Adsorption characteristics of granular activated carbon to typical pharmaceuticals in water

Abstract

Adsorption of four typical pharmaceutical compounds (clofibric acid, carbamazepine, naproxen, and diclofenac) on granular activated carbon was evaluated by batch and dynamic experiments. Coconut shell-based activated carbon was selected as the activated carbon adsorbent for the present experiments based on comparison of the adsorption efficiency and characterization of charcoal-based and coconut shell-based activated carbon. At a carbon dosage of 133 mg·L-1, the equilibrium adsorption capacities of coconut shell-based activated carbon for clofibric acid, carbamazepine, naproxen, and diclofenac were 2.48, 3.0, 2.74, and 2.52 mg·g-1, respectively. Bottles containing each sample were sealed and shaken at 150 r·min-1 at 25℃. Clofibric acid was the most poorly adsorbed, followed by diclofenac, whereas carbamazepine was the most effectively adsorbed. The adsorption kinetics and linear isotherm model obtained are best described by a pseudo-second-order kinetic model and the Freundlich isotherm model, respectively. The adsorption rate was influenced by chemical-adsorption, intrapartical diffusion, surface adsorption, and film diffusion. The adsorption capacity of the coconut shell-based activated carbon for the pharmaceuticals was found to be related to the pKa, lgKow, and the solution conditions. The comparison of the removal of the four target compounds from ultrapure water, unfiltered effluent, and filtered effluent by coconut shell-based activated carbon showed that the ionic strength of the wastewater was the key factor, leading to diminished electrostatic interactions between the activated carbon and pharmaceuticals. Dissolved organic compounds decreased the removal of target compounds to some extent by competing for the adsorption sites in activated carbon. It indicated that carbamazepine was the most adsorbable, and clofibric acid was the least among the four pharmaceuticals by fixed bed column operation on coconut shell-based activated carbon, which was in agreement with batch experiment.