Incineration is often used as a treatment option for soils laden with per- and polyfluoroalkyl substances (PFAS), but shipping and disposal costs can be quite high. As an alternative, the objective of this project is to demonstrate in situ thermal remediation (ISTR) technology for PFAS removal from ex situ soil stockpiles. This field demonstration will determine ISTR effectiveness of PFAS volatilization by evaluating PFAS soil removal efficiency and extracted vapor and condensate treatment efficiency.
Soils will be heated by installing flexible heating elements directly into the soil stockpile. The soil initially will be heated to the boiling point of water to remove soil moisture. Due to the PFAS vapor-liquid equilibrium and bonds holding PFAS to soil, less than 0.1% of PFAS are expected to be removed from soil during the water removal stage. Substantial volatilization is expected to occur once soils reach 350°C. For volatilized PFAS recovery, extracted vapors will be collected by applying a vacuum on the soils; these will then be cooled in a scrubber where PFAS will be transferred to the aqueous phase in a concentrated, low-volume solution. The goal is to demonstrate that this technology can provide greater than 99% reduction of PFAS concentrations in soil. Effluent vapors and process water will be treated using granular activated carbon (GAC) on site.
This approach will provide an innovative technology that results in permanent PFAS removal, thereby protecting human health and the environment. Applied on site, heat (a straightforward and proven technology), also reduces costs and risks associated with off-site transportation and disposal of PFAS-laden material. The technology is scalable and is likely to be suitable for both in situ and ex situ applications.