This proof-of-concept project will investigate a low-temperature per- and polyfluoroalkyl substances (PFAS) extraction from sorbent media by modified supercritical CO₂ (scCO₂) extraction. Building on the preliminary proof-of-concept experiments, the overarching objective is to demonstrate supercritical fluid extraction regeneration of spent sorbents for simulated and real-world samples. The first objective is to demonstrate scCO₂-assisted regeneration of ion exchange resin and granular activated carbon (GAC) sorbent for a range of PFAS. The second objective is bench-scale process optimization for various sorbents and feedstocks (including co-occurring chemicals of concern) and PFAS recoveries for end-of-life treatment. The third objective evaluates end-of life PFAS treatment compatible with effluent composition (slurries, sludges, and solid residues), including ball-milling, supercritical water oxidation, and alkaline hydrolysis. The fourth objective evaluates process scale-up and techno-economic analysis for mobile and stationary platforms. This technology will enable the development of a treatment train for PFAS mineralization. 

The effort will demonstrate sorbent regeneration using modified scCO₂ extraction of spent GAC and ion exchange resin regeneration for PFAS and co-occurring chemicals. In proof-of-concept experiments, spent sorbents impacted with organic compounds (OC) and PFAS will be regenerated using a scCO₂/ co-solvent mixture. It is hypothesized that high co-solvent/scCO₂ miscibility eliminates diffusion transport limitation, enabling rapid PFAS/OC extraction into a single-phase (gas-like) media. At the same time, the addition of acid and ionic modifiers reduces PFAS interaction with sorbents. Experiments will be performed to quantify PFAS desorption efficiencies from (i) PFAS-loaded spent sorbent after exposure to groundwater and surface water matrices in Rapid Small Scale Column Tests studies and (ii) real-world spent sorbents. This effort is a collaboration of academic and industrial partners.

This project addresses critical needs in water treatment: (i) the regeneration of GAC and single-use sorbents and (ii) opportunities for downstream stream management can incorporate a variety of end-of-life technologies for PFAS and other co-occurring chemicals, avoiding the release of gaseous and liquid organic fluorine to the environment. In a broader application, the method can be used for other PFAS-impacted matrices. Successful completion of this effort will ultimately improve the cost-effectiveness of PFAS treatment technologies, directly benefiting the warfighter and installation communities. (Anticipated Project Completion - 2026)