Field Demonstration of a Sonolysis Reactor for Treatment of PFAS-Contaminated Groundwater

Abstract

A mobile treatment system equipped with a custom-built sonolysis reactor was deployed at a site in California to treat groundwater impacted with per- and polyfluoroalkyl substances (PFAS). Extracted groundwater was treated in a 700-kHz sonolysis reactor for batch treatment under different power densities (122, 203, and 305 W/L) and operating temperatures (15°C and 25°C). Sonolytic treatment resulted in 93%–100% removal of the 15 PFAS identified in the groundwater, and PFAS degradation rates increased proportionally with increasing power density and temperature at operating conditions of 25°C. For all experimental conditions evaluated, greater removal was observed for perfluorinated carboxylic acids (PFCAs) [e.g., 95.1% to 100% for perfluorohexanoic acid (PFHxA)] than perfluorinated sulfonic acids (PFSAs) [68.3% to 95.2% for perfluorohexane sulfonate (PFHxS)] for similar carbon chain lengths. Similarly, greater removal was observed for longer-chain PFAS [e.g., 95.4% to 99.5% for perfluorooctanoic acid (PFOA)] compared with short-chain PFAS [56.9% to 90.4% for perfluorobutanoic acid (PFBA)]. Substantial removal of total oxidizable precursors (TOP) and specific precursors [65.5% to 99.1% for 4:2 fluorotelomer sulfonate (FTS), 6:2 FTS, 8:2 FTS, and perfluorooctane sulfonamide (FOSA)] was also observed under all conditions tested. Additionally, formation of nitrate was observed, with concentrations below maximum contaminant levels (MCLs). Overall, the results demonstrate that sonolysis treatment of PFAS-contaminated groundwater can effectively degrade PFAS without the formation of short-chain PFAS and the oxidation byproducts chlorate and perchlorate.