BACKGROUND AND OBJECTIVES The presence of azo dyes in the environment is an issue of major concern since they are highly recalcitrant and toxic. Azo dyes are extensively used in textile industries, and account for more than 50% of the synthetic dyes used worldwide. Releasing azo dyes into water bodies results in aesthetic problems and deteriorates water quality. The aim of this research was investigation on removal reactive azo dyes using biological treatment. MATERIALS AND METHODS To isolate some bacteria able to decolorize two commercial reactive dyes including Reactive Orange 122 (RO122) and Reactive Red 195 (RR195), wastewater samples were collected from activated sludges. The samples were inoculated into R2A medium containing 50 mg L-1 of individual dyes and incubated at 28 °C under static conditions for 10 days. The growth culture was transferred into fresh medium every 7 days and decolorization were examined every day using spectrophotometer. RESULTS AND DISCUSSION Results were demonstrated that the microbial consortium was able to decolorized both RO122 and RR195 dyes due to decreasing the optical density at 495 and 545 nm, respectively. The rate of microbial decolorization of RO122 and RR195 was 81% and 56% after 10 days, respectively. These results shown that the microbial consortium isolated from dye-contaminated environments can decolorize azo dyes. The decolorization rate of the azo dyes depended on the chemical structure and the position of functional groups proximal to the azo bond. Both azo dyes used in this study were reactive and contain one azo group. CONCLUSION The results revealed that the microbial consortium was successfully decolorized both RO122 and RR195. Microbial decolorization technique are very useful to remove textile dyes from environments.
