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สารฮิ วมิ กช่วยเพิ่ มความสามารถการลดสี ... 196 The Journal of the Royal Institute of Thailand Vol. 37 No. 1 Jan.-Mar. 2012 cosmetics, and food (12). The textile industry consumes the largest amount of azo dyes, and its estimated the approximately 10-15% of dyes used for coloring textiles might be lost in waste streams (1). Sulfonated azo dyes are known to be resistant to degradation by aerobic bacteria due to the strong electron-withdrawing property of the azo group thought to protect against attack by oxygenases (28) so that there generally pass biodegradative processes in conventional sewage treatment systems untreated (40, 48). The azo dyes-containing effluents from these industries have caused serious environment pollution, because the presence of dyes in water is highly visible and affects their transparency and aesthetics even if the concentration of the dyes is low (23). Microbial decolorization of sulfonated azo dyes readily occurs under anaerobic conditions by a wide variety of bacteria utilizing several intracellular reductases to reductive cleavage of the azo dyes to produce corresponding colorless aromatic amines (9, 13, 19, 22, 44, 45). These reactions usually occur with rather low specific activities but are extremely unspecific with regard to the microorganisms involved and the dyes converted. In the textile processing industry, a wide range of structurally diverse dyes is used within short time periods in one and the same factory and, therefore, the effluents from the industry are markedly variable in composition (17). Moreover, in the case of sulfonated azo dyes, sulfonic acid substitutions seem to be an effective inhibi- tor of permeation of the dyes through the cell membrane (56) and therefore, intracellular reductases do not function (46). Thus, an extracellular nonspecific biological process may be vital for treatment of the textile effluents. From the currently known biological systems, the required unspecifity may be obtained by using the suitable redox mediator system. The unspecific anaerobic reduction of azo compounds very often low-molecular- weight redox mediators (e.g., flavins or quinones) are involved (14, 26, 29, 42, 43, 50). These mediators are reduced by bacterial enzymes to corresponding their reduced forms (e.g., reduced flavins or hydroquinones) which enable the transfer of redox equivalents to extracellular azo dyes in a purely chemical reaction (14, 42, 50). These alternative redox mediators either occur naturally in groundwater and sediments or are possible additives for stimulating in situ biodecolorization processes. Also, organic matter in the natural environ-