Conversion of liquor brewing wastewater into medium chain fatty acids by microbial electrosynthesis: Effect of cathode potential and CO2 supply

Abstract

Chinese liquor brewing wastewater (CLBW) is rich in ethanol and lactate, but the high extraction cost limits the recovery of carbon resources. In this study, microbial electrosynthesis (MES) was used to upgrade CLBW to biofuels such as medium chain fatty acids (MCFAs), and the effect of different cathode potentials and CO2 supply on the MES production performance was investigated. The results showed that CLBW could be upgraded to the highest caproate concentration and selectivity of 7.98 g/L and 47.10% under −1.0 V/CO2 condition, which were 32.6% and 31.9% higher than the control group. The further decrease of the cathode potential led to the deterioration of MCFAs production performance. Electron donor metabolic analysis showed that −1.0 V promoted the conversion of electron donors to caproate. The superiority of −1.0 V/CO2 condition was further confirmed by pH analysis, the weakly basic pH avoided the toxicity of undissociated carboxylic acids. Electrochemical analysis also indicated that stronger electron transfer ability and higher electrochemical activity occurred at −1.0 V/CO2 condition. The results of microbial diversity analysis showed that Clostridium sensu stricto 12 and Eubacterium would be enriched under −1.0 V/CO2 condition. In addition, co-electron donors in CLBW could effectively avoid the competing acrylate pathway. This study provides a new pathway for MCFAs production.