Carbon‑sulfur metabolic shift in sludge anaerobic digestion system induced by bisphenol S: Interfacial behavior and microbial network restructuring.

The traditional assessment of contaminants' effects on sludge anaerobic digestion system usually concentrates on single endpoint such as methane and ignores the broader metabolic trade-off. This study shows how bisphenol S (BPS), which is largely used instead of other similar chemicals that have been restricted, drives a systematic carbon-sulfur metabolic shift during sludge anaerobic digestion, as systematically investigated through both complementary batch assays and long-term operations. The results showed that BPS has a concentration-dependent, hormetic effect on methanogenesis, with a 7.48% increase at 50 mg/kg TSS and 12.0% inhibition at 200 mg/kg TSS. In contrast, H2S production increased steadily (up to 34.5% at 200 mg/kg TSS), indicating a redirection of microbial electron flow. Mechanism analysis showed that BPS underwent rapid, chemisorption‑dominated adsorption (pseudosecond-order rate constant: 0.748 g/(mg·min), equilibrium capacity: 1.35 ± 0.08 mg/g), interacted with and altered cell membrane, and strongly bonded with the antioxidant enzyme (revealed via molecular docking, -8.55 kcal/mol), collectively triggering reactive oxygen species (ROS) generation and accumulation (quantified via specific fluorescent assays). This selection pressure promoted the growth of oxidation-tolerant sulfate-reducing bacteria (SRBs) and organic degraders over sensitive methanogens, leading the community assembly process to become more deterministic. Importantly, co-occurrence network analysis revealed that BPS exposure changed the topological keystone taxa, increasing the number of connectors with SRBs (such as Desulfovibrio) and protein/amino acid degraders (such as Proteiniclasticum), and module hubs moving towards short chain fatty acid producers. This restructure created better ecological links that directly helped with the transfer of electrons towards sulfidogenesis.