Enhanced caproic acid production with crude glycerol of a biodiesel by-product by Caproiciproducens galactitolivorans

Abstract

The biological production of medium-chain carboxylic acids (MCCAs) by Caproiciproducens galactitolivorans during anaerobic fermentation using biodiesel-waste glycerol as a carbon source was investigated. Crude glycerol is a low-value by-product of the biodiesel production process and a convenient feedstock alternative for the carboxylate platform. Using glycerol as a carbon source would be a reasonable approach to improve a NADH-requiring metabolite caproid acid selectivity by increasing NADH availability. In this study, a well-known MCCAs-producing bacterium, Caproiciproducens galactitolivorans produced caproic acid as a major metabolic product of anaerobic fermentation with crude glycerol. To further enhance the production of caproic acid, also the addition of a non-ionic surfactant, Tween 80, was performed. As a result, 10 g/L of caproic acid production was obtained with 2% Tween 80 supplementation. The concentration of acetic acid and butyric acid were relatively low, and glycerol contributed to the enhancement of caproic acid production selectivity. Moreover, through the in-situ biphasic extractive fermentation, the highest production of 15 g/L and production rate was achieved with high selectivity.