Regeneration of PFAS-laden Granular Activated Carbon in Modified Supercritical CO2 Extraction

Granular activated carbon (GAC) is used widely to treat PFAS-contaminated streams, resulting in large quantities of spent GAC that are landfilled or regenerated for future use. Herein, we report the development and application of supercritical CO2 (scCO2) extraction modified with organic solvent and acid modifier. The method yields > 97% desorption efficiency of PFOA after ~60 minutes of treatment in a continuous flow reactor. The mild extraction conditions at ~100 °C do not trigger the formation of volatile organic fluorine or the alteration of the GAC sorbent properties. Another benefit of using scCO2 in the extraction is the high miscibility of co-solvent/scCO2, which eliminates diffusion transport limitations, enabling rapid PFAS extraction into a single-phase (gas-like) medium. The introduction of an organic co-solvent and the absence of water as a solvent limit hydrophobic interactions between the sorbent and the adsorbate. At the same time, the addition of acid modifiers reduces the electrostatic interactions between PFAS and sorbents. Supercritical fluid extraction (SFE) may prove effective for other types of sorbents, including various ion-exchange resins. The modified SFE process can be an economically effective regeneration scheme, leading to the reuse of sorbents in future adsorption cycles and achieving high PFAS concentration in the effluent for end-of-life treatment technologies.