Supercritical Water Oxidation of PFAS-Laden Granular-Activated Carbon

Abstract Supercritical water oxidation (SCWO) is a promising end-of-life treatment for recalcitrant pollutants; however, the destruction of PFAS loaded onto granular activated carbon (GAC) media and the fate of carbon particles remain poorly understood. We examine the oxidation of aerodynamically suspended spent GAC media in a continuous-flow autogenic SCWO reactor at T ∼ 550–670 °C and residence times of 25–36 s. In globally oxidant-rich conditions, GAC particle destruction efficiencies varied ∼10–100%, showing weak temperature dependence but high sensitivity to slurry composition and particle loading. Elevated CO emissions and incomplete carbon conversion indicate diffusion-limited surface oxidation, in which rapid local consumption of oxidants leads to surface shielding by oxidation products. Experiments with PFAS-loaded GAC indicate that surface shielding can inhibit PFAS destruction efficiency. At T > 600 °C, PFOA destruction approached 99.9%, pointing to activation of the thermal degradation route, whereas PFBS mineralization was limited to ∼98.1–99.7%, decreasing with high GAC loading, suggesting interfacial competition for oxidizing availability. These results demonstrate that SCWO treatment of spent GAC slurries can achieve the destruction of both carbon and PFAS in a single step; however, the process must be optimized to account for diffusion-controlled oxidation at the particle surface.