Enhancing Sedimentation and Trapping Sediment with a Bottom Grid Structure
Publication: Journal of Environmental Engineering
Volume 140, Issue 1
Abstract
One of the great challenges of gravity settling is the difficulty of effectively removing suspended solids from the water column and retaining the settled particles in the settling basin under high inflow rates and short resident times. To address these issues, a new concept of using a bottom grid structure (BGS) for enhancing suspended solids removal by introducing a downward vertical vortex force and reducing disturbances of the bottom settled sediment was proposed and tested in the laboratory. A series of comparative laboratory experiments, without and with BGS, were carried out in a (D) tank. The experimental results revealed that for the tested flow rates ranging from 4 to , the removals of test particles with the BGS in the tank were about 10 to 30% higher than those obtained for the same conditions, but with a smooth tank bottom. Thus, the newly proposed BGS acts as a structure trapping and storing solids. In general, the improvement of particle removal rates was proportional to the inflow rate (or flow speed along the BGS top surface), before reaching a maximum value. This indicated that particles settled in the BGS cell on the tank bottom were effectively protected from disturbances by the fast bottom flows or external forces. To further examine the retention of deposited sediment by the proposed BGS, comparative experiments were conducted by placing particles on the tank bottom before activating inflow, with and without the BGS present. The results showed that for an inflow rate of , 67% of the placed particles were retained in the settling tank with the BGS; without it, the corresponding percentage was just 26%. Thus, the BGS retained 41% more of the particles settled in the bottom. A computational fluid dynamics (CFD) model was also used to describe the hydraulic conditions in the settling tank under various inflow rates and such results were helpful for establishing the relationships between the improved removal of suspended solids and the bottom flow speed and flow patterns in general. BGS offers a great promise of improving the performance of engineering facilities (e.g., stormwater detention ponds) serving to remove suspended solids from environmental flows.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The present study was financially supported by Environment Canada. The experimental support received from YMCA intern Yujin Jeon, and from Brian Trapp, Quintin Rochfort, and Renee McFadyen of the National Water Research Institute is greatly appreciated.
References
Brooke, J. W., Kontomaris, K., Hanratty, T. J., and McLaughlin, J. B. (1992). “Turbulent deposition and trapping of aerosols at a wall.” Phys. Fluids A, 4(4), 825–834.
Camp, T. R. (1946). “Sedimentation and the design of settling tanks.” Trans. ASCE, 111(1), 895–936.
Caporaloni, M., Tampieri, F., Trombetti, F., and Vittori, O. (1975). “Transfer of particles in nonisotropic air burbulence.” J. Atmos. Sci., 32(3), 565–568.
Culp, G., Hansen, S., and Richardson, G. (1968). “High rate sedimentation in water treatment works.” J. Am. Water Works Assn., 60(6), 681.
Cuthbertson, A. J. S., Ervine, D. A., Hoey, T. B., and Heinrich, O. (1998). “Settling characteristics of fine grained sediments in turbulent open channel flow.” Proc., 3rd Int. Conf. on Hydroscience & Engineering, Univ. of Mississippi, Cottbus, Berlin.
Eaton, J. K., and Fessler, J. R. (1994). “Preferential concentration of particles by turbulence.” Intl. J. Multiphase Flow, 20(1), 169–209.
FLUENT. (2003). “FLUENT 6.1 documentation.”, Lebanon, NH, Fluent Ltd.
Hazen, A. (1904). “On sedimentation.” Trans. ASCE, 53(2), 45–71.
He, C., and Marsalek, J. (2009). “A vortex plate for enhancing particle settling.” J. Environ. Eng., 627–635.
King, J. K., and Blanton, J. O. (2011). “Model for predicting effects of land-use changes on the canal-mediated discharge of total suspended solids into tidal creeks and estuaries.” J. Environ. Eng., 920–927.
Madsen, H. I., Vollertsen, J., and Hvitved-Jacobsen, T. (2007). “Modelling the oxygen mass balance of wet retention ponds receiving highway runoff.” Highway and urban environment, G. M. Morrison, and S. Rauch, eds., Vol. 12, Springer, Netherlands, 487–497.
Marchioli, C., and Soldati, A. (2002). “Mechanisms for particle transfer and segregation in a turbulent boundary layer.” J. Fluid Mech., 468, 283–315.
McCuen, R. H. (1997). Hydrologic analysis and design, 2nd Ed., Prentice Hall, Upper Saddle River, NJ.
McLaughlin, J. B. (1989). “Aerosol particle deposition in numerically simulated channel flow.” Phys. Fluids, 1(7), 1211–1224.
Nelson, C. H., Johnson, K. R., and Barber, J. H. (1987). “Gray whale and walrus feeding excavation on the Bering shelf, Alaska.” J. Sed. Res., 57(3), 419–430.
Pan, Y., and Banerjee, S. (1996). “Numerical simulation of particle interactions with wall turbulence.” Phys. Fluids, 8(10), 2733–2755.
Pedinotti, S., Mariotti, G., and Banerjee, S. (1992). “Direct numerical simulation of particle behavior in the wall region of turbulent flow in horizontal channels.” Int. J. Multiphase Flow, 18(6), 927–941.
Reeks, M. W. (1983). “The transport of discrete particles in inhomogeneous turbulence.” J. Aerosol Sci., 14(6), 729–739.
Risk, M. J., and Craig, H. D. (1976). “Flatfish feeding traces in Minas Basin.” J. Sed. Res., 467(2), 411–413.
Schoonover, J. E., and Lockaby, B. G. (2006). “Land cover impacts on stream nutrients and fecal coliform in the lower piedmont of west Georgia.” J. Hydrol., 331(3–4), 371–382.
Shammaa, Y., Zhu, D. Z., Gyurek, L. L., and Labatiuk, C. W. (2002). “Effectiveness of dry ponds for stormwater total suspended solids removal.” Can. J. Civ. Eng., 29(2), 316–324.
Stein, E., and Yoon, V. (2008). “Dry weather flow contribution of metals, nutrients and solids from natural catchments.” Water, Air, Soil Pollut., 190(1–4), 183–195.
Su, D., Fang, X., and Fang, Z. (2010). “Effectiveness and downstream impacts of stormwater retention ponds required for land development.” Proc., World Environmental and Water Resources Congress 2010, Environmental and Water Resources Institute of ASCE.
Viessman, W., and Lewis, G. L. (2003). Introduction to hydrology, 5th Ed., Pearson Education, Upper Saddle River, NJ.
Yager, P. L., Nowell, A. R. M., and Jumars, P. A. (1993). “Enhanced deposition to pits: A local food source for benthos.” J. Mar. Res., 51(1), 209–236.
Yao, K. M. (1973). “Design of high-rate settlers.” J. Environ. Eng., 99(5), 621–637.
Information & Authors
Information
Published In
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Sep 8, 2012
Accepted: Aug 14, 2013
Published online: Aug 19, 2013
Published in print: Jan 1, 2014
Discussion open until: Jan 19, 2014
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.