Computational pore network modeling of the influence of biofilm permeability on bioclogging in porous media

Abstract

For many years, controversy has surrounded the use of biofilm models to describe the distribution of microbial biomass in natural or artificial porous media. This use is often advocated on the basis of the relative mathematical simplicity of the biofilm concept, and of the widespread availability of analytical solutions or numerical implementations. However, microscopic observations consistently point to a patchy, rather than homogeneous, distribution of microorganisms at the pore scale in many porous media of interest, even under conditions of severe bioclogging. Also, bioclogging models involving biofilms tend to underpredict the extent of permeability reductions in all be the coarse-textured materials. In this context, computer simulations described in the present article show that some of the limitations of biofilm models to describe the bioclogging of porous media are linked to the common constitutive assumption that biofilms are impermeable, that is, that nutrient transport occurs through the biofilms only by molecular diffusion. When this restriction is alleviated and liquid flow is allowed in the biofilms, the level of bioclogging achievable by a given biomass is very significantly increased and is comparable to that observed in experiments. In addition, the distribution of microorganisms becomes patchy and exhibits a self-organized periodic pattern with pores either entirely filled with biomass or without any biomass at all, again similar to published microscopic observations. These results suggest that biofilm models should not be ruled out a priori for the quantitative description of bioclogging in porous media, as long as biofilms are allowed to be permeable.

Biomechanical Analysis of Infectious Biofilms

“…Quantifying biomass effluent from complex biofilms grown in a glass-bead reactor in terms of a spatially-averaged model has revealed design principles that could be exploited to control growth and detachment [18]. Spatially-extended models reveal a complex biomass distribution on the scale of reactor pores, with reduced nutrient availability and biofilm growth downstream from clogged pores [52,93]. A suite of techniques has been employed to measure velocity profiles and metabolic fluxes in terms of biofilm age and microbial composition [47], generating a range of data that could be used to validate highly sophisticated and predictive models.…”

“…In addition, the response to surface airflow and known airborne dispersal modes should be considered in the design of nosocomial ventilation systems [38,83]. Flow is also a key consideration for industrial biofilms as overgrowth can cause clogging in biofilm reactors [52,93], although here the goal is to maximise metabolic efficacy rather than microbial eradication.…”

Solute Mass Exchange Between Water Phase and Biofilm for a Single Pore

“…In most PNM of biofilm, usually pores are assumed to have circular cross sections (e.g., Kim and Fogler 2000;Thullner and Baveye 2008). In this subsection, results for the dependencies of the dimensionless mass exchange coefficient ξ * in a pore domain with circular cross section are presented.…”

“…It not only sheds light on physical fundamentals of flow and transport at the pore scale, but also can provide constitutive relationships which appear in upscaled macroscale transport equations, like effective dispersive tensor, effective reaction rate, and relationship between permeability and biofilm volume fraction (Ezeuko et al 2011;Graf von der Schulenburg et al 2009;Hesse et al 2009;Kim and Fogler 2000;Li et al 2006;Stewart and Kim 2004;Suchomel et al 1998a, b;Thullner et al 2002;Thullner and Baveye 2008). Graf von der developed a Lattice-Boltzmann (LB) model to study the coupled interactions between nutrient transport, biofilm growth, and hydrodynamics.…”

“…Biofilm growth was assumed to occur uniformly around the pore walls. Inside a cylindrical pore, either local mass equilibrium (Ezeuko et al 2011) or a first-order kinetic model with a constant mass exchange coefficient was used (e.g., Thullner and Baveye 2008). But, it is worth noting that even in the tubes of a pore network we still need to distinguish non-equilibrium from equilibrium conditions.…”