  Sedimentation is a crucial phenomenon in recovering water from slurries by
separating solid-liquid. Thickeners and sedimentation columns are equipments
widely used in the process industry to reclaim water from process slurries.
This contribution addresses the problem of controlling the turbidity of the
recovered water in a sedimentation column by manipulating the underflow. The
phenomenological model describing the turbidity is too complex to be used in a
control strategy, and it is difficult to identify its parameters using plant
measurements. This work proposes an empirical piece-wise time-delay model for
modeling the turbidity at the top of the column to circumvent these problems. A
systematic design procedure is developed to tune a Proportional Integral
controller guaranteeing closed-loop stability for systems modeled as a
piece-wise time delay model. Experiments in a pilot plant validate the
theoretical results and illustrate the control performance under various
operational scenarios.
