Inhibition of acetogenesis and methanogenesis by inoculating successively ammonia nitrogen-inhibited anaerobic fermentation residues for rapid-efficient propionate accumulation.

High-value compound propionate cannot be directionally accumulated in conventional anaerobic fermentation (AF). In this study, AF residuals containing 5965.5 mg/L total ammonia nitrogen concentration were used as inoculum periodically to inhibit acetate and CH4 production, driving the propionate proportion in volatile fatty acids (VFA) to increase by 4.7 times. In terms of mechanism, AF residuals induced the synergistic enrichment of hydrolytic strain DMER64 sp. and acidogenic strains unclassified_DTU029 and UBA7960 sp., which degraded substrates via hydrolytic genes bglB and abfA. Suppression of pyruvate pathways disrupted acetogenesis, redirecting degraded organics to the enhanced propionate synthesis pathway. Despite dominant archaeal communities of Methanosarcina mazei and Methanoculleus thermophilus, hydrogenotrophic and acetoclastic methanogenesis were limited by inhibited [FeFe] hydrogenase and downregulated coenzyme F420 activity. Importantly, this study holds a profit potential (116.1 USD), and machine learning models accurately predict large-scale VFA yields. This study provides an innovative strategy for the efficient recovery of propionate.