Mechanistic insights into fermentative pathway control during solid-state food waste acidogenesis under autogenic...

The efficiency of two-phase anaerobic digestion hinges on the acidogenic phase, where acidogenic off-gas generates autogenic pressure that alters the physicochemical environment and may affect microbial activity, pathways, and intermediates. However, its mechanistic role under solid-state conditions remains unclear. To address this knowledge gaps, we investigated the effects of autogenic pressure on solid-state food waste acidogenesis, focusing on soluble microbial product (SMP) formation and the associated metabolic responses at the molecular level. Autogenic pressure enhanced acidogenic decomposition, increasing SMP yields from 365.3 ± 10.5 g COD/kg VS_added to 407.1 ± 7.3 g COD/kg VS_added. It initially promoted lactate production, followed by enhanced conversion of lactate to butyrate and acetate functioning by Megasphaera. Metagenomic and metabolite analyses revealed that autogenic pressure increased the abundance of functional genes associated with homoacetogenesis and butyrate synthesis. Incubation experiments further confirmed that acetate, stimulated by autogenic pressure, played a key role in driving the reverse β-oxidation pathway while suppressing the acrylate pathway during lactate conversion. As a result, butyrate production increased by 25 %, while propionate decreased by 43 %. These findings provide new insights into how SMP-producing microbial communities respond to autogenic pressure and demonstrate the potential of self-regulation to enhance product yield and process controllability. This strategy advances sustainable solid waste management and promotes the development of circular bioeconomy.