Simultaneous nitrification-denitrification (SND) has been referred to as a biological process for nitrogen removal where nitrification and denitrification occur concurrently in the same aerobic reactor. SND facilities, investigated in this study, have been shown to remove 80 to 96 percent nitrogen without additional carbon and alkalinity. Carbon availability and bulk dissolved oxygen (DO) concentrations were found to be important process parameters for SND activity. Data suggest that a chemical oxygen demand-to-nitrogen (COD:N) ratio of at least 10.0 is required to achieve significant denitrification; and an optimum bulk DO concentration ranging from approximately 0.3 milligrams per liter (mg/L) to 0.7 mg/L appears to maximize SND activity. However, this low DO condition required for SND provides an environment more susceptible to sludge bulking as observed by the SVI data from the selected SND facilities in this study. A process simulator was used to determine important modeling parameters to predict SND performance at a pilot plant treating synthetic wastewater. Overall, the structure of the process model provided the capabilities to simulate SND performance in the pilot plant. However, important modeling parameters were modified to better predict SND performance.