Interpretation of Experimental Data with Regard to the Activated Sludge Model No.1 and Calibration of the Model for Municipal Wastewater Treatment Plants

The wastewater of the municipal treatment plants Zurich-Werdholzli (350000 population equivalents), Zurich-Glatt (110000), and Wattwil (20000) have been characterized with regard to the activated sludge model Nr.1 of the IAWPRC task group. Zurich-Glatt and Wattwil are partly nitrifying treatment plants and Zurich-Werdholzli is fully nitrifying. The mixing characteristics of the aeration tanks at Werdholzli and Glatt were determined with sodium bromide as a tracer. The experimental data were used to calibrate hydrolysis, heterotrophic growth and nitrification. Problems arising by calibrating hydrolysis of the paniculate material and by measuring oxygen consumption of heterotrophic and nitrifying microorganisms are discussed. For hydrolysis the experimental data indicate first-order kinetics. For nitrification a maximum growth rate of 0.40±0.07 d −1 , corresponding to an observed growth rate of 0.26±0.04 d −1 was calculated at 10°C. The half velocity constant found for 12 and 20°C was 2 mg NH 4 -N/l. The calibrated model was verified with experimental dam of me Zurich-Werdholzli treatment plant during ammonia shock load.