Design expert software version 6

Biodegradation factors namely agitation, temperature, pH, inoculums volume (IV), and salinity were selected to influence the biodegradation of phenanthrene and pyrene using C. sakazakii MM045. The result of combined factors was enhanced based on CCD optimisation using design expert software, version 6.0 (Stat-Ease Inc., Minneapolis, USA). A total of 50 experimental treatments were carried out for each phenanthrene and pyrene (Table 1). Quadratic model significance was determined by t-test and multiple regressions [29] . The response from Cronobacter sakazakii MM045 degradation is the dependent variable, whereas agitation, temperature, pH, IV and salinity are the independent variables. Correlation among variables was assessed based on second-order polynomial and the quadratic model was expressed mathematically. Where Y =% PAH degradation; β₀ = interception coefficient; β₁, β₂, β_3,β_4,β₅ = linear coefficients; β₁₁, β₂₂, β₃₃, β₄₄, β₅₅ = quadratic coefficients; β₁₂, β₁₃, β₁₄, β₁₅, β₂₃, β_24,β₂₅, β₃₄, β_35,β₄₅ = interactions coefficient; x₁, x₂, x_3,x₄, x₅ = rpm, temperature, pH, IV and salinity. Result was finally validated based on prediction by numerical optimization.

The Design-Expert software version 6.0.10 (Stat Ease, Minnesota, MN, USA) was employed to perform the experimental design and statistical analysis. The collected data were also analysed via the ANOVA and Duncan’s tests using the Statistical Analytical System (SAS®) version 6.12 (SAS Institute Inc., Cary, NC, USA). All experiments were performed in triplicates. The optimum point was validated using the root-mean-squared deviation (RMSD), as shown in Equation (3) [22 (link)]: $$\mathrm{RMSD}=\sqrt{\frac{1}{n-1}}\sum _{t=1}{(\hat{y}i–yi)}^2$$
ŷ_i = experimental value;
y_i = expected value;
n = number of sample.