Bio-electrochemical conversion of carbon dioxide to methane in geological storage reservoirs

Geological storage of carbon dioxide (CO2) as currently conceived is not commercially viable. To promote deployment of CO2 capture and storage (CCS), substantial value must be added to CCS operations. We have proposed a subterranean carbon plantation that involves storing CO2 in a geological reservoir, biologically converting the stored CO2 to methane in situ, and harvesting the biogenic methane as a recycled energy source. To examine the durability of methanogenic metabolism under storage reservoir conditions, the methanogenic activity of Methanothermobacter thermautotrophicus (a representative subsurface methanogen) was assessed under nutrient-limited and reduced-pH conditions in actual formation-water-based media. Moreover, to examine the possibility of electrochemically supplying the source of reducing power into the reservoir, methanogen was also incubated in absence of exogenously supplied molecular hydrogen with applied voltage. Applied-voltage-dependent methanogenesis was observed, suggesting that methanogen can utilize electrons and protons as a reducing-power source to reduce CO2 to methane. Towards practical deployment of the electromethanogenic system to utilize CCS reservoirs as energy-reserving tanks, further studies are required to enhance the bio-electromethanogenic activity and optimize well configurations.