Water Quality
Tertiary Treatment: Sand Filters
One of the ways water is purified in nature is by being filtered through the sand and fine gravel particles at the bottom of streams and rivers. Ground water is also purified by passing through layer after layer of sand, gravel and rock under the surface of the earth. As the water passes through these materials, fine particles are trapped and left behind.
The first step in Tertiary treatment consists of passing the wastewater through a bed of material with a rough surface to remove any fine solids that might still be in the water. The tanks in which this is done are called "sand filters."
Pathogen Removal: Disinfection
Next all the cleaned wastewater is fed into the "chlorine contact tank" in which sodium hypochlorite (bleach) is mixed with the water to disinfect it. This kills off any harmful organisms that may have escaped the treatment process.
Dechlorination
Excess chlorine is then removed from the water by treating it with sodium bisulfite. This leaves an effluent that can be safely discharged to the South Branch of the Kishwaukee River.
Quality Assurance
Before discharge, its quality is monitored and it is stringently tested for harmful organisms, or unhealthy levels of any substance. This testing is monitored by the United States Environmental Protection Agency under the directives of the Clean Water Act of 1972.