Removal of Per-and Polyfluoroalkyl Substances (PFAS) in Fixed Bed Anion Exchange Reactors: Factors Determining PFAS Uptake Capacity and Models Predicting PFAS Breakthrough
By Lan Cheng, Pingping Meng, and Detlef Knappe
Water Research
October 13, 2024
DOI: 10.1016/j.watres.2024.122629
Per- and polyfluoroalkyl substances (PFAS) are widespread contaminants with adverse environmental and public health effects. Anion exchange (IX) processes can effectively remove many PFAS from water. Objectives of this research were to (1) quantify the effects of PFAS structure and background water matrix constituents [dissolved organic matter (DOM) and major inorganic anions (bicarbonate, chloride, sulfate, and nitrate)] on PFAS uptake capacity of IX resins (KIX), and (2) develop models that predict PFAS breakthrough in IX column from PFAS structure and background water matrix characteristics. Rapid small-scale column tests were conducted with two IX resins and 19 water matrices to determine breakthrough curves and KIX values for 23 PFAS. A quantitative structure-property relationship (QSPR) was developed that predicts KIX for different PFAS from a newly developed concept, the normalized chain length (NCL). NCL for each PFAS was calculated using a group contribution method, in which the contributions of PFAS structural fragments to NCL were normalized to that of -CF2-, which was assigned a value of 1.00. Relative to -CF2-, contributions of the structural fragments -O-, -CH2-, >CF-CF3, -CHF-, and -SO3H to NCL for the purposes of KIX prediction were 0.34, -1.87, 1.70, 0.00, and 3.65, respectively. DOM and nitrate adversely impacted PFAS removal, while chloride, sulfate, and bicarbonate, when added at concentrations of up to 3 meq/L above native background levels, had negligible effects on KIX. Based on the obtained water matrix effects, pseudo-single solute models were developed for the two tested IX resins, with which PFAS breakthrough curves for fixed bed IX columns can be predicted using only the NCL and the total organic carbon and nitrate concentrations of the influent water.
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