Concentration of active biomass and porosity of the biofilm releation
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In this chapter, the formation of microbial biofilms in porous media is reviewed in depth and with emphasis on the processes occurring at the pore-scale. A computer-aided simulator is also presented for the prediction of the pattern of evolution and the rate of growth of heterogeneous biofilms within the pore space of porous materials. The simulator combines continuum-based descriptions of fluid flow and solute transport with particle-based descriptions of biofilm growth and detachment. Fluid-biofilm interactions are taken into account explicitly via appropriate mechanistic models of flow-induced detachment-reattachment, flow-modulated growth, and flow through porous biofilms. The flow regime, which is imposed in the form of either a constant flow-rate or a constant pressure-drop, is shown to be a key determinant of the balance between the processes of biofilm growth and detachment and affects strongly the degree of clogging of the porous medium. Furthermore, the flow-induced detachment and reattachment processes are shown to be of paramount importance for the downstream migration of biofilms in porous media. Future research toward improved understanding and quantification of biofilm mechanics and fluid-biofilm interactions is required across a wide spectrum of length-scales, time-scales, and force-scales considering both growth- and nongrowth associated physical stresses. To this end, two-pronged approaches combining careful experiments with appropriate theoretical analyses should be pursued