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Site investigations of per- and polyfluoroalkyl substance (PFAS)-impacted areas generate complex mixtures of investigation-derived waste (IDW), including many individual forms of PFAS, other co-occurring chemicals, and volatile organic compounds (VOCs). High energy electron beam (eBeam) technology is a high efficiency, flow-through, non-thermal, chemical free technology that utilizes electron accelerators to generate large numbers of highly energetic electrons. The eBeam technology involves both reduction and oxidation processes without the addition of any chemicals. Depending on the pH of the system, the process can be engineered to promote the formation of either hydroxyl radicals or hydrated electrons. These powerful oxidation-reduction reactions occur almost instantaneously and can be characterized as an advanced oxidation-reduction process (AORP).
In Phase I of this project, eBeam technology was implemented for the degradation of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in IDW materials (soils and groundwater) under laboratory conditions. In addition to evaluating the technical feasibility of eBeam technology, the project team also performed a preliminary economic feasibility analysis. While e-Beam technology demonstrated great promise for the degradation of PFOA and PFOS under laboratory conditions, there was a need to design, fabricate, and utilize continuous flow reactors to test this technology under quasi-realistic conditions. Laboratory experiments using a continuous eBeam test platform will yield high value information on the scaling up of the technology for field testing.
The overall goal of Phase II of this project is to test the implementation of a small-scale batch demonstration of eBeam technology for the breakdown of PFAS in 1 to 3 kg of IDW soil and spent adsorption media (e.g., granular activated carbon (GAC), resins) and in 1L of liquid media (IDW groundwater, still-bottom concentrates, firefighting training area (FFTA) pondwater). The specific objectives of this follow-on research project are to:
Phase I Project Summary
The project initially focused on demonstrating PFOS and PFOA breakdown in sand and distilled water spiked with defined concentrations of PFOS and PFOA. The spiked samples were exposed to defined eBeam doses under specific conditions and analyzed for PFOS and PFOA breakdown. Once doses above 500 kilogray (kGy) were found to achieve PFOS breakdown, the project team applied these treatment parameters on field IDW samples obtained from Pennsylvania (Willow Grove Naval Air Station Joint Reserve Base Willow Grove), and Michigan (Wurtsmith Airforce Base [AFB]). The project team designed special experimental vessels to deliver high doses (500 kGy- 2000 kGy) in batch conditions to Willow Grove groundwater and Wurtsmith soil samples. The pre-and post-eBeam exposed samples were analyzed using both an in-house analytical laboratory as well as the commercial SGS-AXYS laboratory using US Environmental Protection Agency Method 537 coupled with the Total Oxidizable Precursor (TOP) assay.
During Phase II of this study, Texas A&M will partner with the eBeam technology vendor Mevex Corporation and retrofit the existing Texas A&M University eBeam facility with the necessary accelerator upgrades and customized IDW soil and aqueous treatment pipes and vessels. The focus will be to demonstrate a small-scale batch treatment platform to treat PFAS-impacted IDW materials. The proposed small-scale treatment platform will include both an aqueous handling and soil handling systems. The eBeam dose and treatment conditions will be optimized to achieve complete degradation of PFOS and PFOA. The project team will assess the breakdown of shorter chain PFAS (e.g., PFHpA, and PFHxS) as well as short and long chain precursors such as 4:2 fluorotelomersulfonate (4:2 FTS) and 6:2 fluorotelomersulfonate (6:2 FTS), respectively. The treatment goal will be to remediate PFOS and PFOA below the EPA’s Risk Screening Level of 70 ng/L (combined or individually) for aqueous samples and EPA RSL of 130 μg/kg for soil samples which are referenced in the D policy statements. The influence of co-occurring chemicals such as chlorinated solvents and petroleum hydrocarbons on PFAS degradation will be assessed as part of these experiments. Finally, Texas A&M will utilize computer-aided approaches to design and cost-estimate a fixed eBeam technology platform suitable for demonstrating ex situ remediation of PFAS-impacted aqueous and solid IDW samples.
The key findings from Phase I are summarized as follows and are available in thePhase I Final Report.
A 2000 kGy dose reduced PFOS concentration in Wurtsmith AFB soils from 1738 ng/gm to 0.12 ng/g (dry weight basis), a >99.99% reduction. A 2000 kGy eBeam reduced PFOS concentration in Willow Grove groundwater from 3851 ng to 465.5 ng, an 87.91% reduction. The PFOA reduction in Wurtsmith AFB soils at 2000 kGy was 98.6% while in Willow Grove groundwater, PFOA reduction was 53.7%. PFCAs (PFBA, PFPeA, PFHXA, PFOA) and PFSAs (PFBS, PFHXS, PFOS and PFDS) concentrations decreased with increasing eBeam dose. The required dose can be brought down to 1500 kGy with appropriate optimization. An economic analysis of PFAS treatability using eBeam technology suggests it would cost approximately $295/m3 for a fixed eBeam treatment platform for reducing 98% of PFOA and 99.99% of PFOS using a target dose of 1500 kGy. These results highlight that eBeam technology has significant promise as a PFAS remediation technology for soils and aqueous samples; however, further optimization is needed.
Results of Phase I of this project supported further investment in laboratory research to optimize PFAS breakdown and necessary engineering design research to facilitate the installation of a prototype on-site eBeam treatment platform at the appropriate PFAS-impacted site to demonstrate field-scale remediation.
Phase II of this project will yield practical and field implementable information that DoD remedial project managers and environmental engineering consultancy firms can use for harnessing eBeam technology for ex situ remediation of PFAS-impacted IDW materials. Therefore, the major impact of this project will be DoD’s ability to include high-energy eBeam technology as part of its ex situ environmental remediation technology “toolbox”. (Anticipated Phase II Completion - 2025)