CFD Study on Finding Optimum Number of Inclined Plates and Settling Efficiency in a Novel Sedimentation Tank (Lamella Clarifiers) of Wastewater Treatment Unit

Abstract

Relation between the number of inclined plates and the settling efficiency for a wastewater sedimentation tank is studied using CFD (Computational Fluid Dynamics) techniques. A full-scale three-dimensional model is employed for the numerical simulation. The Discrete Phase Model is used to simulate the two-phase flow and the k-ω Shear-Stress Transport (SST) model is used for the turbulence closure. A total of 13 cases were studied and their efficiency is compared. The results show that increasing the number of plates increases total efficiency in the optimum range of 9–13 plates. In fact, the total efficiency decreases sharply as we add more plates than this optimum range and even falls below the value of the original unmodified tank. This is an especially surprising finding because theoretically, the total efficiency should increase with increase in number of plates since there is an increase in settleable area for the sediments. These findings made us realize the necessity of performing a numerical simulation or a scale model experiment before retrofitting with inclined plates to avoid any unintended negative impact on the performance of sedimentation tanks.