The key objective of this project was to develop treatment trains for groundwater impacted with per- and polyfluoroalkyl substance (PFAS). The treatment train consisted of ion exchange (IX) using novel resins coupled with sonochemical destruction of PFAS in waste regeneration brine. While this project focused on IX for removal of the main compounds of regulatory concern (perfluorooctanoic acid and perfluorooctanoic sulfonate), it also examined treatment of the broader range of PFAS (shorter- and longer-chain perfluoroalkyl acids and sulfonates) and precursors of these compounds (fluorotelomer sulfonates [FTS]).

The technical approach consisted of laboratory experiments to identify and test new IX resins combined with a small-scale field study to demonstrate the effectiveness of these resins for removal of a broad range of PFAS from groundwater relative to granular activated carbon (GAC). The sonochemical destruction of PFAS in anion exchange regeneration wastes (still bottoms), and the potential factors that could impact PFAS destruction (high chloride, high total organic carbon [TOC]), was examined. An Excel-based tool was also developed to provide guidance on which media, or combination of media, would be cost-effective for PFAS removal under various conditions. Application of the results of this research will ultimately bolster operational capabilities and warfighter preparedness by mitigating the impacts of these chemicals.

Among the media tested, the general performance observed was single use PFA694E > regenerable resins USA21107, A592E > F400 GAC. All media performed very well for PFAS removal, whereas removal of perfluoroalkyl carboxylic acids and FTS was inversely related to carbon chain length. Regeneration was only effective with inclusion of a co-solvent, and methanol at 70% (w:w) proved to be effective, without any impact on resin performance. PFAS in both simulated and actual regeneration still bottoms were effectively degraded sonochemically (1000 kHz @ 400 W), with high chloride enhancing, and high TOC inhibiting the PFAS degradation efficiency. TOC inhibition was partially mitigated by addition of caustic.

The main benefits of this project were:

1. The development and validation of efficient IX resins and resin systems for removing a broad range of PFAS and precursor compounds from groundwater.
2. The development and testing of resin regeneration wastes treatment approaches to destroy accumulated PFAS and precursors in regenerant waste.
3. Field pilot testing of the treatment train.
4. The preparation of a tool that provides technical and cost guidance for IX resin or GAC treatment based on a given site’s PFAS profile and groundwater chemistry. 

(Project Completion - 2024)