Numerical Simulation On Water Injection, Production And Migration In Aerobic Landfill

Along with the rapid social development and urbanization, theamount of Municipal Solid Waste (MSW) transporting to the placesaccording to the data from government is158million tons in2010at thespeed of3%growth in recent years. It is reported that about2/3cities aresurrounded by MSW in China. So, handling refuse is an urgent task.Landfill is the most commonly used disposition method for MSW inchina. However, the velocity of its degradation is very slow in a closedlandfill. Research shows that the decomposition process of MSW can beaccelerated using water and air injection or methane and other landfillgases can be extracted for further utilization. But the investigation onrelation between the volume of water injection and moisture distributionas well as the volume of water injection and aerobic reaction is at thebeginning stage. Accelerated degradation treatment for dumping site, atype of landfill without any lining, can be carried out under the conditionsof water and air injection, so called Aerobic Bioreactor LandfillTechnology.In the treatment, the underground water pollution caused by leachateraises a critical concern on project feasibility and environmental safety.Based on previous studies, an exploratory study is conducted on moisturetransport and the related models are established. The main research worksare as follows:(1)A three-dimensional moisture transport governing equation isestablished in cylindrical coordinate, which tries to couple the aerobicbio-reaction model through source and sink terms in different scales. Thegoverning equation in a cylindrical coordinate reflects the moisturedistribution better for point sources and vertical well injection than that in rectangular coordinate. Most researchers assume source and sink terms asa constant or a function of time. But in this work it is considered as thefunction of moisture content. The gPROMS software is employed tosolve the models. It can be seen that the later is closer to the actualsituation.(2)The moisture content distribution in point source water injectionis simulated, which includes Steady-state simulation. The influencesof water injection volume, permeability characters (saturated permeabilitycoefficient), the body temperature on the moisture distribution are studiedrespectively. The optimal water flow is0.6m3/d with no leachatetransported across the bottom boundary of landfill as the treatment target.As saturated permeability coefficient increases, the moisture contentincreases and impact area shrinks. It is reported that the optimaltemperature for the aerobic microorganism is about55. Simulationresult shows that the moisture content and the concentration ofmicroorganism increase with the temperature increasing between30and50. Dynamic simulation in inert medium. As different scales need tobe considered in the model, the simulation of dynamic process can getmore complicated, thus the aerobic reaction in dynamic simulation isignored. The results show that the permeation time is about10days underthe pre-set condition.(3)The moisture content distribution in vertical well injection issimulated. The moisture distribution is obtained for water injectionprocess through3m vertical well. In these vertical wells, the optimalwater injection volume is0.4m3/d. Area of influence is similar to pointsource injection in radical direction, but the optimal water volumedecreases.Through theoretical study and site analysis, three-dimensionalmoisture migration model in the injection conditions is established, toovercome defects in one-dimensional, two-dimensional models.Simulation result provides a fundamental reference for landfillmanagement, design and safe operation.