- An advanced mathematical model describing N and P transformations in an SBR treating municipal wastewater has been calibrated based on experimental results. This model is a consequence of intensive field and computer studies carried out for several years. During this time both laboratory-scale and a pilot-scale SBR systems were operated to treat municipal sewage from Beer-Sheva. The study resulted in partial determination of the kinetic and stoichiometric coefficients included in the model. In addition, detailed characterization of organic carbon (based on the COD measure) was done. The final version of the model is based on the concepts proposed by the IAWQ Task Group for Activated-Sludge Modelling. The calibration procedure (AQUASIM) compared theoretical simulated results to actual measurements to estimate the best-fit set of kinetic and stoichiometric parameters. Calibration and validation were based on several dynamic experiments, each of which contains data such as COD, MLSS, NH 4 , NO 3 , NO 2 , PO 4 , DO and OUR. The final version of the model includes 40 stoichiometric and kinetic coefficients and a set of 15 process rate equations. The proposed model can serve for the improvement of process design, analysis, and control.