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Sedimentation tanks remove impurities from liquids, mainly water, through settling or adding a coagulating/flocking agent. They come in two styles: tall and fat for storage and treatment, and long and shallow for water purification. Other liquids can also be cleaned by settling.
A sedimentation tank is a part of the system for removing impurities from liquids, mainly water. In most cases, a settling tank is nothing more than a large tank to hold water, often with a special solids removal system at the bottom. Some tanks are tall and fat, while others are long and very shallow; this is based on the general purpose of the tank. In some sedimentation systems, solid particles can simply settle to the bottom of the tank. Other methods require a special binder to be added to the liquid before settling occurs.
Sedimentation is a common method of removing particles from liquid. Most large systems apply to water, but other liquids can be cleaned by settling. The most common non-aqueous liquids that a sedimentation tank can employ are industrial solvents and cleaners, as well as some types of liquid polymers. However, water is much more common for settling than any other liquid.
The general idea behind a sedimentation tank is very simple. If the water is held still long enough, any solid material suspended in the water will simply sink to the bottom or float to the top of the tank. Since most natural solids are heavier or lighter than water, all a system needs to do to remove solid impurities is scrape debris from the top and bottom of the tank.
To speed up this process, tanks generally have a coagulating or flocking agent placed into the water. The chemicals introduced create a reaction that begins to attract impurities towards them. The agents bind to the impurities and create pellets of collected material. Because these pellets are larger than the solids before, gravity pulls them to the bottom of the tank faster.
This process is common when treating wastewater, but less so in wastewater. In a typical wastewater system, the particles are mostly benign impurities. These impurities are undesirable, but not detrimental, to processes that use water. In the case of sewage, the quantity of bacteria and harmful agents present in the water makes sedimentation more difficult and coagulation less effective.
There are two basic styles of sedimentation tank. Tall and fat tanks are typically used as the initial part of water treatment and are for both storage and treatment. These tanks have enough space for the water to sit for a long time while allowing large debris such as rocks or sticks to settle. Since they store water as well as process it, they must be very large.
The other type of sedimentation tank is long and shallow. This tank design is typically within a water purification system. Because the tank is so shallow, it takes less time for suspended particles to sink to the bottom. These tanks are typically used for the coagulation stage in water treatment.
