A tridimensional mathematical model that considers the turbulent flow inside a bioreactor of municipal waste material (MWM) is studied. The MWM is self-heating by the biological activity of micro-organisms. The model includes the unsteady solution of the turbulent flow field inside the reactor, the energy transport in the flow and the ensuing heat and mass transfer by convection over the MWM load. The MWM is treated as a porous medium and the oxygen depletion and heat generation produced by aerobic bacteria are also included. Turbulence treatment is done with the k-epsilon model. The numerical simulation shows good agreement with experimental measurements available. The results also shed light over some design criteria that can be explored in order to increase the efficiency of the process. (C) 2011 Elsevier Ltd. All rights reserved.