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
1. Primary coagulants
2. 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 :
1. Aluminium sulphate or Alum
2. Ferrous sulphate and Lime (copperas)
3. Chlorinated copperas
4. Magnesium Carbonate
5. Polyelectrolytes
6. 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