Conversion of CO2 into CH4 by methane-producing bacterium FJ10 under a pressurized condition

In this study, fresh water methane-producing bacterium (MPB), strain FJ10, which used H2 as an electron donor and CO2 as an electron acceptor, was isolated and chosen as the primary methanogen for the conversion of CO2 into CH4. Improvements to culture medium to increase methane production were investigated using a fractional factorial design in 32 experiments with six variables under consumption of H2/CO2 at ratios of 4 and 1. The tested nutrient compositions were NaCl, NH4Cl, FeSO4, MgCl2, H2PO4 and yeast extract. Experimental results indicate that yeast extract was essential for the growth of strain FJ10 to impact the conversion of CO2 into CH4. Strain FJ10 generated maximum CH4 production with 5.0 g/l of yeast extract. Moreover, optimal culture conditions for methane production by strain FJ10 were 40 °C and pH 8. Approximately 22–25% of CO2 conversion into CH4 was achieved at an H2/CO2 ratio of 4 and roughly 2.5–6% of CO2 conversion into CH4 was obtained at an H2/CO2 ratio of 1 under different pressurized conditions of 1 atm, 50 atm and 100 atm. Under 100 atm, about 6780 μM CH4 was produced with an H2/CO2 ratio of 4 and 4240 μM CH4 was produced with an H2/CO2 ratio of 1 under the steady state condition. The kinetic model for H2/CO2 utilization and CH4 production under different pressures was verified by experimental data. Model predictions are in good agreement with experimental results. The experimental and modeling approaches in this study can be applied to evaluate the conversion of CO2 into CH4 as an energy source by geo-microorganisms in geological sequestration.