MACROSCALE PROPERTIES OF POROUS-MEDIA FROM A NETWORK MODEL OF BIOFILMPROCESSES

We demonstrate how a network model can predict porosity and permeabili ty changes in a porous medium as a result of biofilm buildup in the po re spaces. A biofilm consists of bacteria and extracellular polymeric substances (EPS) bonded together and attached to a surface. In this ca se, the surface consists of the walls of the porous medium, which we m odel as a random network of pipes. Our model contains five species. Fo ur of these are bacteria and EPS in both fluid and adsorbed phases. Th e fifth species is nutrient, which we assume to reside in the fluid ph ase only. Bacteria and EPS transfer between the adsorbed and fluid pha ses through adsorption and erosion or sloughing. The adsorbed species influence the effective radii of the pipes in the network, which affec t the porosity and permeability. We develop a technique for integratin g the coupled system of ordinary and partial differential equations th at govern transport of these species in the network. We examine ensemb le averages of simulations using different arrays of pipe radii having identical statistics. These averages show how different rate paramete rs in the biofilm transport processes affect the concentration and per meability profiles.