Andrew J. Cooke and R. Kerry Rowe
Department of Civil and Environmental Engineering,
The University of Western Ontario, London, Ontario, Canada N6A 5B9
Abstract
The porosity and specific surface of a porous media coated with an accumulating film is geometrically evaluated to take account of limitations to film growth imposed by contact between particles and the film as it develops around the particles. By representing the media with regularly packed spheres, and assuming a uniform film thickness, equations are derived to allow the calculation of porosity and specific surface area as a function of film thickness for each of the four possible regular packing arrangements for both thin and thick films. It is shown that previous models begin to breakdown at a ratio 2Lt/dp of film thickness, Lt, to particle diameter, dp, of 0.41 for a cubic packing, and 0.15 for an orthorhombic, tetragonal or rhombohedral packing. Thus while the previous models may give acceptable results for thin films, such as those encountered in wastewater engineering, they give erroneous porosities and specific surfaces when used to model the thicker films that occur as landfill leachate collection systems clog. Using the new equations it is shown that the porosity is reduced to 10% of its original value (and thus deemed clogged) for dimensionless film thicknesses 2Lt/dp of 0.39, 0.31, 0.20, and 0.18 for the cubic, orthorhombic, tetragonal, and rhombohedral packing arrangements, respectively, using the corrected equations. The model is intended for use in estimating the clogging rate of landfill leachate collection systems due to the buildup of thick biological and mineral films.
Last revised: 03/01/99