Promoting chain elongation efficiency from food waste by refluxing chain elongation fermentation liquid

Food waste fermentation can produce medium chain fatty acids (MCFAs) through chain elongation, but n-butyric acid normally accounts for the largest proportion of products. In order to fully utilize these n-butyric acid to produce MCFAs, reflux was carried out and five reflux ratios were studied. Results showed that reflux effectively alleviated the inhibitory effect of undissociated n-butyric acid and enhanced the production of MCFAs, the optimum reflux ratio was 100%, n-caproic acid production increased by 707.43 ± 39.54 mg COD/g VS, which was 4.17 times higher than the control without reflux. Reflux can also promote the production of n-valeric acid and heptylic acid. The kinetic analysis also confirmed that 100% was the optimum reflux ratio for improving MCFA production, and the carbon proportion and electron transfer efficiency of n-caproic acid were 45.40% and 85.50% respectively. By refluxing, the microbiomes related to the MCFA production were further enriched. Mass balance analysis of n-caproic acid showed that 100% reflux ratio resulted in a production of n-caproic acid from 88.57 to 152.57 g/kg dry food waste. This study offers a new direction for efficiently utilizing the food waste and a new perspective for improving the production of MCFAs. [Display omitted] •Reflux made use of n-butyric acid in chain elongation liquid for MCFA production.•Reflux alleviated the inhibitory effect of undissociated n-butyric acid.•100% reflux increased production of n-caproic acid by 4.17 times.•Microbiomes related to MCFA production were enriched by reflux.