| Dye wastewaters have been one of the main sources of severe pollution problems worldwide. Conventional chemical and physical techniques possess inherent limitations such as high cost, formation of hazardous by-products, and intensive energy requirements. As a feasible alternative, dye decolorization using microorganisms, has recently received much attention owing to its ease of application, low cost, and environmental benignity. Some fungi have been applied to the treatment of dye effluent, owing their characterizations of broad substrates and tolerance to high concentration of toxic xenobiotics and alkali. To understand the decolorization mechanism of these fungi will provide the theoretical foundation to expand their application to decolorize dye waste, especially basic dye waste.A comparative study on decolorization of RBBR dye by 10 strains in pH5-10 was performed and the results showed that IMER1 has high-efficient decolorization of RBBR, especially including basic pHs. To identify the species of this strain, its ITS sequence is cloned and its colony, spore, conidiophores, and mycelium morphologies are observed under microscope. These results showed that this strain is Myrothecium sp, and named as Myrothecium sp.IMER1..The mechanism of decolorization of RBBR by strain IMER1 was investigated comprehensively. Decolorizing efficiency is indigo carmine>RBBR>congo red>malachite green> bromophenol blue, and the ability of triphenylmethane dyes decolorized by strain IMER1 is poor. It was proved that in the course of decolorization of RBBR the extracellular enzyme, bilirubin oxidase (BOX), has a good correlation with decolorization and playes a key role. The adsorption of the dye by cells is observed at the beginning of the decolorization, then the color becomes faint and finally disappeares when BOX is released by the strain. Additionally, the visual observation and UV spectral analysis demonstrated that decolorization involved biosorption and biodegradation. The kinetics of RBBR decolorization can be described by first-order reaction rate equation, and the K value decreases with the RBBR concentration.Bilirubin oxidase is purified by the five steps, which is demonstrated to be bilirubin oxidase by SDS and native PAGE, and its molecular weight is estimated to be about 64kD.The optimum temperature for enzyme activity is 55°C and the optimum pH for bilirubin and ABTS are 7.5 and 4, respectively. Fe2+ has completely inhibition action, while EDTA,ethanol,acetic acid,glycine have little. The purified BOX can decolorize the 5 dyes.The mechanisms of decolorization of RBBR by BOX and BOX-ABTS were investigated comprehensively. The results of the visual observation and UV spectral analysis of RBBR show that the chromophores of RBBR are decomposed resulting in degradation of RBBR at last. The analysis results of GC-MS and LC-MS indicate that the main intermediate products are phthalic acid and derivatives. The kinetics of RBBR degradation could be described by first-order reaction rate equation.The optimum conditions for the production of BOX show that pH, temperature, glucose are 5.7, 28°C, 8g/L, respectively, the largest production of BOX is 0.643U/mL. The biosynthesis of BOX in PDB is middle phase model. On the other hand, the optimized water content, pH, temperature in solid culture are 83.5%,4.6,23°C, respectively, the largest production of BOX is13.45U/g .Decolorization of basic dye effluent by strain IMER1 and BOX were investigated, including the feasibility of technology in reactor. Both IMER1 and BOX are able to decolorize basic dye effluent, while high concentration dye effluent will inhibit the growth of IMER1. Decolorization rate by ABTS is improved. The mixture of IMER1 and wheat bran is better for decolorization of single dye such as indigo carmine and RBBR than basic-dye-effluent in air lift bioreactor, so it is necessary to redesign the structure of reactor and optimize the program and conditions in order to improve the treatment effect for dye effluent.
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