Coupling between hydrodynamic and biomass in fixed biomass process : Local approach of microscale mecanisms of growth, adhesion and detachment of microorganisms on solid supports.
The biofilms, mainly composed of micro-organisms and exopolymers, develop themself on nonsterile wet surfaces. They are of considerable importance in many industrial and environmental applications, among which biofilters used in water treatment. The strong interaction between the flow and the biofilm development in this type of processes returns very difficult their modelling without drastic progress in the comprehension of phenomena appearing on various scales (biofilm, pore, biofilter). This thesis aims to bring a better comprehension of the mechanisms which control the biofilm growth on a local scale. A flow chamber characterized by a laminar flow profile was developed to allow the in-situ observation and the analysis of cell adhesion, detachment and the growth of P. putida bacteria under sheared flow. The results also showed that the growth kinetics measured in batch was not applied, for low Reynolds number in the case of a biomass fixed to solid support and subjected to a shear stress. The study revealed also, as already shown before in certain research tasks, the biofilms organization in response to the sheared flow. The technique of 3d-reconstruction developed and implemented in complement to the direct optical microscopy allowed a better interpretation of global biofilm architecture and have explained how the microstructure can influence the biofilm friction toward fluid flow. We have simulated the distribution of the local velocity profiles in biofilm microstructure and our estimation of permeability has highlighed the importance of local distribution of biomass in this parameter.