Reducing Sediment Deposition in a Clarification Tank Using Numerical Modeling

Abstract

This study aims to resolve a hydraulic engineering problem using Computational Fluid Dynamics (CFD) method. The problem is related to a sedimentation basin in a water treatment plant of ESKI (Eskisehir Water and Sewerage Administration) which is one of the municipal facilities in Turkey. Accumulation of sediment in distribution channels for the clarification tanks were reported to be generating operation-wise problems. The plant is entirely gravity driven and the flow conditions at various channels are difficult to control. The manual cleaning process of deposited sediment is required periodically during operation due to accumulated sediment in the distribution channels. This work puts an effort for detecting the problem and stopping the sediment deposition purely by simple geometrical improvement using numerical modeling. In this study, the main goal is to offer a reasonable solution based on basic hydraulic principles. Sediment accumulation (as a result of deposition) is characterized by low stream velocity and also low turbulence kinetic energy. Based on the most recent suspended sediment theory, the developed local flow conditions under which the suspended particles start gravitating was identified and used as a criterion for controlling the flow conditions. The objective then was to hydraulically redesign the feeding channels for the clarification tank in an effort to increase the stream velocity and stop the early occurring sediment deposition. Low-velocity flow regions (at the downstream of the channel) were identified using CFD method. Also, initial conditions (water height) were identified and the CFD model was validated by a 1:10 scale physical model of the clarification tank. Consequently, by altering the geometry of the channel, these low power regions were activated in terms of suspension of sediment using contractions in the channel. The results are believed to be leading a low cost but effective solution to the problem which eliminates manual intervention during the treatment plant’s operation

Keywords

• Clarification Tank
• CFD
• physical modelling
• sedimentation
• water treatment

References

1. Bardina, J.E., Huang P.G., Coakley T.J. 1997. Turbulence Modeling Validation, Testing, And Development, NASA Technical Memorandum 110446.
2. Bayazit M., Avci I. 2010. Akarsularda Akım ve Sediment Taşınımı (River Flow and Sediment Transportation), Birsen, Istanbul, Turkey.