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

D.S. Jarman, M.G. Faram, D. Butler, G. Tabor, V.R. Stovin, D. Burt and E. Throp

Abstract

Computational Fluid Dynamics (CFD) can be applied to gain insights into most fluid processes and associated phenomena and so presents potential to add value in the analysis of urban drainage systems. This paper presents a review of CFD studies carried out in this field, with the objective of developing an appreciation of how and where it can be applied. Existing work has tended to focus around the analysis of four types of urban drainage structure, including Combined Sewer Overflows (CSOs), storage and attenuation systems, stormwater sediment interceptors and sewerage conveyance structures. Within the respective studies, the prediction of flowfields, particulate behaviour, water surface profiles and Residence Time Distributions (RTDs) are found to form the main focus, and as such, these are considered in most detail in the paper. It is concluded that CFD presents a number of opportunities in urban drainage system analysis, and that the scope of this opportunity will further develop as both computational hardware and software resources become more advanced.

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

R.Y.G. Andoh, H. Carter, C. Osterrieder, N. Raymond & M.A. Stein

Abstract

Faced with the challenge of addressing Combined Sewer Overflow (CSO) issues, the City of Saco, Maine, adopted an approach which involved improving the transport and management of excess wet-weather flows by implementing a scheme that applied advanced vortex technologies for both flow control and water quality improvement. The application of vortex technology at Saco utilizes vortex flow regulators in the upstream diversion chambers to regulate maximum flows to the existing wastewater treatment plant in order to avoid hydraulic overloading and the diversion of excess combined sewer flows to the new CSO treatment facility. The new facility utilizes an advanced hydrodynamic vortex separator (HDVS) that incorporates a novel non-powered, self-activating and self-cleansing CSO floatables control screening system and accomplishes primary treatment equivalency, disinfection, floatables capture and grit removal all in one vessel. The underflow from the CSO facility comprising sewer debris and solids including grit, sediments, settleable organic solids and floatables, is returned to the headworks at the treatment plant and the clarified, screened and disinfected overflow is discharged to the receiving environment (Saco River) after de-chlorination. The ability to perform several essential unit processes (i.e. Sedimentation, Screening, Disinfection and Grit Removal) all in one vessel resulted in significant savings in the overall project scheme costs on account of the more compact design of the advanced HDVS system coupled with the elimination of additional tanks and vessels that would have been required with the conventional approach. Analytical results from post-construction compliance monitoring have confirmed the efficacy of the system.

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.