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Water
1. The document discusses various aspects of water including its importance for health, definitions of safe water, water requirements, uses, sources, and purification. 2. Key sources of water discussed are rain, surface water sources like reservoirs and rivers, and groundwater sources like wells and springs. Surface water often requires treatment due to potential for contamination while groundwater is generally safer. 3. Water purification methods on a large scale discussed are storage, filtration using slow sand or rapid filters, and disinfection. Proper construction of sanitary wells and tanks can improve small scale water sources.
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Water
- 1.
- 2. In 1981, the34th World Health Assembly in a resolution emphasized that safe drinking water is a basic element of "primary health care" which is the key to the attainment of "Health for All by the year 2000 AD". Water is integrated with other PHC components because it is an essential part of health education, food and nutrition, and also MCH
- 3. Safe and wholesomewater This has been defined as water that is a) free from pathogenic agents b) free from harmful chemical substances c) pleasant to the taste, i.e., free from colour and odour; d) usable for domestic purposes. Water is said to be polluted or contaminated when it does not fulfil the above criteria.
- 4. Water requirement Physiological requirementsfor drinking water have been estimated at about 2 litres per head per day (just for survival). A daily supply of 150-200 litres per capita is considered as an adequate supply to meet the needs for all urban domestic purposes. In India 40 litres of water supply per capita per day was the set target.
- 5. Uses of water (1)Domestic use : on domestic front, water is required for drinking, cooking, washing and bathing, flushing of toilets, gardening etc. (2) Public purposes : cleaning streets, recreational purposes like swimming pools, public fountains and ornamental ponds, fire protection and public parks. (3) Industrial purposes : for processing and cooling;
- 6. Uses of water (4)Agricultural purpose : irrigation (5) Power production from hydropower and steam power; (6) Carrying away waste from all manner of establishments and institutions.
- 7. Sources of watersupply In general, water sources must conform to two criteria : (a)the quantity must be sufficient to meet present and future requirement (b)the quality of water must be acceptable. There are three main sources of water
- 8. Sources of watersupply 1. RAIN 2. SURFACE WATER 3. GROUND WATER Impounding reservoirs Rivers and streams Tanks, ponds and lakes Shallow wells Deep wells Springs
- 9. Rain Rain is theprime source of all water. CHARACTERISTICS : Rain water is the purest water in nature. Physically, it . is clear, bright and sparkling. Chemically, it is very soft water containing only traces of dissolved solids and free from pathogenic agents.
- 10. Rain IMPURITIES : Rainwater tends to become impure as it passes through. the atmosphere. It picks up suspended impurities from the atmosphere· such as dust, soot and microorganisms and gases such as carbon dioxide, nitrogen, oxygen and ammonia.
- 11. Surface water Surface wateroriginates from rain water. It is the main source of water supply in many areas. Surface water is prone to contamination from human and animal sources. As such it is never safe for human consumption unless subjected to sanitary protection and purification before use.
- 12. surface water sources (1)Impounding Reservoirs. (2) Rivers and Streams, (3) Tanks, Ponds and Lakes. In general, surface water supplies possess a high probability of organic, bacterial and viral contamination.
- 13. IMPOUNDING RESERVOIRS These areartificial lakes constructed usually of earthwork or masonry in which large quantities of surface water is stored. Dams built across rivers and mountain streams also provide large reserves of surface water. The area draining into the reservoir is called "Catchment area". One disadvantage of storing water for long periods in reservoirs is the growth of algae and other microscopic organisms, which impart bad tastes and odours to water.
- 15. IMPOUNDING RESERVOIRS CHARACTERISTICS :Impounding reservoirs usually furnish a fairly good quality of water. Water is usually clear, palatable and ranks next to rain water. The water is usually soft and considered to be free of pathogenic organisms. IMPURITIES : The upland surface water derives its impurities from the catchment area, the sources being human habitations and animal keeping or grazing.
- 16. RIVERS Many rivers furnisha dependable supply of water. The chief drawback of river water is that it is always grossly polluted and is quite unfit for drinking without treatment. CHARACTERISTICS : River water is turbid during rainy season; it may be clear in other seasons. The bacterial count, including the human intestinal organisms may be very high.
- 17. RIVERS IMPURITIES : Riversare described as a direct connection between the alimentary canal of the people living upstream and the mouths of those below. Impurities of river water are derived from surface washings, sewage and sullage water, industrial and trade wastes, and drainage from agricultural areas.
- 18. RIVERS SELF-PURIFICATION : Certainamount of self- purification does occur in river water by natural forces of purification such as dilution, sedimentation, aeration, oxidation, sunlight, plant and animal life but these agencies are not sufficient to render the water potable. River water needs purification before it can be used for drinking purposes.
- 20. TANKS Tanks are largeexcavations in which surface water is stored. They are an important source of water supply in some Indian villages. Tanks are recipients of contamination of all sorts. Tanks are often used for washing of clothes, cattle, humans, cooking pots and there may be regular defecation around the edges which will be washed into the tank. Tanks are thus subjected to unlimited possibilities of contamination and are highly dangerous, as a source of drinking water
- 22. Improvement of tanks Acertain amount of natural purification does take place in tank water because of storage, oxidation and other agencies. (1)The edges of the tank should be elevated in order to prevent the entry of surface washings, (2)There should be a fence around the tank to prevent access to animals (3)No one should be permitted to get into the tank directly.
- 23. Improvement of tanks 4)There should be an elevated platform from where people can draw water, 5) The weeds should be periodically removed, 6) The tank should be cleaned at the end of the dry season.
- 25. Sea water Though thissource is plentiful, it has great many limitations. It contains 3.5 per cent of salts in solution. Desalting and demineralization process involves heavy expenditure. It is adopted in places where sea water is the only source available.
- 26. Ground water Rain waterpercolating into ground constitutes ground water. The advantages of groundwater are: (1) it is likely to be free from pathogenic agents, (2) it usually requires no treatment, (3) the supply is likely to be certain even during dry season. (4) It is less subject to contamination than surface water.
- 27. Ground water The disadvantagesare: (1) it is high in mineral content, e.g., salts of calcium and magnesium which render the water hard (2) it requires pumping or some arrangement to lift the water
- 28. WELLS Wells have beenclassified into shallow and deep wells, dug and tube wells. (1) Shallow wells : Shallow wells tap subsoil water i.e. the water from above the first impervious layer in the ground. (2) Deep wells: A deep well is one which taps water from the water-bearing stratum below the first impervious layer in the ground.
- 30.
- 31. WELLS Most of thewells in India are of the shallow type. Shallow wells are liable to pollution from neighbouring sources of contamination such as latrines, urinals, drains, cesspools, soakage pits etc. They are therefore a health hazard to the community if they are not made sanitary. A deep well can also become a health hazard if it is open, poorly constructed and not protected against contamination.
- 32. WELLS Wells may alsobe classified, according to the method of construction, into Dug wells and Tube wells. DUG WELLS They are the commonest type in India. Two types of dug wells exist in our rural areas: (a) the unlined Katcha well and (b) the Masonry or Pucca well.
- 33.
- 34. Masonry or Puccawell
- 35. STEP WELLS They area kind of pucca wells. There is considerable personal contact between theuser and the water. Some may even wash their faces, hands and feet Guineaworm disease is quite a public health problem in areas where step wells are in use. The open dug wells and step wells are a health hazard to the community.
- 37. SANITARY WELL One whichis properly located, well constructed and protected against contamination with a view to yield a supply of safe water
- 38.
- 39. (1) LOCATION The wellshould be located not less than 15 m (50 feet) from likely sources of contamination. Should be located at a higher elevation with respect to a possible source of contamination. The well should be so located that no user will have to carry water for more than 100m.
- 40. (2) LINING The liningof the well should be built of bricks or stones set in cement up to a depth of at least 6 m (20 feet) so that water enters from the bottom and not from the sides of the well. The lining should be carried 60-90 cm (2-3 feet) above the ground level.
- 41. (3) PARAPET WALL Thereshould be a parapet wall up to a height of at least 70-75 cms (28 inches) above the ground. (4) PLATFORM There should be a cement-concrete platform round the well extending at least 1 m (3 feet) in all directions. The platform should have gentle slope outwards towards a drain built along its edges.
- 42. (5) DRAIN There shouldbe a pucca drain to carry off spilled water to a public drain or a soakage pit constructed beyond the "cone of filtration" (area of drainage) of the well. (6) COVERING The top of the well should be closed by a cement concrete cover because the bulk of the pollution is introduced into the well directly through the open top. Open wells cannot be considered sanitary
- 43. (7) HAND-PUMP The wellshould be equipped with a hand-pump for lifting the water in a sanitary manner. The handpump should be of robust construction to withstand rough handling by the people.
- 44. Sanitary wells doesnot guarantee freedom from waterborne diseases unless the consumers observe certain basic precautions at the individual and family level. cleanliness should be enforced in the vicinity of the well. (8) CONSUMER RESPONSIBILITY
- 45. (8) CONSUMER RESPONSIBILITY Washingof clothes and animals, and the dumping of refuse and wastes should be prohibited. Ropes and buckets from individual homes should not be used. Water from the well should be carried in clean sanitary vessels to individual houses.
- 46. (9) QUALITY The physical,chemical and bacteriological quality of water should conform to the acceptable standards of quality of safe and wholesome water.
- 47. TUBE WELLS water whichis bacteriologically safe, and are also cheap in comparison to other sources of supply. The area within 15 m of the tube well should be kept free from pollution. An average well may last for a period of 5 to 10 years.
- 48. SPRINGS When ground water comesto the surface and flows freely under natural pressure, it is called a "spring". Two types- Shallow springs and Deep springs.
- 49.
- 50. WATER POLLUTION Natural andman made impurities A more serious aspect of water pollution is that caused by human activity - Urbanization and Industrialization.
- 51. The sources ofpollution resulting from these are : (a) Sewage: which contains decomposable organic matter and pathogenic agents. (b) Industrial and trade wastes: which contain toxic agents ranging from metal salts to complex synthetic organic chemicals.
- 52. (c) Agricultural pollutants:which comprise fertilizers and pesticides. (d) Physical pollutants: viz heat (thermal pollution) and radioactive substances. Indicators of water pollution includes the amount of total suspended solids, BOD @ 20ºC, concentration of chlorides, nitrogen & phosphorus & absence of oxygen.
- 53. Water Related diseases A. Biological (Water-borne diseases) 1. Those caused by the presence of an infective agent : (a) Viral : Viral hepatitis A, hepatitis E, poliomyelitis, rotavirus, diarrhoea in infants (b) Bacterial : Typhoid and Paratyphoid fever, Bacillary dysentery, Esch. coli diarrhoea, cholera (c) Protozoal : Amoebiasis, giardiasis (d) Helminthic : Roundworm, threadworm, hydatid disease. (e) Leptospiral : Weil's disease
- 54. 2. Those dueto the presence of an aquatic host : (a) Snail : schistosomiasis (b) Cyclops : Guinea worm, fish tape worm.
- 55. B. Chemical -industrial and agricultural wastes These pollutants include detergent solvents, cyanides, heavy metals, minerals and organic acids, nitrogenous substances, bleaching agents, dyes, pigments, sulphides, ammonia, toxic and biocidal organic compounds. Biomagnification of toxins in food chain. Microplastics !
- 56. Purification Of Water 1.Purification of water on a large scale. 2. Purification of water on a small scale.
- 57. Purification of wateron a large scale I. Storage. II. Filtration. III. Disinfection
- 58. 1. STORAGE Natural purification (a)Physical : By mere storage, the quality of water improves. About 90 per cent of the suspended impurities settle down in 24 hours by gravity. The water becomes clearer. This allows penetration of light, and reduces the work of the filters. (b) Chemical : Certain chemical changes also take place during storage. The aerobic bacteria oxidize the organic matter present in the water with the aid of dissolved oxygen. As a result, the content of free ammonia is reduced and a rise in nitrates occurs.
- 59. (c) Biological: A tremendous drop takes place in bacterial count during storage. The pathogenic organisms gradually die out. It is found that when river water is stored the total bacterial count drops by as much as 90 per cent in the first 5-7 days. 1. STORAGE
- 60. 2. Filtration 98-99 percent of the bacteria are removed by filtration, apart from other impurities. Two types of filters are in use – 1. Biological or slow sand filters. 2. Mechanical or Rapid sand filters.
- 61. SLOW SAND ORBIOLOGICAL FILTERS 1. Supernatant (raw) water 2. A bed of graded sand 3. An under-drainage system 4. A system of filter control valves.
- 63. Supernatant water The supernatantwater above the sand bed, whose depth varies from 1 to 1.5M, serves two important purposes : It provides a constant head of water so as to overcome the resistance of the filter bed and thereby promote the downward flow of water through the sand bed.
- 64. Supernatant water It provideswaiting period of some hours (3 to 12 hours, depending upon the filtration velocity) for the raw water to undergo partial purification by sedimentation, oxidation and particle agglomeration.
- 65. The most importantpart of the filter is the sand bed. Thickness of the sand bed -1 metre Sand grains "effective diameter" between 0.2 and 0.3 mm. Sand bed
- 66. The sand shouldbe clean and free from clay and organic matter. The sand bed is supported by a layer of graded gravel 30-40 cm deep which also prevents the fine grains being carried into the drainage pipes. Sand bed
- 68. Water percolates throughthe sand bed very slowly (a process taking two hours or more), and it is subjected to a number of purification processes. mechanical straining, sedimentation, adsorption, oxidation and bacterial action, all playing their part. 0.1&0.4 𝑀3 /hour/𝑀2 of sand bed.(100- 400L).
- 69. Vital layer :When the filter is newly laid, it acts merely as a mechanical strainer, and cannot truly be considered as "biological". But very soon, the surface of the sand bed gets covered with a slimy growth known as "Schmutzdecke", vital layer, zoogleal layer or biological layer. This layer is slimy and gelatinous and consists of thread like algae and numerous forms of life including plankton, diatoms and bacteria. The formation of vital layer is known as "ripening“ of the filter.
- 70. It may takeseveral days for the vital layer to form fully, and when fully formed it extends for 2 to 3 cm into the top portion of the sand bed. The vital layer is the "heart" of the slow sand filter. It removes organic matter, holds back bacteria and oxidizes ammoniacal nitrogen into nitrates and helps in yielding a bacteria-free water. Until the vital layer is fully formed, the first few days filtrate is usually run to waste.
- 71. It consists ofporous or perforated pipes which serve the dual purpose of providing an outlet for filtered water, and supporting the filter medium above. Once the filter bed has been laid, the under-drainage system cannot be seen. Under-drainage system
- 72. Filter box :The first 3 elements (ie.supernatant water, sand bed and under- drainage system) are contained in the filter box. The filter box is an open box, usually rectangular in shape, from 2.5 to 4 metres deep and is built wholly or partly below ground. The walls may be made of stone, brick or cement.
- 73. The filter boxconsists from top to bottom : Supernatant water 1 to 1.5 metre Sand bed 1.2 metre Gravel support 0.30 metre Filter bottom 0.16 metre
- 74. The filter isequipped with certain valves and devices which are incorporated in the outlet- pipe system. The purpose of these devices is to maintain a constant rate of filtration. Filter control
- 75. An important componentof the regulation system is the "Venturi meter" which measures the bed resistance or "loss of head". When the resistance builds up, the operator opens the regulating valve so as to maintain a steady rate of filtration. When the "loss of head" exceeds 1.3 metre it is uneconomical to run the filter.
- 76. Filter cleaning Normally thefilter may run for weeks or even months without cleaning. When the bed resistance increases to such an extent that the regulating valve has to be kept fully open, it is time to clean the filter bed, since any further increase in resistance is bound to reduce the filtration rate. At this stage………….
- 77. The supernatant wateris drained off, and the sand bed is cleaned by "scraping" off the top portion of the sand layer to a depth of 1 or 2 cm.
- 78. This operation maybe carried out by unskilled labourers using hand tools or by mechanical equipment. After several years of operation, and 20 or 30 scrapings, the thickness of the sand bed will have reduced to about 0.5 to 0.8 metre. Then the plant is closed down and a new bed is constructed.
- 79. Advantages of SlowSand Filter 1. Simple to construct and operate. 2. The cost of construction is cheaper than that of rapid sand filters. 3. The physical, chemical and bacteriological quality of filtered water is very high. When working ideally, slow sand filters have been shown to reduce total bacterial counts by 99.9 to 99.99 per cent and E. coli by 99 to 99. 9 per cent.
- 80. RAPID SAND FILTER Rapidsand filters are of two types, 1. The gravity type (e.g. Paterson's filter) 2. The pressure type (e.g. Candy's filter). Both the types are in use.
- 82. Coagulation The rawwater is first treated with a chemical coagulant such as alum, the dose of which varies from 5 to 40 mg or more per liter, depending upon the turbidity and colour, temperature and the pH value of the water.
- 83. Rapid mixing The treatedwater is then subjected to violent agitation in a "mixing chamber" for a few minutes. This allows a quick and thorough dissemination of alum throughout the bulk of the water, which is very necessary.
- 85. Flocculation The next phaseinvolves a slow and gentle stirring of the treated water in a "flocculation chamber" for about 30 minutes. The mechanical type of flocculator is the most widely used.
- 86. It consists ofa number of paddles which rotate at 2 to 4 rpm. The paddles rotate with the help of motors. This slow and gentle stirring results in the formation of a thick, copious, white flocculant precipitate of aluminium hydroxide. The thicker the precipitate or flock diameter, the greater the settling velocity. Flocculation
- 88. Sedimentation The coagulated wateris now led into sedimentation tanks where it is detained for periods varying from 2-6 hours when the flocculent precipitate together with impurities and bacteria settle down in the tank. At least 95 per cent of the flocculant precipitate needs to be removed before the water is admitted into the rapid sand filters.
- 89. The precipitate orsludge which settles at the bottom is removed from time to time without disturbing the operation of the tank. For proper maintenance, the tanks should be cleaned. regularly from time to time, otherwise they may become a breeding ground for molluscs and sponges. Sedimentation
- 90. Filtration The partly clarified water isnow subjected to rapid sand filtration.
- 92. FILTER BEDS Each unitof Filter bed has a surface of about 80 to 90 𝑀2 (about 900 sq. feet). Sand is the filtering medium. The "effective size" of the sand particles is between 0.4-0. 7 mm. The depth of the sand bed is usually about 1 metre (2.5 to 3 feet).
- 93. Below the sandbed is a layer of graded gravel, 36 to 40 cm. (1-1.5feet) deep. The gravel supports the sand bed and permits the filtered water to move freely towards the under-drains. The depth of the water on the top of the sand bed is 1.0 to 1.5 m (5-6 feet). The under-drains at the bottom of the filter beds collect the filtered water. The rate of filtration is 5- 15 𝑀3 / 𝑀2 /hour. (5000L)
- 94. Filtration As filtration proceeds,the "alum-floc" not removed by sedimentation is held back on the sand bed. It forms a slimy layer comparable to the zoogleal layer in the· slow sand filters. It adsorbs bacteria from the water and effects purification. Oxidation of ammonia also takes place during the passage of water through the filters.
- 95. As filtration proceeds,the suspended impurities and bacteria clog the filters. The filters soon become dirty and begin to lose their efficiency. When the "loss of head" approaches 7-8 feet, filtration is stopped and the filters are subjected to a washing process known as "backwashing.
- 96. Backwashing Rapid sand filtersneed frequent washing daily or weekly, depending upon the loss of head. Washing is accomplished by reversing the flow of water through the sand bed, which is called "backwashing". Backwashing dislodges the impurities and cleans up the sand bed.
- 97. The washing isstopped when clear sand is visible and the wash water is sufficiently clear. The whole process of washing takes about 15 minutes. In some rapid sand filters, compressed air is used as part of the backwashing processes. Backwashing
- 99. ADVANTAGES 1. Rapid sandfilter can deal with raw water directly. No preliminary storage is needed 2. The filter beds occupy less space 3. Filtration is rapid, 40-50 times that of a slow sand filter 4. The washing of the filter is easy. 5. There is more flexibility in operation.
- 101. DISINFECTION Capable of destroyingthe pathogenic organisms present, within the contact time available and not unduly influenced by the range of physical and chemical properties of water encountered particularly temperature, pH and mineral constituents; Should not leave products of reaction which render the water toxic or impart colour or otherwise make it unpotable.
- 102. CHLORINATION Chlorine kills pathogenicbacteria, but is has no effect on spores and certain viruses (e.g., polio, viral hepatitis) except in high doses. Apart from its germicidal effect, chlorine has several important secondary properties of value in water treatment : it oxidizes iron, manganese and hydrogen sulphide; it destroys some taste and odour producing constituents; it controls algae and slime organisms; and aids coagulation.
- 103. Action of chlorine When chlorine is added to water, there is formation of hydrochloric and hypochlorous acids. The hydrochloric acid is neutralized by the alkalinity of the water. The hypochlorous acid ionizes to form hydrogen ions and hypochlorite ions, as follows :- H2O + Cl2 HCl + HOCl HOCl H + OCl
- 104. The disinfecting actionof chlorine is mainly due to the hypochlorous acid, and to a small extent due to the hypochlorite ions. The hypochlorous acid (HClO) is the most effective form of chlorine for water disinfection. It is more effective (70-80 times) than the hypochlorite ion.
- 105. Principles of chlorination Waterto be chlorinated should be clear and free from turbidity. Estimate the chlorine demand of water The contact period - The presence of free residual chlorine for a contact period of at least one hour is essential to kill bacteria and viruses
- 106. The minimum recommendedconcentration of free chlorine is 0.5 mg/L for one hour. The free residual chlorine provides a margin of safety against subsequent microbial contamination such as may occur during storage and distribution. The sum of the chlorine demand of the specific water plus the free residual chlorine of 0.5 mg/L constitutes the correct dose of chlorine to be applied.
- 107. CHLORINE DEMAND "Thechlorine demand of water is the difference between the amount of chlorine added to the water, and the amount of residual chlorine remaining at the end of a specific period of contact (usually 60 minutes), at a given temperature and pH of the water". In other words, it is the amount of chlorine that is needed to destroy bacteria, and to oxidize all the organic matter and ammoniacal substances present in the water. The point at which the chlorine demand of the water is met is called the "break-point"
- 108. METHODS OF CHLORINATION Fordisinfecting large bodies of water, chlorine is applied either as 1. chlorine gas 2. chloramine 3. perchloron.
- 109. CHLORINE GAS Chlorinegas is the first choice, because it is cheap, quick in action, efficient and easy to apply. Since chlorine gas is an irritant to the eyes and poisonous, a special equipment known as "chlorinating equipment" is required to apply chlorine gas to water supplies. Paterson's chloronome is one such device for measuring, regulating and administering gaseous chlorine to water supplies.
- 110. CHLORAMINES Chloramines are loosecompounds of chlorine and ammonia. They have a less tendency to produce chlorinous tastes and give a more persistent type of residual chlorine. The greatest drawback of chloramines is that they have a slower action than chlorine and therefore they are not being used to any great extent in water treatment.
- 111. Perchloron or hightest hypochlorite (H.T.H.) Perchloron or high test hypochlorite (H.T.H.) is a calcium compound which carries 60-70 per cent of available chlorine. Solutions prepared from H.T.H. are also used for water disinfection.
- 112. PURIFICATION OF WATERON A SMALL SCALE Household purification of water – BOILING CHEMICAL DISINFECTION Bleaching powder Chlorine solution High test hypochlorite Chlorine tablets Iodine Potassium permanganate
- 113. FILTRATION -Water can be purified on a small scale by filtering through ceramic filters such as Pasteur Chamberland filter, Berkefeld filter and "Katadyn" filter. ULTRAVIOLET IRRADIATION - exposure of a film of water, upto about 120 mm thick, to one or several quartz mercury vapour arc lamps emitting ultraviolet radiation at a wavelength of 254 (Nano- metre). Disinfection of wells – The most effective and cheapest method of disinfecting wells is by bleaching powder.
- 114. HARDNESS Hardness may bedefined as the soap destroying power of water. The hardness in water is caused mainly by four dissolved compounds. These are 1. Calcium bicarbonate 2. Magnesium bicarbonate 3. Calcium sulphate, and 4. Magnesium sulphate.
- 115. types Temporary hardness -due to the presence of calcium and magnesium bicarbonates. Permanent hardness - due to calcium and magnesium sulphates, chlorides and nitrates.
- 116. Hardness in wateris expressed in terms of "milliequivalents per litre (mEq/L)". Drinking water should be moderately hard. Softening of water is recommended when the hardness exceeds 3 mEq/l (150 mg per litre).
- 117. DISADVANTAGES OF HARDNESS 1.Hardness inwater consumes more soap and detergents. 2.When hard water is heated, the carbonates are precipitated and bring about furring or scaling of boilers. This leads to great fuel consumption, loss of efficiency and may sometimes cause boiler explosions.
- 118. 3. Hard wateradversely affects cooking; food cooked in soft water retains its natural colour and appearance. 4. Fabrics washed with soap in hard water do not have a long life. 5. There are many industrial processes in which hard water is unsuited and gives rise to economic losses. 6. Hardness shortens the life of pipes and fixtures.
- 119. Removal of hardness Temporaryhardness (a) Boiling (b) Addition of lime (c) Addition of sodium carbonate (d) Permutit process. Permanent hardness (a) Addition of sodium carbonate (b) Base exchange process.
- 120. BOILING Boiling removes thetemporary hardness by expelling carbon dioxide, and precipitating the insoluble calcium carbonate. It is an expensive method to soften water on a large scale. Ca(HC03)2 -- CaC03 + H2O + C02
- 121. ADDITION OF LIME Lime absorbs the carbon dioxide, and precipitates the insoluble calcium carbonate. Ca (OH)2 + Ca(HC03) 2 2CaC03 + 2H2O
- 122. ADDITION OF SODIUM CARBONATE Sodium carbonate (soda ash) removes both temporary and permanent hardness, (i) Na2 C03 + Ca(HC03)2 2NaHC03 + CaC03 (ii) CaS04 + Na2 C03 CaC03 + Na2 S04
- 123. BASE EXCHANGE PROCESS Inthe treatment of large water supplies, the permutit process is used. Sodium permutit is a complex compound of sodium, aluminium and siilica (Na2 Al2 Si20 H20). It has the property of exchanging the sodium cation for the calcium and magnesium ions in the water.
- 124. When hardwater is passed through the permutit the calcium and magnesium ions are entirely removed by base exchange and the sodium permutit is finally converted into calcium and magnesium permutit. By this process, water can be softened to zero hardness. Permutit process removes both temporary and permanent hardness.
- 125.
- 126. TYPES Susrutha – Antharikshajala / rain water Bhauma jala/ ground water Antariksh jala – 4 Dhara – falling Kara – water from hailstones Taushara – water from dew Haima – water from melting of snow
- 127. Divya Jala There aredifferent types of water mentioned, but Charakacharya considers only one type of Jala; which falls from sky in the form of rain. Such water in the form of rain is known as Divya Jala and it is Sheeta, clean, sacred, devoid of impurities. तत् पतत् पतततं चैव देशकालावपेक्षते|| शीतं शुतच तशवं मृ ंं तवमलं लघु षड्गुणम्| प्रकृत्या तदव्यमुदकं ,...(C.S.S.27/198)
Editor's Notes
- #59 The optimum period of storage of river water is considered to be about 10-14 days. If the water is stored for long periods, there is likelihood of development of vegetable growths such as algae which impart a bad smell and colour to water.
- #72 At the bottom of the filter bed is the under-drainage system.