Remediation of per- and polyfluoroalkyl substance-contaminated soil and groundwater, using electrokinetic and stabilisation methods

Sammanfattning: Per- and polyfluoroalkyl substances, commonly known as PFAS, are emerging contaminants with a worldwide environmental distribution and a concerning (eco)toxicological profile. The omnipresence of PFAS in various environmental media poses risks to the quality of our drinking water sources. Soils can act as inventories of PFAS plumes, which can slowly find their way into water resources. There is an imperative need for treatment applications at the pollution hotspots to prevent the spreading of PFAS into water bodies. This thesis aimed to investigate the potential of two technologies for treating PFAS-contaminated soils and groundwater: one focused on PFAS removal using electrokinetics and the other on their immobilisation in the subsurface using stabilisation with colloidal activated carbon (CAC). The findings of this thesis show that both methods can be promising; however, their effectiveness depends on compound-specific parameters and field considerations at the contaminated sites. The electrokinetic removal was highly effective for short-chain PFAS, with up to 99% removal for PFAS with C≤6 in their perfluorocarbon chain. Electrokinetic removal was also coupled with immobilisation by transporting and entrapping 75% of ∑PFAS to GAC. Conversely, stabilisation with CAC was more successful for long-chain PFAS and more for perfluoroalkyl sulfonates (PFSAs) than perfluoroalkyl carboxylic acids (PFCAs), with lab tests indicating an average of eight times retardation of PFAS in CAC-treated soils. Desorption from CAC was not significant, signifying that immobilisation with CAC can be effective in the long term. Challenges in applying both methods were also identified; electrokinetic remediation can be limited due to the low solubility of certain PFAS and the depletion of ions from the soil matrix, which might increase the complexity of the treatment and its costs. Stabilisation with CAC did not prove viable for the treatment of short-chain PFAS. Moreover, CAC was partially flushed out of the soil, with column tests showing a loss of 22% of the added CAC. These aspects must be considered in full-scale treatment applications to ensure optimal treatment. The PFAS composition is another critical parameter in stabilisation treatment, as the results showed competition among PFAS for sorption sites, with FOSA dominating its counterparts and short-chain PFAS being outcompeted by their long-chain homologues at higher concentrations. Immobilisation was also tested in a field study, which confirmed the results of the lab experiments, exhibiting the potential for PFAS contamination and highlighting the challenges. Nonetheless, the effectiveness of the stabilisation methods needs to be contextualised within the requirements and limitations of each contaminated site. In the future, optimising the technologies studied in this thesis can likely lead to higher efficiency, while combining these methods with other technologies, such as degradation, can be beneficial for the holistic management of PFAS-impacted sites.