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This paper summarises progress of the IAWQ Task Group developing the Scientific and Technical Report (STR) on respirometry in control of the activated sludge process. The significance of respirometry in activated sludge systems is explained from a biochemical background. A classification is proposed which includes all respirometric measuring principles described in the literature. The different respiration rates that can be measured are reviewed and some variables that can be deduced from respiration rate are discussed. Some elementary control concepts will be provided that are necessary for the evaluation of respirometry-based control strategies. Finally, a number of respirometry-based control strategies will be classified and discussed.

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A procedure is presented to estimate biokinetic parameters for heterotrophic and autotrophic process models and to estimate wastewater characteristics in the context of the Activated Sludge Models No. 1 and No. 2. The procedure is based on respirometric measurements at low substrate to biomass ratio (S/X). The addition of nitrification inhibitor is avoided by applying a calibrated nitrification model to the respiration rate data resulting from both heterotrophic and autotrophic degradation. Furthermore, a new procedure is developed for simultaneous assessment of decay coefficients for heterotrophic and autotrophic biomass. The results show that, for a given wastewater/sludge combination S/X can be crucial in obtaining reliable parameter estimates: at a very low ratio not all parameters could be identified. A higher ratio caused problems because of nitrification inhibition.