Skimming Tank

Skimming Tank

Skimming tank is a widely used term in sewage treatment process. Basically it is used in primary treatment of sewage. 

The purpose of primary treatment is to remove suspended solid materials from the incoming waste water. Primary treatment process doesn't remove the colloidal and soluble organic matter .

For removal of oil greases , soaps skimming tank is provided. Sedimentation tank is provided after the skimming tank. 

Skimming Tank

Process of Skimming Tank

In skimming tank we allows the floe of compressed air from the blowbportion of the skimming tank . 

As this air is blown from below portion of the tank hence the rising air bubbles works as a cogulant and this coagulant air bubbles coagulates the greases , soaps to the free surface of the sewage undergoing treatment. 

After the greases risen up to the surface , it gets skimmed off from the tank. 

Sometimes chlorine gas is also blown along with the compressed air .

Why we add chlorine in skimming tank ?

As mentioned above sometimes chlorine gas is blown along with the compressed air or we can add chlorine directly . 

The purpose behind adding chlorine to water is to destroy the colloidal effects of proteins which hold grease in emulsified form. 

Why skimming tanks are not used ?

SkimmimStanks are not used in India the reason behind this is simple as India is a hot country and as oils and greases doesn't get coagulate at high temperature. 

Hence attempts are made to remove them before the enter municipal sewer system by using oil and grease trap.

Grease and Oil trap 

Why we remove oil and grease from sewage water ? 

If oil and greases will not get removed from the sewage water , it will form scum on the surface and interfere with activated sludge treatment process by hindering thr pasaageof oxygen gas and also inhibits biological growth on trickling filter.