Variable

 

Name

Range and levels

-2

-1

0

1

2

X1

Biosorbent dosage, w, g/L

25

30

35

40

45

X2

Initial concentration, Co, mg/L

10

15

20

25

30

X3

pH of aqueous solution

3

4

5

6

7

X4

Temperature, T, K

283

293

303

313

323
Table 4: Levels of different process variables in coded and un-coded form for biosorption of lead using Casuarina leaf powder.