Effective defluorination of per- and polyfluoroalkyl substances in actual water environment by liquid phase microwave discharge: Elucidation of discharge characteristics and mechanism

Abstract

As a novel water treatment technology, plasma technology can generate free radicals in situ and exhibits a favorable effect on the degradation of per- and polyfluoroalkyl substances (PFAS). Nevertheless, the high conductivity and complex composition of the actual water environment can interfere with the defluorination effect of PFAS. To attain the objective of more efficient defluorination of PFAS in actual water environment, the discharge characteristics of liquid phase microwave discharge plasma technology were explored. It was discovered that conductivity had a negligible impact on the discharge. A stable discharge could be attained when the conductivity of the aqueous solution was elevated to 2000 μS/cm, with the defluorination rates of PFOA reaching up to 82.6% and those of PFOS reaching 72.4%. The research findings indicate that the microwave discharge plasma technology has wide applicability and can adapt to various water environments with different electrical conductivities. Based on the research results, the experimental parameters were optimized, and the method to address the difficulty of PFAS defluorination in the actual water environment was identified. After parameter optimization, the defluorination of two types of PFAS can reach approximately 80% in lake and tap water. It indicates that the technology presents substantial advantages in the defluorination of PFAS within the actual water environment.