The preparation of carbon from waste materials is a recent and economic alternative for the removal of dyes. In this study four samples of carbon were obtained by thermal treatment at 1000 degrees C using as precursor the guava seed with different particle sizes. The Taguchi method was applied as an experimental design to establish the optimum conditions for the removal of acid orange 7 in batch experiments. The chosen experimental factors and their ranges were: pH (2-12), temperature (15-35 degrees Q, specific surface area (50-600 m(2) g(-1)) and adsorbent dosage (16-50 mg ml(-1)). The orthogonal array L-9 and the larger the better response category were selected to determine the optimum removal conditions: pH 2, temperature 15 degrees C, S-esp 600 m(2) g(-1) and dosage 30 mg ml(-1). Under these conditions a total removal of acid orange 7 was achieved. Moreover, the most significant factors were the carbon specific surface area and the pH. The influence of the different factors on the adsorption of acid orange 7 from solution is explained in terms of electrostatic interactions by considering the dye species and the character of the surface. (C) 2009 Elsevier B.V. All rights reserved.