Skimming Tank in wastewater treatment| Design | Why they are used?

Oil Skimming tank
Image -Oil Skimming tank

What is Skimming tank?

The tank in which scum formation is created by air diffusion through the sewage is called Skimming tanks.

Skimming Tank Design

oil Skimming tank diagram
Skimming tank Diagram 

Skimming tanks are narrow rectangular tanks which is having at least two longitudinal baffle walls interconnected. Skimming tank are used to remove grease and fatty oils from the sewage. Air diffusors are provided at the bottom of the tank. 

Compressed air applied at the rate varying from 300 to 6000m3/million liters of sewage agitates the sewage, which prevents settling of solids. The air tends to change the oil and grease into a soapy mixture. the soapy mixture is carried to the surface by the air bubbles, sum of which are entrained in it and may be skimmed off.

Why skimming tank are used?

Skimming tank is used to remove Oil and Grease from the wastewater or sewage.

If Oil and grease particles are not removed they may create the following difficulties.

1. When sewage is being discharged into the natural water bodies for disposal, unsightly scum will be formed at the surface which creates bad/foul odour around the natural water bodies. 

The scum retards re-oxygenation and thus causes anaerobic conditions.

2. Oil and grease do not easily digest and that results in creating problems in sludge digestion tanks.

3. When Oil and grease are not removed, They start clogging of filter materials of the trickling filters.

4. If Oil and grease are not removed they may affect Biological activities of the organisms and affect their smooth working.

Oil and grease materials can be removed by floatation or settling method as scum or sludge.

Also Read : Characteristics of Wastewater- Physical | Chemical | Biological

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