Zihao Gao, Haoru Hou, Lin Xiao
Food waste (FW) anaerobic digestion (AD) is strongly affected by feedstock heterogeneity, yet the role of sulfur-rich vegetable fractions remains poorly defined. Here, garlic (GAR), Chinese cabbage (CHC), and cabbage (CAB) were used as representative sulfur-rich vegetables to assess their effects on methane production, redox status, and microbial function during FW AD. At equal volatile solids loading, GAR showed no significant effect, whereas CHC and CAB caused a biphasic response, with delayed methane accumulation and reduced cumulative yield followed by late-stage daily methane production 39.6% and 45.9% higher than the control, respectively. CHC and CAB promoted sulfide accumulation and elevated reactive oxygen species (ROS) during the early stage. Elevated ROS levels were associated with lower NADH/NAD+ ratios, reduced electron transport activity, and volatile fatty acid accumulation, collectively indicating a redox-perturbed state characterized by functional decoupling between acidogenesis and methanogenesis. Metagenomic analysis showed that this early disturbance was followed by functional reassembly of the community. Hydrolytic-acidogenic bacteria sustained fermentation, accompanied by enrichment of genes associated with PFOR-Rnf-mediated energy conservation and the ED and oxidative PPP pathways, while methanogenesis shifted toward acetoclastic and methylotrophic routes. Genome-resolved analysis attributed the genomic potential for PFOR-Rnf-mediated energy conservation to Aminobacterium and Defluviitoga MAGs, and showed that Methanosarcina possessed the broadest oxidative stress defense repertoire, supporting its dominance after ROS perturbation. These findings provide a mechanistic framework linking sulfur-rich feedstock heterogeneity to methane-production dynamics, involving sulfide-associated redox perturbation and subsequent microbial functional reassembly.