Development of a model to describe the performance of electromethanosynthesis in two microbial electrolysis cells with different biocathode sizes

Electromethanosynthesis in a Microbial Electrolysis Cell facilitates CH₄ production through enhanced reaction kinetics and efficient CO₂/CH₄ separation, while concurrently facilitating wastewater treatment. Two MECs which differed in the biocathode projected surface area (1.25 and 0.25 m²) were constructed and operated. The results demonstrated that increasing the electrode size led to increased CH₄ production and improved MEC efficiency. A mathematical model was developed to describe the two MECs in the COMSOL Multiphysics framework, which simulates the growth of six microbial populations, using Butler-Volmer-Monod kinetics, taking into account the impact of the overpotentials. The model captured the effect of the developed overpotentials on substrate consumption and current production and the simulations showed good agreement with the measured variables in terms of reaction rates, leading to a deviation of 2.5 % for organic content removal and < 1 % for electromethanosynthesis. The validation of the model, accounting for varying biocathode sizes, accurately predicted the CH₄ production under all different conditions employed and the highest deviation was 10 %. The developed model provides the foundation for understanding the dynamics of substrate availability, diffusion of species, electrochemical reactions and microbial populations, across multiple chemical pathways, while establishing the framework for predicting the significance of reactor design for efficient electromethanosynthesis.