The study of biofilm in porous media spans a wide range of application going from medical to environmental application. In this paper, we are interested in biofilter. These processes, widely used for pollution removal, are difficult to model. Indeed, biofilm growth is a complex process that involves fluid flow, mass transport and biotransformation : thus, biofilm growth in porous media raises many questions about hydrodynamic -biofilm interactions. In order to have a better understanding of hydrodynamic -biofilm interaction, we have started a study that consists with a experimental work on a laboratory scale pilot. The originality of the experimental apparatus lies in the possibilty to measure many global parameters accounting for the biofilter hydrodynamic evolution with time. Pressure measurement gives access to the permability profile along the column. RTD measurement allows the derivation of the evolution of the mean biofilter porosity with time. Lastly, at the end of a typical experiment, the biofilter is emptied and the concentation of biological material is measured along several section of the biofilter. In order to have a macroscopic description of the biofilter behavior from the physics at the pore scale, this experimental study is supplemented with modelling usin g an upscaling technic. A keypoint in the model consists in the relation between the porous media permeabilty and the amount of biological matter in the biofilter. Many researchers, e.g Vandeviver (1995), Clement (1996), Thullner (2002) have presented mode ls to relate the permeability with porosity in packed bed reactors. They have considered some hypothesis concerning the biofilm structure e.g homogenous and uniform growth of biofilm on the solid media. In this paper we present the methodology used to relate the permeability to the local porosity in the pilot. The resulting relationship is then compared to existing model. Finally, this relationship is used in the model to check the ability of the model to describe the global behavior of the biofilter and explain some effects of the biofilm growth on the hydrodynamic properties of bioreactors.

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