Biogas production using anaerobic groundwater containing a subterranean microbial community associated with the accretionary prism

In a deep aquifer associated with an accretionary prism, significant methane (CH(4)) is produced by a subterranean microbial community. Here, we developed bioreactors for producing CH(4) and hydrogen (H(2)) using anaerobic groundwater collected from the deep aquifer. To generate CH(4), the anaerobic groundwater amended with organic substrates was incubated in the bioreactor. At first, H(2) was detected and accumulated in the gas phase of the bioreactor. After the H(2) decreased, rapid CH(4) production was observed. Phylogenetic analysis targeting 16S rRNA genes revealed that the H(2)-producing fermentative bacterium and hydrogenotrophic methanogen were predominant in the reactor. The results suggested that syntrophic biodegradation of organic substrates by the H(2)-producing fermentative bacterium and the hydrogenotrophic methanogen contributed to the CH(4) production. For H(2) production, the anaerobic groundwater, amended with organic substrates and an inhibitor of methanogens (2-bromoethanesulfonate), was incubated in a bioreactor. After incubation for 24 h, H(2) was detected from the gas phase of the bioreactor and accumulated. Bacterial 16S rRNA gene analysis suggested the dominance of the H(2)-producing fermentative bacterium in the reactor. Our study demonstrated a simple and rapid CH(4) and H(2) production utilizing anaerobic groundwater containing an active subterranean microbial community.