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Coagulation And Flocculation

	Coagulation And Flocculation Coagulation and flocculation make the finely divided suspended and colloidal matter in the water to agglomerate and form floes. This enables their removal by sedimentation or filtration. Substances that cause turbidity and color are usually removed by flocculation and coagulation. These problems are mainly associated with surface waters. Soil erosion, algal growth and animal debris carried by the surface run off are the causes of turbidity. Substances leached from decomposed organic matter, leaves and soil impart color to surface waters.
Flocculation involves gentle mechanical agitation which causes the formation of large floes. Coagulation involves the use of certain chemicals called coagulating agents or coagulants which enable flocculation. The most widely used coagulant is aluminium sulphate which is commonly called as alum.
Certain health hazards have been related to the presence of aluminium residuals following its use in water treatment. In normal conditions aluminium is converted to an insoluble form and is thus removed from the water. Sometimes soluble aluminium may be present in water. In, such cases, if the amount of ingested soluble aluminium is high it may lead a number of health consequences. It may increase the incidence of alzheimer's disease but definitive proof of such consequence is lacking. Because of such possibilities iron salts have been substituted for aluminium as a coagulant.
It is better to avoid treatment processes involving chemical coagulants. If the turbidity and color of raw water are not much higher than the permissible level, chemical coagulation should be employed only when the result of such treatment processes can not be achieved by other treatment processes. Reduction of both turbidity and color can be achieved with slow sand filtration.Coagulation and flocculation are usually sedimentation in large reservoirs for a holding period.

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