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.

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.