The overall goal of this proof-of-concept project is to develop a modified ultraviolet (UV)-reductive treatment (via hydrated electron) system that utilizes the amphipathic properties of per- and polyfluoroalkyl substances (PFAS) at the gas-water interface to enhance PFAS reductive defluorination and reduce treatment energy consumption significantly. Specifically, the project team hypothesizes that the combination of a selected electron source and gas sparging can be applied in a UV system to encourage the localization of hydrated electrons and PFAS at the gas-water interface (or within generated foam) to achieve an exceptionally higher PFAS defluorination rate compared to UV systems without gas sparging. Furthermore, it is hypothesized that the energy demand for PFAS defluorination in the modified UV treatment system can also be significantly reduced by concentrating PFAS within foam generated via gas sparging. The preliminary data show that the generation of foam in the UV system decreased the perfluorooctanoic sulfonate defluorination energy demand 7-fold. This encouraging result suggests that the framework holds exceptional promise for mitigating the energy demand of current UV-reductive treatment systems and can be implemented as a more cost-effective remedial alternative for matrices impacted by PFAS at Department of Defense (DoD) facilities.

Experiments and modeling will be combined to test the hypotheses outlined above and meet the project objective of delivering an energy-efficient UV-reductive treatment system capable of achieving high PFAS defluorination for PFAS commonly present in aqueous film-forming foams (AFFF). To accomplish this, the project team will first perform a series of bench-scale defluorination batch studies using individual PFAS in gas sparged UV reactors containing different electron sources, sparging rates, and pH values under aerobic and anaerobic conditions. Then, water matrices containing PFAS mixtures (e.g., groundwater, firefighting truck rinsate) will be tested to assess the optimized system's feasibility in real-world applications. Experimental work will be aimed at the following:

• Verifying PFAS defluorination is enhanced at the gas-water interface and/or foam phase,
• Identifying critical electron source characteristics that affect the formation of foams and interaction between hydrated electrons and PFAS,
• Improving PFAS defluorination rates through electron source concentration, pH, gas sparging rate, and testing environment (e.g., anaerobic versus aerobic) optimization, and
• Evaluating the optimized system defluorination efficiency in PFAS-containing source water.

The project team will also apply an energy cost analysis to the finalized treatment system to assess its energy efficiency per order of magnitude removal and defluorination ratio versus time.

Successful completion of this research will provide the DoD with the basis for designing a high performance PFAS removal and energy-efficient UV-reductive treatment system that can be applied to improve the remediation of AFFF-impacted source waters and reduce the total energy cost during treatment. The system's energy cost analysis will provide a comprehensive comparison between the developed system and current available UV-reductive technologies to identify their difference in energy cost. Results from this work can significantly benefit practitioners who are in need of cost-effective PFAS destruction technologies. (Anticipated Project Completion - 2024)

Fang, Y., J. Devon, D. Rao, J. Liu, and C. Schaefer. 2024. Destruction of Perfluorooctane Sulfonic Acid (PFOS) in Gas Sparging Incorporated UV-Indole Reductive Treatment System – Benefits and Challenges. Journal of Hazardous Materials, 240:135935. doi.org/10.1016/j.jhazmat.2024.135935.