Use of active consortia of constructed ternary bacterial cultures via mixture design for Congo Red decolorization enhancement

Azo dyes are widely used in textile dyeing which contains toxic and carcinogens compounds. So they must be treated before their discharge into the receptor medium. In this aim, this work is focused on the aerobic decolorization of water soluble azo dye Congo Red (CR) by bacterial consortium (Sphingomonas paucimobilis, Bacillus sp. and Staphylococcus epidermidis). The effect of different combinations of these three strains cultivated in the pure culture in mineral salts medium (MSM) on the decolorization of Congo Red (cell density fixed at OD600 = 1 with the addition of 750 ppm of the dye) was studied using equilateral triangle diagram and mixture experimental design to assess color and COD removal during species growth. Using software analysis (Minitab 14.0), the formulation of pure culture in MSM can be optimized for several responses and the best formulation can be obtained. The results suggested that the highest decolorization and chemical oxygen demand (COD) rates were 100% and 98%, respectively. Very high regression coefficient between the variables and the responses: decolorization and COD removal were R2 = 32.69% and R2 = 52.25%, respectively indicating an excellent evaluation of experimental data by polynomial regression model. FTIR (Fourier transform infrared) and UV–vis analysis confirmed the biodegradation of Congo Red by the bacterial consortium. The produced metabolites were extracted and their phytotoxicity study suggested their low toxicity.