Bioconversion Pathway of CO 2 in the Presence of Ethanol by Methanogenic Enrichments from Production Water of a High-Temperature Petroleum Reservoir

Transformation of CO 2 in both carbon capture and storage (CCS) to biogenic methane in petroleum reservoirs is an attractive and promising strategy for not only mitigating the greenhouse impact but also facilitating energy recovery in order to meet societal needs for energy. Available sources of petroleum in the reservoirs reduction play an essential role in the biotransformation of CO 2 stored in petroleum reservoirs into clean energy methane. Here, the feasibility and potential on the reduction of CO 2 injected into methane as bioenergy by indigenous microorganisms residing in oilfields in the presence of the fermentative metabolite ethanol were assessed in high-temperature petroleum reservoir production water. The bio-methane production from CO 2 was achieved in enrichment with ethanol as the hydrogen source by syntrophic cooperation between the fermentative bacterium Synergistetes and CO 2 -reducing Methanothermobacter via interspecies hydrogen transfer based upon analyses of molecular microbiology and stable carbon isotope labeling. The thermodynamic analysis shows that CO 2 -reducing methanogenesis and the methanogenic metabolism of ethanol are mutually beneficial at a low concentration of injected CO 2 but inhibited by the high partial pressure of CO 2 . Our results offer a potentially valuable opportunity for clean bioenergy recovery from CCS in oilfields.