| With the rapid development of China’s economy,all kinds of garbage and waste generated are also increasing year by year,and garbage disposal has become one of the major hidden dangers threatening urban development.Landfill is currently one of the main means of waste disposal in China.The high temperature generated by the biochemical reaction of waste inside the landfill will cause a temperature gradient in the bottom liner system,and the thermal osmosis driven by the temperature gradient will accelerate the transport of leachate contaminants in the liner system,thus shortening its service life.Consideration of the effects of thermal osmosis during liner design has an important impact on ensuring safe and effective landfill operations.In this paper,the mechanism of thermal osmosis effect in geotechnical body is analyzed,and the range of thermal osmosis coefficient is obtained.The transport law of pollutants in landfill liner system under the effect of thermal osmosis is studied,and the one-dimensional transport model of pollutants through different liner systems under the effect of thermal osmosis is established,the corresponding analytical solutions are obtained,and the dimensionless analysis is carried out.Based on the analytical solutions obtained,Monte Carlo analysis was used to reveal the effects of thermal osmosis coefficient,Soret coefficient and temperature gradient on the antifouling performance of the liner systems.The service performance of double artificial composite liners for hazardous waste landfills under the effect of thermal osmosis was analyzed by using COMSOL Multiphysics 5.6 numerical software.The main conclusions obtained are as follows:（1）Thermal osmosis accelerates the transport of contaminants in the liner system,and the larger the thermal osmosis coefficient,the faster the transport of contaminants.Taking the CCL liner as an example,when the thermal osmosis coefficient increases to 1×10-10m2·K-1·s-1,the bottom concentration and flux are 3 and 12 times higher than those without thermal osmosis.Parametric sensitivity analysis of thermal osmosis revealed that CCL,GMB/CCL and GMB/GCL/AL behaved similarly under the effect of thermal osmosis,and the effect of thermal osmosis on contaminant transport in the liner system was small（<10%）when the thermal osmosis coefficient k T≤1×10-12m2·K-1·s-1,while when the thermal osmosis coefficient k T>1×10-12m2·K-1·s-1,the effect of thermal osmosis on the transport of contaminants in the liner system is more obvious（>20%）.（2）The transport of contaminants in the liner system cannot ignore the effect of thermal diffusion,and the bottom concentration and flux of the liner system both increase with the increase of thermal diffusion coefficient.In the case of CCL liner,for example,when the thermal diffusion coefficient increases to 0.2K-1,the bottom concentration and flux are 1.80 times and5.56 times higher than without thermal diffusion effect.（3）The temperature difference between the top and bottom of the liner system has a large effect on the transport of pollutants,and the temperature effect will accelerate the time of pollutant breakdown through the liner system,and the larger the temperature difference,the more significant the effect will be.Taking CCL liner as an example,the concentration and flux at the bottom of CCL atΔT=100K are 4.38 times and 6.39 times higher than those atΔT=20K,respectively（4）The effect of contaminant transport in GMB/GCL/AL under different bottom boundary conditions was analyzed.When the thermal osmosis coefficient k Tincreases from1×10-12m2·K-1·s-1to 1×10-11m2·K-1·s-1,the bottom concentration is 5.52-5.71 times of pure diffusion and the bottom flux is 18.25-20.34 times under the semi-infinite boundary condition;under the zero flux boundary condition,the bottom concentration is 2.82-2.84 times of pure diffusion;under the zero concentration boundary conditions,the bottom flux is 9.35-10.39 times that of pure diffusion.（5）The simulations of thermal osmosis of the double artificial composite liner were performed using COMSOL Multiphysics numerical software.It was found that the effect of filtrate head was small（<6%change in concentration）;the effect of thermal osmosis on contaminant transport was larger,and the bottom concentration increased by 31%when the thermal osmosis coefficient k Tincreased from 1×10-12m2·K-1·s-1to 5×10-11m2·K-1·s-1.The thickness,fold length and loophole frequency of the secondary liner in the double artificial composite liner have a greater impact on its anti-fouling performance.The bottom concentration decreased by 91.6%when the thickness of the secondary liner increased from 0.5 to 2m;the bottom concentration increased by 3.86 times and 1.7 times when the fold length of the secondary liner increased from 10 to 100m and the loophole frequency increased from 2.5 to 10/ha,respectively.Finally,an example analysis of thermal osmosis was conducted in a hazardous waste landfill,which confirmed that thermal osmosis can effectively promote the transport of pollutants. |
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