those microbial strains may be why VFAs decreased and gas production efficiency improved. Those microbial community changes, fostered by the higher digestate recirculation ratio, are important in continuous dry anaerobic digestion. These results aid continued work aimed at improving continuous, dry anaerobic digestion.