Study On Preparation Of Ce-Mn/Al₂O₃ Catalyst And The Advanced Treatment Of Tannery Wastewater

With the improvement of environmental protection requirements and the implementation of the Discharge Standard of Water Pollutants for Leather and Fur Making Industry?GB30486-2013?,the COD and ammonia nitrogen in the effluent of tannery wastewater can not usually meet the requirements of discharge standards.Fenton oxidation technology has a significant effect on tannery wastewater treatment,but the Fenton has a strict requirement on pH with a high demand of H₂O₂ and ferrous ions,which leads to a large production of sludge easily.In this study,several granular catalysts for fenton-like reaction were prepared and applied to the advanced treatment of tannery wastewater.The preparation process of the catalysts and the catalytic oxidation conditions of the heterogeneous Fenton reaction were investigated and optimized.In the end,tannery wastewater was treated by the heterogeneous Fenton+BAF reactor,then the study also explored the possibility of engineering application,which provided a reference for practical engineering applications of heterogeneous catalysts.?1?The experiments of carrier comparison showed that the best catalyst carrier is activated alumina.The sequence of importance of those factors in the preparation process of the catalyst was calcination temperature>calcination time>Ce content of the impregnation liquid>Mn content of the impregnation liquid.The optimal preparation conditions of the catalysts obtained by single factor experiment and orthogonal experiment were calcination temperature 300°C,calcination time 4 h,Mn content 2.5%in the impregnation liquid,and Ce content 1%in the impregnation liquid.In this condition,the average COD removal of tannery wastewater was 67.20%.?2?Aiming at the process of catalytic degradation of tannery wastewater by Ce-Mn/Al₂O₃,the response surface model was established by Box-Behnken response surface method.In the heterogeneous Fenton-like reaction system,the significance of influence factors was followed the sequence:initial pH>H₂O₂ dosage>catalyst dosage>reaction time.The quadratic response surface model had a high degree of fitness(R²_adj=0.9349).The optimal reaction conditions:catalyst dosage 56.63 g/L,H₂O₂ dosage 280.88 ppm,initial pH 3.51 and reaction time 2 h with the COD removal 80.94%.The response surface plot showed that the catalyst could reach more than 65%COD removal at pH 3⁷ while the degradation process conformed to the second-order reaction kinetics model.?3?The heterogeneous Fenton and BAF reactor were combined to treat the tannery wastewater.The continuous flow experiment did not adjust the pH of raw water.When the influent flow was 12.5 L/h,the HRT of heterogeneous Fenton device was 2 h,and the HRT of BAF device was 4 h,with the system running effectively continuously for two weeks.During the continuous experiment,the water content of catalyst was 0.84 m³/kg,the final COD concentration and the NH₄⁺-N concentration were 60.48 mg/L and 5.1 mg/L,and the color<30 times,which met the standard of the Table 2 in the Discharge Standard of Water Pollutants for Leather and Fur Making Industry?GB30486-2013?.The maximum leaching concentration of manganese ions and cerium ions in the active metal component leaching experiment were 0.67 mg/L and 0.36 mg/L respectively,which was lower than the emission standard,indicating that the secondary pollution of the catalyst was small and the heterogeneous Fenton+BAF reactor had a certain engineering practicability.