Per- and polyfluoroalkyl substances are “a group of chemicals used to make fluoropolymer coatings and products that resist heat, oil, stains, grease, and water,” according to the Center for Disease Control and Prevention. Some of the various products using PFAS include furniture, adhesives, clothing, and non-stick cookware. Unfortunately, these substances do not break down in the environment and can now be found in rivers, and lakes, as well as in animals. Finding cost-effective ways to treat PFAS-contaminated water is critical. The most common treatment for PFAS is sorption via granular activated carbon but it has not been overly successful.
One emerging technology, sonolysis, has shown promise by removing PFAS from aqueous waste streams in a lab environment. The sonolysis process uses ultrasound waves to physically impact and degrade water contaminants, and as such, its effectiveness depends on different factors including ultrasound frequency, power density, solution temperature, solution pH, sparging gas, and water quality.
Researchers Poonam R. Kulkarni, Stephen D. Richardson, Blossom N. Nzeribe, David T. Adamson, Shashank S. Kalra, Shaily Mahendra, Jens Blotevogel, Andrea Hanson, Greg Dooley, Sharyl Maraviov, and Jovan Popovic developed a test to evaluate sonolysis as a destructive technology under field operating conditions to determine performance and scalability. In their study, “Field Demonstration of a Sonolysis Reactor for Treatment of PFAS-Contaminated Groundwater” in the Journal of Environmental Engineering, the authors demonstrate the operation of a pilot-scale sonolysis reactor at a field site for the treatment of PFAS-contaminated groundwater. Learn how this first field application of sonolysis for groundwater treatment can be applied to minimize environmental threats at https://doi.org/10.1061/(ASCE)EE.1943-7870.0002064. The abstract is below.
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.
Read the paper in full in the ASCE Library at https://doi.org/10.1061/(ASCE)EE.1943-7870.0002064.