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

K. Osei, R.Y.G. Andoh, J. MacKinnon and M.G.Faram

Abstract

Laboratory testing of stormwater separators can overcome many of the technical challenges associated with field testing. With laboratory testing, sediment characteristics and the flow rates at which a device is tested are known and measurable before, during, and after the test. This controlled environment ensures that test programmes can be set up to meet specific objectives, and data can be obtained in a repeatable and timely fashion. However there are differences in laboratory test protocols that can have a significant bearing on test results which, if overlooked, can result in invalid comparisons being made between different systems. This paper looks at two protocols for testing separators in the laboratory, normally referred to as the Direct Test Method and the Indirect Test Method. The test methodologies are described and the similarities and differences shown. Results from tests on a stormwater treatment separator using the two protocols are presented. The results show that for the same sediment gradation and flow rate, a difference of over 20% in measured removal efficiency is possible. They also show that the Direct Test Method produces outputs that are more consistent, conservative and representative of the removal efficiencies expected for stormwater treatment separators.

Author

A.G.Stephenson

The problems surrounding how we deal with stormwater run-off and issues such as drought, flooding and water pollution have been well publicised in recent years fuelled, to great extent, by the growing consciousness of climate change. The summer floods of 2007 throughout the UK also led to the publication of several reports such as Sir Michael Pitt’s Interim Review and the more recent Flooding report from the House of Commons Environment Food and Rural Affairs Committee. DEFRA have also published Future Water, the Government’s water strategy for England and all of these documents have heightened awareness of the benefits of sustainable drainage and the contribution that can be made to reduction of flood risk. There are many methods available and approaches in the SUDS ‘toolbox’ but all too often designers are restricted to ‘soft’ or natural options or what have become known as traditional SUDS, failing to consider some of the innovative proprietary solutions that have been used for many years which have provided very robust, cost effective and reliable answers. This paper will use an interesting case study to demonstrate how these systems have been used in conjunction with traditional SUDS options resulting in a complimentary, holistic solution helping create a whole sustainable community.