The goal of this proof-of-concept project was to develop a cost-effective and practical treatment train for the treatment of investigation-derived waste (IDW). The main target of treatment was the aqueous wastes that contain per- and polyfluoroalkyl substances (PFAS) from the use of aqueous film-forming foam (AFFF). The destruction of PFAS is achieved by the application of the advanced reduction process (ARP) using hydrated electrons and the advanced oxidation process (AOP) using hydroxyl radicals. To ensure the efficient use of chemicals and energies, the project team combined nanofiltration (NF) to reduce the volume of IDW. The main objective of this project was to evaluate individual treatment modules and the combined treatment train.

In the one-year time window, the project team has optimized the operation parameters for the three treatment modules (NF, AOP, and ARP), and evaluated the treatment train of combined processes on two IDW samples: fresh groundwater and AFFF-spiked groundwater. The AFFF was diluted by 100x to 100,000x for both NF separation and defluorination treatment with ultra-violet (UV)/sulfite (ARP) and persulfate/hydroxide digestion (AOP). The effect of dilution factor, pH, and the concentration of sulfite and persulfate were systematically investigated. 19F nuclear magnetic resonance was used to probe the dominant PFAS species in AFFF. Fluoride ion and PFAS on and beyond the Environmental Protection Agency (EPA) Method 537.1 analyte list were quantified to evaluate the degradation treatment and the NF separation

NF membranes could purify both the original and AFFF-spiked groundwater. The concentrations for all C4 and longer PFAS were below 50 ng/L in the NF permeate. AOP and ARP were optimized for the treatment of AFFF solutions. The combination of ARP and AOP effectively degraded PFAS on the EPA Method 537.1 analyte list in the presence of groundwater matrix and organic additives in AFFF. Unexpectedly, after the ARP-AOP treatment, small amounts of perfluorcarboxylates were detected in the treated NF permeate, suggesting that some neutral PFAS precursors may be present in IDWs and penetrate the NF membrane. With adequate dilution (e.g., 10,000x), at least 8.6 g/L (0.45 M) of organic fluorine can be defluorinated as fluoride−ion from the original AFFF product. The project team identified the dominant PFAS component in the AFFF as a C6F13-based telomeric structure. The project team also observed different types of PFAS occurrence and transformation in the fresh groundwater versus AFFF-added groundwater. Upon further optimization of the NF and ARP/AOP modules, most PFAS in the fresh and AFFF-spiked groundwater are expected to be deeply or completely destructed.

PFAS degradation by UV-generated hydrated electron is one of the few competitive methods for practical IDW treatment. To further save the capital cost and the consumption of both chemicals and electricity, NF separation can significantly minimize the volume of IDW. The project team has shown that the use of UV, sulfite, and persulfate could effectively treat the real groundwater and adequately diluted AFFF. To meet various remediation needs by SERDP and ESTCP, the project team aims at further improving the efficacy and efficiency for the destruction of concentrated PFAS solutions. The project team also aims at preventing the membrane penetration by specific PFAS precursors. Future work on the structure-selectivity relationship by the membrane interception, as well as further improvement and integration of the ARP/AOP modules for complex water matrices are planned.

Bentel, M., Y. Yu, L. Xu, B. Wong, Y. Men, and J. Liu. 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFASs Remediation and Management. Environmental Science & Technology, 53:3718-3728.

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 & Technology, 55: DOI: 10.1021/acs.est.1c00353.