Preparation Of Modified Sludge Biochar Catalyst And Advanced Treatment Of Biological Pretreated Landfill Leachate By Using Fenton Catalytic Oxidation Methods

In this study,a modified sludge biochar material with high catalytic performance was prepared by pyrolysis using dewatered sludge from an urban sewage treatment plant.Its catalytic effect and mechanism on DMP in different Fenton systems（heterogeneous catalysis and three-dimensional electrocatalysis）were explored,and the advanced treatment efficiency of coagulation sedimentation and different Fenton system combinations on the actual landfill leachate biochemical effluent was further studied.The research results provide technical support for the application of Fenton catalytic oxidation technology based on sludge biochar.The effects of different pyrolysis temperatures and FeCl₃ impregnation concentrations on the preparation conditions of modified sludge biochar were studied,combined with the characterization results of FTIR,Raman and ESR and the degradation effect of DMP,the optimal preparation conditions were obtained as the pyrolysis temperature of 700℃and the impregnation concentration of 50 mmol/L.The best modified sludge biochar（MSB-700-0.05）was further characterized.The results showed that the catalyst surface had more pore structures,graphitized structures and defect structures on the carbon layer,and iron elements existed on the surface in the form of Fe²⁺,Fe³⁺and Fe⁰.The optimal reaction conditions for the degradation of DMP in the modified sludge biochar heterogeneous Fenton system were found to be p H=3,the dosage of H₂O₂ was10 mmol/L,and the dosage of catalyst was 1.0 g/L.Under the conditions,the reaction for 60 min can remove 94.8%of DMP with an initial concentration of 60 mg/L,and the maximum degradation rate constant of DMP was 0.1962 min^-1.During the reaction process,the dissolved amount of iron ions was less than 1.7%,which was dominated by heterogeneous Fenton reaction.The degradation mechanisms include the radical pathway of OH and the non-radical pathway of the material’s defects and graphitized structure as electron donors for electron transfer to H₂O₂ and contaminants.After 5cycles of recycling,the removal rate of DMP still reached 72.6%.The optimum reaction conditions for the degradation of DMP in the modified sludge biochar three-dimensional electrode-electro-Fenton system were found to be p H=3,the electrolyte concentration was 0.05 mol/L,the current density was 10 m A/cm²,and the dosage of MSB-700-0.05 was 1.0 g/L,the air flow was 4.5 L/min and the plate spacing was 1.0 cm.Under the conditions,the removal rate of DMP was 100%after 30min reaction The degradation mechanisms include electrochemical oxidation and radical pathways dominated by OH.MSB-700-0.05 is both a particle electrode and a heterogeneous catalyst.After 5 cycles of recycling,the removal rate of DMP is still 62.4%.The combined technology of"coagulation sedimentation-Fenton oxidation"is used to treat the actual biochemical tail water of landfill leachate.The total COD_Crremoval rate of the biochemical tail water after the combination of coagulation sedimentation and three different Fenton systems can reach more than 90%.Gel chromatography showed that some high molecular weight compounds were oxidized to small molecular organic compounds,and the three-dimensional fluorescence image further indicated that humic substances and fulvic acids were also well removed.Compared with homogeneous Fenton,heterogeneous Fenton and three-dimensional electrode-electro-Fenton system have the advantages of less Fe²⁺dosage,no need to adjust p H after reaction,and easy catalyst recycling.By comprehensively comparing the technical economy of the three Fenton systems,it is recommended to choose the combination technology of"coagulation sedimentation-heterogeneous Fenton oxidation"as the advanced treatment process of the leachate.