Degradation of per- and poly-fluoroalkyl substances (PFAS) using ultrasonication: Effect of reactor materials

This study explores the impact of different reactor/container materials, such as glass and plastic, on the degradation of per- and poly-fluoroalkyl substances (PFAS) using indirect ultrasonication in aquatic media. After subjecting the system to ultrasonication at 130 kHz with a 100 % effective power for 3.0 h, approximately 95 % and 46 % defluorination of perfluorooctanoic acid (PFOA) were achieved in a glass reactor and a polypropylene (PP) reactor, respectively. Under optimal conditions, calorimetry power at the highest applied power averaged 51 ± 0.7 W/L for glass and 55.1 ± 1 W/L for PP. A similar trend was observed for the defluorination of perfluorooctane sulfonic acid (PFOS), 1H, 1H, 2H, 2H-perfluorooctanesulfonic acid (6:2 FTS), and aqueous film-forming foam (AFFF) containing a complex mixture of PFAS, indicating that the glass reactor exhibited higher efficiency in ultrasonic irradiation transportation. The kinetics of PFOA degradation also revealed that a glass beaker facilitated faster removal than PP. The reaction mechanism suggested that the primary pathway involved a pyrolytic reaction, while free radicals also played a contributing role. The effect of free radicals, especially hydroxyl radicals ([rad]OH) was approved by potassium iodide (KI) dosimetry as well as reaction between [rad]OH with benzoic acid (BA) as a radical scavenger. Overall, the findings unambiguously demonstrate how the reactor material affects the indirect ultrasonication of PFAS in an aqueous environment.