Effect of evolving biofilm structures on modeling the flow in bio-clogged porous media

The growth of biofilms changes the hydrodynamics of porous media, which will influence the transport of bacteria and contaminants in natural and engineered systems. Traditionally, biofilms have been modeled as an impermeable domain in porous media, such that no water can enter biofilms and contaminants can only enter biofilms via molecular diffusion. Such a modeling approach is based on the assumption that the permeability of biofilms is the same as that of Extracellular Polymeric Substances (EPS), which are considered to have very low permeability. In this study, we investigate the impacts of biofilm properties on water flow using microfluidic device experiments and pore-scale modeling. E. coli biofilm was established inside a microfluidic channel packed with unisized glass beads in a single layer. A 5*5 mm2 area was live-stained and imaged via confocal microscopy at three different growth stages to represent three biofilm levels in the system. After image analysis using FIJI and AutoCAD software, the flow in the bio-clogged porous media was simulated using COMSOL Multiphysics. In these simulations, biofilm was modeled as a separate permeable domain in porous media instead of an impermeable domain. A Forchheimer-corrected version of the Brinkman equations was applied to simulate the flow in the porous biofilm regions. Two properties of biofilms, namely biofilm porosity (BPO) and biofilm permeability (BPE), were altered to examine their effects on the permeability of the system. It was found that different values of BPO and BPE clearly affect the flow paths, velocity patterns, and permeability of the system. Considering biofilms as impermeable results in significant underestimations of the flow properties. In addition, two simplified modeling scenarios, namely uniform coating and symmetric contact filling, were investigated for a possible abridging in the arduous modeling procedure of the real biofilm geometry.