As potential CO2 geological storage site in CCS, the use of depleted oil/gas reservoirs and aquifer has been proposed. The long-term aim of this research is to establish a biotechnological system to microbiologically convert geologically stored CO2 into methane, as energy resource. To develop a means for the conversion, we focus on technological application of bio-electrochemical reaction using microbially catalyzed electrode. On the electrode surface, methanogenic microorganisms (as biocatalysts) utilize electrical current (electrons) to reduce CO2 (CO2 + 8H+ + 8e- → CH4 + 2H2O). Such “electromethanogenic” system is an attractive option for energy conversion, as the bio-cathode yields methane from electrical current, which can be provided by renewable energy sources. In other words, intermittent electrical energy provided by wind turbines or/and solar cells can be stored in a stable energy form, methane. For such system, recruitment of microorganisms indigenous to the reservoir as the biocatalysts will be a better choice, as they are more likely to maintain the activity within the reservoir. Toward technological application of the bio-electrochemical system in CO2 geological reservoir, we examined bio-electromethanogenic activity of subsurface microbial consortium for the first time. Indigenous microorganisms originated from a formation water of a domestic depleted oil reservoir were inoculated into electrochemical-cultivation reactors. Upon application of constant voltage of -0.75 V, the reactor inoculated with reservoir-indigenous microorganisms produced methane at a rate of 386 mmol day-1m-2 (cathode surface area), which was the highest electromethanogenic production rate so far documented. Moreover, current-to-methane conversion efficiency of the reaction was as high as approx. 90-100%. Thus, we concluded that microorganisms indigenous to the subsurface reservoir are highly capable of electromethanogenic reduction of CO2. Electrochemical and microbial analyses suggested a reaction mechanism, in which electron-releasing bacteria mediated electron transfer from the electrode to methanogenic archaea.

Subsurface bio-electrochemical conversion of carbon dioxide into methane by using indigenous microorganisms

249th National Meeting (2015)

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