types of coagulants

TYPES OF COAGULANTS

SUBMITTED BY:-ASHISH BANSODE

M.E.—WATER RESOURCES ENGINEERING

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.

CLASSIFICATION OF COAGULANTS1) Primary coagulants,2) Coagulant aids

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

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 eithercationic (positively charged), anionic (negatively charged), or nonionic (neutrally charged.)

Different sources of water need different coagulants, but the most commonly used are alum and ferric sulfate.

Reaction:-

Chemical FormulaPrimary Coagulant

Aluminum sulfate (Alum)Al2(SO4)3 

Ferrous sulfateFeSO4 

Ferric sulfateFe2(SO4)3 

Ferric chlorideFeCl3 

ALUMThere 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 aluminum sulfate, 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. 

Advantages and disadvantages of Alum Advantages of alum are,It readily dissolves with water, andIt does not cause the unsightly reddish

brown staining of floors, walls and equipment like ferric sulphate.

Disadvantages of alum are,It is effective only at certain pH range, andgood flocculation may not be possible with

alum in some waters.

Advantages of Ferrous sulphateFerric 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 aluminum 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.

Ferric coagulants may be used in color removal at the high pH values required for the removal of iron and manganese and in softening of water.

Coagulant AidsCoagulant 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.

Common coagulant aids BentoniteCalcium carbonateSodium silicateAnionic polymerNon ionic polymer

Review Coagulation/flocculation is a process used to

remove turbidity, color, and some bacteria from water.  In the flash mix chamber, chemicals are added to the water and mixed violently for less than a minute.  These coagulants consist of primary coagulants and/or coagulant aids.  Then, in the flocculation basin, the water is gently stirred for 30 to 45 minutes to give the chemicals time to act and to promote floc formation.  The floc then settles out in the sedimentation basin.

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