Study On Anaerobic Decolorization Of Azo Dyes By Pseudomonas Sp.

Azo dyes are aromatic compounds with one or more -N=N- groups. They are the largest class and most important of synthetic dyes used in commercial applications. Azo dye are unable to remove completely because of their color fastness, stability and resistance to degradation. At present bacterial decolorization and degradation of azo dyes is considered as the most inexpensive and eco-friendly method.Some bacterial may have a great potential in application because they could grow quickly and have a high tolerance. Studying the characteristics and way of azo dye decolorization by these strians may provide evidence for the biological treatment.In this reaseach, amaranth was choiced as the model pollutant, the characteristics of decolorization by Pseudomonas sp. was studied and optimized the decolorization conditions by Response Surface Method (RSM).Decolorization products were analysed by UV-vis spectrum and Fourier Transform Infrared Spectroscopy (FTTR).With the analysis of decolorization enzymes, the possible way of decolorization amaranth was preliminary infered.The addition of redox mediators (RM)strengthen the treatment of amaranth decolorization.The main research results were as follows:Pseudomonas sp. could use amaranth to maintain its life and reach the decolorization rate of 27.7% in 135h without external carbon source.When glucose, starch, sodium pyruvate was added respectively, all of them could promote amaranth decorization, the kinetics of decolorization reaction was corresponding with the first order reaction kinetics models.Pseudomonas sp. could keep a higher activity of decolorization and degradation under anaerobic circumstance with 1.5g/L of glucose and under pH 7～9, dye concentration 50-200 mg/L. Methyl red, acid orange G, orange I and II, acid red GR and acid red 18 were decolored by Pseudomonas sp..Through Box-Benhnken model and RSM analysis, the decolorization rate could reach 97.3% under the conditions of dye concentration 170mg/L,1.5g/L of glucose, innitial pH 7.2 and cultural time 75h.The strain could realize 9 and 7 times of effective decolorization amaranth respectively under the replace batch decolorization and continuous feeding decolorization. The system of replace batch decolorization had a higher stability and better result.Pseudomonas sp. had a higher tolerance and could decolor continuously. It implied the strain had a broad application prospects.After the addition of AQS, VB2, HA and GAC respectively, all of them promoted the decolorization of amaranth, the result was AQS>VB2>HA>GAC. The decolorization rate in 20h was increased by 7.2,3.0,1.5,1.5 times respectively compared with the non-RM system. In the AQS system external electron donor could also promote the decolorization speed apparently, the result was glucose> sodium pyruvate> sucrose> starch> sodium acetate. When the dosing of AQS was less than 30mg/L, the decorlorization rate increased with the increase of RM concentration, but if the dosing of AQS was more then 30mg/L, the decolorization efficiency was not changed obviously.The decolorization of amaranth by Pseudomonas sp. was in the form of biological adsorption and biodegradation, biodegradation ocupied almost 91% and played a dominate role in the decolorization. The azo reductase and NADH-DCIP reductase were closely related to the degradation of amaranth without RM. Under anaerobic condition the azo bond of amaranth was cleaved and the conjugate structure was destructed, the aromatic amine was produced at the same time. The azo reductase and NADH-DCIP reductase were not detected in the degradation of amaranth with AQS. AQS acted as electron shuttle.