Parts of a Water Treatment System
Municipal water treatment plants and wastewater treatment plants work in very similar ways. In the former, the water is drawn from a freshwater source and destined for a municipal water supply where it will be used for drinking and bathing. In a wastewater treatment plant, used contaminated water is prepared to be safely released back into nature where it may well eventually end up being drawn into a municipal water treatment plant and reused.
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Water Supply
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The first step in a municipal water treatment system is the water supply. In some municipal systems, the water supply is an above-ground source like a lake or reservoir. In other cases, the water supply is a well or other underground source. Some municipal water treatment systems use multiple sources, and in some cases, each source may have its own treatment system.
Screens
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The first step in a water treatment system is often a series of screens designed to filter out large contaminants like rocks, branches and leaves. The initial screen can be as large as 2 inches by 2 inches. If multiple screens are used, the water is first passed through a larger screen, and then through successively smaller screens.
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Pre-sedimentation Basin
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In water that has high sand or silt, content that isn't easily screened out, is sometimes held in a sedimentation basin before being passed into the water treatment plant. The sedimentation basin is designed to allow heavier particles to settle to the bottom. The cleaner water on top is drawn into the plant for further treatment.
Coagulants
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Some waters still have some very fine suspended water particles. In some cases, chemical coagulants, like aluminum or iron salts, are added to the water. The coagulants change the electrical charge of the suspended particles causing them to coagulate together.
Filtration
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Once the coagulants are added, the water is run through a filtration system to remove the coagulated material. The size and type of filtration will depend greatly on the particular needs of each water treatment system.
Disinfection
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In most municipal water treatment systems, the final step in treating the water is to add a disinfectant. This disinfectant is not intended to make the water biologically dead. Instead, it is intended to kill certain known pathogens. In most municipal water systems, the disinfectant is low levels of chlorine.
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References
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