Competitive removal of dissolved organic matter (DOM) and inorganic anions by anion exchange resins (AERs)

Four strong-base anion exchange resins (AERs) with different properties were selected to investigate dissolved organic matter (DOM) removal from river water containing inorganic anions. Rapid sand-filtered water was obtained from a water treatment plant in Tokyo, Japan, and then concentrated by an ultrafiltration membrane for use in ion exchange experiments to simulate high dissolved organic carbon (DOC) and sulfate conditions. AERs removed 23–50% of DOC and 70–80% of UV254 within 30 min despite high sulfate concentration (121 mg/L). Although the materials and structure of the AERs did not affect the reduction of UV254, DOC removal was affected. The highest DOC reduction was achieved by a macroporous polyacrylic AER (Purolite), while the macroporous polystyrene IRA 910 had the lowest DOC removal. A pseudo-second-order kinetic model showed that the rate constants and the initial sorption rates of polyacrylic resins were higher than those by polystyrene resins, suggesting that more hydrophilic structure of AERs exhibited faster DOC removal. Aromatic DOM with a molecular weight (MW) of 800–3,000 Da was almost completely removed by AERs, whereas only half of aromatic DOMs smaller than 800 Da were removed by AERs. Adsorbed DOC comprised less than 6% of all exchanged anions, whereas the adsorbed sulfate was about 90% due to comparatively high concentration of sulfate in the water sample.