This paper presents simulation results for Mahres wastewater treatment plant (WWTP) taking into account hydrodynamic and load variations. The simulations were successfully compared to experimental results obtained in an oxidation ditch. Oxygen concentrations were measured along the length and depth of the ditch and compared to the simulated profiles. A good agreement was obtained for the COD biomass concentration and the oxygen concentration profile. The validated model was used for simulating oxygen concentration profile and the oxygen uptake rate established in the ditch under different load conditions (hydraulic chemical oxygen demand (COD) total Kjeldahl nitrogen (TKN)). Simulation results showed the importance of an adapted aeration management for improving removal efficiency. The situation analysis of Mahres WWTP in 2005 showed that aeration system supplies were often lower than the biomass needs for COD biodegradation endogen respiration and nitrification. (C) 2009 Elsevier B.V. All rights reserved.