Unveiling the role of dissolved CO2 in a metabolic pathway switch during biological methanation

This study investigated the impact 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, 3.8, 4, 4.5, and 5 (v:v)) to manipulate the 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 CO2 above 2 mmol/L, production of CH4 was favored. Conversely, acetate production was favored at lower dissolved CO2 concentrations, with a peak accumulation of 1.94 g/L observed at 0.94 mmol/L of dissolved CO2. This study demonstrates 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.