An Electrolytic Bubble Column with Gas Recirculation for High-Rate Microbial Electrosynthesis of Acetate from CO₂

The H₂-mediated microbial electrosynthesis (MES) reactors can be run in high current density, but it is challenging to ensure high Coulombic efficiency (CE) due to the limited hydrogen solubility. Here, we introduce a unique electrolytic bubble column featuring gas recirculation to tackle the challenge. The bubble column and gas recirculation extended the H₂ retention time and enhanced gas-liquid mixing in the reactor, thereby ensuring a high H₂ uptake efficiency. When a current density of 337 A/m²_cathode (1.2 A/L_catholyte) was applied, the reactor achieved an average acetate production rate of 87 g/m²_cathode/d (2 g/L_catholyte/d), an acetate titer of 15.6 g/L, and an H₂ uptake efficiency of 87%, which significantly exceeded the reported H₂-mediated MES reactors. In addition, the reactor size of 6 L was about 10 times larger than that of previously reported MES reactors. The results indicate that this reactor design is promising for large-scale MES applications.