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Water treatment process

Treatment

Stages

Preliminary Treatment

Preliminary treatment or pretreatment is any physical, chemical or mechanical process used on water before it undergoes the main treatment process. During preliminary treatmen :screens are used to remove rocks, sticks, leaves and other debris; chemicals are added to control the growth of algae; and a presedimentation stage to settle out sand, grit and gravel from raw water.

Coagulation

After preliminary treatment, the next step is coagulation. Coagulation removes small particles that are made up of microbes, silt and other suspended material in the water. Treatment chemicals such as alum are added to the water and mixed rapidly in a large basin. The chemicals cause small particles to clump together (coagulate). Gentle mixing brings smaller clumps of particles together to form larger groups called "floc". Some of the floc begins to settle during this stage.

Flocculation

During the flocculation stage, the heavy, dense floc settles to the bottom of the water in large tanks. As you can imagine, this can be a slow process! Once the floc settles, the water is ready for the next stage of treatment.

Clarification

Clarification occurs in a large basin where water is again allowed to flow very slowly. Sludge, a residue of solids and water, accumulates at the basin's bottom and is pumped or scraped out for eventual disposal. Clarification is also sometimes called sedimentation.

Filtration

Turbidity is a physical characteristic that makes water appear cloudy when suspended matter is present. The filtration process removes suspended matter, which can consist of floc, microorganisms (including protozoan cysts such as Giardia and Cyrptosporidium), algae, silt, iron, and manganese precipitates from ground-water sources, as well as precipitants which remain after the softening process.

These suspended materials are filtered out when water passes through beds of granular material, usually composed of layers of sand, gravel or related substances.

Disinfection

During disinfection, disease-causing organisms are destroyed or disabled. Chlorine (Cl2) is the most common disinfectant used inmajority of countries because it is practical, effective and economical.

Because chlorine dissipates rapidly, the right amount is added at the water treatment plant to make sure disinfection continues while the water is flowing through the distribution system.

Softening & Stabilization

When water is too "hard" (i.e. contains too much calcium, magnesium or other minerals), it forms scale and causes a variety of problems in pipes. Hard water can also result in laundering and washing problems, because it reduces the effectiveness of soaps and detergents.

Conversely, when too many of these minerals are removed, water can become too "soft". Soft water can cause corrosion in pipes.Drinking water plants attempt to maintain a desirable balance between hardness and softness. This is accomplished by adding minerals to soft water and removing them from hard water. (Measure hardness as CaCO3 with a Hach titration procedure based on the USEPA-approved method.)

Contact/Holding Tanks

Treated water is placed in contact tanks to ensure treatment process is complete. Finished water (the term water treatment professionals use) is stored in holding tanks. The tanks provide a water reserve to meet the changing water demands of the communities they serve.

Testing/Water Analysis

EquipmentsTreated watersamples are sent to the KIRIWASCO's laboratory for final analysis to ensure that the treatment process was successfull before it is released to our customers.


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