The Removal And Mechanism Of Residual Organic Matter In Secondary Treatment Effluent Of Urban Sewage By Manganese Ore-ozone System

As a sustainable and stable water source,the secondary effluent of urban sewage treatment plant can be reused after deep treatment,which can solve the problem of water resource shortage to a certain extent.The traditional advanced treatment technology has some problems such as poor ability to treat organic pollutants or high cost.Therefore,in this study,the secondary effluent of a sewage plant in Qingdao was taken as the research object,and manganese ore（MS）,which is rich in resources and cheap,was used as the catalytic material to study the deep purification and removal efficiency of organic compounds in secondary effluent by MS filtration process and catalytic ozone（O₃）oxidation process.The control potential of the process on the precursors of disinfection by-products and the removal ability of fluorescent substances were evaluated.At the same time,the influence of hydraulic load,backwash intensity and other working conditions on the purification efficiency was analyzed.Finally,the mechanism of MS in the process of organic removal was explored.The purification results of residual organic matter in secondary effluent by MS filtration process show that the removal rate of UV₂₅₄ by QS and MS filter column is 3%and 20%,and the removal efficiency of TOC is-0.2%and 12%,respectively.At the same time,3D fluorescence spectrum showed that QS could not effectively reduce the fluorescence intensity,while MS decreased by 6.96%.The chlorine disinfection experiment showed that QS could decrease the production of chloroform and carbon tetrachloride by 8.18%and 18.84%,while MS could decrease 46.9%and 71.31%,respectively.In the process of MS filtration and purification,cation Ca²⁺,Mg²⁺and NH₄⁺can promote the removal of organic matter,while anion can inhibit the removal of organic matter,and the inhibition relationship is PO₄^3->NO₃^->SO₄^2->Cl^-.The control mechanism of MS on organic matter includes the direct degradation of organic matter and the advanced oxidative degradation catalyzed by MS.The experimental results of QS process,MS process,QS+O₃ process and MS+O₃process show that when MS+O₃ filter column combination process has the initial p H neutral value,The O₃ dosage is 1.5 L/min,the influent load is 1.53 m³/（m²·h）,and the reaction time is 120 min,The removal rates of TOC and UV₂₅₄ in MS+O₃ system were13.72%and 31.25%,respectively.The formation potential of trichloromethane,carbon tetrachloride,monobromodichloromethane and dibromodichloromethane decreased by36.86%,49.75%,49.95%and 37.36%,respectively.The removal rates of target benzene series are above 40%,which is obviously better than the other three processes.MS has a higher catalytic capacity for O₃ than QS,among which,MS also has a better control potential for the precursors of disinfection by-products and benzene series.Three-dimensional fluorescence spectrum and molecular weight analysis of the water in and out of each process showed that MS+O₃ process could not only effectively reduce humus and fulvic acid organics,but also completely remove UV₂₅₄ with molecular weight greater than 10 k Da.The DOC removal rates of more than 100 k Da and 30-100 k Da were 90.9%and 75%,respectively.After long-term continuous operation,the removal rates of UV₂₅₄ and TOC in MS+O₃ effluent are 19.5%and7.79%.The physical and chemical properties of MS were characterized by SEM,XPS,XRD and BET.The results show that the surface of MS is granular and has a mesoporous structure with an average pore size of 6.18 nm.The BET specific surface area of MS is 29.74 m²/g,and the BET adsorption and desorption curve has a hysteresis loop,which conforms to H₃ type adsorption.XRD and EDS results show that MS is a natural mineral with amorphous morphology,rich in Si,Al,Fe,Mn metals,among which manganese exists in the form of Mn²⁺,Mn³⁺and Mn⁴⁺.After long-term use,the pore size of MS increases and the adsorption capacity increases,but the loss of manganese is the main reason for the decrease of MS catalytic activity.In MS+O₃process,MS can catalyze O₃ to produce·OH to oxidize organic matter.The mechanism of MS+O₃ process to remove organics in secondary effluent water includes purification removal of MS,oxidation of O₃ and oxidation of·OH generated by O₃ catalyzed by MS.The combination of the three can complete the purification of organics.