The application of the activated sludge model no.1 to a river environment

The current tendency towards an integrated approach for water quality management gives rise to a demand for consistent methods for linking dynamic wastewater treatment models with river water quality models. Linking such models is difficult because of the mutual structural differences with regard to variable and parameter definitions as well as process descriptions. This paper proposes to use the same modelling approach for the simulation of activated sludge treatment and natural self-purification in rivers. Since the standard Activated Sludge Model No. 1 (ASM1) is found to be far more conceptual and consistent than traditional river water quality models, the suitability of the ASM1 modelling approach has been assessed. The traditional ASM1 matrix has been adapted and extended to a river environment and has subsequently served as the basis of an ASM1-type water quality model for the River Dender in Flanders. Sensitivity analyses on this model showed that the most sensitive parameters in the ASM1 formulation of biological decay are the ones determining hydrolysis. The model efficiently calculates BOD concentrations but the predicted DO concentrations are not very accurate, mainly because of the remaining uncertainty about the many ASM1-parameters in river conditions. This indicates the need for determining new typical value ranges for these parameters in a river environment.