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.