What Happens When You Flush?
The process of treatment that begins when the collected wastewaters drain by gravity into the deep wells of the "headworks" at 303 Hollister Avenue, has as its goal the return of useable water to the environment to once again serve the needs of the community.
Mother Nature has always had a slow but very efficient process by which water is taken in by aerobic and anaerobic bacteria that remove organic contaminants which they use as food, filtered through rocks and soil as it is pulled by gravity into the deeper layers of the soil and the rocks beneath it and repurified, so that it is safe for human use when it is again taken up through wells.
What we do at the wastewater treatment plant is to accelerate the same process by which water naturally purifies itself in rivers and streams. We use mechanical and biological processes much like those found in nature to remove solids and contaminants from the wastewater. The process takes 10 to 13 hours from when the wastewater enters the plant headworks. Constant monitoring, sampling and testing assure that the cleansing process is working correctly.
Where Wastewater Comes From
DeKalb Sanitary District Residents
Domestic sources are human wastes from toilets and household wastes from sinks, washing machines, bathtubs and showers. Each house has a private sewer service lateral that collects the wastes from the various drains in the house and carries them by gravity to the connection with the public sewer main (that is usually in the center of the street in front).
Northern Illinois University Students and Staff
Up to 20% of the DeKalb Sanitary District's wastewater comes from the sanitary sewer collection system on the Northern Illinois University campus. The fact that the number of people contributing wastewater to the collection system changes dramatically from hour to hour, from day to day, and from month to month has a major impact on the DeKalb Sanitary District collection system and treatment plant.
Commercial sources (stores, theaters, recreational facilities, etc.) discharge much the same kind of waters as domestic sources. Because food service establishments discharge water contaminated by grease in great quantities, they are subject to special discharge rules that require grease traps to prevent grease discharge to public sanitary sewers. Grease can completely plug sewer lines, creating backups of sewer water that cannot escape in nearby homes and businesses.
Industrial sources are the water used in cleaning equipment, cooling waters and discharges of manufacturing processes. In DeKalb these account for only about 5% of the total flow. Some industrial source wastewaters must be pretreated to remove harmful metals and chemicals before they are allowed to enter the wastewater collection system.
How Wastewater Reaches the Headworks
The Sanitary Sewer Collection System
5 to 50 Million Gallons a Day
An average of 6.72 million gallons of water comes through 130 miles of sanitary sewers throughout the District to reach the "headworks" at the sewer plant each day. The flow never stops, but varies throughout the day. During rain events, the rate of wastewater flow to the plant can increase by a factor up to ten times normal.
Pulled by Gravity through Sanitary Sewer Mains
Most public sewer mains are 8 inches in diameter. Through the action of gravity (with the exception of 7 lift stations), these smaller sewer mains feed into larger ones (up to 18 inches in diameter) that feed into large "interceptor" sewers (up to 36 inches in diameter) that eventually dump into the plant "headworks" where the "raw influent" enters the treatment process.
Separate from Street Sewers
The sanitary sewers maintained by DeKalb Sanitary District are distinct from and separate from the street sewers maintained by the City of DeKalb Street Department, which are generally much larger than sanitary sewers. While the street sewers open to the curbside collection of water run off, the sanitary sewers are sealed and connect only to house or building sewer service laterals.
Illegal Connections Create Backups
Every effort is made by the City of DeKalb and DeKalb Sanitary District to keep street and ground water from entering the sanitary sewers, but leaks, cracks or illegally connected sump pumps or footing tiles can pour hundreds of gallons of water into the sanitary system when it rains. The smaller diameter of sanitary sewers means they cannot handle this rapid inflow, and backups result.