Reduction short-chain volatile fatty acids and CO2 into alcohols in microbial electrosynthesis system

Microbial electrosynthesis system (MES) is an attractive strategy for converting CO₂ into value-added chemicals and biofuels. In this work, it is for the first time demonstrates the feasibility of producing biofuels (eg., ethanol and butanol) from CO₂ and volatile fatty acids (eg. acetic acid and butyric acid) by utilizing Clostridium ljungdahlii ERI-2 as biocatalyst in MES. The highest ethanol and butanol concentration of 12.52 ± 0.57 and 5.85 ± 0.78 mM are obtained at −0.9 V (vs Ag/AgCl) cathode potential, respectively. Furthermore, the trace elements content in growing medium is optimized to improve the production rate of ethanol from acetic acid/CO₂ and butanol from butyric acid/CO₂. Adding suitable Ni²⁺ and WO₄²⁻ in the growing medium resulted in the maximum ethanol and butanol production can be increased 43.3 ± 3.2 % and 32.1 ± 3.5 %, respectively. The analysis of redox cofactor concentration indicates that the NADH is the main reducing force for the improvement of alcohols production. Based on these results, strategies for further improvement of CO₂ to alcohols conversion can be formulated.