Numerical study for one-dimensional non-isothermal transport of organic contaminant in the three-layer composite liner containing a defective geomembrane

Abstract

The non-isothermal case in bottom composite liners not only induces thermal diffusion behavior, but also alters transport parameters. To date, however, limited work has been done on this topic. The present research constructs a model for one-dimensional non-isothermal transport of organic contaminant in the three-layer composite liner containing a defective geomembrane (GMB), which for the first time systematically includes the impacts of temperature-dependent transport parameters, and also considers the multiple transport mechanisms. The developed model is then solved via finite difference, and its rightness is well-proven through comparisons with the two experiment results and the other calculation approaches. After that, the numerical analysis shows that the temperature-dependent transport parameters exert a combined effect on the transport process, in which changes in diffusion coefficients and hydraulic conductivities with temperature remarkably accelerate the transport rate, whereas such a change for distribution coefficients leads to an opposite trend. The barrier performance assessment suggests that the growth of temperature difference in the composite liner, as well as the GMB defects density, reduces the defined breakthrough time ($t_b$) and increases the bottom transport flux. Moreover, 1 cm geosynthetic clay liner is noticed to extend $t_b$ by approximately 2.23 years, while 0.1 m compacted clay liner yields the increment of $t_b$ by about 12.1 years. These findings contribute to the reasonable evaluation of bottom composite liners’ barrier performance at a non-isothermal environment, which could provide guidance for optimizing their engineering design.