Water Purification

Water Purification

Water purification

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Water Purification

S.No.

Contents

Page No.

1

Introduction

3-5

2

Sources of drinking water

5-7

3

Water pollution and its sources

8-12

4

Micro-organisms causing water pollution

13-16

5

History and trends in water filtration

17-19

6

WHO Guidelines for drinking water quality

20-35

7

Comparison of filter types

36

8

Choice of treatment process

37-38

9

Purification of drinking water

39-76

10

Purification of water in rural areas

77-79

11

Hous Houseehold hold purif urific icaation tion of water ater duri durin ng emerg mergen enci ciees and disasters

80-83

12

Rehabilitating treatment works after an emergency

84-89

13

Newer techniques for purification of water

90-94

14

Various water supply prog rogramm rammees and projects in rural ral areas

95-107

15

Review of literature

108-117

16

Summary

118-119

17

Bibliography

120-26

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Water Purification

“Water can be without the company of o f humans but we as humans can only be without water for a few days”.

1. Introduction Water is that chemical substance which is essential for every living organism to survive on this planet. Water is needed by every cell of the organism’s body to perform normal function. In typical usage, water refers only to its liquid form or state, or  state, but the substance also has a solid state, ice, and a gaseous state, water vapor or  vapor  or  steam. steam. Water covers 71% of the Earth's Earth's surface, mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as air  as vapor , clouds (formed of solid and liquid water particles suspended in air), and precipitation and precipitation.. Saltwater oceans Saltwater oceans hold 97% of surface water, glaciers and polar ice polar ice caps 2.4%, and other land surface water such as rivers, rivers, lakes and ponds and  ponds 0.6%. A very small amount of the Earth's water is contained within water towers, towers, biological bodies, manufactured products, and food food stores stores.. Other Other water water is trapped trapped in ice caps, caps, glacie glaciers, rs, aquifers aquifers,, or in lakes, lakes, someti sometimes mes  providing fresh water for life on land1. Water Water moves moves contin continual ually ly through through a cycle cycle of evapora evaporati tion on or transp transpir irati ation on (evapotranspiration), precipitation, and runoff, usually reaching the sea. Winds carry water vapor  over land at the same rate as runoff into the sea. Over land, evaporation and transpiration contribute to the precipitation over land. Clean, fresh drinking water is essential to human and other life. Access to safe drinking water has improved steadily and substantially over the last decades in almost every part of the world. However, some observers have estimated that by 2025 3

Water Purification

more than half of the world population will be facing water-based vulnerability, a situation which has been called a ‘water crisis’ by the United Nations1. Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitate facilitatess industrial industrial cooling and transporta transportation. tion. Approximately Approximately 70 percent percent of freshwater freshwater is consumed by agriculture1. On the contrary, many of the major diseases especially in the developing countries are attributed to lack of safe and wholesome water supply. There can be no state of positive health and well-being without safe water. Water is not only a vital environmental factor to all forms of  life, but it has also a great role to play in socio-economic development of human population. World Health Assembly in a resolution emphasized that safe drinking water is a basic element of  ‘primary health care’ which is the key element to the attainment of “health for all by the year  2000 A.D.” Water is also integrated with other public health care components because it is an essential part of health education and food and nutrition2.

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2. Sources of drinking water There are various sources from which drinking water can be obtained (Figure 1). The following are the main sources3a. Deep Deep grou ground ndwa wate terr b. Sh Shal allo low w groun groundw dwat ater er c. Uplan Upland, d, lake lakess and and rese reserv rvoir oirss d. Rivers, Rivers, canal canalss and and low low land land reser reservoir voirss e. Atmos Atmosphe pheric ric wate waterr gene generat ration ion

f.

Rainwater harvesting or fog collection

g. Sea water

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Figure 1. Sources of drinking water 2a. Deep groundwater- The water emerging from some deep groundwaters may have

fallen as rain many decades or even hundreds of years ago. Soil and rock layers naturally filter  the groundwater to a high degree of clarity before it is pumped to the treatment plant. Such water  may emerge as springs, artesian springs, or may be extracted from boreholes or wells. Deep ground groundwat water er is general generally ly of very very high high bacteri bacteriolo ologic gical al qualit quality y (i.e., (i.e., a low concent concentrat ration ion of    pathogenic bacteria such as Campylobacter or the pathogenic protozoa Cryptosporidium and Giardia) but may be rich in dissolved solids, especially carbonates and sulphates of calcium and magnesium. Depending on the strata through which the water has flowed, other ions may also be  present including chloride, and bicarbonate. There may be a requirement to reduce the iron or 

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manganese content of this water to make it pleasant for drinking, cooking, and laundry use. Disinf Disinfect ection ion is also also requir required. ed. Where Where ground groundwat water er rechar recharge ge is practi practiced ced,, it is equiva equivalen lentt to lowland surface waters for treatment purposes. 2b. Shallow groundwatersgroundwaters- Water emerging from shallow groundwaters is usually

abstracted from wells or boreholes. The bacteriological quality can be variable depending on the nature of the catchment. A variety of soluble materials may be present p resent including potentially toxic metals such as zinc and copper. Arsenic contamination of groundwater is a serious problem in some areas, notably from shallow wells in Bangladesh and West Bengal in the Ganges Delta. 2c. Upland lakes and reservoirs- Typically located in the headwaters of river systems,

upland reservoirs are usually sited above any human habitation and may be surrounded by a  protective zone to restrict the opportunities for contamination. Bacteria and pathogen levels are usually low, but some bacteria, protozoa or algae will be present. Where uplands are forested or   peaty, humic acids can colour the water. Many upland sources have low pH which require adjustment. 2d. Rivers, canals and low land reservoirs- Low land surface waters will have a

significant bacterial load and may also contain algae, suspended solids and a variety of dissolved constituents. 2e. Atmospheric water generation- It is a new technology that can provide high quality

drinking water by extracting water from the air by cooling the air and thus condensing water  vapour.

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2f. Rainwater harvesting or fog collection- It collects water from the atmosphere can be

used especially in areas with significant dry seasons and in areas which experience fog even when there is little rain. 2g. Sea water- Though this water is available in plenty, it has great many limitations. It

contains 3.5% salts in solution. Off shore waters of the oceans and seas have a high salt concentration. Desalting and demineralization process involves heavy expenditure. It is adopted in places where sea water is the only source available.

3. Water pollution and its sources Water intended for human consumption should be both safe and wholesome. This can be defined as the water which is2-

•

Free from pathogenic agents.

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•

Free from harmful chemical substances.

•

Pleasant to the taste.

•

Usable for domestic purposes.

Water pollution-

Water is said to be polluted or contaminated when it does not meet the above mentioned requirements. Because of the unwanted human activities, water pollution is a growing hazard in many developing countries2. Pure uncontaminated water does not occur in nature. It contains impurities of various kinds which can be natural or man-made. These natural impurities are not essentially dangerous. These comprise of various types of dissolved gases like nitrogen, carbon-dio-oxide, hydrogen sulphide sulphide and dissolved minerals minerals like salts of calcium, magnesium, magnesium, sodium sodium etc. A more serious aspect of water-pollution is that which is caused by human activity, and industrialization2. Sources of water pollution 4-

Virtually Virtually all human activities activities produce produce some kind of environment environmental al disturbance disturbance that contam contaminat inatee surrou surroundi nding ng waters waters.. Eating Eating (body (body wastes wastes), ), garden gardening ing (pesti (pesticid cidee and sedime sediment nt runoff) and many other activities create byproducts that can find their way into the water cycle. For convenience, we can assign the large majority of sources of water pollution to three broad categories of waste. (Figure 1) a. Industrial 9

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 b.  b. Agri Agricu cult ltur ural al and and c. Dome Domest stiic wast wastes es

Figure 2. Sources of Water Pollution

3a. Industrial wastes 4- Wastes from industry serve as major sources for all water 

 pollutant  pollutants. s. Many major industrie industriess contribute contribute significantl significantly y to water pollution, pollution, but some of the

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important are the (i) manufacturing (ii) power-generating (iii) mining and construction, and (iv) food processing industries. 3a (i) Manufacturing industries contribute many of the most highly toxic pollutants, including a variety of organic chemicals and heavy metals. In many cases, both the products, such as the paint or the pesticide, and the by products from the manufacturing process are highly toxic to many organisms, including humans. A key problem with such toxic wastes is not just the many kinds produced, but the sheer volume of each kind. Huge quantities of wastes are produced each year, specially by the chemical and metal industries, which are the largest producers of  toxic and hazardous waste by far. 3a (ii) Power generating industries are the major contributors of heat and radioactivity.   Nearl Nearly y all power power plants plants,, whatev whatever er the fuel, fuel, are major major source sourcess of therma thermall (heat) (heat) pollut pollution ion.. Radioactivity from nuclear power plants can pollute waters in a variety of ways, including discharge of mildly radioactive waste water and ground water pollution by buried radioactive waste. 3a (iii) (iii) The mining and constructio construction n industries industries are major contributors contributors of sediment sediment and acid acid draina drainage. ge. Sedime Sediment nt pollut pollution ion occurs occurs because because both both indust industrie riess can denude denude the land land of  vegetation. Construction in particular results in a drastic rise in the rate of land erosion and transportation of sediment into streams. Acid drainage is mainly a product of mining coal and metallic ore minerals. Because acid drainage occurs only in regions where mining is undertaken and this environmental problem is often overlooked. Yet more than 12000 miles (19300kms) of  downstreams in the U.S. have been seriously affected by acid drainage from mining operations. 11

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3a (iv) Food processing industries include slaughter houses, canning factories, and many other other plan plants ts that that produ produce ce larg largee amoun amounts ts of anima animall and and plant plant bodi bodies es that that beco become me oxyg oxygen en demanding wastes in the nearby waters. These are also sources of water borne diseases. 3b. Agricultural wastes 4- These are generated by the cultivation of crops and animals.

Global Globally, ly, agricu agricult lture ure is the leadin leading g source source of sedime sediment nt pollut pollution ion,, from from plowin plowing g and other  other  activities that remove plant cover and disturb the soil. Agriculture is also a major contributor of  organic chemicals, especially pesticides. The other major agricultur agricultural al pollutants pollutants have biological biological aspects. Oxygen demanding demanding wastes are largely body wastes produced by live-stock. Live-stock is a major cause of this type of pollution. Infectious agents are nearly always found in body wastes, so live stock are also major producers of this type of pollutipon. Agriculture is the major source of plant nutrient  pollution through run-off carrying fertilizers applied to crops. 3c. Domestic wastes 4-

These are those produced by house-holds. Most domestic waste is from, sewage or septic tank leakage that ends up in natural natural waters. In the past, some cities dumped untreated or barely barely treated sewage directly into rivers, lakes, or coastal waters. The bulk of domestic waste pollution consists of body wastes and other oxygen demanding wastes. In addition, domestic sources may  be a major contributor contributor of infectious infectious agents. Plant nutrients nutrients occur in the form of nitrogen and  phosphorus. These come not only from human waste, but also from fertilizers used extensively in house-hold lawns and gardens.

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Fate of pollutants 4-

Ultimately, most pollutants find their way into natural waters. This is inevitable given the dissolving power of water and its tendency to flow towards rivers and basins. The natural waters that ultimately absorb the pollutants can be divided between fresh water and marine water. The fresh waters, in turn, can be either surface water (rivers and streams, or lakes) or ground water.

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4. Micro-organisms causing water pollution There are various micro-biological agents which can also cause water pollution if  drinking water gets contaminated with these agents. The pathogenic agents involved include   bacte bacteri ria, a, viruse virusess and protoz protozoa oa which which may cause cause diseas diseases es that that vary vary in severi severity ty from from mild mild gastroenteritis to severe and sometime fatal diarrhoea, dysentery, hepatitis or typhoid fever. Most of them are widely distributed throughout the world. Faecal contamination of drinking water is only one of several faeco-oral mechanisms by which they can be transmitted from one person to another or, in some cases, from animals to people. The human pathogens mainly transmitted in drinking water are given below. Table 1. Waterborne pathogens and their significance in water supplies 5

Pathogen

Health significance

Main route of  exposure

Persistence in Resistance water to chlorine supplies

High

Oral

Moderate

Low

E.coli

High

Oral

Moderate

Low

Salm almonel onella la typhi phi

High High

Oral Oral

Mode Moderrate ate

Low

Shigella

High

Oral

Short

Low

Vibrio cholera

High

Oral

Short

Low

BACTERIA

Campylobacter   jejuni

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Yersinia

High

Oral

Long

Low

Legionella

Moderate

Inhalation

May multiply

Moderate

Pseudomonas

Moderate Moderate

Contact Contact with skin, May multiply

Moderate

enterocolitica

ingestion

Aeruginosa

in

immunosuppressed  patients Aeromonas Aeromonas

Moderate Moderate

Oral, contact contact with May multiply

Low

skin Mycobacterium,

Moderate

atypical

Inhalation, contact May multiply

Low

with skin

VIRUSES

Adenovi Adenovirus ruses es

High High

Oral, Oral,

Inhala Inhalati tion, on,

_

Moderate

contact with skin Enteroviruses

High

Oral

Long

Moderate

Hepatitis A

High

Oral

Long

Moderate

Hepatitis E

High

Oral

_

Norwalk virus Rota virus Small

High

High round Moderate

Oral

_  _

_ 

Oral

_

_ 

Oral

_

_ 

viruses PROTOZOA

Entamoeba

High

Oral

Moderate 15

High

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histolytica Giardia intestinalis

High

Oral

Moderate

High

Cryptosporidium

High

Oral

Long

High

Moderate

Contact with skin, May multiply

 parvum Acanthamoeba species  

High

ingestion

Naegl Naegleri eriaa fowler fowlerii

Balantidium coli

Modera Moderate te

Contac Contactt with with skin skin

May multi multiply ply

Modera Moderate te

Moderate

Oral

_

Moderate

High

Oral

Moderate

Moderate

Moderate

Contact with skin

Short

Low

HELMINTHS

Dracunculus medinencis Schistosoma species

Persistence in water 5-

The persistence of a pathogen in water is a measure of how quickly it dies after leaving the body. In practice, the numbers of pathogen introduced on a given occasion will tend to decline exponentially with time, reaching insignificant and undetectable levels after a certain  period. A pathogen that persists outside the body only for a short time must rapidly find a new susceptible host. It is therefore less likely to be transmitted through a water supply system that

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within a family or some other group living closely together, where lax personal cleanliness will allow the infection to be transferred from one person to another. The persistence of most pathogens in water is affected by various factors, of which sunlight and temperature are among the most important. Life times are shorter, sometimes much shorter, at warmer temperatures. For example enteric viruses may be detected for upto 9 months at around 10 degree celcius, their maximum period of detection.

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Water Purification

5. History and trends in water filtration Filtration of water started thousands of years back. The following are the methods of  filtration that were adopted at that time5a. Early water treatment 6

The earliest recorded attempts to find or generate pure water date back to 2000 B.C. Early Early Sanskr Sanskrit it writi writings ngs outlin outlined ed method methodss for purif purifyin ying g water. water. These These methods methods ranged ranged from from  boiling or placing hot metal instruments in water before drinking it to filtering that water through crude sand or charcoal filters. These writings suggest that the major motive in purifying water  was to provide better tasting drinking water. It was assumed that good tasting water was also clean. People did not yet connect impure water with disease nor did they have the technology necessary to recognize tasteless yet harmful organisms and sediments in water 6. Centuries later, Hippocrates, the famed father of medicine, began to conduct his own experiments in water purification. He created the theory of the “four humors,” or essential fluids, of the the body body that that rela relate ted d dire direct ctly ly to the the four four temp temper erat atur ures es of the the seas season onss6. Acco Accord rdin ing g to Hippocrates, in order to maintain good health, these four humors should be kept in balance. As a  part of his theory of the four humors, Hippocrates recognized the healing power of water. For  18

Water Purification

feverish patients, he often recommended a bath in cool water. Such a bath would realign the temperature and harmony of the four humors. Hippocrates acknowledged that the water available in Greek aqueducts was far from pure in its quality. Like the ancients before him, Hippocrates also also believ believed ed good good taste taste in water water meant meant cleanli cleanlines nesss and purit purity y of that that water. water. Hippoc Hippocrat rates es designed his own crude water filter to “purify” the water he used for his patients. Later known as the “Hippocratic sleeve,” this filter was a cloth bag through which water could be poured after   being boiled. The cloth would trap any sediments in the water that were causing bad taste or  smell6. 5b. Water treatment in the middle ages 6

The ancient civilizations of Greece and Rome designed amazing aqueducts to route water pathways and provided the first municipal water systems. On the American continent, archeol archeologi ogical cal evidenc evidencee sugges suggests ts that that the ancien ancientt Mayan Mayan civil civiliza izatio tion n used used simil similar ar aqueduc aqueductt technol technology ogy to provid providee water water to urban urban reside residents nts.. Furthe Furtherr advance advancemen ments ts in water water techno technolog logy y ended, for the most part, with the fall of these civilizations. During the Middle Ages, few experiments were attempted in water purification or filtration. Devout Catholicism throughout Europe marked this time period, often known as the Dark Ages due to the lack of scientific innovations innovations and experiments. experiments. Because of the low level of scientific scientific experimentati experimentation, on, the future for water purification and filtration seemed very dark 6. The first record of experimentation in water filtration, after the blight of the Dark  Ages, came from Sir Francis Bacon in 1627. Hearing rumors that the salty water of the ocean could be purified and cleansed for drinking water purposes, he began experimenting in the 19

Water Purification

desalination of seawater. Using a sand filter method, Bacon believed that if he dug a hole near  the shore through which seawater would pass, sand particles (presumable heavier than salt  particles) would obstruct the passage of salt in the upward passage of the water; the other side of  the hole would then provide pure, salt-free water. Sadly, his hypothesis did not prove true, and Bacon was left with salty, undrinkable water. His experiment did mark rejuvenation in water  filter experimentation. Later scientists followed his lead and continued to experiment with water  filtration technology6. The first instance of filtration as a means of water treatment dates from 1804, when John Gibb designed and built an experimental slow sand filer for his bleachery in Paisley, Scotland, and sold the surplus treated water to the public at a half penny per gallon 6. He and others improved on the practical details, and in 1829 the method was first adopted for a public supply supply when when James James Simpso Simpson n constr construct ucted ed an instal installat lation ion to treat treat the water water suppli supplied ed by the Chelsea Water Company in London6. By 1852 the practice had become so established, and its advantages so evident, that the Metropolis Water Act was passed requiring all water derived from the River Thames within 5 miles of St. Paul’s Cathedral to be filtered before being supplied to the public6. The first regular examinations of water supplies, including chemical analysis, were initiated in London in 1858. In 1885, following the discoveries of Pasteur, Koch, Escherich, and others during the 1860s and 1870s, they were extended to include bacteriological examination6. The most convincing proof of the effectiveness of water filtration was provided in 1892  by the experience gained in two neighbouring cities, Hamburg and Altona, which drew their  20

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drinking water from the River Elbe, the former delivering it untreated except for settlement, while the latter filtered the whole of its supply when the river became infected from a camp of  immigr immigrants ants,, Hambur Hamburg g suffer suffered ed from from a choler choleraa epidem epidemic ic that that infect infected ed one in thirty thirty of its  population and caused more than 7500 deaths6. In 1885, the first mechanical filters were installed in the USA, and in 1889 automatic   press pressure ure filter filterss were were first first patent patented ed in Englan England, d, since since then then a number number of modifi modificat cation ionss and impr improve oveme ments nts have have been been intr introd oduc uced ed and henc hencee atta attain ined ed vary varyin ing g degr degree eess of popul popular arit ity, y,  particularly in highly industrialized counties6.

6. WHO Guidelines for drinking water quality quali ty (1993 &1996) The purpose of water quality standards it to minimize all the known health hazards, since it is obviou obviously sly imposs impossibl iblee to preven preventt all pollut pollution ion.. The guidel guideline iness for drinki drinking ng water water qualit quality y recommended by WHO relate to the following variables2. I.

Acceptability aspects

II.

Microbiological asp aspects

III.

Chemical as aspects

IV.

Radiological aspects

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6 I. Acceptability Acceptability aspects2- The following are the criteria which water should satisfy in

order to be acceptable for drinking purposesa. Phys Physic ical al par param amet eter erss b. Inorga Inorganic nic const constitu ituen ents ts 6 I (a). Physical parameters- The ordinary consumer judges the water quality by its

 physical characteristics. The provision of drinking water that is not only safe but also pleasing in appearance, taste and odour is a matter of high priority. This can be determined by many different constituents. (i) Turbidity - Drinking water should be free from turbidity. Turbidity in water is caused

  by particulate matter that may be present as a consequence of inadequate treatment or from resuspension of sediment in the distribution system. Turbidity interferes with disinfection and microbiological determination. Water with turbidity less than 5 nephelometric turbidity units is usually acceptable to consumer. (ii) Colour- Drinking water should be free from colour which may be due to the presence

of coloured organic matter, metals such as iron and manganese, or highly coloured industrial wastes. The guideline value of colour above 15 TCU can be detected in a glass of water. (iii) Taste and odour - Taste and odour originates from natural and biological sources,

from contamination by chemicals or as a by-product of water-treatment. Taste and odour may develop during storage and distribution. It is indicative of some form of pollution or malfunction during water treatment or distribution. No health based guideline is proposed for taste and odour. 22

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(iv) Temperature - Cool water is generally more palatable. Low water temperature tends

to decrease the efficiency of treatment process, including disinfection and may thus have a deleterious effect on the drinking water quality. However, high temperature water enhances the growth of microorganisms. No guideline value is recommended for temperature. 6 I (b).Inorganic constituents- The following range of inorganic constituents should be

 present in water to make it suitable for drinking purposes(i) Chlorides Chlorides- Since the chloride content of the water varies from place to place, it is

necessary first of all to determine the normal range of chlorides of the unpolluted surface and ground water in the given locality. The standard prescribed for chloride is 200mg/litre. The maximum permissible level is 600mg/litre. (ii) Hardness- The taste range of calcium ion is in the range of 100-300mg/litre. In some

instances water hardness in excess of 500mg/litre is tolerated by consumers. (iii) Ammonia - Ammonia in the environment originates from metabolic, agricultural and

industrial processes and from disinfection with chloramine. Natural levels in the ground and surfac surfacee waters waters are usuall usually y below below 0.2mg/ 0.2mg/li litre tre.. Anaero Anaerobic bic ground ground waters waters may contain contain upto upto 3mg/litre. Intensive rearing of farm animals can give rise to much higher levels in surface water. Ammonia in water is an indication of possible bacterial, sewage and animal waste pollution. Ammonia in water can compromise disinfection and c an cause taste and odour odou r problems. (iv) pH- One of the main objectives in controlling the pH is to minimize corrosion and

incrustation in the distribution system. pH less than 7 may cause severe corrosion of metals in 23

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the distribution pipes. At pH levels above 8, there is progressive decrease in the efficiency of  disinfection process. An acceptable pH of drinking water is between 6.5 and 7.5. (v) Hydrogen sulphide - The taste and odour threshold of hydrogen sulphide in the water 

ranges from 0.5-0.1 mg/litre. The ‘rotten –eggs’ like smell of hydrogen sulphide in the drinking water is noticed in some ground waters and in the stagnant drinking water because of the depletion of oxygen. The presence of hydrogen sulphide in the drinking water is easily noticed  by the consumer and requires immediate correction. (vi) Iron- Anaerobic ground water may contain ferrous ion in concentrations of several

mg/litre with causing discoloration of turbidity in water when directly pumped from the well. On exposure exposure to the atmosphere, atmosphere, the ferrous ferrous ion oxidizes oxidizes to ferric ferric ion giving giving an objectionabl objectionablee smell smell and ‘reddish-brown’ colour to the water. At level above 0.3mg/litre, iron stains plumbing and laundry fixtures. (vii) Sodium- The taste threshold depends upon the associated anion and the temperature

of the soluti solution. on. At the room temper temperatur ature, e, the averag averagee taste taste thresh threshold old for sodium sodium is about about 200mg/litre. (viii) Sulphate- The presence of sulphate in the drinking water can lead to the

develo developme pment nt of unusual unusual taste taste to the drinki drinking ng water. water. It is genera generall lly y conside considered red that that taste taste impairment is minimal below 250mg/litre. It has been found that the addition of calcium and magnesium to the distilled water considerably improves the taste.

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(ix) Total dissolved solids - These can have important effect on the taste of the drinking

water. The palatability of water with a TDS level of less than 600mg/litre is considered to be good. Water with considerably low concentration of TDS is sometimes unacceptable because of  flat, insipid taste. Water with TDS levels below 1000mg/litre is generally accepted by the consumers. (x) Zinc- Zinc imparts an undesirable astringent taste to the water. Tests indicate a taste

threshold concentration of 4mg/lite. Water having concentration more than this may appear  opales opalescent cent and develop develop a greasy greasy film on boilin boiling. g. Drinki Drinking ng water water seldom seldom contain containss zinc zinc at concentration more than 0.1mg/litre. (xi) Manganese - Manganese concentration below 0.1mg/litre is usually acceptable to the

consumers. In concentrations above this level stains sanitary ware and laundry, and causes an undesirable taste in beverages. It may lead to accumulation of deposits in the distribution system. (xii) Dissolved oxygen - It is influenced by the raw water temperature, composition,

treatment and any chemical or biological processes taking place in the distribution system. Depletion of dissolved oxygen in the water supplies can encourage microbial reduction of nitrate to nitrite and sulphate to sulphide, giving rise to odour problems. No health based guideline value has been recommended. (xiii) Copper - It may interfere with intended uses of water. It increases the corrosion of 

galvanized and steel fittings. Staining of laundry ware occurs at copper concentrations above 1mg/litre.

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(xiv) Aluminium- The presence of aluminium at concentrations in excess of 0.2mg/litre

often leads to the deposition of aluminium hydroxide floc in the deposition system and the exacerbation of discoloration of water system. Substances and parameters in drinking water that may give rise complaints from consumers are given in Table 2.

Table 2. Substances Substances and parameters parameters in drinking-water drinking-water that may give rise to complaints complaints from consumers2Constituents or

Levels likely to give rise to

26

Reasons for consumer

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characteristrics

consumer complaints

complaints

Physical parameters

Colour

15 TCU

Appearance

Taste and odour

_

Should be acceptable

Temperature

_

Should be acceptable

Turbidity

5 NTU

Appearance

Inorganic constituents

Aluminium

0.2mg/l

Depositions, discolouration

Ammonia

1.5mg/l

Odour and taste

Chloride

250mg/l

Taste, corrosions

Copper

1mg/l

Staining of laundary and sanitary ware

Hardness

_

High-scale deposition, low possible corrosion

Hydrogen sulphide

0.05mg/l

Odour and taste

Iron

0.3mg/l

Staining of laundary and sanitary ware

Manganese

0.1mg/l

Staining of laundary and sanitary ware

Dissolved oxygen pH

_

Indirect effects

_

Low pH-corrosion, high pHtaste, soapy feel

Sodium

200mg/l

Taste

Sulphate

250mg/l

Taste, corrosion

Total dissolved solids

1000mg/l

Taste

Zinc

3mg/l

Appearance, taste

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6II. Microbiological Microbiological aspects 2- The water meant for drinking purposes should be free

from bacteria, viruses and other microorganisms which can cause disease in human beings. The following are the main microbiological aspects that a drinking water should possessa) Bacte Bacteri riolo ologic gical al indi indica cator torss b) Virol Virologi ogica call aspe aspect ctss c) Biol Biolog ogic ical al asp aspec ects ts 6II a) Bacteriological indicators- Natural and treated waters vary in microbiological

quality. Ideally, drinking water should not contain any micro organisms which are pathogenic. It should be also free from bacteria indicative of pollution with excreta. Failure to provide adequate  protection, effective treatment and disinfection of drinking water will expose the community to the risks of outbreaks of intestinal and other infectious diseases. Those that are more prone to water-borne diseases are the infants and young children and the effective dose for them is also lower as compared as compared to the adults. The primary bacterial indicator recommended for this purpose is the coliform group of  microo microorga rganis nisms ms as a whole. whole. Supple Supplemen mentar tary y micromicro-org organi anisms sms like like faecal faecal-st -strep reptoc tococc occii and sulphi sulphitete- reduci reducing ng clostr clostridi idia, a, may someti sometimes mes be useful useful in determ determini ining ng the origin origin of faecal faecal  pollution. (i) Coliform organisms - These include all the aerobic and facultative anaerobic, gram-

negative, non-sporing, non-motile and motile rods capable of fermenting lactose at 35 to 37 deg. C in less than 48 hours. These include both the faecal and non-faecal organisms. Typical

28

Water Purification

organisms organisms of the faecal type include E. Coli and of the non-faecal non-faecal group is Klebsiella Klebsiella aerogens. aerogens. The reason why coliform organisms are chosen as indicators for faecal pollution rather than water-borne pathogens directly•

The The colif colifor orm m orga organi nism smss are are grea greatl tly y pres presen entt in the the hum human an int intes esti tine ne . thes thesee orga organi nism smss are are

fore foreig ign n to pota potabl blee wate waterr and and hence hence thei theirr pres presen ence ce in wate waterr is indi indicat cativ ivee of any any faec faecal al contamination. •

They They are are eas easil ily y dete detect cted ed by by cul cultu ture re met method hodss- as smal smalll as as one one bact bacter eria ia in in 100m 100mll of of wat water er..

•

They They surv surviv ivee lon longer ger than than path pathog ogen ens, s, whic which h die die out more more rapi rapidl dly y tha than n col colif ifor orm m bac bacil illi li..

•

The The coli colifo form rm bac bacil illi li hav havee great greater er res resis ista tanc ncee to the the for force cess of natu natura rall puri purifi fica cati tion on tha than n the the

water borne pathogens. (ii) Faecal streptococci - These types of organisms regular occur in faeces, but much in

smaller numbers than E. coli. The finding of faecal streptococci inwater is regarded as important confirmatory evidence of recent faecal pollution of water. Streptococci are highly resistant to drying and may be valuable for routine control testing after laying new mains for repairs in distribution systems or for detecting pollution by surface run-off to ground or surface waters. (iii) Clostridium perfringens - They also occur regularly in faeces, though generally in

much smaller numbers than E. Coli. The spores are capable of surviving in the water for a longer  time time are usually usually resist resistant ant to chlori chlorinat nation ion used used in water water works. works. The presence presence of spores spores of  clostridium in water is indicative of faecal contamination and their presence in absence of  coliform organisms suggests that faecal contamination occurred at some remote time. 29

Water Purification

6II b) Virologi Virological cal aspects aspects- Drin Drinki king ng wate waterr shou should ld be free free from from any any viru viruse ses. s.

Disinfection with 0.5mg/L of free chlorine residual after contact period of 30 minutes after a pH of 8.0 is sufficient to inactivate virus. The free chlorine should be available in all water supplies in areas suspected of the endemicity of hepatitis A. ozone has also been shown to have effective anti-viral properties if residual ozone levels can be maintained to 0.2 to 0.4mg/L for 4 mins. But it is not possible to maintain ozone residual in distribution system. 6II c) Biological aspects- The following biological aspects should be met by drinking

water(i) Protozoa (ii) Helminths (iii) Free-living organisms (i) Protozoa - Species of protozoa have been known to be transmitted by the ingestion of 

contaminated drinking water include Entamoeba histolytica and Giardia species. These can be introduced into the water sully through human or animal contamination. Rapid or slow sand filtration removes high proportion of pathogenic protozoa. (ii) Helminths- The infective stages of many parasitic roundworms and flatworms can be

transmitted to man through drinking water. A single mature larva or fertilized egg can cause infection and such infective stages should be b e absent from drinking water.

30

Water Purification

(iii) Free-living organisms organisms - These include fungi, algae etc. The most common problem

with these are their interference in the operation of water treatment process, colour, turbidity, taste and odour of finished water. 6III. Chemical aspects 3- There are few chemical constituents of water that can lead to

acute health problems except through massive accidental contamination. In such instances, the water usually becomes undrinkable owing to unacceptable taste, odour and appearance. The  problem associated with chemical constituents of drinking water arise primarily from their ability to cause cause adverse adverse health health effect effectss after after prolon prolonged ged period periodss of exposur exposuree like like heavy heavy metals metals and substances that are carcinogenic and have toxic effects. The presence of certain chemicals above prescribed limits may lead to the rejection of  ground water. These can be organic or inorganicarsenic, cadmium, cadmium, 6III 1. Inorgan Inorganic ic constitu constituents ents-- These substances include arsenic, chromium, cyanide, fluoride, lead, mercury, nickel, nitrate, selenium etc. a) Arsenic- It is introduced into the drinking water through the dissolution of ores, from

industrial effluents, and from atmospheric deposition. The average daily intake of inorganic arsenic in water is estimated to be similar to that from food. A provisional guideline value for  arsenic in drinking water of 0.01mg/litre is established. b) Cadmium - This metal is used in steel industry and plastics. Cadmium compounds are

used in batteries. Water pollution by cadmium is mainly caused by contamination from waste-

31

Water Purification

water, fertilizers and local air pollution. Levels of cadmium in the drinking water are usually less than 1g/litre. A guideline value for cadmium is established at 0.003 1g/litre. c) Chromium- It is widely distributed in the earth’s crust. The adsorption of calcium

after oral exposure is relatively low and depends upon the oxidation state. The guideline value of  chromium is 0.05mg/litre which is considered unlikely to give rise to significant health risks. d) Cyanide- The acute toxicity of cyanide is high. Cyanides can be found in some foods,

  parti particula cularl rly y in some some develo developin ping g countri countries, es, and they they are usuall usually y found found in drinki drinking ng water, water,   primarily primarily because of industrial industrial contamination. contamination. Effects on thyroid thyroid and nervous nervous system system were obse observ rved ed in some some popul populat atio ions ns but thes thesee were were long long-t -ter erm m effe effect cts. s. The The guide guideli line ne value value of  0.07mg/litre is considered to be safe. e) Fluoride- Fluoride accounts for 0.3g/kg of the earth’s crust. Inorganic fluorine

comp compou ounds nds are are used used in the the produ product ctio ion n of alum alumin iniu ium m and and fluo fluori ride de is rele releas ased ed duri during ng the the manufacture and use of phosphate fertilizers. Levels of daily exposure of fluoride depend on the geographical area. If diets contain fish and tea, exposure via the food can be particularly high. Additional intake also results from the use of fluoride toothpastes. Levels in raw water are generally below 1.5mg/litre, but ground water may contain about 10mg/litre of fluoride in areas rich in fluoride –containing minerals. High fluoride levels above 5mg/litre have been found in countries like India, China and Thailand. Such high levels sometimes lead to dental and skeletal fluoro fluorosis sis.. Fluori Fluoride de is someti sometimes mes added added to drinki drinking ng water water to preven preventt dental dental caries caries.. Solubl Solublee fluorides are readily absorbed in the gastrointestinal tract after intake in drinking water. The guideline value suggested is 1.5mg/litre. 32

Water Purification

f) Lead- Lead is present in tap water to some extent as a result of its dissolution from

natural sources, but primarily from household plumbing systems or the service connections to homes. homes. Placen Placental tal transfe transferr of lead occurs in humans as early as 12th 12th week of gestat gestation ion and continues throughout development. Young children absorb 4-5 times as much lead as adults. Lead Lead is a general general toxicant toxicant that that accumu accumulat lates es in the skelet skeleton. on. Infant Infantss and children children are most most susceptible to its adverse effects. Lead also interferes with calcium metabolism both directly and indirectly interfering with calcium metabolism. Lead is also toxic to both central and peripheral nervous system. The health- based guideline value of lead is 0.01mg/litre. g) Mercury - Mercury is present in inorganic form in surface and ground water in

concentrations usually less than 0.5mg/litre. The kidney is the main target for inorganic mercury. The guideline value of mercury is 0.001mg/litre. 0.0 01mg/litre. h) Nitrate and nitrite - These are naturally occurring ions that are part of the nitrogen

cycle. cycle. Natura Naturall lly y occurr occurring ing nitrat nitratee level level in surfac surfacee and ground ground water water are generall generally y a few milligrams per litre. In general, vegetables are the main source of nitrate intake when levels in drinking water are below 10mg/litre. When the level exceeds 50mg/litre, drinking water becomes the main source of nitrate intake. The guideline value of nitrate in drinking water is solely to  prevent methamoglobinaemia, which depends upon the conversion of nitrate to nitrite. Selenium levels in drinking water vary greatly in different different geographical geographical i) Selenium- Selenium areas, and are usually much less than the guideline value of 0.01mg/litre. Food stuffs are the main principal source, and the levels depend upon the geographical area of production. Selenium

33

Water Purification

is an essent essential ial elemen elementt for humans and forms forms an integr integral al part part of the enzyme enzyme glutathi glutathione one  peroxidase. Most selenium compounds are water soluble. 6III 2. Organic constituentsconstituents- These include (a) Polynuclear aromatic hydrocarbons and

(b) Pesticides. The guideline values of some of the organic chemical constituents like in water  are as shown in Table 2. (a) Polynuclear aromatic hydrocarbons- A large number of polynuclear aromatic

hydrocarbons (PAHs) from a variety of combustion and pyrolysis sources have been identified in the environment. The main source of human exposure to PAHs is food, with drinking water  contributing only minor amounts. Little information is available on the oral toxicity of PAHs, especially after long-term exposure. Benzo (a) pyrene, which constitutes a monor fraction of total PAHs have been found to be carcinogenic in mice by the oral route of administration. Some PAH compounds have been found to be carcinogenic by non-oral routes, Benzo (a) pyrene has been found to be mutagenic in a number of in vitro and in vivo assays. Table 3. WHO Guideline values for health related organic constituents 2

34

Water Purification

Orga Or gani nicc ccon onsstitue tuents nts

Uppe perr lim limiit of of con conce cen ntra tratio tion (µ (µg/l) g/l)

Chlorinated alkanes

Carbon tetrachloride

2

Dichloromethane

20

Chlorinated ethenes

Vinyl chloride

55

1,1- dichloroethene

30

1,2-dichloroethene

50

 Aromatic hydrocarbons

Benzene

10

Toluene

700

Xylenes

500

Ethlybenzene

300

Styrene

20

Benzolalpyrene

0. 7

35

Water Purification

The following recommendations are made for the PAH group

Because of the close association of the PAH with suspended solids, the application of  treatment, when necessary to achieve the recommended level of turbidity will ensure that PAH levels are reduced to a minimum.



Cont Contam amin inat atio ion n of wate waterr with with PAH PAH shou should ld not not occur occur duri during ng wate waterr treat treatme ment nt or  distributi distribution. on. Therefore Therefore the use of local-coallocal-coal-tar tar based and similar materials materials for pipe linings and coatings on storage tanks should be discontinued.



In situation where contamination of drinking water by PAH has occurred, the specific comp compoun ounds ds pres presen entt and and the the sour source ce of cont contam amin inat atio ion n shoul should d be ident identif ifie ied, d, as the the carcinogenic potential of PAH compounds varies. (b) PesticidesPesticides- The pesticides that are important in connection with water quality

incl include ude chlo chlori rinat nated ed hydr hydroc ocar arbo bons ns and thei theirr deri deriva vati tive ves, s, pers persis iste tent nt herb herbic icid ides es,, soil soil insect insectici icides des,, pestic pesticide idess that that are easily easily leached leached out from from the soil, soil, and pesti pesticid cides es that that are 36

Water Purification

systemically added to water supplies for disease vector control. The recommended guideline values given in Table 3 are set at a level to protect human health. Table 4. Guideline values for certain pesticides 2

Pesticides

Upper limit of concentration (µg/l)

Aldrin/dieldrin

0.03

Chlordane

0.2

DDT

2

2,4-D

30

Hepatochor and hepatochor epoxide

0.03

Hexachlorobenzene

1

Lindane

2

Methoxychlor

20

Pentachlorophenol

9

6 IV. Radiological aspects 4- The effects of radiation exposure are called ‘somatic’ if 

they become manifest in the exposed individual, and ‘hereditary’ if they affect the descendants. Malignant disease is the most common delayed somatic effect. For some somatic effects such as carcinogenesis, the probability of an effect occurring rather than its severity is regarded as a function of dose without a threshold. Whereas for other somatic effects the severity of the effect varies with the dose, a threshold therefore may exist for such effects.

37

Water Purification

Radioactivity in drinking water should not only be kept within safe limits, it should also  be kept as low as possible within those limits. The guideline values recommended take account for both naturally occurring radioactivity and any radioactivity that may reach the water surface as a result of man’s activities. Below this value, the water can be considered potable and safe without any further radiological examination. The activity of the radioactive material is the number of nuclear disintegration per unit of  time. The unit of radioactivity is becquerel; 1Bq= 1 disintegration per second.

The proposed guidelines areGross alpha activity- 0.1Bq/L Gross beta activity -1.0 Bq/L

38

Water Purification

7. Comparison of filter types Filters may be divided into two types- pressure and gravity. Pressure filters consist of  closed vessels (usually steel shells) containing beds of sand or of other granular material through which water is forced under pressure. These filters are frequently used in certain industrial situations, and a number have been installed for public water supplies7. They are especially suitable in plants where a high degree of automation is necessary, in remotely situated treatment   plants that have to operate with only occasional attendance, and in systems where for some reason reason it is desirable desirable to have only a single single pumping stage between the inlet and the distribut distribution ion system. As their initial cost may be high, especially when their component parts have to be imported, their principal use is in the industrialized countries where they are manufactured7. The 39

Water Purification

 basic mechanism involved in the pressure and gravity type of filters is the same. The only difference is that raw water pump is used to generate necessary pressure to reduce suspended solids in the water. These are basically used to filter the water in swimming pool7. A gravity filter consists essentially of an open-topped box (usually made of concrete), drained at the bottom, and an d partly filled with a filtering medium (normally clean sand). Raw water  is admitted to the space above the sand, and flows downward under the action of gravity. Purifi Purificat cation ion takes takes place place during during the downwar downward d passag passage, e, and the treate treated d water water is discha discharge rged d through the under drains. In turn, gravity filters are sub divided into slow and rapid types, the latter operating at rates 20-50 times faster than those of the former, and hence requiring only some some 2-5% 2-5% of the the area area neede needed d for for slow slow sand sand filt filter ers. s. In prac practi tice ce the the redu reduct ctio ion n in spac spacee requirements is partially offset by the additional pretreatment stages needed for rapid filtration, and the figure is likely to be nearer to 20%7.

8. Choice of treatment process In its natural state, during its passage through the hydrological cycle, water is constantly changing in chemical and bacteriological composition. Polluting and purifying processes are continually at work. At the moment of evaporation from the ocean’s surface it is virtually a pure compound of hydrogen and oxygen; when it reaches the point of condensation it is mixed with carbon dioxide and other gases; during its fall to earth it collects dust particles and dissolves further gases, both those naturally occurring and those present as pollutants in the air 7. On reaching the ground and during its passage above or within the ground it not only dissolves minerals from the rocks with which it comes into contact but also requires a load of suspended 40

Water Purification

solids (many of organic origin) and an infinite variety of living matter, ranging from microorganisms through a number of animal and vegetable species to large and complex aquatic life forms, such as fish and water weeds. At the same time it is being acted upon by sunlight, aeration, aeration, biological oxidation, oxidation, settlement, settlement, chemical chemical reactions, reactions, and the action of predators in the ascending food chain, all of which tend to convert these organisms that might be hazardous to humans into harmless and even beneficial bene ficial forms7. Man, extracting water at any stage of this cycle, makes use of these natural processes of    pur purif ific icat atio ion n and and crea create tess condi conditi tion onss that that will will enab enable le them them to be spee speede ded d up in time time and and compressed in space. However, complex or sophisticated modern processes may be, each has (with one exception) its counterpart in nature. Even modern desalination and demineralization techni techniques ques derive derive from from natura naturall proces processes ses;; distil distillat lation ion plants plants simula simulate te evapora evaporati tion on from from the surface of the sea; osmotic and membrane techniques attempt to do what the fish’s skin, the vegetable cell wall, and the human kidney is continuously achieving; freezing separation can be seen in the formation of largely fresh-water ice in the ocean. Among the conventional treatment method methods, s, sedime sedimenta ntati tion, on, micro microsta staini ining, ng, floccul flocculati ation. on. Filtra Filtrati tion, on, aerati aeration, on, and ultrav ultraviol iolet et disinfection have their counterparts in natural processes acting on surface and ground waters7. The exception referred to above is the addition of concentrated chemicals to raw or  treated water either to intensify one of the natural processes (eg, a coagulant to speed up flocculation) or to inactivate living organisms (eg, chlorine to disinfect water or kill algae). A significant difference between natural and artificial processes arises in the latter case; in nature

41

Water Purification

the organisms die away and are consumed, settled and strained out, while disinfection kills them without removing them and at the same time adds an additional constituent to the treated water 7. Undoubtedly the introduction of chlorination at the beginning of the present century greatly greatly increased our ability ability to ensure the safety safety of drinking water supplies supplies7. It was an entirely new approach to water treatment and a technical innovation of the greatest importance - today it would be hailed as a major “breakthrough”. As a result there has been a tendency in some quarters to regard it as a process complete and sufficient in itself rather than to look upon it as a usef useful ul stag stagee in a compl complex ex trea treatm tmen entt patt patter ern, n, as a seco second nd line line of defe defens nsee in the the even eventt of  malfunctioning of other processes, as a means of inactivating that small percentage of pathogens that inevitably slip through the various stages of conventional treatment. It is also frequently forgotten that to achieve efficient disinfection, the water must be prepared for chlorination by the  prior removal of substances that would tend to inhibit the disinfecting properties of chlorine7.

9. Purification of drinking water Purification of water can be done according to the demands like2I. Purification of water on a large scale. II. Purification of water on a small scale. 42

Water Purification

III. Other water purification techniques.

9 I. Purification of water on a large scale 2

The purpose of water treatment is to produce that quality of water that is safe to drink and that can be easily used for other domestic purposes. The method of treatment that is desired depe depends nds upon upon the the natu nature re of the the raw raw wate waterr and and the the desi desire red d quali quality ty of wate waterr for for exam exampl plee groundwater needs less treatment than surface water which tends to be more turbid and polluted as compared to groundwater. Purification of water involves 3 stages2(A) Storage (B) Filtration (C) Disinfection 9 I (A). Storage - Water is drawn out from the source and impounded in natural and

artificial reservoirs. Storage provides a reserve of water from which further pollution is excluded. As a result of storage, a very considerable amount of purification takes place. This is natural  purification and it can be looked from 3 angles2-

43

Water Purification

(i) Physical Physical- By mere storage, the quality of water improves. About 90%of suspended

impu impuri riti ties es sett settle le down down in 24 hours hours by gravi gravity ty.. The The wate waterr beco become mess clea cleare rer. r. This This allo allows ws  penetration of light, and reduces the work of filters2. (ii) 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 nitrate occurs2. (iii) Biological 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% in the first 5-7 days. This is one of the greatest benefits of storage. The optimum period of storage of river water is considered to be about 10-24 days. If  the water is stored for long periods, there is likelyhood of development of vegetable growths such as algae which impart a bad smell and colour to water 2. 9 I (B). Filtration - This is the second and the most important stage in the purification of 

water as 98-99% of bacteria are removed a part from other impurities. Basically, there are two types of filters(i) Biological or slow sand filters 2 (ii) Rapid sand or mechanical filters 2

44

Water Purification

9 I (B) (i) Slow-sand filtration 9 I (B) (i) 1.Elements of a slow sand filter 7

The figure below shows the various elements that go up to make up a slow-sand filter.

Figure 3. Slow-sand filter a. A supernatant (raw) water reservoir , the principal function of which is to maintain a

constant head of water above the filter medium, this head providing the pressure that carries the water through the filter. within in upon upon whic which h the the vario various us b. A bed bed of filt filter er medi medium um (nea (nearl rly y alwa always ys sand sand)) , with  purification processes takes place. c. An under-drainage system , which fills the dual purpose of supporting the filter medium

while presenting the minimum possible obstruction to the treated water as it emerges from the filter bed; and

45

Water Purification

d. A system of control valves to regulate the velocity of flow through the bed, to prevent

the level in the raw water reservoirs from dropping below a predetermined minimum during operation, and to permit water levels to be adjusted and the backfilling to take  place when the filter is put back into operation after cleaning. The first three of these features are contained within single open-topped filter-box, the control valves being usually in adjacent structures. The box is usually rectangular in shape, from 2.5 to 4m in depth, and built wholly or partly below ground. To save space (particularly in larger  installations) the walls are normally vertical or near or near vertical, and may be made of stone,  brick, or concrete according to which is most easily obtainable at the site. Sloping slides and variety of lining materials may be found in the more remote locations where land is plentiful and economy of construction is the first consideration7. At the bottom of the box, is the under-drainage system, which may consist of false floor  of porous concrete or a system of porous or unjointed pipes, surrounded and covered with graded gravel to support the sand-bed and they prevent the fine grains being carried into the drainage  pipes. Above the under drainage-system is the sand itself, to a thickness of 0.6 to 1.2m, above which the raw water will lie to a depth of 1-1.5m. Special mention should, however be made of the outlet weir and valve to control the rate of flow. For reasons that will be fully explained it is most undesirable that the water level in the filter box should drop down below the surface of the filter medium. To eliminate the possibility

46

Water Purification

of this happening, a weir is incorporated in the outlet pipe system. It accomplishes the dual  purpose of maintaining a minimum water depth within the filter box and of aerating the outgoing water to some extent, so that oxygen is absorbed and dissolved gases, which might otherwise impart unpleasant tastes and odours to the treated water, are released. Moreover, it renders the operation of the filter independent of fluctuations in the water level in the clear water reservoir 7. Clear water reservoir is the reservoir which collects purified water after the filtration process. 9 I (B) (i) 2. Purification in a slow-sand filter 7

The raw water enters the water resting above the filter bed, awaiting its downward  passage through the medium. The raw water reservoir is about 1-1.5m deep, and the average time the raw water will remain here varies from 3 to 12 hours, depending upon the filtration velocity. The heavie heavierr parti particle cless of suspen suspended ded matter matter start start to settle settle,, and some some of the lighter lighter parti particle cless coalesce, so becoming more amenable, to subsequent removal. During the day, and under the influence of sunlight, algae are growing and are absorbing carbon-dioxide, nitrates, phosphates, and other nutrients from the water to form cell material and oxygen. The oxygen dissolves in the water as it is formed and enters into chemical reaction with organic impurities, rendering these, in turn, more assimilable by the algae. On the surface of the sand there is a thin slimy matting of material, largely organic in origin, known as the  schmutzdecke, or filter skin, through which the water must pass before reaching reaching the filter medium itself. The schmutzdecke schmutzdecke consists of threadlike threadlike algae and numerous other forms of life, including plankton, diatoms, protozoa, rotifers, and bacteria. It is intensely active, the various micro-organisms entrapping, digesting, and breaking down organic matter  47

Water Purification

contained in the water passing through. Dead algae from the water above and living bacteria in the raw water are alike consumed within this filter skin, and in the process simple inorganic salts are formed. At the same time nitrogenous compounds are broken down and nitrogen is oxidized. Some Some colour colour is remo remove ved, d, and and a cons consid ider erabl ablee prop propor orti tion on of iner inertt susp suspen ende ded d parti particl cles es is mechanically strained out7. Having passed through the schmutzdecke, the water enters the filter-bed and passes through downwards through the interstices between the sand grains- a process that normally takes several hours. A significant property of the sand bed is adsorption, a phenomenon resulting from electrical forces, chemical bonding, and mass attraction interacting in a way that is not yet completely understood. Adsorption takes place at every surface at which water comes in contact with a sand grain. To appreciate the extent of this action it is necessary to visualize the interior of  the sand bed as a series of grain surfaces over which the water must pass. The aggregate area of  these surfaces is extremely high; in one cubic metre of filter sand there will be some 15000m2 (one and a half hectares) of surface. Over this the water passes in a laminar flow that is constantly changing direction as it leaves one grain and meets the next. At each change of  direction gravity and centrifugal forces act upon every particle carried by the water 7. Between the grains are the pores or open spaces, totaling some 40% of the total volume of  the bed. Water passing over a grain surface surface is suddenly suddenly slowed down each time it enters one of  these pores, and as a result millions of minute sedimentation basins are formed in which the

48

Water Purification

smallest particles settle onto the nearest sand grains before the water continues on its downward  path. Hence during the passage of water through the bed, every particle, bacterium, and virus is  brought into contact with the surfaces of the sand grains, to which they become attached by mass attraction or though the operation of electrical forces. The surfaces become coated with a sticky layer, similar in composition to the schmutzdecke, but without the larger particles and the algae, which which have failed failed to penetr penetrate ate.. It sustai sustains ns s teemin teeming g mass mass of micromicro-org organi anisms sms,, bacter bacteria, ia,  bacteriophages, rotifers and protozoa, all feeding on the adsorbed impurities and on each other. The living coating continues through some 40cm of the bed, different life forms predominating at different depths, with the greatest activity taking place near the surface, where food is most  plentiful7. The food consists essentially of particles of organic origin carried by the water. The sticky coating holds the particles until they are broken down, consumed, and formed into cell material, which in turn is assimilated by other organisms and converted into inorganic matter such as water, carbon-dio-oxide, nitrates, phosphates, and similar salts that are carried downward by the  passing water. As the depth from the surface increases, the quantity of organic food decreases and the struggle among the various organisms becomes fiercer. Other bacteria then predominate, utilizing the oxygen content of the water and extracting nutrients that would otherwise have  passed unchanged in solution through the filter. As a consequence the raw water which entered the bed laden with a variety of suspended solids, micro-organisms, and complex salts in solution, has, in its passage through some 40-60 cm of filter medium, becomes virtually free of all such

49

Water Purification

matter, containing only some some simple inorganic salts in solution. Not only only has practically every harmfu harmfull organi organism sm been been removed removed but also also the dissol dissolved ved nutrie nutrients nts that that might might encour encourage age the subsequent growth of bacteria or slimes. It may be low in dissolved oxygen and may contain dissolved carbon-dio-oxide but subsequent aeration caused by falling over the discharge weir  will go far to remedying both these defects7. 9 I (B) (i) 3. Limitations of slow-sand filters 7- Certain conditions may be encountered

that may offset the advantages of slow sand filtration and may lead to the choice of rapid filters as a more appropriate treatment method. 

Where land is restricted or very expensive, the much larger area needed for biological filters may add considerably to the capital cost, or even rule out this form of treatment as a practical proposition.



In countr countries ies where where the constru constructi ction on methods methods are largel largely y mechan mechanize ized d and where where the importation of such materials as steel and cast-iron pipe work presents no problems, the reinforced concrete construction and metal fittings of rapid filters may be cheaper to construct than the more-extensive non-reinforced construction of slow filters.



Where unskilled labour for cleaning is in short supply it may be easier and cheaper to recruit the skilled staff required to operate and maintain rapid filters than to retain the necessary the labour force.



In climate where the winters are very cold it may be necessary to install expensive structural precautions against freezing. At the same time the efficiency of purification will be adversely affected by low temperatures.

50

Water Purification



Where the water to be treated is liable to severe and sudden changes in quality or where certain types of toxic industrial wastes or heavy concentration of colloids may be present, the working of biological filters can be upset. u pset.



Certain types of algae may interfere with the working of the filters, the usual result being the premat premature ure choking, choking, which which calls calls for frequent frequent cleani cleaning. ng. In such such cases cases it may be necessary to cover the filter-beds to exclude light- a comparatively expensive addition to capital cost unless it is possible to use locally available materials for the p urpose.

9 I(B) (i) 4.Advantages of slow-sand filters 7- The following are the advantages of slow

sand filtration. a) Quality of treated water - No other single process can effect such an improvement in

the physical, chemical, and bacteriological quality of normal surface waters. The delivered does not support after growth in the distribution system, and no chemicals are added, thus obviating one cause of taste and odour problems.

b) Cost and ease of construction construction - The simple design of slow sand filters makes it easy

to use local materials and skills in their construction. The cost of imported materials and equipment may be kept to almost negligible proportions, and it is possible to

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reduce reduce the use mechanize mechanized d plant plant to the minimum minimum and to economi economize ze on skille skilled d supervision.

operation - The cost of operation lies almost wholly in the cleaning c) Cost and ease of operation

of the filter-beds, which may be carried out either mechanically or manually. In develo developin ping g countr countries ies and elsewh elsewhere ere where where labour labour is readil readily y availab available, le, the latter  latter  method will be used, in which case virtually the whole of the operating cost will be returned to the local economy in the form of wages. No compressed air, mechanical stirring, or high- pressure water is needed for back-washing, thus there is a saving not only in the provision of plant but also in the cost of fuel or electricity.

d) Conservation of water - In water-short areas, biological filters have the additional

advantage of not requiring the regular flushing to waste of wash water.

e) Disposal of sludge - Sludge storage, dewatering, and disposal are less trouble some

with slow sand filters than with the mechanical filters, particularly when the latter  contain chemical coagulants. Since the sludge from the biological filters is handled in a dry state there is virtually no possibility of polluting neighbouring water courses, and the waste material is usually accepted by farmers as a useful dressing for their  land land,, the the mixt mixtur uree of sand sand and and orga organi nicc matt matter er bein being g espe especi cial ally ly suit suitab able le for  for  conditioning heavy clay soils.

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9 I (B) (ii) Rapid sand or Mechanical Filtration

In 1885, the first rapid sand filters were installed in the USA. Since that time, they have gained considerable popularity especially in highly industrialized countries2.

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Figure 4. Rapid sand or Mechanical filter

Rapid sand filters are of 2 types, the gravity type (eg Paterson’s filter) and the pressure type (eg Candy’s filter). Both the types are in use. The following are the steps involved in the  purification of water by rapid sand filters2. 9 I (B) (ii) 1.Coagulation- The raw water is first treated with a chemical coagulant such

as alum, the dose of which varies from 5-40 mg or more per litre, litre, depending upon the turbidity turbidity and colour, temperature and the ph of the water.

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9 I (B) (ii) 2.Rapid mixing- The treated water 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. 9 I (B) (ii) 3.Flocculation- This phase involves slow and gentle stirring of the treated

water in a ‘flocculation chamber’ for 30 minutes. This is usually done mechanically with a flocculator which consists of number of paddles which rotate 2 to 4 ppm. This stirring results in the formation of thick, copious, white precipitate of aluminium hydroxide. The thicker the  precipitate, the greater is the settling velocity. sedimentation tanks 9 I (B) (ii) 4.Sedimentation- The coagulated water is led into the sedimentation where it is detained from periods ranging from 2-6 hours. This leads to the settlement of  floccu flocculent lent precip precipita itate te along along with with impuri impuritie tiess and bacter bacteria. ia. At least least 95% of the floccul flocculent ent   precipitate should be removed before the water is fed into the rapid sand filters. For proper  maintenance, the tank should be cleaned regularly. 9 I (B) (ii) 5.Filtration- The partly clarified water is subjected to rapid sand filtration. As

the filtration proceeds, the ‘alum-loc’ 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  bacteria from the water and effects purification. purification. Oxidation Oxidation of ammonia also takes place during the passage of water through the filters. 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, the filtration is stopped and the filters are subjected to a  process known as ‘back-washing’. 55

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9 I (B) (ii) 6.Back-washing 2- These kinds of filters need frequent washing daily or 

weekly depending upon the loss of head. This is done by reversing the flow of water through the sand bed, which is called as ‘back-washing’. This process dislodges the impurities and cleans up the sand bed. The washing is stopped when clear sand and wash water is visible. The whole  process  process takes about 20 minutes. minutes. In some types of rapid sand filters, filters, compressed compressed air is used as a  part of the back-washing process. 9 I (B) (ii) 7. Advantages of rapid-sand filters 2- The following following are the advantages of 

rapid sand filtration-

•

Rapid sand filters can deal with raw water directly. No preliminary stage is needed.

•

The filter beds occupy less space.

•

Filtration is rapid. rapid. 40-50 times faster as compared to the slow-sand filters.

•

The washing of the filter is easy.

•

There is more flexibility in operation.

9 I (C). Disinfection56

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Various disinfection processes used in drinking-water treatment to inactivate pathogenic microbes8. 1. Pretreatment oxidation — in which oxidants are added to water early in the treatment

 process. Primary disinfection disinfection — a common common component component of primary treatment of drinking-wa drinking-water, ter, 2. Primary and important because granular filter media do not remove all microbial pathogens from water. 3. Secondary disinfection — used to maintain the water quality achieved at the treatment

 plant throughout the distribution system up to the tap. Factors affecting disinfection 8-

The principal factors that influence disinfection efficiency are disinfectant concentration, contact time, temperature and pH. Disinfectant concentration and contact time are integral to disinfect disinfection ion kinetics kinetics and the practical application application of the CT concept concept (CT being the disinfectant disinfectant concentration multiplied by the contact time). The pH of the disinfectant solution affects the reaction kinetics. For example, the disinfection efficiency of free chlorine is increased at lower   pH values, whereas that of chlorine dioxide is greater at alkaline pH levels. Monochloramine is formed within seconds in the pH range 7–9, at chlorine to ammonia nitrogen ratios of less than 5:1 and at 25°C; monochloramine is also predominant when the pH is greater than 5. Other  factor factorss that that influe influence nce micro microbia biall sensit sensitivi ivity ty to disinf disinfect ection ion includ includee attachm attachment ent to surfac surfaces, es, encapsulation, aggregation and low-nutrient growth. Increased resistance to disinfection may

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result result from from attach attachmen mentt or associ associati ation on of microo microorga rganis nisms ms to variou variouss parti particula culate te surfac surfaces, es, including: • macroinvertebrates • particles that cause turbidity • algae • carbon fines • glass A study showed that the majority of viable bacteria in chlorinated water were attached to particles. Another study reported that aggregation of  Acinetobacter strain  Acinetobacter  strain EB22 increased its resistance to disinfection, making the bacteria 100-fold more resistant to hypochlorous acid (HOCl) (HOCl) and 2.3-fold 2.3-fold more resistant to monochloram monochloramine. ine. Several Several investigat investigators ors have isolated isolated encapsulated bacteria from chlorinated water and concluded that production of the extracellular  capsul capsulee helped helped protec protectt bacter bacteria ia from from chlori chlorine. ne. Another Another study study report reported ed that that  Pseudomonas aeruginosa grown in distilled water was markedly more resistant to acetic acid, glutaraldehyde, chlorine dioxide and a quaternary ammonium compound than cells cultured on tryptic soy agar. Similarly, some investigators found that bacteria grown in a chemostat at low temperatures and submaximal growth rates caused by nutrient limitation (conditions thought to be similar to the natural aquatic environment) were resistant to several disinfectants8.

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9 I (C) 1. Pretreatment Oxidation 8

Water utilities often add oxidants early in the treatment process to8: i.

Maximi Maximize ze the the cont contact act time time with with the oxidant oxidant..

ii. ii. Oxid Oxidiz izee comp compou ounds nds for subs subseq equen uentt remo remova vall by the the trea treatm tmen entt proc proces esss (eg. (eg. iron iron or  manganese). iii. Provide initial treatment treatment in sufficient sufficient time for water to be further treated if if necessary (eg. Oxidation of taste and odour compounds). iv. Control Control growth of microorganis microorganisms ms and higher organisms organisms (eg. Zebra mussels) mussels) on intake structures and in treatment basins. v. Improve Improve particle particle removal removal in subsequent subsequent clarifica clarification tion and filtrati filtration on processes. processes. There are a number of potential problems with pretreatment oxidation. Variable source water conditions mean that variable or high levels of oxidant may be needed. This may lead to over overdo dosi sing ng of prepre-ox oxid idan ants ts,, which which can can resu result lt in “pin “pink k colo colour ured ed”” wate waterr when when pota potass ssiu ium m   perma permangan nganate ate is misapp misapplie lied. d. Also, Also, the proces processs can produce produce oxidat oxidation ion by-pro by-produc ducts ts such such as trihalomethanes (THMs), haloacetic acids and bromate. For example, in using chlorine as a  pretreatment oxidant, chlorinated by-products can form rapidly. This often limits the application of chlorine to a later stage of the treatment process, when precursor material has been removed. A further problem is that oxidants can lyse algal cells, releasing liver or nerve toxins, or creating objectionable tastes or odours. One concern with using pre-oxidants for disinfection is that

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 particulate material may interfere with microbial inactivation. Such material protects bacteria and viruses from disinfectants by creating an instantaneous disinfectant demand (preventing the mainte maintenanc nancee of a disinf disinfect ectant ant residu residual al in subseq subsequent uent treatm treatment ent steps) steps) and by shield shielding ing the microbe microbe from the oxidant. The effect effect of particulate particulate material on disinfecti disinfection on of cysts or oocysts oocysts has not been widely evaluated. Some investigators studied the effect of turbidity on disinfection of  Cryptosporidi Cryptosporidium um parvum oocysts oocysts by chlori chlorine ne dioxid dioxidee or perman permangana ganate, te, and found found that that  particulate material did not interfere with disinfection once the increase in oxidant demand had  been satisfied. They hypothesized that protozoan cysts were too large to be completely shielded from the disinfectant. 9 I (C) 2. Primary disinfection 8

A disinfection barrier is a common component of primary treatment of water. Primary disinfection is typically a chemical oxidation process, although ultraviolet (UV) irradiation and membrane treatment are gaining increased attention. This section looks at different types of  disinfectant — chlorine, monochlorine, chlorine dioxide, ozone, UV light and mixed oxidants —  in terms of their effectiveness against various pathogenic microorganisms. 9 I (C) 2 (i) Chlorine (a) Mode of action

Chlorine Chlorine gas and water react to form HOCl (hypochlor (hypochlorous ous acid) and hydrochloric hydrochloric acid (HCl). In turn, the HOCl dissociates into the hypochlorite ion (OCl–) and the hydrogen ion (H+), according to the following reactions: 60

Water Purification

(1) Cl2 + H2O⇔ HOCl + HCl (2) HOCl ⇔ H+ + OCl–  The reactions are reversible and pH dependent: 

 between pH 3.5 and 5.5, HOCl is the predominant species



  bet betwee ween n about about pH 5.5 5.5 and and 9.5, 9.5, both both HOCl HOCl and and OCl– OCl– spec specie iess exis existt in vario various us  proportions



above pH 8, OCl– predominates. The OCl– and HOCl species are commonly referred to as free chlorine, which is

extrem extremely ely reacti reactive ve with with numero numerous us compone components nts of the bacter bacterial ial cell. cell. HOCl HOCl can produc producee oxidation, hydrolysis and deamination reactions with a variety of chemical substrates, and  produces physiological lesions that may affect several cellular processes. Chlorine destroys microorganisms by combining with proteins to form N-chloro compounds. Chlorine was later  found to have powerful effects on sulfhydryl groups of proteins and to convert several amino acids by oxidation into a mixture of corresponding nitriles and aldehydes. The exact product of the reaction depends on chlorine concentration and pH. Cytochromes, iron-sulfur proteins and nucleotides are highly vulnerable to oxidative degradation by HOCl, suggesting that chlorine causes physiological damage primarily to the bacterial cell membranes. Respiration, glucose transport and adenosine triphosphate levels all decrease in chlorine-treated bacteria. Electron microscopy of chlorinated bacteria has demonstrated morphological changes in the cell membrane. In addition, chlorination can kill microbes by disrupting metabolism and

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  protein synthesis, or by modifying purine and pyrimidine bases and thus causing genetic defects. Nearly 100 years of chlorination for disinfection of drinking-water has demonstrated the effectiveness of this process for inactivation of microbial pathogens, with the notable exception of Cryptosporidium8.

b) Effectiveness of chlorine against bacteria and viruses 8

Certain bacteria show a high level of resistance to free chlorine. Spore forming  bacteria such as Bacillus or Clostridium are highly resistant when disseminated as spores. Acid-fast and partially acid-fast bacteria such as Mycobacterium and Nocardia can also be highly resistant to chlorine disinfection. One study showed that nearly all of the bacteria surviving chlorine disinfection were Gram positive or acid fast possibly because Gram positive bacteria have thicker walls than Gram-negative ones. Enteric viruses are generally more resistant to free chlorine than enteric bacteria. Viruse Virusess associ associate ated d with with cellul cellular ar debris debris or organi organicc parti particle cless may requir requiree high high levels levels of  disinfection due to the protective nature of the particle surface. Chlorination effectively inactivates viruses if the turbidity of the water is less than or equal to1.0 nephelometric turbidity unit (NTU). It requires a free chlorine residual of 1.0 or greater for 30 minutes, and a pH of less than 8. (c) Effectiveness of chlorine against protozoa 8-

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Water Purification

Protozoan cysts such as Entamoeba histolytica and Giardia lambia are highly resistant to chlorine disinfection and may require prolonged contact times at high chlorine residuals (2-3mg/l) (2-3mg/l) to achieve achieve 99.9% inactivation. inactivation. Chlorine based disinfect disinfectants ants are generally generally not effective at inactivation of Cryptosporidium and early studies found that Cyptosporidium oocycts were resistant to a variety of disinfectants, including bleach. Chlorine disinfection has has not not been been effe effect ctiv ivee

in prev preven enti ting ng outb outbre reak akss

of cryp crypto tosp spor orid idio iosi siss caus caused ed by

Cyptosporidium in drinking recreational water.

9 (C) 2(ii) Monochloramine(a) Mode of action

In dilute aqueous solutions (1–50 mg/l), chlorine reacts with ammonia in a series of   bimolecular reactions: HOCl + NH3→ NH2Cl (monochloramine) + H2O HOCl + NH2Cl→NHCl2 (dichloramine) + H2O HOCl + NHCl2 →NCl3 (trichloramine) + H2O These competing reactions are dependent upon pH and the relative chlorine to nitrogen concentration (expressed as Cl2:N). To a lesser degree they are also dependent upon temperature and contact time. The reaction of HOCl and ammonia will convert all the free

63

Water Purification

chlorine chlorine to monochlorami monochloramine ne at pH 7–8 when the Cl2:N ratio is equimolar (5:1 by weight) or  less. A study examined the reaction of monochloramine with several amino acids and tripeptides. Exposure of alanine, tyrosine and gylcine to the disinfectant for several hours at 25oC and pH 8.0 converted these compounds to organic chloramines. The sulfhydryl groups of cyst cystin inee were were oxid oxidiz ized ed to disu disulf lfid ides es.. Reac Reacti tion on of mono monochl chlor oram amin inee with with hemin hemin (an (an important component of enzymes such as cytochromes, catalases and peroxidases) resulted in  products that could not be reactivated by reducing compounds. The author concluded that monochl monochlora oramin minee may kill kill bacter bacterial ial cells cells by reacti reacting ng primar primaril ily y with with membra membrane ne bound bound enzymes8.

(b) Effectiveness of monochloramine

Monochloramine is not recommended as a primary disinfectant because of its weak  disinfecting power. This disinfectant is not effective for inactivation of Cryptosporidium. In systems using monochloramine, free chlorine is usually applied for a short time before addition of ammonia, or an alternative primary disinfectant is used (e.g. ozone, chlorine dioxide). (c) By-products of disinfection with monochloramine

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Water Purification

Treatment to produce a monochloramine residual poses the risk of nitrite formation in the distributi distribution on system, system, especially in low-flow low-flow stagnant stagnant areas, because bacteria on surfaces surfaces and in deposits may nitrify any slight excess of ammonia. 9 (C) 2(iii) Chlorine dioxide

It is a strong oxidant that can be used to control iron, manganese and taste and odour  causing compounds. It has also been used as a secondary disinfectant in many European countries.

(a) Mode of action-

Chlorine dioxide is highly soluble in water (particularly at low temperatures), and is effective over a range of ph values (ph 5-10). Theoretically, chlorine dioxide undergoes five valence changes in oxidation to chloride ionClO2 + 5e-

→

Cl- + 2O2-

However, in practice, chlorine dioxide is rarely reduced completely to chloride ion. Chlorine dioxide is thought to inactivate microorgani microorganisms sms through through direct direct oxidation oxidation of tyrosine, tyrosine, methionyl, methionyl, or cysteine cysteine containing containing   prote proteins ins,, which which interf interfere eress with with import important ant struc structur tural al region regionss of metabo metabolic lic enzyme enzymess or  membrane proteins. In water treatment, chlorine dioxide has the advantage of being a strong disinfectant. (b) Effectiveness of chlorine dioxide against bacteria and viruses-

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Water Purification

Chlorine dioxide is roughly comparable to free chlorine for inactivation of bacteria and viruses at neutral pH, but is more effective than free chlorine at pH 8.5 8. (c) Effectiveness of chlorine dioxide against protozoa-

Chlorine dioxide is an effective disinfectant for control of Giardia lambia and Cryptospor Cryptosporidium idium.. The amount required required for inactivati inactivation on is less as compared to free chlorine  but more as compared to ozone. (d) By products of disinfection with chlorine dioxide-

The chlorine in chlorine dioxide exists in +4 oxidation state, compared to an oxidation state of +1 for chlorine in free chlorine (in hypochlorous and hypochlorite ions). This means that chlorine and chlorine dioxide have different pathways for disinfection and formation of   by-products  by-products when used in drinking water treatment. treatment. For example, chlorine chlorine dioxide dioxide does not  produce significant levels of halogenated organic by-products. Chlorine dioxide forms undesirable inorganic by-products (chlorite and chlorate ions) upon its reaction with constituents of water such as dissolved organic carbon, microbes and inorganic ions. Therefore, a water utility may need to provide additional treatment depending on the level of these inorganic by-products and their specific regulatory requirements. 9 (C) 2(iv) Ozone

Ozone has been used for more than a century for water treatment, mostly in Europe, although its use is now spreading to other countries.

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(a) Mode of action

The mechanism by which ozone inactivates microbes is not well understood. Ozone in aqueous solution may react with microbes either by direct reaction with molecular ozone or by indirect reaction with the radical species formed when ozone decomposes. Ozone is known to attack unsaturated bonds, forming aldehydes, ketones or carbonyl compounds. Additionall Additionally, y, ozone can participate participate in electrophil electrophilic ic reactions, reactions, particular particularly ly with aromatic compounds, and in nucleophilic reactions with many of the components of the microbial cell. Carbohydrates and fatty acids react only slightly with ozone, but amino acids, proteins,  protein functional groups (e.g. disulfide bonds) and nucleic acids all react very quickly with it. It is likely, therefore, that microbes become inactivated through ozone acting on the cyto cytopl plas asmi micc memb membra rane ne,, the the prot protei ein n stru struct ctur uree of a viru viruss capsi capsid, d, or nucl nuclei eicc acid acidss of  microorganisms8. Free radicals formed by the decomposition of ozone are generally less effective for  microb microbial ial inacti inactivat vation ion than than molecu molecular lar ozone, ozone, becaus becausee microb microbial ial cells cells contai contain n a high high concentratio concentration n of bicarbonate bicarbonate ions that quench the free radical radical reaction, and many microbial microbial cells also contain catalase, peroxidase, or superoxide dismutase to control the free radicals  produced by aerobic respiration. In addition, some bacteria contain carotenoid and flavonoid   pigm pigmen ents ts that that prot protec ectt them them from from ozone ozone.. Thes Thesee fact factor orss can can acco account unt for for repo report rtss that that heterotrophic bacteria may be less susceptible to ozone inactivation than Giardia8. (b) Effectiveness of ozone against bacteria and viruses

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Water Purification

Of the vegetative bacteria, Escherichia coli is one of the most sensitive, while Gram  positive positive cocci (Staphyloc (Staphylococcus occus and Streptococ Streptococcus), cus), Gram-posit Gram-positive ive bacilli bacilli (Bacillus (Bacillus)) and mycobacteria are the most resistant. Mycobacterium avium can be effectively controlled by low doses of ozone, whereas the organism is highly resistant to free chlorine Viruses are generally more resistant to ozone than vegetative bacteria, although phage appear to be more sensitive than human viruses8. (c) Effectiveness of ozone against protozoa

For the protozoa Giardia lamblia and Naegleria gruberi, ozone inactivation did not follow follow linear linear kineti kinetics, cs, due to an initia initiall latent latent phase. phase. Ozone Ozone is effect effective ive for remova removall of  Cryptosporidium. Generally, excystation and vital staining are more conservative measures of oocyst inactivation than animal infectivity. Reliance on excystation and vital staining alone could greatly overestimate disinfection requirements for Cryptosporidium8. (d) Effectiveness of ozone against algal toxins

Ozonation is an effective process for destruction of both intracellular and extracellular algal toxins. Essentially complete destruction of microcystins, nodularin and anatoxin-a can be achieved if the ozone demand of the water is satisfied8.

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9 (C) 2(v) Ultraviolet light (a) Mode of action

UV light can be categorized as UV-A, UV-B, UV-C or vacuum-UV, with wavelengths ranging from about 40 to 400 nm. The UV light effective for inactivating microorganisms is in the UV-B and UV-C ranges of the spectrum (200–310 nm), with maximum effectiveness around 265 nm. Thymine bases on DNA and ribonucleic acid (RNA) are particularly reactive to UV light and form dimers (thymine–thymine double bonds) that inhibit transcription and replication of nucleic acids, thus rendering the organism sterile. Thymine dimers can be repaired in a process termed ‘photoreactivation’ in the presence of  light, or ‘dark repair’ in the absence of light. As a result, the strategy in UV disinfection has  been to provide a sufficiently high dosage to ensure that nucleic acid is damaged beyond repair 8. (b) Effectiveness of UV against bacteria and viruses

UV is an effective disinfectant for bacteria and viruses. Bacillus subtilis spores are commonly used as a bioassay organism because of their resistance to inactivation requiring very high dosage of UV light. Adenoviruses are double-stranded DNA viruses and are very resistant to UV inactivation. Typical doses used for drinking-water disinfection would not be effective for treatment of adenoviruses. (c) Effectiveness of UV against protozoa

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Water Purification

Most of the early work on UV disinfection of Giardia and Cryptosporidium relied upon excystation or vital staining to determine viability and found that UV inactivation was not effective for Giardia cysts or Cryptosporidium oocysts. However, more recent work using mouse infectivity or cell culture showed that low or medium-pressure mercury vapour UV lamps, or pulsed UV technology. Similar sensitivities to UV inactivation have recently been shown for Giardia. (d) Guidelines and standards relating to the use of UV radiation 8-

Recently, guidelines have been developed to evaluate the effects of reactor design, selection of UV lamps, performance standards for lamp ageing and fouling, and the accuracy of UV sensors. Standards for the installation and operation of UV systems are important  because the effectiveness of UV disinfection can be impaired by the transmittance of the water, colour and the presence of particulate material. 9 (C) 2(vi) Solar water disinfection (SODIS System) 9

Solar water disinfection is a method of treating relatively small amounts of water at the point of use. There are three ways in which solar radiation can be used to eliminate  pathogens. The first is through heating, second through the use of natural UV radiation and third through the use of mixture of both thermal and UV effects. None of these methods is yet widely used but laboratory experiments and field programmes show that some systems have good potential to produce potable water.

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Thermal heating from the sun can be via the solar cookers or from simply exposing  black-painted containers to the sun. In many systems temperatures can reliably reach over 55 degree Celcius killing many pathogens. With the cookers and some of the other systems the temperature of the water can easily exceed 65 degree Celcius, a pasteurization temperature capable of inactivating nearly all enteric pathogens.

Figure 5. SODIS System 8

The use of heating and UV radiation to simultaneously disinfect water is used by a number number of differ different ent solar solar treatm treatment ent system systems. s. The widest widest known known is the SODIS SODIS (Solar  (Solar  Disinf Disinfect ection ion)) syste system m which which is suitab suitable le for low-in low-incom comee countri countries. es. The only only equipm equipment ent

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required is locally available bottles to contain the water. This technique is being tested in various parts of the world. The half of the bottle furthest from the sun should be painted with  black paint to improve the heat gain from the absorption of thermal radiation (Figure 4), and the bottle can be laid on a dark roof to further increase the potential temperature rise in the water. The water requires several hours of strong sunlight to obtain the advantageous energy  between UV dosage and temperature rise9 (Figure 5).

Figure 6. Application of SODIS System 72

Water Purification

9 (C) 2(vii) Mixed oxidants 8

The use of mixtures of oxidants for microbial inactivation has gained attention as a way to maximize the efficiency of current disinfectants. The chemistry of mixed oxidant  production is complex, resulting in a solution of free chlorine, chlorine dioxide, ozone and various oxidation states of chlorine. The oxidants can be produced from a sodium chloride  brine in an electrolytically generated cell. Some researchers have found that the mixed oxidant process is equivalent to free chlorine for inactivation of biofilm samples. Additional research is needed to better understand the chemistry of seemingly incompatible oxidants within the mixed oxidant reaction.

 Sequential disinfection8

Other approaches to combining the advantages of various oxidants have used sequential sequential disinfecti disinfection. on. Some investigat investigators ors reported reported that the sequential sequential combination combination of free chlori chlorinat nation ion follow followed ed by monochl monochlora oramin minati ation on produc produced ed superi superior or oocyst oocyst inacti inactivati vation on compared to the sum of both disinfectants examined separately. The combination of free chlorine (1 mg/l for 60 min) and chloramines (2 mg/l for 240 min) are typical values that might be found in conventional treatment plants. Similar synergies have been seen for ozone and chloramines, free chlorine and chlorine dioxide, and chlorine dioxide followed by free chlorine or chloramines. Combinations of disinfectants require further investigation, and may  provide important insights into inactivation mechanisms and disinfection theory.

9 I (C) 3. Secondary disinfection 8 73

Water Purification

This section looks at the use of secondary disinfection to maintain water quality in distribution systems.

a) Maintenance Maintenance of of water water quality quality in the the distribution distribution systems

The purpose of a secondary disinfection is to maintain the water quality achieved at the treatm treatment ent plant plant throug throughout hout the distri distribut bution ion syste system m up to the tap. tap. Second Secondary ary disinfection provides a final partial barrier against microbial contamination and serves to control bacterial growth. The practice of residual disinfection has become controversial, with some opponents arguing that if biological stability is achieved and the system is well maintained, the disinfectant is unnecessary.

b) Factors Factors affect affecting ing microb microbial ial occurr occurrence ence

b) i Disinfectant residual and disinfectant level 

The growth of bacteria and occurrence of coliforms depend on a complex interaction of many factors including water temperature, disinfectant type and residual,   pipe pipe materi material, al, corros corrosion ion and other other enginee engineerin ring g and operat operation ional al parame parameter ters. s. Recent Recent research has indicated that various disinfectants differ in their ability to interact with  biofilm bacteria. Monochloramine, although a much less reactive disinfectant than free chlorine, is more specific in the type of compounds that it will react with. Therefore, monochloramine can be more effective than free chlorine at penetrating and inactivating certain types of biofilm, particularly those containing corrosion products. A study of 30 74

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distri distribut bution ion syste systems ms showed showed a differ differenc encee in the densit density y and occurre occurrence nce of colifo coliform rm  bacteria between systems using free chlorine and those using chloramines. Modelling indicates that the penetration of free chlorine into a biofilm is limited by its fast reaction rate rate.. Free Free chlo chlori rine ne is esse essent ntia iall lly y consu consume med d befo before re it can can react react with with the the bact bacter eria iall components of the film. Chloramines, on the other hand, are slower reacting; they can diffuse into the biofilm and eventually inactivate attached bacteria, a mechanism that has  been demonstrated using an alginate beed model. Some authors showed that free chlorine did not effectively penetrate alginate beads containing bacterial cells, but chloramines did  penetrate into the alginate material and reduced bacterial levels nearly one million-fold over a 60 minute interval. In addition to the type of disinfectant used, the residual maintained at the end of  the distribution system was also related to coliform occurrences. Systems that maintained dead-end free chlorine levels of less than 0.2 mg/l or monochloramine levels of less than 0.5 mg/l had substantially more coliform occurrences than systems maintaining higher  disinf disinfect ectant ant residu residuals als.. Syste Systems ms with with high high assimi assimilabl lablee organi organicc carbon carbon (AOC) (AOC) levels levels needed to maintain high disinfectant residuals to control coliform occurrences. Therefore, maintenance of a disinfectant residual alone does not ensure that treated waters will be free of coliform bacteria.

b) ii Biostability

The presence of biodegradable organic matter in water will promote bacterial growth, and may be related to the occurrence of coliform bacteria in distribution systems. 75

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Biodegradable organic matter is commonly measured as AOC or biodegradable dissolved organic carbon (BDOC). Some investigators showed that AOC concentrations increased in water samples treated with increasing chlorine doses.

b) iii Corrosion control and pipe materials 8

Corrosion of iron pipes can influence the effectiveness of chlorine-based disinfectants for inactivation of biofilm bacteria. Free chlorine is affected to a greater  extent than monochloramine, although the effectiveness of both disinfectants is impaired if corrosion rates are not controlled. Improving corrosion control can improve the ability of residual disinfectants to control bacterial growth. The pipe surface itself can influence the composition and activity of biofilm populations. Biofilms develop more quickly and suppor supportt a more more divers diversee microb microbial ial populat population ion on iron iron pipe pipe surfac surfaces es than than on plasti plasticc   polyvi polyvinyl nylchl chlori oride de (PVC) (PVC) pipes, pipes, even even with with adequat adequatee corros corrosion ion control control,, biolog biological ical treatment of water to reduce AOC levels and consistently maintained chlorine residuals.

b) iv Pressure, cross-connection control and maintenance

Microbial quality of drinking-water cannot depend only on maintenance of a residu residual al disinf disinfect ectant ant.. The extens extensive ive nature nature of the distr distribu ibutio tion n system system,, with with many many kilometres of pipe, storage tanks, interconnections with industrial users and the potential for for tamp tamper erin ing g and and vand vandal alis ism, m, provi provide dess oppor opportu tuni niti ties es for for conta contami minat natio ion. n. Cros Crosssconnections are a major risk to water quality. Although the risk can be reduced by vigilant control programs, complete control is difficult to achieve and water utilities 76

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worldwide face challenges in maintaining an effective cross-connection control program. Despite the best efforts to repair main breaks using good sanitary procedures, main  breaks provide an opportunity for contamination to enter the distribution system. Utilities typically isolate the affected section and repair, superchlorinate and flush the repaired  pipe. However, it may be difficult to achieve flushing velocities sufficient to remove all contaminated debris; also, microbiological tests to check the final water quality may not detect contaminating organisms. Backflow devices to prevent the entry of contaminated water are important as a distribution system barrier. Because of high costs, backflow devices are installed mainly on service lines for facilities that use potentially hazardous substances (e.g. hospitals, mortuaries, dry cleaners and industrial users). It is not common for all service connections to have backflow devices, so the possibility of back-siphonage exists at certain points. Also, installation of backflow devices for all service connections would make routine checking of the devices nearly impossible and, without routine inspection, the proper functioning of the units cannot be assured. Even when backflow devices have been installed, contamination events have occurred. For example, the failure of a backf backflo low w check check valve valve allo allowed wed wate waterr stor stored ed for for fire fire prot protec ecti tion on to ente enterr the the distributi distribution on system system in Cabool, Cabool, Missouri Missouri (USA)8. A broken vent in the storage tank  allowed birds to enter and contaminate the water with Salmonella. Three people died from Salmonella infection. Recent research is focusing on transient pressure waves that can result in hydrau hydrauli licc surges surges in the distri distribut bution ion system system.. These These waves waves have both a positi positive ve and negative amplitude, meaning that they can create transient negative pressures (lasting 77

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only a few seconds) in a distribution system, which may be missed by conventional  pressure monitoring. Because these waves travel through the distribution system, any  point where water is leaking out of the system is a potential entry point for microbes during the brief period of negative pressure.

c) Other non-chlorine disinfectants 8

Non-chlorine disinfectants include other halogens (iodine, bromine) and a variety of metals metals.. Variou Variouss author authorss have have propos proposed ed these these altern alternati ative ve disinf disinfect ectant antss for use in drinking-water supplies, although currently none have gained widespread acceptance. A combin combinati ation on of copper copper and silver silver ions ions can inacti inactivate vate bacter bacteria ia and viruse viruses, s, althoug although h contact times may be long (hours to days). Some studies showed that low levels of  chlorine (0.1 mg/l) combined with silver (38 μg/l) and copper (380 μg/l) resulted in inactivation of E. coli in tap water within 120 seconds. Photocatalytic titanium dioxide has also been examined for disinfection of water. 9 II. Purification of water on a small scale or Household purification of water.

Three methods are available that can be used for purification of water on an individual or domestic scale. They can be used either singly or in combination2. 9 II a) Boiling

This is a satisfactory method for purifying water for domestic purposes. To be effective the water must be brought to a ‘rolling boil’ for about 5 to 10 minutes. It kills all  bacteria, cysts, ova and spores and yields sterilized water. Boiling also removes the hardness 78

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of water by driving driving off carbon dioxide and precipitating precipitating the calcium carbonate. The taste of  water is altered but it is harmless. While boiling is an excellent method of purifying water, it offers no ‘residual protection’ against subsequent microbial contamination2. 9 II b) b) Chemical disinfection- It can be done by using following chemicals(i) Bleaching powder- Bleaching powder or chlorinated lime is a white amorphous

 powder with a pungent smell of chlorine. When freshly made it contains about 33% of  available chlorine. But when exposed to air and light it rapidly loses it chlorine content. Therefore it should be stored in a cool and dark place in a closed container that is resistant to corrosion. So it is mixed with lime to retain its strength and is called as ‘stablized bleach’. That amount of bleaching powder has to be added to the water which can produce ‘free’ residual chlorine of 0.5mg/litre at the end of one hour contact2. (ii) Chlorine solution- Chlorine solution may be prepared from bleaching powder. If 

4kg of bleaching powder with 25 percent available chlorine is mixed with 20 litres of water, it will give a 5% solution of chlorine. It should also be kept in a cool and dark place in a closed container 2. (iii) High test hypochlorite or perchloron- It is a calcium compound which contains

60 to 70% available chlorine. It is more stable than bleaching powder and deteriorates less on storage. Solutions prepared from HTH are also used for water disinfection2. (iv) Chlorine tablets- These are available under various trade names like ‘halazone’

tablets in the market. They are good for disinfecting small quantities of water but they are 79

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expensi expensive. ve. The Nation National al Enviro Environme nmenta ntall Engine Engineeri ering ng Resear Research ch Instit Institute ute,, Nagpur Nagpur has formulated a new type of chlorine tablet which is 15 times better than ordinary halogen tablets. A single tablet of 0.5g is sufficient to disinfect 20 litres of water 2. (v) Iodine- It can be used for emergency disinfection of water. Two drops of 2%

ethanol solution of iodine will suffice for one litre of clean water. A contact time of 20 to 30 minutes is needed for effective disinfection. Iodine does not react with ammonia and organic compounds to any great extent; hence it remains in its active molecular form over a wide range of pH values. High costs and the fact that the element is physiologically active are its major disadvantages2. (vi) Potassium permanganate- Once it was widely used but now its no longer used

to disinfect water. Although it is a powerful oxidizing agent but it is unable to kill all the  pathogenic microorganisms. It also alters the color, taste and smell of water 2.

9 II c) Filtration

Water can be purified on a small scale by filtering through ceramic filters such as Pasteur  ‘Chamberland filter’, ‘Berkefeld’ filter and ‘Katadyn’ filter . The essential part of  the the filt filter er is the the ‘can ‘candl dle’ e’ whic which h is made made of porc porcel elai ain n in the the Cham Chambe berl rlan and d type type and of  kieselgurh or infusorial earth in the Berkefeld filter. In the Katadyn Filter, the surface of the filter is coated with a silver catalyst so that the bacteria coming in contact with the surface 80

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are killed by the oligodynamic action of the silver ions which are liberated into the water. Filter candles of the fine type usually kill bacteria found in drinking water, but not the filter    passing viruses. Filter candles are liable to be lodged with impurities and bacteria. They should be cleaned with a hard brush under running water and boiled at least once a week. Only clean water should be used with ceramic filters. But these types of filters are not suitable for use under Indian conditions2.

9 III. Other water purification techniques

Other popular methods for purifying water, especially for local private supplies are list listed ed belo below. w. In some some count countri ries es,, some some of thes thesee meth method odss are are also also used used for for larg largee scal scalee

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municipal municipal supplies. supplies. Particula Particularly rly important important are distilla distillation tion (de-salin (de-salination ation of seawater) seawater) and reverse osmosis. 9 III (a) Carbon filtering 2-Charcoal, a form of carbon with a high surface area,

absorbs many compounds including some toxic compounds. Water passing through activated charcoal is common in household water filters and fish tanks. Household filters for drinking water sometimes contain silver to release silver ions which have an anti-bacterial effect. 9 III (b) Distillation 2- It involves boiling the water to produce water vapour. The

vapour contacts a cool surface where it condenses as a liquid. Because the solutes are not normally vaporized, they remain in the boiling solution. Even distillation does not completely   puri purify fy water water,, beca becaus usee of cont contam amin inan ants ts with with simi simila larr boil boilin ing g poin points ts and and dropl droplet etss of  unvaporized liquid carried with the steam. However, 99.9% pure water can be obtained by distillation. Distillation does not confer any residual disinfectant and the distillation apparatus may may be the the idea ideall plac placee to harb harbou ourr Legi Legion onnai naire res' s' dise diseas ase. e. Legi Legionn onnai aire res, s, dise diseas asee is an infect infectiou iouss diseas diseasee caused caused by bacteri bacteriaa belongi belonging ng to the genus genus Legion Legionell ella. a. Legionellosis infect infection ion normal normally ly occurs occurs after after inhali inhaling ng an aeroso aerosoll (suspe (suspensi nsion on of fine fine parti particle cless in air) air) contain containing ing Legion Legionell ellaa bacter bacteria. ia. Such Such partic particles les could could origin originate ate from from any infect infected ed water  water  source. When mechanical action breaks the surface of the water, small water droplets are formed, which evaporate very quickly. If these droplets contain bacteria, the bacteria cells remain suspended in the air, invisible to the naked eye but small enough to be inhaled into the lungs.

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9 III (c) Reverse osmosis2- Mechanical pressure is applied to an impure solution to

force pure water through a semi-permeable membrane. Reverse osmosis is theoretically the most thorough method of large scale water purification available, although perfect semi permeable membranes are difficult to create. Unless membranes are well-maintained, algae and other life forms can colonize the membranes. 9 III (d) Ion exchange- 2 Most common ion exchange systems use a zeolite resin bed

to replace unwanted Ca2+ and Mg2+ ions with benign (soap friendly) Na+ or K+ ions. This is the common water softener. 9 III (e) Electrodeionization 2- Water is passed between a positive electrode and a

negative electrode. Ion selective membranes allow the positive ions to separate from the water toward the negative electrode and the negative ions toward the positive electrode. High  purity deionized water results. The water is usually passed through a reverse osmosis unit first to remove non-ionic organic contaminants.

10. Purification of water in rural areas 83

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Wells are the main source of water supply in the rural areas. The need often arises to disinfect them sometimes on a mass scale, during epidemics of cholera and gastroenteritis. The most effective and cheapest method of disinfecting the wells is by bleaching powder. Steps in well disinfection 210 (A) Find the volume of the water in the well

•

Measure the the depth of the the water column- h metre metre

•

Measure the diameter of well-

•

Take the average of several readings of the above measurements.

•

Calculate the total volume of the well by the formula-

d metre

Volume (litres) = 3.14×d2 × h × 1000 100 0 4

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Figure 7. Well Chlorination 10 (B) Find the amount of bleaching powder required for disinfection.

Estimate the chlorine demand of the well and calculate the amount of bleaching powder  required to disinfect the well. Roughly, 2.5gms of good quality of bleaching powder would be required to disinfect 1,000 litres of water. This will give an approximate dose of 0.7mg of  applied chlorine per litre of water. 10 (C) Dissolve bleaching powder in water.

The bleaching powder required to disinfect the well is placed in a bucket and made into a thin paste. Not more than 100gms should be put in one bucket of water. More water is added till the bucket is three-fourths full. The contents are stirred well and allowed to sediment for 5 to 10 minute minutess when when lime lime settle settless down. down. The supern supernata atant nt soluti solution on which which is chlori chlorine ne soluti solution, on, is transferred to another bucket and the chalk or lime is discarded. 10 (D) Delivery of chlorine solution into the well.

The bucket containing the chlorine solution is lowered some distance below the water  surface, and the water is agitated by moving the bucket both vertically and laterally. This should  be done several times so that the chlorine solution mixes intimately with the water inside the well. 10 (E) Contact period

A contact period of one hour is allowed before the water is drawn for use. 85

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10 (F) Orthotolidine test

It is a good practice to test for residual chlorine at the end of one hour contact. If the ‘free’ residual chlorine is less than 0.5mg/litre, the chlorination procedure should be repeated  before any water is drawn. Wells are best disinfected at night after the day’s draw off. During epidemics of cholera, wells should be disinfected everyday.

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11. Household water treatment following emergencies and disasters Following an emergency, families frequently lack access to a safe source of drinking water. In this situation, it is critical to communicate to families the need to make water safe by themselves, at home or in shelters, to protect themselves from disease10. Household water treatment is effective, simple, and inexpensive. It is especially applic applicabl ablee to populat population ionss recover recovering ing from from a disast disaster er situat situation ion who often often lack lack facil faciliti ities es and resources. For example, if household bleach is available, a dilute chlorine solution can be made up and used to disinfect water. Water can also be safely treated by exposing it to sunlight. All that is required is a discarded clear plastic bottle. Another option to treat water at home is the use of simple ceramic pot filters moulded by local artisans. If available, commercially produced tablets containing chlorine, or sachets with combined flocculation and disinfection properties, can also effectively remove pathogens from water. All the approaches described improve the microbial quality of water and significantly reduce episodes of diarrhoeal disease. The "best" option should be selected according to local requirements. What is most important is that households treat their water using a method or  technol technology ogy that that is prompt promptly ly availa available ble and which which is most most applica applicable ble and accepta acceptable ble to the community in question10. Households should continue treating water until their supply is tested

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and found to be safe, or advised by local authorities. Some of these methods have already been discussed above in detail.

11 a) Chemical disinfection 10- Following emergencies, chlorine or iodine tablets may

have been distributed. If this is the case, water should be treated using the directions that come with the tablets. Alternatively, water may be disinfected by the use of existing types of chlorine compounds. At doses of a few mg/litre and contact times of about 30 minutes, free chlorine generally inactivates >99.99% of enteric bacteria and viruses, provided water is clear. Trained  personnel or community members should prepare a 1% chlorine stock solution from sodium hypochlorite (liquid bleach), calcium hypochlorite or high-test hypochlorite (powdered chlorine). The amount of chlorine needed depends mainly on the concentration of organic matter in the water and should ideally be determined for each situation. This solution should be added to water  to leave a free residual residual chlorine concentratio concentration n of 0.4 to 0.5 mg/l after 30 minutes, minutes, which can be determined using a special test kit. If this is not available, a slight smell of chlorine is a crude indicator.

11 b) Solar disinfection 10- Solar disinfection is an effective water treatment method that

is applicable to emergencies, especially when no chemical disinfectants are available. Ultraviolet rays from the sun are used to inactivate pathogens present in water. This technique involves exposing water in clear plastic bottles to sunlight for a day, for example on the roof of a house. In emergencies, empty bottles can be used that are left over from an initial shipment of  drinking water. Bottles need to be cleaned, filled to three quarters full and shaken thoroughly 20 88

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times, before being filled completely. The bottles are then exposed to sunlight for 6 hours (or for  2 days if the sun is obscured by clouds). The water should be consumed directly from the bottle or transferred in a clean glass for drinking. To be effective, solar disinfection must be applied to relatively clear water.

11 c) Filtration 10- If filters are available, then water filtration is another option to purify

water. Ceramic filters with small pores, often coated with silver for bacteriostasis, have been shown to be effective at removing microbes and other suspended solids. Filters need to be cleaned cleaned regularly regularly.. Monthly Monthly maintenance maintenance consists of scrubbing scrubbing the ceramic ceramic filter filter element element to unclog pores and washing the receptacle tank and spigot to prevent bacterial growth. If properly maintained, they have a long life. Ceramic filters can be mass-produced or manufactured locally.

11 d) Combined flocculation/chlorination systems 10- Commercially available sachets

can also dramaticall dramatically y improve improve the microbial quality quality of drinking water. These are formulated formulated to coagulate and flocculate sediments in water followed by a timed release of chlorine. These typically treat 10 litres of water. The water is normally stirred for few minutes and then strained, and then allowed to stand for another half hour. Please follow the instructions on the packet.

11 e) Boiling 10- Following a disaster many families will lack the facilities and fuel to boil

water. However, if practical, households can disinfect their drinking water by bringing it to a rolling boil, which will kill pathogens effectively except at high altitudes.

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11 f) Safe storage 10- Regardless of whether household water is initially of acceptable

microbiological quality, it often becomes contaminated with pathogens of fecal origin during transport and storage due to unhygienic storage and handling practices. Studies show that the use of contai container nerss with with narrow narrow opening openingss for filling, filling, and dispen dispensin sing g devices devices such such as spouts spouts or  taps/spigots, protect the collected water during storage and household use. Improved containers  protect stored household water from the introduction of microbial contaminants via contact with hands, dippers, other fecally contaminated vehicles or the intrusion of vectors.

 International Network to Promote Household Water Treatment and Safe Storage-

A number of the collaborating organizations in WHO's International Network to Promot Promotee Househo Household ld Water Water Treatm Treatment ent and Safe Safe Storag Storagee are respon respondin ding g in their their indivi individual dual capacities to the South Asia tsunami disaster. Members and their partners have reacted, for  exampl example, e, by donati donating ng floccul flocculati ation/ on/dis disinf infect ection ion sachet sachets, s, distri distribut buting ing bleach, bleach, and provid providing ing information on various household treatment technologies10.

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12. Rehabilitating water treatment works after an emergency It is very essential to re-maintain water supply in the community after any emergency. In urban areas, the population may be entirely reliant on the public water supply system for their  drinking water 11. Modern water treatment works (WTWs) rely on inputs of chemicals, electricity and skilled operators as well as the constructed plant and machinery (Figure 8). Clean water then needs to be delivered but piped systems can be prone to leaks, intermittent operation and contamination.

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Figure 8. Water Treatment Works Requirements

Managing a water supply system is a complicated task and it is strongly recommended that a suitably qualified engineer is responsible for the rehabilitation of an y system. Distribution systems are based on a series of large (trunk) water mains that feed into smalle smallerr pipes. pipes. Concent Concentrat ratee on trunk trunk mains mains before before moving moving onto onto local local distri distribut bution ion networ networks. ks. Reservoirs are needed at various points in the system to ensure continuous supplies of water.

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Both pipes and reservoirs need to be physically undamaged and clean11. The following priorities should be set up-

12 (a) Distribution first 11 - The first requirement is to get water into the distribution

system, with only enough treatment to ensure that the water is free of gross contaminants that may block or damage the pipes and pumps used. The order of rehabilitation should be:

•

Intake

•

Pumps and trunk water mains

•

Local distribution pipes

•

Storage reservoirs

•

Water treatment

This may involve by-passing all or part of the WTW (water treatment works). Initially water water may be pumped pumped direct directly ly from from the source source into into the distri distribut bution ion system system,, withou withoutt any treatment apart from the intake screens or simple sedimentation without chemicals. Storage in service reservoirs is important as it can ensure a continuous supply – intermittent supply can lead to contamination of water in the pipes and deprive people at the end of the pipes of water.

12 (b) Checking for leaks 11- Reducing leakage can improve both the quantity and quality

of water available to the public, but the distribution system is difficult to assess because it will be  buried and spread out over the whole urban area. Repair obviously leaks first as they are likely to 93

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 be the largest. Ask the public to report problems and sightings of leaks and puddles. Offer a small reward for information – this will be cost effective as it will quickly identify problem areas in the distribution network. Meters and pressure tests may also identify leaks and broken pipes.

12 (c) Risk assessment assessment 11- There are many chances for water to become recontaminated

once it leaves the WTW (such as improper handling or pollution through leaking pipes) so investments in water quality improvements need to be assessed by looking at the whole system and seeing the impact at the point of use. If water in the distribution system cannot be guaranteed to stay clean, it may be better to supply some users (such as hospitals) with water in a tanker, that can be disinfected and the quality maintained. Simple treatment can be provided at a more local level, such as chlorinating local water storage tanks. Pumps may be used at various stages, such as pumping water from the intake to the WTW or from the WTW to the distribution system. In some cases the water can flow for all or part of its way through the WTW under gravity. Replacement parts may take time to be delivered, so ask an engineer to make an early assessment of the state of the pumps. Power for pumps should be given priority over every other use – even over hospitals.

12 (d) Providing treatment in stages 11 - The order of water treatment is important – for 

example coarse filtration needs to take place before finer filtration and chlorination needs to take  place only once the water is physically clean and there is little chance of re-contamination during delivery or use. The order of WTW rehabilitation activities should be: 

Source protection (preventing pollution in the first place) 94

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

Physical treatment (screening, aeration, settlement, filtration)



Chemical treatment (coagulation, pH correction)



Disinfection (chlorination)

12 (e) Repairs, restoration and operation 11 - The damage to a water supply system will

vary according to the cause of the emergency. Floods may inundate and pollute the whole system, necessitating cleaning of the whole WTW and piped system and repairing or replacing electrical equipment. Damage to the electric motors for water pumps are a main cause of failure of the whole system. Earthquakes or landslides may leave machinery unharmed but break pipes or tanks. War or civil unrest may lead to looting or wanton damage, especially to mechanical and electr electrica icall plant. plant. Any precar precariou iouss situat situation ion may disrup disruptt inputs inputs of chemica chemicals, ls, electr electrici icity ty and technical expertise. Once part of the WTW has been re-commis re-commissioned sioned,, it will need to be operated. operated. Other  tasks include measuring the quality of the water to ensure that the WTW is being operated efficiently. Spare parts, water quality testing kits and other consumables will all be required.

•

Chemicals- Modern WTW rely on the addition of chemicals to aid the treatment process.

These include alum to help settlement, lime for adjusting the pH of the water and chlorine for disinfection. There may be a long time delay in gaining new supplies so the need for  chemicals should be identified and suppliers contacted. A reduced level of treatment can  be provided if chemicals are in short supply, using what materials are available where they are most needed (e.g. for disinfecting water supplies to hospitals). 95

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•

Power- It can be supplied by mobile generators if mains supplies are not available or 

reliable.

•

Maintenance- This includes manual tasks, such as cleaning screens, removing settled

sludge and lubricating pumps. The filters will begin to get clogged with solids. Pipes need to be checked for leaks.

12 (f) Other actions 11 – The following actions can also be taken up as a part of the rehabilitation works.



Pollution prevention: A more effective way of increasing the quality of water may be to

reduce the need for treatment in the first place. Preventing pollution from occurring in the first first place by providing providing environmental environmental sanitation sanitation (management (management and disposal disposal of excreta, excreta, solid solid waste waste and rainwa rainwater ter), ), contro controlli lling ng erosio erosion n and restri restricti cting ng public public access access to the catchment of the water source can reduce the amount of contaminants that have to be removed removed from from the water. water. Restor Restoring ing sewage sewage collec collectio tion n and treatm treatment ent may be more more important than a complete WTW. 

Public information: information: The The publi publicc shou should ld be kept kept info inform rmed ed of devel developm opmen ents ts in the the

availability and quality of water. They can help in reducing wastage and identifying leaks in the distribution system.

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13. Newer Water Purification Purification Techniques

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Research is being conducted worldwide in order to develop newer methods which can  be used to purify water and that too at an affordable cost. Some of the newer techniques are mentioned below13 a) Point-of-use water purification using rechargeable polymer beads 12

‘Halo-pure’ is one such enabling technical advance in the development of an entirely new   bioci biocidal dal medium medium in the form form of chlori chlorine-r ne-rech echarg argeab eable le polyst polystyr yrene ene beads beads that that is based based on  patented chemistry inventions from the Department of Chemistry at Auburn University. The discoveries were natural but creative outcome of a series of studies, covering more than a decade of research, focused on stabilizing chlorine on water insoluble, synthetic polymer surfaces.

Figure 9. Halo-Pure reversibly binds chlorine

The fundamental fundamental principles principles of the technology technology are deceptively deceptively simple to understand, understand, althou although gh their their incorp incorpora oratio tion n into into a reliab reliably ly reprod reproduci ucible ble and practi practical cal medium medium for water  water  sanitation has taken years of intense effort and research. Porous polystyrene beads are similar to those used for water softener resin beds, are modified chemically so as to be able to bind chlorine

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or bromine reversibly in its oxidative form. One way to think of this compound is as solid-state chloramines, biocidal in its own right, by virtue of giving up their chlorine to microbes that come in contact with them. But, unlike chloramines in a swimming pool, these surfaces are quite capable of repeatably taking up chlorine and establishing a stable chlorine bond. All that is required is enough free chlorine to surround the binding site. Almost no free chlorine is released when the beads are placed into the water flow. Typical levels range from 0.05 ppm to 0.20 ppm free available chlorine. This is not enough to kill anything without lengthy incubation. Hence, the swift efficacy of HaloPure depends on intimate contact between the microbes and the bound halogen on the polymer. What you have, then, is a solid surface, effectively biocidal on contact to contaminants in the water and repeatedly rechargeable when periodically exposed to free halogen. In this way, a powerful antimicrobial component can be introduced into a water purifier  that will not run out of steam, and have to be discarded. Instead, it can have its power regularly and conveniently “topped up” by the user. Organisms make contact with the display of chlorine, for example, on the surface of the beads, and pick up enough halogen to inactivate them in short order. Those not killed within seconds suffer a near-death experience, and succumb quickly in the product water as the adherent chlorine slowly damages the organism to the point of fatal consequences. Interestingly, because the halogen attaches to the organism it can be stripped off  as well. In the case of bacterium, if the halogen is stripped off before it has killed the organism, the bacterium can recover. However, for viruses such as polio, the damage is irreversible11. The technology holds the promise of reducing the impact of water borne diseases throughout the developing world. Its widespread use could contribute to the realisation of UN goals for access to safe water for all by 2015. And it could do so without resort to the massive 99

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infrastructure investments that are needed to reach this goal using more conventional centralised sanitation and distribution approaches11. 13 b) Water treatment using the seeds of the Moringa oleifera tree 13

Using natural materials to clarify water is a technique that has been practiced for  centuries and of all the materials that have been used, seeds of the Moringa have been found to  be one of the most effective. Studies have been conducted since the early 1970's to test the effectiveness of Moringa seeds for treating water. These studies have confirmed that the seeds are highly effective in removing suspended particles from water with medium to high levels of  turbidity (Moringa seeds are less effective at treating water with low levels of turbidity). Moringa oleifera seeds treat water on two levels, acting both as a coagulant and an antimicrobial agent. It is generally accepted that Moringa works as a coagulant due to positively charged, water-soluble proteins, which bind with negatively charged particles (silt, clay, bacteria, toxins, etc) allowing the resulting “flocs” to settle to the bottom or be removed by filtration. The antimi antimicro crobia biall aspect aspectss of Moring Moringaa contin continue ue to be resear researched ched.. Findin Findings gs suppor supportt recomb recombina inant nt   proteins both removing microorganisms by coagulation as well as acting directly as growth inhibitors of the microorganisms. While there is ongoing research being conducted on the nature and characteristics of these components, it is accepted that treatments with Moringa solutions will remove 90-99.9% of the impurities in water 12. Solutions of Moringa seeds for water treatment may be prepared from seed kernels or  from the solid residue left over after oil extraction (presscake). Moringa seeds, seed kernels or 

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dried presscake can be stored for long periods but Moringa solutions for treating water should be  prepared fresh each time. In general, 1 seed kernel will treat 1 liter (1.056 qt) of water. Dosage Rates: Low turbidity NTU<50 1 seed per p er 4 liters (4.225 qt) water  Medium turbidity NTU 50-150 1 seed per 2 liters (2.112 qt) water  High turbidity NTU 150-250 1 seed per pe r 1 liter (1.056 qt) water  Extreme turbidity NTU >250 2 seeds per 1 liter (1.056 qt) water  13 c) Water purification using aerobic granular sludge technology 14

With the new aerobic granular sludge technology, aerobic (thus oxygen using) bacterial granules are formed in the water that is to be purified. The great advantage of these granules is that they sink quickly and that all the required biological purifying processes occur within these granules. The technology therefore offers important advantages when compared to conventional water purification processes. For example, all the processes can occur in one reactor. Moreover, there is no need to use large re-sinking tanks, such as those used for conventional purification. Such large tanks are needed for this because the bacteria clusters that are formed take much longer time to sink than the aerobic granule sludge. The aerobic granular sludge technology is very promising, and has been nominated for the Dutch Process Innovation Award. The technology is now in the commercialisation phase. In the

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coming years, further research will be continued. Testing of this purification method is being done on a larger scale. The first installations are already in use in the industrial sector. 13 (d) Resin Based Treatment for Colour and Organic Impurities Removal 15

The rapid industrialization during the last few decades has resulted in tremendous increa increase se in demand demand of water water for industrie industries. s. A large large quantit quantity y of water water used used is ultima ultimatel tely y discharged into water bodies and land as waste water from various unit operations related to various industrial processes, and is responsible for their pollution. Attempts have been made to   preven preventt the advers adversee aesthe aesthetic tic effect effectss associ associate ated d with with indust industria riall waste waste water water discha discharge rgess by accelerating the removal of colour during treatment of the variety of industrial wastes. Colour  removal is also important if the water has to be made suitable for drinking purpose because many times underground water comes with colour and this colour has to be removed prior p rior to drinking. Among the manufacturing operations, the textile dying and finishing industries are directly directly affecting affecting colour; colour; which is the most noticeable noticeable characteristic characteristic of both the raw waste and treated effluent from this industry. Although biological treatment of these waste waters is usually effective in removing a large portion of oxidizable matter, but it is frequently ineffective in removing colour. The present method for colour removal uses a green colour basic dye, an anion exchange resin called ‘Duolite A 171/SC’ and a column made of borosil glass of height 40cm. From the results it was concluded that resin treatment is a better method than conventional biologic  process even at much higher filtration rate.

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103

Co ver  ag e

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of  55, sli

14. Various Water Supply Programmes and Projects in Rural Areas  pp 06 The Accelerated Rural Water Supply Programme (ARWSP) was introduced in 1972ed 7 73 by the Government of India to assist the States and Union Territories (UTs) to accelerate  ba un the pace of coverage of drinking water supply. The entire programme was given a Mission ck  co approach with the launch of the Technology Mission on Drinking Water and Related Water  ver  ha Management in 1986. Later in 1999 Department of Drinking Water Supply was formed to give  bit ed more emphasis on Rural Water Supply programme15. ati ha Co  bit on a) Bh Bhara aratt Nirm Nirman an Pro Progra gramm mmee ver  b) Swaj Swajal aldh dhar ara a

ati s ag

on c) Water Water qua qualit lity y in rura rurall bas areas ar e eas ed s d) Water quality monitoring monitoring surveillance programme programme of  and surveillance on of  e) First First water water qualit quality y surv survey ey wa 20 f) Su Subb-Mi Miss ssio ion n Pro Proje ject ctss Co ter  03 g) Other Indian drinkingmp water projects with Internatio International nal Collaborati Collaboration on qu reh sur  alit ens ve y 16 14 (a) Bharat Nirman Programme ive y aff  20

wit Ac ‘The Bharat Nirman Programme’ is a step taken towards building up a strong Rural ect

tio h Indi In diaa by stre streng ngth then enin ing g the the infr in fras astr truc uctu ture re in six six area areass viz. viz. (1) (1) Hous Housin ing, g, (2)R (2)Roa oads ds,, (3) (3) 05ed  pri n Electrific Elect ation, (4) Communicat Communication(Te lephone), ), (5) Drinking Drinking Water Water and Irrigatio Irrigation, n, with the 06 rification, haion(Telephone Pla ori help to of a plan to be implemented  bit in four years, from 2005-06 to 2008-09. The primary ty n resp re onsib ibil ilit ity y of prov provid idin ing g drin dr king ng water water faci facili liti ties es in the the count country ry rest restss with with Stat Statee 20spons atiinki Ac 104

AP ng  pro 99)  ble . Water Purification

ms of  ars eni c, flu15. Review of Literature ori “Chemical Contamination of California Russel HH and Jackson RJ (1987) 18, study on “Chemical de   Drinking Water ” revealed the presence of 1,2-dibromo-3-chloropropane in California’s Central an Valley in 1979. Increased monitoring since then has shown that other pesticides and industrial d chemic chemicals als are presen presentt in drinki drinking ng water. water. Contam Contamina inants nts also also includ includee natura naturally lly occurri occurring ng sal substances such as asbestos and even the by-products of water chlorination. Therefore various init measures are taken to prevent water pollution by inacting various laws and programs. . Cohn P, Bove F etal (1993) 19, study on “ Drinking Water Contamination And The

 Incidence Of Leukemia And Non-Hodgkin’s Lymphoma” Lymphoma” in 75 towns of New Jersey suggested a link between trichloroethylene (TCE) and perchloroethylene (PCE) in drinking water and the incidence of certain types of leukemias and Non-Hodgkin Lymphomas (NHL). Among females PCE and TCE were associated with the incidence of high grade lymphomas while in males diffuse large cell NHL was also associated with highest TCE category. Reducing the Risk of  Harris BL, Hoffman BW and Mazac FJ (1997) 20, study on “  Reducing Ground Water Contamination by improving Livestock Holding Pen Management ” revealed that the open lots or holding pens for feeding or holding live stock can be sources of groundwater  cont contam amina inati tion on and and the the pote potent ntia iall for for the the live live-s -sto tock ck feed feed yard yardss or hold holdin ing g pens pens to pollu pollute te

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groundwater depends on site selection, stocking density and slope. Moreover, live stock waste can most easily contaminate ground water if the facility or area of animal concentration is locate located d over coarse-t coarse-text exture uress permea permeable ble soils soils or if the water water table table is at or near the surfac surfacee concluding concluding that maintaining maintaining separation separation distance from wells, checking checking run-off run-off control, control, cleaning cleaning the feed lot, utilizing utilizing manure and checking checking abandoned abandoned live stock yards can certainly reduce the risk of ground water contamination. Contamination on Crisis: Crisis: Carson S and White S (1998) 21, study on “Sydney “Sydney Water Contaminati Manufacturing Dissent ” revealed the presence of Giardia and Cryptosporidium in the Sydney water supplies in Australia emphasizing the need for keeping high standards in public health. It was found that 50 cryptosporidium oocysts and 22 giardia cysts were present in 100 litres of  water advising people to boil the water before they drink till proper remedial steps are being taken. Mulugeta T and Faris K (1999) 22, study on “ Home-made water contamination in Jimma

town” town” using 100 randomly selected households that used treated water supplied by the town water treatment plant revealed that the effort made by the households to retain the quality of  water is encouraging. Easy access (i.e. shorter distance) to water sources (i.e. tap) make the households to practice good water handling and use enough water for hygiene purposes. The importance of hygiene education on how to maintain the quality of water in homes should not be neglec neglected ted as water water handlin handling g in homes homes is one of the hygiene hygiene behavio behaviorr that that determ determine iness the transmission of enteropathogens.

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Nevondo TS and Cloete TE (1999) 23 study on “ Bacterial and chemical quality of water 

in the Dertig village settlement ” using water samples from 5 water sources for a period of 13 weeks revealed that the chemical quality of all the water sources analysed was acceptable. In contrast, however, the bacterial quality of all the water sources, as suggested by the indicator  organisms used, exceeded the standards for potable water. Various pathogenic bacteria were also identified from the different water sources. Birds and some animals inhabiting the water can also contaminate the water through direct defecation and urination. Over-grazing and other poor  farming practices, common in rural areas, may result in large quantities of top soil ending up in the river after heavy rains, and thereby contributing to high turbidity. Daniel Karthe (2000) 24, study on “Drinking water contamination in Calcutta” using

water samples from 20 locations spread all over Calcutta during the 1999 post monsoon and the  pre monsoon season of 2000 revealed fecal coliform contamination contamination of tap water in some areas. areas. Moreover, lead was the only heavy metal found to exceed the maximum permissible limits in 39% of the drinking drinking water samples samples with with a maximu maximum m value value of upto upto 93mg/l 93mg/l.. Also, Also, public public awareness regarding problems related to drinking water contamination was checked with the help of standardized questionnaire given to 181 randomly selected people revealing that only few  people have knowledge about their causes and some even replied that they do not do anything to  purify the water they drink. Ahmad S, Sayed MH, Faruquee MH. Etal (2001) 25, study on “ Arsenic in Drinking and 

 Pregnancy outcomes” outcomes” in a group of 192 women of reproductive age (15-49 yrs) who were chroni chronicall cally y exposed exposed to arseni arsenicc through through drinki drinking ng water water to identi identify fy the pregnan pregnancy cy outcom outcomes es

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revealed revealed that the adverse adverse pregnancy pregnancy outcomes in terms of spontaneous spontaneous abortion, abortion, still still birth, and  pre-term birth rates were significantly higher in the exposed group than those in the non-exposed group. Also, skin manifestations due to chronic arsenic exposure were present in 22.9% of the respondents.  Drinking water contamination contamination in Walkerton, Walkerton, Ontario: Ontario: R Holme (2003) 26, study on “ Drinking  positive resolutions from a tragic event ” revealed contamination of drinking water with E.Coli and Camylobacter jejuni in water supply in Walkerton, Ontario in May 2000. Seven people died and 2000 were ill as a result. A judicial enquiry was set up to look into the circumstances surrounding the outbreak and also introduction of a new Drinking Water Regulation was done that incorporated some significant requirements for drinking water providers. Major feature of  this key regulation was the requirement to produce an independent Engineer’s Report on all  public water systems. Sharma S, Singh I and Virdi IS (2003) 27, report on “Microbial “Microbial contamination of 

various water sources in Delhi” Delhi” using 29 samples of waste water, 10 samples of surface water, 100 samples of ground water and 100 samples of drinking water from entire regions of Delhi revealed the presence of various water borne pathogens like Vibrio Cholerae and E.Coli in various various water sources in Delhi. Delhi. The presence of coliform coliform of faecal faecal origin origin in a majority majority of these samples showed that microbial contamination in ground water was wide spread and even deeper  layers of ground water may not be regarded as free from disease-causing micro-organisms. “Microbial  Souz Souza-G a-Guge ugelm lmin in M, Lima Lima C, Lima Lima S. etal etal (2003 (2003)) 28, study on “Microbial  Contamination in Dental Unit Waterlines” Waterlines ” using samples of waterlines of 15 dental units from 108

Water Purification

  priva private te dental dental clinic clinicss reveal revealed ed the presen presence ce of biofil biofilm m in Dental Dental Unit Unit Waterl Waterline iness (DUWL) (DUWL) indicating that the formation of biofilm is a universal problem and that pathogens from patients and the dental clinic environment can be cultivated from biofilm removed from DUWLs. Several methods of reducing the level of contamination in dental unit waterlines have been proposed, one of them being the use of a separate supply line independent of o f main line serving the clinic. Kilvington S, Gray T, Dart J. etal (2004) 29, study on “ Acanthamoeba Keratitis :The

  Role of Domestic Tap Water Contamination in the United Kingdom Kingdom”” using a sample of tap outlets from the homes of 27 patients with culture proven Acanthamoeba Keratitis revealed the   prese presence nce of Free Free Living Living Amoebae Amoebae (FLA) (FLA) includ including ing Acantha Acanthamoe moeba ba in water water storag storagee tanks tanks accounting for the significantly greater risk of Acanthamoeba Keratitis in U.K. supporting advice to avoid using tap water in contact lens care routines and adhering strictly to the manufacturer’s recommended lens hygiene procedures and use only sterile approved solutions for storage of  contact lens. Mohammed M Amro (2004) 30, study on “Factors Affecting Chemical Remediation of 

Oil Contaminated Water-Wetted Soil” using two types of oil samples and a soil sample revealed that the most significant factors affecting the removal efficacy of hydrocarbon compounds using chemical solvents from the water-wetted soil are the age of contamination and the composition of crude oil due to the alteration of wettability. It also provides guidelines for possible prevention of contamination with groundwater including chemical extraction from different types of soil, immediate action to remove the oil from contaminated sites, knowing the oil composition, using

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toluene toluene to remove remove the hydrocarbons hydrocarbons from water and monitoring monitoring inspection inspection and maintenance maintenance of  the pipelines and other souces pof p of oil contamination. Mohammed Mohammed M Amro (2004) 31, study on “Treatment “Treatment Techniques of Oil-Contaminated 

Soil and Water Aquifers Aquifers”” reveal revealed ed many many remedi remediati ation on techni techniques ques availa available ble to treat treat the oiloilcontaminate sites in off-shore as well as on-shore like Air sparging, Slurping, Soil air suction. However However the removal removal efficac efficacy y of these these methods methods depends depends on the type of the soil, weather  weather  conditions, penetration depth, sensitivity to the location and the toxicity of the chemicals. As there is no universal method that can be generally applied to completely remove the oil from contaminated sites, thus, preventing oil spills or leakages should b e the first concern. Jeong HJ and Yu HK (2005) 32, study on “The “The role of domestic tap water in

 Acanthamoeba contamination in contact lens storage cases in Korea Korea”” using 207 domestic tap water samples samples revealed revealed that domestic tap water, water, especially especially when supplied from roof storage storage tanks, tanks, is a source source of Acanthamoeba contamination contamination concluding concluding that contact lens wearers wearers should should  be aware of the risks associated with Acanthamoeba in tap water supplied from water storage tanks emphasizing the need for more education about the hygiene maintenance of water storage tanks. “Saline Water Contamination of the Saha DK and Choudhary DK (2005) 33, study on “Saline   Aquifer Zones of Eastern Kolkata” Kolkata” using Vertical Electrical Soundings (VES) revealed that mixing of fresh and brackish ground water has created environmental problems in certain areas of Kolkata. Aquifer zone at some depths south of Bhangar canal is vulnerable for saline water  contaminati contamination on as larger part of this area is occupied occupied by brackish/salin brackish/salinee water in the subsurface. subsurface. 110

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Also, ground water at shallow subsurface at many places upto a depth of 50m appears to be saline/brackish. Voltz M, Louchart X etal (2005) 34, study on “ Process of water contamination by

 pesticides at catchment scale in Mediterranean areas areas”” revealed that trace amounts of pesticides are present in surface and underground water bodies, far from the sites of pesticide application. Moreover, the intense rainfall events of semi-arid climates combined with often discontinuous soil cover by crops are well-known to cause intense overland flow and erosion, and thereby high leaching potential for pesticides. Lee SH and He J (2006) 35, study on “ Effect on Activated Fibre in Decentralized 

  Household Drinking Water Purification System System”” using an acrylic rectangular tank, 60cm in length, 20 cm in width and 70 cm in height with five internal compartments revealed that slow sand sand filtr filtrati ation on was consist consistent ently ly superi superior or in removi removing ng many many water water qualit quality y parame parameter terss when when Activated Carbon Fibre (ACF) was added. ACF played an important role in removing color, combining slow sand filtration with ACF enhanced the water purification process of slow sand filtration concluding that slow sand filtration has good potential to meet WHO guidelines for  water purification. “Sediment and Water  Yoshida M, Abderhaman L and Slimani (2006) 36, study on “Sediment Contamination with Mercury Caused by Industrial Waste and Waste Water in Oued El Harrach,  Alger ” using three sediment and five water samples from Oued El Harrach river basins revealed extraordinary high concentration of mercury in Oued El Harrach sediments and water. Other  heavy metals such as As, Cu, Pb, Cr and Cd were also detected in the river water and sediments. 111

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These pollutions are probably caused by the discharge of the un-treated industrial waste/waste water in the Oued El Harrach river. Martin D, Belanger D etal (2007)37, study on “Drinking Water and Potential Threats to

Human Health in Nunavik : Adaptation Strategies under Climate Change Conditions” using four   Nunavik  Nunavik communitie communitiess revealed revealed that the water from the individual individual home storage storage conditions conditions was much more contaminated than the water at the collection sites therefore residents should be made aware aware of the import importance ance of cleani cleaning ng their their contain containers ers adequat adequately ely between between filli fillings ngs.. Variou Variouss  proposals were also designed to prevent potential health problems like community environmental monitoring, maintaining water treatment facilities, involving health care workers in water quality testing, providing alternatives to chlorine treatment, raising awareness of water risks, cleaning water storage tanks and documenting gastroenteric disease. Moshtaghi H and Boniadian M (2007) 38, study on “Microbial “Microbial Quality of Drinking 

Water in Shahrekord (Iran)” (Iran)” using 100 tap water samples and 90 mineral water samples revealed the presence of pathogenic bacteria like Coliform species, E.Coli and Citrobacter in the drinking tap water of Shahekord city suggesting that emphasis be put on catchment management to limit contaminati contamination on of raw water and to ensure that the number of E.Coli in the source water remain remain low. “Use of Bacterial Indicators for  Shamabadi N and Ebrahimi M (2007) 39, study on “Use Contam Contamina inati tion on in Drinki Drinking ng Water Water of Qom” Qom” usin using g samp sample less coll collect ected ed from from all all wells wells,, a big big reservoir supplying big part of the city’s water, main pipeline networks, settling and resting reservoirs and finally treated water consumed by people under a suitable condition revealed that 112

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25% of the samples from main water resources of Qom city were contaminated with confirm but no conta contami minat natio ion n dete detect cted ed in trea treate ted d water water.. 16.7% 16.7% of samp sample less were were cont contam amin inat ated ed with with Pseudomonas aeruginosa after subculturing, but 11.8% of treated water samples confirmed to be contaminated with this bacterium in the second subculture emphasizing the need to repair and renew pipeline networks, cracks and erosions. Furusawa T, Maki N and Suzuki S (2008) 40, study on “ Bacterial contamination of 

drinking water and nutritional quality of diet in the areas of the western Solomon Islands devastated by the April 2, 2007 earthquake/tsunami” earthquake/tsunami” using 45 water samples from six earthquake and tsunami affected villages revealed that 92% and 80% of drinking water in the camps and villages, respectively were judged unsafe, in total only 38% of water sources tested were judged safe safe while while 66.7% 66.7% of water water sample sampled d from from steel steel water water tanks tanks was safe, safe, diarrh diarrhea ea preval prevalence ence increased after the disaster and the villagers had moderately sufficient dietary intakes suggesting the need for the provision of safe water or purifiers, education regarding water, and hygienerelated management in order to minimize water-borne diseases in devastated villages. Geetha A, Sivakumar P, Sujatha M etal (2008) 41, stud study y on “  Assessment of 

Underground Water Contamination and Effect of Textile Effluents on Noyyal River Basin In and   Around Tiruppur Town, Tamilnadu Tamilnadu”” using 26 sampling locations revealed that the underground water quality was contaminated at few sampling sites due to the industrial discharge of the effluents on to the river or land from the Tiruppur town highlighting the importance to take   per perio iodi dical cal moni monito tori ring ng of the the unde underg rgro roun und d wate waterr quali quality ty in this this regi region on for for our our futu future re sustainability.

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Mary Tiemann (2008) 42, report on “  Perchlorate Contamination of Drinking Water:

 Regulatory Issues and Legislative Actions” Actions” revealed the presence of Perchlorate (an explosive component of solid rocket fuel) in drinking water supplies especially in California and has also  been found in milk and many foods raising concern that the potential health risks of perchlorate exposure has increased and some states and Members of Congress have urged the Environmental Protection Agency (EPA) to set up a drinking water standard for perchlorate. Wu J, Yue J etal (2008) 43, study on “Use “Use of Caffeine and Human Pharmaceutical 

Compounds to Identify Sewage Contamination Contamination”” using water samples from upstream, middlestream and downstream points along Rocher Canal revealed that caffeine is a suitable chemical tracer to identify human-source contamination because of its early detection, compared with other chemicals monitored. Moreover high correlation was found between caffeine concentration and fecal coliform density in the Rocher Canal water samples demonstrating that caffeine is highly related to the human-source contamination. The existence of pharmaceuticals can also be employed for conforming sewage contamination.

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16. Summary It is very clear that water is an inseparable part of not only humans but of every organism on this planet. One cannot even think of surviving surviving without water. water. We as humans, utilize utilize water  not only for drinking purposes but also to perform our daily activities like bathing, washing, cleaning etc. Water is also needed by every industry or factory as a basic raw material to manufacture any kind of product. Water intended for drinking purposes should be safe and wholesome so that it should not cause any disease or discomfort after drinking. 115

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Water can be obtained from various sources like deep groundwater, shallow ground waters, upland lakes and reservoirs, rivers and canals etc. On the other hand there are various source sourcess which which can pollut pollutee water water by harmfu harmfull chemica chemicals ls for eg. Indust Industria rial, l, Agricul Agricultur tural al and Dome Domest stic ic Wa Wast stes es.. Ther Theree are are also also vario various us micr microo-or orga gani nism smss whic which h can can poll pollut utee water water like like  pathogenic bacteria, viruses, protozoa and helminths. These micro-organisms can contaminate water sources and can lead to the spread of water-borne diseases. Water is being purified since   pre-hi pre-histo stori ricc times times by employ employing ing variou variouss techni techniques ques.. With With the advance advancemen mentt in science science and technology, new techniques have come-up to purify water not only for commercial purposes but also for domestic purposes. Water purification methods like slow sand filtration and rapid sand filt filtra rati tion on are are used used to puri purify fy wate waterr for for drin drinki king ng purpos purposes es on comm communi unity ty leve level. l.

Vari Variou ouss

disinfection processes like chlorine disinfection, ozone disinfection, ultra-violet disinfection and solar disinfection are used to disinfect water before it is let off for house-hold utilization. Household purification of water is also done by boiling the water, disinfecting water with the help of  chemicals like chlorine, iodine, potassium permanganate and the use of house-hold water filters. There are other water purification techniques which can also be applied on local levels like carbon filterin filtering, g, distillation, distillation, reverse reverse osmosis. Even in the rural areas, areas, disinfection disinfection of water is done. As we know that wells are the main source of water supply in the rural areas therefore disinfection of wells is mandatory especially during the spread of epidemics. Disinfection of  wells is achieved with the help of chlorine solution by making a paste and mixing it with the well-water well-water.. There are various various new water purificatio purification n techniques techniques which have come up to purify water like purifying water by using rechargeable polymer beads, using the seeds of Moringa oleifera tree, purifying water by using aerobic granular sludge technology etc. 116

Water Purification

There are various water supply programmes started by Government o f India in rural areas like The Accelerated Rural Water Supply Programme (ARWSP), Bharat Nirman Programme, Swajal Swajaldhar dharaa etc. etc. These These progra programme mmess contrib contribute ute toward towardss provid providing ing accept acceptabl ablee qualit quality y and quantity of drinking water in rural areas. Moreover, tackling various problems linked with water   purificat  purification, ion, controllin controlling g water pollution pollution and educating educating public public regarding regarding water consumption consumption are also covered by these projects. It should be noted that each and every technique explained in the various sections have their advantages and disadvantages which are listed along with them. Before setting up any water   purification plant, it should be made clear that there are certain guidelines given by WHO which one has to follow in order to make the water best suitable for drinking water purposes. Any indust industry ry or syste system m concern concerned ed with with the purifi purificat cation ion of drinki drinking ng water water should should meet meet all the guidelines and criteria made by the WHO.

17. Bibliography 1) Wa Wate terr Wiki Wikipe pedi dia, a, Available URL- en.wikipedia.org/wiki/Water  en.wikipedia.org/wiki/Water  Accessed on- 23/03/09 117

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2) K. Park, Preventive and Social Medicine, M/S Banarsidas Bhanot Publishers, 20th

Edition, 2009, Pg 617-634.

3) Wa Water ter purifi purificat cation ion-Wi -Wikip kipedi ediaa Available URL- en.wikipedia.org/wiki/Water_purifica en.wikipedia.org/wiki/Water_purification tion Accessed on- 23/03/09

4) Mc Kinney Kinney and Schoc Schoch, h, Enviro Environme nmenta ntall Scien Science ce Syste Systems, ms, Jones Jones and Bartle Bartlett tt

Publishers, 3rd Edition, 2003, Pg 366-372.

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8) LeChevall LeChevallier ier M and Au Au KK, Inactivat Inactivation ion (disinfec (disinfection) tion)   pro proce cess sses es,, Wa Wate terr Trea Treatm tmen entt and and Path Pathog ogen en Cont Contro rol: l: Proc Proces esss Effi Effici cien ency cy in Achieving Safe Drinking Water, World Health Organization, 2004.

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and Pathogen Control: Process Efficiency in Achieving Safe Drinking Water. World Health Organization 2004.

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Available URL: www.echonet.org Accessed on- 15/03/09.

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Impu Impuri riti ties es Remo Remova val, l, Proc Procee eedi ding ngss of The The Nati Nation onal al Conf Confer eren ence ce on Civi Civill Engineering: Advancement and Challenges, 2007, Pg 349-352, Civil Engineering Department, M.M. Engineering College, Mullana.

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Development-Government Development-Government of India. Available URL - www.ddws.nic.in/arwsp.htm Accessed on-24/03/09

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Leukem Leukemia ia And Non-Ho Non-Hodgk dgkin’ in’ss Lymph Lymphoma oma.. The New Jersey Jersey Depart Departmen mentt Of  Health 1993, USA.

20) Harris Harris BL, Hoffman Hoffman BW and Mazac FJ. Reducing Reducing the Risk of Ground Ground Water 

Contamination by improving Livestock Holding Pen Management, Rural Well Water Assessment. Texas Agricultural Extension Service 1997.

21) Carson Carson S and White White S. Sydney Sydney Water Contaminat Contamination ion Crisis: Crisis: Manufacturing Manufacturing

Dissent. Science and Public Policy 1998; 25(4): 265-271.

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Inte Integr grat ated ed Deve Develo lopm pmen entt For For Wa Wate terr Supp Supply ly And And Sani Sanita tati tion on,, 25th WEDC Conference, Ethiopia, 1999.

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23) Nevond Nevondo o TS and Cloete Cloete TE. TE. Bacter Bacterial ial and chemic chemical al qualit quality y of water water in the

Dertig village settlement. Water SA 1999; 25, (2): 215-220.

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Hygi Hygien ene: e: Chal Challe leng nges es of the the Mill Millen eniu ium, m, 26th WEDC WEDC Conf Confer eren ence ce 2000 2000,, Bangladesh.

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outcomes. Environmental Health Perspectives 2001; 109(6): 629-631.

26) Holm Holmee R. Drin Drinki king ng wate waterr cont contam amin inat atio ion n in Wa Walk lker erto ton, n, Onta Ontari rio: o: posi positi tive ve

resolutions from a tragic event. Water Science and Technology 2003; 37(3); 1-6.

27) Sharma Sharma S, Singh Singh I and Virdi Virdi IS. Microb Microbial ial contamin contaminati ation on of variou variouss water  water 

sources in Delhi. Journal of Current Science 2003; 84(11): 1398-1399.

28) Souza-Gugelmin M, Lima C, Lima S. etal. Microbial Contamination in Dental

Unit Waterlines. Brazilian Dental Journal 2003; 14(1): 55-57.

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29) Kilv Kilvin ingt gton on S, Gray Gray T, Dart Dart J etal etal.. Acan Acanth tham amoe oeba ba Kera Kerati titi tiss :The :The Role Role of 

Dome Domest stiic Tap Tap Wa Wate terr Cont Contam amin inat atio ion n in the the Unit United ed King Kingdo dom. m. Jour Journa nall of  Investigative Ophthalmology & Visual Science 2004; 45(1): 165-169.

30) Moha Mohamm mmed ed M Amro Amro.. Fact Factor orss Affe Affect ctin ing g Chem Chemic ical al Rem Remedia ediati tion on of Oil Oil

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