| Along with economic development, the amount of MSW (municipal solid waste) is growing gradually, causing serious pollution of environment and destruction of the ecological balance.At present, China's annual output of MSW is from 1.2-1.4 million ton, and the per capita garbage production is from 450 to 500 kg, and also increases by 5 per cent to 10 percent per annum.In the disposal methods of solid waste, sanitary landfill is one of the main methods of the MSW disposal. The landfill liner settings are the most critical technology in this disposal method. Generally, high-density polyethylene membrane (HDPE) and clay are used as landfill liner.However, due to mechanical damage and the construction of laying technology, the high density polyethylene film will be damaged and cause leakage. But through the traditional clay can effectively prevent the movement of water or aqueous solution of the low-tension, the clay is susceptible to the impact of organic pollutants, resulting the shrinkage cracks in impermeable layer of clay and losting blocking ability. So researching on the new structure for impermeable layer of solid waste landfill undoubtedly has an important theoretical and practical value. And the layer has not only a function of impervious, but also has interception capabilities. At the same time, to a certain extent, the layer also should own the self-sealing / self-healing capacity. The impermeable layer also could avoid enormous economic investment for excavation of solid waste landfill when the layer is damaged.In this paper, through the research on retention pollutants mechanism of modified bentonite, the adsorption rule of pollutants in the leachate by modified bentonite is studied. Through the investigation on impermeable performance of double impermeable layer with the addition of fly ash, lime, the self-sealing / self-healing properties and the interception of pollutions, a self-sealing / self-healing impermeable layer has been conducted which could meet the environmental request. The innovations are as follows:(1) A "self-sealing / self-healing" impermeable layer model of the sanitary landfill barriers has been conducted. Formation mechanism of self-sealing / healing in the composite impermeable layer has been discussed, and the destructive test showed that the "self-sealing / self-healing" layer had a good self-healing function, simultaneity the excavation difficulties had been conquered after the traditional impermeable layer damaged, so a new way of thinking for landfill impervious layer settings has been opened up.(2) Investigations conducted into availability and feasibility of the salty modified bentonite, acidified bentonite, roasting bentonite, short-chain organobentonite, long-chain organobentonite, dual-cation (long-chain and short-chain quaternary ammonium salts) organobentonite and anionic-cationic organobentonite. Experiments showed that roasting bentonite and dual-cation organobentonite had good effection and they can be used as reactive materials, so the research partly filled the gaps of using modified bentonite as a sanitary landfill impermeable materials .(3) Feasibility of using new double-impermeable layer (clay / modified bentonite) as landfill system impervious liner was explored. The simulation experiments of double-impermeable layer showed that modified bentonite used asactive material laid under "the inactive layer"-clay can effectively retainedthe pollutants in leachate, and the impervious effect tested good, in order to reduce organic pollutants in landfill leachate to come into groundwater and make barrier effect to maintain a clean groundwater environment.This papers divided into two parts: modified bentonite interception and the self-sealing / self-healing properties of the composite impermeable layers. The study on the modified bentonite interception and the impermeable properties of impermeable layers contains single interception effect of pollutants in impermeable layers and that of double-layer. Research on he self-sealing / self-healing properties of composite impermeable layer contains impermeable effect of single impermeable layer and that of double-layer. On this basis, the self-sealing / self-healing capacity of a single impermeable layer and that of double impermeable layer were studied. Specific conclusion of the study include :(1) In the static experiments of inorganic modify, when the concentration of MgCl2 was 2 mol/L, the removal of pollutants in landfill leachate was obvious. When the concentration of H2SO4 was 0.5 mol/L, the removal was the best, and with the increase of H2SO4, the removal efficiency increases were not evident. Bentonite modified by roasting by 450℃had better removal of leachate. Therefore, the conditions for inorganic modified bentonite were determined that the concentration of MgCl2 was 2 mol/L, the concentration of H2SO4 was 0.5mol/L and the roasting temperature was 450℃.(2) The permeability coefficient of the modified bentonite impermeable layer and the interception capability was synthesized, although the modified bentonite lost part of the impermeable performance, to varying degrees the adsorption properties of bentonite had been increaced, and get the goal of reducing pollution.(3) Clay/roasting bentonite always maintained the permeability coefficient at about 1.31×10-8 cm/s, and the average of permeability coefficient of clay/double-cation organobentonite was 4.21×10-8cm / s. Although the seepage performance of clay / double-cation organobentonite was worse compared to the clay / roasting bentonite impermeable layer, but both can be achieved national standard, so these two structure of impermeable layer can be used as a solid waste landfill impermeable layer. Because of the best interception of roasting bentonite and double cation organobentonite, they were used as double impermeable layer. In the same leakage, the attenuation capability of COD in clay / organobentonite impermeable layer was better than roasting bentonite. In the initial stages of the experiments, the removal efficiency of TN and NH4+ were very well and clay / roasting bentonite had the lasting attenuation adsorption capacity for NH4+ and TN, but the adsorption of clay / organobentonite impermeable layer quickly reached saturation. The adsorption capacity of Mn, Fe, Zn and Cr in the two soil columns was strong.(4) Adding fly ash and lime to clay improved the clay shortcomings of cracking and low intensity, and fly ash also has strong ability to remove pollutants, so they can be used as the addition materials of clay liner. Landfill liner added blast furnace slag drastically increased the permeability coefficient, thus it was not suitable as a sanitary landfill liner's adding material.(5) The permeability coefficient of landfill liner influenced by adding materials, activators, and the leachate.1) The trend of permeability coefficient mainly influenced by materials and relevant activators.The double-layered landfill liner, added lime and fly ash, had similar permeability coefficient with clay liner. The changes mainly caused by its small particles migration and blockage. Pozzolanic reaction play roles after 2 months later.2) The permeability coefficient of water was significantly higher than that of landfill leachate when the composite liner added by activators of CaCl2, and Na2SO4.Precipitation produced by the reaction between CaCl2 and CO32-,SO42-,S2- plugged pores in the liner, which greatly reduced the permeability coefficient.Therefore, the permeability coefficient of the 19th column added CaCl2 was 10-7 cm/s to water, while dropped to 10-11 cm/s to leachate. At the same time, SO42- in the Na2SO4 reduced to S2-. The S2- could generated precipitation with the vast majority of metal ions in the leachate. So precipitation between activators and leachate was another kind of self-healing/self-sealing mechanism.(6)Self-healing/self-sealing effect was influenced by landfill liner's running time, the amount of lime added.1) In the beginning of the experiment, the K of liner added 20 per cent of lime was 4.54×10-4cm/s, after 23 days the K fluctuated between 1.5-1.6×10-7cm/s, tending to be stable. The K of liner with 30% lime in the soil column experiment was 2.2×10-4cm/s at the beginning, and 8.75×10-7 cm/s to the end of the experiment.The results showed that with the ever-increasing amount of lime, the SH/SS effect can't be further enhanced, while it had declined. Lime content should be controlled in a certain range,in the experimental conditions the amount of lime controled to 10% -20% was suitable.2) With the same amount of lime and the same leachate of water, but fractured at different time, the SS/SH effects were also different. The longer standing, the greater the consumption of lime, the less lime in the presence of the liner the more slowly the permeability coefficient reduced.SS/SH capacity of the liner constrained by time, in the exerimental condition, with 20% lime, 20cm infiltration head, no activators and with water as leachate, the SS/SH capacity remained in 13 days, but 30 days later the SS/SH capacity decreased significantly.(7)All composite clay liners had a certain degree of capacity for retarding pollutants of NH4+, COD, liners added the activators of CaCl2, Na2SO4 both lowered the retarding capacity, and the CaCl2 lowered the capacity greater, and released much more Cl- than other soil columns. Double-layer composite liners had stronger ability to adsorpt of the high concentration of metal ions, and released less ions of low concentration.The liners containing activators caused serious inorganic pollution, the pollution of alkalinity and inorganic salt should be taken into consideration when comes to actual application. Therefore, the double-layered fly ash liner without activators should be the optimal choose in the project, which was of low pollution and able to self-seal/self-heal.
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