Enhanced volatile fatty acids production from Chinese cabbage waste by pretreatment

Effects of cellulase pretreatment, thermal pretreatment, and a combined cellulase–thermal pretreatment on the anaerobic fermentation performance of Chinese cabbage waste (CCW) were investigated. The combined pretreatment enhanced the structure loosenness and porosity of CCW, resulting in a 10.2 % increase in the hydrolysis rate and a 7.4 % increase in reducing sugar content. In this group, acid productivity and caproic acid yields were 0.57 g VFA/g VS and 7351 mg COD/L, respectively, which were 18.1 % and 30 % higher than those in the control group. Cellulase pretreatment significantly enhanced the butyrate production, which was consistent with the higher Clostridium spp. abundance observed in this group. Although thermal pretreatment significantly enhanced the release of soluble chemical oxygen demand (SCOD), resulting in substantial increases of 38.7 % in acetic acid and 73.8 % in propionic acid production, respectively, it did not improve the total volatile fatty acids (VFAs) yield. Lactobacillus and Weissella were selectively enriched in this group, leading to lactic acid accumulation during the initial fermentation stage and a high yield of propionic acid in the later stages. In the cellulase-thermal pretreatment group, the relative abundance of Prevotella increased to 20.70 %. This major rumen bacterium can degrade polysaccharides in plant cell walls, thereby facilitating carboxylic acid production.