Integrating Syngas Fermentation into a Single-Cell Microbial Electrosynthesis (MES) Reactor

This study presents a series of experiments to test the integration of syngas fermentation into a single-cell microbial electrosynthesis (MES) process. Minimal gas–liquid mass transfer is the primary bottleneck in such gas-fermentation processes. Therefore, we hypothesized that MES integration could trigger the thermodynamic barrier, resulting in higher gas–liquid mass transfer and product-formation rates. The study was performed in three different phases as batch experiments. The first phase dealt with mixed-culture fermentation at 1 bar H2 headspace pressure. During the second phase, surface electrodes were integrated into the fermentation medium, and investigations were performed in open-circuit mode. In the third phase, the electrodes were poised with a voltage, and the second phase was extended in closed-circuit mode. Phase 2 demonstrated three times the gas consumption (1021 mmol) and 63% more production of acetic acid (60 mmol/L) than Phase 1. However, Phase 3 failed; at –0.8 V, acetic acid was oxidized to yield hydrogen gas in the headspace.