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The experimental model of CCD is shown in Table 4. All the other factors used in this study were constant: 0.5% (w/v) sodium chloride, 200 mg/L dye concentration, 18 h culture (OD 610 nm = 0.5) of 7.5% (v/v) inocula, 37 °C temperature and 48 h incubation period. The correlation and relationship of these factors and their measured response in CCD can be described by linear quadratic model as in Equation (4):
formula
4
where Y is the percentage of decolourisation, β0 is the intercept term, β1, β2 and β3 are linear coefficients of each significant factor, β11, β22, β33 are quadratic coefficients, β12, β13, β23 are interaction coefficients and X1, X2, X3, X4 are coded factors. The best experimental model was determined by coefficient R2. A regression model equation was used to find the predicted optimal values of the selected factor and to subsequently reveal the interaction of these factors within a stipulated level (Zhao et al. 2010). The maximum decolourisation potential of the bacteria was verified under predicted optimal condition, obtained in RSM. Experiments were conducted in triplicate and the decolourisation percentage was compared to the predicted result from RSM.
Table 4

CCD matrix for optimisation of dye decolourisation

Run orderPt typeBlocksYeast extract % (w/v)Lactose % (w/v)pH
0.1 0.1 
1.0 0.1 
0.1 1.0 
1.0 1.0 
0.1 0.1 
1.0 0.1 
0.1 1.0 
1.0 1.0 
−1 −0.20 0.55 
10 −1 1.31 0.55 
11 −1 0.55 −0.20 
12 −1 0.55 1.31 
13 −1 0.55 0.55 3.63 
14 −1 0.55 0.55 10.36 
15 0.55 0.55 
16 0.55 0.55 
17 0.55 0.55 
18 0.55 0.55 
19 0.55 0.55 
20 0.55 0.55 
Run orderPt typeBlocksYeast extract % (w/v)Lactose % (w/v)pH
0.1 0.1 
1.0 0.1 
0.1 1.0 
1.0 1.0 
0.1 0.1 
1.0 0.1 
0.1 1.0 
1.0 1.0 
−1 −0.20 0.55 
10 −1 1.31 0.55 
11 −1 0.55 −0.20 
12 −1 0.55 1.31 
13 −1 0.55 0.55 3.63 
14 −1 0.55 0.55 10.36 
15 0.55 0.55 
16 0.55 0.55 
17 0.55 0.55 
18 0.55 0.55 
19 0.55 0.55 
20 0.55 0.55 
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