On-line estimation of the maximum specific growth rate of nitrifiers in activated sludge systems

The on-line estimation of the maximum specific growth rate of autotrophic b iomass is addressed in this article. A general nitrification process model, which is valid for any realistic flow pattern, is used to develop the esti mation algorithm. Depending on the measurements available, two estimation e quations are derived. While both require measuring the nitrification activi ty of the activated sludge, one requires the additional measurement of the nitrifiable nitrogen concentrations at the two ends of the bioreactor, and the other requires the nitrate nitrogen concentrations at the same location s. The algorithm also requires some stoichiometric and kinetic parameters. However, sensitivity analysis shows that the estimate is insensitive to the parameters other than the autotrophic decay rate. Compared to the existing algorithms, the algorithm developed in this article does not rely on the a ssumption of ideal flow pattern in the plant and does not require an error- prone estimate of the autotrophic biomass concentration. Experimental and s imulation studies show that the algorithm performs well and is robust to in fluent variations and accidental sludge losses. (C) 1999 John Wiley & Sons, Inc.