Sequential fermentation of food waste in an integrated system to improve n-caproate production

Abstract Biological production of n-caproate through chain elongation is economically attractive, yet its application is limited due to the low caproate production and high cost of substrates. In this study, caproate production from food waste (FW) was carried out in an integrated system using the biofilm of C. kluyveri. The biofilm formed onto the carrier exhibited a high stability and productivity of caproate. An average production of 14.8 g/L which was 70.0% of the theoretical production was obtained with biofilm recovery for seven successive batch tests. In contrast, a high caproate production of 18.5 g/L was obtained from the fed-batch fermentation, which accounted for 83.5% of the theoretical production and was ascribed to the alleviation of inhibitory effects of ethanol, acetate and undissociated caproic acid to cells, and high robustness of biofilm. Analysis of the Fourier transform infrared (FTIR) and X-ray diffraction (XRD) indicated that the structure of wheat straw tended to be more stable due to the increase of crystallinity. The mass balance revealed that the amount of caproate accounted for 2.6 wt% (on wet basis) of the FW hydrolysate. This study provides an alternative way for valorizing FW in the production of value-added chemicals.