Coagulants

The process of removal of suspended solids in water by the use of chemical agents is known as coagulation.

1. GOVERMENT ENGINEERING COLLEGE, BHARUCH Name : Kaptan sagar r Enrollment No. : 130140106021 Topic : Coagulants Sub : Water and Waste Water Engineering

2. Coagulation The process of removal of suspended solids in water by the use of chemical agents is known as coagulation. Coagulation is carried out for the filtration and purification of water.

3. Classification of Coagulants Primary coagulants Coagulant aids

4. Primary Coagulants Primary coagulants neutralize the electrical charge of particles in the water which causes the particles to clump together. Coagulant aids add density to slow-settling flocs and add toughness to the flocs so that they will not break up during the mixing and settling processes.

5. Chemically, coagulant chemicals are either metallic salts (such as alum) or polymers. Polymers are man-made organic compounds made up of a long chain of smaller molecules. Polymers can be either cationic (positively charged), anionic (negatively charged), or non-ionic (neutrally charged).

6. Different sources of water need different coagulants, but the most commonly used are alum and ferric sulphate. Reaction : -

7. The following are common coagulants used : Aluminium sulphate or Alum Ferrous sulphate and Lime (copperas) Chlorinated copperas Magnesium Carbonate Polyelectrolytes Sodium aluminate

8. Alum There are a variety of primary coagulants which can be used in a water treatment plant. One of the earliest, and still the most extensively used, is aluminium sulphate, also known as alum. Alum can be bought in liquid form with a concentration of 8.3%, or in dry form with a concentration of 17%. When alum is added to water, it reacts with the water and results in positively charged ions.

9. Advantages & Disadvantages of Alum Advantages : It readily dissolves with water, and It does not cause the unsightly reddish brown staining of floors, walls and equipment like ferric sulphate. Disadvantages : It is effective only at certain pH range, and Good flocculation may not be possible with alum in some waters.

10. Advantages of ferrous sulphate Ferric hydroxide is formed at low pH values, so that coagulation is possible with ferric sulphate at pH values as low as 4.0. Ferric hydroxide is insoluble over a wide range of pH values than aluminium hydroxide except for the zone of 7.0 to 8.5. The floc formed with ferric coagulants is heavier than alum floc . The ferric hydroxide floc does not redissolve at high pH values.

11. Coagulant Aids Coagulant aid is an inorganic material. When used along with main coagulant, improves or accelerates the process of coagulation and flocculation by producing quick forming, dense and rapid-settling flocs . Coagulant aids when added increase the density to slow-settling flocs and toughness to the flocs so that they will not break up during the mixing and settling processes.

12. Common coagulant aids Bentonite Calcium carbonate Sodium silicate Anionic polymer Non ionic polymer

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