Authors

D. Egarr, M.G. Faram, T. O’Doherty, D. Phipps and N. 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 to determine the residence time and the results have been compared with 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

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

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.