Enhanced biogas production by co-digestion of crude glycerol and ethanol with palm oil mill effluent and microbial community analysis

Abstract

Valorization of biodiesel-derived crude glycerol and its hydrolysis product (ethanol) as a co-substrate supplemented to palm oil mill effluent (POME) to enhance biogas production efficiency under mesophilic anaerobic digestion was investigated. Based on our previous studies, the concentrations of each co-substrate were varied in the range of 1–5% v⋅v−1. The optimum concentrations of crude glycerol and ethanol were 1% and 5% v/v, respectively. They could increase both methane production (nearly 2 fold) and methane yield (1.98–2.09 fold based on volatile solids (VS) and 1.6–1.87 fold based on COD). However, they exhibited oppositely in the methane production rate; the 1% crude glycerol was 38% lower while 5% ethanol exhibited a 67% higher methane production rate than the control (POME). The results clearly indicated that the methane production rate from 5% ethanol was 2.7 times higher than that from the 1% crude glycerol. Microbial community analysis revealed that the dominant bacteria in both co-substrates biogas production process were Sandarakinotalea sp., Lachnobacterium sp., Blautia sp., Marinobacter sp., Anaerotruncus sp., Clostridium sp., Enterobacter sp., and Acinetobacter sp. The Blautia sp. was dominant in the presence of 1% crude glycerol than 5% ethanol. The archaea communities were dominated by hydrogenotrophic methanogen (Methanoregula sp. and Methanoculleus sp.) and acetoclastic methanogen (Methanosarcina sp. and Methanospirillum sp.). Therefore, ethanol was a better co-substrate than crude glycerol. Nevertheless, biogas production from POME with crude glycerol as co-substrate was anticipated to strongly increase by enhancing the growth (or bioaugmentation) of Blautia sp. and Methanosarcina sp.