The researcher team aims to develop an innovative, effective, and practical ex situ treatment train system for rapid removal and complete destruction of per- and polyfluoroalkyl substances (PFAS) in groundwater at Department of Defense (DoD) sites. The system will also remove co-occurring chemicals (e.g., petroleum hydrocarbons and chlorinated solvents). The treatment train contains three core components- (i) oxidative pre- and post-treatment, (ii) PFAS adsorption, and (iii) adsorption material regeneration using reductive PFAS defluorination. To build a robust bench-scale system for successful groundwater treatment, the researchers aim to elucidate governing mechanisms, fill knowledge gaps, and obtain technical details regarding the three core components and overall performance of the treatment train system, including:

• Factors determining the rate and extent of PFAS defluorination by ultraviolet (UV)-excited hydrated electrons
• Parameters determining the rate and capacity of PFAS adsorption by clay-based materials
• Impacts of oxidative pre- and post-treatment
• Strategies of clay adsorbent regeneration and system performance in groundwater treatment

The research team believes the following reasons support the oxidation-adsorption-defluorination treatment train. First, PFAS defluorination directly in groundwater requires excessive time, energy, and chemicals. Instead, defluorination of adsorption-enriched PFAS for adsorbent regeneration may significantly reduce the capital cost, and be time-insensitive and unaffected by other components in groundwater. Second, reuse of adsorption materials may further reduce treatment cost. Third, oxidative pretreatment is highly beneficial because it may (i) remove organic co-occurring chemicals, (ii) eliminate organic co-occurring chemical competition during PFAS adsorption, and (iii) convert recalcitrant PFAS to labile PFAS for enhanced defluorination. There are four technical tasks corresponding to the research objectives:

• Compare different oxidation technologies on co-occurring chemical removal and PFAS transformation
• Develop and optimize organic-modified clay materials for PFAS adsorption from groundwater
• Investigate effects of PFAS structure, UV irradiation energy and intensity, and electron source chemicals on the defluorination rate and extent
• Test and improve the oxidation-adsorption-defluorination treatment train for groundwater treatment

The project combines lab experiments (core) and computational simulations (supplemental). Key activities include UV photoreactions, chromatography and spectroscopy characterization of PFAS and products, adsorption material preparation and characterization, and operation of bench-scale reactor chain.

The treatment train system design is grounded with the solid preliminary data (e.g., PFAS defluorination results show high promise) and systematic knowledge (e.g., adsorption theory and oxidation mechanism guiding the treatment chain design). The effort will lead to the development of a successful and practical solution to remediate PFAS-impacted groundwater from DoD sites. Results from this project will also provide novel and fundamental understanding on (i) PFAS defluorination by UV-induced hydrated electrons, (ii) material design for PFAS adsorption, and (iii) integration of multiple technologies for optimized treatment in complex groundwater matrices. Knowledge can be transferred to a broad scope of water/wastewater treatment. Results may also impact the design of future fire-fighting formulations based on their environmental treatability. (Anticipated Project Completion - 2023)

Bentel, M.J., Y. Yu, L. Xu, Z. Li, B.M. Wong, Y. Men, and J. Liu. 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFAS) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management. Environmental Science and Technology, 53(7):3718-3728. doi.org/10.1021/acs.est.8b06648.

Bentel, M., Y. Yu, L. Xu, B. Wong, Y. Men, and J. Liu. 2020. Degradation of Perfluoroalkyl Ether Carboxylic Acids with Hydrated electrons: Structure-Reactivity Relationships and Environmental Implications. Environmental Science and Technology, 54(4):2489-2499. doi.org/10.1021/acs.est.9b05869.

Bentel, M., Z. Liu, Y. Yu, J. Gao, Y. Men, and J. Liu. 2020. Enhanced degradation of Perfluorocarboxylic Acids (PFCAs) by UV/Sulfite Treatment: Reaction Mechanisms and System Efficiencies at pH 12. Environmental Science and Technology Letters, 7(5):351-357. doi.org/10.1021/acs.estlett.0c00236.

Dong, Q., X. Min, J. Huo, and Y. Wang. 2021. Efficient Sorption of Perfluoroalkyl Acids by Ionic Liquid-Modified Natural Clay. Chemical Engineering Journal Advances, 7:100135. doi.org/10.1016/j.ceja.2021.100135.

Gao, J., Z. Liu, M. Bentel, Y. Yu, Y. Men, and J. Liu. 2021. Defluorination of Omega-Hydroperfluorocarboxylates (ω-HPFCAs): Distinct Reactivities from Perfluoro and Fluorotelomeric Carboxylates. Environmental Science and Technology, 55(20):14146-14155. doi.org/10.1021/acs.est.1c04429.

Liu, Z. M. Bentel, Y. Yu, C. Ren, J. Gao, V. Pulikkal, M. Sun, Y. Men, and J. Liu. 2021. Near-Quantitative Defluorination of Perfluorinated and Fluorotelomer Carboxylates and Sulfonates with Integrated Oxidation and Reduction. Environmental Science and Technology, 55(10):7052-7062. doi.org/10.1021/acs.est.1c00353.

Liu, Z., Z. Chen, J. Gao, Y. Yu, Y. Men, C. Gu, and J. Liu. 2022. Accelerated Degradation of Perfluorosulfonates (PFSAs) and Perfluorocarboxylates (PFCAs) by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies. Environmental Science and Technology, 56(6):3699-3709. doi.org/10.1021/acs.est.1c07608.