Effects of Chemical Oxidants on Perfluoroalkyl Acid Transport in One-Dimensional Porous Media Columns

Abstract

In situ chemical oxidation (ISCO) is a remediation approach that is often used to remediate soil and groundwater contaminated with fuels and chlorinated solvents. At many aqueous film-forming foam-impacted sites, perfluoroalkyl acids (PFAAs) can also be present at concentrations warranting concern. Laboratory experiments were completed using flow-through one-dimensional columns to improve our understanding of how ISCO (i.e., activated persulfate, permanganate, or catalyzed hydrogen peroxide) could affect the fate and transport of PFAAs in saturated porous media. While the resultant data suggest that standard ISCO is not a viable remediation strategy for PFAA decomposition, substantial changes in PFAA transport were observed upon and following the application of ISCO. In general, activated persulfate decreased PFAA transport, while permanganate and catalyzed hydrogen peroxide increased PFAA transport. PFAA sorption increased in the presence of increased aqueous polyvalent cation concentrations or decreased pH. The changes in contaminant mobility were greater than what would be predicted on the basis of aqueous chemistry considerations alone, suggesting that the application of ISCO results in changes to the porous media matrix (e.g., soil organic matter quality) that also influence transport. The application of ISCO is likely to result in changes in PFAA transport, where the direction (increased or decreased transport) and magnitude are dependent on PFAA characteristics, oxidant characteristics, and site-specific factors.

Treatment of perfluoroalkyl acids by heat-activated persulfate under conditions representative of in situ chemical oxidation

“…Few studies to date have investigated the affect of ISCO treatment on subsurface mobility of PFASs. One research group observed decreased PFAA transport in column studies with persulfate treatment at room temperature, 50 but further research is needed to assess the impact of persulfate treatment on transport of polyfluorinated compounds under heat-activation conditions.…”

A review of emerging technologies for remediation of PFASs

“…This “molecular brush” mechanism of surface interaction may also prove to be relevant in fate and transport of PFASs in the environment. For PFAAs, sorption typically increases with decreasing pH and increasing concentration of calcium (Ca 2+ ; ionic strength; Higgins & Luthy, ; McKenzie, Siegrist, McCray, & Higgins, ). At increasing ionic strengths the authors have observed a diminished ratio of straight chains to branched chain PFOS, which may be accounted for by the “molecular brush” sorption mechanism described earlier.…”

Occurrence and behavior of per‐ and polyfluoroalkyl substances from aqueous film‐forming foam in groundwater systems

“…Lower pH has also been shown to increase sorption, as has substituting calcium for sodium in solution for anionic PFAS, suggesting that while organic carbon effects dominated sorption to soil, ionic effects are also significant (Higgins & Luthy, ). A study on the impact of remediation oxidizers ( in situ chemical oxidation) on PFCA mobility found that the oxidizers had little impact on the PFCAs, but did greatly impact mobility, with permanganate and peroxide increasing transport and persulfate reducing transport (McKenzie, Siegrist, McCray, & Higgins, , ). It was thought that especially permanganate, but also peroxide, liberated soil organic matter and increased the mobility of the PFAAs, while persulfate had little impact on soil organic matter.…”