Initial
 pH

NR /Aqueous solution

NR /Incinerated sludge suspension

Equilibrium
pH

Species (nm)

Species (nm)

NR+H

NR

NR+H

NR

2.41

519.5

-

518.5

-

2.62

4.26

520

-

503

-

5.82

5.24

519.5

-

501

-

6.34

6.04

521.5

-

503

-

6.55

8.15

-

452.5

-

453

7.02

10.14

-

451

-

454

7.74

12.01

-

453.5

-

450.5

11.45

NR: Conjugate base form; NR+H: protonated cation of NR dye.
Table 2: The position of the absorption band maxima of NR in aqueous solution and upon adsorption on incinerated sludge as a function of pH for [NR] =50mg/L, [Incinerated sludge]=1g/L, T=298K and contact time of 80 min.