in this paper a software sensor based on a fuzzy neural network approach was proposed for real-time
estimation of nutrient concentrations. In order to improve the network performance, fuzzy subtractive
clustering was used to identify model architecture, extract and optimize fuzzy rule of the model. A split
network structure was applied separately for anaerobic and aerobic conditions was employed with
dynamic modeling methods such as autoregressive with exogenous inputs and multi-way principal component analysis (MPCA). The proposed methodology was applied to a bench-scale anoxic/oxic process for
biological nitrogen removal. The simulative results indicate that the learning ability and generalization of
the model performed well and also worked well for normal batch operations corresponding to three data
points inside the confidence limit determined by MPCA. Real-time estimation of NO 3 , NHþ 4 and PO3 4 concentration based on fuzzy neural network analysis were successfully carried out with the simple on-line
information regarding the anoxic/oxic system.