Meta-omics analysis revealed structural and metabolic shifts of acidification communities after feeding with thermal hydrolysis pretreated food waste

In this study, a reduced total volatile fatty acid (VFA) yield (VFA/tCOD, P = .003) and accumulated fractions of butyric acid (BA) (BA/total VFA, P < 0.001) was observed after feeding the arrested anaerobic digestor with thermal hydrolysis pretreated food waste. Further analysis through meta-omics revealed a reduction in the diversity of acidification communities (Shannon index, P = .03), indicating a sterilization effect of THP on the indigenous microbes in the feedstock. Additionally, although both the community-level acidification genetic potential and transcriptional activities were reduced (DNA and mRNA RPKM log2 fold change = 1.77 and 0.11, respectively) after the inclusion of THP, the remaining microbial communities exhibited an elevated mRNA/DNA RPKM ratio in acidification-related genes, especially within the AA and BA metabolic networks. This suggested that the elevated BA fraction might stem from improved chain-elongation activities using AA as a precursor. Furthermore, the inclusion of THP in the feedstock changed the main functional microbial groups of BA production (via the gene crt-buk2) from Selenomonas and Bacteroides to Prevotella and Megasphaera. Overall, these results reveal a complex shift in the acidification community and provide new insights to evaluate THP technologies behind the formed black box of VFA production performance.