Zimm-Bragg Model Applied to Sorption of Dyes by Biopolymers: Alginic Acid and Xanthan

Abstract

Dyes and dyeing processes are widely used as a means of introducing color into fibers or fabrics. Dyes should be easily introduced into the fiber and then, the color must be reasonably permanent (wash-fast) and stable to light (light-fast). Dyes exhibit considerable structural diversity and are classified by their chemical structure, application to the fiber type and/or solubility. A general classification accommodates these compounds as anionic (acid, direct and reactive dyes); cationic (basic dyes); and non ionic (disperse dyes). Disperse Yellow 54 (DY54) is a typical dye which can be used in dispersed form to color polyester, polyamides, nylon, acrylic fibers and plastics. Direct Black 22 (DB22) is a cationic compound (at neutral pH) that imparts color to cotton, cellulose, leather, wool and silk (Holme, 2000; Ali, 2005). The chemical structures of DY54 and DB22 are represented in table 1. Despite the fact that supercritical methods (Ozcan et al., 1997; Joung & Yoo, 1998; Guzel and Akgerman, 1999; Lee et al., 1999; Sung & Shim, 1999; Shinoda and Tamura, 2003; Hou & Dai, 2005) have been developed to improve the performance of dyeing processes, still conventional (dye baths) methods are widely used (Holme, 2000). During dyeing processes great amounts of unfixed dyes (which vary considerably depending on dye-fiber affinity and dyeing process parameters) may be lost to the effluent. The release of these effluents in water streams results in serious environmental impacts. The development of an environmentally benign methodology for the removal of dyes from textile wastewaters still represents a major technological challenge. It is well known that textile industries, pulp mills and dyestuff manufacturing discharge highly colored wastewaters which represent an aesthetic problem and reduce photosynthetic activity in the receiving water into which they are discharged. Nowadays, many dyes are designed for their chemical stability (wash and light fastness) and do not undergo biochemical degradation readily. For instance, anthraquinone based dyes are more resistant to biodegradation (oxidation rates are very slow) due to their fused aromatic structures (Baughman & Weber, 1994). Since azo dyes are the most widely used, several degradation methods have been implemented to remove them from water, among them, anaerobic treatments predominate. The main drawbacks of this approach are its elevated cost and the production of carcinogenic aromatic amines which limits macro-scale application (Ogawa & Yatome, 1990; Knapp & Newby, 1995; Weber & Adams, 1995).