Application of advanced oxidation processes for effective Reactive Red 241 degradation

Advanced oxidation processes (AOPs) were investigated for the Reactive Red 241 (RR 241) degradation in aqueous solutions. Nine different methods were tested: the Fenton process, Fenton combined with Sodium Percarbonate (Fenton-SP), Fenton with MgO₂ (Fenton-MgO₂), and the UV/TiO₂ process utilizing both low-pressure (LPL) and medium-pressure (MPL) lamps. Additionally, the methods included UV(MPL)/H₂O₂, UV(MPL)/Fenton, and UV(MPL)/Fenton-like processes. For each method, optimal conditions (pH, reaction time, and reagent dosages) were identified. The dye concentrations in the treated solutions were as follows: 0.67 mg/dm³ for the Fenton process, 0.73 mg/dm³ for Fenton-SP, and 0.83 mg/dm³ for Fenton-MgO₂. The UV(MPL)/Fenton-MgO₂ method achieved a degradation efficiency comparable to the Fenton process. Among all the methods tested, the highest degradation efficiency of RR 241 was achieved using the UV(MPL)/H₂O₂ process, which reduced the dye concentration to 0.53 mg/dm³. Conversely, the lowest degradation efficiency was recorded in the UV(LPL)/TiO₂ process, where the dye concentration was 4.09 mg/dm³. Chromatographic analysis confirmed the presence of RR 241 intermediates. The highest number of these intermediates was observed with the UV(MPL)/TiO₂ process, likely due to its broader wavelength range and higher light intensity. In contrast, the UV(MPL)/Fenton processes resulted in the lowest number of by-products, indicating more complete mineralization.