Multicomponent hydrodynamic model for heterogeneous biofilms: Two-dimensional numerical simulations of growth and interaction with flows

Abstract

We develop a tricomponent (ternary) hydrodynamic model for multiphase flows of biomass and solvent mixtures, which we employ to simulate biofilm. In this model, the three predominant effective components in biofilms, which are the extracellular polymeric substance (EPS) network, the bacteria, and the effective solvent (consisting of the solvent and nutrient, etc.), are modeled explicitly. The tricomponent fluid mixture is assumed incompressible as a whole, while intercomponent mixing, dissipation, and conversion are allowed among the effective components. Bacterial growth and EPS production due to the growing bacterial population are modeled in the biomass transport equations. Bacterial decay due to starvation and natural causes is accounted for in the bacterial population dynamics to capture the possible bacterial population reduction due to the depletion of the nutrient. In the growth regime for biofilms, the mixture behaves like a multiphase viscous fluid, in which the molecular relaxation is negligible in the corresponding time scale. In this regime, the dynamics of biofilm growth in the solvent (water) are simulated using a two-dimensional finite difference solver that we developed, in which the distribution and evolution of the EPS and bacterial volume fractions are investigated. The hydrodynamic interaction between the biomass and the solvent flow field is also simulated in a shear cell environment, demonstrating the spatially and temporally heterogeneous distribution of the EPS and bacteria under shear. This model together with the numerical codes developed provides a predictive tool for studying biomass-flow interaction and other important biochemical interactions in the biofilm and solvent fluid mixture.

Lattice Boltzmann-Based Approaches for Pore-Scale Reactive Transport

“…Biofi lm spreading is typically computed using a continuum or discrete model as shown in Figure 2. Since a majority of pore-scale biofi lm models in literature adopt a discrete representation of the biomass, this approach will be explained in (Alpkvist and Klapper 2007;Wang and Zhang 2010;Lindley et al 2012;Zhang and Klapper 2014). The LBM earlier described for hydrodynamics and reactive transport can be applied for biogeochemical reactive transport.…”

“…Detachment can include several mechanisms, including erosion of small pieces from the outer surface of the biofi lm and sloughing of larger sections (IWA Task Group 2006). A recent trend is to use a relatively rigorous bio-mechanical model of biofi lms to study detachment and related processes (Dupin et al 2001;Klapper and Dockery 2010;Lindley et al 2012). Several studies adopting a discrete biofi lm model use mechanical principles to simulate detachment in porous media systems.…”

Multicomponent model of deformation and detachment of a biofilm under fluid flow

“…For the sake of simplicity, we assumed that the densities of the phases are equal. This is justified, because biofilms are composed mostly of water and can be regarded as an incompressible material with constant density [10,13]. The total energy of the two-phase mixture system is expressed as the sum of the kinetic, cohesion and elastic energies [30] …”

“…In [12][13][14], a phase-field approach [15,16] was used to model biofilm interaction with external flow using a one-fluid multiphase formulation. In these papers, the biofilm was treated as a single incompressible fluid consisting of a polymer network.…”

“…Many of these models focus on slow timescale events such as biomass growth or decay, whereas only a few papers have considered fast flow-biofilm interaction or biomass detachment [11,13,25,26,28], and tried to delineate the effect of viscoelasticity of biomass on the constitutive behaviour and failure of the biofilm under different flow conditions. Yet, previous experimental studies indicate that biofilm sloughing detachment (i.e.…”