Water purification process | Community pharmcy notes

Water purification :

It is a great importance in community medicine. Water may be purified either in a large scale or in a small scale.
Water purification process , B pharmacy notes


Large scale purification of water :

It involves five main steps 
1.  Protection
2.  Storage
3.  Coagulation and sedimentation
4.  Filtration
5.  Disinfection

(1)  Protection :

Water source must be protected from human feces and also from human and animal contact.

(2)  Storage :

It is done in natural and artificial reservoir for 10-14 days. Considerable amount of purification occurs due to biological, chemical and physical changes. Storage more than 2 weeks is not recommended since it leads to growth of algea.

(3)  Filtration :

It removes 98-99 % of bacteria and other impurities. Two types of filter are used 
1.  Slow sand filter
2.  Rapid sand filter

Disinfection :

It involves chlorination.

Chlorination :

It is the addition of chlorine to purified water for further purification. It is the cheapest and most reliable method for water purification.

Advantages of chlorination :

1.  It kills pathogenic bacteria.
2.  It oxidises iron, manganese and H2S.
3.  It destroyes colour and odour producing constituents.
4.  It contros algae and similar organisms.
5.  It aids coagulation.

Mechanism of action :

When chlorine is added to water, hydrochloric and hypochlorous acids are formed. Hydrochloric acid is neutralized by the alkaline nature of water. Hypochlorous acid ionises to form hydrogen and hypochlorite ion.

H2O   +   Cl2   --------->     HCl    +    HOCl
           HOCl    ---------->    H     +     OCl

The disinfection action of chlorine is mainly due to hypochlorous acid.

Method of chlorination :

Usually chlorination is done with chlorine gas. For this an equipment is used called Peterson's chloronome. Chlorine is best because it is cheap and quick in action.

Small scale water purification :

1.  Boiling :

Boiling of water kills bacteria, spores, eysts and ova. It removes hardness. Boiling is a satisfactory method of water purification for domestic purpose.

2.  Chemical disinfection :

It is done with bleaching powder, chlorine, iodine or potassium permanganate. But chemical disinfection are not suitable for domestic purpose.

3.  Filtration :

Water can be filtered in a small scale by filtration. Three types of domestic filters are used. They are
1.  Pasteur chamberland  2.  Berkefeld  3.  Katadyn filter.







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