Senior Engineer, Principal Technologist
Field Demonstration of Infrared Thermal Treatment of Per- and Polyfluoroalkyl Substances (PFAS)-contaminated Soil from Subsurface Investigations
Because no cost-effective on-site IDW treatment options exist for per- and polyfluoroalkyl substances (PFAS), CH2M HILL/Jacobs, Battelle Memorial Institute, Iron Creek Group, SGS AXYS, and the Colorado School of Mines are demonstrating infrared thermal treatment of PFAS-impacted IDW soil using a transportable treatment unit. The ability to treat soil onsite with a scalable system, provides a sustainable solution to managing soil IDW. The treatment system can be loaded on a flat-bed truck and is purposefully designed to be energy efficient to economical treat contaminated soil for onsite reuse at remote sites. Two batches (up to 10 tons) of different concentrations of soil are being treated. The objectives of this pilot study include (1) evaluating whether infrared thermal treatment technology can effectively remove PFAS from contaminated soil that allows for soil re-use on site, (2) documenting the fate of PFAS in the treatment process, and (3) demonstrating that the PFAS removed from soil and transferred to vapor-phase can be captured. On site re-use is defined by the Alaska Department of Environmental Control promulgated “migration to groundwater” standards for perfluorooctanoic acid and perfluorooctane sulfonate of 1.7 and 3.0 micrograms per kilogram, respectively. The study will teat two batches of approximately 10 tons (20 to 30 drums) of soil during a 1-week pilot test period per batch using indirect-fired infrared heat with a target temperature of 350C, based on several phases of recent bench-scale study. Treatment will occur by heating in a zero-oxygen environment (to reduce volatilization) to desorb PFAS, then forcing the heated PFAS-laden gas through a core heating conduit traversing the interior of the compartment. The flow of heated gas is redirected from the core heating conduit to a space between the exterior of the bin and the interior of the bin’s housing insulator, to provide indirect heating to the contaminated material (aka “Dual Heating”). Resulting vapors are condensed in an exhaust header through numerous vapor outlets allowing for high-temperature treatment with no moving parts and therefore minimal maintenance. During each treatment batch, soil samples will be collected daily, and vapor cartridges, condensate, vapor-phase granular activated carbon (VGAC) and wipe samples from the treatment chamber will be collected before and after treatment. Results will be used to confirm the mass of PFAS removed and captured, assess where it is captured, and how PFAS are removed from the soil and retained on the vapor-phase. While some PFAS may be destroyed at the relatively low target temperature (350C), the goal of the technology is not to destroy PFAS, which could generate fluorine and ultimately hydrofluoric acid. Detailed analysis of PFAS, including TOPA, will help understand the initial composition of the soil and how PFAS in transforms in the system. Earlier bench-scale tests have demonstrated almost complete removal of PFAS from AFFF-impacted soil at 350C within 4 days. Currently, results are not available but will be for the presentation. Collected data will allow for a mass balance evaluation to assess the PFAS desorption process, including destruction, confirm capture on VGAC, and determine project success.