Biofilm growth and the related changes in the physical properties of a porous medium: 2. Permeability

Abstract

Growth of a biofilm in a porous medium reduces the total volume and the average size of the pores. The change in the pore size distributions is easily quantified when certain geometric assumptions are made. Existing models of permeability or of relative permeability can be manipulated to yield estimates of the resulting reduction in permeability as a function of biofilm thickness. The associated reductions in porosity and specific surface can be estimated as well. Based on a sphere model of the medium, the Kozeny‐Carman permeability model predicts physically realistic results for this problem. Using a cut‐and‐random‐rejoin‐type model of the medium, the permeability model of Childs and Collis‐George yields qualitatively reasonable results for this problem, as does a generalization of the relative permeability model of Mualem. Permeability models of Kozeny‐Carman and of Millington and Quirk lead to unrealistic results for a cut‐and‐random‐rejoin‐type medium. The Childs and Collis‐George and the Mualem models predict that the permeability reduction for a given volume of biomass is greatest when the porous medium has uniform pore sizes.

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

“…The module for updating the PSD with changes in mineral volume is based on the film approach by Taylor et al [18], which assesses the effect of bacterial growth on flow and transport in saturated porous media. The authors state that the extension of their model to the case of unsaturated flow is straightforward.…”

“…In this paper, we assume a unique functional dependency of on and therefore neglect hysteresis in the water retention. The drainable pore-size density function (or PSD) is obtain y differentiation of the cumulative PSD with respect to [18,54]: ed b .…”

“…The new saturated conductivity after an incremental change in mineral volume is obtained from [18,54]:…”

“…Existing approaches that account for continuum-scale hydraulic property changes due to biological activity or mineral reactions include statistical grain size analysis [14], discrete description of mineral geometries [15] and estimates of changes in pore-size distributions (PSD's) [16][17][18]. In these models, the effects of mineral reactions on constitutive relations are considered for saturated conditions.…”

Processes in Microbial Transport in the Natural Subsurface

“…The primary differences between these two descriptions is that the structured models have the potential to represent the influence of biofilm structure on mass transfer (both diffusion and convection within the fluid and biofilm phases) and on momentum transfer (i.e., the change in permeability due to reduction in the pore volume), whereas unstructured models do not. Typically, structured biomass models are represented as either (1) continuous biofilm on the solid surface [182,183] or (2) discontinuous patchy film [123,175,187]. As discussed by Baveye and Valocchi [142], there has been perhaps too much emphasis on making the distinction between the two kinds of models rather than focusing on the fundamental transport and reaction processes that apply to the biofilm system (the early debate regarding the appropriateness of the various conceptual models is reflected in the exchanges of [141,142,157,186]).…”