Experimental Study On Co-Treatment Of Biochemical Tailwater From Landfill Leachate By Coagulation And Persulfate Catalytic Oxidation

Landfill leachate,as a kind of high-concentration organic wastewater that is difficult to be treated,has become an urgent problem to be solved due to its complex composition,poor biodegradability and high pollutant concentration.Therefore,it is necessary to find more appropriate treatment technology for its in-depth treatment.In this study,the biochemical tail water of landfill leachate was treated by coagulation-persulfate catalytic oxidation.The single factor experiment was carried out to optimize the treatment process and evaluate the coagulation removal effect of various coagulants on the organic matter in the biochemical tail water.On this basis,Cu/Mn bimetallic supported activated carbon was prepared to catalyze the persulfate oxidation and further remove the organic matter in the coagulated effluent.The changes of organic compounds before and after the reaction were analyzed by UV-VIS and 3D-EEM.The results showed that:（1）the coagulant effect of iron coagulant on biochemical tail water of leachate was obviously better than that of aluminum coagulant,and ferric chloride（FC）was determined as the best coagulant.For the coagulation treatment of biochemical tail water of landfill leachate,the optimal dosage of FC is 800 mg/L without additional adjustment of p H,and the optimal dosage of polyacrylamide（PAM）is 200 mg/L.At this time,the removal rates of COD_Cr,UV₂₅₄ and chroma are 57.5%,74.8%and 95.2%,respectively.The residual COD_Cr value was 469.7 mg/L.（2）The persulfate oxidation reaction is greatly affected by temperature.When the reaction temperature is lower than 60℃,persulfate basically does not decompose to produce sulfate radical and react with organic matter in the biochemical tail water of landfill leachate.Under the optimal reaction condition,that is,the reaction temperature is 90℃,the COD_Crremoval rate of Na₂S₂O₈ and K₂S₂O₈ system can reach 94%within 30 min,and the residual COD_Cr value is only 36.7 mg/L.（3）Cu/Mn bimetallic supported activated carbon material was effectively prepared.According to the influence of metal type and metal load on persulfate catalytic activation,Cu-KMn/AC was selected as the best catalyst for persulfate system.Secondly,through single factor study,obtained the optimal dosage of Na₂S₂O₈,K₂S₂O₈ with Cu/Mn bimetallic supported activated carbon catalyst is 6 g/L,7g/L and 4g/L,respectively,under the optimal experimental conditions of reaction temperature of 50℃,reaction time of 90 min,without adjusting p H.In Na₂S₂O₈ and K₂S₂O₈ systems,the COD_Cr removal rate and residual COD_Crvalues were 83.2%,83.4%,93.0 mg/L and 99.7 mg/L,respectively.Under the same reaction conditions,KHSO₅ dosage of 15 g/L was added for 4 h.The COD_Cr removal rate and residual COD_Cr values in KHSO₅ system were 81.9%and 90.6 mg/L,respectively.（4）The analysis of UV-VIS and 3D-EEM showed that the aromatization degree,molecular weight and polymerization degree of organic matter decreased in the biochemical tail water of landfill leachate after treatment,DOM aromaticity was weakened,the aromatic ring structure in the biochemical tail water was reduced,and organic matter such as humic acid and fuluric acid were effectively degraded after oxidation by sulfate system.It can be concluded that the persulfate catalytic oxidation system can oxidize or even mineralize most organic matter,and can degradeπ-π*and most benzene ring organic matter with conjugate system.（5）In this study,a feasible coagulation-persulfate catalytic oxidation process of landfill percolation biochemical tail water was explored with a new idea,which provided a new idea and theoretical basis for the technical optimization of the relevant treatment process of leachate.