Clarification Efficiency of Plate Settlers Analyzed by CFD Modelling

Sedimentation is a crucial process of water treatment facilities, where the gravity settling of suspended solids occur. The sedimentation tanks in conventional water treatment plants occupy a large area and consume up to 30% of the total construction cost. The use of plate settlers is an economical technology which increase the efficiency and capacity of sedimentation tanks. This study investigated the effectiveness of plate settlers compared to the plain settlers using the rectangular tanks in a water treatment plant. The ANSYS CRX 17.2 software was used as the CFD tool for meshing and calculating the results. Four cases including a plain settler and three plate settlers with plates installed at 3, 1 and 0.5 m spacing were analyzed in this study for the comparison of performances. The length, thickness and inclination angle of plates were kept constant. Installing plates reduced the large vortex zones and created a more up-flow distribution of streamlines allowing particles to settle easily compared to the plain settling tank. The efficiency of sedimentation was improved by increasing the number of plates in plate settlers. This is due to the increasing effective settling area of tanks. The inclined plates had different effects on the suspended solid removal efficiency in solids with different diameters, which might be difficult to characterize by experimental studies. The sedimentation efficiency of the particles with larger diameters have higher efficiency than the small diameter particles. The Computational Fluid Dynamics modelling can be used to accurately predict the suspended particle removal efficiency in plain settling and plate settling tanks, and therefore can be used to optimize their design.