Combined Sewer Overflow Management
DocumentsDate added
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
Authors
Professor Robert Y.G. Andoh
Abstract
The conventional approach to the rehabilitation and improvement of collection system service levels has been to enhance system capacity and transfer increased flows to central wastewater treatment facilities, which in turn often results in the need for upgrading the treatment works to handle increased flows. The paper highlights why the implementation of satellite treatment systems within the collection systems (away from end of pipe) provides significant benefits from both a process and public health standpoint compared with the conventional approach.
Aspects of wastewater characterization, in particular settling velocity distributions, and its relevance on the performance of physical unit processes such as sedimentation and filtration are described and used to explain why satellite treatment makes sense. The satellite CSO treatment facilities at Columbus, Georgia which have undergone more than 5 years of peer reviewed intensive monitoring are described and used as a case example to highlight the benefits and significant cost savings that accrue from implementing satellite treatment systems within collection systems.
Authors
R.Y.G. Andoh, A.J. Stephenson and P. Collins
Abstract
The need for a more holistic approach in the development of solutions to wet-weather induced problems in urban drainage systems is advocated. A review of current approaches to resolving problems of premature overflows and flooding is presented outlining a case example of the successful application of non-conventional approaches, techniques and devices that assist in the better management and control of wet-weather flow sources. This involves the seeking of solutions within the upstream portions of drainage systems by intercepting, containing, controlling and treating excess wet-weather flows before they cause hydraulic and water quality problems in downstream areas (sections of the drainage system). These approaches have been found to be more cost-effective than conventional solutions and involve the implementation of distributed/decentralised schemes which in turn offer improved opportunities for wider community and other stakeholder involvement leading to the realisation of amenity and other non-structural benefits.
Authors
S.P. Hides, R.Y.G. Andoh and P. Carroll
Abstract
Sewer systems evolved as part of the human development process to meet the challenges of effectual draining of urbanizing areas. In the recent history of human development, following the implementation of wastewater treatment plants to control point sources, a shift occurred with wet-weather induced overflows from sanitary sewer systems (SSOs) and combined sewer systems (CSOs) being deemed to be a major cause of water quality impairment in urban streams, rivers and other receiving waters. The general move was towards separate sewers, one to convey foul water (sewage) and the other to convey the supposedly cleaner stormwater runoff to the nearest watercourse.
With the increased awareness, in more recent times, of the adverse environmental impacts of stormwater runoff and other diffuse wet-weather discharge sources, the need has arisen for stormwater control and treatment systems. There is a need now for a more holistic approach to be adopted in the development of solutions to wet-weather induced problems in the drainage of urban catchments. This paper reviews approaches to the management of urban wet-weather such as stormwater runoff, premature overflows, basement backups and flooding; outlining case examples of the successful application of non-conventional, innovative, novel and emerging approaches, techniques and devices that assist in the better management and control of inflow sources and water quality. This involves the seeking of solutions within the upstream portions of drainage and sewer systems by intercepting, containing, controlling and treating excess wet-weather flows before they cause hydraulic and water quality problems in downstream areas / sections of drainage systems.
