Adsorption of Organic Micro-pollutants by zeolite granules: Batch and column studies

Abstract

The presence of organic micro-pollutants (OMPs) has caused increasing contamination of aquatic systems. In recent years, the selective adsorption of target OMPs by zeolites have been proved efficient for OMP removal. For the potential application of zeolites in the wastewater treatment plants, zeolite granules are preferably used in order to avoid the post-filtration for zeolite powders. Therefore, the knowledge on the performance of zeolite granules for the removal of OMPs should be fully understood. In this research, BEA and MOR zeolite granules were used as adsorbents for the removal of 11 OMPs from water, which were carbamazepine, diclofenac, 1H-benzotriazole, methyl-benzotriazole, hydrochlorothiazide, sulfamethoxazole, clarithromycin, propranolol, trimethoprim, metoprolol and sotalol. The aims of this study were: (1) to investigate the adsorption capacity and kinetics of the 11 OMPs by zeolite granules in both demineralized water and wastewater (WW), in batch experiments; (2) to predict the breakthrough curve of columns packed with zeolite granules by using a mathematical model combining the parameters determined by batch experiments. It was found that the charge and hydrophobicity of OMPs were the two main factors that affected the adsorption capacity of OMPs by zeolites, while the effect of OMP size on the adsorption capacity was negligible. The OMP adsorption capacities by zeolite granules were less than OMP adsorption capacities by zeolite powders. The fittings of the IPD model to the adsorption kinetic data showed that film diffusion and intra-particle diffusion were both the rate-limiting steps in the adsorption of OMPs by zeolite granules. Furthermore, the adsorption capacity and rate of OMPs in WW were lower in comparison with OMP adsorption in demineralized water, which could be caused by the higher pH in WW and the pore-blocking effect by background organic matters. In the column experiments, it was found that OMP breakthrough percentage in the column was determined by both the adsorption capacity and kinetics of OMPs by zeolite granules. In the breakthrough model, the kinetic and isotherm constants from batch experiments overestimated the adsorption rate and capacity of zeolite granules in the columns, and the overestimated isotherm constant was the main factor that caused the deviation of the model prediction. With a lower isotherm constant, the model was able to provide good resemblance between modelled and measured breakthrough curves. Furthermore, with a known breakthrough curve at a certain EBCT, the model was able to determine a proper isotherm constant, which can be used to predict the breakthrough curve at a different EBCT.