PFAS degradation using a hyperbolic vortex plasma reactor

Abstract This study investigates the removal of per- and polyfluoroalkyl substances (PFAS) using a hyperbolic vortex plasma discharge under various plasma-atmospheric conditions demonstrating varied degradation times for PFAS of different chain lengths. Experiments with spiked long-chain perfluorooctane sulfonic acid in deionized (DI) water show that bipolar ‘flashover’ plasma polarity achieves more effective degradation compared to monopolar positive or negative polarity. For a spiked PFAS matrix of varying chain lengths in DI water, results indicate that the production of reactive species in the gas phase by plasma discharge, and their subsequent dissolution in water through the water vortex, enables the degradation of short-chain perfluorobutanoic acid in the bulk liquid. In contrast, the degradation of long-chain PFAS primarily occurs at the gas-water interface, likely due to direct interactions between the plasma and the PFAS molecules. The addition of the Hyamine 1622 surfactant during treatment significantly enhances the degradation of both short- and long-chain PFAS in DI water, groundwater, and industrial effluent. The results of groundwater treatment indicate that the presence of high concentrations of other substances, particularly anions, slows down the degradation of PFAS, especially short-chain PFAS with carboxylic acid groups. Depending on the conditions and the type of PFAS, degradation can be achieved up to 99% after 75 min of treatment, with typical energy input around 7.2 kJ L −1 or 2 kWh m −3 .