Table 1.

Values for Plackett-Burman design

Low level	High level	Variable	Factor
5 mg/L	25 mg/L	A	Selenium concentration
25 °C	31 °C	B	Temperature
24 h	48 h	C	Inoculum age
15 g/L	25 g/L	D	Glucose concentration
4	7	E	pH
150 rpm	250 rpm	F	Aeration
1%	3%	G	Inoculum volume
50 mL	100 mL	H	Volume
0 h	9 h	I	Selenium adding time
24 h	72 h	J	Incubation time
7 g/L	13 g/L	K	Peptone concentration