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, chemical-free, advanced oxidation reduction process (AORP) that utilizes high energy electrons to create significant amounts of highly reactive free radicals. The research hypothesis was that eBeam technology can be used to degrade perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in IDW materials (soils and groundwater).
The specific objectives of this project were:
- To quantify the effectiveness of eBeam technology at breaking down PFOS in soil and water under controlled experimental conditions, and
- To characterize the effectiveness of eBeam at destructive treatment for a mixture of PFAS present in actual IDW samples collected from multiple sites.
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.
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.
The results support 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.