Efficiency And Mechanism Of Electrochemical Oxidation For Decomplexation Of Cu-DOMs In Biologically Treated Landfill Leachate

High concentration of copper（Ⅱ）contained in landfill leachate easily interacts with dissolved organic matters to form complex,which is called Cu-DOMs.The process of complexation makes it migrate more quickly and strengthenes biological toxicity,which poses a potential threat to environment.However,most traditional technologies can not meet the requirements of removal of stable Cu-DOMs.Due to the lack of methods on quantitative and qualitative analysis of Cu-DOMs in practical wastewater,it is still difficult to remove complexes in practical wastewater such as landfill leachate with high concentration of heavy metals and dissolved organic compounds.In this study,electrochemical oxidation technology with outstanding advantages of high efficiency,low energy consumption and clean and easy operation was used to remove Cu-DOMs in biotreated landfill leachate.A integrated treatment device for decomplexation of Cu-DOMs was set up,and Magnéli-phase Ti ₄O₇ membrane was used as anode.One method on quantitative and qualitative analysis of Cu-DOMs in the biotreated landfill leachate has been established.Based on it,the parameters were optimized and mechanism of decomplexation was researched on,which is of great significance to the popularization and application of electrochemical oxidation on removal of heavy metal complex.In this study,Magnéli-phase Ti ₄O ₇ membrane was characterized.Results indicated that Magnéli-phase Ti ₄O ₇ membrane was porous meterial and its pore structure was dominated by large pores.The electrochemical active surface area is much bigger than its physical surface area,which means that Magnéli-phase Ti₄O₇membrane has more electrochemically active sites.Ti₄O₇ is main compositon of Magnéli-phase Ti ₄O₇membrane with high conductivity.Results of electrochemical performance tests showed that faster transmission of charge on the surface of the anode meaned that more charges transmit between organic matter and electrode surface or active species.Higher electrochemical stability and higher oxygen evolution potential indicated Magnéli-phase Ti ₄O₇ membrane is an ideal material for decomplexation by electrochemical oxidation.The linear relationship between the Dln A ₃₅₀ and the concentration of Cu-DOMs in the biologically treated leachate was established with methods of adding copper called parallel method and dilution.The results of differential spectral curves with peaks splitting and then fitting showed that the concentration of Cu-DOMs in water samples is negatively correlated with the intensity of Gaussian peak near wavelength of 250 nm(ΔA₂₅₀)and 400 nm(ΔA₄₀₀).The establishment of methods on quantitative and qualitative analysis of Cu-DOMs is an important theoretical basis of research on decomplexation in practical wastewater.The effect of operating parameters on decomplexation by electrooxidation was investigated with the change of current density,initial concentration of chloride,initial p H and electrolytic time.The results indecated that optimal removal of Cu-DOMs was 47.4%when 20 m A cm^-2 was applied to electrodes for 90 min without adding Cl^-(3 300mg L^-1)on the condation of p H=6.63.The electrooxidised mechanism of decomplexation was investgated,combined with the results of 3D fluorescence spectroscopy（3D-EEM）,electron spin resonance spectroscopy（ESR）,full ultraviolet spectrum（UV-Vis）and Fourier transform infrared spectroscopy（FT-IR）analysis.These samples were obtained in different eleclytic time with optimal operating parameters.The process of electrooxidation generated active species such as active chlorine,·OH,and Cl O₂·,which could attacking bond of C-N for decarboxylation.These active species could also breaking the bond between Cu（Ⅱ）and groups such as polyhydroxy phenols and carboxyl by attacking bond of Cu-O.NH₄⁺,NO₃^-and N₂were generated and organic matter was mineralized into CO₂.The dissociated Cu²⁺is reduced to Cu⁰ on the cathode or to form basic copper carbonate.The molecular weight distribution of DOMs related to Cu-DOMs was analyzed by exclusion chromatography.The fraction of AMW>10 k Da decreased significantly,and more organic compounds were transformed into low-molecular weight compounds.To differentiate portions in 0 min,30 min and 90 min,samples were separated by XAD-8 and XAD-4 resins.Results showed that the porcess of electrooxidation could promote the transformation of hydrophobic organics such as humic acid to transphilic and hydrophilic organics,which was benefit for decomplexation of Cu-DOMs.