Occurrence and Fate of Ultrashort-Chain and Other Per- and Polyfluoroalkyl Substances (PFAS) in Wastewater Treatment Plants

To better understand the fate of per- and polyfluoroalkyl substances (PFAS) during conventional and advanced wastewater treatment, 42 PFAS (C3–C14 perfluorocarboxylic acids (PFCAs), C3–C10 perfluorosulfonic acids (PFSAs), per- and polyfluoroethers, and perfluoroalkyl acid (PFAA) precursors) were investigated through the treatment trains at two municipal wastewater treatment plants (WWTPs) using a targeted analysis, the total oxidizable precursor (TOP) assay, and the estimation of partitioning to sludge. Short-chain (C3–C7) PFAAs were found in higher concentrations in wastewater samples, while long-chain (≥C8) PFAAs dominated in sludge samples. PFAA concentrations were elevated by the wastewater treatment processes, particularly after biological treatment (191.3 and 185.1% increases of PFAAs at WWTP-A and B). After TOP oxidation, PFCAs, particularly short-chain ones, increased considerably (up to 311.4 and 409.3% increases of PFCAs at WWTP-A and B). The study results indicated that the transformation of precursors into shorter chain PFAAs by biological treatment and the partitioning of longer chain PFAS into sludge streams are key factors determining the fate of PFAS in WWTPs. With the increasing impact of short-chain PFAS over time, future research should focus on the evaluation of the fate and distribution of historical and emerging PFAS in WWTPs.