Photocatalytic treatment of wastewater containing simultaneous organic and inorganic pollution: Competition and operating parameters effects

In the present study, methylene blue (MB) removal from aqueous solutions via the photocatalytic process using TiO2 as a catalyst in the presence of external ultra-violet light (UV) was investigated. The results of adsorption in the absence of UV radiation showed that adsorption reached an equilibrium state at 60 min. The experimental kinetic data were found to be well fitted by the pseudo-second-order model. Furthermore, the isotherm study suggested that dye uptake by TiO2 is a chemisorption process with a maximum retention capacity of 34.0 mg/g. The photodegradation of MB was then assessed under various experimental conditions. The related data showed that dye mineralization decreased when dye concentrations were increased and was favored at high pH values and low salt concentrations. The simultaneous presence of organic and inorganic pollution (Zinc) was also evaluated. The effect of the molar ratio Zn²⁺/MB⁺ in the solution at different pH values and NaCl concentrations was also monitored. The corresponding experimental results showed that at low values of Zn²⁺ in the solution (30 mg/L), the kinetic of the MB removal became faster until reaching an optimum at Zn²⁺/MB⁺ concentrations of 60/60 mg/L; it then slowed down for higher concentrations. The solutions’ carbon contents were measured during the degradation process and showed total mineralization after about 5 h for the optimal Zn²⁺/MB⁺ condition.