PFOA Promoted Microbial-Derived Disinfection Byproduct Precursors in Aged Iron Pipes under Hydraulic Stagnation

oexistence of perfluorooctanoic acid (PFOA) and iron particles in drinking water distribution systems (DWDS) threatens water quality by mediating disinfection byproduct (DBP) formation. This study systematically investigated the regulatory effects and intrinsic mechanisms of PFOA on microbial-derived DBP precursors in aged iron pipes under hydraulic stagnation, with a specific focus on in-situ formed and pre-formed Fe-PFOA complexes under simulated drinking water conditions. Comparative analysis revealed that in-situ formed Fe-PFOA complexes induced by 100 ng/L PFOA (denoted as FP1) exhibited significantly larger particle sizes and higher turbidity compared to the PFOA-free pure iron particle control (Ctrl). After 20-day hydraulic stagnation, FP1 enhanced microbial abundance, elevated extracellular polymeric substance (EPS) protein proportions, and promoted trihalomethane (THM) and haloacetic acid (HAA) formation after chlorination (DBPs formed from the extracted EPS corresponded to ~19.4% to total THMs, triple that to HAAs). Spearman analysis identified Phreatobacter as a key mediator linking EPS proteins and THM formation. Mechanistically, Under hydraulic retention conditions, iron particles bound to PFOA triggered genus-level shifts in community structure, such as increased abundance of the genus Phreatobacter and decreased abundance of the genus Nevskia, accompanied by elevated levels of protein-based EPS. Phreatobacter may be involved in protein-based EPS-related processes and the formation of THM precursors.