Focused ultrasound technology for the direct degradation of per- and polyfluoroalkyl substances (PFAS): a sustainable approach to contaminant remediation

Despite increasing concerns regarding the persistence and toxicity of per- and poly-fluoroalkyl substances (PFAS), effective and scalable degradation methods remain limited. In this study, we applied focused ultrasound technology to directly degrade persistent organic pollutants, specifically PFAS. The primary objectives were to identify the optimal reaction conditions and elucidate the underlying degradation mechanisms. Ultrasound reaction experiments were conducted using aqueous solutions of perfluoro-octanoic acid (PFOA) to validate the stepwise degradation and mineralization tendencies of PFAS through fluoride ion quantification and non-target analysis. The results showed that PFAS degradation occurred through the progressive cleavage of carbon-carbon and carbon-fluorine bonds, leading to the sequential shortening of long-chain PFAS into short-chain derivatives. Furthermore, acoustic pressure field analysis was employed to determine the optimal ultrasound conditions that maximized cavitation effects. A spiked petrochemical wastewater matrix achieved a PFOA removal efficiency exceeding 99.9 %. The focused ultrasound process effectively removed trace-level multi-species PFAS (e.g., PFHxA, PFHpA, PFPeS, and diPAP) detected in actual groundwater samples. This study demonstrates the practical applicability and environmental compatibility of focused ultrasound as a direct technology for PFAS degradation, which operates without requiring high temperature, high pressure, or external oxidants.