Enhanced Biodecolorization Of Azo Dyes By The Anthraquinone Dyes Intermediators

Azo dyes are widespread environmental pollutants associated with the textile, cosmetic, food colorants, printing, and various other purposes. 10%-15% of these dyes are released into the environment during the process of producing or using. The release of these compounds into the environment is undesirable, not only because of their color but also because many azo dyes and their breakdown products are toxic and/or mutagenic to life. Among kinds of methods, anaerobic-aerobic biotreatment may present a relatively efficient way and be the most frequently applied methods to remove dyes from wastewater. Anaerobic process is a time-consuming process, reflected by the requirement of long reaction times. Enhancement by redox mediator is an effective method to increase the performance of anaerobic decolorization. Some quinones such as anthraquinone, naphthoquinone are powerful redox mediators, while they are also pollutant and more difficult to break down as the secondary pollutions.The purpose of this dissertation is to find new redox mediator or technology to reduce the secondary pollutions caused by redox mediators. Three aspects are included in this paper. Enhanced biodecolourization of azo dyes by the anthraquinone dyes intermedaitors bromoamine acid (BAA) were studied, and BAA can be easily degraded under aerobic condition. The bacterial cells were immobilized by entrapment in calcium alginate (CA), and the reusing without adding BAA was studied. The bacterial cells and anthnaquinone were co-immobilized, and then the decolourization and reusing were also investigated.The suspended bacterium community could enhance the biodecolourization of many kinds of azo dyes using bromoamine acid (BAA) as redox mediator, the optimum conditions for Acid Red 3R were as follows: pH 6-9, temperature 30℃, glucose, BAA and initial dye concentrations 400-600 mg/L, 19-34.2mg/L and≤900mg/L, respectively. Under these conditions, the maximal decolourzation rate was about 95%, which was reached within 7 h for suspended cells and 14 h for immobilized bacteria. However, the latter needed 38-57mg/L BAA as redox mediator and inoculation amount 120g/L. In addition, after 7 cycles without BAA addition, the decolourzation rate of Acid Red 3R by immobilized bacteria retained over 85%.Enhanced biodecolourization of azo dyes by co-immobilized quinone-reducing community and anthraquinone were also investigated. After the co-immobilization, the bacterium and the redox mediator get closer, which can enhance biodecolourization of different kinds of azo dyes. The optimum conditions for Acid Red 3R were: pH6~9, temperature 30℃, inoculation amount 120g/L, the maximal decolourization rate was reached within 12 h. After 10 cycles, the decolourization rate of Acid Red 3R by co-immobilized beads retained over 88%.