The hydrodynamic behaviour of a pilot-scale sedimentation tank has been analyzed as a function of the flow and type of feed. As part of a qualitative approach, the main flow lines have been determined under different experimental conditions, including the purge ratio, which does not seem to significantly affect flow patterns. Quantitative analysis has been carried out by the study of the residence times distribution (RTD) in order to quantify the volumes of the different regions of the settler, including dead volumes, and in order to establish the model (dispersion model, tank in series model and a combined model) that better describes the hydrodynamic behaviour of the tank. Among all the configurations studied here, the most suitable are those fed through a distributor with a centre inlet section in medium flow conditions and fed through a distributor with a lower inlet section in low flow conditions. It can therefore be concluded that a change in the arrangement of feed inlet can allow a device to handle higher volumes by maintaining the flow conditions that improve sedimentation. (c) 2007 Elsevier B. V. All rights reserved.