Enhanced degradation and defluorination of perfluorooctane sulfonate (PFOS) in tap water using gas-dispersed cold atmospheric plasma

Abstract

Abstract Per- and polyfluoroalkyl substances (PFAS) are extremely persistent contaminants owing to the exceptional chemical stability of carbon–fluorine (C–F) bonds. Consequently, conventional wastewater treatments are largely ineffective, as they capture but fail to destroy PFAS, leading to the accumulation of concentrated wastes. In this study, we demonstrate that gas dispersion-assisted cold atmospheric plasma (CAP) enables rapid degradation and partial defluorination of perfluorooctane sulfonate (PFOS) in tap water. Operating under ambient conditions, CAP generates a rich mixture of oxidative and reductive reactive species, including solvated electrons and hydroxyl radicals, which are proposed to contribute to PFOS degradation and defluorination. Air gas dispersion enhances hydrodynamic mixing and enriches PFOS at the plasma-liquid interface, promoting interfacial microdischarges and concentrated short-lived reactive species that enhance oxidative and reductive degradation pathways. At high PFOS concentrations in tap water, gas dispersion-assisted CAP achieved 99.99% PFOS degradation with partial defluorination of 35%. With gas dispersion, degradation followed apparent first-order kinetics, with a rate constant of 0.42 1/min and a half-life of 1.6 min. In both conditions, with and without gas dispersion, analysis of measured transformation products (TPs) revealed stepwise degradation pathways of PFOS, with fluorine mass balance recoveries ranging from 31 to 106%. The lowest electrical energy per order ( EEO ) achieved was 39 kWh/m 3 /order. These results demonstrate the efficient degradation of PFOS, while the measured fluoride ion release confirms partial defluorination, highlighting gas dispersed CAP as a promising chemical-free and energy-efficient technology for PFAS remediation in water systems.