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

Household purification of water during emergencies 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 programmes and projects in rural areas

95-107

15

Review of literature

108-117

16

Summary

118-119

17

Bibliography

120-26

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“Water can be without the company of 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, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the 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 vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Saltwater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earth's water is contained within water towers, biological bodies, manufactured products, and food stores. Other water is trapped in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land1. Water moves continually through a cycle of evaporation or transpiration (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

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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 facilitates industrial cooling and transportation. Approximately 70 percent of 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 groundwater b. Shallow groundwater c. Upland, lakes and reservoirs d. Rivers, canals and low land reservoirs e. Atmospheric water generation 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 groundwater is generally of very high bacteriological quality (i.e., a low concentration 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 6

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manganese content of this water to make it pleasant for drinking, cooking, and laundry use. Disinfection is also required. Where groundwater recharge is practiced, it is equivalent to lowland surface waters for treatment purposes. 2b. Shallow groundwaters- 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 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 pollutionWater 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 and dissolved minerals like salts of calcium, magnesium, sodium etc. A more serious aspect of water-pollution is that which is caused by human activity, and industrialization2. Sources of water pollution4Virtually all human activities produce some kind of environmental disturbance that contaminate surrounding waters. Eating (body wastes), gardening (pesticide and sediment 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

Water Purification

b. Agricultural and c. Domestic wastes

Figure 2. Sources of Water Pollution

3a. Industrial wastes4- Wastes from industry serve as major sources for all water pollutants. Many major industries contribute significantly to water pollution, but some of the 10

Water Purification

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. Nearly all power plants, whatever the fuel, are major sources of thermal (heat) pollution. 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) The mining and construction industries are major contributors of sediment and acid drainage. Sediment pollution occurs because both industries can denude the 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

Water Purification

3a (iv) Food processing industries include slaughter houses, canning factories, and many other plants that produce large amounts of animal and plant bodies that become oxygen demanding wastes in the nearby waters. These are also sources of water borne diseases. 3b. Agricultural wastes4- These are generated by the cultivation of crops and animals. Globally, agriculture is the leading source of sediment pollution, from plowing and other activities that remove plant cover and disturb the soil. Agriculture is also a major contributor of organic chemicals, especially pesticides. The other major agricultural pollutants have biological aspects. Oxygen 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 wastes4These are those produced by house-holds. Most domestic waste is from, sewage or septic tank leakage that ends up in natural waters. In the past, some cities dumped untreated or 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 of infectious agents. Plant 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 pollutants4Ultimately, 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 bacteria, viruses and protozoa which may cause diseases that vary in severity from 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 supplies5

Pathogen

Health significance

Main route of exposure

Persistence in Resistance water to chlorine supplies

High

Oral

Moderate

Low

E.coli

High

Oral

Moderate

Low

Salmonella typhi

High

Oral

Moderate

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

Contact with skin, May multiply

Moderate

enterocolitica

ingestion

Aeruginosa

in

immunosuppressed patients Aeromonas

Moderate

Oral, contact with May multiply

Low

skin Mycobacterium,

Moderate

atypical

Inhalation, contact May multiply

Low

with skin

VIRUSES Adenoviruses

High

Oral,

Inhalation,

_

Moderate

contact with skin Enteroviruses

High

Oral

Long

Moderate

Hepatitis A

High

Oral

Long

Moderate

Hepatitis E

High

Oral

_

_

Norwalk virus

High

Oral

_

_

Rota virus

High

Oral

_

_

Oral

_

_

Small

round Moderate

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

Naegleria fowleri

Moderate

Contact with skin

May multiply

Moderate

Balantidium coli

Moderate

Oral

_

Moderate

High

Oral

Moderate

Moderate

Moderate

Contact with skin

Short

Low

HELMINTHS Dracunculus medinencis Schistosoma species

Persistence in water5The 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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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 treatment6 The earliest recorded attempts to find or generate pure water date back to 2000 B.C. Early Sanskrit writings outlined methods for purifying water. These methods ranged 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 water6. 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 body that related directly to the four temperatures of the seasons6. According 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 believed good taste in water meant cleanliness and purity of that water. Hippocrates 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 ages6 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, archeological evidence suggests that the ancient Mayan civilization used similar aqueduct technology to provide water to urban residents. Further advancements in water technology 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 and experiments. Because of the low level of scientific experimentation, the future for water purification and filtration seemed very dark6. 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

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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 when James Simpson constructed an installation to treat the water supplied 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 immigrants, Hamburg suffered from a cholera epidemic that infected one in 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 pressure filters were first patented in England, since then a number of modifications and improvements have been introduced and hence attained varying degrees of popularity, particularly in highly industrialized counties6.

6. WHO Guidelines for drinking water quality (1993 &1996) The purpose of water quality standards it to minimize all the known health hazards, since it is obviously impossible to prevent all pollution. The guidelines for drinking water quality recommended by WHO relate to the following variables2. I.

Acceptability aspects

II.

Microbiological aspects

III.

Chemical aspects

IV.

Radiological aspects

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6 I. Acceptability aspects2- The following are the criteria which water should satisfy in order to be acceptable for drinking purposesa. Physical parameters b. Inorganic constituents 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- 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 surface waters are usually below 0.2mg/litre. Anaerobic ground waters may contain 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 can cause taste and odour 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 to the atmosphere, the ferrous ion oxidizes to ferric ion giving an objectionable 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 solution. At the room temperature, the average taste threshold for sodium is about 200mg/litre. (viii) Sulphate- The presence of sulphate in the drinking water can lead to the development of unusual taste to the drinking water. It is generally considered that 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 opalescent and develop a greasy film on boiling. Drinking water seldom contains 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 and parameters in drinking-water that may give rise to complaints from consumers2Constituents or

Levels likely to give rise to

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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, lowpossible 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

_

Indirect effects

pH

_

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 aspects2- 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) Bacteriological indicators b) Virological aspects c) Biological aspects 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 microorganisms as a whole. Supplementary micro-organisms like faecal-streptococci and sulphite- reducing clostridia, may sometimes be useful in determining the origin of faecal pollution. (i) Coliform organisms- These include all the aerobic and facultative anaerobic, gramnegative, 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

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

The coliform organisms are greatly present in the human intestine . these organisms are

foreign to potable water and hence their presence in water is indicative of any faecal contamination. •

They are easily detected by culture methods- as small as one bacteria in 100ml of water.

•

They survive longer than pathogens, which die out more rapidly than coliform bacilli.

•

The coliform bacilli have greater resistance to the forces of natural purification than 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 are usually resistant to chlorination used in water works. The presence of 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

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6II b) Virological aspects- Drinking water should be free from any viruses. 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 absent from drinking water.

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(iii) Free-living 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 aspects3- 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 adverse health effects after prolonged periods of exposure like heavy 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 inorganic6III 1. Inorganic constituents- These substances include arsenic, cadmium, 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-

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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, particularly in some developing countries, and they are usually found in drinking water, primarily because of industrial contamination. Effects on thyroid and nervous system were observed in some populations but these were long-term effects. The guideline 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 compounds are used in the production of aluminium and fluoride is released during 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 fluorosis. Fluoride is sometimes added to drinking water to prevent dental caries. Soluble fluorides are readily absorbed in the gastrointestinal tract after intake in drinking water. The guideline value suggested is 1.5mg/litre. 32

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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. Placental transfer of lead occurs in humans as early as 12th week of gestation and continues throughout development. Young children absorb 4-5 times as much lead as adults. Lead is a general toxicant that accumulates in the skeleton. Infants and children are 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. h) Nitrate and nitrite- These are naturally occurring ions that are part of the nitrogen cycle. Naturally occurring nitrate level in surface and ground water are generally 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. i) Selenium- Selenium levels in drinking water vary greatly in different geographical 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

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is an essential element for humans and forms an integral part of the enzyme glutathione peroxidase. Most selenium compounds are water soluble. 6III 2. Organic constituents- 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 constituents2

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Organic constituents

Upper limit of concentration (µg/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

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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.  Contamination of water with PAH should not occur during water treatment or distribution. Therefore the use of local-coal-tar based and similar 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 compounds present and the source of contamination should be identified, as the carcinogenic potential of PAH compounds varies. (b) Pesticides- The pesticides that are important in connection with water quality include chlorinated hydrocarbons and their derivatives, persistent herbicides, soil insecticides, pesticides that are easily leached out from the soil, and pesticides 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 pesticides2

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 aspects4- 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.

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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

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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 supplies 7. 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 it is desirable to have only a single pumping stage between the inlet and the distribution 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 manufactured 7. 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 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. Purification takes place during the downward passage, and the treated water is discharged 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 2-5% of the area needed for slow sand filters. In practice the reduction in space 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 air7. 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, biological oxidation, settlement, chemical 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 forms7. Man, extracting water at any stage of this cycle, makes use of these natural processes of purification and creates conditions that will enable them to be speeded up in time 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 techniques derive from natural processes; distillation plants simulate evaporation 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 methods, sedimentation, microstaining, flocculation. Filtration, aeration, and ultraviolet 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 water7. Undoubtedly the introduction of chlorination at the beginning of the present century greatly increased our ability to ensure the safety of drinking water 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 useful stage in a complex treatment pattern, as a second line of defense in the event 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 scale2 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 depends upon the nature of the raw water and the desired quality of water for example 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- By mere storage, the quality of water improves. About 90%of suspended impurities settle down in 24 hours by gravity. The water becomes clearer. This allows 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- 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 water2. 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 filters2 (ii) Rapid sand or mechanical filters2

44

Water Purification

9 I (B) (i) Slow-sand filtration 9 I (B) (i) 1.Elements of a slow sand filter7 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. b. A bed of filter medium (nearly always sand), within upon which the various

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 filter7 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 heavier particles of suspended matter start to settle, and some of the lighter particles 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 the filter medium itself. The schmutzdecke consists of 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 colour is removed, and a considerable proportion of inert suspended particles 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 water7. 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 is 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 have failed to penetrate. It sustains s teeming mass of micro-organisms, bacteria, 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 simple inorganic salts in solution. Not only has practically every harmful organism been removed but also the dissolved nutrients that might encourage 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 filters7- 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 countries where the construction methods are largely mechanized and 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.  Certain types of algae may interfere with the working of the filters, the usual result being the premature choking, which calls for frequent cleaning. In such 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 purpose.

9 I(B) (i) 4.Advantages of slow-sand filters7- 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- 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

51

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reduce the use mechanized plant to the minimum and to economize on skilled supervision.

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

of the filter-beds, which may be carried out either mechanically or manually. In developing countries and elsewhere where labour is readily available, the 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, the mixture of sand and organic matter being especially suitable for conditioning heavy clay soils.

52

Water Purification

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.

53

Water Purification

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, depending upon the turbidity and colour, temperature and the ph of the water.

54

Water Purification

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. 9 I (B) (ii) 4.Sedimentation-The coagulated water is led into the sedimentation tanks where it is detained from periods ranging from 2-6 hours. This leads to the settlement of flocculent precipitate along with impurities and bacteria. At least 95% of the flocculent 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 from the water and effects purification. 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

Water Purification

9 I (B) (ii) 6.Back-washing2- 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 takes about 20 minutes. In some types of rapid sand filters, compressed air is used as a part of the back-washing process. 9 I (B) (ii) 7. Advantages of rapid-sand filters2- The 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. 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

Water Purification

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. 2. Primary disinfection — a common component of primary treatment of drinking-water,

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 disinfection8The principal factors that influence disinfection efficiency are disinfectant concentration, contact time, temperature and pH. Disinfectant concentration and contact time are integral to disinfection kinetics and the practical application of the CT concept (CT being the 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 factors that influence microbial sensitivity to disinfection include attachment to surfaces, encapsulation, aggregation and low-nutrient growth. Increased resistance to disinfection may

57

Water Purification

result from attachment or association of microorganisms to various particulate surfaces, 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 EB22 increased its resistance to disinfection, making the bacteria 100-fold more resistant to hypochlorous acid (HOCl) and 2.3-fold more resistant to monochloramine. Several investigators have isolated encapsulated bacteria from chlorinated water and concluded that production of the extracellular capsule helped protect bacteria from chlorine. Another study reported 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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Water Purification

9 I (C) 1. Pretreatment Oxidation8 Water utilities often add oxidants early in the treatment process to8: i. Maximize the contact time with the oxidant. ii. Oxidize compounds for subsequent removal by the treatment process (eg. iron or manganese). iii. Provide initial treatment in sufficient time for water to be further treated if necessary (eg. Oxidation of taste and odour compounds). iv. Control growth of microorganisms and higher organisms (eg. Zebra mussels) on intake structures and in treatment basins. v. Improve particle removal in subsequent clarification and filtration 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 overdosing of pre-oxidants, which can result in “pink coloured” water when potassium permanganate is misapplied. Also, the process can produce oxidation by-products 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

59

Water Purification

particulate material may interfere with microbial inactivation. Such material protects bacteria and viruses from disinfectants by creating an instantaneous disinfectant demand (preventing the maintenance of a disinfectant residual in subsequent treatment steps) and by shielding the microbe from the oxidant. The effect of particulate material on disinfection of cysts or oocysts has not been widely evaluated. Some investigators studied the effect of turbidity on disinfection of Cryptosporidium parvum oocysts by chlorine dioxide or permanganate, and found 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 disinfection8 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 gas and water react to form HOCl (hypochlorous acid) and hydrochloric acid (HCl). In turn, the HOCl dissociates into the hypochlorite ion (OCl–) and the hydrogen ion (H+), according to the following reactions: 60

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(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  between about pH 5.5 and 9.5, both HOCl and OCl– species exist in various proportions  above pH 8, OCl– predominates. The OCl– and HOCl species are commonly referred to as free chlorine, which is extremely reactive with numerous components of the bacterial cell. HOCl can produce 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 viruses8 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 Grampositive bacteria have thicker walls than Gram-negative ones. Enteric viruses are generally more resistant to free chlorine than enteric bacteria. Viruses associated with cellular debris or organic particles may require high 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 protozoa8-

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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) to achieve 99.9% inactivation. Chlorine based disinfectants are 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 not been effective in preventing outbreaks of cryptosporidiosis caused 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

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chlorine to monochloramine 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 cystine were oxidized to disulfides. Reaction of monochloramine with hemin (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 monochloramine may kill bacterial cells by reacting primarily with membrane 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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Treatment to produce a monochloramine residual poses the risk of nitrite formation in the distribution system, especially in low-flow stagnant areas, because bacteria on 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 actionChlorine 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- + 2O2However, in practice, chlorine dioxide is rarely reduced completely to chloride ion. Chlorine dioxide is thought to inactivate microorganisms through direct oxidation of tyrosine, methionyl, or cysteine containing proteins, which interferes with important structural regions of metabolic enzymes 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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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 8.58. (c) Effectiveness of chlorine dioxide against protozoaChlorine dioxide is an effective disinfectant for control of Giardia lambia and Cryptosporidium. The amount required for inactivation is less as compared to free chlorine but more as compared to ozone. (d) By products of disinfection with chlorine dioxideThe 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 when used in drinking water treatment. For example, chlorine 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. Additionally, ozone can participate in electrophilic reactions, particularly 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 cytoplasmic membrane, the protein structure of a virus capsid, or nucleic acids of microorganisms8. Free radicals formed by the decomposition of ozone are generally less effective for microbial inactivation than molecular ozone, because microbial cells contain a high concentration of bicarbonate ions that quench the free radical reaction, and many 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 pigments that protect them from ozone. These factors can account for reports that heterotrophic bacteria may be less susceptible to ozone inactivation than Giardia8. (b) Effectiveness of ozone against bacteria and viruses

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Of the vegetative bacteria, Escherichia coli is one of the most sensitive, while Grampositive cocci (Staphylococcus and Streptococcus), Gram-positive bacilli (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 linear kinetics, due to an initial latent phase. Ozone is effective for removal 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 repair8. (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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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 radiation8Recently, 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 System8

The use of heating and UV radiation to simultaneously disinfect water is used by a number of different solar treatment systems. The widest known is the SODIS (Solar Disinfection) system which is suitable for low-income countries. The only equipment 71

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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

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9 (C) 2(vii) Mixed oxidants8 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 disinfection. Some investigators reported that the sequential combination of free chlorination followed by monochloramination produced superior oocyst inactivation 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 disinfection8 73

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

a) Maintenance of water quality in the distribution systems The purpose of a secondary disinfection is to maintain the water quality achieved at the treatment plant throughout the distribution system up to the tap. Secondary 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 affecting microbial occurrence

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 material, corrosion and other engineering and operational parameters. 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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distribution systems showed a difference in the density and occurrence of coliform 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. Free chlorine is essentially consumed before it can react with the bacterial 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 disinfectant residuals. Systems with high assimilable organic carbon (AOC) 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 materials8 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 support a more diverse microbial population on iron pipe surfaces than on plastic polyvinylchloride (PVC) pipes, even with adequate corrosion control, biological 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 residual disinfectant. The extensive nature of the distribution system, with many kilometres of pipe, storage tanks, interconnections with industrial users and the potential for tampering and vandalism, provides opportunities for contamination. Crossconnections 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 backflow check valve allowed water stored for fire protection to enter the distribution system in Cabool, 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 hydraulic surges in the distribution system. These waves have both a positive 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 disinfectants8

Non-chlorine disinfectants include other halogens (iodine, bromine) and a variety of metals. Various authors have proposed these alternative disinfectants for use in drinking-water supplies, although currently none have gained widespread acceptance. A combination of copper and silver ions can inactivate bacteria and viruses, although 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 off carbon dioxide and 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) 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 container2. (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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expensive. The National Environmental Engineering Research Institute, 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 water2. (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 water2.

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 filter is the ‘candle’ which is made of porcelain in the Chamberland 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 listed below. In some countries, some of these methods are also used for large scale

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municipal supplies. Particularly important are distillation (de-salination of seawater) and reverse osmosis. 9 III (a) Carbon filtering2-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) Distillation2- 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 purify water, because of contaminants with similar boiling points and droplets 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 be the ideal place to harbour Legionnaires' disease. Legionnaires, disease is an infectious disease caused by bacteria belonging to the genus Legionella. Legionellosis infection normally occurs after inhaling an aerosol (suspension of fine particles in air) containing Legionella bacteria. Such particles could originate from any infected 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 semipermeable 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) Electrodeionization2- 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 disinfection210 (A) Find the volume of the water in the well •

Measure the depth of the water column- h 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 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 minutes when lime settles down. The supernatant solution which is chlorine solution, 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 applicable to populations recovering from a disaster situation who often lack facilities 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 technology that is promptly available and which is most applicable and acceptable to the community in question10. Households should continue treating water until their supply is tested 87

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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 disinfection10- 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 chlorine concentration of 0.4 to 0.5 mg/l after 30 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 disinfection10- 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) Filtration10- 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 regularly. Monthly maintenance consists of scrubbing the ceramic filter 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 systems10- Commercially available sachets can also dramatically improve the microbial quality of drinking water. These are 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) Boiling10- 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 storage10- 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 containers with narrow openings for filling, and dispensing devices such as 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 StorageA number of the collaborating organizations in WHO's International Network to Promote Household Water Treatment and Safe Storage are responding in their individual capacities to the South Asia tsunami disaster. Members and their partners have reacted, for example, by donating flocculation/disinfection sachets, distributing bleach, and providing 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 water11. 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 any system. Distribution systems are based on a series of large (trunk) water mains that feed into smaller pipes. Concentrate on trunk mains before moving onto local distribution networks. 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 first11 - 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 may be pumped directly from the source into the distribution system, without 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 leaks11- 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 assessment11- 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 stages11 - 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 operation11 - 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 electrical plant. Any precarious situation may disrupt inputs of chemicals, electricity and technical expertise. Once part of the WTW has been re-commissioned, it will need to be 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 actions11 – 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 place by providing environmental sanitation (management and disposal of excreta, solid waste and rainwater), controlling erosion and restricting public access to the catchment of the water source can reduce the amount of contaminants that have to be removed from the water. Restoring sewage collection and treatment may be more important than a complete WTW.



Public information: The public should be kept informed of developments in 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 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 beads12 ‘Halo-pure’ is one such enabling technical advance in the development of an entirely new biocidal medium in the form of chlorine-rechargeable polystyrene beads that is 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 principles of the technology are deceptively simple to understand, although their incorporation into a reliably reproducible and practical medium for 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 tree13 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 antimicrobial aspects of Moringa continue to be researched. Findings support recombinant 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 water12. 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 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 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 technology14 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 Removal15 The rapid industrialization during the last few decades has resulted in tremendous increase in demand of water for industries. A large quantity of water used is ultimately 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 prevent the adverse aesthetic effects associated with industrial waste water discharges 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 to drinking. Among the manufacturing operations, the textile dying and finishing industries are directly affecting colour; which is the most noticeable 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 06 pp 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 un ba the pace of coverage of drinking water supply. The entire programme was given a Mission co ck 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) Bharat Nirman Programme ver b) Swajaldhara

ati s ag

on c) Water quality in ruralbas areas e ed s d) Water quality monitoring of and surveillance programme on of e) First water quality survey wa 20 f) Sub-Mission Projects Co ter 03 g) Other Indian drinkingmp water projects with International Collaboration 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 India in six areas viz. (1) Housing, (2)Roads, (3) 05- by strengthening the infrastructure ed pri n Electrification, (4) Communication(Telephone), (5) Drinking Water and Irrigation, with the 06 ha Pla ori help to of a plan to be implemented bit in four years, from 2005-06 to 2008-09. The primary ty n responsibility of providing drinking water104 facilities in the country rests with State 20 Ac ati 08Ye

19 to tiv on

09 ar

tac 99 ity s.

kli (C AP ng 99) pro ble . Water Purification

ms of ars eni c, flu15. Review of Literature ori Russel HH and Jackson RJ (1987)18, study on “Chemical Contamination of California 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 chemicals are present in drinking water. Contaminants also include naturally occurring 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. y. Cohn P, Bove F etal (1993)19, study on “Drinking Water Contamination And The Incidence Of Leukemia And Non-Hodgkin’s 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. Harris BL, Hoffman BW and Mazac FJ (1997)20, study on “Reducing the Risk of 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 contamination and the potential for the live-stock feed yards or holding pens to pollute 105

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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 located over coarse-textures permeable soils or if the water table is at or near the surface concluding that maintaining separation distance from wells, checking run-off control, cleaning the feed lot, utilizing manure and checking abandoned live stock yards can certainly reduce the risk of ground water contamination. Carson S and White S (1998)21, study on “Sydney Water Contamination Crisis: 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” 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 neglected as water handling in homes is one of the hygiene behavior that determines 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 of tap water in some areas. Moreover, lead was the only heavy metal found to exceed the maximum permissible limits in 39% of the drinking water samples with a maximum value of upto 93mg/l. Also, 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” in a group of 192 women of reproductive age (15-49 yrs) who were chronically exposed to arsenic through drinking water to identify the pregnancy outcomes 107

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revealed that the adverse pregnancy outcomes in terms of spontaneous abortion, 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. R Holme (2003)26, study on “Drinking water contamination in Walkerton, Ontario: 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 contamination of various water sources in 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 water sources in Delhi. The presence of coliform of faecal origin in a 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. Souza-Gugelmin M, Lima C, Lima S. etal (2003)28, study on “Microbial Contamination in Dental Unit Waterlines” using samples of waterlines of 15 dental units from 108

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private dental clinics revealed the presence of biofilm in Dental Unit Waterlines (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 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” using a sample of tap outlets from the homes of 27 patients with culture proven Acanthamoeba Keratitis revealed the presence of Free Living Amoebae (FLA) including Acanthamoeba in water storage 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 to remove the hydrocarbons from water and monitoring inspection and maintenance of the pipelines and other souces pof oil contamination. Mohammed M Amro (2004)31, study on “Treatment Techniques of Oil-Contaminated Soil and Water Aquifers” revealed many remediation techniques available to treat the oilcontaminate sites in off-shore as well as on-shore like Air sparging, Slurping, Soil air suction. However the removal efficacy of these methods depends on the type of the soil, 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 be the first concern. Jeong HJ and Yu HK (2005)32, study on “The role of domestic tap water in Acanthamoeba contamination in contact lens storage cases in Korea” using 207 domestic tap water samples revealed that domestic tap water, especially when supplied from roof storage tanks, is a source of Acanthamoeba contamination concluding that contact lens wearers 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. Saha DK and Choudhary DK (2005)33, study on “Saline Water Contamination of the Aquifer Zones of Eastern 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 contamination as larger part of this area is occupied by brackish/saline water in the 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” 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” 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 filtration was consistently superior in removing many water quality parameters 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. Yoshida M, Abderhaman L and Slimani (2006)36, study on “Sediment and Water 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 communities revealed that the water from the individual home storage conditions was much more contaminated than the water at the collection sites therefore residents should be made aware of the importance of cleaning their containers adequately between fillings. Various 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 Quality of Drinking Water in Shahrekord (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 contamination of raw water and to ensure that the number of E.Coli in the source water remain low. Shamabadi N and Ebrahimi M (2007)39, study on “Use of Bacterial Indicators for Contamination in Drinking Water of Qom” using samples collected from all wells, a 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 contamination detected in treated water. 16.7% of samples were contaminated 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” 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 while 66.7% of water sampled from steel water tanks was safe, diarrhea prevalence 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, study on “Assessment of Underground Water Contamination and Effect of Textile Effluents on Noyyal River Basin In and Around Tiruppur Town, 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 periodical monitoring of the underground water quality in this region for our future sustainability. 113

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Mary Tiemann (2008)42, report on “Perchlorate Contamination of Drinking Water: Regulatory Issues and Legislative 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 of Caffeine and Human Pharmaceutical Compounds to Identify Sewage 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 without water. We as humans, 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 sources which can pollute water by harmful chemicals for eg. Industrial, Agricultural and Domestic Wastes. There are also various micro-organisms which can pollute water 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-historic times by employing various techniques. With the advancement in 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 filtration are used to purify water for drinking purposes on community level.

Various

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 filtering, distillation, reverse osmosis. Even in the rural areas, 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. There are various new water purification 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

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There are various water supply programmes started by Government of India in rural areas like The Accelerated Rural Water Supply Programme (ARWSP), Bharat Nirman Programme, Swajaldhara etc. These programmes contribute towards providing acceptable quality and quantity of drinking water in rural areas. Moreover, tackling various problems linked with water purification, controlling water pollution and educating public regarding water 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 industry or system concerned with the purification of drinking water should meet all the guidelines and criteria made by the WHO.

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