Table 1.

Factors and levels of response surface analysis.

Variables	Unit	Symbol	Variables level
			Low −1	Center 0	High  + 1
MB initial concentration	mg/L	X1	50	100	150
BRB addition amount	G	X2	0.05	0.1	0.15
Reaction time	min	X3	30	90	150
Reaction temperature	°C	X4	20	30	40
pH	–	X5	6	8	10