depSIM: Numerical 3D-Simulation and its Potential for Landfills

The biological, chemical and physical processes in the waste body are closely connected with each other and can be described mechanically. Therefore a number of differential equations are needed and implemented in the model. The porous media body is examined under the acceptance of a compressible gas phase, a materially incompressible solid state, an organic phase and a liquid phase. For the verification of the numerical model the long time behavior (100 years) was simulated. Further details on the model and the mechanical background are summarized in Robeck, Ricken and Widmann: A finite element simulation model of biological conversion processes in landfills (Waste Management 2011, Volume 31). The developed model allows a differentiated (time wise and locally) calculation and represen-tation of the temperature, the organic conversion rate, the local pressure ratios and the gas current speeds. By the detailed calculation of the gas speeds at every point of the dump an essential improvement arises compared with conventional arithmetic models for gas forecast and gas capture. These forecast models are based on estimated initial parameters. This allows only forecasts for a complete dump or a dump segment, but allows no coupled calculation of the relevant parameters. The model depSIM offers a spatially differentiated consideration of the gas produc-tion. However, just a spatially exact, quantitative forecast of the gas production is necessary for dump operator and authorities. The right forecast is elementary for the right dimensioning of the gas collection system and gas treatment and the possible use in combined heat and power units. All gas streams can be shown with the simulation model along the dump surface spatially and time wise differentiated. This allows a locally differentiated dump gas management with a division in areas with active or passive gas collection or to estimate the feasibility of a methane oxidation layer.