The adsorption on activated carbons of dark colored compounds contained in sugar beet vinasse was studied. Four commercial activated carbons with different properties (particle size, residual acidity and microporous properties) were respectively checked for efficiency at two temperature levels (25 degrees C and 40 degrees C) and at four pH levels (2,3.5,7, 10). The adsorption of organic molecules was determined by quantifying the amounts of total polyphenolic compounds and total organic carbon. The results showed that the adsorption capacity of dark colored compounds was enhanced by the decrease in both temperature and pH values of the solution. In this study, it is shown that this capacity depends on activated carbon characteristics which can be classified in the following order: particle size > residual acidity > microporous volume. Three models (Langmuir, Freundlich and Dubinin-Radushkevich) were tested from experimental data and compared. The Langmuir model provided the best correlation on all the activated carbons studied. (C) 2007 Elsevier Ltd. All rights reserved.