Efficient caproate production from ethanol and acetate in open culture system through reinforcement of chain elongation process.

The open culture system exhibits several advantages in bioconversion of complex substrates into caproate, yet it is urgent to develop an advanced approach to overcome the low fermentative efficiency. In this study, three reinforcement techniques were employed to reinforce the chain elongation in the open culture system, including bioaugmentation, pretreatment of anaerobic sludge (AS) and addition of cell carrier. Results showed that the caproate production was improved to 48.9 mmol/L using bioaugmentation technology. With removal of methanogen by alkaline-thermal pretreatment, the caproate production increased to 94.8 mmol/L. The highest caproate production of 130.5 mmol/L was obtained with addition of cell carrier, which was explained by the formation of biofilm. The genus Clostridium_sensu_stricto capable of medium chain fatty acids production dominated the microbiome of the AS. This study provides an insight that efficient caproate production can be achieved in the open culture system by reinforcing the pathway of chain elongation. [Display omitted] • Caproate production was improved in the open culture system. • Acetate competition was reduced via eliminating acetoclastic methanogen. • The biofilm on the cell carrier reinforced the pathway of chain elongation. • The genus Clostridium_sensu_stricto dominated the microbiome of anaerobic sludge. [ABSTRACT FROM AUTHOR]