Harnessing Methanococcus maripaludis for CO$_2$ to CH$_4$ conversion: modeling of microbial electrosynthesis

This study presents a dynamic one-dimensional model for methane (CH$_4$) production in a two-chamber microbial electrosynthesis (MES) reactor, integrating biological and electrochemical processes. Using Methanococcus maripaludis S2 as a pure culture, the model simulates carbon dioxide (CO$_2$) conversion under controlled voltage and pH conditions. It incorporates Monod-based microbial kinetics, intracellular redox mediator dynamics, and electrochemical losses (ohmic, activation, and concentration), enabling prediction of CH$_4$ production rates in response to operational parameters such as substrate and biomass concentration, and applied voltage. The high level of agreement (R$^2$ = 0.9595) between the numerical simulations and the experimental data confirmed the reliability of the model. Results indicated that higher initial CO$_2$ concentrations enhanced CH$_4$ generation but may lead to long-term inhibition, whereas moderate CO$_2$ levels facilitated stable performance. Increased biomass accelerates production without affecting final CH$_4$ yields. Voltage optimization revealed a performance threshold beyond which further increases offer no benefit. ... mehrSensitivity analysis highlights back-electromotive force ($\epsilon$) and mediator yield (Y$_M$) as the most influential parameters, suggesting targets for efficiency improvement. Numerical results show that CH$_4$ production rates peaked at 9.75 [mmol m$^{-2}$d$^{-1}$], corresponds to 156 mg CH$_4$ per electrode surface area per day. This model offers a predictive framework for optimizing MES operation and reducing experimental workload for sustainable biofuel production from CO$_2$.