Assessing Rapid Small-Scale Column Tests for Treatment of Perfluoroalkyl Acids by Anion Exchange Resin

Bench-scale column experiments were performed to evaluate the applicability of employing rapid small-scale column tests (RSSCTs) for the removal of perfluoroalkyl acids (PFAAs) from groundwater, using ground and unground anion exchange resins (AERs). Specifically, experiments were designed to assess the applicability of scaling the overall rate of PFAA uptake to the AERs by r(-2), where r is the AER particle radius. Two commercially available AERs were examined. Such scaling is generally assumed to be appropriate if uptake is controlled by intraparticle diffusion with a constant diffusion coefficient. Results showed that, for each AER tested, short-chained PFAAs migrated through the columns more rapidly than the longchained PFAAs. Also, for a given perfluorinated chain length, the perfluorinated carboxylates migrated through the AERs more rapidly than the corresponding perfluorinated sulfonates. PFAA elution through the AERs was well-described by the Thomas model, which assumes rate-limited uptake and Langmuir-type sorption. Results also showed that appropriate scaling (r(-2)) was valid as long as PFAA adsorption to (or near) the AER particle surface was taken into account by scaling the equilibrium sorption capacity to r(-0.5). Including these scaling factors resulted in excellent agreement between the ground and unground AER results. These results suggest that the RSSCT approach to expedite bench-scale testing can be applied for PFAA uptake onto AERs, although the impacts of various groundwater geochemical conditions and the presence of a broader range of polyfluoroalkyl and perfluoroalkyl substances on the appropriateness of the RSSCT approach remains unknown.