Optimization of ozonation/adsorption combined method for the removal of toxic metals and COD using sewage sludge based carbon/TiO₂/ZnO nanocomposite

The sewage sludge carbon/titanium dioxide/zinc oxide (SSC/TiO₂/ZnO) nanocomposite was synthesized via pyrolysis method and its potential was investigated for the removal of Ni(II), Cu(II) and COD from aqueous solutions and industrial wastewaters during the ozonation/adsorption combined method. The synthesized nanocomposites were characterized using FTIR, FESEM, TEM and EDX analysis. The effect of ozonation/adsorption, catalyst type, contact time, pH, catalyst dosage, TiO₂/ZnO ratio and the initial concentration of effluents on the removal of Ni(II), Cu(II) and COD from aqueous solutions in a single system and the influence of initial concentrations of effluents on their removal in a ternary system from industrial wastewater of Iran were investigated. The optimum removal of Ni(II), Cu(II) and COD was obtained using SSC/TiO₂/ZnO catalyst under optimum ozone flow rate of 500 ml min⁻¹, TiO₂:ZnO ratio of 3:1, SSC to TiO₂-ZnO ratio of 1:2, pH values of 5, 6 and 5.5 for Ni(II), Cu(II) and COD removal, catalyst dosage of 1 g l⁻¹ and reaction time of 30 min. The reusability of the catalyst for the removal of Ni(II), Cu(II) and COD was also examined for five runs. Then, the central composite design (CCD) was used to investigate the interaction effects of initial concentrations of Ni(II), Cu(II) and COD on the simultaneous removal of Ni(II), Cu(II) and COD from aqueous solutions in a ternary system. The obtained results showed that the ozonation/adsorption combined method using the synthesized SSC/TiO₂/ZnO nanocpomosite is as an efficient method for the removal of heavy metal ions and organic matters from industrial wastewater. (paper)