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This work deals with the cohesion and detachment in biofilm systems for two electron acceptors and for two electron donors. Biofilms were developed on plates, under very low shear stress for one month and then subjected to an erosion test for two hours in a Couette-Taylor reactor. Biofilm was characterised in terms of average thickness and residual TOC mass. It was found that the biofilm structure is very heterogeneous and stratified. The top layer, which represents 60% of the biofilm mass, is very fragile and can be easily detached; the basal layer, which represents 20% of the biofilm mass, is very cohesive and can resist shear stresses up to 13 Pa. Between these two layers, a middle layer of intermediary cohesion represents 20% of the initial biofilm mass.

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Titanium oxide (TiO 2) submicron powders have been treated by Chemical Vapor Deposition (CVD) in a vibrofluidized bed in order to deposit silicon layers of nanometer scale on each individual grain from silane (SiH 4). Experimental results show that for the conditions tested, the original granular structure of the powders is preserved for 90% of the initial bed weight while the remaining 10% consists of agglomerates in millimetre range found near the distributor of the reactor. A comparison between experimental and modelling results using the MFIX code shows that for Geldart's Group B alumina particles (Al 2 O 3), the model represents both the bed hydrodynamics and silane conversion rates quite well. The future objective is to extend the simulation capability to cohesive submicron powders in order to achieve better predictability of the phenomena governing ultrafine particles.

International audienceThe Computational Fluid Dynamics code MFIX was used for transient simulations of siliconFluidizedBed Chemical Vapor Deposition (FBCVD) from silane (SiH4) on coarse alumina powders. FBCVD experiments were first performed to obtain a reference database for modelling. Experimental thermal profiles existing along the bed were considered in the model. 3D simulations provide better results than 2D ones and predict silane conversion rate with a mean deviation of 9% compared to experimental values. The model can predict the temporal and spatial evolutions of local void fractions, gas and particle velocities, species gas fractions and silicon deposition rate. We aim at mid term to model FBCVD treatments of submicronic powders in a vibrated reactor since we have performed experiments proving the efficacy of the process to treat submicronic particles

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