After a large storm, do you ever wonder where the rain or melted snow goes? Sanitary sewers and stormwater drains are underground water and wastewater infrastructure systems. They are often confused and presumed to have the same functions, but it is important to know the difference between the systems.
Sanitary sewers consist of underground pipes that carry wastewater from bathrooms, sinks, kitchens, etc. Sanitary sewers transport wastewater to wastewater treatment plants, where the water is treated, filtered, disinfected and discharged. Storm sewers are designed to collect rain, snow, and other surface water runoff. These systems are not designed to carry sewage or any other hazardous waste since the water is not flowing to a wastewater treatment plant. Stormwater drains and sewers discharge untreated water to local streams, rivers, and other bodies of water. Combined sewers contain both wastewater and surface water runoff.
Combined sewers often overflow when they accumulate a large volume of rainfall or melted snow. When overflowing occurs, combined sewers can dump millions or even billions of gallons of untreated or partially treated water into local waterways. Some cities have identified this issue and are installing "smart sewers" to detect heavy water flows. Smart sewer systems include sensors and valves that detect when the sewer system is in danger of overflowing. In a smart sewer system, water will be redirected to areas of the underground sewer system that are not as full to ensure that less water escapes to local waterways before going through treatment.
South Bend, Indiana, has had some success with adapting to smart sewer systems. In 2008, the city decided to install a smart sewer system to reduce the flow of untreated water to the St. Joseph River. Before the installation of smart sewers, typical untreated flow to the river was estimated at 2 billion gallons annually. Recent monitoring has shown a reduction to about 340 million gallons, an improvement of nearly 85% since 2008. In South Bend, plans are underway to measure the flow to the river and the quality of the overflow. Measuring the quality of the overflow will help to paint a better picture of the environmental impact of untreated water. The city also used the data collected from the sewer's sensors to develop a long-term control plan, estimated to save 500 million dollars in comparison to the original long-term plan.
Learn more about South Bend, Indiana's case study
Nadella, Rajeev. “Trends and the Future of Smart Sewerage Management in Smart Cities.” About Smart Cities®, 28 May 2021, www.aboutsmartcities.com/automatization-trends-future-smart-sewerage-management/.
Putzier, Konrad. “10 Big Ideas to Improve Life in Small and Midsize Cities.” The Wall Street Journal, Dow Jones & Company, 10 June 2021, www.wsj.com/articles/10-big-ideas-to-improve-life-in-small-and-midsize-cities-11623333659.
“South Bend, Indiana Uses Smart Technology to Monitor and Regulate Wastewater Levels.” Environmental Resilience Institute Part of the Prepared for Environmental Change Grand Challenge, eri.iu.edu/erit/case-studies/south-bend-indiana-uses-smart-technology-to-monitor-and-regulate-wastewater-levels.html.