Abstract

The paper describes a novel drop shaft system that relies on the use of a selfactivating, non-powered and no moving part air intake control system to prevent instabilities and provide smooth transitions between air-entrained vortex flow modes and pipe full operating modes. This allows more compact drop pipe arrangements to be deployed within a single drop structure, also providing for maintenance access. These systems therefore do not require auxiliary maintenance or air shafts resulting in significant project cost savings. Further optimization of the system has involved the use of compact hydraulic break, rotary flow energy dissipation structures at the base of the vertical drop pipes resulting in a space efficient and effective system for controlling flows into deep tunnels. The operational characteristics of the novel drop shaft system including the basis for more effective flow control and elimination of unstable flow conditions are described in detail in this paper. The paper also includes case studies of its successful application in a number of deep tunnel schemes and at a wastewater treatment plant.

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, M.G. Faram, I. Guymer, T. O’Doherty, N.Syred

Abstract

The fluid residence time characterisation of a 3.4m diameter Hydrodynamic Vortex Separator (HDVS) has been carried out over a range of flowrates. Computational Fluid Dynamic (CFD) modelling has also been undertaken for the same conditions and validated against the experimental results, for which reasonable correspondence has been found. Using the results from the CFD modelling and batch inactivation results from the disinfection of secondary treated wastewater, it is shown that the theoretical performance of a HDVS as a contact vessel for disinfection can be predicted.

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. 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.