Three-Dimensional Simulation on the Water Flow Field and Suspended Solids Concentration in the Rectangular Sedimentation Tank
Publication: Journal of Environmental Engineering
Volume 134, Issue 11
Abstract
A 3D computational fluid dynamics model for describing the water flow and suspended solids (SS) concentration distribution in a rectangular sedimentation tank is presented. The interfacial momentum transfer, buoyant forces, and the effect of sediment-induced density currents are considered. A convection-diffusion equation, which is extended to incorporate the sedimentation of activated sludge in the field of gravity, governed the mass transfer in the clarifier. The double-exponential law is used to describe the dependence of the settling velocity on the concentration. The results show that during the dynamic settling process of the sludge, the mud surface rose slowly, and a period of time later, the mud surface kept stability and reached dynamic equilibrium in the tank. The distribution of velocity along the axis in the rectangular tank is not uniform, and the surface return flow is found. The turbulent kinetic energy is larger and dropped drastically in the inlet zone, while in the settling zone the turbulent kinetic energy is relatively small. Density current is formed, and the clear water zone, flocculation zone, lamella zone, and compression zone are found. Furthermore, under certain operational conditions, the influence of inlet baffle length on SS settling in the rectangular sedimentation tank is discussed. The prediction by the present model for liquid flow and SS concentration is confirmed by the experimental measurement in a rectangular sedimentation tank in Sweden reported by Larsen in 1977.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The work was carried out by the Department of Environmental Engineering, University of TianJin, China, and supported by CDAJ-CHINA. This research was supported by the National Basic Research Program of China (973 Program) (Grant No. UNSPECIFIED2007CB714101), the Natural Fund for Distinguished Young Scholars of China (Grant No. UNSPECIFIED50525927), and the Natural Science Foundation of China (Grant No. NSFC50579045).
References
Adams, E. W., and Rodi, W. (1990). “Modeling flow and mixing in sedimentation tanks.” J. Environ. Eng., 116(7), 895–913.
Auton, T. R., Hunt, J. C. R., and Prud’Homme, M. (1988). “The force exerted on a body in inviscid unsteady non-uniform rotational flow.” J. Fluid Mech., 197, 241–257.
Cai, J. B., Duan, X. B., and Zhang, L. (2003). “Numerical simulation of flow in sedimentation tanks.” J. Chongqing Jianzhu Univ., 25(4), 64–69.
Cai, J. B., Zhu, L., and Duan, X. B. (2004). “Numerical simulation for rectangular settling tanks.” J. Hohai Univ. (Natural Sciences), 32(1), 27–31.
Celik, I., Rodi, W., and Stamou, A. (1985). “Prediction of hydrodynamic characteristics of rectangular settling tanks.” Proc., Int. Symp. on Refined Flow Modeling and Turbulence Measurements, 641–651.
Cheremisinoff, P. N. (1995). Handbook of water and wastewater treatment technology, Marcel Dekker, New York.
Civicism Designing Institute of Beijing. (1986). Water supply and drainage designing handbook, Ministry of Construction of Peoples Republic of China, Beijing.
Ekama, G. A., Barnard, J. L., and Günthert, F. W. (1997). “Secondary settling tanks: Theory, modelling, design and operation.” Scientific and Technical Rep., IAWQ, London.
El Tahry, S. H. (1983). “ equation for compressible reciprocating engine flows.” J. Energy, 7(4), 345–353.
Gao, T. Y., and Gu, G. W. (1999). Water pollution control engineering, Higher Education Press, Beijing.
Gosman, A. D., Issa, R. I., Lekakou, C., Looney, M. K., and Politis, S.(1992). “Multidimensionsl modeling of turbulent two-phase flows in stirred vessels.” AIChE J., 38(12), 1946–1956.
Guo, S. C. (2004). “Computer numerical modeling of sedimentation tanks.” Environment Engineering, Dong Hua Univ., China.
Imam, E., and McCorquodale, J. A. (1983). “Simulation of flow in rectangular clarifiers.” J. Environ. Eng., 109(3), 713–730.
Imam, E., McCorquodale, J. A., and Bewtra, J. K. (1983). “Numerical modeling of sedimentation tanks.” J. Hydraul. Eng., 109(12), 1740–1754.
Jeppson, U. (1996). “Modelling aspects of wastewater treatment processes.” Ph.D. thesis, Lund Institute of Technology, Sweden.
Kim, H. S., Shin, M. S., and Jang, D. S. (2005). “Study of flow characteristics in a secondary clarifier by numerical simulation and radioisotope tracer technique.” Appl. Radiat. Isot., 63(4), 519–526.
Krebs, P., Vischer, D., and Gujer, W. (1995). “Inlet-structure design for final clarifiers.” J. Environ. Eng., 121(8), 558–564.
Lance, M., and Bateille, J. (1991). “Turbulence in liquid and phase of a uniform bubbly air-water flow.” J. Fluid Mech., 222, 95–118.
Larsen, P. (1977). “On the hydraulics of rectangular settling basins, experimental and theoretical studies.” Rep. No. 1001, Dept. of Water Resources Engineering, Lund Institute of Technology, Lund Univ., Sweden.
Launder, B. E., and Spalding, D. B. (1974). “The numerical computation of turbulent flows.” Comput. Methods Appl. Mech. Eng., 3, 269–289.
Lin, S. D. (2001). Water and wastewater calculations manual, McGraw-Hill, New York.
Lyn, D. A., Stamou, A. I., and Rodi, W. (1992). “Density currents and shear-induced flocculation in sedimentation tanks.” J. Hydraul. Eng., 118(6), 849–867.
Naser, G., Karney, B. W., and Salehi, A. A. (2005). “Two-dimensional simulation model of sediment removal and flow in rectangular sedimentation basin.” J. Environ. Eng., 131(12), 1740–1749.
Ni, J. R., Wang, G. Q., and Zhang, H. W. (1991). Basic theories of solid-liquid two-phase flow and their recent applications, Science Press, Beijing.
Rodi, W. (1979) “Influence of buoyancy and rotation on equations for the turbulent length scale.” Proc., 2nd Symp. on Turbulent Shear Flows, Imperial College, London, 37–42.
Takács, I., Patry, G. G., and Nolasco, D. (1991), “A dynamic model of the clarification-thickening process.” Water Res., 25(10), 1263–1271.
Zeng, G. M., Ge, W. H., and Qin, X. S. (2002). “Numerical modeling on the movement of water and SS in two-dimensional sedimentation tanks of sewage factory.” Environ. Sci. Chin., 22(4), 338–341.
Zhou, S., and John, A. M. (1992). “Influence of skirt radius on performance of circular clarifier with density stratification.” Int. J. Numer. Methods Fluids, 14(8), 919–934.
Zhou, S., and McCorquodale, J. A. (1992), “Modeling of rectangular settling tanks.” J. Hydraul. Eng., 118(10), 1391–1405.
Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 134 • Issue 11 • November 2008
Pages: 902 - 911
Copyright
© 2008 ASCE.
History
Received: Dec 6, 2007
Accepted: Jun 6, 2008
Published online: Nov 1, 2008
Published in print: Nov 2008
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.