Toward In Situ Sequestration of Multicomponent PFAS Using Injectable Adsorbent Suspensions

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.