Microbial decolorization of reactive dyes in an anaerobic-aerobic treatment system

Abstract

In this work, bacterial strains isolated from a textile wastewater treatment facility were used to decolorize reactive dyes. Mixed culture of strain S1 and A5 performed the highest decolorization for monoazo, metal complex monoazo, diazo and anthraquinone dyes. Base on 16S rRNA gene sequence analysis, the strains were shown to belong to the genus Paenibacillus. Optimal decolorizing conditions were determined. Nitrate and Cu[superscript 2+] were found to cause inhibition of azo dyes removal. Anthraquinone-2,6-disulfonate increased the reduction rate of azo dyes by strain A5. This quinone is enzymatically reduced, the resulting hydroquinone then reduces the azo dye outside the cells by chemical redox reaction. It was suggested that the membrane-bound NADH:quinone oxidoreductase of respiratory chain is responsible for this activity. In the case of anthraquinone dye, the decolorization was found to result from biosorption of the dye onto the surface of biomass. The feasibility of using a fluidized bed reactor operated as sequencing batch reactor to decolorize azo dyes by alginate-immobilized cells of strain S1 and A5 was proved: color was reduced by the anaerobic phase, meanwhile, chemical oxygen demand was mainly removed in the subsequent aerobic phase.