Operating a Collection System Like a Treatment Plant: A Cost Effective Way to Reduce Overflows

The Metropolitan Sewer District of Greater Cincinnati (MSDGC) has one of the most challenging collection systems in the country to manage during wet weather as it contains more than 200 combined sewer overflow points. Together these overflows discharge over 11 billion gallons of sewage into the Ohio River and its tributaries during a typical year. The utility is under two consent decrees to reduce these overflows, with the cost of compliance exceeding 3.2 billion dollars. With sewer rate increases over the last ten years bringing the typical household’s bill close to the limits of affordability, MSDGC looked to find new ways to address their wet weather challenges that were less capital intensive.To accomplish this challenge, the District turned to innovative practices and technologies that would help meet the federally mandated overflow reductions at a lower cost. It became clear that leveraging technology to operate their collection system as an extension of the receiving treatment plant would allow them to optimize the use of existing infrastructure during wet weather, and MSDGC embarked on the path of building a SCADA system that would allow it to realize this objective. By implementing a 4-element framework enabled by a SCADA system, MSDGC gained the ability to collect data from the field, visualize it in real time, control wet weather flows in real time, and apply algorithms to optimize the operations of the system. In early 2015, the District deployed its new Wet Weather SCADA system covering its largest service basin and has been expanding and improving it contiously. It is able to guide wet weather control based on flow predictions and real time data, detect river intrusion, and provide advanced alerting to operations and maintenance staff. The final capability was achieved by leveraging the existing wet weather control facilities and simply tying their control into the new wet weather SCADA system.The ability to control assets over a large geographic area in a cohesive manner during wet weather provides the opportunity to fill pipes, store, and treat wastewater in a manner that could not previously be done by allowing available capacity elsewhere to be identified and used before overflows occur. For example, MSDGC has demonstrated that a storage tank or wet weather treatment facility can be activated to reduce overflows occurring many miles away even when it is not needed for wet weather flow management in its own region. MSDGC’s new Wet Weather SCADA System will save tens of millions of dollars in capital investments needed to reduce wet weather overflows by maximizing the available conveyance and treatment capacity of its existing infrastructure.