WATER POLLUTION
Hydrosphere covers more than 75 per-cent of the earth’s surface either
as oceans (salt water) or as fresh water. Hydrosphere includes sea,
rivers, oceans, lakes, ponds, streams etc.
Most of the earth’s surfaces water is in the oceans, which contains about
35 parts per thousand of dissolved salt of the remainder, most of fresh
water with salt content of 0.2% of found either in lakes and ponds (still
water) or in rivers and streams (running water).
Pollution of water is the presence of some foreign organic, inorganic,
biological, radiological or physical substances in the water. These
substances contaminate water by degrading its quality which may cause
health hazard or decrease the utility of water.
There are two principle sources of water surface water and ground
water. Surface water comes from streams, lakes, rivers, shallow wells
and reservoirs created by damming. Most surface water contains
suspended solids, organic and inorganic substances, microbes and
other biota. If these substances are present in water in optimum level,
they do not cause pollution.
Common Sources of Water Pollution
Common sources of water pollution are as follows:
i. Sewage: A main source of pollution is raw or partially
treated sewage discharged into rivers, lakes and streams.
The discharge of huge quantities of municipal and domestic
wastes and sewage pollute many water bodies. Sewage
consists of the excreta (faeces and nitrogenous wastes) of
animals. It is rich in organic matter and nitrogen compounds.
ii. Industrial Wastes: Various types of industrial
wastes are continuously poured in streams, rivers and
lakes. The industries that cause pollution are printing,
electroplating, soap manufacture, food products,
rubber and plastics, chemicals, textiles, steel, sugar
factories, glass manufacture etc. If industrial wastes
are not released directly into water bodies, they can
also percolate through the soil and pollute the ground
water.
iii. Fertilizer Pollution: Adding large amount of inorganic fertilizers to crop fields result
in the nutrient enrichment of streams, rivers and
lakes. A major part of fertilizer become available for
excessive algal growth. This is more true for
nitrogenous fertilizers (which are readily soluble)
than phosphatic ones.
iv. Radioactive Wastes: Many radioactive
isotopes escape to water reservoirs, rivers and
seas from nuclear power reactors. They enter the
food chain in ecosystem. These wastes may
accumulate in the bodies of aquatic animals like
fishes causing harm to them as well as animals
which eat them.
v. Oil Pollution: Oil is a major pollutant in the sea. Oil
spillages from tankers act as a toxic substance and affects
the aquatic organisms. Surprisingly, the effect of oil on
phytoplankton appears to be slight, but oil pose serious
threat to marine animals especially fishes and birds.
vi. Thermal Pollution: Various industries
require water for cooling. Thermal pollution is the
discharge of hot water into river and estuaries from
power stations. This raises the temperature of the
water, thereby increasing the metabolic rate and
oxygen consumption of microorganisms. This makes
it all the more difficult for fish to survive.
vii. Mining Wastes: Mining causes water
pollution in the form of acid drainage from coalmines,
debris and saw weeds from hydromining methods.
viii. Silt Pollution: Earth moving construction
projects, deforestation and flood result in the
production of silt in streams and lakes. This may
interrupt or prevent the reproduction of fish by
smothering eggs laid on the bottom.
Classification of Water Pollutants
Water is used for various purposes like bathing, excretion, laundry, food preparation,
cleaning of floors and equipment etc. After using the water, manufacturing plants, industries,
residential, and commercial establishments discharge wastewater which is contaminated by
many pollutants.
Water pollutants can be classified into the
following categories:
(a) Suspended matter (Solids) comprises of
silt, sand, mineral codes.
(b) Thermal discharges waste hot water
returned to the original water bodies.
(c) Pathogens (Bacteria, Viruses, Protozoa, Helminths)
(d) Natural Organic Pollutants
(e) Synthetic Organic Compounds (Detergents, Pesticides, Fertilizers)
(f) Inorganic Chemicals (Acids, Alkalies, Metals)
(g) Radioactive substances
(h) Sediments.
Effects of Water Pollution
(a) Phosphorus and Nitrates from fertilizers and detergents contaminate surface waters
where they act as nutrients and promote the growth of oxygen consuming algae which
reduce the D.O. level of water, killing fish and other aquatic organisms.
(b) Industrial effluents result in the addition of poisonous chemicals such as Arsenic,
Mercury, Cadmium, Lead etc. which kill aquatic organisms and may reach human body
through contaminated food (i.e. fishes etc.)
(c) Domestic, commercial and industrial effluents (petroleum refineries, paper mills,
distilleries, tanneries, slaughter houses) contaminate the water with organic pollutants.
These provide nutrition for micro-organisms
which decompose the organic matter and
consume oxygen and reduce the dissolved
oxygen level of the aquatic system there by
killing the aquatic organisms.
(d) Non-biodegradable pesticides
(especially organochlorines) travel through
food chains and ultimately reach human body where they accumulate in the fatty tissues and
affect the nervous system.
(e) Water borne infectious enteric diseases like typhoid, bacillary dysentery, cholera and
amoebic dysentery are the predominant health hazards arising from drinking contaminated
water.
(f) Fluoride containing pollutants cause fluorosis i. e. neuromuscular, respiratory gastro
intestinal and dental problems.
(g) Thermal pollution of water reduces the D.O. level of the aquatic system making it
incapable of supporting life.
(h) Oil pollutants have been known to be responsible for the death of many water birds and
fishes.
Control of Water Pollution
The following measures can be taken to control water pollution:
i. Control of Thermal Pollution:
For minimising thermal pollution, hot water should
be cooled before release from factories, and
removal of forest canopies and irrigation return
flows should be prohibited.
ii. Prohibition:
Besides reserving separate water supplies for
livestock, the following prohibition should be enforced to avoid contamination of the main
sources of drinking water.
(a) Bathing and washing of clothes in rivers and streams.
(b) Discharging untreated or treated domestic, commercial and industrial sewage in water
bodies.
iii. Judicious Use:
Pesticides (preferably less stable) and fertilizers should be very judiciously used to avoid
chemical pollution of water through agricultural farm run-offs.
iv. Reuse of Water:
The treated waste water can be reused for several purposes, for instance:
(a) Treated water can be reused for recreation purposes like fishing and boating.
(b) Treated water can be reused as industrial water
supply.
(c) Reclaimed waste water can be used for irrigation
or municipal purposes.
(d) Treated water can be reused for cooling
processes in thermal plants.
(e) In area of acute water scarcity, waste water
treated to the highest standards can be reused as
potable water (provided there is public acceptance
for waste water use).
v. Legislation:
For effective control of water pollution, legal provisions regarding water pollution should be
enforced by a special administrative machinery comprising of highly qualified and
experienced personnel.
CASE STUDY
The Damodar Valley: Durgapur Asansol Profile:
The river Damodar originates from Chhotanagpur plateau in Bihar, crosses about 500 km
through Bihar and W. Bengal and joins the Hooghly river opposite Falta at a distance of 58
km. South of Calcutta. The Damodar valley from Durgapur to Asansol forms the largest
industrial complex in West Bengal and the eastern region. This area is known as the “River
of India”.
Its high record of pollution is due to indiscriminate discharge of huge quantities of pollutants
generated by industries, mining and mineral processing industries which are concentrated
on both sides or in the proximity of the river.
Besides mining, transport and trade, there are some 50 large, 100 medium and 200 small
industries units extending from Giddi in Hibar to Durgapur in West Bengal along the mid-river
stretch of 300 km. The river segments upstream of Giddi and downstream of Bardhaman are
much less significant in terms of water pollution.
Indian Iron and Steel Co., Cycle Corporation of India, Carew and Co., Bengal Paper Mill and
Durgapur steel plant discharge various types of pollutant (some are non-degradable and
persistent) which accumulate in Durgapur barrage water.
The concentration of these toxic pollutants in barrage water are above the permissible limits
for surface water. Thus tannin – lignin (0.9 ppm), NH3 (0.5-6 ppm), phenol (0.002 ppm) are
found in barrage water, exceeding their respective tolerance limits.
It should be noted that the barrage water remains the sources of domestic water supply for
Durgapur city. The conventional water treatment methods fail to remove organic matter,
phenol and toxic metals so that these find their way into domestic water supply.
Furthermore, in the process of water treatment, chlorination enhances toxicity of water by
formation of toxic chloramines and chlorophenols through reactions with NH3 and phenol
respectively. Thus the residents of the city are constantly exposed to these toxic pollutants in
their domestic water supply.
On the other hand, the downstream river (beyond Durgapur barrage) is contaminated by
Tamla Nalah and HFC drain. The Tamla Nalah delivers a heavy pollution load to the river-
phenol (0.02 – 2.0 ppm), NH3 (10-40 ppm), C.O.D. (80-350 mg/I), sulphide (1.5-15 ppm), Hg
(0.01-0.05 ppm) which are deposited in the river bed. The sediments containing these
parameters in 10 to 100 fold excess act as storehouse of these pollutants and supply these
pollutants continuously by leaching action throughout the river course in the region.
People in the industrial belt are constantly exposed to health hazards due to synergic effect
of water pollution and industrial air pollution. The incidences of liver diseases such as
hepatitis, jaundice, dysentery etc. and respiratory diseases such as bronchitis, bronchial
asthma, pulmonary tuberculosis etc. are quite high in the INDUSTRIAL BELT.
