The occurrence of emerging contaminants in wastewaters, and their behaviour during wastewater treatment and production of drinking water are key issues in the re-use of water resources. The objective of this study was the adsorption of caffeine and diclofenac from aqueous solutions on fixed beds of granular activated carbon. Several operation conditions on the shape of breakthrough curves were investigated. Adsorption equilibrium is reached after 3 days for caffeine and after 14 days for diclofenac. In caffeine, breakthrough times, corresponding to C/C-0 = 0.02 were found to be 19.1, 47.6 and 48.5 h for the columns operating with bed weights of 0.6, 0.8 and 1.0 g, respectively. Saturation times (corresponding to C/C-0 = 0.95) were found to be 91.8, 114.3 and 121.0 h, respectively. The activated carbon is not an efficient adsorbent for diclofenac. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.