Rapid Removal of PFAS from Investigation-derived Waste in a Pilot-scale Plasma Reactor

Abstract

A pilot-scale plasma reactor installed into an 8 × 20 ft. mobile trailer was used to rapidly and effectively degrade poly- and perfluoroalkyl substances (PFAS) from liquid investigation-derived waste (IDW; development and purge water from monitoring wells) obtained from 13 different site investigations at Air Force installations. In the raw water, numerous PFAS were detected in a wide concentration range (~10 to 105 ng/L; total oxidizable precursors (TOP) ~102 to 105 ng/L, total fluorine by combustion ion chromatography (CIC) ~102 to 5 × 106 ng F/L). The concentration of total PFAS (12 perfluorocarboxylic acids (PFCAs) and perfluoroalkyl sulfonates (PFSAs)) in the 13 samples ranged between 2.7 and 1440 μg/L and the concentration of perfluorooctane sulfonate (PFOS) plus perfluorooctanoic acid (PFOA) ranged between 365 and 73,700 ng/L. Plasma-based water treatment resulted in rapid perfluoroalkyl acids (PFAAs) removal from 4 L individual IDW samples with faster rates for longer-chain PFCAs (C ≥ 8) and PFSAs (C ≥ 6) than for PFCAs and PFSAs of shorter chain length.In nine of the 13 IDW samples both PFOS and PFOA were removed to below United States Environmental Protection Agency’s (USEPA’s) health advisory concentration level (HAL) concentrations in < 1 minute whereas longer treatment times (up to 50 minutes) were required for the remaining four IDW samples due to either extremely high solution electrical conductivity which decreased the plasma-liquid contact area (one IDW sample) or high concentrations of PFAAs and their precursors; the latter were found to be converted to PFAAs during the treatment. Overall, 36 to 99% of the TOP concentration present in the IDWs were removed during the treatment. There was no effect of non-PFAS co-contaminants on the degradation efficiency. Overall, the results indicate that plasma-based water treatment is a viable technology for the treatment of PFAS-contaminated IDW.