Decolorization of a Textile Azo Dye, Novacron Red SB, by Naturally Occurring Bacteria

Bangladesh faces devastating surface and groundwater pollution due to the discharge of untreated or poorly treated wastewater streams from textile industries. These effluents contain highly toxic azo dyes and numerous other chemicals that pose serious risks to public health. The biological treatment, based on the activity of naturally occurring bacteria, has exhibited enormous potential as an alternative method of decolorizing azo dyes besides the conventional physicochemical treatment. This study aimed to isolate natural bacteria from industrial wastewater outlets and assess their efficiency in decolorizing the azo dye Novacron Red SB. Initially, we selected five efficient isolates, which we further screened, and finally selected three isolates as strong dye decolorizers. We also conducted a comprehensive investigation to characterize the isolates morphologically, culturally, physiologically, and biochemically, which identified the organisms as Bacillus megaterium, Klebsiella aerogenes, and Corynebacterium rathyi. We have also configured the optimal conditions for maximum dye decolorization by varying dye concentration of 0.005-0.010%, exposure time of 24-72 h, and co-substrates such as glucose, peptone, and ammonium acetate, applying a wide temperature range of 25-45°C and a pH range of 4-9. Optimization studies exhibited distinct decolorization profiles: B. megaterium achieved maximum decolorization of 79% at pH 6.5, K. aerogenes exhibited 75% decolorization at pH 8, while C. rathyi showed 67% removal at pH 7 and all at 37°C. Notably, all the bacteria reduced the dye better at 0.005% dye concentration after 72 h of incubation in the presence of ammonium acetate as a co-substrate at 37°C and pH 6.5-8. The outcomes of this study thus indicate a high potential of natural bacteria in treating textile dye effluents.