Decolorization disperse dyes

The ability to use azo dyes as sole energy and carbon source by bacteria to be able to reduce the azo bond aerobically by a cometabolic way has been reported [2,4]. A mixture of four structurally different dyes (Acid Red 88, Reactive Black 5, Direct Red 81, and Disperse Orange 3) was used as sole source of carbon and nitrogen to select six strains of bacteria tested for the ability to decolorize the dyes individually or in mixtures a S. putrefaciens strain was identified as the most efficient [45]. 

Conventional treatment processes for these dyes prior to discharge involve ozonation. While a simple water-soluble monoazo dye such as A07 is easily oxidized by ozone, the larger diazo dyes such as NBB are difficult to destroy by ozonation. While oxidative ozonation is a popular treatment process, the sodium borohydride catalyzed reductive decolorization of these dyes is also used. The other example shown above, DB79, is water insoluble and is finding increased application in the dyeing of polyester and other synthetic fabrics. Traces of the disperse dye have been reported in river bed sediments in Quebec, Canada, receiving dye waste from upstream manufacturers. 

Kolekar YM, Pawar SP, Gawai KR, Lokhande PD, Shouche YS, Kodam KM (2008) Decolorization and degradation of Disperse Blue 79 and Acid Orange 10, by Bacillus fusiformis KMK5 isolated from the textile dye contaminated soil. Bioresour Technol 99 8999-9003... 

Initial adsorption of the dyes on fungal biomass followed by degradation was observed in cultures of Irpex lacteus, Phanerochaete chrysosporium, Trametes versicolor, and Trichophyton rubrum [46 -9]. In P. sajor-caju, it was observed that Disperse Blue 79 and Acid Red 315 were incompletely or not degraded, but a decolorization was reached due to adsorption to the mycelium [38]. Also algae can be used as biosorbents of azo dyes [50]. 

An inverse relation between the efficiency of decolorization and the dye concentration has frequently been observed. This fact can be ascribed to several factors, the main of which can be considered the toxicity of the dyes at higher concentrations [41, 45, 51-53]. With Reactive Red 3B-A, concentrations from 100 to 2,000 ppm were tested with C. bifermentans [5]. At concentrations less than 200 ppm, 90% decolorization within 12 h was observed, while at very high dye concentration (>1,000 ppm), the decolorization rate decreased. Khalid et al. [54] observed an inverse relationship between the velocity of the decolorization reaction and the dye concentrations between 100 and 500 mg L 1 azo dye (Reactive Black 5, Direct Red 81, Acid Red 88, and Disperse Orange 3) by Shewanella putrefaciens. A decrease in decolorization percentage at a Acid Black 210 initial concentration growing from 100 to 400 ppm was also observed with V. harveyi, but the decrease was low [44]. 

Two bacterial Shewanella species, S. putrefaciens and S. oneidensis, previously selected on the basis of their ability to degrade azo dyes, were also tested in saline medium at different salt concentrations of up to 10% to evaluate their potential to decolorize four structurally different azo dyes Reactive Black 5, Direct Red 81, Acid Red 88, and Disperse Orange 3. Full decolorization was reached at salt concentrations up to 6% the decolorization velocity was inversely related to salt concentration. The rate of decolorization was increased by yeast extract and a calcium source, while was decreased by glucose and by a nitrogen source [54]. 

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