Influence Of Submerged Combustion Evaporation On Characteristics And Binding Potential For Cd Of Leachate Organic Matter

Membrane concentration is the major treatment technology for landfill leachate.However,membrane retentate?MR?rich in salinity and refractory organic matter is difficult to treat.Recently,Submerged Combustion Evaporation?SCE?has been successfully applied to reduce the quantity of MR,and is highly adaptive to the MR with high sanility or high organic compounds,or to MR with both of them.Humic Substances?HS?are the major composition of organic matter in MR,which could be separated,concentrated and then applied to remediation of heavy metal contamination.As the only technology for MR reduction,what influences of SCE on the recyclable characters of organic matter is still unknown.Ultrafiltration method was used to study changes of composition and structure of organic matter after evaporation.Meanwhile,the specific binding indexes of organic matter for Cd were obtained based on isothermal adsorption experiments,so as to evaluate influences of SCE and the binding potential of recycled organics for Cd in SC,which will provide supports to complete leachate treatment technology chain.The high molecular weight organics?>10 kDa?dominated in both MR and SC,with percentages of more than 40%.During the treatment in SCE,organics in middle molecular weight?2.5-10 kDa?were damaged,which could be attributed to the change of molecular structure of fulvic acid?FA?in HS.Humic acid?HA?was refractory to high temperature,and the percentage of HS with molecular weight more than 10 kDa increased from 56%to 70%after SCE treatment.The Ultraviolet-visible spectroscopic indexes of E₂₅₀/E₃₆₅,E₂₅₄/E₄₃₆,and the Aromaticity?Ar?index from Nuclear Magnetic Resonance integration manifested a positive relationship between Ar and molecular weight of organic matter.Besides,analyses of element compostion and NMR integration showed organic matter with high molecular weight had higher carboxylic acid content and higher element content ratios between nitrogen,oxgen and carbon than small organics.After evaporation,the molecular weight of HA increased,which was the same as its Ar,carboxylic acid,nitrogen and oxgen contents in organics.FA experienced opposite change as that of HA.Using the Non-Ideal Competitive Adsorption model to similate binding properties of organic matter for Cd showed that after evaporation,the binding capacity of carboxylic acid for Cd increased from 3.76 to 4.65 mol/kg-TOC,and the stoichiometric number of a single proton binding site for Cd increased;the binding capacity of hydroxyl for Cd decreased from 0.68 to 0.40 mol/kg-TOC,but the affinity constant for Cd?log K?increased from 6.17 to 6.69,showing its high competition ability with proton.According to characteristic changes of humic substances during SCE,evaporation in low temperature increased the entire aromaticity of humic substances?led by the change of HA?.Therefore it increased the affinity of organics for Cd.But at the same time,it reduced the content of oxygen containing functional groups?led by the change of FA?,contributing to the decrease of acid adsorption sites density.In general,organic matter in SCE residue had better adsorption performance compared with organics in MR,and it had comparable ability with purified natural HS.