| The removal of trace anionic organic acids with carboxylic functional groups, such as pharmaceutically active compounds (PhACs), by anion exchange resins was studied. In this study, the removal of Ibuprofen (IBP) and Diclofenac (DCF) were evaluated at environmentally relevant concentrations (< 100 ng/L) and at higher concentrations (> 10 mg/L). These target compounds were selected for this work because they can be used as surrogates for trace anionic organic compounds in water. Both compounds are polar and acidic (anionic) in aqueous solution so that they can be removed by the ion exchange process. Few studies have evaluated PhACs removal by the ion exchange (IX) process. The overall objective was to develop combined adsorption and ion exchange models and to evaluate the relation between the resin dose needed and the removal of trace anionic organic compounds in the presence of competing anionic organic compounds present in natural organic matter (NOM)/effluent organic matter (EfOM) and inorganic compounds (e.g. sulfate) from wastewater impacted drinking water sources. In addition, the IX process for the removal of PhACs coupled with a microfiltration (MF) membrane was discussed for the purpose of IX resins separation.;The removal was found to be the sum of the physical adsorption of the ion plus the ion exchange (IX) of the ion at pH values above the pKa. The performance can be modeled by applying existing IX and adsorption equilibrium theories such as Freundlich equation and mass action laws with selectivity coefficient (separation factor) to chloride ion. For example, at a pH above 7, DCF (pKa 4.2) is completely dissociated and physical adsorption as well as ion exchange play a role in removing the ionized DCF, that is, the ionized target compounds can be adsorbed or ion exchanged by anionic resins. In the case of DCF, adsorption is important as well as IX, indicating that for the more hydrophobic DCF (log KOW = 4.5, log D=1.7 at pH 7), adsorption plays a greater role compared to IBP (log KOW = 3.5, log D=1.4 at pH 7). In this paper, a three-component batch reactor equilibrium model based on ion exchange and adsorption theories was developed and thus the impact of sulfate, NOM (Fulvic acid) or bulk EfOM, as a competing anion, was well expressed by the modified three-component IX equilibrium model. |
