Efficient production of medium chain fatty acids in microbial electrosynthesis with simultaneous bio-utilization of carbon dioxide and ethanol

Microbial electrosynthesis (MES) is a promising technology for chemicals production driven by renewable en-ergy. However, how the medium chain fatty acids (MCFAs) production in MES is affected by the method of chain elongation is not clear, and no direct evidence is provided yet for a simultaneous bio-utilization of CO2 and ethanol. In this study, different methods of chain elongation in MES reactors were investigated. During in-situ chain elongation, a maximum caproate concentration of 11.9 +/- 0.6 g L-1 was achieved, while the C6 specificity (56.4% +/- 0.5%) was much lower than that of ex-situ chain elongation (78.7% +/- 1.5%). Carbon distribution and reduction degree balance indicated a simultaneous bio-utilization of CO2 and ethanol, and it was validated by the isotope tracer technique. MCFAs-forming microbes, acetogens, and electrochemically active microorganisms were enriched. This study provides fundamental insights relevant to the carbon and electron fluxes driven by electricity.