An Updated Process Model for Carbon Oxidation, Nitrification, and Denitrification

Abstract

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.