Comparison of systemic, compartmental and CFD modelling approaches: Application to the simulation of a biological reactor of wastewater treatment

Nowadays there exist two main approaches to simulate the hydrodynamics of chemical reactors: the systemic method, based on the description of a given reactor as a limited number of elementary reactors, and the more theoretical CFD approach, based on the resolution of the Navier-Stokes equations in a large number of computing cells. This work describes another recent modelling approach based on the description of the reactor as a network of both structural and functional compartments. The complete methodology to build such a model, using CFD simulations, tracer experiments, mass transfer and chemical processes, is described. The simulation results with such a model are then compared to those obtained with the systemic and CFD models in the case of a biological gas-liquid reactor for wastewater treatment, involving oxygen transfer and complex biological kinetics. This work shows that the compartmental model gives results very similar to those of a full CFD simulation but with lower calculation time (10 times in most cases) with the advantage of remaining almost as simple to manipulate as the systemic approach. (C) 2009 Elsevier Ltd. All rights reserved.