Coupling Dynamic Model Of Landfill Leachate Contaminant Release And Transport And Its Application

With the development of economy and the increment of population, the production of municipal solid waste in China is increasing year by year. It has been the urgent affairs to treat it timely, safely and hygienically. The landfill method has been widely utilized home and abroad, because it has some advantages such as simple process, less investment and big treatment capacity. But the treatment and control of the landfill leachate which is considered as a main pollution source of subsurface environment, has be a difficult problem during the development of landfill technology, which involves many key scientific problems such as the prediction of water quality and quantity. But because the production and evolution of landfill leachate is complex, and it belongs to a multidisciplinary intersect problem, the prediction model of water quality and quantity develops slowly and it has restricted the development of landfill leachate treatment technology and pollution control technology, and even the development of sanitary landfill technology. So, in this paper the nonlinear law of the landfill leachate migration and transformation in subsurface environment was revealed by a series of laboratory test, the H-M-C coupling model which described the organic pollutant migration and transformation in the refuse landfill body, unsaturated soil and saturated aquifer were established, the concentration distribution and development trend of organic pollutant of landfill leachate in soil-water system was forecast. The main research contents are as follows:1. The autqgenic water is the important inner source of landfill leachate, its release has important effect on the landfill leachate output and transportation. The laboratory test which for studying the autqgenic water production law was developed by using the self-developed test system, and the effect of different environment and different initial autqgenic water content on the production rate of autqgenic water was discussed. The mathematical expression of the source-sink term of the mass conservation equation which described landfill leachate water transportation was put forward by comparative analysis of three nonlinear fitting functions.2. The refuse landfill body can be considered as a kind of deforming porous medium, so the nonlinear change of its saturated hydraulic conductivity directly affects the migration and transformation of landfill leachate. So, in this paper the laboratory test which for studying the nonlinear change law of the saturated hydraulic conductivity of refuse landfill body was developed, the effect of filling time and porosity on it was discussed, and the nonlinear and dynamic change law of the saturated hydraulic conductivity of refuse landfill body with filling time and porosity was revealed. Base on the experimental results, the nonlinear constitutive model between the saturated hydraulic conductivity and the porosity at different filling time was put forward.3. Soil-water characteristic curve describes the nonlinear relationship between water content and matrix suction, and it's the basic parameter constitutive relationship for calculating saturated-unsaturated water transport. Aiming at the waste with different degradation time and different porosity, the experiment for testing the relationship curve between water content and matrix suction was developed. The parameter inversion method for soil-water characteristic curve was given, and the VG model parameters were derived using it. It offers the basic and essential parameter constitutive model for simulation.4. The prediction of water quality and quantity can provide important theoretical basis and data foundation for the design of landfill treatment system and the determination of pollution control measures. Considering the settlement deformation of the landfill body, the saturated and unsaturated seepage of landfill leachate water, the hydrolyse of insoluble and degradable organics in solid phase, the biodegradation of soluble and degradable organics in solid phase and aqueous, the growing of aerobic and anaerobic bacteria, and the consumption of dissolved oxygen, the kinetic models which described the transportation and transformation of landfill leachate in subsurface environment were established.5. For dealing with the moving boundaries of the water and solute transport models which caused by the settlement deformation of the landfill body, the ALE method was introduced to solve the coupling models, the water and solute transport models under ALE description and its finite element numerical solution were given, and the corresponding calculation program were developed.6. By using the self-developed program, the transportation and transformation process of organic pollution and bacteria in landfill site during the landfill settlement was simulated by considering none hydraulic action, infiltration of surface water, and intrusion of groundwater, and the effect of the hydraulic condition on the distribution law was studied. The simulation results accorded with the practical situation, and it verified the reliability of the mathematical model and the numerical program in this paper.7. The stability and the seepage prevention of high and steep slope were the key technical problems in valley type landfill site. Relying on Chang Shankou landfill project, aiming at these key technical problems, and considering the possible seepage problem of vertical seepage control system, four conditions were simulated to display the transportation and the distribution of organic pollution in subsurface environment using the self-developed program. The preliminary anti-seepage scheme of vertical seepage control system was given by comprehensively analyzing the simulation results and combining with the stability of high and steep slope.