An updated process model for carbon oxidation, nitrification, and denitrification.

The currently available comprehensive activated sludge models, ASM#1 (Grady et al., 1986) and its successor ASM#3 (Gujer et al., 1999), do not adequately describe nitrification and denitrification, with respect to ammonia oxidation inhibition, nitrite accumulation, or emissions of nitric oxide and nitrous oxide. A new comprehensive activated sludge process model, the Activated Sludge Model for Nitrogen (ASMN), is presented. The ASMN incorporates two nitrifying populations-ammonia-oxidizing bacteria and nitrite-oxidizing bacteria-using free ammonia and free nitrous acid, respectively, as their true substrates. The ASMN incorporates four-step denitrification (sequential reduction of nitrate to nitrogen gas via nitrite, nitric oxide, and nitrous oxide) using individual, reaction-specific parameters. Simulation results for ammonia, nitrate, soluble substrate, and biomass concentrations determined by using ASMN for three activated sludge process configurations under steady-state and dynamic municipal-type influent conditions are shown to be comparable with ASM#1 results.