Computer simulation of gas generation and transport in landfills. III: Development of lanfills’ optimal model

In Parts I and II of this series a 3D model was developed for transport and reaction of gaseous mixtures in landfills, and was utilized, through computer simulations, to investigate the effect of various factors on the gases’ concentrations and the landfill's total pressure, under quasi-steady state and dynamic conditions. A fundamental problem with modelling of landfills is the severe shortage of publicly available experimental data for their static and dynamical properties, which hinders the development of accurate models for them. In the present paper we address this problem by formulating it as one of optimization, whereby the optimal spatial distributions of the porosity, permeability, tortuosity factor, and the total potential of various types of wastes for producing the gases in a landfill are determined, given some limited experimental data for a property of the landfill, such as the amount of methane which is extracted from it over a period of time. The numerical simulator developed previously is coupled to the Genetic algorithm in order to optimize the parameter space that characterizes the landfill's morphology and the reaction properties of the wastes. Since the parameter space can be very large, containing thousands of parameters to be optimized, we utilize massively parallel computations with message-passing interface technique in order to develop the optimal model. It is shown that, not only does the optimization technique reproduce accurately the data based on which the optimal model is developed, but also provides accurate predictions for the future behavior of the landfill's properties.