PFAS Thermal Remediation: Should It Be On Your List of Options?

The need for remediation of poly- and perfluoroalkyl substances (PFAS) is growing substantially as a result of increased regulatory attention to this emerging contaminant. Stockpiles of PFAS contaminated soils are growing and a permanent solution to remediate and clean these piles (and other source zones not yet addressed) is needed.

Fortunately, recent studies have shown that thermal conductive heating (TCH) can be an effective treatment for PFAS. In this blog post, we’ll explain how that can work.

TCH Technology has been used by TerraTherm to remove recalcitrant contaminants for more than 20 years, and we have been involved in using it to remediate dozens of polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), pesticide, and dioxin sites. Although PFAS chemicals were designed to resist heat, we know that at high enough temperatures, they become volatile and can be extracted from the subsurface.

Additionally, PFAS compounds have limits to their thermal stability, especially in the presence of calcium carbonates, allowing thermal decomposition and evaporation of the degradation products at temperatures readily achievable with TCH (350 to 400°C)^[1]. Several studies have documented the thermal decomposition of PFAS at elevated temperatures, resulting in the production of smaller chain perfluorinated linear and cyclic aliphatic C4-C8 compounds with smaller molecular weights and lower vapor pressures than the parent PFAS compounds, that are easier to remove in the vapor phase. ^{[2] [3] [4]} .

Laboratory studies conducted by TerraTherm and our European partner Krüger have shown that our TCH technology delivers better than 99.99% removal of the targeted PFAS contaminants from soil. Soil samples from an aqueous film forming foam (AFFF) handling facility, containing initial PFAS concentrations close to 200 mg/kg, were tested in a laboratory scale treatability study. The soil was heated to temperatures from 250°C to 500°C and soil samples as well as vapor and condensate samples were collected for analysis during and after the study. The studies were designed to simulate the removal of PFAS during TCH full scale treatment either in situ or using the TerraTherm In Pile Thermal Desorption (IPTD®) concept.

Results of the study show that the thermal conductive heating process reduces the targeted PFAS concentrations by 99.998% at treatment temperatures of 350 to 400 °C within seven days of maintaining the target temperature. Due to their designed-in resistance to elevated temperature, effective remediation of PFAS compounds requires longer thermal treatment residence time at the target temperature - weeks rather than days - as compared with the typical design basis for many other organic compounds. However, the clear conclusion of the study was that the targeted PFAS compounds are efficiently removed from the soil by heating to temperatures of 350 to 400°C for seven days.

TerraTherm is currently preparing to extend the laboratory studies to a pilot-scale ESTCP project at Peterson SFB in Colorado Springs, CO (ER23-8372) and there is every reason to believe this remedy demonstration will be just as effective in the field. Since TerraTherm first implemented the TCH technology more than 20 years ago, we have implemented dozens of high temperature TCH applications in exactly the same way the successful PFAS thermal treatment laboratory studies were performed. With Krüger, we have implemented two high temperature IPTD™ projects together, treating more than 60,000 cy per batch. While the projects were targeting different recalcitrant chemicals than PFAS, the thermal treatment concept (target temperature and time at temperature) was no different than what is required for full scale PFAS treatment.

Concerned about PFAS contamination on your site? Share the project details with us, and our expert team will reach out to discuss tailored thermal remediation solutions.

^[1] Paul J. Krusic et al.: Journal of Fluorine Chemistry 126 (2005) 1510–1516

^[2]  J. A. Conesa, R. Font: Polymer Engineering & Science, 41, 12 (2001)  p. 2137–2147

^[3]  Lucia Odochian et al.: Thermochimica Acta 598 (2014) 28–35 (DOI: 10.1016/j.tca.2014.10.023)

^[4] R.K. Singh et al.:Environ Sci Technol. 2019 Mar 5;53(5):2731-2738. doi: 10.1021/acs.est.8b07031.