One-dimensional modeling of secondary clarifiers using a concentration and feed velocity-dependent dispersion coefficient

A one-dimensional model of activated sludge secondary clarifiers with a dispersion term dependent on concentration and feed velocity was developed. Motivation for this model was derived from an analysis of a model employing a constraint on the gravity flux which has been shown to give excellent fits to a previously published data set. It was noted that the gravity flux constraint disappears as the level of discretization is increased, a difficulty which our model overcomes. Data collected from a full-scale clarifier at the Kanapaha Water Reclamation Facility were used to evaluate our model. Better matches to observed concentration profiles were achieved with our model than with the gravity-flux-constraining model. In addition, our model, when calibrated using data from experiments in which the sludge blanket reached steady levels, successfully predicted the outcomes of five experiments which exhibited continuously rising blankets. These failures to reach steady blanket levels were not predicted by either limiting total solids flux theory or the gravity-flux-constraining model.