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OPIMIZATION OF COMBINED SEWER OVERFLOW CONTROL SYSTEMS
Citation:
O'Connor*, T P., F Lai*, C Fan*, AND R Field*. OPIMIZATION OF COMBINED SEWER OVERFLOW CONTROL SYSTEMS. Presented at 5th International Conf: Diffuse/Nonpoint Pollution and Watershed Management, Milwaukee, WI, 6/1-15/2001.
Description:
The highly variable and intermittent pollutant concentrations and flowrates associated with wet-weather events in combined sewersheds necessitates the use of storage-treatment systems to control pollution. A strategy should be adopted to develop an optimized combined sewer overflow (CSO)-control system which maximizes the use of the existing system, before constructing new facilities, and sizes storage volume in concert with the treatment rate to obtain the lowest cost storage-reatment system. This paper describes the components, hardware and strategies to create such a system. 1) analyze where the most economical system components are (e.g., maximizing in-sewer storage by simple CSO-flow-regulator adjustments, installing dynamic regulators that respond to remote sensing devices and direct more flow to the publicly-owner-treatment works (POTW)). 2) analyze low-cost modifications to POTW. The most expensive options, constructing new parallel facilities at the POTW and additional storage or treatment facilities, should be considered last. An important part of CSO-control system planning is the determination of the economic break-even point between the required storage volume and treatment capacity. It is not economical to design storage facilities beyond an optimum tank volume since the rate of cost increases more rapidly than the pollution removal benefit for retaining the flow or larger, infrequent storms. To effectively employ control technologies in a combined system, the functions, applicability, and idiosyncrasies of their individual designs must be clearly understood. Unlike sanitary-0sewer wastewater, with easior to establish diurnal pollutant distributions and hydraulic loadings, CSO characteristics are dependent on sewer system and sewershed and solids rainfall characteristics which vary during a storm event. Accordintly, it is important to characterize CSO on a site-specific basis since the build up of solids, which are subsequently resuspended during intensive storm flows, is a function of the local topography, geology and antecedent dry-weather periods. Many existing POTWs have treatment limitations due to interceptor capacity, expansion costs, and space availability. Therefore, along with capacity enhancement, optimization alternatives must include upstream modifications (e.g., high-rate, satellite treatment/storage in the proximity of an upstream CSO point and catchbsin modifications) and management options (disconnecting roof drains and real-time control). Each system requires its own optimization plan since no one method of storage, treatment, or O&M has been demonstrated as a cure all. Only through the evaluation of the total sewershed system can the appropriate methodology and technology be chosen for CSO-control optimization.