Research On Degradation Of AZO DYE By AZO Reductase And Titanium Dioxide Photocatalytic Method

Wastewater generated by the textile industry is intractable industrial wastewater. It is well known that it is rather difficult to treat the textile wastewater mainly due to their complex compound structure and high stability in the environment. Numerous evidences showed that azo dyes make ~ 60%-70% contribution to the overall textile wastewater. Because on one side azo dyes can not be degraded effectively in the nature, on the other side no matter azo dye itself or their reduced products exhibit poisonous to life body, it is of significance to remove these azo dyes from the environment. This thesis is composed of the following two parts:In the first part, we focus on the azo reductase from E.coli. Firstly, we amplified the azor gene from the genomic DNA of E.coli JM109, and then constructed the recombinant plasmid and expressed the heterogeneous target protein. The degradation experiment on the intact cell showed that azo dyes could be removed more effectively and efficiently under the anaerobic condition when compared with aerobic condition, indicating that the absence of oxygen is helpful for the removal of azo dyes. Following the purification using Ni2+-NTA affinity chromatograph method, we detected the degradation capability against methyl red or methyl orange. In addition, we investigated the effect of NADH on the intrinsic fluorescence and FMN fluorescence emission by means of steady-state fluorescence spectroscopic method. This data provided some useful information and guidance for the further study on enzymatic activity and mechanism. Based on this wild type plasmid, we constructed the saturation mutagenesis library on Arg59 amino acid residue, which is located in the binding pocket between AzoR and substrates. Subsequently, we tried to develop one available screening method. More work needs to be done to optimize the screening method.In the second part, we carried out the photo-catalyzed degradation of azo dyes, and found that different from the case of azo reducate, where methyl orange could only be removed very slowly, the treatment of light irradiation in the presence of TiO2 and H2O2 gave rise to the enhancement of the degradation rate.