Modeling and controlling clarifier–thickeners fed by suspensions with time-dependent properties

• A model for controlling the sedimentation process in a thickener is presented.
• Two PDE describe the dynamics of the solids fraction and the solid settling velocity.
• A numerical scheme and a regulator are proposed and simulations are performed.

A one-dimensional model of the process of continuous sedimentation in a clarifier–thickener unit is presented. The governing model is expressed as a system of two nonlinear partial differential equations for the solids volume fraction and the varying settling velocity of the solids as functions of depth and time. This model extends the well-known model for the dynamics of a flocculated suspension in a clarifier–thickener advanced by Bürger et al. (2005). Operating charts are calculated to be used for the control of steady states, in particular, to keep the sediment level and the underflow volume fraction at desired values. A numerical scheme and a simple regulator are proposed and numerical simulations are performed.