Per- and polyfluoroalkyl substances (PFAS) are widespread in soil and groundwater throughout the United States. This project will demonstrate destruction of PFAS in several aqueous-impacted media using a bench-scale supercritical water oxidation (SCWO) system. Specific objectives include following:

• Assess the destruction of PFAS and formation of byproducts (if any) across a range of impacted media;
• Integrate and apply a suite of analytical tools to perform a quantitative mass balance of PFAS and fluorine to validate PFAS destruction has occurred and understand the fate of fluorine in the process; and
• Evaluate the appropriateness of materials of construction and corrosion impacts to system components.

SCWO is a process that occurs above the supercritical point of water in the presence of oxygen. Above the supercritical point, there is no distinction between gas and liquid, and the properties of the fluid change dramatically, facilitating mass transfer and reaction kinetics. At these conditions, the carbon-fluorine bond dissociation energy is overcome, and recalcitrant compounds such as PFAS are mineralized to products including carbon dioxide, water, hydrofluoric acid, and salts. SCWO results in destruction of PFAS (in less than 10 seconds) rather than transferring them from one media to another, and is equally effective on short and long-chain perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids. Furthermore, it is not inhibited by organic co-occurring chemicals, such as petroleum hydrocarbons and volatile organic compounds; these chemicals can serve to provide heat during the oxidation process, which can offset utility cost.

This project will validate SCWO to destroy PFAS-impacted media, evaluate effects of operating conditions (i.e., residence time and oxidant dosing), and demonstrate that a quantitative mass balance can be achieved using a suite of analytical tools.

Successful application of SCWO will provide a cost-effective technology for on-site destruction of PFAS-impacted media. Because SCWO destroys PFAS rather than transfer them from one media to another, the need for disposal of a secondary (concentrated) waste stream is eliminated. Data generated by this study will provide the foundation for applying and optimizing operation of larger-scale mobile systems that will be able to operate individually or in conjunction with other treatment technologies to address PFAS source areas. (Anticipated Project Completion – 2025)