Many communities working to reduce combined sewer overflows use monitoring with computer modeling to identify bottlenecks and areas with unused capacity or unusually high flows. Unfortunately, this approach doesn't always provide the level of detail sewer managers need to design effective systemwide solutions.
South Bend, Ind., is one such community. Fortunately, a local company — EmNet LLC — chose the city of 108,000 along the St. Joseph River to test a system developed with the University of Notre Dame and Purdue University using an Indiana 21st Century Research and Technology Fund grant. The system — CSONet — deploys distributed real-time control and monitoring to maximize conveyance and storage throughout the entire sewer system, reducing the potential for overflows.
CSOnet is a wireless network of monitoring points called instrument nodes (INodes) and data acquisition points called “gateways.” An INode is a composite fiberglass manhole cover rated to the American Association of State Highway and Transportation Officials' HS-20 highway strength standard that contains a battery-operated computer and antenna. It gathers data from a sensor mounted in the sewer and transmits it to a gateway.
Installing an INode and the gateways may be done in-house or by a sewer contractor. The gateways then are mounted on poles and receive power from the traffic signals or power lines. Signal cable in a conduit is run from the valve or pump to the gateway. It then determines how wide the valve should open or how fast a pump should run and sends the appropriate output signal through that cable to the actuator pump, which then operates the valve or pump.
The equipment begins functioning almost immediately. The gateway collects data from the INodes and uploads it to a secure Web site via a cellular connection. It then “talks” with other gateways in the area to determine which valves to open and close to maximize flows systemwide.
The Gateways replace the centralized computing center of a SCADA system, while the INodes replace the cabinets, programmable logic controllers, antennae, high-powered radios, and power supplies of permanent monitoring locations. Because every monitoring and control point behaves similarly, the system is easier to understand and use than SCADA.
Its decentralized nature also makes the system scalable and allows it to be incrementally installed, enabling sewer managers to expand deployment as needs change. It integrates with any existing SCADA system and communication infrastructure, so it can view data from SCADA systems and data from CSOnet can be viewed through an existing SCADA interface.
South Bend's pilot demonstration showed that automating a retention basin and coordinating its control with conditions in other parts of the sewer system doubled storage capability. Public works managers realized they'd underutilized capacity in many parts of the system, and in February they decided to roll out CSOnet throughout the city's 20-square-mile combined sewer system.
In its first phase, CSOnet has been used for real-time monitoring of 110 sites, making South Bend's the most densely monitored combined sewer system in the country, if not the world. The sites include all 36 outfalls, several locations through its interceptor line and trunk lines, every river crossing, and existing retention basins.
The data gathered from real-time monitoring is now being used to:
- Create compliance reports.
- Provide early detection and warning of illegal overflows and potential basement backups through alarms on the city's SCADA interface and through the CSOnet Web site. Soon, CSOnet also will be able to send alarms as text messages to sewer department employees.
- Determine potential areas for overflow storage.
- Further calibrate the computer model.
- Identify potential bottlenecks.
- Develop a proactive maintenance plan.
Next year, the department moves to the next step: from real-time monitoring to real-time control of its sewer system. CSOnet will be used to maximize inline and offline storage, reducing overflow by hundreds of millions of gallons, and to control flows into the treatment plant.
Studies show that balancing flows could reduce the amount of overflows by 25% for each storm event.
— Timothy Ruggaber is operations director for EmNet LLC, Granger, Ind.