Effectiveness of enriched microbial culture under mesophilic and thermophilic condition in palm oil mill effluent for anaerobic digestion of Brachiaria mutica

In this study, we investigated the effectiveness of microbial enrichment in enhancing the anaerobic digestion of lignocellulosic biomass of anaerobically digested sewage sludge in a complex substrate under both mesophilic (305 K) and thermophilic (328 K) conditions. Palm oil mill effluent (POME) was used as the enrichment culture, and Brachiaria mutica (paragrass) as a representative of a lignocellulosic biomass with relatively low lignin content (ca. 10 wt%). The microbial enrichment was found to increase the hydrolytic activities of the sludge more than twofold, and to increase the bacterial diversity, especially under the mesophilic condition. The microbial enrichment was also found to increase the diversity of methanogenic archaea and the methanogenic activities of the sludge. When compared with the original sludge, the enriched microbial culture under the mesophilic condition increased the methane yield from 275 to 312 cm(3) STP/g VS added. However, despite increased hydrolytic, acetogenic and methanogenic activities, the enriched microbial culture under the thermophilic condition failed to enhance methane production in a long-term anaerobic digestion of paragrass.