SOUTH DAKOTA Department of
Environment & Natural Resources

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Pierre, SD 57501
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Surface Water


Photograph of a chlorine contact basin at a wastewater treatment plant.

Disinfection involves destroying harmful bacteria that are present in the wastewater. The most common method of disinfection is chlorine. Ultraviolet light and other chemicals, such as bromine, fluorine, and peroxide, are also occasionally used.

This picture shows a chlorine contact basin. Chlorine is added to the water. The water then passes through this series of baffles to allow time for the chlorine to destroy the bacteria.

High levels of chlorine can be harmful to aquatic life. Therefore, after chlorination, the wastewater is usually dechlorinated to eliminate the toxicity of the chlorine.

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