Response surface models are multivariable polynomial models, mostly used to determine a set of variables that optimize a response (i.e., COD concentration in this study). Five medium components viz. soybean, glycerol, maltose, MgSO4 and NaCl were selected to generate the model for response optimization. The circumscribed central composite design (CCD) was used to study the interaction effect between the above mentioned variables/ factors. The uncoded and coded values of the variables at five levels of CCD have been summarized in Table 1. For five variables, thirty six run CCD design containing ten star points, ten centre points and sixteen axial points were generated by using ccdesign function of the statistical tool box of MATLAB 7.10.0 (R2010a) (Math Works Inc., USA). The activity of COD was estimated for each experimental run. A quadratic response surface model was generated and its polynomial coefficients were calculated using statistical tool box of MATLAB. The experimental results were fitted to the quadratic equation (Eq 1) given by regstat function of the statistical toolbox of MATLAB to determine the coefficients of the equation and to obtain an optimum response surface model. Download: PPTPowerPoint slide
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Table 1. Independent variables and their coded and un-coded values.
matlab 7.10.0 r2010a 317
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