This project aims at achieving deep destruction of a wide collection of per- and polyfluoroalkyl substances (PFAS) in the complicated real water matrices, such as aqueous film-forming foam (AFFF)-impacted groundwater and fire suppression system rinsing water. The project team will build a novel treatment train integrating electrochemical oxidation (EO) and ultra violet/sulfite reduction (UV/S) modules. The proposed EO system has been proven for the rapid destruction of long-chain PFAS and deep destruction of organic matters but faces the challenge in treating short-chain PFAS. The UV/S system has high efficacy in treating most PFAS regardless of chain length, but the performance can be significantly inhibited by background light-adsorbing organics. Therefore, this project will maximize the strengths of the two technologies to destroy all PFAS in complicated water matrices, which often include high loads of organics and salts. The specific objectives to achieve in this one-year proof-of-concept project include:

• Achieving complete removal and deep (>95%) defluorination of various model PFAS pollutants in the synthetic water by the integrated EO−UV/S treatment train system,
• Evaluating the treatment efficacy in the presence of challenging water matrices, and
• Minimizing the consumption of electrical energy and chemicals.

Both EO and UV/S are proved to be cost-effective for the removal of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) (< 20 kWh/m³ to obtain > 90% destruction of PFOS and PFOA) in leachate and AFFF. This project aims at a more challenging target—the near-complete defluorination of short-chain PFAS and telomers in diluted AFFF. The project team will use EO to break down long-chain PFAS and telomer precursors and eliminate light adsorbing water matrice. The UV/S process will destroy the residual short-chain PFAS. The project team will build an integrated EO-UV/S reactor and optimize several configuration parameters to enhance the mass transfer and UV light adsorption. They will then perform parallel studies to systematically investigate (i) the promotional roles of UV irradiation and surfactants on EO treatment and (ii) the effects of residual oxidants (e.g., free chlorine produced after EO) and organic content on UV/S treatment. The destruction of PFAS to F⁻ will be quantitatively characterized by ultra-high-performance liquid chromatography and ion chromatography. Lastly, the project team will validate the performance of the EO-UV/S treatment train in the treatment of AFFF-impacted groundwater and equipment rinse water.

The results from this project will contribute to both fundamental science and practical engineering. Specifically, the project team anticipates obtaining an in-depth understanding of the destruction and defluorination of short-chain PFAS by oxidation and reduction pathways. The outcomes of this project will prove that PFAS are not “forever” chemicals. Instead, they can be readily decomposed in a rationally designed treatment train. The results will strongly promote knowledge transfer to a field demonstration project through the collaboration with the remediation industry and to the PFAS research community. (Anticipated Project Completion - 2024)

Yunqiao, G., Z. Liu, N. Yang, S. Yang, L.E. Quispe-Cardenas, J. Liu, and Y. Yang. 2024. Near-Complete Destruction of PFAS in Aqueous Film-Forming Foam by Integrated Photo-Electrochemical Processes. Nature Water, 2:443-452. doi.org/10.1038/s44221-024-00232-7.

Liu, Z., B. Jin, D. Rao, M.J. Bentel, T. Liu, J. Gao, Y. Men, and J. Liu. 2024. Oxidative Transformation of Nafion-Related Fluorinated Ether Sulfonates: Comparison with Legacy PFAS Structures and Opportunities of Acidic Persulfate Digestion for PFAS Precursor Analysis. Environmental Science & Technology, 58(14):6415-6424. doi.org/10.1021/acs.est.3c06289.