Operating charts for continuous sedimentation II: step responses

Abstract. The process of continuous sedimentation of particles in a liquid has often been predicted by means of operating charts and mass-balance considerations, where the underlying constitutive assumption is the one by Kynch. Much more complex operating charts (concentration-flux diagrams) can be obtained from a onedimensional model of an ideal continuous clarifier-thickener unit. The engineering concept of ‘optimal operation’ is defined generally as a special type of solution of the model equation, which is a conservation law with a source term and a space-discontinuous flux function. All qualitatively different step responses (with the unit initially in optimal operation in steady state) are presented and classified in terms of operating charts. Quantitative information relating several interesting variables are also presented concerning, for example, the time until overflow occurs as a function of the feed concentration and flux.