Per- and polyfluoroalkyl substances (PFASs) are persistent contaminants with adverse environmental and public health effects. Concerns about the presence of PFASs in drinking water have led to a demand for effective PFAS treatment methods. Ion exchange (IX) resins have gained attention as a treatment alternative for PFAS removal because they may be more effective for short-chain PFAS removal, including poorly understood fluoroethers, than granular activated carbon. The aims of this research were to (1) develop a scale-up procedure, based on the rapid small-scale column test (RSSCT), to predict PFAS removal in field-scale IX contactors and (2) assess the effects of PFAS characteristics (e.g., insertion of ether oxygen atoms) and background water matrix constituents (e.g., dissolved organic carbon, major anions) on PFAS removal by IX resins.<br/><br/>To develop a scale-up approach, we explored both constant and proportional diffusivity design options for RSSCTs and compared RSSCT results to pilot-scale PFAS removal data. RSSCTs were conducted with macroporous and gel-type, single-use IX resins that were crushed to yield different particle size fractions. Our results show that the constant diffusivity design effectively simulated PFAS removal kinetics in field-scale IX columns. Regarding PFAS properties, IX resin use rate decreased exponentially with increasing PFAS chain length within a given PFAS sub-class. PFASs with a sulfonic acid group were more effectively removed than those with a carboxylic acid group. Additionally, insertion of ether oxygen atoms adversely impacted PFAS removal. PFAS removal efficiency was also impacted by background water matrix constituents. By conducting RSSCTs with background water matrices that differed in total organic carbon (TOC) concentrations but matched in terms of major inorganic ions, we found IX resin use rate increased with increasing TOC concentration for PFAS with a high affinity for the IX resin. In contrast, IX use rates were not as strongly impacted by TOC concentration for PFAS that break through early. Moreover, we found that nitrate adversely affected PFAS removal, while the effects of chloride, sulfate, and bicarbonate were negligible when added at concentrations of 3 meq/L. This research will support the design of future IX treatment processes in the context of remediation and drinking water treatment.

Removal of per- and polyfluoroalkyl substances by anion exchange resins: Scale-up of bench-scale column data and effect of background water matrix constituents

ACS Spring 2022

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