The effect of biofilm growth on the clogging of a biofilter is studied on a laboratory scale pilot. At the steady state, pressure, porosity and biomass concentration profiles are used to study the evolution of the permeability with the biomass content : it is seen that the EPS and biomass micro structuration have a strong effect on the permeability reduction. That explains why Kozeny-like models found in literature fail to predict the actual permeability values. This finding is of primary importance to derive correlations or theoretical permeability laws which can be implemented in simple, operational engineering models for the design of biofilters. Among all the available theoretical models, the Vandevivere model (1995) seems the most appropriate. In term of biological kinetics, the analysis shows that kinetics parameters are flow dependent which is consistent with recent observations on the biofilm behaviour grown under different hydrodynamic conditions. One main conclusion is that the knowledge of macroscopic laws such as the permeability-porosity relationship is not sufficient to account for the coupling between hydrodynamic and biomass growth in porous media: those models often use classical kinetic law (Monod, Haldane…) with constant parameters (at least independent on the flow rate). As biofilms are bacterials communities able to adapt their metabolisms to external conditions, and in particular to hydrodynamic conditions, it seems that the predictive character of such models could be improved using flow rate (or shear) dependant effective kinetic parameters to take into account those effects.

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