An assessment of thermal desorption as a remediation technique for per- and polyfluoroalkyl substances (PFASs) in contaminated soil

Sammanfattning: Per- and polyfluoroalkyl substances (PFASs) are a diverse group of persistent organic pollutants. PFASs have a wide area of applications such as stain repellent for paper, textile, furniture and industrial products such as aqueous film forming foams (AFFFs) used for firefighting. However, during production, usage and disposal, PFASs can be released into the environment and can therefore be a threat to humans and the ecosystems. Thus, it is important to develop soil remediation techniques for PFASs. The aim of this thesis has been to evaluate if thermal desorption can be used as a remediation method for PFASs-contaminated soil. The idea of thermal desorption is to vaporize the PFASs by high temperature, extract the PFASs from the soil by vacuum pumping and then trapping the PFASs into an air filter. The air filter can then be removed and incinerated at a high temperature to degrade PFASs. The thermal desorption has been performed in an oven at various temperatures (i.e. 150 °C, 250 °C, 350 °C, 450 °C and 550 °C) during time periods of 15 min, 45 min and 75 min for clay soil, loamy sand soil and a mixed soil from Arlanda airport. After the thermal desorption the PFASs have been extracted in methanol and then measured with an Ultra-performance liquid chromatography tandem mass-spectrometer (UPLC-MS/MS). The results show that the method is a success. 6 of 14 PFASs in the soil from Arlanda airport and all PFASs in the clay soil and the loamy sand soil reached a removal efficiency above 90 %. The results also show that all PFASs in all soils have been desorbed below the guide line value for perfluorooctane sulfonate (PFOS) for less sensitive land use, 3 mg/kg dw, given by Swedish Geological Institute (SGI). All samples have reached this limit above thermal desorption in 450 °C with treatment time 75 min.