Bio-electroreduction of CO2 to acetate: Impact of the inorganic carbon feeding regime on microbial electrosynthesis

The microbial electrosynthesis (MES) system has the potential to convert carbon dioxide (CO 2 ) to organic commodities for carbon neutrality . In this study, the effect of the inorganic carbon feeding regime on the MES reactors was investigated using three different reactors. R1 was continuously fed with 100 % CO 2 gas and an initial bicarbonate concentration of 167 mg-C/L. R2 and R3 were continuously fed with an N 2 -based gas containing 20 % CO 2 , along with initial bicarbonate concentrations of 167 mg-C/L and 667 mg-C/L, respectively. The results showed that R1 exhibited the highest acetate production at an average rate of 15.3 g/(m 2 ·d), while R2 and R3 had no sign of acetate accumulation. Moreover, the cathodic biofilms demonstrated a more significant contribution to MES performance than suspended biomass. These indicated that gaseous CO 2 was much preferred over bicarbonate in the MES system, since the former had a stronger affinity to biofilm cells. In addition, the acetogen Acetobacterium wieringae was significantly enriched in the cathodic biofilm of R1 (53.2 %), while acetate-consuming bacteria Mesotoga was enriched in R2 and R3 (12.1–12.2 %), suggesting higher CO 2 partial pressure could inhibit acetate oxidation . Overall, this study highlights the importance of optimizing inorganic carbon supplying strategies for the successful operation of MES systems. • Three MES reactors were operated with different inorganic carbon feeding regimes. • Gaseous CO 2 was preferred than bicarbonate due to stronger affinity to biofilm cells. • Acetobacterium wieringae was enriched under higher level of gaseous CO 2 supply. • Cathodic biofilms contributed more to the MES activity than the suspended biomass.