Study On The Effect Of Soil Fractal Feature On COD Migration Of Landfill Leachate

Landfill sites produce leachate contains large amounts of pollutants, which contain a considerable number of carcinogenic, cancer-promoting substances. The highest concentration of COD is90000mg/L, it will bring out a serious harm to groundwater and soil pollution. However, soil particles and pore distribution have direct impact on water and contaminant migration pathways in soil, thus affect the migration of contaminants in soil. Currently, the systematic study on fractal characteristics of soil particles and pores of domestic and foreign scholars and COD migration are rarely combined.This paper selects six kinds of particle, pore fractal dimension of soil samples for different grain size experiments, mercury test, penetration test, adsorption experiments and leaching experiments and so on, analyze the relationship between adsorption capacity, the permeability capacity and the soil fractal characteristics and the effect of soil fractal characteristics on COD migration, then use Hydrus-ld software to simulate and predict migration of COD in the silt vadose zone in Kaifeng Luhuagang landfill to illustrate the effect of fractal feature on COD migration in the vadose zone media.Study on the relationship between fractal dimension of soil particles and the soil adsorption capacity of COD shows:with the increase of clay content, soil particle size distribution fractal dimension increases, the equilibrium adsorption capacity and adsorption distribution coefficient increases, they both are a positive correlation.Relationship between fractal dimension of soil particle size distribution and its corresponding permeability coefficients can use exponential function to express, a comprehensive analysis shows that: with the increase of fines content, the fractal dimension increases, its permeability coefficient decreases; if not, it will be the opposite phenomenon.Soil hydraulic conductivity and porosity fractal dimension have a good correlation, he relation curve between micro pores, small pores, large pores and permeability coefficient is similar with the relation curve between total pore dimension and permeability coefficient in form, their relationship is an exponential function, but they have different trend change points, the relationship between four curves is not a simple weighted sum.The relation curve between fractal dimension of soil particles and biological degradation coefficient is quadratic formula, the general trend shows that:with the increase of particle dimension, biodegradable coefficient first decreases and then increases.The relationship between particle and pore fractal dimension and stabilization time of concentration flow is the particle dimension or porosity dimension increases, the COD concentration reached a steady stream will need longer time.Under the circumstances of5m thick silt porous and clay porous, the simulation and prediction of COD migration in landfills Hydrus-ld shows that:When COD concentration is4000mg/L, vadose zone media is silt, time of COD concentration exceeds over I type, II type,111type standard is72.07h,79.85h,83.74h; at the same leachate concentration, when vadose zone media is clay whose partical and pore dimension is larger, time of COD concentration exceeds over I type, II type, Illtype standard is1706.77h,1852.1h,1945.76h, the migration time extends23times.Select soil with larger particle and pore fractal dimension soil to be the sarking under the solid waste landfill or groundwater pollution control project cushion barrier to effectively extend the exceeding time of COD concentration in groundwater is reasonable. The innovation of this paper is it have a comprehensive study on the relationship between soil fractal characteristics and its adsorption capacity, soil fractal characteristics and its permeability coefficients, as well as the effect of soil fractal characteristics on COD migration in vadose zone.