Application of the mixture design to optimise the formulation of active consortia to decolorize azo-dye methyl red

With the aid of analysis software (Minitab 14.0), the formulation of pure culture in Mineral Salts Medium (MSM) can be optimized for several responses and the best formulation can be obtained. The influence of the different mixtures of three strains in the pure culture in MSM on the flavor components in decolorization of Methyl Red (with initial total cell density fixed at OD600 = 1 and in addition of 750 ppm of dye) was studied using equilateral triangle diagram and mixture experimental design to assess color and COD removal during species evolution. The regression model on microorganism composition and main metabolites was established. The results suggested that the highest predictable specific decolorization rate and Chemical Oxygen Demand (COD) were 77.97 and 93.77%. Based on these, the response values that satisfied all expectations were optimized, and the optimal composition of the mixed consortium for the dedolorization and COD removal were (Sphingomonas paucimobilis 45.20%, Bacillus sp 61.94% and Staphylococcus epidermidis 80.00%) and (Sphingomonas paucimobilis 77.03%, Bacillus sp 86.42% and Staphylococcus epidermidis 71.74%) respectively. Very high regression coefficient between the variables and the responses: decolorization and COD removal were respectively R²=0.96 and 0.81 indicated excellent evaluation of experimental data by polynomial regression model.