Selective enrichment of electrode-associated cells enhances CO2 conversion to acetate in microbial electrosynthesis cells

초록

Microbial Electrosynthesis (MES) converts CO2 into valuable products (e.g., acetate, volatile fatty acids, and CH4) through electron transfer facilitated by electroactive bacteria. Both electrode-attached and suspended cells can obtain reducing power from electron donors such as electrode and by-products (e.g., H2, formate) in MES. This study compared the performance of electrode-attached and suspended cells for acetate production. Potential application and periodic medium replacement at different rates were applied to enrich electrode-attached cells selectively. H2 and formate were each used as electron donors for suspended cells, and the addition amounts were pre-adjusted to ensure a constant cycle. As a result, the electrode-attached cells with 100% medium replacement achieved the highest acetate production (0.50 f 0.02 g/L/day) and Coulombic efficiency (86 f 3.4%), whereas 50% medium replacement with both electrode-attached and suspended cells was slightly lower (0.36 f 0.01 g/L/day, 77 f 2.1%). The formate-augmented and H2-augmented MES produced only 0.29 f 0.01 and 0.17 f 0.01 g/L/day of acetate, respectively. Field emission scanning electron microscopy revealed an aggregated electrode-attached biofilm and mediators supporting direct electron transfer. In separated cultures in serum bottles, electrode-attached cells showed higher protein content and specific acetate production rate, which were higher than those of suspended cells. A comparison of the performance of electrode-attached/suspended cells through selective enrichment suggested that the electron transfer of electrode-attached cells can improve the CO2 conversion and efficiency of MES.

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