Volatile fatty acids (VFAs) production from sludge and chicken manure anaerobic co-fermentation: Effects of mixing ratio and microbial mechanisms

Aimed at exploring the effects of co-fermentation with different dewatered sludge (DS) and chicken manure (CM) ratios on volatile fatty acid (VFA) production, five experimental groups with different DS/CM ratios were set up, the microbial community and the activity of functional enzymes were discussed in this study. The highest concentration of VFAs reached 153.74 mgCOD/gVSS at the ratio of 1:3, and dominated by acetic and propionic acids, which was 1.37 times higher than the control group. The addition of CM contributed to the accumulation of soluble chemical oxygen demand (sCOD) and promoted the release of NH4+-N and PO43--P. High-throughput sequencing results indicated that co-fermentation enriched hydrolytic and acidogenic bacteria to promote the hydrolysis and acidification processes and facilitated the accumulation of VFAs. Firmicutes were the dominant phylum in all experimental groups, and 1:3 ratio was more satisfied with acidogenic bacteria (such as Bacillus and Clostridium_sensu_stricto_1). Meanwhile, the abundances of glycolysis/gluconeogenesis, amino sugar, and nucleotide sugar metabolisms exceeded other groups. Furthermore, this condition exhibited the highest abundances of acetyltransferase [EC: 2.3.1.8] and acetate kinase [EC: 2.7.2.1], which were 2.71 and 1.66 times higher than that in the control group, respectively.