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

The effects of feedstock to inoculum (F:I) ratio and percolate recirculation time (PRT) were studied for the highsolids 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.