Computing Shear Flow and Sludge Blanket in Secondary Clarifiers
Publication: Journal of Hydraulic Engineering
Volume 125, Issue 3
Abstract
Recent developments in computing turbulent and buoyant flow in sedimentation tanks are introduced. The test case is a circular, center-feed secondary clarifier with inclined bottom and central sludge withdrawal. Axisymmetry is assumed, and the flow and settling processes are modeled in a radial section by using the k-ε turbulence model on a two-dimensional, nonorthogonal grid. The computation domain includes the sludge blanket where the viscosity is affected by the rheological behavior of the sludge. The aim of the present study is to evaluate the sensitivity of the flow and concentration fields to parameters that characterize (1) the rheological properties of highly concentrated regions; (2) the settling of sludge; and (3) the effect of stratification on the turbulent diffusion. The overall appearance of the fields proves to be similar, whereas the regions of high velocities and high gradients are strongly affected by using different parameters or approaches on rheology, settling, and diffusive transport, resulting in different sludge blanket heights.
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References
1.
Adams, E. W., and Rodi, W. ( 1988). “Prediction of density-driven flows in settling basins.” Rep. SFB 210/T/41, University of Karlsruhe, Karlsruhe, Germany.
2.
Anderson, N. E. ( 1945). “Design of settling tanks for activated sludge.” Sewage Works J., 17(1), 50–63.
3.
Bokil, S. D., and Bewtra, J. K. ( 1972). “Influence of mechanical blending on aerobic digestion of waste activated sludge.” Proc., 6th Int. IAWPRC Conf. on Water Pollution Res., Int. Assoc. on Water Pollution Research and Control, London, 421–438.
4.
Bretscher, U., Hager, W., and Hager, W. H. ( 1984). “Untersuchungen über die Strömungs- und Feststoff-Verteilungen in Nachklärbecken.” gwf-wasser/abwasser, Munich, Germany, 125(2), 81–90 (in German).
5.
Bretscher, U., Krebs, P., and Hager, W. H. (1992). “Improvement of flow in final settling tanks.”J. Envir. Engrg., ASCE, 118(3), 307–321.
6.
Dahl, C. P. ( 1993). “Modelling of flow field and settling in secondary settling tanks,” PhD thesis, University of Aalborg, Aalborg, Denmark.
7.
Dahl, C. P., Larsen, T., and Petersen, O. ( 1994). “Numerical modelling and measurement in a test secondary settling tank.” Water Sci. and Technol., 30(2), 219–228.
8.
Dick, R. I., and Ewing, B. ( 1967). “The rheology of activated sludge.” J. Water Pollution Control Fed., 39(4), 543–560.
9.
Ekama, G. A., et al. ( 1997). “Secondary settling tanks: Theory, modelling, design and operation.” IAWQ Scientific and Tech. Rep. No. 6, International Association on Water Quality, London.
10.
Günthert, F. W. ( 1984). “Ein Beitrag zur Bemessung von Schlammräumung und Eindickzone in horizontal durchströmten runden Nachklärbecken von Belebungsanlagen.” Rep. No. 49, Institute for Water Quality Management, Technical University of Munich, Munich, Germany (in German).
11.
Hazen, A. ( 1904). “On sedimentation.” Trans., ASCE, 53, 45–71.
12.
Hinze, J. O. ( 1975). Turbulence: An introduction to its mechanism and theory . McGraw-Hill Series in Mechanical Engineering, McGraw-Hill, New York.
13.
Krebs, P. ( 1991). “The hydraulics of final settling tanks.” Water Sci. and Technol., 23(4–6), 1037–1046.
14.
Krebs, P., Stamou, A. I., García-Heras, J. L., and Rodi, W. ( 1996). “Influence of inlet and outlet configuration on the flow in secondary clarifiers.” Water Sci. and Technol., 34(5–6), 1–9.
15.
Krebs, P., Armbruster, M., and Rodi, W. ( 1998a). “Strömung und Sedimentation in Absetzbecken.” Rep. No. 742, Institute for Hydromechanics, University of Karlsruhe, Karlsruhe, Germany (in German).
16.
Krebs, P., Armbruster, M., and Rodi, W. (1998b). “Laboratory experiments of buoyancy-influenced flow in clarifiers.”J. Hydr. Res., 36(5), 831–851.
17.
Larsen, P. ( 1977). “On the hydraulics of rectangular settling basins.” Rep. No. 1001, Dept. of Water Res. Engrg., Lund Institute of Technology, Lund, Sweden.
18.
Launder, B. E., and Spalding, D. B. ( 1974). “The numerical computation of turbulent flows.” Comp. Methods Appl. Mech. Engrg., 3, 269–289.
19.
Lyn, D. A., and Zhang, Z. ( 1989). “Boundary-fitted numerical modelling of sedimentation tanks.” Proc., 23rd IAHR Conf., National Research Council, Ottawa, Canada, A331-A338.
20.
Lyn, D. A., Stamou, A. I., and Rodi, W. (1992). “Density currents and shear-induced flocculation in sedimentation tanks.”J. Hydr. Engrg., ASCE, 118(6), 849–867.
21.
Rhie, C. M., and Chow, W. L. ( 1983). “Numerical study of the turbulent flow past an airfoil with trailing edge separation.” AIAA J., 21, 1525– 1532.
22.
Rodi, W. ( 1987). “Examples of calculation for flow and mixing in stratified fluids.” J. Geophys. Res., 92(C5), 5305–5328.
23.
Rodi, W. ( 1993). Turbulence models and their application in hydraulics, 3rd Ed., Balkema, Rotterdam, The Netherlands.
24.
Rodi, W., Majumdar, S., and Schönung, B. ( 1989). “Finite-volume method for two-dimensional incompressible flows with complex boundaries.” Comp. Methods in Appl. Mech. and Engrg., 75, 369–392.
25.
Schamber, D. R., and Larock, B. E. (1981). “Numerical analysis of flow in sedimentation basins.”J. Hydr. Div., ASCE, 107(5), 575–591.
26.
Stone, H. L. ( 1968). “Iterative solution of implicit approximation of multidimensional partial differential equations.” SIAM J., 5, 530–558.
27.
Szalai, L., Krebs, P., and Rodi, W. (1994). “Simulation of flow in circular clarifiers with and without swirl.”J. Hydr. Engrg., ASCE, 120(1), 4–17.
28.
Takács, I., Patry, G. G., and Nolasco, D. ( 1991). “A dynamic model of the clarification-thickening process.” Water Res., 25(10), 1263–1271.
29.
Van Doormaal, J. P., and Raithby, G. D. ( 1984). “Enhancements of the SIMPLE method for predicting incompressible fluid flows.” Numer. Heat Transfer, 7, 147–163.
30.
van Marle, C., and Kranenburg, C. (1994). “Effects of gravity currents in circular secondary clarifiers.”J. Envir. Engrg., ASCE, 120(4), 943– 960.
31.
Zhou, S., and McCorquodale, J. A. (1992). “Modelling of rectangular settling tanks.”J. Hydr. Engrg., ASCE, 118(10), 1391–1405.
32.
Zhou, S., McCorquodale J. A., and Vitasovic, Z. (1992). “Influences of density on circular clarifiers with baffles.”J. Envir. Engrg., ASCE, 118(6), 829–847.
33.
Zhu, J. ( 1991a). “FAST-2D: A computer program for numerical simulation of two-dimensional incompressible flows with complex boundaries.” Rep. No. 690, Institute for Hydromechanics, University of Karlsruhe, Karlsruhe, Germany.
34.
Zhu, J. ( 1991b). “A low diffusive and oscillation-free convection scheme.” Communications in Appl. Numer. Methods, 7, 225–232.
Information & Authors
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Published In
Journal of Hydraulic Engineering
Volume 125 • Issue 3 • March 1999
Pages: 253 - 262
History
Received: Dec 9, 1997
Published online: Mar 1, 1999
Published in print: Mar 1999
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