Effect of inoculum types and microbial community on thermophilic and mesophilic solid-state anaerobic digestion of empty fruit bunches for biogas production
Methane production from solid-state anaerobic digestion (SS-AD) of empty fruit bunches (EFB) using recycling solid-anaerobic digested (S-AD) sludge and liquid-anaerobic digested (L-AD) sludge as inoculum was investigated under thermophilic (55 °C) and mesophilic conditions (40 °C). The methane production rate of LAD sludge (2.98-3.27 L-CH 4 L −1 reactor d −1) was 1-2 times higher than recycling SAD sludge (1.36 L-CH 4 L −1 reactor d −1) as inoculum. Methane production of LAD and SAD sludge inoculum was 53.5-54.1 and 31.2-39.0 m 3 CH 4 tonne-1 EFB, respectively. The SS-AD of EFB with LAD and SAD sludge under thermophilic condition had specific methane activity of 34-96 times higher than the mesophilic condition. Clostridium sp., Methanosaeta sp., and Methanoculleus sp. were responsible for the SS-AD of EFB with LAD sludge inoculum. The LAD sludge was suitable inoculum for SS-AD of EFB in terms of methane production rate, cellulose degradation efficiency, biogas production, and microbial activity.