EGCG-Enhanced Ferrous-Activated Peroxydisulfate Processes for Shigella flexneri Biofilm Inactivation: Efficacy, Underlying Mechanisms, and Practical Implications

Shigella flexneri (S. flexneri), as a common foodborne and waterborne pathogen, poses a serious health threat, with its biofilm formation significantly increasing disinfection difficulty. Ferrous-activated peroxydisulfate (Fe2+/PDS) is effective for pollutant removal but limited by unstable Fe2+. To address this issue, the present study developed an epigallocatechin gallate (EGCG)-enhanced Fe2+/PDS system for inactivating S. flexneri biofilms. The biofilm biomass and viability were assessed via crystal violet staining and CLSM. The results showed that comparable biomass reduction and inactivation was achieved with the EGCG-enhanced system at much lower iron loading. Mechanistic analysis revealed that compared with the original system, the EGCG-enhanced system maintained a higher effective Fe2+ concentration, likely contributing to a more stable Fe2+/Fe3+redox cycle. High-valent Fe species and multiple reactive oxygen species were also observed in the enhanced system which might contribute to the biomass reduction and inactivation. Compared with the Fe2+/PDS system, the EGCG-enhanced system developed in this work achieved a broader pH adaptability and stronger anti-interference capability in tap water, and exhibited lower biological toxicity. These findings provide new perspectives for green disinfection technologies and agricultural waste utilization.