Sedimentation tank and equipment
Sedimentation tank and equipment
Introduction
Sedimentation is a natural treatment of water or wastewater which allows suspended particles, coarse disperse phase, coagulated and flocculated impurities to settle out of water or wastewater under the influence of gravity. The procedure is vitally necessary in modern water and waste water treatment plants as it provides a high degree of purification. Moreover, the procedure is critical as the impurities present in water form solid aggregates which settle at the bottom of the tank in the form of sludge and are periodically removed.
Critical parameters for successful sedimentation are (among others):
1. The dispersion of the effluent in the tank
2. The geometry of the tank which must facilitate quiescent sedimentation and precipitation of solids.
3. The volume of the tank which must allow accurate retention times in order to ensure the precipitation of solids.
4. The proper function of the scraper in order to remove the formed sludge from the bottom of the tank.
Sedimentation tank and equipment
1. SEDIMENTATION TANK
The shape of a sedimentation tank may be either long, rectangular or circular in design and the bottom of the tank is sloped to facilitate the flow of the formed sludge to the centre of the tank. In the centre, at the bottom of the tan, there is a base where the bearings and shaft of the scraper are supported. On the circumference of the tank the weir for the liquid overflow is constructed.
2. BOTTOM SCRAPER
A mechanical scraper scrapes the sludge from the sloped bottom of the sedimentation tank. It is a rotary shaft in which several metal sheets are hung in order to facilitate the removal of formed sludge with the minimum amount of trapped water. The bottom bearing is made of a polymer with antifriction properties and the scraper shaft leans against the bearing. It is made of stainless steel.
3. THE SLUDGE COLLAR
It is a bottomless container for the dispersion of the sludge in the tank. It is coupled with the
scraper and therefore rotates.
4. LIQUID OVERFLOW WEIR
The overflow weir is made of stainless steel and it leans against the walls of the tank in order to utilize the whole volume of the tank and to forbid the formation of eddies. The overflow weir ensures the equiponderance overflow of the refined liquid to the liquid collection tank.
5. SLUDGE OUTLET PIPELINE
The formed sludge is periodically removed from the bottom of the tank to a tank located next to the sedimentation tank.
6. SURFACE SCRAPER 
On the surface of the sedimentation tank there is a surface scraper similar to the bottom scraper. The surface scraper continuously removes the floating impurities and leads them back to the aeration tanks.
7. SEDIMENTATION ACCESS BRIDGE
It is a 1m width bridge made of steel to facilitate access to the rotary motor. Bridge, surface and bottom scrapers lean against a “stretcher” and the latter rotates on the perimeter of the sedimentation tank.
8. TANK FOR THE COLLECTION OF THE REMOVED SLUDGE
It is a tank located next to the sedimentation tank and is connected to the bottom of the sedimentation tank with a pipeline. It is equipped with air pumps that serve a dual purpose; first to remove activated sludge and secondly for waste/water recirculation.