Application of mathematical models in design and operation of biological nutrient removal systems is becoming more important with the legislations getting stricter. Recent developments in computer technology enabled development of computer programs that are able to solve complex models required to describe the processes taking place in activated sludge plants. In this study, methods for determining COD and nitrogen fractions and kinetic and stoichiometric parameters for domestic and industrial wastewaters are evaluated, and wastewater is fractionated using actual plant measurements and results of previous studies in literature. In addition, IWAQ Activated Sludge Model Number 1 (ASM1) is applied to Comodepur Wastewater Treatment Plant Italy using ASM 1 run-time simulation environment. Due to limitations of the software for simulating the behavior of the WWTP, benchmark configuration of the model had been used and Post Denitrification has not been included in the study. Mostly default kinetic and stoichiometric parameters offered by IWAQ Task Group are used in simulations some of them had been calibrated to get closer values to the measured ones.