Table 2.

Experimental ranges and levels of the process parameters used in the Box–Behnken design.

Variable	Symbol	− 1	0	+ 1
pH	X1	3	7	11
Contact time(min)	X2	20	50	80
MSW compost ash dosage (g)	X3	0.5	1.25	2
RR198 concentration (mg L−1)	X4	20	60	100