Excavated vs novel in situ soil washing as a remediation strategy for sandy soils impacted with per- and polyfluoroalkyl substances from aqueous film forming foams

This study investigated the mobilization of a wide range of per- and polyfluoroalkyl substances (PFASs) present in aqueous film-forming foams (AFFFs) in water-saturated soils through one-dimensional (1-D) column experiments with a view to assessing the feasibility of their remediation by soil desorption and washing. Results indicated that sorption/desorption of most of the shorter-carbon-chain PFASs (C ≤ 6) in soil reached greater than 99% rapidlyafter approximately two pore volumes (PVs) and were well predicted by an equilibrium transport model, indicating that they will be readily removed by soil washing technologies. In contrast, the equilibrium model failed to predict the mobilization of longer-chain PFASs (C ≥ 7), indicating the presence of nonequilibrium sorption/desorption (confirmed by a flow interruption experiment). The actual time taken to attain 99% sorption/desorption was up to 5 times longer than predicted by the equilibrium model (e.g., ∼62 PVs versus ∼12 PVs predicted for perfluorooctane sulfonate (PFOS) in loamy sand). The increasing contribution of hydrophobic interactions over the electrostatic interactions is suggested as the main driving factor of the nonequilibrium processes. The inverse linear relationship (R 2 = 0.6, p < 0.0001) between the nonequilibrium mass transfer rate coefficient and the Freundlich sorption coefficient could potentially be a useful means for preliminary evaluation of potential nonequilibrium sorption/desorption of PFASs in soils.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Assessment of Mobilization Potential of Per- and Polyfluoroalkyl Substances for Soil Remediation

Nguyen

Bräunig

Kookana

et al. 2022

“…Various physical and chemical treatment processes have been explored to remove PFASs from environmental media . Physical treatment processes such as adsorption, − ion exchange, − and membrane filtration , are effective for contaminated water or aqueous waste streams (e.g., soil washing), but they produce solid or liquid wastes containing high concentrations of PFASs that still require defluorination to alleviate long-term environmental impacts. While conventional and advanced chemical treatment methods such as oxidation (e.g., ozone, UV/H 2 O 2 ) are largely ineffective for destruction of PFASs, a number of advanced methods are being developed including electrochemical oxidation, sonolysis, bioremediation, advanced reduction, and nonthermal plasma. − In general, these latter technologies are unproven at scale and/or poorly defluorinate PFASs in time frames that are useful for full-scale application.…”

Section: Introductionmentioning

confidence: 99%

Critical Review of Thermal Decomposition of Per- and Polyfluoroalkyl Substances: Mechanisms and Implications for Thermal Treatment Processes

Wang

Lin

et al. 2022

103

Per-and polyfluoroalkyl substances (PFASs) are fluorinated organic chemicals that are concerning due to their environmental persistence and adverse human and ecological effects. Remediation of environmental PFAS contamination and their presence in consumer products have led to the production of solid and liquid waste streams containing high concentrations of PFASs, which require efficient and cost-effective treatment solutions. PFASs are challenging to defluorinate by conventional and advanced destructive treatment processes, and physical separation processes produce waste streams (e.g., membrane concentrate, spent activated carbon) requiring further post-treatment. Incineration and other thermal treatment processes are widely available, but their use in managing PFAS-containing wastes remains poorly understood. Under specific operating conditions, thermal treatment is expected to mineralize PFASs, but the degradation mechanisms and pathways are unknown. In this review, we critically evaluate the thermal decomposition mechanisms, pathways, and byproducts of PFASs that are crucial to the design and operation of thermal treatment processes. We highlight the analytical capabilities and challenges and identify research gaps which limit the current understanding of safely applying thermal treatment to destroy PFASs as a viable end-of-life treatment process.

“…While Quinnan et al and Schaefer et al measured PFAS concentrations using field-deployed lysimeters in AFFF-impacted unsaturated zone soils, neither of these studies evaluated how PFAS porewater concentrations (and correspondingly the PFAS mass discharge to underlying groundwater) change with PFAS mass removal from the soil. A recent field study estimated the mass of PFOS removed during in situ soil flushing using tap water and showed that up to 73% of the PFOS mass in the vadose zone was removed. However, this study only focused on PFOS, and PFOS porewater concentrations were not measured as a function of PFOS mass removal.…”

Section: Introductionmentioning

confidence: 99%

Leaching of Perfluoroalkyl Acids during Unsaturated Zone Flushing at a Field Site Impacted with Aqueous Film Forming Foam

Schaefer

Lavorgna²,

Lippincott³

et al. 2023

While several studies have focused on perfluoroalkyl acid (PFAA) leaching from soils, field studies evaluating the relationship between PFAA mass removal and porewater concentrations as the PFAA source becomes depleted are lacking. Herein, in situ water flushing was performed at a site historically impacted with AFFF to accelerate the leaching of PFAAs from unsaturated soils in a highly characterized field test cell. Porous cup suction lysimeters were used to assess the changes in PFAA porewater concentrations as a function of PFAA mass removal from the unsaturated soils, where flushing was intermittently paused to determine ambient PFAA porewater concentrations. Results showed that the fractional decreases in PFAA porewater concentrations during flushing exceeded the fractional decrease in PFAA mass removal from the soil. PFOS porewater concentrations decrease by 76% (with negligible rebound) compared to only a 7.4% decrease in overall PFOS mass removed from the unsaturated zone. Overall, the results observed herein suggest that, when considering soil impacts to groundwater, less stringent soil cleanup criteria than those that consider an equivalent relationship between mass removal and mass discharge may be appropriate. In addition, remedial approaches that remove only a modest fraction of the PFAA soil mass may be protective of underlying groundwater, particularly for perfluorinated sulfonates with at least six carbons.