Environmental Health

1. Environmental Health KEMU 2014

2. Water • A necessity for life. • Without water, human body dehydrates and the physiological processes become severely impaired leading to death • 3\4 earth is covered with water. Amount of water is fixed about 1500 million/km3. • Uses: water is used domestically, for agricultural purposes( about 70% of the total world use of fresh water), industry (23%) and municipal use. • Types of Water: • - Potable Water: water which can be used for drinking purposes is called potable water. • - Clean Water: one which is free from contamination and safe for human consumption as determined by laboratory analysis, sanitary survey, and continued use.

3. - Polluted water: water which has suffered impairment of physical qualities through addition of substances causing turbidity and producing color , odor or taste. • - Contaminated water: which may carry infection due to addition of human or animal waste or which has been rendered unwholesome by hazardous chemical compounds. • Sources of Water: 3 major sources of water. • - Rain Water: normally the purest form of water as it is ‘distilled water'. It receives impurities the moment it condenses. The softness of rain water makes it useful in washing and absence of lime salts makes it desirable for cooking.

4. - Surface Water: includes rivers, creeks, and smaller streams, lakes ponds and man made impounding reservoirs. Composition is highly variable depending upon the characteristics of the catchment basin. Surface waters are directly exposed to pollution by surface wash and waste. Because of large yield of surface sources , most large cities depend on them for water. • - Ground Water: rainwater percolating through the ground constitutes ground water. As water percolates through the underlying subsoil and rocks to various depths below the surface, it reaches a stratum which does not permit it to go further called the ‘impervious stratum’. Above this is a stratum of soil which is saturated with water called the zone of saturation. l water it holds is called ground water. And the upper surface of subsoil water is called ‘water table’.

5. Water, as it percolates through the soil is subjected to a natural process of purification and bacteria and particulate matter are filtered out to a degree. Generally the greater the distance water travels through the soil the greater the reduction in bacterial count. • Ground Water can be accessed through natural springs, horizontal wells or infiltration galleries • - Springs: the natural outflow of subsurface or ground water at the earths surface is called a spring. These are formed in following cases • - when the pervious layer lies between two impervious layers • - in case there is a sudden steep slope below the normal water table • - if water is collected in the subsoil due to presence of an impervious strata. • types of springs are gravity springs, which may be shallow. Deep or artesian springs ( mineral content is high, quality of water is good and can be used for drinking without treatment), springs due to a fault in a rock and thermal springs.

6. Wells: wells are classified according to nature of aquifer tapped, method of construction or by flow conditions • - Shallow well: this taps water from above the upper strata. Quantity of water varies through out the year and they generally dry up in summers. Quality is not good as water likely to be contaminated . • - Deep Wells: is constructed by tapping an aquifer which lies below the impervious layer. Quantity is large and no quick fluctuations in water levels. • - 2. Method of Construction: • - a. open or dug wells: tap the subsoil water table, maybe dug up to 30 m or more below the ground depending upon the uppermost impervious layer of earth

7. -b. Driven Well: is one in which a casing pipe is driven into the ground by means of a hammer or water jet. These wells are also called percussion wells. Quantity of water obtained is small , quality however is good and water can be utilized for domestic purposes. • - c. Tube Well: this is a tube or pipe fitted at the bottom with a filter and sunk into the ground to tap underground water is known as a tube well. • - d. Artesian Wells: when a hole is dug out or drilled in the middle of an aquifer enclosed between two impervious strata, water comes out in the form of a fountain under great pressure.

8. Sanitary Well • wells are the commonest source of water in rural areas so it is important to know the sanitary measures which may be taken to make the well water safe. • A sanitary well is one which is so located and built as to provide adequate protection from contamination and pollution. There are many ways by which a well may be contaminated • By Surface Water: this may be washed straight down the mouth of the well if the ground surface around the well has sunk. Can be prevented by building a headwall 0r parapet about 1 meter high with cement lining on both sides and sloping outwards on the top. • Seepage Water from Surface: this is usually through the top few meters of the well lining. Well lining should be made waterproof for the top 3 meters

9. Vessel used for drawing water: preferable to use a pump of some kind. • Polluted Ground Water: this can happen if the location of the well is too close to pit latrines or refuse dumps. There should be no source of pollution in the cone of filtration of a well. • Cone of Filtration: of a well is the name of the area drained by a well and is an imaginary inverted cone with the apex in the center of the well and a radius of at least four times the depth of the well. • Quantity of Water in a well: usually needed when a well has to be disinfected. Formula to calculate is : • Quantity in liters = sq. of diameter of well in meters * depth of water in meters * 800

10. Water Pollution • Water is never ‘pure’ in a chemical sense. Contains dissolved and suspended impurities. These comprise: • Dissolved Gases: eg. Hydrogen sulfide, carbon dioxide, ammonia , nitrogen • Dissolved Minerals: eg. Salts of calcium, magnesium, sodium • Suspended impurities: eg. Clay, silt, sand , mud • Microscopic plants and animals

11. More serious aspect of pollution is caused by human activity-urbanization and industrialization. Sources of pollution resulting from these are: • Sewage: containing decomposable organic matter and pathogenic agents • Industrial and Trade Wastes: containing toxic agents ranging from metal salts to complex synthetic organic chemicals • agricultural pollutants : comprising fertilizers and pesticides • Physical pollutants: heat and radioactive substances

12. Hazards of Water Pollution • Hazards may be classified into two broad groups: • Biological Hazards: these comprise the classical ‘water borne diseases’ by the presence of an infective agent or an aquatic host in water. • Those caused by presence of an infective agent: • Viral: viral hepatitis, poliomyelitis • Bacterial: cholera, typhoid, para typhoid, bacillary dysentry, Esch. Coli diarhhoea, Rota virus diarrhoea in infants • Protozoal:amoebiasis, giardiasis • Helminthic: round worm,whip worm, threadworm, hydatid disease • leptospiral: Weil’s disease

13. Those due to the presence of an aquatic host • Cyclops: guinea worm , fish tape worm • Snail: Schistosomiasis • Chemical Hazards: chemical pollutants from industrial and agricultural wastes are increasingly finding their way into public water supplies. These include: detergent solvents, cyanides, heavy metals, minerals and organic acids, nitrogenous substances, bleaching agents, dyes, pigments, sulfides, ammonia and other organic compounds.

14. Hardness of Water • Hardness may be defined as the ‘soap-destroying’ power of water. Water is considered hard if large quantities of soap are required to produce lather. The hardness in water is caused mainly by four dissolved compounds: • Calcium Bicarbonate • Magnesium Bicarbonate • Calcium Sulphate • Magnesium Sulphate Hardness is classified as carbonate and non carbonate. Carbonate Hardness is also termed ‘temporary’ and is due to the presence of Calcium and magnesium bicarbonates.

15. The ‘non-carbonate’ hardness also termed as ‘permanent’ hardness is due to calcium and magnesium sulphates, chlorides and nitrates. • Hardness is expressed in terms of ‘milli equivalents per liter. 1 mEq/l of hardness producing ion is equal to 50 mg CaCO3 in one liter of water. • Disadvantages of Hardness: • Hardness in Water consumes more soap and detergents • When hard water is heated , the carbonates are precipitated and bring about furring or scaling of boilers • adversely effects cooking. Food cooked in soft water retains its natural colour and appearance.

16. Fabrics washed in hard water do not have a long life • Hardness shortens the life of pipes and fixtures Removal of Hardness: • Temporary Hardness: removed by boiling, addition of lime, addition of sodium carbonate, permutit process • Permanent Hardness: removed by addition of sodium carbonate, base exchange method. • Boiling: removes temporary hardness by expelling carbon dioxide and precipitating the insoluble calcium carbonate. Is an expensive method to soften water on a large scale.

17. b) Addition of Lime: Lime absorbs the carbon dioxide and precipitates the insoluble calcium carbonate. In the ‘Clark’s Method’ , one ounce of quick lime is added to every 700 gallons of water for each degree of hardness. c) Addition of Sodium Carbonate: Sodium carbonate(soda ash) removes both temporary and permanent hardness d) Base Exchange Process: In the treatment of large supplies, the permutit process is used. Sodium Permutit is a complex compound of sodium, aluminium and silica. It has the property of exchanging the sodium cat ion for the calcium and magnesium ions in the water. By this process , water can be softened to zero hardness. After permutit has been used for sometime , it loses its effectiveness but may be regenerated by treating with conc. Solution of NaCl and MgCl is formed.

18. Purification of Water • Large scale water supplies are derived either from deep wells or surface water. Deep wells are usually satisfactory while surface waters are generally contaminated and require some form of purification to render them safe for domestic use • Public water supply Is one which supplies water to 25 0r more families. • Methods of purification in common use are storage, flocculation and coagulation, sedimentation, filtration and chlorination. This treatment removes color, turbidity, micro organisms, colloidal particles and some dissolved substances. These conventional methods however donot remove dissolved synthetic organic materials. • 1. Storage: one of the best means of improving water quality. Cannot be relied upon as a soul measure of purification, it is valuable as a preliminary to other processes.

19. Storage reduces the bacterial content of water and also the suspended matter in it. Chemical changes assoc. with storage include a fall in free ammonia and rise in Nitrates because of the oxidizing action of aerobic bacteria upon organic matter. Growth of algae may result in change in taste and odor hence storage beyond 2 weeks is not recommended. Copper Sulphate may be added to stored water to control algae • 2) Sedimentation: storage for several days allows heavier particles to settle down but where storage capacity is limited or water contains finely suspended material , sedimentation may be hastened by addition of a chemical coagulant called Alum( Aluminum Sulphate) dose is 35 mg/liter to the water in a sedimentation tank and after a detention period of 4-6 hours , clarified water can be taken out. if the water becomes acidic lime must be added to it to neutralize it. Sedimentation is usually a preliminary to filtration and helps rapid clogging of filters

20. 3) Filtration: through sand is the oldest and most universally used method of purification. Two main types of filters are commonly in use: • - slow sand or biological filters using fine sand • - rapid sand or mechanical filters using coarse sand • Slow Sand or Biological Filters: First used for water treatment in 1804 in Scotland and subsequently in London. Generally accepted as the standard method of water purification. These consist of: • Supernatant /raw water • A bed of graded sand

21. C) an under drainage system • D) a system of filter control valves • Super natant Water: The supernatant water above the sand bed, whose depth varies from 1-1.5m, 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; and secondly , it provides a waiting period of some hrs. for the raw water to undergo partial purification by sedimentation , oxidation and particle agglomeration. The level of supernatant water is always kept constant.

22. b) SAND Bed: is the most important part of the filter. Its thickness is about 1.2 meters. The sand grain are carefully chosen and have a diameter bw 0.15- 0.35mm. The sand should be clan and free from clay and organic matter. The sand bed is supported by a layer of graded gravel which also prevents the fine grains being carried into the drainage pipes..Water percolates through the sand bed gradually and is subjected to a number of purification processes namely mechanical straining, sedimentation, adsorption, oxidation and bacterial action. Vital Layer: Soon the surface of the sand bed gets covered with a slimy growth known as ‘schmutzdecke’, vital layer or zoogleal/biological layer. This layer is slimy and gelatinous and consistes of threadlike algae and plankton, diatoms and bacteriae. The formation of the vital layer is called ‘ripening’ of the filter and takes few days for the vital layer to form fully and once formed it extends for2-3 cm into the top portion of the sand bed.it removes organic matter, holds back bacteria and oxidizes ammoniacal nitrogen into nitrates and yields bacteria free water.

23. c) Under-drainage system: is at the bottom of the filter bed. Consists of porous or perforated pipes which serve the dual purpose of providing an outlet for filtered water and supporting the filter medium above. Filter Box: the first 3 elements (the supernatant water, sand bed and under drainage system) are contained in the filter box. The filter box is an open box and rectangular in shape. d) Filter Control: The filter is equipped with certain valves and devices which are incorporated in the outlet pipe system. The purpose of these devices is to maintain a steady rate of filteration. The filter may run for weeks and 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. At this stage the supernatant water is drained off, and sand bed is cleaned by scaping off the top portion of the sand layer to a depth of 1-2 cm.

24. Advantages of Slow sand Filter are • Simple to construct and operate. • Cost of construction is cheaper than rapid sand filters • Physical, chemical and bacteriological quality of filtered water is very high • Reduce bacterial counts by 99.9%

25. Rapid Sand Filters: are of two types: Gravity type( Paterson’s filter) and pressure type( Candy’s filter) . Though initial cost is high, these occupy very little space and are cost effective in the long run. The following steps are involved in the purification of water by rapid sand filters: • Coagulation: when raw water is passed through this filter , it is subjected to coagulation. Alum is used in the dose of 5-40 mg/liter depending on turbidity and colour. The PH has to be adjusted by adding lime or soda ash. • Rapid Mixing: The treated water is subjected to rapid mixing in a mixing chamber for a few minutes.This allows a quick and thorough dissemination of alum throughout the water which is needed.

26. Flocculation: The next phase is a slow and gentle stirring of water in a flocculation chamber for about 30 minutes.the slow and gentle stirring results in the formation of a thick and copious white flocculant precipitate of aluminium hydroxide. • Sedimentation: The coagulated water is now led into sedimentation tanks where it is detained for 2-6 hrs when the flocculant precipitate together with impurities and bacteria settle down in the tank. The precipitate or sludge is removed from time to time without disturbing the operation of the tank.

27. Filteration: the partly clarified water is now subjected to rapid sand filteration. Filter Beds: The filter bed in rapid sand filter has coarser sand and the rate coffilteration is 5-15m3/m2/hr. As Filteration proceeds the alum-floc not removed by sedimentation is held back on the sand bed.it forms a slimy layer comparable to 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. As filteration proceeds the suspended impurities and bacteria clog the filters. When the ‘loss of head’ approaches 7-8 ft., filteration is stopped and the filters are subjected to a washing process known as ‘back-washing’.

28. Back-Washing: These filters require frequent washing daily or weekly. Washing is accomplished by reversing the flow of water through the sand bed which is called back washing. Backwashing dislodges the impurities and cleans up the sand bed. The washing is stopped when clear sand is visible and the wash water is sufficiently clear. The whole process takes about 15 minutes. • Advantages: the rapid sand filters can deal with raw water directly, no preliminary storage is required. The filter beds require less space. Filteration is rapid.Washing of filter is easy and there is more flexibility of operation.

29. Disinfection: Chlorination: In water works practice , the term disinfection is synonymous with chlorination. Chlorination is one of the greatest advances in water purification. Chlorine kills pathogenic bacteria. Apart from its germicidal effect, chlorine oxidizes iron, manganese and hydrogen sulphide, destroys some taste and odour producing constituents , controls algae and aids ccoagulation. Action of Chlorine: When chlorine is added to water , here is formation of hydrochloric and hypochloric acid. HCl is neutralized by alkalinity of water. The hypochlourous acid ionizes to form H and hypochlorite ion . Chlorine acts best as a disinfectant when the ph of water is around 7 because of the predominance of hypochlorous acid.

30. Principles of Chlorination: In order to ensure proper chlorination • The water should be clear and free from turbidity • Chlorine demand of water should be estimated. The ‘chlorine-demand’ of water is the difference between the amount of residual chlorine remaining at the end of a specific period of contact (about 60 mins) at a given temperature and ph of water. In other words it is the amount of chlorine that is required to destroy bacteria and oxidize all 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’. If further chlorine is added the break point free chlorine begins to appear in the water.

31. Method of Chlorination: For disinfecting large bodies of water, chlorine is applied either as chlorine gas, chloramine or perchloron. Chlorine gas is the first choice . Chloramines have a slower action and are loose compounds of chlorine and ammonia. Perchloron is a calcium compound which carries 60-70 % of available chlorine. • Break-point Chlorination: Addition of chlorine to water produces chloramines. If chlorine dose in water is increased, a reduction in residual chlorine occurs due to destruction of chloramines by added chlorine. This fall in residual chlorine will continue with further increase in chlorine dose and after a stage , the residual chlorine begins to increase in proportion to the added dos of chlorine. This point at which the residual chlorine appears and all combined chlorines are completely destroyed is the breakpoint. Break point chlorination achieves the same results

32. As super chlorination and therefore can be construed as controlled super chlorination. • Purification of water on a small scale: Three methods are generally available, which can be used singly or in combination a) Boiling: To be effective , water must be brought to a ‘rolling-boil’for 10-20 minutes. offers no residual protection against subsequent microbial contamination. b) Chemical Disinfection: 1) Bleaching Powder: bleaching powder or chlorinated lime ia a white amorphous powder with a pungent smell of chlorine. The principle in chlorination is to ensure a ‘free’ residual chlorine of 0.5 mg/l at the end of one hourcontact. 2) Chlorine Solution: may be prepared from bleaching powder. 3) High test hypochlorite: is a calcium compound which contains 60-70% available chlorine.it is more stable than bleaching powder.

33. 4) Chlorine Tablets: eg. Halazone tablets. Good for disinfecting small quantities of water but are costly. • 5) Iodine: may be used for emergency disinfection of water. Two drops of 2% ethanol solution of iodine will suffice for 1 liter of water. 20-30 minutes of contact time is required for effective disinfection. High costs and the fact that the element is physiologically active are its major disadvantages. • 6) Potassium Permanganate: a powerful oxidizing agent , it is not a satisfactory agent for disinfecting water. • C) Fiteration: water can be purified on a small scale by filtering through ceramic filters such as Pasteur chamber land filter. The essential part of the filter is a ‘candle’ made of porcelain.