Independent parameters

Range and level

2

−1

0

+1

+2

pH (X₁)

2

3

4

5

6

Initial Cr concentration (X₂), mg/L

10

15

20

25

30

Biosorbent dosage (X₃), g/L

10

15

20

25

30

Temperature (X₄), K

283

293

303

313

323