Toward In Situ Sequestration of Multicomponent PFAS Using Injectable Adsorbent Suspensions

Abstract

The potential application of available adsorbents for in situ polyfluoroalkyl substances (PFAS) sequestration, including the release of previously sequestered PFAS under changing groundwater chemistries, was investigated using batch studies. Injectable adsorbent suspensions (IASs) were prepared from 2 anion-exchange resins (A-IXR and L-IXR), a powdered activated carbon, an activated charcoal, a surface-modified organoclay–carbon composite (NMC+ n ), and a carbonaceous-clay-organic material (ROAC). The IAS was amended to water-saturated sand after which multicomponent PFAS sorption and desorption with deionized water and simulated groundwater were investigated. PFAS sorption was instantaneous and chain-length-dependent, reaching approximately 100% in the IAS-amended sand, except for ROAC. In general, PFAS sorption isotherms were nonlinear, with larger sorption capacities of the long-chain than short-chain PFAS. The sorption capacity of the A-IXR (IAS) amendment was 2.5 times the capacities of the other amendments. In simulated groundwater (AGW), PFAS were released (5–100%) from the IAS amendments, especially from A-IXR, affecting mostly the short-chain PFAS and the perfluorocarboxylic acids. The release was attributed to anion exchange and electrical double-layer compression effects driven by the coexisting ions in AGW. Such a considerable release of short- and long-chain PFAS especially from anion-exchange resins should not be overlooked during decision-making regarding in situ PFAS sequestration.

Dynamic Column Studies of Multicomponent PFAS Sequestration Facilitated by Four Contrasting Injectable Adsorbent Suspensions and Associated PFAS Release in Simulated Groundwater

“…This rapid PFAS breakthrough is consistent with the minimal PFAS retention that was observed in the unamended sand during batch studies. 24 Also, breakthrough was chain-length dependent, as demonstrated by the positive correlation (R 2 = 0.63, p = 3.9 × 10 −9 ) between the perfluorinated chain length and breakthrough time (C t /C 0 = 0.05) of each PFAS (Figure S3). In general, the relative effluent concentrations of the short chain PFAS reached saturation within the first 2 PV (Figures 1 and S4−S13).…”

“…Four different IASs (0.4 to 1.2 μm, with corresponding viscosities ranging from 0.9 to 1.0 cP at 25 °C) were prepared from bulk (as supplied) commercially available adsorbents as described in our previous study. 24 The bulk adsorbents include:…”

“…Given that our previous batch studies already reported the influence of ionic composition and strength on PFAS sorption and desorption in bulk adsorbents 23 and PFAS desorption from IAS-amended sand using AGW, AGW was specifically utilized in this study to investigate the potential release of previously sequestered PFAS in the column study. 24 At the end of each column experiment, the spent column residues were dissected and oven-dried. The water-extractable PFAS and total (solvent)-extractable PFAS in the residues from each column sections were analyzed for PFAS mass balance purposes.…”

“…The detailed mechanisms of PFAS adsorption to the bulk adsorbents and IAS-amended sand have been described extensively in our previous studies. 23,24 When compared to PFOS, PFNA, and PFDA, the BTC of the long chain PFAS (PFHxS, PFHpA, and PFOA) exhibited relatively reduced extended arrival waves after increasing the influent PFAS concentration 100 times (Figure 1). However, when compared to the short chain PFAS, the retardation of PFHxS, PFHpA, and PFOA in the A-IXR column increased by 6-, 1-, and 3-folds, respectively.…”

“…In our recent batch studies, we investigated the effectiveness of 3 commercial adsorbents for multicomponent PFAS sorption and desorption, under different pH of simulated groundwater, index ion, and ionic strengths. 23 In our previous study, 24 4 different commercial adsorbents were used to prepare injectable adsorbent suspensions (IASs) that were amended to sand, after which PFAS sorption, including desorption using a simulated groundwater containing coexisting anions and cations, was investigated to interrogate the effectiveness of the adsorbents for PFAS in situ sequestration. We reported that information on potential desorption of previously sequestered PFAS is important in determining the effectiveness of an in situ technique, especially considering field applications.…”