Sedimentation tanks are also known as settling tanks or wastewater clarifiers. The process of sedimentation is designed to remove large particles of contamination from water and wastewater. The removal of sedimentation is important because of the dangers of bacteria attaching or absorbing large particles in water. Sedimentation tanks can be installed before or after water and wastewater completes the treatment process.
Although the sedimentation process can be completed by a number of specific processes, the main aim is to use gravity to separate solid particles from the liquids that will pass on to later stages of treatment. As particles settle in the sedimentation tank, large pieces of solid waste fall to the bottom of the sedimentation tank into what is called the sludge zone. The area above the sludge zone is deeper than the sludge zone and contains recently introduced liquids still to be settled at one end and liquids that have completed the settling process at the other.
There are two basic types of sedimentation tank designs: the rectangular and circular designs. The rectangular tank is designed with an effluent inlet at one end of the tank and an outlet pipe for liquids that have passed through the sedimentation process at the other end of the tank. The rectangular tank relies on the large solid particles settling as they pass slowly through the tank. By the time the liquid reaches the outlet pipe the larger particles have settled to the bottom of the tank. Circular tanks are designed differently, with an inlet pipe at the bottom of the tank positioned close to a sludge removal pipe. The removal pipes for cleaner liquids is located close to the surface of the tank.
Sedimentation tanks have been researched using different forms of settling processes, including passive settling and agitation. The most efficient and commonly used form of settling is passive, where water is allowed to travel from upstream to downstream, allowing particles to settle without any agitation to disturb the particles at the bottom of a tank. Many circular sedimentation tanks use a top arm that rotates in a circular motion to collect floating debris.
One of the biggest considerations when designing a sedimentation tank is the time allowed for particles to settle into the sludge zone and not be passed on to later stages of the process. In a basic design, water is held in sedimentation tanks for between two and three hours. A longer process would result in reduced efficiency of the sedimentation process.