Intensification of agriculture in the Brittany region (France), and in particular that of the swine production, has led to an excessive production of wastes by the piggery farms. Alternatives to the use of livestock wastes as fertiliser are necessary. For this purpose, biological nitrogen removal by nitrification and denitrification, is generally believed to provide most economical means of controlling nitrogen. However, the design and the management of the treatment system must be optimised in order to meet the regulations and reduce the treatment costs. Due to processes complexity, heuristic optimisation is rarely efficient and a model-based approach is often necessary (Coelho et al., 2000). The aim of this work was to develop and calibrate a model to simulate the systems treating the piggery wastewaters.