Respirometric calibration and validation of a biological nitrite oxidation model including biomass growth and substrate inhibition

The modelling of the nitrification process of high-strength ammonium wastewater must be designed to consider it as a two-step reaction with substrate inhibition. Consequently, kinetic and stoichiometric parameters of both steps are required. In this work, the second step in the nitrification process was studied: a biological nitrite oxidation model was formulated, calibrated and validated using only oxygen uptake rate (OUR) measurements. The model included biomass growth and substrate inhibition. First, the biomass yield coefficient for nitrite-oxidising biomass was determined. Then, a respirometric experiment with one nitrite pulse of 500 mg N–NO2− L−1 was performed to estimate the rest of the model parameters. The practical identifiability study showed that the parameters were strongly correlated. Hence, a new experimental design consisting of two consecutive pulses and a delayed third one was designed to improve the parameter identifiability. Both experimental designs were compared using contour plots of the objective function and optimal experimental design criteria for parameter estimation. It was concluded that the parameter identifiability was improved with the new experimental design. Finally, the estimated parameters were validated and the pH effect on the inhibition coefficient was evaluated.