Gas Generation, Transport, and Extraction in Landfills

A model describing the generation, transport, and extraction of gas in a landfill has been developed. In the model the landfill gas is assumed to be an equimolar mixture of CH 4 and CO 2 . The waste is thought to comprise three classes of materials differing in their degree of biodegradability but all following first-order biodegradation kinetics. The model describes changes in the total pressure and not the partial pressures of the individual components. It predicts the pressure field inside a landfill, where gas extraction occurs from a number of wells placed at arbitrary points. The wells are assumed to be one-dimensional line sinks with uniform gas extraction rates. When the walls of the landfill are impermeable to flow, the model equations can be solved analytically. The full problem describing a landfill with permeable walls is treated numerically. The effect of the various parameters, such as gas-extraction rates, generation rates, and permeabilities are discussed.