SMALL SCALE WATER PURIFICAION IN ENGLISH
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} Water Purification is the process of
making water clean and safe to drink.
Normally it is discussed under two headings:
} 1. Purification of water on a large
scale.
} 2. Purification of water on a small
scale.
} Small scale purification of
water is needed to provide safe drinking
water to a small population. It is done in two ways –
} (1) Household purification of water
} (2) Disinfection of wells
HOUSEHOLD PURIFICATION OF WATER-
} Main methods for household
purification of water are as follows-
} 1. Boiling
} 2. Chemical disinfection
} 3. Filtration
BOILING-
} Boiling is a satisfactory method of
purifying water for household drinking purposes. Boiling kills all bacteria,
spores, cysts and ova and yields sterilized water. Boiling also removes
temporary hardness by driving off carbon dioxide and precipitating the calcium
carbonate.
} Water should be boiled preferably in
the same container in which it is to be stored to avoid contamination during
storage. Water should be boiled for 20 minutes. The taste of water is altered
on boiling, but this is harmless.
CHEMICAL DISINFECTION-
} (1) Adding Bleaching powder: Bleaching
powder or chlorinated lime (Ca0Cl2 ) is a white amorphous powder with a pungent
smell of chlorine. It provides free chlorine when dissolved in water, this
chlorine kills pathogenic organisms present in water.
} Bleaching powder should be stored in
a dark, cool, dry place in a closed container that is resistant to corrosion.
The principle in chlorination is to ensure a "free“ residual chlorine of 0.5
mg/litre at the end of one hour contact.
} (2) Adding chlorine solution:
Chlorine solution is prepared from bleaching powder. If 4 kg of bleaching
powder with 25 per cent available chlorine is mixed with 20 litres of water, it
will give a 5 per cent solution of chlorine. Ready-made chlorine solutions in
different strengths are also available in the market.
} (3) High test hypochlorite: High test
hypochlorite (HTH) or perchloron is a calcium compound which contains 60 to 70
per cent available chlorine. It is more stable than bleaching powder and
deteriorates much less on storage.
} (4) Chlorine tablets : These tablets
are manufactured in various strengths and are now available in plenty, in the
Indian market at a cheap rate. A single tablet of 0.5 g is sufficient to
disinfect 20 litres of water.
} (5) Iodine : Iodine may be used for
emergency disinfection of water. Two drops of 2 per cent ethanol solution of
iodine will sufficient for one litre of clear water. A contact time of 20 to 30
minutes is needed for effective disinfection.
} (6) Potassium permanganate: Once
widely used in India but now it is no longer recommended for water
disinfection. Although a powerful oxidizing agent, it is not a satisfactory
agent for disinfecting water.
FILTRATION-
} Water can be purified on a small
scale by filtering through ceramic filters. The essential part of a filter is
the "candle" which is made of porcelain or infusorial earth.
} Mainly there are three types of
filter used for domestic purpose . These are Pasteur Chamberland filter,
Berkefeld filter and "Katadyn" filter. Pasteur chamberland filters
contains porcelin candle, berkefeld filters contains infusorial candles.
} In the Katadyn filter, the surface of
the filter is coated with a silver catalyst so that bacteria coming in contact
with the surface are killed by the "oligodynamic“ action of the silver
ions, which are liberated into the water.
} Filter candles of the fine type
usually remove bacteria found in drinking water, but not the filter-passing
viruses. Filter candles are logged with impurities and bacteria after some
time. They should be cleaned by scrubbing with a hard brush under running water
and boiled at least once a week.
} Nowadays more sophisticated RO
filters and UV filters are also available in the market for domestic use. These
fitlers are costly but very effective for water purification
DISINFECTION OF WELL-
} Wells are the main source of water
supply in the rural areas. Wells are disinfected time to time specially during
epidemics of cholera and gastroenteritis. The most effective and cheapest
method of disinfecting wells is by bleaching powder.
} For disinfecting wells is by
bleaching powder following steps are taken.
} 1. measure volume of water in the
well by this formula
VOLUME (LITERS ) = 3.14XD2XH/2X1000
depth of water column- (h) metre and diameter of well- (d) metre
} 2. calculate the amount of bleaching
powder required to disinfect the well. Normally 2.5 gm bleaching powder would
be required to disinfect 1,000 litres of water.
} 3. Dissolve required quantity of
bleeching powder in watar.
} 4. make thin paste of solution by
adding bleaching powder into one bucket
of and fill it with water.( fill only 3/4th )
} 5. stir well to make smooth thin
solution and keep it 10 minutes for sedimentation.
} 6. take supernatant solution into
another bucket and discard lime paste.
} 7. The bucket containing the chlorine
solution is lowered some distance below the water surface, and the well water
is agitated by moving the bucket violently both vertically and laterally to mix
chlorine solution with water.
} 8.
the water should be allowed to use for drinking only after one hour of
contact period.
} 9. it is a good practice to disinfect
ell at night and start using water next morning. It will allow sufficient
contact time.
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