Removal of isoproturon from aqueous solution by adsorption onto a commercial activated carbon

Abstract

INTRODUCTION Nowadays the number of hazardous compounds occurring in the water environment is increasing. The substances called as priority compounds, detailed in the Water Framework Directive (2000/60/CE), are of special concern; pesticides such as isoproturon are included in this category. The objective of this experimental work was to evaluate the removal of isoproturon from water by adsorption onto a commercial activated carbon. Equilibrium and dynamic adsorption experiments were carried out. MATERIALS AND METHODS Isoproturon was used in the experiments without any further purification. Ultrapure water was used in the adsorption tests. Granular activated carbon supplied by Calgon was used in the study. Batch adsorption experiments were accomplished, in order to study the kinetic and equilibrium adsorption data. Therefore, fixed-bed adsorption tests were carried out, obtaining the breakthrough curves of the system. Isoproturon concentration in the samples was determined by HPLC technique. RESULTS AND DISCUSSION The equilibrium time onto Calgon F400 activated carbon was achieved after 300 hours. The obtained equilibrium adsorption isotherm could be classified as L1-type, according to Giles classification, with a maximum adsorption capacity of 316 mg.g-1. As a result of the fixed-bed adsorption experiments, isoproturon breakthrough curves onto F400 activated carbon at different initial concentration (50-150 µg.L-1), volumetric flow rate (2.0-3.0 mL.min-1) and mass of adsorbent (0.1-0.3 g) were obtained. The breakthrough curves showed a low slope-profile, indicating a slow mass transport rate due to a high diffusional resistance, probably attributed to the orientation of the molecule in the inner pores and/or to the high microporous nature of the adsorbent. CONCLUSIONS A batch adsorption capacity of 316 mg.g-1 and saturation adsorption capacities from 9.6 to 21.6 mg.g-1 were obtained onto the commercial activated carbon. The hydrophobic nature and low water solubility of isoproturon molecule could enhance the affinity towards the hydrophobic surface of the carbon. The presence of an aromatic ring on its structure contributes to a higher interaction with the carbonaceous surface. ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support from Ministerio de Economía y Competitividad Contract CTM2014-53485-REDC-TRAGUANET, CTQ2014-59011-R REMEWATER and by Comunidad de Madrid through REMTAVARES Network S2013/MAE-2716.