Bioconversion of CO2 to methane energy by Methanococcus maripaludis in newly-designed bioreactor system: Kinetic characteristics, parameter optimization and grid-quality production.

Carbon dioxide enhanced oil recovery (CO2-EOR) is widely used for carbon capture, utilization, and storage in Chinese oilfields, but part of injected CO2 returns with produced oil, reducing carbon-reduction efficiency. Bioconverting this CO2 to methane energy by methanogens benefits the technology, yet on-site high-efficiency conversion meeting natural-gas grid standards remains challenging. This study used a newly-designed triple-tank bioreactor to investigate CO2-to-methane conversion and methanogenic kinetics of Methanococcus maripaludis. Under gas permeation mode, methane production, OD600 and coenzyme F420 content were measured, with kinetics calculated via the modified Gompertz model. Optimal conditions: 150 rpm stirring, H2/CO2 of 4:1, 20 mL·min-1 gas injection (40 min). Multi-stage continuous conversion achieved 10.95 mmol·L-1·d-1 methane production rate (97.4 % methane proportion), with residual H2 and CO2 both < 2 % (meeting grid standards). This work provides optimized operational parameters and theoretical support for scaling CO2-to-methane conversion, offering key insights for carbon capture, utilization, and storage in oilfields.