Authors

D.S. Jarman, M.G. Faram, G. Tabor

Abstract

The current climate of interest in water-environmental issues has lead to increased use of a dvanced computer-based simulation techniques in the evaluation and improvement of water management systems. This paper reviews the usage history of computational fluid dynamics (CFD) techniques by a supplier of technologies for urban water management, leading to the development of insights and guidance on the ado ption of such tools, presented in the context of a number of practical case studies. The paper finds that CFD methods offer genuine opportunities and can yield direct tangible benefits. However, this is reliant on organ isations having a realistic understanding of what such approaches can offer, their limitations, and also having an appreciation of the long-term commitment that is required to achieve maximum value.

Authors

R. Y.G. Andoh1, D. A. Egarr and M. G. Faram

Abstract

Hydrodynamic Vortex Separators (HDVSs) have been used extensively as solid-liquid separators throughout the water industry. In recent years their application scope has been extended through adaptation to allow unit processes such as solids separation, screening and disinfection to be accomplished within the same vessel. The paper reviews the current state of understanding of HDVS operation, focusing in particular on their use as Combined Sewer Overflow and wet-weather treatment systems for high-rate chemical disinfection. This includes a review of the role Computational Fluid Dynamics (CFD) has played in providing detailed insights into their operating mechanisms, which has lead to the generation of improved knowledge and provided scope for physical (e.g. configurational) and operational (e.g. chemical dosing) design optimisation. It is found that macro flow field behaviour has a key bearing on operational effectiveness, in terms of determining the efficiency with which chemical contacting can take place, and this is an area where CFD analysis offers particular promise. The paper also presents and discusses data from full scale monitoring and performance evaluations including those undertaken as part of regulatory compliance reporting for a full-scale installation in the United States, confirming the efficacy of these devices in practice.

Authors

D A Egarr, MG Faram, T O’Doherty

Abstract

A hydrodynamic vortex separator (HDVS) has been studied under laboratory conditions by using a specifically designed rig. Pressure tapping points placed at eight locations, six external and two internal, have revealed an even radial pressure distribution on the outer walls and central shaft. The ability of the HDVS to separate particulates has been studied. The particulates have been characterized by measurements of particle diameter and settling velocity, which have allowed efficiency cusps to be plotted against dimensionless groups used by other researchers. Owing to an unsatisfactory reduction of the data to a single curve by plotting the efficiency against dimensionless groups, an efficiency law has been determined based on the logistic equation and describes the separation efficiency in terms of the inlet flowrate, volume of the separator, and particle diameter and density.

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

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.