PFAS in Activated Sludge Wastewater Treatment: Process-Level Insights into Transformation and Removal

We analyzed 41 PFAS in wastewater and sludge from three municipal activated sludge wastewater treatment plants (WWTPs) in Iowa to characterize the occurrence and fate of PFAS across treatment processes. Minimum concentrations of untargeted perfluoroalkyl acid (PFAA) precursors were estimated using the total oxidizable precursor (TOP) assay, and perfluorooctanesulfonic acid (PFOS) isomer distributions were evaluated. Short-chain PFAS (e.g., perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA)) were more abundant than long-chain homologues in both wastewater and sludge matrices. Linear PFOS concentrations increased relative to branched PFOS concentrations following aeration, but they decreased more rapidly than those of branched isomers during secondary clarification. Aeration basin effluents exhibited the highest target PFAS concentrations, indicating precursor transformation during biological treatment, while subsequent declines after secondary clarification reflected partitioning to solids. These process-level patterns show that biological and physical processes exert opposing effects on target species abundance─enhancing precursor oxidation while simultaneously removing PFAS through solids separation. Accounting for both targeted PFAS and untargeted PFAA precursors, an average of 42 ± 29% of total PFAS were removed from the aqueous phase during wastewater treatment. Influent PFAS fingerprints and plant-specific operation governed effluent PFAS composition more strongly than did bulk wastewater characteristics.