Evaluating the Performance of Novel Cyclodextrin Polymer Granules to Remove Perfluoroalkyl Acids (PFAAs) from Water

Abstract

Cyclodextrin polymers (CDPs) are promising adsorbents for the removal of per- and polyfluoroalkyl substances (PFASs) from water. For CDPs to be implemented in packed-bed filtration (PBF) systems, CDP powders must be processed to produce CDP granules of a defined size. In this study, we introduce CDP granules with average particle diameters (dp) of 84–718 μm produced from a CDP powder by means of high-shear spray granulation. We evaluated the performance of the CDP granules in batch studies to evaluate the adsorption kinetics, capacity, and affinity for six perfluoroalkyl acids (PFAAs). We also performed rapid small-scale column test (RSSCT) experiments for three of the CDP granules (dp = 84, 175, 359 μm) to test whether the assumptions of constant diffusivity (CD) or proportional diffusivity (PD) are appropriate for these CDP granules. We found that CDP granules exhibit slower adsorption kinetics than the CDP powder (rate constants ranging between 0.2 and 2.7 g mg–1 h–1 for all PFAAs and all CDP granules), but that CDP granules of varying sizes exhibit relatively consistent adsorption kinetics. Adsorption capacity (139–479 μmol g–1) and affinity (0.6–149 L mg–1) were relatively constant across CDP granules of varying particle diameters for all PFAAs but adsorption capacity decreased and adsorption affinity increased for longer-chain PFAAs. Data from the RSSCT experiments suggest that neither the assumption of CD nor PD are unequivocally appropriate for CDP granules and that an improved understanding of mass transfer limitations as a function of particle size is essential. Overall, our results demonstrate the potential for novel CDP granules to be implemented in PBF systems for the removal of PFAAs from water.