Study On Enhanced Coagulation Pretreatment Of Leachate Membrane Concentrate In Waste Incineration Plant

Membrane concentrate is resulting from the extensive application of membrane separation technology in leachate treatment,which contains high concentration of pollutants,especially salinity,conductivity.Concentrate is harder to be biochemical degraded compared to leachate,and combination process is widely used to achieve better effect.As a commonly used pretreatment technology,coagulation has advantages of simple,economical and effective.In this paper,enhanced coagulation was used to treat municipal solid waste incineration（MSWI）leachate membrane concentrate,The main contents and conclusions are as follows:（1）The characteristics of three kinds of membrane concentrates were analyzed,which produced by the two stage tight ultraltration（TUF）,spacer tube reverse osmosis（STRO）,nanofiltration（NF）,respectively.The best coagulants and optimum conditions are determined by single factor experiments.Results show that the coagulant of poly silicate aluminum ferric（PSAF）have better effect than other coagulants in treatment of membrane concentrates.The optimum coagulation conditions:the dosage of PSAF is 50g/L,the dosage of PAM is0.08g/L,the initial pH of 7 for TUF membrane concentrate,the dosage of PSAF is 40 g/L,the dosage of PAM is 0.03 g/L,the initial pH of 5 for STRO membrane concentrate,the dosage of PSAF is 35 g/L,the dosage of PAM is 0.07 g/L,the initial pH of 5 for NF membrane concentrate.（2）The influence of stirring conditions are studied with orthogonal experiment.The removal effect of COD_Cr,UV₂₅₄ and chroma:fast stirring speed>fast stirring time>slow stirring speed.The removal effect of turbidity:fast stirring time>fast stirring speed>slow stirring speed.The influence of fast stirring speed on removal rate of four pollutants:COD_Cr>chroma>UV₂₅₄>turbidity,the influence of fast stirring time and slow stirring speed on removal rate of four pollutants:chroma>UV₂₅₄>turbidity>COD_Cr.The optimum stirring conditions for COD_Cr and chroma removal:fast stirring speed 400 r/min,time 120 s and slow stirring speed 80 r/min,the optimum stirring conditions for UV₂₅₄ removal:fast stirring speed 500 r/min,time 120 s and slow stirring speed 60 r/min;and the optimum stirring conditions for turbidity removal:fast stirring speed 400 r/min,time 120 s and slow stirring speed 60 r/min.（3）The removal characteristics of refractory organic compounds are studied by ultraviolet-visible spectroscopy and three-dimensional excitation-emission matrix fluorescence spectroscopy.The aromatization degree is obviously reduced as the values of E₂₅₄ and E₂₈₀ decreased.The values of E₂₄₀/E₄₂₀,E₃₀₀/E₄₀₀ and E₂₅₀/E₃₆₅ increased,which indicate that the degree of humus structuration and polymerization decreased,and the molecular weight decreased.The decrease of E₂₅₃/E₂₀₃ indicated that the types of substituents on aromatic rings decreased.Three-dimensional fluorescence spectroscopy analysis showed that the fulvic acid in ultraviolet region is completely removed,and the removal effect of fulvic acid in visible region is 90%⁹5%.There are peaks of tyrosine-like substances or soluble microbial degradation products after coagulation,which indicate that the biodegradability of the concentrates are significantly improved.