What does coagulation involve?
Coagulation is the process by means of which the colloidal particles are destabilised (i.e. the nature of the colloidal particles is changed so that they form flocs through the process of flocculation that can be separated from the water). Destabilisation is achieved through the addition of chemicals (called coagulants) to the water.
Different chemicals can be used as coagulants. The most common coagulants are aluminium sulphate, ferric chloride, lime, and polyelectrolytes. Coagulant-aids are also sometimes used. These are substances added in very small quantities to improve the action of the primary coagulant (See fact sheet on Coagulant Chemicals).