Removal of Per- and Polyfluoroalkyl Substances (PFAS) in fixed bed anion exchange reactors: Factors determining PFAS...

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 (K_IX), and (2) develop models that predict PFAS breakthrough in packed bed IX columns from PFAS structure and background water matrix characteristics. Rapid small-scale column tests were conducted with two IX resins and 18 water matrices to determine breakthrough curves and K_IX values for 23 PFAS. A quantitative structure-property relationship (QSPR) was developed that predicts K_IX 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 K_IX 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 K_IX. 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.