This article reports the antagonistic and synergistic adsorption involved in the multicomponent removal of acid blue 25 dye (AB25) and heavy metal ions (Zn2+, Ni2+, Cd2+) from ternary systems using an activated carbon modified with wastes of egg shell. Adsorption experiments were performed in ternary mixtures: Zn2+-Ni2+-AB25, Ni2+-Cd2+-AB25 and Zn2+-Cd2+-AB25 where Taguchi experimental designs have been used to study the adsorbent performance and to identify the antagonistic and synergistic adsorption caused by the simultaneous presence of these water pollutants. Results indicated that these systems might show both competitive and synergistic adsorption. Dye AB25 enhanced the removal of these metallic species and reduced the competitive adsorption between the metal ions present in multicomponent solution especially for Cd2+. This synergistic adsorption caused by AB25 depends on the concentrations of dye and heavy metals, and the improvement of metal adsorption is also dependent on the metal ion. This improvement of the adsorption capacity of activated carbon could be caused mainly by the ion exchange between the heavy metals and the ion Na+ from the auxochrome functional group of the dye molecule. Traditional multicomponent isotherm models and a model based on the response surface methodology have been employed and compared in the modeling of multicomponent adsorption data. This study provides new experimental data and new findings on the multicomponent adsorption of water pollutants using activated carbon. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.