Comparative Analysis of Influent and Effluent Measurements of PFAS at Wastewater Treatment Facilities

Per- and polyfluoroalkyl substances (PFAS) are infamous for their persistence as emerging environmental contaminants. While new treatment technologies are evolving to reduce PFAS at known sites of environmental contamination, the efficacy of traditional wastewater treatment plants (WWTPs) to reduce the suite of PFAS congeners is relatively unknown. The present research used a mass balance approach to assess the apparent removal efficiency of PFAS at a major regional wastewater treatment facility in the Great Lakes region. Since the sewer sheds for this facility are primarily combined, the sampling and analysis considered both dry- and wet-weather events. Samples of influent and effluent were collected and analyzed using solid phase extraction and ultrahigh performance liquid chromatography-tandem mass spectrometry. A significant feature of the present research is the comparison of removal characteristics observed at this facility with those presented in previous studies for the most common PFAS compounds found in domestic wastewater, i.e., perfluorooctanoic acid, perfluorooctane sulfonic acid, perfluorohexane sulfonic acid, perfluorohexanoic acid, perfluorononanoic acid, 6∶2 fluorotelomer sulfonic acid, and perfluorobutane sulfonic acid. The comparison uses the apparent removal efficiency (ARE), which represents the difference between influent and effluent mass divided by the influent mass. While most all the examined WWTPs display a negative apparent removal efficiency for each congener (effluent mass exceeds the measured influent mass of the particular congener), the urban WWTP of the present study has a more positive removal profile. This research provides potential explanations for the measured AREs while noting that the complexity of PFAS transformations as well as the large number of known congeners make current approaches of estimating removal efficiency fraught with errors.