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The Activated Sludge Model No. 2 is introduced as a further development of Activated Sludge Model No. 1. Model No. 2 introduces phosphorus accumulating organisms (PAO) and allows us to simulate the behaviour of biological nutrient removal activated sludge systems. Typical wastewater composition and a set of stoichiometric and kinetic parameters are provided in order to make reasonable predictions. The model has not yet been calibrated or verified in any full-scale application. This report contains a simplified version of the full Model No. 2; the full model is published in the final report of the Task Group (Henze et al., 1994).

Four anaerobic-aerobic sequencing batch reactors were operated with either acetate or glucose as the main carbon sources under phosphorus poor or rich conditions. Limited phosphate loading may suppress the development of polyphosphate accumulating organisms (PAOs) leading to establishment of microbial communities without polyphosphate accumulation. These microbial communities were dominated by glycogen accumulating organisms (GAOs). PAO communities were established under the P rich loading conditions. Both PAO and GAO sludges clearly show that acetate absorption was accompanied by glycolysis with subsequent accumulation of PHAs. Glucose was anaerobically converted to PHAs and glycogen. Glycolysis in PHA synthesis was indicated by the presence of a PHA component polymer, 3-hydroxyvalerate (3HV). It is suspected that synthesis of 3HV is via formation of the intermediate metabolite Propionyl-CoA which consumes reducing power and enables microorganisms to maintain intracellular reduction oxidation potential. When glucose was injected, acetate and propionate were detected in the bulk solution suggesting that fermentation may have taken place. Respiratory quinone analyses and fluorescent in situ hybridization with an RNA targeted oligonucleotide probe revealed that there was no significant difference in microbial communities among the sludges tested.

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