Purification Of Water Small Scale

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

Boiling Rolling 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. 2. 3. 4. 5. 6.

Bleaching Powder Chlorine solution High test hypochlorite Chlorine tablets Iodine 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 solution prepared 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

THANK YOU