| A two-dimensional model (BioClog) combining ground water flow, multiple species transport, reactions, particulate and biological matter exchange, and subsequent permeability variance is developed for modelling the clogging of landfill leachate collection system drainage layers. The drainage layer is represented in profile. An iterative, finite element solution is utilized to compute the new hydraulic heads, ground water velocities and the position of the surface each time step. The transport of nine species are modelled, including volatile fatty adds, suspended active and inert biomass, dissolved calcium, and suspended inorganic solids. Reactions are incorporated into the point source or sink terms. The clog material in each element is represented using active biofilms, an inert biofilm, and an inorganic film.; The acetogenesis of propionate and butyrate, methanogenesis of acetate, and subsequent growth of the active biofilms are predicted using a biofilm model. Decay produces inert biofilm. Matter exchange between the fluid and films is represented using attachment and detachment models. The model links fatty acid utilization by the biomass to calcium carbonate precipitation, producing inorganic film. Changes to the microbial community and leachate chemistry are thus predicted.; Porosity, specific surface and hydraulic conductivity are calculated based on the thickness of the clog films and thus vary spatially and temporally. The model also includes an integrated, alternate method for very thin mounds, boundary conditions specific to experimentation, such as point sources, and can solve one-dimensional clogging problems (such as column experiments).; In column experiments wherein gravel was permeated with landfill leachate, the model showed encouraging agreement with the observed clogging, specifically the calculated quantity and composition of the clog matter (biomass and mineral), along with the associated decrease in porosity. In real-scale test cell experiments wherein clogging of a portion of the drainage layer was simulated, satisfactory agreement was achieved for porosity, film thickness, chemical oxygen demand (COD) and calcium. A set of full size hypothetical field cases is demonstrated.; By identifying and quantitatively linking many microbiological, chemical, and transport mechanisms, the model helps elucidate the phenomena controlling the rate and extent of clogging, and predicts the subsequent changes to the position of the surface.; Keywords: Clogging, landfills, leachate collection systems, modelling, biofilm, mineral precipitation, unconfined flow... |
