Graphic and textile industries are large water users, since they use water mostly as a solvent in their coloring processes, which in turn means that they need efficient systems for waste water treatment. The coloring water has several negative effects on the environment.
Over the last few years, increasing attention to ecology promoted growth in the use of adsorption technology for treatment of industrial waste water. In adsorption, the most commonly used adsorbent is activated carbon, which is very effective, but its price is problematic. One of the solutions could be biodegradable adsorbents which are affordable and represent the most common waste in the food industry. In this paper, the efficiency of milled and pre-dried mandarin peelings as an example of an adsorbent was tested in the adsorption of direct dye from the hard and soft water. It was found that the adsorption of direct dye onto activated carbon in granules is more effective than onto mandarin peelings. The adsorption of the direct dye onto activated carbon in hard water follows closely by Langmuir and Freundlich's isotherms, however adsorption onto mandarin peelings does not follow any of the assumed adsorption isotherm. The adsorption of the dye onto activated carbon in granules in soft water
it is so good that reaches the limit values that let discharged into surface waters, while the adsorption of the dyes onto mandarin peels does not reach the desired values.