variavel0=<b>H. L. Brandão</b> - heloisa@labsin.ufsc.br UFSC
<b>A. A. Ulson de Souza</b> - augusto@enq.ufsc.br UFSC
<b>S. M. A. Guelli  U. Souza</b> - selene@enq.ufsc.br UFSC
<b>Abstract.</b> In this work it is developed a model of one equation that describes the profile of substrate concentration in a fluidized bed reactor, being considered the effects of dispersion, convection and reaction in the liquid phase, as well as diffusion and reaction inside the biofilm. The model takes into account the different heterogeneity scales: the first one, the reactor, constituted of bioparticles and fluid; and, the second one - biofilm - constituted by the microorganisms and polysaccharide matrix. The volume averaging method is applied to different scales successively to obtain one differential equation to describe the concentration in the reactor since the condition of local mass equilibrium is valid. In the coefficients of the model, there is the information of the previous scales. The modeling is applied to the denitrification process in a fluidized bed bioreactor, with sand as the support and ethanol as the carbon source, in order to get the nitrate and nitrite concentration profiles inside the bioreactor, for different recirculation rates. The numerical results are compared with the experimental results from literature presenting a good concordance.
<b>Keywords.</b> Biofilm, Fluidized-bed bioreactor, Denitrification, Volume averaging method, Mass transfer.