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CFD (Computational Fluid Dynamics)

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file icon Pollutants Washout - The Missing Dimension in Urban Stormwater Treatmenthot! 05/16/2007
Authors
R.Y.G. Andoh1, R.M. Alkhaddar , M.G. Faram and P. Carroll
Abstract
Several configurations of proprietary ‘flow-through’ stormwater treatment devices have evolved to address the need for compact and effective systems that remove sediment and other pollutants from stormwater runoff. Whilst a number of these systems have been the subject of several field monitoring and independent laboratory studies, differences between design methodologies, unit sizes and capacity, test protocols and site conditions in the field have made direct comparisons of results very difficult. Most studies to date have focused mainly on the pollutant removal efficiency (effectiveness) of these systems.

Though removal efficiency is a good indicator of a devices’ effectiveness in terms of separating pollutants from stormwater, particularly under low flow conditions, it does not provide a complete description of device efficacy especially in terms of its ability to retain previously captured pollutants under moderate or high flows. The phenomenon of ‘Washout’ defined as the tendency to re-suspend (re-entrain) and discharge previously captured pollutants is of particular importance in practice as stormwater treatment devices are typically maintained on an infrequent basis.

The paper describes results of work undertaken at Liverpool (JM) University to determine sediment retention performance of different stormwater treatment chamber configurations under controlled laboratory conditions that provides a true comparative assessment using identical testing protocols and methodologies. General conclusions drawn from the results include the observation that the phenomenon of “pollutants washout” from stormwater treatment chambers is very real and must be taken into account in system selection for practical application. The rate of stored pollutants washout was found to be extremely sensitive to chamber design with re-suspension and washout rates ranging from close to zero to close to 100 percent depending on device configuration, nature and type of flow modifying components and whether or not sediments are stored in isolated storage zones.

file icon Evaluation of different configurations of stormwater treatment chambershot! 07/28/2004
Authors
David A. Phipps, PhD, Rafid M. Alkhaddar, PhD, James Dodd, Michael G. Faram, PhD, Pamela J. Deahl, P.E.
Abstract
With the objective of reducing the polluting impact of urban run-off on receiving watercourses, various proprietary treatment technologies have evolved, including ‘flow-through’ devices that are designed to intercept and store pollutants such as sediments and floatables for later removal and safe disposal. Frequently, the performance of chambers is stated in terms of ‘ability to remove pollutants from the inflow’, often at discrete flowrates. However, a parameter that is often overlooked is chamber ‘retention efficiency’, the ability of chambers to retain stored pollutants once collected. The paper presents the findings of both simulation and experimental studies of different designs of treatment chamber, focussing in particular on the ‘retention efficiency’ parameter. It is concluded that chambers in which the pollutants storage region is isolated from the main treatment area are likely to be most effective.
file icon Experimental investigation into solids re-entrainment in hydrodynamic vortex separatorshot! 06/17/2004
Authors
Dr D A Phipps, Dr R M Alkhaddar, Mr James Dodd, Dr M G Faram, Professor R Y G Andoh and Miss Cathryn Roberts
Abstract
Hydrodynamic Vortex Separators (HDVS) are used for removing solids from stormwater before discharge into watercourses and for Combined Sewer Overflow (CSO) and wastewater treatment. Their internal geometry generates flow patterns which promote solids separation and deposition in a hopper at the base. This study examines re-entrainment of captured solids at a range of flow rates, for four separator configurations. Dye-tracer experiments for one configuration have shown that the hopper region is a slow mixing zone (SMZ), with the rate of mixing and interchange with the main body of flow depending on overall flow rate. With the hopper part filled, dye tests showed minimal mixing of interstitially held water; supporting the view that removal of solids will occur only from the top of the bed. The onset and extent of reentrainment occurring when the hopper was full of sediment was found to depend on the configuration, with a general increase in its occurrence with increasing flows. The study highlights the importance of providing isolated zones for sediment collection and adequate shielding of the collected sediment.
file icon Assessment of modular block stormwater storage systemshot! 06/17/2004
Authors
file icon An efficiency formula for a hydrodynamic vortex separatorhot! 08/24/2005

Authors

Darrell A. Egarr, Mike Faram, Tim O’Doherty and Nick Syred

Abstract

Hydrodynamic vortex separators (HDVSs) are low energy solid-liquid separation systems. They have been applied for a number of duties including wastewater treatment, combined sewer overflow treatment and storm water treatment. Such systems operate whereby solids settle due to the force of gravity and sufficient residence time for this to take place is provided by the rotary nature of the path of the fluid through the separator. In this study, the HDVS is considered operating without an underflow component which may be the case in practice, for example, where collected solid material is removed on a batch basis.

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