Abstract
Remediation of soil contaminated with per- and polyfluoroalkyl substances (PFAS) is critical due to the high persistence and mobility of these compounds. In this study, stabilization and solidification (S/S) treatment was evaluated at pilot-scale using 6 tons of soil contaminated with PFAS-containing aqueous film-forming foam. At pilot-scale, long-term PFAS removal over 6 years of precipitation (simulated using irrigation) in leachate from non-treated contaminated reference soil and S/S-treated soil with 15 % binder and 0.2 % GAC was compared. PFAS removal rate from leachate, corresponding to reduction in leaching potential after 6 years, was >97 % for four dominant PFASs (perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS) and perfluorooctanesulfonic acid (PFOS)), but low (3%) for short-chain perfluoropentanoic acid (PFPeA). During the pilot-scale experiment, PFAS sorption strength (i.e., soil-water partitioning coefficient (Kd)) increased 2- to 40-fold for both reference and S/S-treated soil, to much higher levels than in laboratory-scale tests. However, PFAS behavior in pilot-scale and laboratory-scale tests was generally well-correlated (p < 0.001), which will help in future S/S recipe optimization. In addition, seven PFASs were tentatively identified using an automated suspect screening approach. Among these, perfluorohexanesulfonamide and 3:2 fluorotelomer alcohol were tentatively identified and the latter had low removal rates from leachate (<12 %) in S/S treatment.
Highlights
Contamination of soil and groundwater with per- and polyfluoroalkyl substances (PFASs) is impacting drinking water delivery systems globally, and is posing a risk to human health and the environment (Murakami et al, 2009; Li et al, 2018a; Gellrich et al, 2013; Gyllenhammar et al, 2015)
In leachate samples from the reference soil, 10 of the 18 target PFASs (PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFBS, PFHxS PFOS, 6:2 fluorotelomer sulfonic acids (FTSAs), and FOSA) were detected in concentrations ranging between 0.0026 μg L-1 (PFNA) and 32 μg L−1 (PFOS)
Treatment of PFAS-contaminated soil by resulted in high long-term removal from leachate of compounds tested in the pilot-scale experiment
Summary
Contamination of soil and groundwater with per- and polyfluoroalkyl substances (PFASs) is impacting drinking water delivery systems globally, and is posing a risk to human health and the environment (Murakami et al, 2009; Li et al, 2018a; Gellrich et al, 2013; Gyllenhammar et al, 2015). Remediation techniques based on stabilization, where PFASs are chemically immobilized by adding sorbents (e.g., activated carbon), are receiving growing attention as soil mitigation methods (Shen et al, 2019). These techniques have been shown to reduce PFAS leaching considerably (> 99 % for perfluorooctasulfonate (PFOS)) (Kupryianchyk et al, 2016; Hale et al, 2017a; McGregor, 2018a). A promising alternative is stabilization and solidification (S/S) (Sörengård et al, 2019a), where a solidifying binder (e.g., cement, bentonite, lime) is added to the soil, combining chemical binding and physical hydrogeological protection that decreases contaminant transport by leaching. The treated soil developed a monolithic structure with 4000 kPa unconfined compressive strength (UCS), indicating reliable long-term physical durability, and conservative leaching tests (crushed to < 2 mm) showed reduced leaching (by > 99.9 %) of most PFASs (except those with perfluorocarbon chain length < 4) (Sörengård et al, 2019a)
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