Biodegradated Behavior Of Synthetic Dyes In Laccase Mediator System

Synthetic dyes have been largely and widely used in various industries including paper dying, food processing, printing, and cosmetics. Subsequently, how to treat dye wastewater efficiently and economically is a big problem. To solove it, lots of techniques have been developed, including physical, chemical and biological methods. Among which, biotechnology draws much attention recently due to green and environment-friendly. In this work, laccase(EC 1.10.3.2), a multi-Cu oxidase, was chosen because it shows high selectivity and specificity to degrade phenolic and arylamine compounds, and can realize rapid degradation of a variety of synthetic dyes when introducing certain redox reagent as the mediator. The work was consisted of several parts: the degradation mechanism to double azo dye, screening of new mediator and the preparation of laccase magnetic nanoparticles.(1) Laccase/1-hydroxybenzotriazol(HBT) mediated oxidation of disazo dye Acid Red 73(AR 73)Disazo dyes were the most popularly used dyes in industry. However only few of reports on their application and theoretic study, previous study mainly focused on the study of monoazo dyes. Here, a disazo dye, Acid Red 73(AR 73) was used to investigate the degradation behavior and mechanism in laccase/1-hydroxybenzotriazol(HBT) system. Physicochemical parameters were investigated and the optimal degradation rates of AR 73 were occurred at pH 4.0, temperature 50 oC, and enzyme activity 2.5 U/mL. The possible degradation mechanism of AR 73 by the laccase-HBT system was also proposed based on 14 intermediates determined by gas chromatography- mass spectrometry(GC-MS) and liquid chromatography- mass spectrometry(LC-MS) technology.(2) Acid green 1(AG 1), a new laccase mediatorMediators can greatly enhance the degradation rate of synthetic dyes by laccase. Until now, mediators seldom applied into practice due to high price. Acid green 1(AG 1), one industrial dye, has a similar molecular structure to 1-nitroso-2-naphthol-3, 6-disulfonic acid(NNDS), which menat it could be a potential mediator of laccase. So here, the mediating ability of AG 1 was investigated in detail using malachite green(MG) as model. The degradation conditions were optimized. The results showed that the mediating ability of AG 1 was equeally to that of HBT, one well known mediator of laccase. Laccase/AG 1 system was apt to degrade triarylmethane-type dyes. Most importantly, the optimal amount of AG 1 was only 19.3 wt% of HBT.(3) Preparation of laccase magnetic nanoparticles through chelating interaction and its application on the degradation of synthetic dyesFree laccase is easy to be denatrued and can not be used repeatedly. After immobilization, the reusiable of laccase can be realized and its service life can be prolonged. In this work, a soft and non-destructive method was proposed to immobilized laccase on the surface of EDTA functionalized magnetic Fe3O4 synthesized by coprecipitation step through chelating interaction. By this means, the laccase fixing amount can be up to 22.3 wt%. Using guaiacol as substrate, the highest activity of the immobilized laccase was occured at pH 3.5 and 50 oC. The as prepared laccase magnetic nanoparticles showed high stability and can be used repeatedly.