Treatment of per- and polyfluoroalkyl substances (PFAS): A review of transformation technologies and mechanisms

Perfluorinated and polyfluoroalkyl substances (PFAS) are a large class of synthetic organic chemicals whose structures contain fully or partially fluorinated carbon chains with different chain lengths and functional groups, and have been widely used since they were first synthesized in the 1940 s. Their unique fluorine-carbon bonds provide exceptional thermal and chemical stability, rendering them highly persistent in the environment, often referred to as 'forever chemicals' in contemporary scientific literature. PFAS have been found to have adverse effects on human health and environmental quality. PFAS degradation hinges on the disruption of carbon-carbon and carbon-fluorine bonds. This review delineates the degradation technologies of PFAS, including chemical oxidation, chemical reduction, ultrasonication, photolysis, electrochemistry, thermal degradation, mechanochemistry and microbial degradation. It offers a comparative analysis of these eight technologies based on degradation efficiency, defluorination efficiency, and degradation rate. Among these technologies, mechanochemical transformation is emerging as a promising approach in detoxifying PFAS. Mechanochemical treatment can be achieved at ambient temperature and pressure by the high-energy milling of the polluted materials. Future work should focus on the scaleup and economics of the advanced treatment technologies to treat and remediate PFAS and other highly recalcitrant pollutants.