Selective Enrichment of Electrode-Associated Cell Enhances Co2 Conversion to Acetate in Microbial Electrosynthesis Cell

Abstract

Microbial electrosynthesis (MES) converts CO2 into valuable products (e.g., acetate, volatile fatty acids, and CH4) through electron transfer by electroactive bacteria. Each cell of different distributions is known to obtain reducing power from different electron donors such as electrodes and by-products (e.g. H2, formate) in MES. This study compared the acetate productivity of electrode-attached cells, which mainly perform direct electron transfer (DET), and suspended cells, which perform indirect electron transfer (IET) in MES. The periodical medium replacement allows the selective enrichment of electrode-associated EAB, which facilitates DET-driven MES of CO2. Whole medium replacement achieved the highest acetate production (0.50 ± 0.02 g/L/day) and Coulombic efficiency (86 ± 3.4%), whereas 50% medium replacement resulted in slightly lower acetate production and Coulombic efficiency (0.36 ± 0.01 g/L/day, 77 ± 2.1%). The formate-augmented and H2-augmented MES only produced 0.29 ± 0.01 and 0.17 ± 0.01 g/L/day of acetate. Field emission scanning electron microscopy revealed an aggregated electrode-attached biofilm in DET-driven MES. A separate culture of electrode-attached cells in the serum bottle exhibited a higher protein content and specific acetate production rate than those of the suspended cell inoculated culture. This study examined the acetate production performance of electrode-attached/suspended cells under different culture conditions in MES, showing that DET might improve the productivity and efficiency of CO2 conversion.

Keywords: Microbial electrosynthesis, Acetate production, Electron transfer mechanism, Electrode-attached cell