Authors

Darrell A. Egarr, Michael G. Faram, Timothy O’Doherty, David A. Phipps, Nicholas Syred

Abstract

A Hydrodynamic Vortex Separator (HDVS) has been modelled using Computational Fluid Dynamics (CFD) in order to predict the residence time of the fluid at the overflow and underflow outlets. A technique which was developed for use in Heating, Ventilation and Air Conditioning (HVAC) was used. The results have been compared to those determined experimentally. It is shown that in using CFD, it is possible to predict the mean residence time of the fluid and to study the response to a pulse injection of tracer. It is also shown that it is possible to apply these techniques to predict the mean survival rate of bacteria in a combined separation and disinfection process.

Authors

D.A. Phipps, R.M. Alkhaddar and M.G. Faram

Abstract

In recent years, various proprietary treatment technologies have evolved to reduce the polluting impact of urban run-off on receiving watercourses. The majority are ‘flow-through’ devices, designed to intercept and store pollutants in submerged chambers for later removal and safe disposal. Frequently, the performance of such systems is described solely in terms of ‘ability to remove pollutants from the inflow’, usually at specified discrete flowrates. However, it is suggested that this is insufficient to give a true assessment of performance and a critical parameter that is often overlooked is chamber ‘retention efficiency’, the ability of a chamber to retain stored pollutants once collected. In the current study, this parameter is investigated experimentally for a range of chamber configurations. Cylindrical chambers with different inlet orientations, internal components and hence flow dynamics are considered. The study identifies retention efficiency as being a major differentiator between designs, and concludes that chambers in which captured pollutants are stored in regions that are hydraulically isolated from the main treatment area are likely to be the most effective in practice.

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.

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.

Authors