Key challenges to treating per- and polyfluoroalkyl substance (PFAS) impacted sites include the broad range of PFAS present, the presence of polyfluorinated precursors that transform into perfluoroalkyl acids (PFAAs), the recalcitrance of PFAAs, and the current lack of in situ approaches for implementing aggressive chemical treatment processes. As no single treatment technique can address all of these challenges, the objective of this project was to develop a set of combined in situ and ex situ treatment approaches for the efficient and effective treatment of PFAS-impacted groundwater through the evaluation of the feasibility and effectiveness of a range of treatment train approaches, cost drivers, and challenges for field-scale implementation.

The treatment train approach centered on a novel plasma PFAS destruction technology that includes (A) pre-treatment of PFAS and PFAA precursors in situ to eliminate or reduce PFAA source zones, and (B) pumping pre-treated groundwater for follow-on ex situ treatment. Options for in situ treatment include persulfate oxidation and oxygen addition by sparging. The ex situ treatment approaches for removal of PFAA, including perfluorooctanoic acid and perfluorooctanesulfonic acid, were direct plasma treatment of pumped groundwater and ion exchange (IX), including IX resin regeneration with plasma treatment of IX regenerant solution. Results were integrated from two sites to develop conceptual designs of viable treatment trains along with the identification of associated cost drivers, limitations, and challenges to field-scale implementation.

Schematic Diagram of the In Situ/Ex Situ Treatment Train

Precursor transformation was effective using persulfate and oxygen in batch tests and transport cells and was found to reduce PFAA source zones. IX regenerant solutions comprised of methanol and brine were explored, and regenerant solution performance was comparable between the solutions even in different resins. Plasma was successful in the treatment of PFAS in groundwater, pre-oxidized groundwater, and in concentrated IX regenerant solution, including PFAA precursors, long-chain, and short-chain compounds under optimized reactor conditions/configurations and under a broad range of groundwater conditions. The incorporation of plasma into treatment trains that include pre-oxidation and concentration by IX individually or combined is appropriate and effective. The conceptual designs enhanced understanding of approaches for and limitations to integrating various PFAS treatment methods.

The limitations of current PFAS treatment options, such as traditional sorbents, may be overcome by replacing or combining multiple technologies to obtain a more effective system that results in no waste product and can be implemented fully on site. This project assessed newly developed treatment methods and combinations for both treatment and implementation, resulting in a more protective and efficient treatment option. Implementation of this research holds profound implications for improving the management of PFAS, directly addressing mission readiness by safeguarding the health of the warfighter and communities. (Project Completion - 2023)

Singh, R. K., N. Multari, C. Nau-Hix, R. H. Anderson, S.D. Richardson, T.M. Holsen, and S.M Thagard. 2019. Rapid Removal of Poly- and Perfluorinated Compounds from Investigation-Derived Waste (IDW) in a Pilot-Scale Plasma Reactor. Environmental Science and Technology, 53(19): 11375-11382. doi.org/10.1021/acs.est.9b02964.

Shojaei, M., A. Joyce, P.L. Ferguson, and J. Guelfo. 2022. Novel Per- and Polyfluoroalkyl Substances in an Active-Use C6-based Aqueous Film Forming Foam. Journal of Hazardous Materials Letters, 3:100061. doi.org/10.1016/j.hazl.2022.100061.

Shojaei, M., N. Kumar, and J. Guelfo. 2022. An Integrated Approach for Improved Liquid Chromatography Mass Spectrometry Based Determinations of Total PFAS in AFFF and AFFF-impacted Soils. Environmental Science and Technology, 56(20):14517-14527. doi.org/10.1021/acs.est.2c05143.
 
Shojaei, M., N. Kumar, S. Chaobol, K. Wu, M. Crimi, and J. Guelfo. 2021. Enhanced Recovery of Per- and Polyfluoroalkyl Substances (PFASs) from Impacted Soils Using Heat Activated Persulfate. Environmental Science and Technology, 55(14):9805-9816. doi.org/10.1021/acs.est.0c08069.