Brewery CO2 conversion into acetic acid at an optimized set of microbial electrosynthesis process parameters

Direct utilization of unpurified industrial CO2 is desired to minimize feedstock transportation and purification costs and develop cost-efficient carbon utilization technologies. To this end, utilization of brewery CO2, which is a readily available yet underexplored carbon source, is feasible via microbial electrosynthesis (MES) technology, though the productivity indicators remain lower. This study provides insights into enhancing the MES productivity from unpurified brewery CO2 through optimization of feed rate and cathode potential (Ecathode), besides assessing the impact of catholyte recirculation on overall production parameters. At an Ecathode of -1 V, the Acetobacterium-dominated enriched mixed microbial culture produced up to 6.6 g/L acetic acid at 85 % coulombic efficiency and cell voltage (Ecell) of 2.98 V from brewery CO2 fed continuously at 0.7 L/d rate. Acetic acid production decreased at the lower or higher Ecathode and gas feed rate conditions, emphasizing the importance of maintaining an optimal balance between the gas flow rate and Ecathode to achieve efficient H2-mediated production. With the catholyte recirculation loop in reactors operated under the optimized Ecathode and feed rate conditions, acetate production enhanced further to 7.6 +/- 0.65 g/L at 92 % coulombic efficiency and 2.9 V Ecell. The improved productivity can be attributed to better mixing and retention of CO2 and H2 in MES reactors, besides the enhanced growth and dominance of key CO2-fixing acetogens belonging to Acetobacterium and Eubacterium genera under the catholyte recirculation condition. The findings suggest that fine-tuning various process parameters is pivotal to achieving the desired MES productivity.