Numerical Simulation of Gas Flow in Sanitary Landfills

The stabilization of refuse placed in sanitary landfills and the quality and rate of production of gases in landfills are principally the result of complex biological processes. A numerical model has been developed for simulating one-dimensional flow of a mixture of methane, carbon dioxide and nitrogen through sanitary landfills. Finite-difference approximations to the differential gas flow equations were derived with an implicit time stepping scheme. The nonlinear finite-difference equations were solved iteratively using the Newton-Raphson method. An explicit formulation was also explored, but the time step size required for stability was prohibitively small. The boundary condition at the landfill-air interface includes the assumption that the total pressure cannot drop below atmospheric pressure within a thin layer at the top of the landfill cover. The model was applied to data from two recent landfills. The pressure and concentration profiles predicted by the model are close to field observations.