Hydrothermal Technologies for On-Site Destruction of Site Investigation Wastes Impacted by Per- and Polyfluoroalkyl Substances (PFAS)

Timothy Strathmann | Colorado School of Mines



The overall goal of this project is to evaluate the effectiveness of applying nascent hydrothermal conversion technologies to destroy per- and polyfluoroalkyl substances (PFAS) and co-occurring chemicals present in PFAS investigation-derived waste (IDW) materials generated at Department of Defense (DoD) facilities. Specifically, the research team suggests that hydrothermal reaction conditions can be coupled with low cost reactive amendments (e.g., sulfite, zerovalent iron) to effectively degrade and defluorinate the full range of PFAS structures identified at aqueous film-forming foam (AFFF)-impacted sites. The preliminary data show successful defluorination of an AFFF mixture subjected to hydrothermal reaction with a low-cost reducing agent sulfite, commonly used in wastewater treatment and food preparation industries. Although maybe counterintuitive, energy input requirements for hydrothermal processing of wet materials is significantly lower than incineration and other technologies that require drying of waste materials before processing. Thus, these findings suggest a potentially promising platform for removing DoD liabilities associated with AFFF-impacted waste materials generated during site investigations.

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Technical Approach

ER18-1501 Graphic

Bench-scale laboratory experiments will be conducted to quantify the destruction and defluorination of representative PFAS and associated co-occurring chemicals (e.g., jet fuel) in aqueous and soil samples subjected to hydrothermal reaction conditions (250 – 350C, 5-20 MPa) and amended with a range of low-cost reactive amendments, including reducing and oxidizing agents, and acids and bases. Experiments will examine the reactivity of different AFFF formulations (e.g., 3M, Chemguard, Ansul) in addition to the more commonly studied perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). Decomposition of individual PFAS will be accomplished by application of liquid chromatography with quantitative time-of-flight mass spectrometry (LC-QToF-MS [liquid chromatography with quantitative time-of-flight mass spectrometry detection]) together with an extensive target screening list of PFAS (presently >1500 structures). Experiments will culminate with reactions involving actual site investigation waste samples under the most promising reaction conditions and amendments to provide a proof-of-concept for this innovative strategy. Finally, the energy requirements for on-site hydrothermal reactor system will be estimated and compared to energy requirements for incineration of the same waste materials.

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Successful completion of this research will provide the DoD with a technological path forward for managing PFAS-impacted IDW on-site and eliminating potential liabilities associated with these materials when transported off site. Demonstration of co-occurring chemical destruction under the same conditions would further expand the applicability of the technology to an even wider range of sites (e.g., fuel hydrocarbons, halogenated solvents). (Anticipated Completion - May 2019)

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Hao, S., Y.J. Choi, B. Wu, C. Higgins, R. Deeb, and T.J. Strathmann. 2021. Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF). Environmental Science & Technology. 55: 3283-3295. https://doi.org/10.1021/acs.est.0c06906

Wu, B., S. Hao, Y. Choi, C.P. Higgins, R. Deeb, and T.J. Strathmann. 2019. Rapid Destruction and Defluorination of Perfluorooctanesulfonate by Alkaline Hydrothermal Reaction. Environmental Science & Technology Letters, 6:630-636. DOI: 10.1021/acs.estlett.9b00506

Yu, J., A. Nickerson, Y. Li, Y. Fang, and T.J. Strathmann. 2020. Fate of Per- and Polyfluoroalkyl Substances (PFASs) during Hydrothermal Liquefaction of Municipal Wastewater Treatment Sludge.Environmental Science: Water Research & Technology, 6:1388-1399. DOI: 10.1039/c9ew01139k

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Points of Contact

Principal Investigator

Timothy Strathmann

Colorado School of Mines

Phone: 303-384-2226

Program Manager

Environmental Restoration