Degradation of perfluoroalkyl substances using UV/Fe0 system with and without the presence of oxygen

The wide presence of per- and poly-fluoroalkyl substances (PFAS) in the environment is a global concern, thus their degradation is an imminent task. In this study, oxidative and/or reductive degradation of three representative PFAS - perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorooctane sulfonate (PFOS) was achieved using nanoscale zero-valent iron (Fe⁰ NPs) under ultraviolet (UV) light, both with and without the presence of oxygen. Higher degradation and defluorination rates were obtained for a longer chain PFNA compared to PFOA, and a higher removal of PFAS was achieved without the presence of O₂ compared to that with O₂. The degradation followed first-order reaction kinetics, and obtained the highest rates of 97.6, >99.9, and 98.5% without the presence of O₂ for PFOA, PFNA, and PFOS, respectively. The degradation rates increased with an increase in the nanoparticle concentrations in the range of 1-100 mg/L. In addition to fluoride ions, shorter chain perfluorocarboxylic acids (PFCAs) were detected as the main intermediates during PFAS degradation; PFHpS and 6:2 FTS were also detected during PFOS degradation. Hydroxyl radicals (·OH) and superoxide radicals (·O₂^-) were not involved in the degradation of PFOA, but likely involved in the degradation of PFOS. Emerging contaminants PFAS degradation using the UV/Fe⁰ system is a cost-effective technology owing to the low cost and recyclability of Fe⁰ nanomaterials, low energy consumption in the system, and its capability to degrade PFAS both with and without the presence of oxygen. This technology can be potentially applied to treat PFAS-contaminated waters in the environment.