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

Abstract

<p>The microbial electrosynthesis (MES) system has the potential to convert carbon dioxide (CO2) 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 % CO2 gas and an initial bicarbonate concentration of 167 mg-C/L. R2 and R3 were continuously fed with an N2-based gas containing 20 % CO2, 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/(m²·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 CO2 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 CO2 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.</p>