High-solids anaerobic digestion of organic fraction of municipal solid waste: Effects of feedstock to inoculum ratio and percolate recirculation time

[Display omitted] •High-solids anaerobic digestion (HSAD) process was investigated for OFMSW.•Feedstock to inoculum (F:I) ratios and percolate recirculation times were studied.•Methane recovery was more critically affected by F:I ratios (VS basis).•F:I = 1 achieved up to 86% recovery of theoretical methane potential of OFMSW.•F:I = 2 handled 45% higher VS than F:I = 1 with only 16% lower methane recovery. The effects of feedstock to inoculum (F:I) ratio and percolate recirculation time (PRT) were studied for the high-solids anaerobic digestion (HSAD) of the organic fraction of municipal solid waste (OFMSW). Six mesophilic HSAD systems were operated at different F:I ratios (1 to 3 kg VS/kg VS; PRT = 2.5 h/d) and PRTs (1.5 to 3.5 h/d; F:I = 2 kg VS/kg VS). The F:I ratio of 1 provided up to 86% of the theoretical methane potential of OFMSW. In contrast, F:I ratio of 3 provided only 34% methane recovery due to volatile fatty acids (VFAs) accumulation and pH drop. Despite F:I ratio of 2 could provide 70% methane recovery, it could enable almost 45% higher organics processing capacity (VS basis) and lower solids washout during percolate recirculation, as compared to the F:I ratio of 1. However, different examined PRTs showed marginal impacts on methane yields with comparable changes in profiles of percolate characteristics.