| Along with the development of industry and the remarkable improvement of people’s living standard, the domestic garbage has been grown rapidly, which leads to particular attention to landfill leachate. The characteristics of landfill leachate are strong stench, abundance of complicated compositions and high toxicity that are difficult to be disposed by biological treatment methods. Therefore, the pretreatment methods of landfill leachate are particularly important. The aim of this research is to lucubrate the classical technologies and develop new technologies. Chemical coagulation, struvite, adsorption method by honeycomb cinders, microwave digestion method and oxidation method had been used in landfill leachate pretreatment. From these studies, it could be obtained high efficient processes and mechanisms of actions, which could be provided data base, theoretical directions and applications references. The contents of this research mainly included as follows:(1) Coagulation method. In this research, the coagulation method would be adopted to pretreat fresh landfill leachate, which generally used to pretreat old landfill leachate. AICl3, A12(SO4)3, FeCl3, Fe2(SO4)3and PAC were used as coagulants. Under optimum conditions such as coagulants doses, pH and reaction time, the results of experiments were shown as follows:the color efficiency:PAC＞AlCl3＞FeCl3＞A12(SO4)3=Fe2(SO4)3; the TS efficiency:PAC＞Fe2(SO4)3＞Al2(SO4)3＞FeCl3＞AlCl3; the NH4+efficiency:FeCl3＞Fe2(SO4)3＞Al2(SO4)3>PAC＞AlCl3; the CODcr efficiency:AlCl3>A12(SO4)3=Fe2(S04)3>PAC＞FeCl3. And the PO3-4efficiencies were all obtained at100.0%in this experiment using different coagulants. The UV spectrum analysis of raw/pretreated landfill leachate was manifested that the absorption peaks and intensities of pretreated landfill leachate were even fewer than these of raw landfill leachate. And the effects on the pretreatment of landfill leachate by aluminum salt as coagulants were better than that of ferric salt as coagulants. The SEM-EDS analysis of precipitates after experiments was demonstrated that the coagulation methods were not only used to effectively remove color, TS, NH4+, CODcr and PO3-4, but also used to effectively remove some inorganic and metal anions in raw landfill leachate. Furthermore, It was certified that the coagulation performance of aluminum salt coagulants were better than that of ferric salt coagulants for pretreatment of landfill leachate once again. In kinetics of reactions, the results were shown that the rates of reactions were closer to the second/third order kinetic model, which could explain the reasons of low removal efficiencies of pollutants in raw landfill leachate with short time. This method was characteristics of operate simple, rapid reaction, small occupied area, steady performance and great treatment efficiencies, et al. However, the disadvantages of this method were high cost and abundant of excess sludge produced.(2) Pretreatment of landfill leachate by struvite method. In this research, when pH was9.5, reaction temperature was20-30℃, the molar ratio of [Mg2+]/[NH4+]/[PO43-] was1:1:1.4, the reaction time was15min and the settling time was20min, the efficiencies of color, TS, NH4+and CODcr were obtained at81.3%,52.5%,100.0%and43.4%, respectively. And no surplus PO3-4existed in pretreated landfill leachate. The UV spectrum analysis of raw/pretreated landfill leachate was manifested that the absorption peaks and intensities of pretreated landfill leachate were even fewer than these of raw landfill leachate. The SEM-EDS analysis of precipitates after struvite method was demonstrated that the structures of precipitate mainly included cubic, acicular and cylinder crystals. In particularly, the cubic and acicular crystals were identified as struvite, and the cylinder crystals were identified as magnesium phosphate. In addition, the surface of crystals was surrounded by other elements, which confirmed that this method could not only remove NH4+, but also remove other pollutant in raw landfill leachate. In kinetics of reactions, the results were shown that the rate of reaction were closer to the first order kinetic model. The precipitates after experiment could be reused as slow release fertilizer by purification.(3) Pretreatment of landfill leachate by honeycomb cinders adsorption method. The honcycomb cinders were pretreated by distilled water, NaOH solution, HCl solution, CH3CH2OH and CH3COOH, respectively. The results of this experiment showed that the color, TS, NH4+, CODcr and PO3-4removal efficiencies were61.3%,52.5%,27.7%,39.3%and100.0%when honeycomb cinders pretreated by HCl solution doses of20.0mg·L-1, pH of9.5, reaction temperature of20℃, reaction time of15min and settling time of20min. The UV spectrum analysis of raw/pretreated landfill leachate was manifested that the absorption peaks and intensities of pretreated landfill leachate were even fewer than these of raw landfill leachate. SEM-EDS analysis and XRD analysis of precipitates after experiment illustrated that the adsorption ability of honeycomb cinders pretreated by HCl solution was better than that of honeycomb cinders pretreated by other solutions. In kinetics of reactions, the results were shown that the rates of NH4+and CODcr reactions were closer to the third order kinetic model, and the rate of color reaction was closer to second/third order kinetic model. The honeycomb cinders adsorption method was characteristic of friendly environment, waste control by waste, simple operation, steady performance, low cost, occupying small area, et al. The precipitates after experiment could be reused.(4) Pretreatment of landfill leachate by microwave digestion method. The color, CODcr and PO3-4removal efficiencies were obtained at75.0%,90.6%and100.0%, respectively, when microwave power of900W, pH of2.0and reaction time of15min. However, the NH4+removal efficiency was only6.5%. The UV spectrum analysis of raw/pretreated landfill leachate was manifested that the absorption peaks and intensities of pretreated landfill leachate were even fewer than these of raw landfill leachate. In kinetics of reactions, the results were shown that the rates of color and CODcr reactions were closer to the first order kinetic model. This method was advantages of good treatment effect, simple operation, occupying small area, none stench of the pretreated landfill leachate, none precipitates produced, which could be further developed and used.(5) Pretreatment of landfill leachate by oxidation method using oxidants. In this research, KMnO4, NaClO, H2O2and Fenton were used as oxidants to pretreated raw landfill leachate. The results were demonstrated that the treatment efficiencies of landfill leachate using KMnO4as oxidant were as follows:color68.8%, NH4+14.4%, CODcr47.6%and PO3-4100.0%; the treatment efficiencies of landfill leachate using NaCIO as oxidant were as follows:color50.0%, NH4+40.8%, CODcr59.6%and PO3-4100.0%; the treatment efficiencies of landfill leachate using H2O2as oxidant were as follows:color68.8%, NH4+3.2%, CODcr53.9%and PO3-4100.0%; the treatment efficiencies of landfill leachate using Fenton as oxidant were as follows:color82.5%, NH4+10.1%, CODcr64.2%and PO3-4100.0%. The UV spectrum analysis of raw/pretreated landfill leachate was manifested that the absorption peaks and intensities of pretreated landfill leachate were even fewer than these of raw landfill leachate. In kinetics of reactions, the rates of NH4+and CODcr reactions were closer to third order kinetic model when KMnO4used as an oxidant. When NaCIO was used as an oxidant, the rate of NH4+reaction was closer to third order kinetic model, and the rate of CODcr reaction was closer to first order kinetic model. When H2O2was used as an oxidant, the rates of NH4+and CODcr reactions did not go well. When Fenton was used as an oxidant, the rate of NH4+reaction was closer to the third order kinetic model, and the CODcr reaction was closer to the second order kinetic model. (6) Pretreatment of landfill leachate by microware-oxidants-struvite. Under the optimum conditions, the color, NH4+, CODcr, PO3-4and TS efficiencies of landfill leachate using microware-KMnO4-struvite were75.0%,100.0%,93.1%,100.0%and99.9%, respectively. The color, NH4+, CODcr, PO3-4and TS efficiencies of landfill leachate using microware-NaClO-struvite were75.0%,100.0%,91.5%,100.0%and99.9%, respectively. The color, NH4+, CODcr, PO3-4and TS efficiencies of landfill leachate using microware-H2O2-struvite were100.0%,100.0%,90.0%,100.0%and99.9%, respectively. The color, NH4+, CODcr, PO3-4and TS efficiencies of landfill leachate using microware-Fenton-struvite were100.0%,100.0%,92.0%,100.0%and99.9%, respectively. The UV spectrum analysis of raw/pretreated landfill leachate was manifested that the absorption peaks and intensities of pretreated landfill leachate were even fewer than these of raw landfill leachate. Moreover, the treatment effect of landfill leachate using microware-H2O2-struvite was the better than that of other combined methods.The aim of this research was to propose deeper theory mechanism of classical method for landfill leachate, and provide new study directions of new pretreatment methods. The results of this research enriched techniques which we currently use, and could provide simply new combined physicochemical methods, which could supply new thinkings and processes for landfill leachate pretreatment. Thus, this research is provided with important theoretical significance and wide application. |
PDF Full Text Request