Anaerobic fermentation of watermelon waste juice for volatile fatty acids production: performance and microbial community

In this study, the potential of the material phase (watermelon waste juice (WWJ), watermelon waste residue (WWR), and watermelon waste (WW)) for the production of volatile fatty acids (VFAs) was discussed in order to improve fermentation efficiency and reduce fermentation time. In addition, the effects of inoculum level, initial pH, temperature and sodium 2-bromoethanesulfonate (BES), and reflux inoculum on the yield of VFAs and the evolution of the microbial community structure were also investigated. The results showed that the inoculum facilitated the fermentation, while inappropriate pH and temperature affected the production of VFAs. The maximum yield of VFAs produced by fermentation with WWJ as substrate was 149.34 mg COD/g VS, which was 2.20 and 1.69 times higher than that of WWR and WW, respectively, and the main product was acetate. The reflux inoculum could further increase the yield of VFAs by 30.01% to 194.98 mg COD/g VS, and the time to reach the maximum yield was also advanced by 1 day. Microbial analysis showed that Firmicutes and Lactobacillus were the major phylum and genus, both of which were positively associated with VFAs yield. This work provides a reliable pathway for watermelon rind resource utilization.