The Analytical Model For Organic Contaminant Transport In Composite Liners Considering The Coupled Effect Of Consolidation And Diffusion

Landfill leachates contain many contaminants with high concentrations and high toxicity.Leachate contaminants have become a great threat to the surrounding environment. Though the standard liner systems were constructed for many landfills to mitigate leachate contaminant transport, the groundwater and soils beneath the landfills were polluted by the leachate contaminants, especially organic contaminants.The components and the environmental issues of the landfill leachate from China and the foreign countries were summarized and analyzed in the present paper. The landfill leachate contaminants were summarized and the typical values for design purpose were suggested. And the environmental issues induced by landfill leachate were classified and the reasons were analyzed in the present paper. One-dimensional analytical models, including quasi-steady-state small deformation model (SDSS) and quasi-steady-state large deformation (LDSS) model, were developed to investigate the behavior of organic transport in landfill composite liner system considering coupled effect of consolidation, diffusion and degradation. The first and second type bottom boundary conditions are used to derive the analytical solutions. Single free draining boundary conditions and double free draining boundary conditions were used to investigate the effect of consolidation on the transport of contaminant in liner system, On the basis of the analytical solutions, the effect of consolidation on organic contaminant transport through liner system was investigated. Furthermore, the different deformation models were applied to analyze the effect of consolidation on contaminant transport. Finally, the performance of landfill liner system was studied and different liner systems were also evaluated. The main conclusions are as follows:(1) The analytical models for organic contaminant transport in the landfill composite liner system considering coupled effect of consolidation, diffusion and degradation were developed. The bottom boundary conditions are assumed to be zero concentration or zero flux. The generalized integral transform technique (GITT) was used to derive the analytical solutions. The different consolidation models (LDSS and SDSS) and different draining conditions were considered.(2) The geomembrane composite barriers provide much better diffusion barriers for the organic contaminants than the single CCL. For instance, the bottom flux for the case with single CCL can be 1.5 times larger than that for the case with GMB/CCL considering diffusion and consolidation for organic contaminant.(3) For the SDSS model and double free draining boundary conditions, with the increase of consolidation of liner the organic contaminant transport were reduced.However, under single free draining boundary conditions, with the increase of consolidation of liner the organic contaminant transport were accelerated and increased. For zero flux boundary condition and single free draining boundary condition,the steady-state bottom concentration for r-0.76yr-1 can be 1.4 times larger than that for without considering consolidation. In contrast, for double free draining boundary condition,the steady-state bottom concentration for r=0.76yr-1 can be 1.3 times less than that for without considering consolidation.(4) Adsorption and degradation have a great influence on the contaminant transport in the liner system. The contaminant bottom concentrations and fluxes decrease with the increase of adsorption of liner and degradation of organic contaminant. The steady state bottom flux for the case with psKd=10 can be 6.6 times less than the case without considering adsorption of liner. The steady state bottom concentration and bottom flux for the case with t1/2=300 years can be 3.3 and 2.4 times larger than the case with t1/2=3 years considering degradation of organic contaminant.(5) The initial void ratio of clay has a great influence on the contaminant transport in the liner system. With the increase of initial void ratio of clay, the bottom concentration of organic contaminant increases. For the case with t=5years, the bottom concentration for the case with e0=2 can be 1.5 and 3.1 times larger than the case with e0=1.5 and e0=1, respectively. This may be due to the fact that the effect of consolidation is greater for the case with large initial void ratio of clay.