Transport and fate of microorganisms in porous media: A theoretical investigation

Processes in microbial transport in the natural subsurface

“…Therefore, in unstructured models the biomass is a fully penetrable volumeless component which assumes that a linear relation exists between mass of substrate consumed and mass of biomass produced and that no diffusion limitations affect the transfer of substrate mass from solution into the biomass. This approach has been taken in model construction [25,144,159,162], in column studies that focus on bacterial transport [69,120] and in intermediate-scale flow cell studies that focus on active degradation and growth and coupled transport [130,169]. For instance, Macquarrie et al [162] used this approach in treating biomass involved in aerobic degradation as a volumeless species undergoing transport, with equilibrium partitioning of biomass between aqueous and attached phases.…”

“…Straining is the trapping of microbes in pore throats that are too small to allow passage and is exclusively a result of pore geometry [25]. Estimates based on purely geometric relations between the effective diameter of biocolloids and the diameter and packing (coordination number) of grains suggest that mass removal by straining is not significant where the colloid diameter is less than 5% of the porous media grain diameter [25,51,155,167,176,177]. It should be noted that in natural heterogeneous porous media, a fraction of the pore diameters may be small enough to cause straining of colloidal particles even though the average grain diameter passes this rule of thumb for non-significance of straining.…”

“…The literature contains a helpful clarification on the use of the analytical expressions for g [70], as well as a summary of CFTÕs major assumptions and the implications for modeling bacterial transport in natural porous media [83]. Sedimentation is filtration due to gravity [25,167] and depends on particle buoyancy [185]. Many natural bacteria and viruses are neutrally buoyant, in which case sedimentation is negligible.…”

“…Both random motility (taxis in the absence of a chemical gradient) and chemotaxis have been cited as potential means of transport for subsurface organisms [8,25,60,80,99]. Quantitatively, random motility is an effective diffusive flux for microorganisms that depends on the local spatial gradient in aqueous microorganism concentration, and chemotaxis is a flux of microorganisms associated with the gradient in nutrient supply.…”

Effects of transverse mixing on transport of bacteria through heterogeneous porous media

“…Even these models for transport through porous media are relatively complex, containing a plethora of parameters that can be difficult to estimate [Corapcioglu and Haridas, 1984]. To help resolve the parameter estimation problem, investigators have used transport parameters (dispersivity, in particular) determined from data on a conservative tracer and have assumed that these can be applied to colloid transport as well [e.g., Harvey and Garabedian, 1991; Saiers et al, 1994; Saiers and Hornberger, 1996a].…”