Quercetin impairs biofilm electron transfer to simultaneously suppress H₂S and CH₄ in sewers

The synergistic emission of H 2 S and CH 4 in urban sewage networks has become a major environmental challenge that requires urgent solutions. Traditional chemical control methods are characterized by low specificity and are ineffective in disrupting the intrinsic microbial syntrophic relationships. In this study, a novel anti-electro-syntrophy strategy was developed through the exogenous addition of the natural flavonoid quercetin, which impaired the biofilm electron-transfer capacity and reduced the emission of both gases. This proposed strategy was validated using a laboratory-scale sewage network simulation system. The results showed that the presence of quercetin significantly suppressed the production of both H 2 S (70.9%) and CH 4 (45.8%). Under high-dose and prolonged exposure, electrochemical analysis of the reactor effluent revealed a decline in overall electrochemical activity, as indicated by decreased redox peak currents and exchange current densities, which is consistent with impaired electron-transfer performance. Metagenomic analysis revealed that quercetin significantly downregulated key genes associated with electron transfer and redox-carrier synthesis, including sulfur-metabolism pathways (e.g., PWY66-426) and TCA-related pathways; this is consistent with impaired electron supply to sulfate-reducing bacteria and methanogenic archaea, although direct methanogenic pathway genes were not detected and the CH₄ inhibition mechanism requires further verification. Overall, quercetin was confirmed as an efficient bifunctional inhibitor. This study provides theoretical references and a green solution for gas control in sewers.