Liquid and Floc Trajectories in a Lamellar Settler: Simulations and Comparison with RPT Experimental Results in a Solid–Liquid Suspension System

The motion of solid aggregates (flocs) in a settler is crucial for the sedimentation efficiency. While the liquid flow patterns have been examined to model sedimentation, the effects arising from the liquid–solid suspension are less explored. Experimentally assessing the floc movements is difficult due to the inherent opacity of the media. This work aims to determine floc trajectories in a lamellar settler using radioactive particle tracking (RPT) and compare the results with those of computational fluid dynamics (CFD) simulations. A bank-scale unit already tested for a feedlot wastewater treatment process was used for the experiments. The free motion of a tracer representing the flocs was determined with the aid of a set of scintillation detectors using a simplified RPT methodology recently proposed. Experimental and simulated trajectories were compared through the Jensen–Shannon divergence, indicating that they are statistically indistinguishable. Floc settlement times estimated from the simulations overestimate the experimental values for the liquid flow rate used for the design. For double the design flow rate, the sedimentation time increases, and the estimated values are fairly coincident. The solid sediments act as a velocity buffer, stabilizing the flow and damping eddy formation, thus increasing the tolerance to high flow rates and abrupt hydraulic changes. Results highlight the importance of combining trajectory tracking with simulations to analyze floc motion, offering new insights into the design and operation of lamellar settlers.