IAWQ Activated Sludge Model No.2, with the parameter values recommended by the IAWQ Task Group, was capable of predicting the behavior of a nutrient removal activated sludge pilot plant in Japan rather well except for the profile of NH4-N and NOx-N. The model was calibrated for the process and procedures for the calibration of the model are proposed. By applying the proposed calibration procedures, Activated Sludge Model No.2 has been satisfactorily calibrated to simulate the steady state behavior of the process in terms of organic matter and nitrogen removal. but, sometimes, selection of the specific growth rate of nitrifiers gives very sensitive effect on nitrate concentration in the effluent. It is indicated that the rate of anaerobic processes is affected by hydrolysis of particulate organic or slowly biodegradable substrates, and the hydrolysis can be the rate limiting step of the removal of organic matters or, sometimes, nitrogen and phosphorus. At the moment, it is rather risky to estimate the anaerobic hydrolysis rate, the anaerobic substrate uptake rate by phosphate accumulating organisms and the PHA yield with respect to polyphosphate utilization simultaneously only by using static data. The present case shows how relevant calibration procedures can be developed with limited static data.

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