Macro-scale modeling concepts for bacterial growth and transport in advective two-phase porous media systems

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Porous media provide excellent living conditions for bacteria because their habitat is protected but still allows a continuous nutrient supply. As a consequence, microorganisms exist and make a substantial contribution to many environmental and engineered porous media systems. When these porous media systems are used for engineered or industrial applications it is important to understand the interaction between flow, transport and microbiological processes. A variety of modeling methods exists in the literature, but they were predominantly developed for single-phase porous media systems. Since, in addition, the opaque nature of porous media makes it difficult to observe and understand bacterial processes which occur in the pores (e.g. attachment/detachment and formation of biofilms), these processes are insufficiently understood.In this project artificial porous structures between two glass plates, referred to as glass-silicon-glass micromodels, will be applied to investigate the behavior of bacteria in porous media saturated by two phases. These transparent quasi two-dimensional micromodels allow the direct observation of bacterial processes, as e.g. growth, transport, and attachment/detachment, by microscopic analysis. The bacteria used for laboratory experiments belong to the class of methanogenic archaea. The detailed interpretation of the experimental results by image processing will allow to generate spatially and temporally resolved data of bacterial counts and their structure and movement. An improved mathematical model describing the bacterial growth and movement in two-phase porous media systems will be developed based on these data sets. The model intends to consider the bacterial growth under non-nutrient limited conditions, the existence of different bacterial structures (plankton and biofilm), their individual transport properties and attachment and detachment processes. For testing and parametrizing the newly developed model, it will be numerically implemented based on a diagonally implicit Runge-Kutta time discretization method which is well suited to incorporate the strong non-linear source terms.The application of the theoretical model is devoted to the technology of microbial underground methanation, which leads to the transformation of the injected hydrogen and carbon dioxide to methane by intensive bacterial reactions.