Pharmaceutical emerging pollutants removal from water using powdered activated carbon: Study of kinetics and adsorption equilibrium

Pharmaceutical products and their byproducts which are present in wastewater and superficial water are becoming an environmental problem. A large effort has been made to introduce new and more efficient treatment processes for removing these emerging pollutants. Among them, activated carbon is currently being studied to be implemented in wastewater treatment plants. In the present study the equilibrium and kinetics of the adsorption of carbamazepine (Cbz) and sildenafil citrate (Sil) onto powdered activated carbon are presented. Batch experiments were performed to assess the potential of this kind of activated carbon for removing these recalcitrant pharmaceuticals from aqueous systems. In addition, its adsorption efficiency was compared with the granular activated carbon. The isotherms of Langmuir, Freundlich, Langmuir-Freundlich and Redlich-Peterson were applied. Pseudo-first and pseudo-second order models, as well as a combined model and an intraparticle diffusion model were assayed on the results obtained. Linear and non-linear analyses were carried out to compare the best fitting isotherms and kinetics. The Langmuir isotherm was a good fit for the adsorption of Sil, whereas the Redlich-Peterson isotherm described the adsorption of Cbz. The experimental results for both pharmaceuticals follow a kinetic of pseudo first order. Comparative studies preparing the solutions with distilled water, dechlorinated water and wastewater were performed. No significant differences were observed in these studies. When initial concentrations similar to those found in surface waters for both pharmaceuticals were evaluated, removal efficiencies greater than 85% were obtained. Therefore, the use of this kind of activated carbon seems to be an efficient tool for the removal of recalcitrant emerging pollutants, such as Sil and Cbz.