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

Abstract

A novel biofilm model is described which systemically couples bacteria, extracellular polymeric substances (EPS) and solvent phases in biofilm. This enables the study of contributions of rheology of individual phases to deformation of biofilm in response to fluid flow as well as interactions between different phases. The model, which is based on first and second laws of thermodynamics, is derived using an energetic variational approach and phase-field method. Phase-field coupling is used to model structural changes of a biofilm. A newly developed unconditionally energy-stable numerical splitting scheme is implemented for computing the numerical solution of the model efficiently. Model simulations predict biofilm cohesive failure for the flow velocity between O(10 À3 ) and O(10 À2 ) m s 21 which is consistent with experiments. Simulations predict biofilm deformation resulting in the formation of streamers for EPS exhibiting a viscous-dominated mechanical response and the viscosity of EPS being less than O(10) kg m À1 s À1 . Higher EPS viscosity provides biofilm with greater resistance to deformation and to removal by the flow. Moreover, simulations show that higher EPS elasticity yields the formation of streamers with complex geometries that are more prone to detachment. These model predictions are shown to be in qualitative agreement with experimental observations.

Response of Simulated Drinking Water Biofilm Mechanical and Structural Properties to Long-Term Disinfectant Exposure

“…A previous study also suggested that protein-rich regions on the Lactobacillus johnsonii bacteria surface were stiffer than that of polysaccharide-rich regions 45 . Because stiffer biofilms may be more stable against shear stress, 16 less detachment and release of biofilm-associated pathogens in DWDS would be expected. Therefore, although long-term disinfection could not significantly remove biofilms, less detachment of stiffened biofilms is expected.…”

“…10–13 Biofilm elasticity and cohesiveness are shown to be essential for the detachment of biofilms and biofilm-associated pathogens. 14–16 Therefore, comprehensive understanding of the mechanical and structural properties for drinking water biofilms will provide information to predict, assess, and aid in controlling the risk of pathogens associated with DWDS biofilms.…”

The physics of biofilms—an introduction

“…(39) becomes a modified Cahn-Hilliard equation) and a free surface film state is found to form, where spinodal decomposition is a possible mechanism [330]. This approach has been extended to include EPS with an additional phase field, which reproduces the cohesive failure of biofilm under shear flow [333], and with the inclusion of a viscoelastic model of the EPS [334].…”

Biomechanical Analysis of Infectious Biofilms

“…Continuum representations of the biofilm as constitutively linear elastic [21,26,28,92], non-linear elastic [12,27], viscous [20], or viscoelastic [95] bodies is challenging as the interface must be tracked using stress and displacement matching; simplifications such as a one-way coupling or reduced dimensionality are sometimes employed. Interface tracking is not required for phase field models, which have been employed to argue that low matrix elasticity is required for streamers to form [94] and to investigate the role of cohesion on interface stabilisation [51]. The non-overlapping range of feature sets and problems considered makes it difficult to discern a coherent picture from these modelling studies, but it is hoped that the advent of full-featured simulations (e.g.…”

“…Reactor geometries are designed to expose high surface areas of the biofilm to flow, such as porous media [18,99] or fibres [47,94], and biomass effluent and other quantities measured.…”