Study Of Synergetic Degradation And Decolorization Of Azo Dye By Mixed Consortium

Treatment of dyeing wastewater is considered to be one of the most challenging tasks due to stable chemical structure of dyes recalcitrant to biodegradation. The majority (over 50%) of industrially synthesized dyes are azo dyes. Researchers have been focusing their attention on screening of effective microorganisms to decolorize azo dyes and its application to dyeing wastewater treatment. Individual strain has low efficiency in decolorization and cannot degrade azo dye completely, causing second pollution. Mixed consortium is capable of overcoming these shortcomings. The study of the co-culture of mixed consortium to degrade azo dye can provide technological support as well as theoretical foundation for treatment of dying wastewater.Mixed consortium QM, with remarkable ability to decolorize the Direct Blue 289(DB289), was isolated from the dyeing wastewater. Two groups of strains were purified and obtained: fungi M3 and bacteria Q1. Decolorization rate of DB289 by individual strain was low, but the co-culture of two strains enhanced decolorization efficiency. The results showed that the two strains exhibited syngersitic ability in decolorizing the azo dyes. Morphological, biochemical characterization as well as 16SrDNA, 18SrDNA gene sequences analysis indicated that the strain Q1 was Bacillus cereus and the strain M3 was Geotrichum candidum.The study of conditions for DB298 decolorization by mixed consortium QM was carried out. Optimal conditions was initial pH 7 and temperature at 30℃under static condition. Mixed consortium QM in this study seemed to be salt-tolerating in decolorization. Compared with individual strain, mixed consortium QM in decolorization adapt to environmental conditions on a wider scope. Besides, it was capable of decolorizing structurally different azo dyes, and exhibited a broader dye-decolorizing spectrum.Studies have shown that decolorization of azo dyes by mixed consortium QM was carried out under conditions of co-metabolism. Glucose, ammonium chloride is more suitable as carbon and nitrogen sources for decolorization of co-metabolism. Response Surface Methodology (RSM) have been applied to optimize the three major factors for co-metabolism decolorization: glucose, ammonium chloride, dye concentration. The RSM analysis indicated that the optimized conditions for the above factors are 2.80g / L, ammonium chloride: 1.60g / L, dye: 0.15g / L respectively. At the dye concentration of less than 500mg / L, the decolorization process of mixed consoritium QM in DB 289 fits the first-class kinetics model. The relationship between the decolorization rate and dye concentration is in accordance with the Haldane Inhibition Equation. The Equation isThe study of the mechanism of DB289 decolorization by individual strain (Q1 and M3) and mixed consortium QM was investigated. The result showed that the strain Q1 was decolorized under the low oxidation-reduction potential (ORP). Initially the decolorization by the strain M3 was achieved by absorption of mycelium, and the decolorizaiton rate was low.The decolorizaiton rate increased on the 4th and 5th. The decolorization rate is in positive proportion to the activity of Laccase. Decolorization rate of DB 289 by crude Laccase (the enzyme activity is 6450U/L) produced by Geotrichum candidum reached 90.2% after 1.5h. During the decolorizaiton process of DB 289 by mixed consortium QM, the strain M3 can reduce ORP of the culture significantly. UV-Vis scan, HPLC as well as HPLC-MS was used to analyze the intermediate of DB289 decolorization. The result showed low molecular compounds produced with DB289 reduction were further degraded by mixed consortium. The intermediates were generally suggested to be aromatic amines such as 3-hydroxy-2,7-amino-naphthalene sulfonate and phthelic acid. The possible degradation pathway was therefore proposed. It is inferred that the first step of the decolorization is the cleavage in azo bonds of DB289 followed by the formation of aromatic amines, which is further degraded to phthelic acid. The mechanism of decolorization by mixed consortium QM was probably that initially ORP was reduced remarkably by the strain M3 , low ORP promoted decolorization of DB289 by the strain Q1, the intermediate of decolorization can be further degraded by the strain M3, which might involve the Laccase produced by the strain M3.The strain Q1 was immobilized with calcium alginate, and the strain M3 with nylon net carrier. Decolorization capacity was retained during the decolorization of DB289 by immobilized mixed consortium. Scanning Electron Microscopy confirmed that after decolorization the consortium grew well in the carriers. UV-Vis scan, HPLC analysis shows that immobilized mixed consortium can degrade DB 289 efficiently. Decolorization of DB 289 by immobilized mixed consortium fits the first-class kinetics. It has a continuous decolorization capacity. Treatment of real dyeing wastewater by the immobilized mixed consortium showed that they could partially remove color and COD.