Study On The Binding Of Copper/Iron Metals Onto Organic Matter In Landfill Leachate By Molecular Spectroscopic Techniques

Dissolved organic matter（DOM）in leachate from municipal solid waste landfill contains a variety of active functional groups,which can interact with metals to form complexes,change the activity of metals,inhibit the precipitation and adsorption of metals,interact with soil,water,and mineral surfaces,and affect the migration and transformation of metals.Studying the interaction mechanism and influencing factors of DOM in landfill leachate with metals ions is of great significance for understanding the environmental behaviors of metals pollutants in landfill leachate and optimizing the environmental remediation methods in metals polluted areas.In this dissertation,taking the raw liquid and membrane concentrate of landfill leachate produced by Heimifeng landfill as the treatment object,the effects of p H,concentration of Cu and Fe ions and treatment methods of leachate on the interaction between DOM in landfill leachate and Cu/Fe metals were studied by Ultraviolet-visible absorption spectra（UV-Vis）,Excitation-emission matrix（EEM）and characterization of UV spectral characteristic parameters such as S_275-295,S_R,Dslope_240-280 and Dslope_325-375.The main findings of this thesis are listed below:1:The UV-Vis absorption spectra of DOM in LL and MCLL changed imperceptibly following Cu and Fe addition because DOM contained complex and diversified functional groups that absorb UV-Vis light.Cu and Fe ions initially combined with DOM in LL,causing variation in the UV-Vis absorption spectra.Differential log-transformed absorption spectra was employed to magnify the subtle variation in raw UV-Vis absorption spectra,which showed increases in intensities of characteristic peaks after metals interaction,and the increase of intensity at shorter wavelengths was more conspicuous,indicating the heterogeneity of the sensitivity of these chromophores in binding with different metals.2:The interaction of metals ions with DOM in both LL and MCLL induced the elevation of aromaticity,which is dependent of metals species and leachate compositions.The binding of Cu（II）onto DOM was stronger than that of Fe（III）,and the metals binding tendency of DOM in LL was stronger than that in MCLL.The values of S_275-295 and S_R decreased with the increase of metal ion concentration,indicating an increase in molecular weight/molecular size after interaction with metals.The values of Dslope_240-280 and Dslope_325-375 increased with the increase of metal ion concentration,indicating that phenols and discrete carboxyl groups participated in the binding of metal ions.The discrete carboxyl groups and phenols in Cu-DOM reaction system had the characteristics of higher participation and stronger activity.3:By looking at the EEM diagram of DOM,it was found that:fluorophores in LL-DOM was mainly composed of aromatic proteins（tyrosine-like）and microbial metabolism by-product（tryptophan-like）;MCLL samples exhibited peaks at Ex/Em 230/450 nm and 320/420 nm,which were related to fulvic-like and humic-like substances as a result of humification and concentration.With the increase of Cu and Fe concentrations,the fluorescence intensity decreased significantly with different extents depending on the peak positions.The complexation reaction between Cu and DOM was stronger than Fe.4:Two components were identified for both LL and MCLL by PARAFAC analysis.LL-DOM C1 and MCLL-DOM C1were both classified as humic-like component,while the LL-DOM C2 can be ascribed to protein-like component,and MCLL-DOM C2 was associated with fulvic-like component.The extent in the decrease of Cl and C2 scores of DOM in MCLL/LL with Cu was much higher than that with Fe,suggesting stronger binding characteristics of Cu with fluorophore in DOM.5:Humic acid-like components in LL had stronger binding propensities towards metals than protein-like components,while fulvic acid-like component in MCLL had stronger binding propensities towards metals than humic acid-like components.Although the log K value of Fe was higher than that of Cu,the intial percentage of fluorescence intensity involved in binding of Cu was much higher than that of Fe,suggesting more suitable environment for Cu-DOM complexation than Fe.This study may help to better understand the physicochemical properties of DOM,as well as the interactions between metals and DOM in landfill leachates.