Degradation and defluorination of perfluorooctane sulfonate (PFOS) forever chemical in water using hydrodynamic cavitation treatment

Per- and polyfluoroalkyl substances (PFAS), also known as ''forever chemicals,'' are persistent environmental contaminants that pose significant risks to human health and aquatic ecosystems. Their extreme chemical stability primarily due to the strong carbon–fluorine (C–F) bond, the strongest bond in organic chemistry makes them highly resistant to degradation, even under harsh oxidative conditions. This study examines the degradation and defluorination of PFAS using a catalyst-free and chemical-additive-free orifice-based hydrodynamic cavitation (HC) treatment system. In HC, the rapid formation and subsequent collapse of cavitation bubbles generate intense shockwaves, localized high pressures, and elevated temperatures. These extreme conditions create a highly reactive physicochemical environment capable of initiating PFAS breakdown and promoting effective defluorination. In this study, perfluorooctane sulfonate (PFOS), a representative long-chain PFAS, was selected at initial concentrations of 1 mg/L and 5 mg/L. Treatments were conducted under intense HC conditions (inlet orifice pressure of 48 bar; cavitation number of 0.03) with varying treatment durations. The results demonstrated increased PFOS degradation with treatment time along with detection of released fluoride ions indicating effective cleavage of C–F bonds. PFOS degradation reached 37%, and the degree of defluorination was 20% related to initial PFOS, respectively. The degradation followed first-order kinetics, with rate constants ranging from 0.7 × 10⁻³ to 40 × 10⁻³ 1/min. At an electrical energy per order (EEO) of 7–598 kWh/m3/order, the corresponding electrical energy input required for PFOS degradation ranged from 1 to 75 kWh/m3. These findings underscore the potential of HC as a scalable and effective PFAS treatment technology.