Removal of dyes from aqueous solution by activated carbon from sewage sludge of the municipal wastewater treatment plant

Activated carbon from sewage sludge of the municipal wastewater treatment plant was obtained by chemical activation with ZnCl2 as activator. Then, it was used as an adsorbent for the removal of Acid Scarlet GR and Methylene Blue from aqueous solution. The effects of contact time, temperature, and initial dye concentration were investigated. The experimental data were analyzed by the Langmuir and Freundlich adsorption models. Kinetic adsorption data were discussed using the pseudo-first-order model and pseudo-second-order model. Thermodynamic parameters, such as enthalpy (Delta H degrees), entropy (Delta S degrees), and Gibbs free energy (Delta G degrees), were calculated. The results showed that the equilibrium data fitted well with the Freundlich model for the adsorption of Methylene Blue on the activated carbon. However, adsorption data for Acid Scarlet GR were both fitted with the Langmuir isotherm and the Freundlich isotherm. The adsorption kinetic of Methylene Blue and Acid Scarlet GR on the activated carbon was both more accurately represented by pseudo-second-order model. The values of Delta H degrees, Delta S degrees, and Delta G degrees for adsorption of Methylene Blue were 53.01 kJ/mol, 190.12 J/mol and -2.78 kJ/mol, respectively. The absorption process of Methylene Blue was a spontaneous and endothermic reaction. The values of Delta H degrees, Delta S degrees, and Delta G degrees for adsorption of Acid Scarlet GR were 32.78 kJ/mol, 104.00 J/mol and 2.26 kJ/mol, respectively. The adsorption process of Acid Scarlet GR was less effective.