COAGULATION AS PRIMARY TREATMENT OF WATER

Coagulation is the process used to make bigger sized particles by adding certain chemicals called as coagulants. These coagulants attach and react with the impurities in water and convert them into settled sizes. 

GENERAL COAGULANTS

Some coagulants that are used for coagulation are as follows:

• Aluminium sulphate
•  Chlorinated copperas
• Ferrous sulphate and lime
• Magnesium Carbonate
• Polyelectrolytes
• Sodium aluminate

1) Aluminium Sulphate

It is also known as filter alum or alum. Its chemical formula is Al₂ (SO4)₃, 18 H₂O. Alum is an effective coagulant and its use in water treatment is universal. Alum in water treatment is supplied and used in the form of flakes, solid lumps and in solution form.

The benefits from alum are as follows:

• It reduce the taste and odor.
• It reduces the turbidity of water.
• It is cheap.
• It is simple in working and not require skilled supervision.
• It produce crystal clear water.
• The floc formed by this coagulant is better.
• The floc formed is tough and can not be broken easily.

Normally bicabonate alklanity is present in water. The chemical reaction involved in this is:

Al₂ (SO4)₃. 18 H₂O + 3Ca(HCO₃)₂   ----->       2Al (OH)₃ + 3CaSO₄ + 18 H₂O + 6CO₂

_{The aluminium hydrooxide formed is not soluble in water. It acts as floc. Some of permanent hardness is caused due to calcium sulphate and carbon dioxide cause hardness.}