CHAPTER 2: Topic: POLLUTION-WATER
Learning Objectives:
· Awareness about water pollution created by the man.
· What are the types of water pollutants
· What are the causes of water pollution
· Effects of water pollution
Introduction
Water is essential for every living body. Every kind of reaction taking place on this earth is dependent on the
presence of water in one form or the other. Water covers more than 70 per cent of earth’s surface; 97.3 per
cent is in ocean and 2.7 per cent is fresh water. The fresh water is held up in ice cap and glaciers (72.2%),
ground water and soil moisture (22.4%), lakes and swamps (0.35%), atmosphere (0.04%) and stream
channels (0.01%).
Water is considered to be an important factor for assured agricultural and industrial production, and for
domestic uses.
Water is vital to our basic existence, but it is facing considerable dangers. Most of the ways in which water
is used represent a strain on water resources. Increasing population, urbanisation, agricultural activities and
industrialisation, accompa-nied by a greater mechanisation in every sector of life, have led to a constant
increase in requirements placed upon water.
Water pollution is producing hazards for many kinds of use, and for the supply of public drinking water in
particular. It has been estimated that 90 per cent of the available water in Gaza is polluted. The water
resource in the long term should be managed in such a way that:
· The ecological balance of water should be ensured or reestablished
· The supplies of pure water for the population, agriculture energy generation and industry are ensured.
· All other uses of water that serve the public remain feasible in the long term.
This can be achieved by precautionary planning, prohibition and restrictions on the discharges of pollutants,
the regulations of levies and charges as well as agreements with industry.
1. Sources of water pollution
The primary sources of water pollution are industrial wastes, agricultural and related activities, and urban
wastes.
a. Industrial Wastes
The major industries releasing wastes into water include food processing, textiles, chemicals and
petroleum products, rubber and plastics, leather, paper, pharmaceuticals and mineral processing.
The most common pollution is caused by proteins, oils, foodstuffs and carbohydrates in the wastes of glue
and gelatine factories, and the waste water of slaughter houses, wastes of paper and textile factories,
synthetic detergents causes chemical pollution. Even small amounts of these substances prevent aeration
and thereby reduce the efficacy of purification system.
· Some industries release the toxic substances which affect: the color, clarity, temperature and other
properties of water.
· The water discharged from thermal plants raises the temperature of lakes and rivers, and changes
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environmental conditions, thus affecting plant and animal life.
· The pollution also affects the taste and smell of drinking water for human consumption. Disposed city
water and the wastes of food manufacturing plants cause intensely bad odors owing to the large number of
nitrogen-containing substances.
· Industrial waste waters containing iron, manganese, phenols and other chemicals give water a
characteristic unpleasant odor and taste. Health standards normally require that drinking water be
odorless and tasteless.
Industrial wastes and particularly sewage are often disposed off on the banks of rivers, streams and canals
without being subjected to any purification process. This causes a proliferation of disease causing bacteria,
as well as sinusitis, ear, nose and throat infections, intestinal diseases, liver ailments and typhoid in persons
who swim in these waters.
Nuclear energy plants and atomic explosives in the atmosphere are the causes of radioactive pollution. When
it rains, radioactive material falls on the earth, mixes with eventually reaches human beings through the food
chain. The wastes of nuclear power plants are among the most serious environmental pollutants. Today,
these wastes are either buried into earth or stored at the bottom of the sea. Seepage can happen from the
storage depots.
b. Agricultural and Related Activities
Modern methods of irrigation and application of fertilizers to the soil is used to increase the crop yield.
Animal dung, plant and animal wastes, the surface flow of pastures, and the dust-soil resulting from
erosion, solid and liquid wastes, including stems and straw, that result from agricultural activities are
termed as agricultural pollution.
Transportation of sediments takes place during soil erosion from riverbeds anti dams, urban development
activities, and excavating and banking of earth for construction of inter-city highways or inner city roads
and buildings.
The significant effect of soil erosion is the phenomenon of eutrophication caused by phosphorus, which is
one of the most important plant nutrients. When it is added to the soil, phosphorus is absorbed by small
particles of soil and does not dissolve in large amounts. Phosphorus and other nutrients, which are carried
in this way together with sediment, cause an increase in certain types of moss growing in lakes and rivers.
The high level of respiration and oxygen consumption, which then occurs in the rivers, causes a reduction
in the kinds of plants and-animals living there. This phenomenon is known as eutrophication.
The chemical fertilizers applied to land for the purpose of increasing crop yield cause pollution, the most
harmful type resulting when nitrogen and phosphorus undergo chemical change within the system of
nature. It is only natural that productivity increases when chemical fertilizers are applied to agricultural
land. However, it is necessary to determine to what extent these fertilizers affect water pollution.
Although specific quantities of nitrogen and phosphorus are necessary for all living creatures, excessive
amounts of these elements pose drawbacks. For example, many groups of fish species have been found to
die of nitrogen poisoning as a result of excessive amounts of this element. “
Insecticides and herbicides are used to combat insects and weeds, in areas where high quality and high
yielding crops are grown. These chemicals mix with water sources thus causing pollution problems.
Chemicals used in pest and weed control affect the environment in a variety of ways, for example, they
cause pollution of air, water, and soil.
Moreover, insecticides and herbicides enter and remain in the soil for many years, get transported from
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water resources to food chains and finally penetrate into animal and human bodies.
c. Urban Waste Water
Two major sources of this kind of pollution are garbage and sewage while the threat of contagious
diseases forces cities to have closed sewage systems. These systems cause contamination of drinking
water through sewage. Since the foul water in sewage canals is generally disposed off in rivers, lakes or
seas, liquid urban wastes are an important cause of water pollution.
The coliform bacteria, especially Escherichia coli, are naturally occurring, harmless bacteria found in
the human intestine and faeces. Their level in water gives an indication of the degree of faecal
contamination. The higher the coliform count, the more likely it is that the water contains some
pathogenic agents form faecal contamination.
After wastewater treatment, large amount of wastewater produced in the major cities is released
indiscriminately to the sea or discharged on open land areas. Each Indian family disposes off
approximately 50 kg/week of wastes in the sewage water. Bombay city alone produces more than 3500
tones of garbage and 200 million tones of sewage daily. Sewage water carries high load of organic matters
(BOD) and large amount of plant nutrients.
Table 6.1: Nutrient status (mg/l except pH) of sewage effluents
Sample
pH
BOD
N
P
K
S
No.
1
7.1
95.00
53.00
8.00
124.90
20.6
2
7.2
107.28
58.10
6.92
80.70
34.2
3
7.1
78.46
45.00
8.36
60.23
19.7
4
7.4
115.70
34.00
5.73
77.53
24.3
5
7.6
98.67
40.00
4.82
82.80
31.2
6
7.2
150.47
29.73
6.30
59.27
32.2
7
7.4
102.34
48.21
7.44
50.23
20.4
8
7.7
118.23
52.60
4.21
67.18
19.0
Rapid population expansion and urbanisation, facilities for the treatment and proper sanitary disposal of
municipal wastewater lag far behind the development of sewerage systems. As a result, hundreds of
kilometres of river beds carry the flow of untreated or partially treated wastewater from the cities and towns.
This leads to pollution of ground water and in the case of flowing streams there is odour nuisance, breeding
of mosquitoes and poisoning of fish.
2. Agents of water pollution
Ecological functions of water and their use by various development activities are affected due to various
types of pollutants and effluents. Generally, these can be categorised into following groups:
Organic and inorganic matters
· Heavy metals
· Colour
· Radioactive substances
· Polychlorinated biphenyls
· Heat.
· Floating and suspended substances
a. Organic and Inorganic Matters
When the organic matters dissolve in water, they are being used in the form of energy and nutrients during
decomposition process.
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Pollutants in organic matter:
· Oxygen-consuming substances,
· Harmful to aquatic life when the oxygen consuming substances are relatively in large quantities,
· Toxic in nature on long-term basis.
The amount of oxygen consumed by organic matter in water depends upon various factors, like amount of
oxygen in the water and the amount of water in rivers. Lakes and streams help in slowing down of
decomposition process and oxygen can dissolve better in cold water. Depletion of oxygen in the sewerage
water depends upon the quantity of sludge in a particular time period. For consuming and destroying the
solid materials and bacteria, oxygen is required by aerobes and protozoa. This oxygen comes from the
dissolved oxygen (DO) in the water. The amount of oxygen required to sustain these organisms is called the
biological oxygen demand (BOD). The chemical oxygen demand (COD) refers to the oxygen being used in
converting organic wastes to inorganic materials.
What is the Relation Between BOD & COD, how it is Related with the Pollution?
When the BOD and COD levels start to overtake the DO levels then rivers begin to die. The level of
dissolved oxygen contents in some water bodies can be increased and BOD and COD levels have fallen,
which has resulted in the reduction of biodegradable matters. This applies to those particular rivers which
are passing through or situated near densely populated and highly industrialised cities and towns. Adverse
impact of depletion of oxygen in water is that the survival of water bodies which need oxygen becomes
impossible. The death of fish and zooplankton in water bodies is every day story of aquatic ecology and
environment. Rising of anaerobic species which can live without oxygen, produce foul smelling toxic
products of anaerobic respiration.
Table 6.2: Chemistry of aerobic and anaerobic decomposition
In general, in all watercourses the level of dissolved oxygen should not be below 3 ppm and should not
exceed 5 ppm limit. These levels are the most suitable for aquatic life, but sometimes the oxygen limit in
water depends upon a variety of aquatic bodies. The aquatic ecosystem is also polluted due to addition of
inorganic matters like phosphates and nitrates. The addition of 10-25 per cent of phosphates and nitrates in
water is the result of application of chemical fertilizers, which cause eutrophication.
b. Heavy Metals
Most of the chemicals released from industries, agricultural fields, households and various other sources
enter into the air and soil, and finally penetrate into the surface and ground water. These chemicals, the socalled trace elements, are poisonous in nature and disturb the ecosystem and have severe adverse effects on
human, plant and animal health. Among these heavy metals are (essential for human, plant and animal life in
low concentrations):
1. Arsenic (As): Arsenic exists as ordinary grey crystalline arsenic, black metalloid arsenic and yellow
arsenic. It occurs in elemental form, combined with sulphur as realgar (As2S2) or orpiment (As2S) and with
oxygen as white arsenic (As2O2).
Causes: vomiting, abdominal pains, dermatitis, bronchitis, carcinogenic to tissue of mouth, oesophagus,
larynx and bladder; and even leads to death.
2. Cadmium (Cd): soft, silvery-white metal, found associated with zinc ores and in the rare mineral
greenockite used in manufacturing of fusible alloys, electroplating and making control rods in nuclear
reactors.
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Causes: Japanese itai- itai disease, adversely affect the kidneys, liver and reproductive organ heart and lungs.
Cadmium is harmful to both fauna and flora because most of them absorb it and it remains in the plant and
animal tissues.
3. Cyanides: used in metal plating industry, for the heat treatment of metals, in some pesticides and
disinfectants. These are highly toxic chemicals whose inhalation or ingestion leads to nausea and even death.
4. Iron (Fe): The role of iron in the formation of chlorophyll in plants, abundant in soils because it is a
constituent of most of the minerals. Iron is a highly objectionable constituent in water both for household
and industrial use. Iron also affects the taste of beverages. Water courses can become fouled by the masses
of stringly growths associated with iron oxidizing microbes.
5. Lead (Pb): The addition of lead to petrol has caused its widespread distribution. It is a serious pollutant
near heavy metal smelters. Lead can enter the water from many sources like the mining and smelting of lead
bearing ores and metals, lead plumbing, paints and ceramic glazes, and the careless disposal of lead-zinc
batteries in the garbage.
Causes: Lead poisoning can lead to anemia, brain damage, and loss of kidney function. Children are
particularly susceptible to lead contamination. Most of the people uptake lead from drinking water, food and
air.
(vi) Manganese (Mn): widely in nature and used for manufacturing of steel. It is an important
micronutrient of soil. The metal is not a serious pollutant and most of the global water contains 0.005 to 1
mg Mn per litre of water.
Causes: Large concentration of Mn affects animals adversely, causing cramps, tremors and hallucinations,
manganic pneumonia and renal degeneration Manganese is a reddish-white, hard, brittle metal. It is difficult
to remove this chemical and the concentration of manganese should not exceed more than 0.005 ppm.
(vii) Mercury (Hg): Mercury is used extensively in plastic and chemical industries. It is found in various
forms like quicksilver, elemental mercury vapour, mercuric salts and organic mercury. Sources of mercury
releases to the environment include the recovery of metals, the burning of coal, the use of paint, and the
production of chlorine and caustic soda. Mercury is released from soil and vegetation in areas flooded by
new dams.
Causes: Methyl mercury in aquatic environment is very toxic, accumulates in the human body especially in
the kidney, brain, liver and intestine. It has been reported that accumulation of mercury is as high as 5000
times the amount found in fish, and is passed on to man which is highly toxic in nature. It is a liquid metal
which damages the nervous system on inhalation or ingestion, especially of its organic compounds.
(viii) Nickel (Ni): Nickel is commonly present in surface water in low concentration and relates to the
group of metals of iron-cobalt. It is soluble in ground water having a pH value of less than 6.6. Nickel is an
important constituent of alloys and also used as a catalyst in hydrogenation of vegetable oil. Volcanic
activities and wind erosion of soil particles each account for 40-50 per cent of air borne nickel.
Causes: Low amount of nickel is toxic to human health and a wide variety of plants. It has been reported
that human body contains an average of 10 mg of nickel. Main sources of this heavy metal are ocean,
atmospheric, industrial and municipal water High concentration of nickel can also cause physiological
disturbances in leaves of plants. In animals, it can cause dermatitis and respiratory disorders, including lung
cancer.
(ix) Zinc (Zn): It is an essential micronutrient, hard, bluish-white metal that occurs as calamine, zincite, and
zinc blend. It is used in alloys, especially brass, and in the galavanising of iron. Zinc is an essential and
beneficial element in human metabolism and does not appear to have a serious effect on human health.
Causes: One of the major determinants of the toxicity of zinc and other heavy metals is the water’s degree of
hardness. When the hardness increases, toxicity decreases. Fish, which can survive in water having 8 ppm of
copper concentration, were killed by water with a combination of one ppm of zinc.
c. Radioactive Substances
The radioactive substances enter into the water courses in the following different ways:
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· Processing of uranium ore
· Washing of contaminated clothes from laboratories
· Wastes from research laboratories where radioisotopes are used. Wastes generated from hospitals where
isotopes are used for diagnostic and therapeutic purposes
· Waste water released from nuclear power stations
· Waste generated during nuclear weapon testing.
d. Polychlorinated Biphenyls (PCBs)
Polychlorinated biphenyls (PCBs) are compounds used as insulators, transformer oils, heat exchangers,
plasticizers and a variety of other industrial acids. PCBs are toxic, as are chemicals used as industrial PCB
substitutes such as diphenyl, triphenyl, diphenyl ether, and alkyl naphthalenes. PCBs enter the aquatic
environment through sewage, leachates from solid waste dumps, spills and atmospheric deposition from
incomplete combustion.
e. Heat
Waste heat is produced when electricity is generated in power plants, and may be conducted away into
surface waters. The discharge of cooling water may have adverse consequences on the quality of the
receiving water. Various industries situated in rivers are using water for cooling purposes and release the
recycled hot water in the river leading to thermal pollution. The impact of hot water is that the temperature
of aquatic environment increases and it endangers the aquatic ecosystem. Changing water temperature can
change the species composition. Heat also increases the solubility capacity of some chemicals and decreases
the solubility of gases like oxygen.
e.g.: Blue-green algae which produce significant amount of toxins develop better in warm water than in cold
water.
f. Floating and Suspended Substances
Oil, grease, and other wastes like garbage on the surface water pollute the aquatic environment. On one side,
they create nuisance for the water-sporters and on the other hand, create toxicity in the water. Oil, grease,
and other wastes like garbage on the surface water pollute the aquatic environment. On one side, they create
nuisance for the water-sporters and on the other hand, create toxicity in the water.
e.g.: sea fire takes place as a result of oil leakage in the tankers leading to death of the aquatic fauna.
Even suspended organic and mineral solids, pesticides, silts, etc. clog the water flow and make the water
muddy and cloudy. These undissolved solids can affect the water physically for a long period.
3. Color
The presence of color in water means those hues inherent within the water itself which are formed from
colloidal substances and materials in solution. Color in water may occur because of the presence of humic
acids, fulvic acids, metallic ions, suspended matter, phytoplankton, weeds and industrial effluents. The
natural color of water gets changed due to entry of various chemicals used in industries, household and in
different processing units. For example, iron oxide and sulphate add red and yellow colors in the natural
water. They are not only harmful to the human, plant and animal life, but create foul smell and nuisance in
drinking water. Wastewaters released from distillery and dying units change the natural color of water into
brown to red.
4. Water pollution control
There is no any single formula or tool to control the water pollution. Various techniques, methodologies,
strategies, rules and acts jointly can form a platform to reduce the level of water pollution. There are
methods to check the industrial wastes, urban wastes, domestic as well as agricultural wastes.
1. Self Purification of Water
Every river, canal and stream has a self-purification capacity. It may be physical, chemical or biological in
nature.
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· Physical purification takes place when the chemicals are absorbed and the suspended particles settle
down slowly.
· Chemical purification occurs when organic and inorganic acids are neutralized by reaction with lime
(calcium carbonate).
· Biologically, purification occurs when microorganisms are able to degrade the organic matter that
reaches water ways.
In general, three types of treatment are adopted to purify the waste water.
4. Primary treatment
5. Secondary treatment
6. Tertiary treatment
Primary Treatment
In primary treatment, a combination of screens, filters, grit chambers and sedimentation tanks are joined
one after the other as shown in the figure. At the end, the water is treated with chlorine gas, which kills
the harmful bacteria, viruses, fungi, etc.
The by-products like sludge and other solid materials can be used as manures. About 60 per cent of the
solid materials and 30 per cent oxygen demanding wastes are removed by primary treatment.
Disadvantage: carcinogenic compound like trihalomethanes are created due to chlorination various types of
dissolved organic matters, salts, fats, etc. cannot be separated from wastewater.
Secondary Treatment
It is a biological method of purifying waste water where organic matters break down. In this method, the
organic matters are biologically degraded by different types of microorganisms under controlled conditions.
The biological oxidation of organic matter takes place under aerobic condition and wastes are aerated with
supply of oxygen for the microorganisms. The sludge materials settle down in the sedimentation tank and
can be removed through sludge digester. The purified water can be finally treated with chlorine gas where
harmful organisms can be killed.
Secondary treatment of wastes is accomplished by digesting them in an anaerobic digester with high
temperature. The microorganisms break down the organic matter into sludge and produce methane gas,
which can be used as a source of energy.
Thus, there are two main processes during secondary treatment:
a. Trickling filter. The wastes are passed through a trickling filter where long pipes rotate slowly over a bed
of stones, dripping wastes onto an artificial detritus food chain comprising bacteria, fungi, protozoa, snails
and insects. The organic compounds are consumed by bacteria and fungi, which are fed upon by the
protozoans, which, in turn, are consumed by snails and insects.
b. Activated sludge process: The sewage is pumped into a huge tank where it is mixed with air bubbles and a
bacteria-rich sludge for several hours. The organic matter is consumed by bacteria and the mixture is
pumped out to a sedimentation tank, allowing the sludge to settle out for reuse. Both primary and secondary
treatments remove about 90 per cent of the oxygen-demanding organic wastes. The secondary treatment is
more beneficial than primary treatment in relation to removal of the wastes from the water.
Table 6.3: Performance of primary and secondary stages of sewage treatment
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However, most of the salts, nitrates, phosphates, pesticides and radioactive materials still remain in the waste
streams. As most of the plants have only primary and secondary treatment facilities, a large amount of plant
nutrients is still being added to water bodies.
Tertiary Treatment
Tertiary treatment is a chemical method of cleaning polluted water. In this method, chemicals remaining in
the waste water are removed after primary and secondary treatments. For example, when the iron or
aluminium salts are added in the waste water, the precipitation of
phosphorus occurs. Nitrogen compounds including ammonia can be separated by chemical processes. The
major tertiary methods include:
a. Coagulation and sedimentation: The inorganic chemicals are precipitated by addition of alum, lime or iron
salts.
b. Adsorption: Activated carbon is used to filter the wastes for removing chlorinated hydrocarbons.
c. Oxidation: Organic contaminants are oxidized by several agents like ozone and potassium permanganate.
d. Reverse osmosis: Water is passed through a membrane impermeable to dissolved ions.
e. Biological methods: Algae and water hyacinths grown in ponds can be used to consume nitrates and
phosphates. The dissolved organic materials can be directly removed from the water by certain aquatic
plants such as duckweed.
5. Enforcement of Standards
Central Pollution Control Board has set up the standards to protect the water resources for various uses. The
Central Pollution Control Board and State Pollution Control Boards have set up the Effluent standards and
are being enforced through the Prevention of Water Pollution Act, 1974.
· Industries and municipal corporations must build sewers to collect and transmit the waste water to a
treatment plant before discharge to the river.
Marine Pollution
The marine environment is one of the main components of the natural environment and is closely linked to
the inland water resources. The pressure on the marine environment is due to pollution from on shore
sources, the use of the sea for transport, the exploitation of its energy and mineral resources, and its use as a
dumping ground for certain types of wastes. Estuaries are highly sensitive zones subject to pressure
from port, industrial, urban and tourist activities. The development of economic activities and the
urbanisation of coastal areas have put pressure on the marine environment with dangerous effects on coastal
ecosystems. Construction along the coast such as for industrial and tourist development, for example, affects
the marine environment by way of the discharge of pollutants, changes in currents and encroachments on the
sea.
Table 6.4: Pollution control standards adopted by the Central Pollution Control Board
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