Juhe Liu, Edson Lopez, Joseph A. Charbonnet

Per- and polyfluoroalkyl substances (PFAS) are a class of widely used anthropogenic emerging contaminants which are linked to adverse human and ecosystem health. Their physicochemical properties make PFAS highly persistent and bioaccumulative in the environment. Wastewater treatment facilities (WWTFs) aggregate PFAS-containing waste streams including municipal sewage, industrial discharges, and firefighting wastewater. WWTFs then convey PFAS to the environment via effluent and biosolids. New federal and state-level regulations have focused many WWTFs on PFAS management. Conventional wastewater treatment processes cannot mineralize PFAS and PFAS behavior within these wastewater treatment processes is poorly characterized. In order to improve PFAS removal in WWTFs, more information is needed about how PFAS behave within wastewater treatment unit processes. This study investigates the fate and transport of PFAS, including perfluoroalkyl acid (PFAA) precursors, within six Iowa WWTFs. These WWTFs employ a range of biological and chemical treatment processes. Grab samples of aqueous and solid phases were collected from key operational stages within each WWTF from 2022 to 2023. These samples underwent solid phase extraction and analysis via liquid chromatography-tandem mass spectrometry (LC/MS-MS) to quantify 43 target PFAS in both wastewater and biosolids matrices. We estimated the PFAA precursor concentrations in the influent and effluent of wastewater unit processes total oxidizable precursor (TOP) assay. These data are combined with bulk water quality measurements, including the concentrations of nitrate, total Kjeldahl nitrogen, total phosphorous, and total organic carbon to determine how wastewater treatment processes influence the fate and transport of PFAS. Our results provide greater nuance about PFAS fate in distinct but geographically proximate wastewater systems than previously available. For example, a medium-sized WWTF (6.41 MGD flow rate) employing traditional activated sludge processes removed most influent target PFAS from the aqueous phase. Targeted PFAA precursors were converted to perfluorocarboxylic acids (PFCAs), but aqueous PFCA concentrations changed little due to their partitioning to biosolids. Conversely, a WWTF with comparable influent PFAS concentrations and a much lower flow rate (1.75 MGD) demonstrated markedly different trends. That WWTF, which employs biologically active membrane filtration, discharged much greater PFCA concentrations in its effluent than its influent, and failed to fully oxidize all targeted PFAA precursors. This research provides insights into the mechanisms by which precursor PFAS are transformed into the terminal PFAAs of greatest regulatory concern for WWTFs, and into the partition of PFAS to the biosolid or aqueous phases. Our results will provide a better understanding of the transformation from precursor PFAS to terminal PFAAs under different operational conditions and could improve PFAS removal by WWTFs. These results have implications for wastewater and solids management strategies, as PFAS are increasingly regulated.