Mechanism For Catalytic Ozonation Removal Of PPCPs From Solution With Manganese Based Oxides And The Application In Coupled Biological Aerated Filter Process

The current treatment process of the urban sewage treatment plant could not effectively degrade the drugs and personal care products（PPCPs）in the sewage and caused potential harm to human body and ecological environment when they were discharged into the urban water system.In this study,it was proposed to develop the catalytic ozonation coupled biological aerated filter to efficiently remove PPCPs from the municipal sewage plant.The existence of ionic polyvalent state（Mn（II）/Mn（III）or Mn（III）/Mn（IV））in manganese oxide made Mn O_x had good single-electron transfer efficiency and oxygen mobility in lattice,and became an excellent catalyst.However,the high recovery cost limited its wide application.Firstly,the efficient and easy to recover manganese based magnetic catalysts were prepared by a simple method,and catalytic ozonation system was established to study the degradation mechanism of typical PPCPs.In order to further evaluate the applicability of catalysts,a kinetic model was established to evaluate and predict the removal effect of this catalytic system on PPCPs in sewage.Finally,the catalytic ozonation system coupled with biological aerated filter process was applied to the advanced treatment of secondary effluent to verify its feasibility in practical application.The main research contents and conclusions were as follows:（1）Preparation and catalytic performance evaluation of manganese based oxides.The Mn_xO_y/γ-Fe₂O₃ and Mn_xCu_yO_z/γ-Fe₂O₃ were prepared by co-precipitation-annealing method.In addition,chloramphenicol（CAP）and sulfamethazine（SMT）,which were detected in high content of sewage and difficult to be removed by traditional sewage treatment process,were used as target pollutants to evaluate the established catalytic system.In the Mn_xO_y/γ-Fe₂O₃ system,the degradation ratio of CAP was 86.9%within 60 min;SMT could be completely removed within 30 min,and the salinity of the SMT solution could reach 61.9%within 90 min.And in the Mn_xCu_yO_z/γ-Fe₂O₃ system,the degradation ratio of CAP could reach 100%within 60 min,and the salinity of the CAP solution could reach 64.8%within 90 min.In the established catalytic systems,the removal effect of Mn_xCu_yO_z/γ-Fe₂O₃ on PPCPs was the best,and with the increase of ozone,catalyst dosage and solution p H,the removal effect of catalyst system on pollutants increased.And Mn_xCu_yO_z/γ-Fe₂O₃ had good magnetism and could achieve rapid solid-liquid separation.（2）The mechanism of catalytic ozonation degradation.In catalytic ozonation system,the contribution ratio(f_·OH-cata)of·OH generated from the catalytic decomposition of ozone by manganese based catalyst to the degradation of pollutants was 91.5%,and the contribution ratios of ozone(f_O3)and·OH(f_·OH-aq)generated from the decomposition of ozone to the degradation of pollutants were 6.9%and 1.6%,respectively.However,in the ozonation system,the f_O3 and f_·OH-aq were 80.9%and 19.1%,respectively.The degradation of pollutants by the catalytic system followed the·OH mechanism,and the active sites on the surface of manganese catalyst-hydroxyl group played roles in promoting the decomposition of ozone.The CO₃^2-/HCO₃^-,PO₄^3-,and humic acid could react with·OH rapidly,and also PO₄^3-occupied the surface hydroxyl group through ligand exchange to inhibit the production of·OH,which reduced the catalytic degradation effect.During the catalytic process,the valence states of Fe,Mn and Cu ions in the catalyst changed,indicating that the ions directly participated in the catalytic ozonation reaction.The HOO·generated during the reaction would reduce the high valence metal ions to the low valence state to maintain the stability of the catalyst.The removal of CAP by catalytic ozonation was via denitrification and hydroxylation,and the degradation of SMT was via desulfurization and hydroxylation.The evaluation and prediction results of bacteriostatic circle method and EQSAR model showed that the catalytic ozonation could effectively control the ecotoxicity of PPCPs in water environment.（3）The chemical kinetics model predicted the removal effect of PPCPs by manganese based oxides catalytic system.The chemical kinetics model of heterogeneous catalytic ozonation was established based on the reaction kinetics constant of O₃/·OH with pollutants and the quasi-first order rate constants of pollutants adsorption.The experimentally measured and predicted removal ratios correlated well in all reaction systems(linear correlation coefficients:R²_{Phosphate buffer}was above 0.950 and R²_{Secondary effluent} was 0.893-0.979).According to the model calculation of k_O3∫[O₃]dt,k_·OH∫[·OH]dt and k_adt,it could be seen that pollutants were mainly removed by O₃/·OH oxidation degradation,and the removal of pollutants by catalyst adsorption could be ignored.Based on this point,the model could be simplified,and the removal ratios of PPCPs could be effectively predicted only depending on the rate constant of O₃/·OH reaction with pollutants and the exposure of O₃/·OH(R²_{Phosphate buffer} was 0.973-0.998 and R²_{Secondary effluent} was 0.893-0.970).（4）Mn_xCu_yO_z/γ-Fe₂O₃ catalytic system coupled with biological aerated filter（BAF）process.The catalytic ozonation system coupled BAF process was developed for the advanced treatment of the secondary effluent of the sewage treatment plant.The removal ratios of cephalosporins in secondary effluent by catalytic ozonation system coupled BAF process was above 45%,and the removal ratios of other PPCPs were above 90%.And the COD and NH₄⁺-N in the secondary effluent decreased from 54.26 mg/L and 77.43 mg/L to 14.65 mg/L and15.73 mg/L,respectively,which was 33.0%and 15.4%higher than that of BAF process.In addition,increasing the hydraulic retention time in the BAF system could improve the removal ratios of COD and NH₄⁺-N.The application of this process had certain guiding significance for the actual secondary effluent advanced treatment,and had broad application prospects.