Bioconversion of CO₂ to methane energy by Methanococcus maripaludis in newly-designed bioreactor system: Kinetic...

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.