Wastewater (or sewage) originates from many sources, including homes, businesses, schools, and industries, and includes water from showers, sinks, dishwashers, laundries, car washes, hospitals, and food processing operations.  According to the U.S. Environmental Protection Agency, the average American produces 100 gallons of wastewater each day.

 

Most homes, businesses, and institutions are connected to a sewer system that conveys their wastewater to a public wastewater treatment plant.  Sanitary sewer systems carry only domestic and industrial wastewater, while combined sewer systems also carry stormwater runoff.  At the treatment plant, the wastewater is purified and returned to the environment to be reused.

 

The North Shore Sanitary District (District) provides wastewater treatment for the eastern part of Lake County, Illinois.  The District serves over 300,000 residents within its Service Area.  The District owns and operates three advanced sewage treatment plants with a combined average design capacity of 63.4 million gallons a day and over 125 miles of interceptor sewers.  The local collector sewers within incorporated areas of the District’s Service Area are owned by the local municipality.  The sanitary and stormwater sewers within the District’s Service Area are separate systems; therefore, there are no combined sewer systems.

 

The wastewater treated at the District’s sewage treatment plants passes through a series of five major treatment processes.  In addition, the solids produced by the wastewater treatment processes are treated and disposed separately.  Wastewater treatment requires an intricate balance of physical, biological, and chemical processes which are described below.

 

• Preliminary Treatment includes screening to remove large objects (such as sticks, rags, leaves, and trash) and the settling of grit (inorganic material such as sediment, sand, stones, etc) which could clog pipes and disable treatment plant pumps downstream.  The screened material is collected and disposed of at a municipal landfill, while the wastewater flows to primary treatment.
• Primary Treatment involves the removal of the settled and floating solids.  Solids removed from this process are treated in the solids handling portion of the plant.
• Secondary Treatment utilizes naturally occurring microorganisms which digest organic material, reduce nutrients, and eventually settle as solids.
• Tertiary (or Advanced) Treatment is used to further improve the quality of the water.  Deep bed sand filters are used to significantly reduce the suspended solids and further purify the wastewater.  After tertiary treatment, over 90% of solids have been removed from the wastewater.
• Disinfection is the final step in the wastewater treatment process.  Ultraviolet light disinfects the treated water before it is discharged into the receiving water body to protect the public from exposure to pathogens.  The Waukegan Sewage Treatment Plant (STP) and Gurnee STP discharge treated effluent to the Des Plaines River and the Clavey Road STP discharges treated effluent to the Skokie River.
• Solids Handling involves the treatment of the biosolids removed from the wastewater treatment processes.  The solids that are removed during the wastewater treatment processes still contain a large amount of water so to reduce the volume of solids and disposal costs, the solids are thickened and then dewatered by belt filter presses.  The dewatered biosolids are then loaded into trailers and transported to the Zion Sludge Recycling Facility for drying prior to disposal.