Purification of water

Household purification of water

1. Boiling

2. Chemical disinfection

3. Filtration

Disinfection of wells

1. Steps in well disinfection

2. Double pot method

BoilingRolling boil for 5-10 minutes

Kills bacteria, spores, cysts and ova and yields sterilized water

Removes temporary hardness by driving off carbon dioxide and precipitating calcium carbonate

Taste is altered but is harmless

No residual protection

Same container should be used for storing to prevent residual contamination

Chemical disinfection

1. Bleaching Powder

2. Chlorine solution

3. High test hypochlorite

4. Chlorine tablets

5. Iodine

6. Potassium Permanganate

1.Bleaching powder (Chlorinated lime)

White amorphous powder with a pungent smell of chlorine

freshly made contains 33% 'available chlorine'

unstable on exposure to air, light and moisture rapidly loses its chlorine

mixed with excess of lime retains its strength - stabilized bleach

stored in dark, cool, dry place, closed container resistant to corrosion

chlorine contents of the stock should be frequently checked

principle in chlorination is to ensure a free residual chlorine of .5 mg/liter at the end of 1 hour of contact

2. Chlorine solutionprepared from bleaching powder

4 kg of bleaching powder with 25% available chlorine is mixed with 20 ltrs of water will give 5% solution of chlorine

readymade chlorine solutions with different strengths are also available in the market

is subject to loss of chlorine on exposure to light or on prolonged storage

the solution should be kept in dark, cool and dry place in a closed container

3. High test hypochlorite

perchloron is a calcium compound which contains 60-70% available chlorine

more stable than bleaching powder and deteriorates much less on storage

solutions prepared from HTH is also used for water disinfection

Chlorine tablets

trade names like halazone tablets

good for small quantities of water, but costly

National environmental engineering research institute, Nagpur formulated a new type of chlorine tablet 15 times better than ordinary one

plenty of them at various strengths are there in Indian Market at various rates

5. Iodine

emergency disinfection of water

2 drops of 2% ethanol solution for 1 liter of clear water - contact period of 20-30 min

iodine does not react with ammonia or organic compounds to any great extent

hence it remains in molecular form over a wide range of pH values and water conditions and persists longer than chlorine or bromine

iodine is unlikely to become a municipal water disinfectant

high costs and the fact that the element is physiologically active are the major disadvantages

6. Potassium permanganate

once widely used

now no longer recommended

powerful oxidizing agent but not a satisfactory agent for disinfection of water

it may kill cholera vibrios but not other bacteria

alters the color taste and smell of water

Filtration

Pasteur Chamberland filter - porcelain candle

Berkefield Filter- kieselgurh or infusorial earth candle

Katadyn Filter- surface coated with a silver catalyst, oligodynamic action of the silver ions which are liberated into the water

Filter candle removes the bacteriae but not the viruses

filter candles are liable to be logged with impurities and bacteriae

they should be cleaned by scrubbing with a hard brush under running water and boiled at least once a week

only clean water should be used with ceramic filters

although effective not suitable for widespread use under Indian conditions

Disinfection of wells - steps

find the volume of water in the well

find the amount of bleaching powder required

dissolve bleaching powder in water

delivery of chlorine solution into the well

contact period

orthotoluidine arsenite test

Find the volume of water in the well

measure the depth of water column... h mtr

measure the diameter of the well.......d mtr

take the average of above readings

substitute h and d in vol = 3.14 d2h x 1000

4

1 cubic meter = 1000 ltrs of water

Find the amount of bleaching powder required

estimate the chlorine demand of well water by Horrock's apparatus and calculate the amount of bleaching powder required to disinfect the well

roughly 2.5 gms is required to disinfect 1000 ltrs of water

this gives approximate dose of 0.7 mg applied chlorine per liter of water

Dissolve bleaching powder bleaching powder required is taken in one bucket ( not more than 100 gms in one bucket) and made into a thin paste

more water is added till the bucket is 3/4 th full

contents are stirred and allowed to sediment for 5-10 minutes when the lime settles down

the supernatant solution is transferred to another bucket and the chalk or lime is discarded

Delivery of chlorine solution into the well

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

this should be done several times

Contact period

Contact period of 1 hour is allowed before the water is drawn for use

Orthotoluidine arsenite test

if free residual chlorine is less than 0.5 mg/ liter the chlorination procedure is repeated

wells are best disinfected at night after the day's draw off

during epidemics of cholera wells are disinfected every day

The double pot method

to ensure a constant dosage of chlorine to well water during emergencies

Devised by National Environmental Engineering and Research Institute, Nagpur

Method uses 2 cylindrical pots one inside the other

for the outer pot inside height and diameter are 30 cm and 25 cm respectively

a hole 1cm in diameter is made in each pot

outer pot it is 4 cm above the bottom

a mixture of 1 kg of bleaching powder and 2kg of coarse sand ( approx 2mm. in diameter) is prepared and slightly moistened with water

the inner pot is introduced into the outer one and the mouth of the latter closed with polythene foil

the use of 2 pots makes it possible to have larger holes without the risk of over chlorination

the double pot is lowered into the well by means of a rope attached to the well kerb

the pot should be immersed at least 1m below the water level to prevent damage by the buckets

device works for 2-3 weeks in a small household wells containing about 4500 liters of water having a draw off rate of 360-450 liters /day

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