Aqueous film forming foam (AFFF) contain zwitterionic, cationic, and anionic per- and polyfluoroalkyl substances (PFAS). Recent studies revealed that zwitterionic, and to a lesser extent cationic, PFAS contribute to a significant fraction (up to 97%) of total PFAS in firefighter training area (FTA) soil, and approximately 52% of the PFAS transported downgradient was associated with polyfluorinated precursors. Substantial retention of PFAS found in the source zone highlights the need for effective remediation of precursors in source zones to mitigate long-term transport/transformation of PFAS to the downgradient areas.

The presence and the degradation of hydrocarbon surfactants might potentially affect the fate of the precursors in source zone soils, an important research question that has not been investigated. Together, the soil-bound precursors and the hydrocarbon surfactants point out a large knowledge gap on factors controlling the fate of these biodegradable precursors in the source zone soils, and the influence hydrocarbon surfactants might have on the precursors in the source zones. This proposed research is intended to bridge this knowledge gap and provide information that is critical for future development of a cost-effective treatment strategy for PFAS in source zone soils. The overarching goal of this proof-of-concept project is to develop an integrated treatment system for the effective treatment of PFAS-laden soils in source zones. The treatment strategy is based on the “Release-Capture-Destruction” concept.

This research is built on the knowledge of biodegradation of PFAS, the advanced analytical methods for characterization and identification of PFAS and co-occurring chemicals in AFFF and AFFF-impacted matrices, and the novel hydrothermal destruction technology for PFAS defluorination. The technical approach consists of the following tasks:

1. Determine factors affecting biodegradation of soil-bound precursors (Task 1);
2. Accelerate biodegradation of precursors in soil via bioaugmentation (Task 2);
3. Determine the efficiency of PFAS removal by magnetic activated carbon (MAC) in soil slurry (Task 3);
4. Assess whether hydrothermal alkaline treatment technology can destroy PFAS in spent MAC (Task 4).

Successful implementation of this research will provide the Department of Defense (DoD) with a new treatment strategy to effectively remediate source zone soils due to AFFF applications. Each of the technologies (i.e., “Release-Capture-Destruction” technologies) described in this project can be further tailored for a specific treatment endpoint for a given AFFF-impacted matrix.

Soils and sediments containing strongly bound PFAS, particularly zwitterionic precursors, are recognized as long-term PFAS sources to downgradient groundwater. The results of this study will fill the knowledge gaps about the poorly understood effects of co-occurring hydrocarbon surfactants on the fate and biotransformation of PFAS, and decipher the factors controlling biodegradation of the soil-bound precursors into more mobile perfluoroalkyl acids (PFAA) for subsequent treatments (i.e., capture and destruction technologies). The new knowledge to promote biodegradation of soil-bound precursors will not only lead to the success of the treatment train of PFAS in soils but also provide a foundation for the future development of precursor bioremediation. The successful application of MAC to sorb mobile PFAAs produced from precursor biodegradation, followed by using hydrothermal liquefaction for the destruction of PFAS-laden MAC, will provide strong proof for the “Release-Capture-Destruction” remediation strategy for PFAS-laden soils that are present in numerous DoD sites. (Anticipated Project Completion - 2023)

Yang, S.H., L. Shan, and K.H. Chu. 2022. Fate and Transformation of 6:2 Fluorotelomer Sulfonic Acid (6:2 FTSA) Affected by Plants, Nutrients, Bioaugmentation, and Soil Microbiome. Environmental Science and Technology, 56(15):10721–10731. doi.org/10.1021/acs.est.2c01867.