Rice straw anaerobic digestion enhancement through bioaugmentation: effect on the microbial community

Abstract The degradation of agricultural residues by anaerobic digestion and their bioconversion to methane is still hampered by the search for pretreatment strategies due to the lignocellulosic content that limits the efficiency of the process. Adding an enriched microbial consortium could be an alternative for the biological treatment of lignocellulosic biomass. During the degradation process, it is necessary to study the dynamics and structure of the microbial community. The objective of this study was to evaluate the addition of an enriched microbial consortium, and its effect on the methane-producing prokaryotic community during the anaerobic digestion of rice straw. The consortium was characterized by diversity, microbial community dynamics, and taxonomic identification. The rice straw anaerobic digestion was bioaugmented using the microbial consortium in 10 L semi-continuous stirred tank reactors (35 ± 2°C) for 70 days of operation at increasing organic loading rates up to 1.8 g VS L-1 d-1. Relative to the control reactor, higher and more stable methane production was obtained with the biological treatment strategy. The metagenomic method allowed identification down to the genus and species level of microbial consortium and the prokaryotic community within the reactors. From the knowledge of the diversity and dynamics of the microbial community, possible preferential metabolic pathways were presumed. The enhanced anaerobic degradation of rice straw by the microbial consortium and its effect on the methane-producing microbial community demonstrated that it could be used as a bioproduct for the treatment of agricultural waste for energy purposes.