Surfactant-assisted ultrasonic degradation of per- and polyfluoroalkyl substances (PFAS): Effect of surfactant concentration

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants known for their resistance to conventional degradation methods. Ultrasonic degradation, a promising advanced oxidation technique, has emerged as a potential solution for breaking down PFAS in water systems. This study investigates the impact of surfactants on the ultrasonic degradation of various PFAS. Three types of surfactants—dodecyltrimethylammonium chloride (DTAC, cationic), sodium dodecylbenzene sulfonate (SDBS, anionic), and Triton X-100 (TX-100, non-ionic) were tested to assist the degradation of PFAS such as perfluorooctanoic acid or PFOA, perfluorooctane sulfonate or PFOS, 6:2 fluorotelomer sulfonate or 6:2 FTS, as well as real-world samples such as aqueous film-forming foam (AFFF), and form fractionate (FF) wastes. Ultrasonication with surfactants was tested at around critical micelle concentration (CMC, high concentration range of 0.25–20 mM) and equal molar concentration (low concentration range of ∼0.02 mM) with that of PFAS. Surfactants around CMC did not enhance PFOA, PFOS and 6:2 FTS degradation. Still, they inhibited their degradation, likely due to the competition at the cavity bubble-water interface to shield PFAS from degradation. However, when low concentrations of surfactants were used, particularly at an equal molar concentration with that of PFAS, the degradation was enhanced. The enhancement was also validated for real-world samples of AFFF and FF. The findings provide insights into the interaction between surfactant and PFAS towards the degradation pathway, revealing surfactant-assisted ultrasonic degradation for PFAS remediation.