Mechanisms For Contaminant Transport In Landfill Composite Liners Under Thermal Effect And Its Optimization Design Method

High temperature inside the landfill will significantly reduce the breakthrough time for contaminant breakthrough liner system.Leachate head,the holes and wrinkles on geomembrane(GMB)also play important roles in performance of composite liner system.In order to evaluate the performance of liner system,it is crucial to investigate the combined effects of temperature,leachate head,contaminant concentration and defects in GMB on contaminant transport in the liner systems.The environmental issues of the landfill leachate from China and the foreign countries were summarized and analyzed,the environmental issues induced by landfill leachate were classified and the reasons were analyzed.A testing device was developed to evaluate the migration parameters of organic contaminant transport in the GMB.The effect of temperature field on the antifouling performance of landfill liner system was investigated.The mechanisms of contaminant transport in the soil,geomembrane(GMB)and the geosynthetic clay liner(GCL)under temperature gradient were revealed.And the range of the related parameters,such as thermal diffusion coefficient,interface conductivity of composite liner and the length of the wrinkles on GMB were obtained.Contaminant transport in the liner systems considering thermal diffusion was then investigated.Several analytical solutions were obtained,including the analytical solution for contaminant transport in the compacted clay liner(CCL)considering thermal diffusion,the analytical solution for contaminant transport in the CCL considering coupled effect of advection and thermal diffusion,and the analytical solution for contaminant transport in the GMB/CCL composite liner system,considering coupled effect of advection and thermal diffusion.On the basis of the proposed analytical solutions,Mento Carlo method was used to investigate the effect of leachate head,Soret coefficient,temperature and the length of the connect wrinkles on the antifouling performance of the landfill liner systems.The main conclusions are as follows:(1)Partitioning and diffusion experiments have been conducted to investigated the migration of bisphenol A(BPA)on high density polyethylene(HDPE)geomembrane.Batch tests were conducted to investigate the adsorption characteristic of BPA in loess(L)and loess-bentonite(LB).The partitioning and diffusion experiments indicated the partition coefficient and diffusion coefficient for BPA on HDPE geomembrane were 1.4 and 6.32×10-15m2/s,respectively.It suggests that the HDPE GMB can be a very effective diffusive barrier for BPA in a landfill application.Batch tests indicated the adsorption capacity of LB to BPA increased by a factor of 1.95-2.18,when the loess was amended by 10%bentonite.The sorption capacity of L and LB increased by 2.33%-26.52%,when the ambient temperature increased from 25? to 45?.(2)An analytical solution for one-dimensional contaminant diffusion in CCL considering thermal potential were developed.The average degree of diffusion of the CCL system for different boundary conditions and initial solute concentration distribution is introduced based on the analytical solution.On the basis of the proposed analytical solution,the effect of temperature and Soret coefficient on the contaminant transport in CCL system were investigated.The results indicated that the effect of thermal diffusion should be considered in the design of landfill clay liners since this effect is still considerable even when the temperature at the surface of the clay liner decreases to 30?.(3)An analytical model for contaminant transport in CCL considering advection and thermal diffusion was developed.On the basis of the proposed analytical model,the effect of leachate head,temperature,Soret coefficient and the bottom boundary conditions on the contaminant transport in CCL system were investigated.The results indicated the effect of leachate head on the contaminant transport in CCL is much larger than the temperature and Soret coefficient.The effect of thermal diffusion should be considered(>10%)only in the case with a large Soret coefficient(e.g.5×10-2 K-1)and the temperature difference on the surface of CCL reaches 40 ?.(4)An analytical model for contaminant transport in GMB/CCL composite liner considering advection and thermal diffusion was developed.On the basis of the proposed analytical model,Monte Carlo method has been used to investigate the relative importance of the involving migration parameters to contaminant transport in GMB/CCL and GMB/GCL/AL composite liner.The results indicated with the length of the connected wrinkles increased from 100m to 1000m,the bottom concentration and bottom flux for contaminant in the composite liners increased by a factor of 9.8 and 49.6,respectively.(5)On the basis of POLLUTEv7 software,a method to evaluate the maximum waste loading for landfill based on the background chloride concentration in ground water or aquifer was proposed.In this method,the leachate head and the initial concentration of chloride in leachate have linear relationship with the waste loading,and the breakthrough time for chloride was assumed to be 50 years.The result suggests the maximum waste loading for single and double composite liner system landfill ranges from 1.093×105 to 1.305×105 m3/ha and 2.544×105 to 4.2265×105m3/ha,respectively,in the case with different background chloride concentrations.(6)Based on the existed analytical solution for contaminant transport through the CCL and GMB/CCL composite liner systems,data fitting method was used to optimize the design of CCL,and the simplified calculation formulas were proposed.The simplified calculation formulas have considered the coupled effect of leachate head,contaminant species,breakthrough standard and retardation factor.The simplified calculation method was used to the optimization design of landfill liner system for Xi'an Jiangchungou landfill and Hangzhou Tianziling landfill.