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Fate, Transport, and Transformation of Per- and Poly-Fluorinated Substances (PFAS) in Wastewater Treatment Plants
Citation:
Modiri, M., B. Crone, P. Potter, AND Marc C. Mills. Fate, Transport, and Transformation of Per- and Poly-Fluorinated Substances (PFAS) in Wastewater Treatment Plants. 6th International Symposium on Bioremediation and Sustainable Environmental Technologies, Austin, TX, May 08 - 11, 2023.
Impact/Purpose:
Per- and Polyfluoroalkyl substances (PFAS), also known as “forever chemical” are a complex group of recalcitrant chemicals that are ingredients in a variety of applications such as AFFF firefighting foam and consumer products. Some PFAS have been found to be harmful to human health and the environment. The objective of this study is to assess spatial and temporal variability of PFAS in WWTPs and evaluate potential transformation and/or biotransformation of PFAS in these systems. Initial data indicated that for most of the WWTPs studied here, the measured PFAS mass increased in effluent compared to influent which was attributed to potential PFAA/intermediate generation from precursors though different treatment processes including biological nutrient removal systems or wet oxidation processes. The results of this study will provide details on the fate and transport of PFAS in a WWTP and may lead to more effective risk management for contaminated sources. The results of this study may be of interest to EPA Program Offices, Wastewater Treatment Utilities, and communities impacted by PFAS.
Description:
Per- and Polyfluoroalkyl substances (PFAS), also known as “forever chemical” are a complex group of over 4800 manufactured chemicals that are ingredients in various everyday products. The wide-spread use of PFAS in different applications ranging from non-stick surfaces to aqueous film forming foams (AFFFs) for firefighting and their persistence in the environment have resulted in PFAS detections in the influent, effluent, and sludge and biosolids of many wastewaters treatment plants. Poly-fluorinated PFAS that can degrade to generate perfluoroalkyl acids (PFAAs), known as stable end-metabolites, are referred to as precursors. Precursors in WWTP sewage can be converted into PFAAs or other intermediates through the wastewater treatment processes such as biological treatments. As a result, the concentrations/masses of PFAAs and/or intermediates can increase from influent to effluent. Understanding the prevalence of these precursor compounds provides a basis for understanding PFAS fate in WWTPs. However, the analytical standards are limited to < 100 PFAS compounds limiting the quantification of most of the PFAS compounds including precursors. Therefore, closing the PFAS/organofluorine mass balance in such systems remains a challenge. The objective of this study is to assess spatial and temporal variability of PFAS in WWTPs and evaluate potential transformation and/or biotransformation of PFAS in these systems. As part of an Environmental Protection Agency (EPA) study, we evaluated the spatial and temporal variability of PFAS in six different WWTPs. PFAS analysis include but not limited to EPA-1633 draft method, total organic fluorine (TOF) and total oxidizable precursors (TOP) assay. More specifically, the main activities of this study were to 1) collect biweekly samples of up to 16 locations in WWTPs to understand the spatial variability of PFAS in these systems, 2) perform intensive sampling including daily sampling and 8 hour sampling periods to better assess the temporal variability, 3) conduct a comprehensive data interpretation and analysis to evaluate the potential precursor degradation occurring in different treatment processes including any biological or oxidation processes, 4) integrate the flowrates and solids loading rates into PFAS analysis to assess the mass transport of PFAS in these systems, 5) perform additional PFAS analysis including TOF and TOP assay to assess the organofluorine mass balances, and 6) to make recommendations for possible PFAS removal from different streams especially recycling flows in WWTPs. Initial data indicated that for most of the WWTPs studied here, the measured PFAS mass increased in effluent compared to influent which was attributed to potential PFAA/intermediate generation from precursors though different treatment processes including biological nutrient removal systems or wet oxidation processes. Although the study is still going on, our initial hypothesis for candidate precursors is polyfluoroalkyl phosphate monoesters (PAPs) and polyfluoroalkyl phosphate diesters (diPAPs) which have been documented in WWTP samples at much higher concentrations than commonly measured PFAS and they have been shown to biodegrade to PFAAs. We will test this hypothesis by measuring these compounds in WWTP samples. Additional results showed that the high concentration of oxidizable organic matter in these samples resulted in incomplete oxidation of PFAA precursors in TOP assay leading to underestimation of precursors mass in WWTPs when compared to total organofluorine data. In addition, for some WWTPs, high non-PFAS organic fluorine sources resulted in high total adsorbable organic fluorine (typically performed on liquids) leading to a challenge in assessing PFAS associate organic fluorine while extractable organofluorine (typically performed on solids) provided more promising results given the selectivity of the extraction method for PFAS compared to other organofluorine compounds such as pharmaceuticals.