The adsorption in some natural materials containing chitin namely, Squid (Loligo vulgaris) and Sepia (Sepia officinalis) pens, and Anodonta (Anodonta cygnea) shells for color removal from textile wastewaters was studied. A reactive and a direct green dyestuff, the Cibacron green T3G-E (CI reactive green 12) and the Solophenyl green BLE 155% (CI direct green 26) from CIBA, respectively, were selected for this study. Continuous experiments in a packed column at 20 degrees C with the natural materials showed a large internal resistance to mass transfer. In order to improve the adsorbents performances, the materials were submitted to chemical treatment (demineralization and/or deproteinization). Isotherms at 20 degrees C were determined for all systems and compared with the ones using the materials after chemical treatment. These results were fitted by both Langmuir and Freundlich models. The determined parameters showed that equilibrium adsorption capacities increased at least five times. These results and the mathematical simulation of the column runs showed that there are improvements both in equilibrium and kinetic data. The adsorbents physical and chemical properties before and after chemical treatment were briefly characterized in order to investigate the changes responsible for those improvements. Biodegradation of the direct dyestuff was observed during the column operation using both the Anodonta shell and Sepia pen. For these two systems the chemical treatment of the materials did not improve the color removal. Biodegradation was included in the developed model and the influence of the model parameters on the system behavior was analyzed.