Nutrient Removal Evaluation Using the ASM2d Model

Models can play an important role in the evaluation of upgrading strategies for biological nutrient removal. In this paper the calibration of ASM2d to a pilot plant with an intermittent aerobic/anoxic reactor is discussed. The performed modeling study was part of a retrofit study. An existing plant, removing only COD and where phosphorus was chemical precipitated, had to be upgraded towards full biological nutrient removal. Emphasis was put on the practical aspects of calibrating ASM no 2d efficiently. The calibration procedure was based on an 'expert approach' rather than on a system engineering approach. With only changing three parameters (reduction factors, analysis rates for PAOs and the decay rate for autotrophs), the model proved well capable of describing the performance of the pilot plant. A second set of parameter adjustments was tested. Good results were obtained as well, but more parameters had to be changed. New findings are that oxygen entering the treatment plant via the influent has an important influence on the simulated phosphate effluent concentrations. Further, reactions occurring in the final clarifier effect the effluent concentrations. This is indicated by the necessity to introduce and assign a virtual volume to the settler where reaction can occur. Both factors are extremely important to focus attention to because they are different between a pilot plant and a full scale system.