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| Category: Science |
Date published: March 2, 2011 |
Dyes are intensely colored substances that can be used to produce a significant degree of coloration when dispersed or reacted with other materials .The dye molecule can be considered to be structured from two components, the dye chromophore and the dye functional group.
Organic dye industry has been developing rapidly today, approximately 10,000 types of dyes are produced annually and used in diverse applications, the annual world production amounts to nearly one million tons, more than half of them are azo dyes [22,35]. Azo compounds constitute the largest and most diverse group of dyes and pigments used in commercial applications. Over 3000 different azo dyes are used to satisfy the consumer demand for color appeal in textiles, paper, gasoline, food stuffs, leather and printing applications [12,39]. Dyes make our world beautiful but it brings pollution, they are released into the environment as industrial effluents from food, cosmetic, drug, textile and dyestuff factories. Recent estimation indicates that approximately 12% of the synthetic dyes used in textile processes each year are lost to waste streams during manufacturing and processing operations, and that 20% of these losses are released into the environment through effluents from waste water treatment plants. These compounds are quite difficult to be removed in water treatment procedures, and can be transported from municipal sewage water to rivers because of their high water solubility [43, 44].
Interest in the environmental behavior of dyes arise largely from concerns about toxicity. Some synthetic dyes may be pathogenic if they are consumed in excess. It has also been shown that synthetic precursors, intermediates and degradation products of these dyes could be potential health hazards owing to both their toxicity and carcinogenicity [40]. Dyes of aromatic structures [11], dyes with azo bonds, nitro- or amino-groups are carcinogenic [13], metal-based complex dyes, such as chromium-based dyes, can lead to the release of chromium (that is carcinogenic) into water supplies [3,7]. The majority of dyes may cause allergic responses, skin dermatoses, eczema [27,37], affect the liver [21,27], the lungs [4], the vasco- circulatory system [28], the immune system [26], and the reproductive system [14, 27] of experimental animals as well as humans.
Sulphonated azo dyes (that are our interest in this work) possess acidic groups in their chemical structure, the sulphonic acid groups in particular are often present as sulphonate anions and provide very good water solubility. In addition, azo dyes have been shown to undergo reduction in natural water ways and the environment, the degradation products include amines, and some of them are known to be carcinogenic. Their presence in effluent and industrial waste-water is of considerable interest because of the potential for contamination of ground and drinking water supplies by compounds that may cause health risks. Therefore the detection, identification, and quantification of azo dyes in waste water at low levels is important for the protection of natural waters [29,30]. Stained waste water has to be treated to reduce ecological consequences [23]. Dyes in waste water can be eliminated by various methods, including flocculation, precipitation, reverse osmosis, adsorption [25], and also oxidative-reductive chemical and photo chemical [24] processes, other techniques comprise radiation and decolorization with ozone in combination with H 2O2. At present, the major techniques in treating dye waste water [22] are biological treatment, activated carbon method and light degradation.
Source:An Najah University
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