Degradation of Toluene in Treatment of Refinery Wastewater by Photocatalytic Oxidation Technology in a Bubble Column Reactor Using ZnO-TiO2 Composite Nanocatalyst and Packing Material

Oxidation bubble column reactors (BCRs) are useful for treating wastewater because of their effective mass transfer and mixing capabilities. However, because of the low oxidation level of the pollutants, the BCRs' ability to remove toluene is restricted. A packing material and a ZnO-TiO2 composite nanocatalyst in the BCR were used in this study to improve the degradation of toluene. Additionally, the superficial gas velocity (i.e., 0.4, 0.8, 1.2, 1.6, 2, 2.4, and 2.8 cm/s) was used to assess the gas holdup, pressure decrease, and diameter of the bubble. The optimal superficial gas velocity was determined to be 2.4 cm/s. Using packing materials and a ZnO-TiO2 composite nanocatalyst in the BCR, a total (100 %) removal of toluene was accomplished at toluene concentrations of 10, 20, 30, and 40 ppm at reaction periods of 50, 60, 70, and 80 minutes, respectively. Additionally, two ZnO-TiO2 composite nanocatalyst dosages (i.e., 0.04 and 0.12 g/L) were added to the reaction mixture; the ideal dose was determined to be 0.12 g/L. Therefore, four treatment methods (air and H2O2) alone, (air and H2O2/ packing), (air and H2O2/ZnO-TiO2 composite nanocatalyst), and (air and H2O2/ packing/ZnO-TiO2 composite nanocatalyst) were used to evaluate four toluene concentrations in the BCR (i.e., 10, 20, 30, and 40 ppm). Last but not least, the results gave a clear reaction mechanism explaining the oxides BCR, and the applied treatment process can be employed effectively to remove toluene from wastewater at a cheap cost, with minimal energy consumption, and with a straightforward operation.