Utilization of dissolved CO₂ to control methane and acetate production in methanation reactor

This study investigated the influence of dissolved CO₂ on the selection of metabolic pathway using a methanation membrane bioreactor supplied with H₂/CO₂. Various ratios of H₂/CO₂ were applied (3.3, 3.8, 4.0, 4.5, and 5.0 (v/v)) to manipulate dissolved CO₂ levels in the medium. The findings revealed a correlation between the concentration of dissolved CO₂ and the production of CH₄ (positive) and acetate (negative). Specifically, at a dissolved concentration of CO₂ above 2.0 ± 0.2 mmol/L, production of CH₄ was favored. At the opposite, acetate production was favored at lower dissolved CO₂ concentrations, with a maximum concentration of 1.9 g/L observed at 0.9 mmol/L of dissolved CO₂. This study demonstrates that the modification of dissolved CO₂ levels in a methanation bioreactor can provide a strategy for the selection of metabolic pathways and microbial communities, thereby offering a promising opportunity for optimizing the conversion of CO₂ into high-value products such as CH₄ and acetate.