Increased CODH activity in a bioelectrochemical system improves microbial electrosynthesis with CO

Biological CO conversion has attracted considerable interest because of the demand for syngas valorization and the simultaneous treatment of toxic components in industrial flue gases. The oxidation of CO can produce additional reducing equivalents in the form of electrons and protons by the water gas shift reaction (WGSR) via carbon monoxide dehydrogenase (CODH). Such reducing energy decreases the thermodynamic and kinetic barriers of the bioconversion of gaseous carbon and increases the product yield. This study examined the effects of yeast extract, leading to increased CODH activity, on electrosynthesis with CO in an electrode-assisted bioelectrochemical system. The specific CODH activity was significantly higher (90.2 ± 2.6 nmol mg-1 min-1) when the yeast extract was added compared to electrosynthesis without the yeast extract (11.8 ± 1.1 nmol mg-1 min-1). After 483 h, the levels of acetate and volatile fatty acids (VFAs) were 3.5 and 0.8 g L-1, respectively, when the CODH activity was higher, but only 1.3 and 0.2 g L-1, respectively, in cultures with lower CODH activity. The maximum coulombic efficiency of electrosynthesis with CO was two times higher than the conventional electrosynthesis using CO2 with higher CODH activity, whereas it was only half with lower CODH activity. The results show that an increase in CODH activity can be an efficient approach to enhance the electrosynthesis of CO.