A two-step nitrification model was built by simplifying the standard activated sludge model No.1

and dynamic dissolved oxygen(DO)simulation can be done for aerobic nitrification process in a sequencing batch reactor(SBR)with constant aeration intensity.The parameters in the model could be distinguished into two groups by model identification:in a group parameter values can be directly obtained

including yield coefficient

DO saturation coefficient(or substrate coefficient)

and in other group parameter values needed to be estimated by optimization algorithm.Adopting the parameter values recommended by literatures

dynamic processes were simulated for important process variables

which revealed multi-DO levels and fitted well with the real response trend in SBR operation.Optimal experimental design method was employed for obtaining dynamic DO data of aerobic nitrification process in the SBR with typical aeration intensity

from which the values of KLa and SOeq could be determined by theoretical analysis and second order differential treatment of these data.Then

further parameter estimation could be optimal based on the model identification and KLa determination.