The influent COD of municipal wastewaters has been categorised into fractions: readily (soluble) and slowly (particulate) biodegradable, and soluble and particulate unbiodegradable. Procedures are presented for determining the division into these four categories, as are experimental methods for determining the maximum specific growth rate of the heterotrophs within the IAWPRC Task Group model structure. Some of the procedures are dependant on knowledge of the heterotroph yield and endogenous mass loss rate constants; comment is made on suggested values.

The development of a general model for biological nutrient removal in activated sludge systems is discussed. The general model is a mechanistic model based on the International Association on Water Pollution Research and Control (IAWPRC) (now IAWQ) model for carbonaceous energy removal, nitrification, and denitrification (Activated Sludge Model No. 1 [ASM1]), and the Wentzel et al. (1989a and b) model for biological phosphorus removal, with a number of modifications. A fermentation process has been included for the conversion of readily biodegradable chemical oxygen demand (COD) to short‐chain fatty acids (assuming a loss of COD from the system). Hydrolysis of enmeshed slowly biodegradable COD under anoxic and anaerobic conditions has been incorporated, as well as anoxic growth of polyP organisms. These modifications and others are discussed in this paper. The matrix representation and a description of the model processes are also presented, as well as a brief outline of influent wastewater characterization.

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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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The Blue Plains Advanced Wastewater Treatment Plant (Washington, D.C.) uses methanol as an external carbon source in a postdenitrification process, to achieve low effluent total nitrogen concentrations. This becomes more difficult in winter, at lower mixed liquor temperatures and higher flows, as a consequence of the kinetic behavior of the methanol-utilizing heterotrophs. The paper reports on an experimental batch test study conducted on Blue Plains postdenitrification sludge to investigate (1) the maximum specific growth rate of methanol-utilizing heterotrophs (l METH ); (2) the temperature dependency of the growth rate; and (3) the efficacy of alternate substrates (ethanol, acetate, and sugar). A limited number of tests were conducted on sludge from two other treatment plants with methanol addition. Water Environ. Res., 80, 417 (2008).

Experimental observations indicate that the magnitude of biological excess P uptake is linked strongly to the magnitude of P release in the anaerobic reactor. A theory describing the kinetics of P release is presented in terms of the readily biodegradable COD in the influent, the non-polyP heterotrophic mass, the anaerobic mass fraction and the reactor flow regime. Observed P release conforms well to that predicted over a wide range of wastewater characteristics and process conditions.