With the aim to increase the efficiency of the aeration tanks of municipal wastewater treatment plants, the implementation of a biological model system (ASM1) into the CFD code ANSYS CFX (R) is presented for modeling a full-scale aeration tank and verified with experimental data. Taking into account the biological processes, hydrodynamics and gas-liquid mass transfer, simulations were performed and compared to experimental concentration profiles for ammonium and nitrate. The assumptions made are explained in detail. While the simulated ammonium concentration profile is in good agreement with the measured values, deviations occur for the nitrate profile. However, the CFD simulations exceed the prediction accuracy of conventional 0D simulation software.