SENSITIVITY ANALYSIS OF A ONE-DIMENSIONAL CONVECTION-DIFFUSION MODEL FOR SECONDARY SETTLING TANKS

ABSTRACT One-dimensional models describing the flow and settling process in secondary settling tanks have great potential with respect to process control. Most of these models are based on a conservation equation that is discretized by dividing the settler into a fixed number of horizontal layers. In this article, the focus is on convection-diffusion models, which—in contrast to other one-dimensional models—ensure mesh-independent concentration profiles. The sensitivity of a prototype convection-diffusion model with respect to its parameters and the loading and operational conditions is studied by means of steady-state simulations. Based on the results, the importance of each of the model parameters is assessed. For each combination of parameter values, loading conditions, and operational variables considered in the study, the minimum number of layers required to obtain a practically mesh-independent concentration profile is determined on the basis of a newly developed objective criterion. This analysis leads to the identification of those factors having a large influence on the numerical behavior of the model.

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