The aim of this paper is to present a coupling model for calculating both the hydrodynamic and anaerobic digestion processes in expanded granular sludge bed (EGSB) bioreactors for treating wastewaters. The bioreactor is modeled as a dynamic (gas-solid-liquid) three-phase system. An existing set of experimental data of three case studies based on the start-up and operational performance of EGSB reactors is used to adjust and validate the model. A novel parameter, the specific rate of granule rupture, is defined for calculating the biomass transport phenomena. Values around 1 x 10(-20) dm d(2) g(-1) are calculated for this parameter. Bioreactor performances were analyzed through the main variable profiles such as pH, COD, VFA and VSS concentration. A good agreement was obtained among experimental and predicted values. It seems to indicate that the proposed EGSB model is able to reproduce the main biological and hydrodynamic successes in the bioreactor. (C) 2011 Elsevier B.V. All rights reserved.