Smoldering Treatment of PFAS: Investigation of Mass Balance and Volumetric Scale Up for Field Implementation

The chemical properties of perfluoroalkyl and polyfluoroalkyl substances (PFAS) pose a significant remediation challenge. This study investigated smoldering combustion to destroy PFAS while scaling up from the lab to field implementation. The first phase consisted of bench-scale tests using a model soil system. Calcium oxide (CaO) was used as a soil amendment in some of the test cases. For all test conditions, greater than 99.9% removal of PFAS was achieved. Post-treatment soils without CaO amendments were found to have a significant reduction in total fluorine concentrations, while the fluorine concentrations in soils with CaO amendments were similar following treatment. This suggests that fluorine emissions from smoldering treatment of PFAS are captured by the presence of the calcium ion (Ca²⁺). Using new analytical methods, we better characterized the mass balance of the system. These lab results were carried out in a pilot study using soils from a PFAS-impacted site. Two large-scale tests treating 10 m³ of soil were completed. Results of the large-scale smoldering tests agreed with the results from the lab phase. The results from both phases provide a greater understanding of the fate of PFAS when it is treated by smoldering and detail the first large-scale demonstration of smoldering treatment for PFAS-impacted soils.