"The objective of this study is to apply recent advances in activated sludge process modeling to the simulation of oxygen utilization rates in full-scale activated sludge treatment plants. This is done by calibrating the International Association for Water Pollution Research and Control (IAWPRC) Model and associated SSSP (Simulation of Single-Sludge Processes for Carbon Oxidation, Nitrification, and Denitrification) micro-computer software to operating data at six full-scale activated sludge treatment plants. Field data were used to calibrate the key biological parameters contained in the model so that the oxygen utilization rates, dissolved oxygen concentrations, mixed liquor volatile suspended solids concentrations, and process performance simulated by the model matched the corresponding quantities observed in the treatment plants. The results showed that the model and associated software package provide a useful capability to analyze, simulate, and predict oxygen utilization rates. It was possible to obtain reasonable agreement between the measured and simulated values of oxygen uptake rate, dissolved oxygen concentration, and other process parameters at most of the plants studied. The key model parameters were the heterotrophic yield coefficient, heterotrophic decay constant, and autotrophic maximal specific growth rate constant This information is of value to engineers in the cost-effective design and operation of wastewater treatment systems because it provides a data base of applicable stoichiometric and kinetic model parameters that the engineer can use, with appropriate judgment, to similate and predict the behavior of oxygen transfer systems in wastewater treatment."