Waste C1 Gases as Alternatives to Pure CO₂ Improved the Microbial Electrosynthesis of C4 and C6 Carboxylates

Abstract

Waste C1 gases as alternatives to pure CO2 can potentially facilitate the practical application of microbial electrosynthesis (MES) for chemical production and further decrease the total cost. This work evaluated the impact of the CO fraction on MES of C2–C6 carboxylates. Using the CO/CO2 mixture as the substrate in MES favors simultaneous acetogenesis, solventogenesis, and chain elongation. The test of CO-50% achieved the best performance of production of C4 and C6 carboxylates, of which the specificity based on the electron recovery was 43.11 ± 1.31% for acetate, 34.11 ± 0.11% for butyrate, and 15.41 ± 1.48% for caproate, while the lag phase was 32 days for butyrate and 44 days for caproate. However, the specificity observed with pure CO2 (CO-0% test) was 85.37 ± 3.24% for acetate, 10.68 ± 2.54% for butyrate, and 0% for caproate. The increase of CO fraction decreased the electron recovery to methane. Microbial diversity analysis demonstrated that the elevated CO fraction increased the relative abundance of Acetobacterium as well as Clostridium. This study proved that waste C1 gases as alternatives to pure CO2 could stimulate the generation of C4 and C6 carboxylates in MES.