With the recent release of the U.S. EPA’s drinking water health advisory for PFOA and PFOS of 70 parts per trillion (ppt), the DoD has an urgent need for effective remedies to treat groundwater impacted primarily by aqueous film forming foam (AFFF) releases. Key challenges to treating per- and polyfluoroalkyl substance (PFAS)-impacted sites include (1) the broad range of PFAS typically present; (2) the common presence of polyfluorinated precursors that can transform into perfluoroalkyl acids (PFAAs) such as PFOA and PFOS by natural or anthropogenic biological or chemical processes, serving as a long-term source of these compounds in groundwater; (3) the recalcitrance of PFAAs, particularly perfluoroalkyl sulfonates such as PFOS that can only be destroyed by very aggressive chemical treatment processes; and (4) the current lack of in situ approaches for implementing aggressive chemical treatment processes. Because no single treatment technique can address all of these challenges, treatment train approaches are necessary that address precursors, implement efficient and cost-effective ex situ treatment, and ultimately result in chemical destruction.
The objective of this project is to develop a set of combined in situ/ex situ treatment approaches for efficient and effective treatment of PFAS-impacted groundwater. The research team will evaluate the feasibility and effectiveness of a range of treatment train approaches, and estimate and compare the scaled-up cost and design challenges for implementation.
The general treatment train approach centers around a novel plasma PFAS destruction technology and includes (A) pre-treatment of PFAS and their 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 that will be evaluated include persulfate oxidation and oxygen addition by sparging or slow-release amendment. The ex situ treatment approaches that will be evaluated for removal of PFAAs, including PFOA and PFOS, are direct plasma treatment of pumped groundwater and ion exchange (IX). IX will incorporate IX resin regeneration, with plasma treatment of IX regenerant solution. These approaches in combination can result in a protective remediation approach that can be implemented fully on-site. The holistic approach seeks to manage the challenge of PFAS precursors, to efficiently separate PFAS from groundwater using media that can be regenerated and reused, and to ultimately destroy PFAS on site.
Each major component of the treatment train will be investigated in terms of effectiveness, rate, and efficiency under a range of treatment conditions including the presence of common PFAS site co-occurring contaminants. In situ oxidation experiments will vary oxidation approaches, including aggressive chemical oxidation, oxygen sparging, and slow release oxidant infusion; oxidant dose; and treatment time in batch tests. Evaluation of the impact of these treatment approaches on post-treatment PFAS mass flux will then be evaluated in treatment cells.
IX has been proven effective for removing PFAAs from water sources; this research will focus on resin regeneration and optimization of the regenerant solution for maximum treatment, recovery, and reuse. Destructive treatment of PFAS including PFOA and PFOS using plasma has been demonstrated; this project focuses on optimizing treatment conditions for a range of site conditions, as well as on treatment of post-oxidation groundwater and treatment of IX regenerant solution residue containing concentrated PFAAs. Research results will be integrated to determine viable combinations of these approaches. Conceptual designs of viable treatment trains will be prepared for up to three sites based on research results with the goal of identifying any limitations and challenges to cost-effective implementation.
Discovering and demonstrating an effective and efficient treatment approach for PFAS is essential. The limitations of current treatment options, such as granular activated carbon (GAC), may be overcome by replacing the technologies or by combining multiple technologies to obtain a more cost-effective overall treatment system that results in no waste product and which can be implemented fully on site. This project will assess newly developed treatment methods and combinations for both treatment and cost effectiveness, which will result in a more protective and efficient treatment option for the DoD. (Anticipated Project Completion - 2021)