The Brazilian pine-fruit shell (Araucaria angustifolia) is a food residue, that was used as biosorbent for the removal of non-hydrolyzed reactive red 194 (NRR) and hydrolyzed reactive red 194 (HRR) forms from aqueous solutions. Chemical treatment of Brazilian pine-fruit shell (PW), with chromium (Cr-PW), with acid (A-PW), and with acid followed by chromium (Cr-A-PW) were also tested as alternative biosorbents for the removal of NRR and HRR from aqueous effluents. It was observed that the treatment of the Brazilian pine-fruit shell with chromium (Cr-PW and Cr-A-PW) leaded to a remarkable increase in the specific surface area and average porous volume of these biosorbents when compared to unmodified Brazilian pine-fruit shell (PW). The effects of shaking time, biosorbent dosage and pH on biosorption capacity were studied. In acidic pH region (pH 2.0) the biosorption of NRR and HRR were favorable. The contact time required to obtain the equilibrium was 24 h at 25 degrees C. The equilibrium data were fitted to Langmuir, Freundlich, Sips and Redlich-Peterson isotherm models. For NRR reactive dye the equilibrium data were best fitted to the Sips isotherm model using PW and A-PW as biosorbents, and Redlich-Peterson isotherm model using Cr-PW and Cr-A-PW as biosorbents. For HRR reactive dye the equilibrium data were best fitted to the Sips isotherm model using PW, A-PW and Cr-A-PW and the Redlich-Peterson isotherm model for Cr-PW as biosorbent. (C) 2007 Elsevier B.V. All rights reserved.