The use and disposal of per- and polyfluoroalkyl substances (PFAS) has led to soil and water pollution. Many commercial water treatment systems rely on separating PFAS from water, resulting in PFAS-laden adsorbents [e.g., single-use ion exchange (IX) resin or granular activated carbon (GAC)] and brines (e.g., IX regenerant solutions, membrane retentates). Thermal treatment of PFAS-laden water treatment residual wastes (adsorbents and brines), spent carbon adsorbents, and soils is an emerging opportunity to address end-of-life disposal and adsorbent reuse. The objective of this project is to use advanced analytical techniques to obtain a better understanding of the behavior of PFAS during thermal treatment to improve the management of PFAS-laden wastes and regeneration of spent adsorbents. The research scope includes both the thermal regeneration of spent GAC and the incineration of PFAS-laden solid and liquid wastes, including (i) spent GAC and single-use IX resin, (ii) concentrated brine streams from IX and membrane treatment, (iii) aqueous film-forming foam (AFFF) impacted water, and (iv) AFFF-impacted soils.

This project will lead to full-scale design guidelines for the thermal treatment of PFAS-laden materials. There are five major tasks to accomplish the objective:

1. Develop standard operating procedures to quantify total and target PFAS and incineration byproducts in relevant solid, liquid, and gas matrices,
2. Determine the thermal behavior of PFAS present in PFAS-laden wastes and spent GAC,
3. Determine the effect of incinerator operating parameters and waste type on the fate of PFAS in a multi-compartment incinerator,
4. Determine the effect of using additives to improve PFAS defluorination at lower temperatures and reduce the formation of harmful byproducts, and
5. Determine the performance of thermally regenerated GAC to treat PFAS-laden waters and conduct a life-cycle analysis and life-cycle cost analysis of the thermal treatment management approaches to feed into other SERDP and ESTCP projects being performed by the project team.

The project team will use a state-of-the-art analytical approach for quantifying PFAS in solids, liquids, and gases that specifically include particle induced gamma-ray emission (PIGE) spectroscopy and liquid and gas chromatography mass spectrometry. The speed and low-cost of PIGE will allow far more possibilities to be tested within the project duration and budget.

Schematic of a general two-stage thermal treatment system with air pollution control devices installed to treat the produced gases. Potential products and their potential to be captured in typical air pollution control devices are shown. Products formed will depend on temperature, gas mixture (e.g., pyrolysis, combustion), waste components (e.g., calcium), gas turbulence, and residence time.

Dealing with PFAS wastes has become a significant focal point for the Department of Defense, and thermal treatment of PFAS-laden materials and conversion to innocuous byproducts will play a key role in the end-of-life PFAS management strategy. This integrated research will lead to the improved operation of waste incinerators for PFAS, improved lifecycle assessment of PFAS adsorbent treatment systems, and reduced human or ecosystem exposure to PFAS. (Anticipated Project Completion - 2025)

Wang, J., Z. Lin, X. He, M. Song, P. Westerhoff, K. Doudrick, and D. Hanigan. 2022. Critical Review of Thermal Decomposition of Per- and Polyfluoroalkyl Substances: Mechanisms and Implications for Thermal Treatment Processes. Environmental Science and Technology, 56(9):5355-5370. doi.org/10.1021/acs.est.2c02251.