What is the use of Sedimentation in Wastewater treatment process?
The deposition of sediments is known as sedimentation. It occurs when suspended particles settle out of the fluid in which they are entrained and collide with a barrier. This is due to their movement through the fluid in reaction to the forces operating on them: gravity, centrifugal acceleration, and electromagnetism.
Settling is the process of suspended particles dropping through a liquid, whereas sedimentation is the end product of settling. Sedimentation is an excellent treatment method for producing a clearer effluent that may then be filtered. Much of the solids are removed by gravity settling in the sedimentation operations; particles that do not settle and stay suspended 'carry over' to the filtering phase, where they can be removed by filters.
The energy of the transport agents that spread the sediment over the basin mediates the link between sediment supply and sedimentation rates, which are two separate quantities. High sediment supply, for example, does not always imply high sedimentation rates, since sediment may skip high-energy places and concentrate in low-energy areas where the transport agent is unable to transfer its whole sediment load.
Sedimentation in wastewater treatment systems
In wastewater treatment, a sedimentation tank removes particulates from the wastewater. The collected sediments, also known as sludge, built at the bottom of the sedimentation tank, must be removed on a regular basis. To help in the settling process, coagulants are usually added to the water before sedimentation. There are frequently further treatment stages after sedimentation.
When sedimentation is used to treat wastewater, it is followed by secondary treatment, which may include a trickling filter, activated sludge, or another purification method that uses microorganisms to remove soluble contaminants.
Just before a developed treatment wetland, a sedimentation tank or at least a silt trap is frequently installed.
Sedimentation tanks have traditionally been created using three simple principles:
1: The rate of overflow
2: Loading rate of the weir; and
3: Retention time in the hydraulic system.
However, this has resulted in the development of an empirical basis for the design of effective settling tanks.
The following are the general concepts of any sedimentation tank design:
1. The goal is to remove settleable solids (SS) and reduce the SS content of sewage, lowering the biochemical oxygen demand in the process (BOD).
2.All sedimentation tanks are designed using the gravity settling theory in generally quiet settings.
3.Sedimentation units are provided in three phases of treatment in a typical sewage treatment plant.
4. Sedimentation tanks are made to work in a continuous flow mode. They are generally rectangular or round in form and have sludge-collecting mechanical components. The bottom of sedimentation tanks is typically flat (up to 15°) and features sludge hoppers with rather steep sidewalls, with the exception of tanks designed for continuous sludge removal (final sedimentation tanks in activated sludge plants). Mechanical scrapers transport settled sludge on the tank floor into hoppers for later extraction.
5.Imhoff or two-story tanks combine sedimentation and digesting in one container. Such devices are only used in small plants with populations of less than 5000 people.
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