The Division owns and operates three sewage treatment facilities. They are the Woodridge Greene Valley facility rated at 12 MGD (million gallons per day), placed in service in 1983, the Knollwood facility rated at 10 MGD, placed in service in 1987, and
the Nordic facility rated at 0.5 MGD, placed in service in 1984.
Woodridge - Greene Valley Wastewater Facility
Serves portions of the unincorporated areas in the City of Lisle, Village of Woodridge, City of Naperville and City of Wheaton. Our Woodridge-Greene Valley Plant is the largest of the three county owned wastewater treatment facilities. The Woodridge Greene
Valley Treatment Plant is designed to clean 12 million gallons per day of wastewater. The treatment plant uses biological and physical processes to clean the wastewater, which will be described during the remainder of this tour. Did you know a drop
of water leaving your house can be cleaned and put back into the river within 24 hours?
Once the wastewater enters the plant, the large materials such as plastics and other debris is removed by mechanical bar screens. This material is then compacted and taken to the landfill for disposal.
The wastewater is then pumped into aeration tanks, which contain aerobic microorganisms. We provide ideal conditions for the organisms, by pumping air into the bottom of the tank and mixing the microorganisms with the wastewater. The microorganisms
consume (eat) the contaminants (their food) in the wastewater and produce carbon dioxide, clean water and more microorganisms. As the air rises to the top of the tank, the organisms use it to breathe, much the same as we do.
As the organisms and clean wastewater flow from the aeration tanks, they must be separated, which is done in final settling tanks. The heavier organisms settle to the bottom of these tanks, are collected, and pumped back into the front of
the aeration tanks. The clean water flows over the weirs around the parameter of the tank into the next biological process.
Although most of the contaminants have been removed from the wastewater at this point, there are some nutrients (ammonia nitrogen) which is left in the wastewater and cannot be discharged into the river. The removal of these nutrients is
done by trickling the water over media which has a lot of surface area. The microorganisms in this process grow on the surface area of the media and remove the nutrients from the wastewater as it passes by them. These microorganisms grow and will
eventually fall off the media.
The wastewater is gathered at the bottom of the towers and pumped s through these filters so any of the organisms which have fallen off the media can be removed. This is a physical process which filters the wastewater through a 30 inch bed
of sand and will automatically backwash when the sand becomes plugged.
Now the contaminants and nutrients have been removed and the wastewater is ready to be put back into the environment. However, before we discharge the clean water to the river, we disinfect using chlorine in these contact tanks which will
kill any remaining bacteria. The clean water is then discharged into the East Branch of the DuPage River.
Knollwood Wastewater Facility
The Knollwood facility serves the City of Darien, the Village of Willow brook, the Village of Burr Ridge and unincorporated areas in the southeast part of the County. The estimated population of this area is 60,000. In 1999, the Knollwood facility operated
at 94% of capacity. The facility utilizes a secondary treatment process which consists of preliminary treatment of grit removal and fine bar screening for removal of paper, wood, and plastic products. Biological treatment is provided by complete-mix
aeration tanks. Biologically treated waste is directed to clarifiers that separate the biological solids form the treated liquid. This effluent is then chlorinated for disinfection and dechlorinated prior to discharge to the Des Plaines River. Waste
biological solids are hauled to the Woodridge - Greene Valley facility for further processing.
Nordic Wastewater Facility
Serves portions of the Village of Itasca and the Village of Addison and unincorporated areas in the northern part of the County. The estimated population of this area is 2,000. In 1999, the Nordic Facility operated at 73% of capacity. This facility utilizes
a tertiary treatment process. This consists of preliminary treatment of bar screening for removal of paper, wood and plastic products. Biological treatment is provided by coarse bubble aeration tanks. Biologically treated waste is directed to clarifiers
that separate the biological solids form the treated liquid. This effluent is further processed through sand filters, then disinfected using ultraviolet light prior to discharge to Springbrook Creek. Waste biological solids are stabilized by aerobic