A Study On Leachate Transport Of MSW Landfill Under Coupled Temperature-Seepage Action

Landfill is the main method of MSW disposal in China. MSW landfill generates high concentration of leachate, which can induce secondary pollutants to surrounding water body, when treated improperly. In order to control landfill leachate, it's necessary to do some research on landfill leachate transport. Based on biochemical reaction mechanisms of landfill biodegradation and in view of convection, dispersion, diffusion, adsorption and organic biodegradation, the author established advection-dispersion transport model of landfill leachate, furthermore, the analytical solution of one-dimensional migration equation was solved.Based on the theory of solute transport in landfill, the author did the simulated experiment indoor. In this foundation, the effect of temperature change on leachate transport was analyzed, which caused the change of chemical index of landfill leachate.According to the theory of permeation fluid mechanics and thermodynamics of porous medium, thermal effect and seepage theory in landfill site were analyzed. From the non-isothermal angle, the interaction mechanism between, the moisture transfer and temperature change in landfill site was analyzed theoretically. Temperature change has an effect on seepage field, which manifests two aspects: one the one hand, temperature change influences seepage field by hydraulic conductivity tensor in the landfill body; one the other hand, temperature grads themselves also influence seepage field, moreover, the higher temperature gradient is, the stronger the effect it has on seepage field is, on this basis the author established the governing equation of seepage field which was affected by temperature change. By analyzing the effect that leachate transport had on temperature field, this thesis established the governing equation of temperature field, the results showed that: the distribution of temperature field and the distribution of seepage field are closely-related in the landfill body, the higher hydraulic gradient is, the stronger the effect it has on temperature field.Based on the analysis of coupling action between temperature and seepage field in the landfill site, the coupled double-field model for leachate transport was established. The finite element numerical solution method of the mathematical model was presented, also the analytical solution of one-dimensional simplify model was solved. By analyzing simplify model, it was shown that: the higher hydraulic gradient was, the more obvious the effect of seepage on temperature was, and the less obvious the effect of temperature on seepage was. When seepage flows from where the temperature is high to where the temperature is low, the temperature increases and the hydraulic head decreases; when seepage flows from where the temperature is low to where the temperature is high, the temperature decreases and the hydraulic head increases.