ZnO-MgO/Al₂O₃ Ozone Catalytic Oxidation For Refractory Organic Wastewater

With the acceleration of industrialization and urbanization in China,the types and discharges of refractory organic wastewater are increasing,which poses a huge threat to the water environment and human health.Advanced oxidation is a process that uses external conditions to generate hydroxyl radicals to mineralize refractory organic pollutants in a relatively short period of time.Ozone catalytic oxidation technology is a kind of advanced oxidation technology.Compared with other advanced oxidation processes,it has the advantages of wide application range and simple operation.The key to its technology lies in the preparation and application of catalysts.At present,the research on the active components of catalysts is mainly concentrated.For transition metal oxides,transition metal oxides are easily affected by the water quality of the water,and there is a risk of secondary pollution caused by ion dissolution.MgO as a cleaning material has high catalytic activity,but powdered catalysts are difficult to recycle and reuse,so In this project,the ZnO-MgO/γ-Al2O3 catalyst was prepared by impregnation using alumina(γ-Al2O3)pellets as a carrier,which reduced the risk of secondary pollution caused by the dissolution of heavy metal ions and the active components in the preparation process.The loading,catalyst drying temperature and time,roasting temperature and time were optimized;and methyl orange(MO)was used as the representative of refractory organic wastewater,and the ozone flow rate,ozone concentration,initial concentration of methyl orange and initial methyl orange were explored.The effect of pH on the catalytic oxidation process of ozone has preliminarily inferred the mechanism of the reaction process;it also treats a variety of practical refractory organic wastewater such as pharmaceutical wastewater,chemical park wastewater,landfill leachate wastewater and so on.The paper draws the following main conclusions:(1)The preparation conditions of the ZnO-MgO/γ-Al2O3 catalyst are that the active component loading is 2 mmol/g,the ZnO:MgO(molar ratio)is 1:3,the drying temperature is 100℃,the drying time is 4 h,and the calcination temperature is 400℃,roasting time 2 h,under the same ozone dosage,the catalytic oxidation of ozone can improve the removal effect of methyl orange by 45%compared with ozone oxidation.(2)When the initial concentration of methyl orange simulated wastewater with an initial concentration of 90 mg/L and a volume of 2 L is simulated under a neutral condition,in a small test experiment,when the mass ratio of ozone dosage to methyl orange is 3.5:1 The TOC removal rate of methyl orange wastewater by ozone catalytic oxidation can reach 96.53%,which is 47.19%higher than that of ozone oxidation alone.Ozone catalytic oxidation can achieve deep mineralization of methyl orange wastewater.(3)Because hydroxyl radicals are extremely unstable and difficult to be quantitatively measured,the free radical inhibitor tert-butanol was added to the reaction system,and it was found that the ozone catalytic oxidation effect was significantly inhibited in the presence of tert-butanol.Hydroxyl radicals are produced in the process,and the catalyst has a certain degree of adsorption for organic pollutants,and the adsorption accelerates the reaction.Therefore,the reaction system follows the coordination of the surface of the catalyst and the hydroxyl radical(·OH)The reaction mechanism of the combination of the two.(4)In the treatment of wastewater from chemical parks with a COD of 2230 mg/L and pharmaceutical wastewater with a COD of 228 mg/L,it was found that when the effluent COD meets GB 18918-2002,the cost of ozone catalytic oxidation is ozone oxidation 1/5 and 1/3;when treating the landfill leachate ultrafiltration water with COD of 560 mg/L,it was found that when the effluent COD meets the GB/T 31962-2015 standard,the cost of ozone catalytic oxidation is only 1/2 of ozone oxidation.The ZnO-MgO/γ-A12O3 catalyst greatly reduces the energy consumption required for this reaction process.After more than 4 times of treatment of methyl orange simulated wastewater,the removal rate of ZnO-MgO/γ-Al2O3 ozone to TOC remains above 96%,indicating that the ZnO-MgO/y-Al2O3 catalyst has high catalytic activity and Stability,ZnO-MgO/γ-Al2O3 ozone catalytic oxidation has certain application prospects in the advanced treatment of refractory organic wastewater.