This project aims to develop a novel in situ groundwater remediation strategy that uses a highly reactive, ligand-coordinated, zero-valent metal, embedded into a colloidal activated carbon support, to reductively degrade per- and polyfluoroalkyl substances (PFAS) in the subsurface environment. This strategy will substantially reduce the energy consumption by ex situ pump-and-treat, and represent a major step forward in creating a reactive particulate carbon amendment (rPCA) for PFAS. The method is most active toward long-chain PFAS and their precursors. The promise of this project is supported by the recent discovery that ligand-coordinated zero-valent zinc powders rapidly degrade long-chain and non-branched perfluoroalkyl carboxylic acids and perfluorosulfonic acids for up to 60% of defluorination.

The approach combines fundamental laboratory work to identify the most active ligand-coordinated zero-valent metal (L-M⁰) for PFAS destruction, immobilization of the L-M⁰ on a practically useful support, batch and column testing, and a limited-scope in situ field test to explore the longevity of PFAS destruction activity. Work thus far has focused on Zn⁰, but it is hypothesized other low redox potential metals will be similarly or more active. Therefore, the project team will first screen and compare five low-cost and environmentally benign metals with low standard redox potentials (Mg⁰ −2.37V, Al⁰ −1.66V, Ti⁰ −1.63V, Zn⁰ −0.76V, and Fe⁰ −0.44V). Also, the project team will use several common L families to create L-M⁰ systems, such as N,N-bidentate1 (e.g., R₂bpy, R=various electron-donating and withdrawing groups), that have been shown to alter the electronic structure and activity of M⁰. Structure-activity relationships will be developed from the results to identify the most promising L-M⁰ systems, and these will be fine tuned by altering metal particle size and surface chemistry. Reaction mechanisms will also be explored to improve L-M⁰ design. The most promising L-M⁰ systems will be impregnated into a colloidal activated carbon (CAC) support to create a rPCA with the goal of enhancing PFAS sorption and residence times for enhanced reaction, and corresponding PFAS destruction rates will be tested in batch for a variety of water quality conditions. PFAS destruction rates will then be tested under the most relevant groundwater quality conditions in laboratory column experiments to evaluate the combined effects of mass transport and reaction, and in a single down-well column experiment that circulates well water at Naval Air Station Jacksonville through the column for PFAS destruction for several months. A model will be developed to simulate the batch and column experiments and extend the results to larger scales.

This research will lead to highly active L-M⁰-CAC materials that can be directly injected into impacted aquifers as a rPCA and will act as both a sorption and reaction barrier, thereby destroying PFAS and mitigating the risk that PFAS will breakthrough the PCA zone. The new technology has the potential to substantially reduce the energy consumption by ex situ pump-and-treat. In particular, the method is most active toward destruction of long-chain PFAS and their precursors. Successful implementation of this research holds profound implications for improving the DoD's management of PFAS, directly addressing mission readiness by safeguarding the health of the warfighter and their communities. (Anticipated Project Completion - 2027)