Application Of Mn（Ⅱ）@γ-Al₂O₃ Catalytic Ozonation In Petrochemical Secondary Effluent

Petrochemical wastewater generally contains biodegradable organic matter during biological treatment,which is tough to meet the Emission standard of pollutants for petroleum chemistry industry（GB 31571-2015）.Catalytic ozonation is widely employed in petrochemical industry due to its high mineralization in refractory wastewater.However,the treatment efficiency of catalysts on different wastewater varies greatly,and there are few studies on catalysts prepared for petrochemical secondary effluent.In this paper,Mn（Ⅱ）@γ-Al₂O₃ ozone catalyst with high activity was prepared from secondary effluent of a petrochemical plant.The preparation conditions,structure,physical and chemical properties,catalytic performance,and mechanism of catalytic ozonation were systematically studied.Artificial neural network（ANN）modeling was done with MATLAB（2019a）,and the catalytic performance of Mn（Ⅱ）@γ-Al₂O₃ was predicted by model calculation,guiding the preparation of catalyst.The main conclusions are as follows:（1）Mn（Ⅱ）@γ-Al₂O₃ ozone catalyst suitable for petrochemical secondary effluent was proved.The optimum preparation conditions were as follows:Impregnation of Mn（NO₃）₂ at 0.01 mol/L for 8 h and calcination at 550℃for 3 h.The catalyst was characterized by a layered pore structure,and Mn element was loaded on theγ-Al₂O₃carrier with the form of Mn O and Mn₂O₃.（2）Operating conditions and efficiency of Mn（Ⅱ）@γ-Al₂O₃ catalyzed ozonation of petrochemical secondary effluent were studied.Under the conditions of catalyst of 300g/L,ozone dosage of 40 mg/L,air intake rate of 40 mg/L,and influent COD of 60 mg/L,the effluent COD was 30.2 mg/L,meeting the standard（GB 31571-2015）.The catalyst showed excellent stability,repeating use 10 times,TOC removal was 41.74%,and decreased by only 6.24%.（3）The reaction process and mechanism of Mn（Ⅱ）@γ-Al₂O₃ catalyzed ozonation of petrochemical secondary effluent were revealed.The reaction mechanism was dominated by Hydroxyl radical,supplemented by surface coordination complexation.The removals of hydrophobic acid and hydrophobic basic organics reached 39.14%and56.76%in petrochemical secondary effluent by catalytic ozonation,respectively.When c(SO₄^2-)and c（HCO₃^-）increased from 0 to 1000mg/L,the removals of hydrophobic acid and hydrophobic basic organics decreased by 8.85%-11.60%and 34.81%-51.85%,respectively.（4）The ANN model for predicting the performance of catalysts was established.The root means square error and R² of the TOC removal of experimented value and ANN predicted value were 1.16 and 0.9659,respectively.The optimal preparation conditions of Mn（Ⅱ）@γ-Al₂O₃ predicted by ANN coupled with the enumerated method were as follows:Impregnation of Mn（NO₃）₂ at 0.155 mol/L for 8.5 h and calcination at 600℃for 3.5 h.