Preliminary Treatment
Preliminary water treatment involves two components, the physical filtration of objects from the water, and the addition of chemicals to stop algae growth. Water is passed through screens, which remove objects such as sticks, paper and other debris from the water before it enters the water treatment process. Chemicals, such as chlorine, are added in order to stop algae from growing in the water, during some of the water treatment steps to come.
Coagulation and Flocculation
Alum and similar substances which bond with salts and other small particles suspended in the water are added. The alum is mixed well into the water, then allowed to bond with the salts and other particles to create larger particles known as "floc." The water is kept in a large basin where the floc can begin to separate and settle. The water is finally drained through screens once again, with the finer mesh on the screens separating out the majority of the floc particles.
Clarification
The "Clarification" stage (also known as "Sedimentation") allows the recently-filtered water to sit in a large basin long enough for the removal of particles which had been too small to be filtered out by flocculation filtering. As the water sits undisturbed, these particles will slowly begin to settle to the bottom of the basin. The particles will settle into a sludge of sediment, allowing the water to be drained above the sludge line, and the sediment to be scraped from the bottom of the basin.
Water Softening and Stabilization
Depending on the minerals that are left in the water after it's been clarified, it may be considered to be "hard" or "soft." Both types of water can lead to mineral buildup and pipe damage. The addition of minerals to the clarified water can "soften" hard water and "harden" soft water. Key minerals in this process include magnesium and calcium, the levels of which are balanced carefully, so as to create relatively stable water with a neutral pH.
Filtration
Once water stabilization has occurred and the magnesium, calcium and pH levels have been balanced so as to make the water relatively neutral, a final filtration stage occurs in order to remove any additional sediment that may still be in the water. A fine screen is used when filtering, removing any material that might remain which is large enough to be filtered out. The water will generally be much clearer after this step occurs, since even clarified and stabilized water may appear slightly cloudy. After the final filtration, the water can be stored in water tanks for use, and chemicals, such as fluoride, may be added to the water in storage as the city or locale where it is being stored dictates.
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