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The 2 k-factorial PBD trials were carried out in order to select the important factors that influence decolourisation of remazol golden yellow by M. endophyticus ES37 and also to evaluate the relative importance of the significant factors that are involved in the process. Scrutinised factors and their actual values are shown in Table 1. Plackett–Burman experimental design, depicted in Table 2, is based on the first-order model Equation (2) as follows:
formula
2
where Y is the response, Xi is factor levels, i is the factor number, β0 is the model intercepts term, βi is the linear effect, βii is the squared effect, and βij is the interaction effect between Xi and Xj on the dye decolourisation process.
Table 1

Actual values of factors for PBD

Test variableLactose % (w/v)Yeast extract % (w/v)pHTemperature (°C)Inoculums size % (v/v)Dye concentration (mg/L)Incubation period (h)
Low level (−) 0.1 0.1 30 100 24 
High level (+) 1.0 1.0 45 10 300 72 
Test variableLactose % (w/v)Yeast extract % (w/v)pHTemperature (°C)Inoculums size % (v/v)Dye concentration (mg/L)Incubation period (h)
Low level (−) 0.1 0.1 30 100 24 
High level (+) 1.0 1.0 45 10 300 72 
Table 2

Plackett–Burman experimental design for screening of significant factors on dye decolourisation

Run orderLactose % (w/v)Yeast extract % (w/v)pHTemperature (°C)Inoculum size % (v/v)Dye concentration (mg/L)Incubation period (h)DV-1*DV-2*
1.0 0.1 30 100 72 
1.0 1.0 45 100 24 
0.1 1.0 30 10 100 24 −1 
1.0 0.1 45 300 24 −1 −1 
1.0 1.0 45 10 100 72 −1 −1 
1.0 1.0 30 10 300 24 −1 
0.1 1.0 45 300 72 −1 
0.1 0.1 45 10 100 72 −1 
0.1 0.1 45 10 300 24 
10 1.0 0.1 30 10 300 72 −1 
11 0.1 1.0 30 300 72 −1 
12 0.1 0.1 30 100 24 −1 −1 
Run orderLactose % (w/v)Yeast extract % (w/v)pHTemperature (°C)Inoculum size % (v/v)Dye concentration (mg/L)Incubation period (h)DV-1*DV-2*
1.0 0.1 30 100 72 
1.0 1.0 45 100 24 
0.1 1.0 30 10 100 24 −1 
1.0 0.1 45 300 24 −1 −1 
1.0 1.0 45 10 100 72 −1 −1 
1.0 1.0 30 10 300 24 −1 
0.1 1.0 45 300 72 −1 
0.1 0.1 45 10 100 72 −1 
0.1 0.1 45 10 300 24 
10 1.0 0.1 30 10 300 72 −1 
11 0.1 1.0 30 300 72 −1 
12 0.1 0.1 30 100 24 −1 −1 

*DV 1 and 2, dummy variable; +1, high concentration; −1, low concentration.

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