This paper reviews some recent developments in the modelling of the biological treatment of wastewaters with particular reference to the activated sludge process. The bacterial kinetics of completely-mixed reactors are discussed emphasising the need to have a variable yield. Modelling complications of variable yields are noted in particular those caused by de-coupling growth and substrate utilization. Other methods of solution are considered including relating the yield to the sludge age.

Modelling developments in fixed-film reactors are briefly examined, comparing the refinement in the chemical/physical description with the lack of refinement in the ecological representation.

The aims of modelling are reviewed and some fruitful areas in operational models and computer-aided-design are identified.

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© IWA Publishing 1982
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