Removal of pharmaceuticals by clay-polymer sorbents: Batch and filtration experiments

Abstract

Significant concerns have been raised up due to the presence of organic micropollutants in surface waters. The ability of two polymer-clay sorbents (Tct-bent; Pnb-bent) based on a functionalized cationic starch was examined for the removal of three pharmaceuticals: atenolol (AT), sulfamethoxaxole (SMX) and diclofenac (DC). In batch experiments, the Tct-bent complex which exhibited a planar conformation of the polymer on the clay surface and higher cationic charge density showed higher sorption of DC and SMX over those of Pnb-bent but similar with AT. An analysis of the sorption by fitting to Langmuir equation showed a preferential sorption of DC over SMX on the polymer-clay complexes: lesser sorption sites (lower Ro) but more energetically favored (higher binding coefficient, KL). The sorption mechanisms of DC and SMX on Tct-bent were determined by thermal and infrared techniques: DC molecules formed an ion pair including hydrogen bonds through their secondary amine groups; SMX sorbed by strong electrostatic interactions followed by proton transfer involving its sulphon-nitrogen group and the hydroxyl moieties of the composite. Filtration experiments showed a better performance of the columns made of Tct-bent on DC and SMX over that of GAC (Figure 1). Accordingly, there are certain pollutants as those capable of protonation in solution (AT) that are sorbed on the developed hydrophobic domains of the polymer but in a smaller extension than GAC. Therefore, further studies should address the possibility of using mixed filters containing polymer-clay composites and GAC for a more efficient filtration. The filtration processes were successfully modeled by using an adsorption-convection model which enabled predictions under different operational conditions.