Dry mesophilic and thermophilic semi-continuous anaerobic digestion of cow manure: Effects of solid loading rate on the process performance

Abstract

Four solid loading rates (SLRs) of 3-9 kg TS/m3 day at fixed 20% total solids (TS) content were chosen in this study and assessed under two distinct circumstances: mesophilic and thermophilic under dry semi-continuous cow manure (CM) digestion. This research aimed to investigate the production of biogas, volatile solid reductions and volatile fatty acids (VFAs) concentration effects on process efficiency. This was done in 100 days of operation. The findings indicated that the production of biogas and volatile solid reduction in both digesters showed similar patterns of decrements alongside increasing SLRs. In all test cases, the best performance of the digesters was found at the SLR of 3 kg TS /m3 day, which was under thermophilic conditions. The methane yielded 0.39 m3 CH4/kg VS (65 % CH4). Meanwhile, the mesophilic reactor recorded the production of 0.25 m3 CH4/kg VS (60 % CH4). A 35.89 % increment in methane production was observed in the thermophilic state. About 67 % and 62 % of volatile solids reduction were observed in the thermophilic and mesophilic digesters, respectively. In contrast, it was observed that volatile fatty acids showed inhibitory effects at the SLR of 9 kg TS/m3 day, which in turn decreased the digesters’ performance.