Discrete element method to study biofilm deformation in fluid flow

Abstract

Biofilms are the assemblage of one or more types of microorganisms, which are usually found attached and grew on surfaces, embedded in their extracellular polymeric substances (EPS). They could form diverse morphologies to adapt to different environments, especially in a flow system such as water filtration. Hydrodynamic conditions have a significant impact on the deformation and detachment of biofilm, which has been primarily investigated by the experiments. However, relevant modelling research is lacking. Therefore, the individual based model (IbM) is adopted to study the biofilm-fluid interaction in present work. In the first part of this work, the discrete element method was utilized to simulate the biofilm growth, deformation and detachment, where the fluid was mimicked by applying a simple shear force. Due to the fact that the biofilms would also affect the flow pattern in return, the simply one-way approach was then extended to a two-way coupled computational fluid dynamic – discrete element method (CFD-DEM) model. Biofilm deformation and detachment was investigated at varied inlet flow velocity. We have also studied the effect of the EPS content on the deformation and detachment of biofilms. Furthermore, the strain-stress curves during biofilm deformation have been captured by loading and unloading the fluid shear stress. Biofilm streamer (filamentous structure of biofilm) motion under different flow conditions is important for a wide range of industries as well. The flow-induced oscillations and cohesive failure of single and multiple biofilm streamers have been investigated based on the CFD-DEM model. In this section, we have studied the effect of streamer length on the oscillation at varied flow rates. The predicted single biofilm streamer oscillations in various flow rates agreed well with experimental measurements. We have also investigated the effect of the spatial arrangement of streamers on interactions between two oscillating streamers in parallel and tandem arrangements. Besides, cohesive failure of streamers was studied in an accelerating fluid flow, which is important for slowing down biofilm induced clogging