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How do clarification and disinfection work during drinking-water treatment?
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water
Water is the most plentiful compound on Earth and is essential to life. Although water molecules are simple in structure (H2O), the physical and chemical properties of water are extraordinarily complicated.
Clarification and disinfection are essential, distinct stages in the purification of drinking water, serving to remove physical impurities and eliminate harmful pathogens, respectively.1
Clarification
Clarification is a multi-step process designed to remove suspended particles and reduce turbidity. It typically involves:2
- Coagulation and Flocculation: Chemicals are added to the water to cause small suspended particles to clump together. Large paddles then mix the water, encouraging these particles to form larger masses known as "floc".3
- Sedimentation: The water flows slowly through a sedimentation basin, allowing the heavy floc to settle at the bottom as sludge, which is then removed.34
- Filtration: Because sedimentation does not remove all impurities, the water is passed through porous media, such as sand or anthracite, to trap remaining particles, microorganisms, and algae.32
Disinfection
Disinfection is the final step in the treatment process, intended to destroy pathogenic bacteria, viruses, and protozoa to prevent waterborne disease. This is achieved by applying disinfectant agents, most commonly chlorine or its compounds. To mitigate risks associated with chlorine, some facilities utilize ozone, ultraviolet radiation, or hydrogen peroxide.35