Sedimentation Tanks for Wastewater Treatment

A sedimentation tank is a storage tank in which wastewater is filled and stored overtime to remove the suspended particles present in the water. These particles fall to the bottom of the tank because of gravity and the use of flocculants which have been added to the wastewater in primary treatment. 

Continuous Flow Sedimentation Tank 

Most tanks are designed to be continuous flow type tanks however a number in smaller wastewater treatment plants are designed as a fill and settle type where the tank is filled, and the particles left to settle. Conical based tanks are preferred as this slows flow of water through the tank allow sediments to fall to the cone. 

Some continuous flow tanks are called horizontal flow tanks which is twice the length as the width and the flow is needed to flow more distance to settle the particles. 

Fill & Settle Tanks 

After settling the cleaner water is drawn off through decanting valves down the side of the tank leaving the particles in the cone to be drain later. However, a number of these tanks are rectangular flat base tanks that are fitted with weirs and can sometimes be used as 3 stage tanks with a mixer to apply coagulants and flocculants. 

Rectangular Sedimentation Tanks 

Rectangular sedimentation tanks or micro-clarification tanks are used in. primary water treatment requiring settlement or clarification of liquids or the bulk removal of solids from wastewater. Coagulation and flocculation reagents may be added to the liquid to increase the settling velocity. The reagents cause the suspended solids and particles to settle after clumping together to form a sludge in the settlement tank.  

Dirty water enters the tank settling zone from a high-level inlet where particles and sediment sink to the base of the cone. The water rises and passes over a saw tooth weir which retains any floating debris or foam. A flanged drain outlet is on each of the chambers allowing a complete flush down for dirty water and sludge removal. 

Primary Tanks 

Primary Sedimentation Tanks is a sedimentation tank where water is stored, rests and the sludge collect at the bottom. Floating water Is draw off discharged to a filter where the activated sludge process takes place which then leads on to Secondary Sedimentation. 

Secondary Tanks 

Secondary Sedimentation Tanks is where the water is taken after the activated sludge stage which smaller particles are removed.

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