Impact of natural organic matter characteristics and inorganic anions on the performance of ion exchange resins in natural waters

Ion exchange (IX) process is increasingly used as a cost-effective treatment for the removal of natural organic matter (NOM) from drinking water. However, fundamental studies under the influence of variable NOM characteristics and inorganic anions have often been overlooked. This is important given NOM characteristics (such as charge density and molecular weight) and inorganic anions concentrations are geographically and seasonally variable. We examined the performance of a strongly basic IX resin for the simultaneous removal of NOM, inorganic ions and micropollutants (Perand polyfluoroalkyl substances (PFAS) and algal toxins), from different surface and recycled waters. The results indicated >70% removal of NOM for ∼20,000 Bed Volumes (BV) with an uptake of NOM fractions following the order of their respective charge densities. IX pore blockage and consequent site reduction was observed in the presence of higher molecular weight NOM fractions (breakthrough ∼7,000 BV). Moreover, NOM and inorganic ions breakthrough corresponded to ∼85–90% site occupancy (in meq) in the absence of pore blocking compounds. IX also provided simultaneous removal of inorganic ions (>90%) and charged micropollutants. Complete removals of Microcystin-LR and multiple longand short-chained PFAS were achieved at environmentally relevant concentrations with dosages of 1,000 mg/L (or 4.5 mL/L) or higher.