Improving Fluid Flow in Clarifiers Using a Highly Porous Media
Publication: Journal of Environmental Engineering
Volume 132, Issue 10
Abstract
The theory behind ideal sedimentation tanks assumes that the fluid moves in uniform flow. Numerous studies have shown numerous nonuniform flow patterns, which explains why the solids removal efficiency of real clarifiers does not match theory predictions. This problem gets worse when the influent flow rate exceeds what the clarifier was designed to handle. This research shows that introducing a highly porous bed of “dendrite” fibers into clarifiers designed for the pulp and paper industry removed some of the nonuniformities as shown in a residence time distribution (RTD). These clarifiers have RTDs that are similar to their waste treatment counterparts. So, it is expected that the new technology will have similar effects in waste treatment systems. The bed acts as a resistor to nonaxial flow, reducing radial and angular components of velocity. It is also shown that the greatest effect on the bulk flow patterns occurs when the bed is positioned such that all of the overflow passes through it. Increasing the bed thickness also increases the effect. Analysis of these results was performed with a new model for RTDs based on the Weibull distribution, which is mathematically similar to the equation for a mixed flow RTD.
Get full access to this article
View all available purchase options and get full access to this article.
References
Barnhill, G. D. (1982). “Dregs clarification with an inclined plate separator.” Pulp Pap., 45(7), 12–13.
Bays, R. A. (1980). “Characterization study of two aerated lagoons.” TAPPI Environmental Conf., TAPPI, Atlanta, 149–155.
Bevington, P. R., and Robinson, D. K. (1992). Data reduction and error analysis for the physical sciences, 2nd Ed., McGraw-Hill, New York.
Camp, T. R. (1936). “A study of the rational design of settling tanks.” Sewage Works J., 8, 732–750.
Campbell, B. K. (2003). “Improving green liquor clarifier performance through the addition of a packed bed of dendrite fibers.” Ph.D. thesis, Institute of Paper Science and Technology, Atlanta.
Campbell, B. K., and Empie, H. J. (1998). “An investigation of green liquor clarifier design features.” International Chemical Recovery Conf., TAPPI, Tampa, Fla., 1037–1045.
Coe, H. S., and Clevenger, G. H. (1916). “Methods for determining the capacities of slime settling tanks.” Trans. AIME, 55, 356–385.
Cornell, C. F. (1992). “Cooking liquor preparation.” Chemical recovery in the alkaline pulping processes, R. P. Green and G. Hough, eds., 3rd Ed., TAPPI Press, Atlanta.
Deininger, A., Gunthert, F. W., and Wilderer, P. A. (1996). “The influence of current on circular secondary clarifier performance and design.” Water Sci. Technol., 34 (3–4), 405–412.
Everitt, B. S. (1998). The Cambridge dictionary of statistics, Cambridge University Press, London.
Fitch, E. B. (1956). “Flow path effect on sedimentation.” Sewage and Industrial Waste Journal, 28, 1–14.
Grijspeerdt, K., Bogaert, H., and Vestraete, W. (1996). “Design and verification of a model secondary clarifier for activated sludge.” J. Chem. Technol. Biotechnol., 67, 404–412.
Hazen, A. (1904). “On sedimentation.” Trans. Am. Soc. Civ. Eng., 53, 45–71.
Krebs, P., Vischer, D., and Gujer, W. (1995). “Inlet-structure design for final clarifiers.” J. Environ. Eng., 121(8), 558–564.
Kynch, G. J. (1952). “A theory of sedimentation.” Trans. Faraday Soc., 48, 166–176.
Levenspiel, O. (1999). Chemical reaction engineering, 3rd Ed., Wiley, New York.
Lindborg, C., Wiberg, N., and Seyf, A. (1992). “Studies of the dynamic behavior of a primary settling tank.” Water Sci. Technol., 34(3–4), 213–222.
Metcalf and Eddy, Inc. (1991). Wastewater engineering: Treatment, disposal, and reuse, 3rd Ed., McGraw-Hill, New York.
Murphy, K. L., and Timpany, P. L. (1967). “Design and analysis of mixing for an aeration tank.” J. Sanit. Engrg. Div., 93, 1–15.
Silveston, P. L., et al. (1979). “On the use of residence time distributions for the design of clarifiers.” Can. J. Chem. Eng., 57, 83–87.
Taebi-Harandy, A., and Schroeder, E. D. (1995). “Analysis of structural features on performance of secondary clarifiers.” J. Environ. Eng., 121(12), 911–919.
Talmadge W. P., and Fitch E. B. (1955). “Determining thickener unit areas.” Ind. and Eng. Chem.: Eng. Des. and Proc. Dev., 47(1), 38–41.
Villemonte J. R., et al. (1967). 2nd Int. Conf. on Water Pollution Research, Munich, Germany.
Wallace, A. T. (1967). “Design and analysis of sedimentation basins.” Water and Sewage Works, 45, R219–R222.
Walpole, R. E., and Myers, R. H. (1993). Probability and statistics for engineers, 5th Ed., Prentice-Hall, Englewood Cliffs, N.J.
Zhou, S., and McCorquodale, J. A. (1992). “Influence of skirt radius on performance of circular clarifier with density stratification.” Int. J. Numer. Methods Fluids, 14, 919–934.
Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 132 • Issue 10 • October 2006
Pages: 1249 - 1254
Copyright
© 2006 ASCE.
History
Received: May 5, 2004
Accepted: Apr 10, 2006
Published online: Oct 1, 2006
Published in print: Oct 2006
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.