• Published : 2005.02.28


A computer program is developed for the prediction of the flow pattern and the removal efficiency of suspended solid (SS) in a circular secondary clarifier. In this study the increased density effect by SS on hydrodynamics has been systematically investigated in terms of Froude Number (Fr), baffle existence, and a couple of important empirical models associated with the particle settling and Reynolds stresses. A control-volume based-finite difference method by Patankar is employed together with the SIMPLEC algorithm for the resolution of pressure-velocity coupling. The k-ε turbulence and its modified version are incorporated for the evaluation of Reynolds stresses. The calculation results predicts well the overall flow pattern such as the waterfall phenomenon at the front end of the clarifier and the bottom density current with the formation of strong recirculation especially for the case of decrease of Fr. Even if there are some noticeable differences in the prediction of two turbulence models, the calculated results of the radial velocity profiles are generally in good agreement against experimental data appeared in open literature. Parametric investigation has been systematically made with the Fr and baffle condition with detailed analysis.



  1. Stamou, A. I., 'Modelling of settling tanks a critical review,' 3rd International Conference, Water Pollution 95, Porto Carras, Greece, 25-28 April (1995)
  2. Zhou, S. and McCorquodale, J. A, 'Influence of density on circular clarifiers with baffles,' J. Environ. Eng., 118(6), 829-847 (1992a)
  3. Lee, E. J., Park, B. S., lang, D. S., and Lee, S. J., 'A numerical study on the design of primary clarifier:SS concentration and FTC,' KSEE, 18(11), 1335-1346 (1996)
  4. Zhou, S. and McCorquodale, J. A, 'Modeling of rectangular settling tanks,' Journal of hydraulic Engineering, 118(10), 1391-1405 (1992b)
  5. McCorquodale, J. A. and Zhou, S., 'Effect of hydraulic and solids loading on clarifier performance,' Journal of hydraulic research, 31(4), 461-478 (1993)
  6. Brouckaert, C. J. and Buckley, C. A., 'The use of computational fluid dynamics for improving the design and operation of water and wastewater treatment plants,' Water Sci. Technol., 40(4-5), 81-89 (1999)
  7. Kim, H. S., Shin, M. S., lang, D. S., lung, S. H., and Gang, D. H., 'A study of SS-driven flow characteristics in a final clarifier,' KSEE, 26(2), 629-634 (2004)
  8. Patankar, S. V., Numerical heat transfer and fluid flow, McGraw-Hili Company (1980)
  9. Mazzolani, G., Pirozzi, F., and d'Antonoi, G., 'A generalized settling approach in the numerical modeling of sedimentation tanks,' Water Sci. Technol., 38(3), 95-102 (1998)
  10. Takacs, I., Patry, G. G., and Nolasco, D., 'A dynamic model of the clarification thickening process,' Water Res., 25(10), 1263-1271 (1991)
  11. Shin, M. S., Kim, H. S., lang, D. S., Lee, Y. S., and Lee, S. N., 'A numerical and experimental study on the mixing characteristics of stratified thermal storage,' Environ. Eng. Res., 8(1), 41-47 (2003)
  12. Kim, H. S., 'Numerical modeling of SS separation, thermal drying and incineration pollutant abatement in a sludge and wastes related combined system,' Ph. D. Thesis, Chungnam National Univ. (2004)
  13. McCorquodale, J. A. and Zhou, S., 'Density currents in clarifiers,' Proc., 1987 Nat. Conf. Hydr. Engrg., ASCE, Williamsburg, Va., 56-61 (1989)
  14. Lyn, D. A, Stamou, A I., and Rodi, W., 'Density currents and shear-induced flocculation in sedimentation tanks,' Journal of hydraulic Engineering, 118(6), 849-867 (1992)
  15. Shin, M. S., Kim, H. S., lang, D. S., Kim, D. C., and Ohm, T. I., 'Development of a computer progran for the prediction of SNCR process of a 2-D combustor,' Environ. Eng. Res., 6(1), 7-15 (2001)