POLLUTION
Human activities directly or indirectly affect the environment adversely. A stone crusher adds a lot of suspended particulate matter and noise into the atmosphere. Automobiles emit from their tail pipes oxides of nitrogen, sulphur dioxide, carbon dioxide, carbon monoxide and a complex mixture of unburnt hydrocarbons and black soot which pollute the atmosphere. Domestic sewage and run off from agricultural fields, laden with pesticides and fertilizers, pollute water bodies. Effluents from tanneries contain many harmful chemicals and emit foul smell. These are only a few examples which show how human activities pollute the environment. Pollution may be defined as addition of undesirable material into the environment as a result of human activities. The agents which cause environmental pollution are called pollutants. A pollutants may be defined as a physical, chemical or biological substance unintentionally released into the environment which is directly or indirectly harmful to humans and other living organisms.
Pollution
may be of the following types:
• Air pollution
• Noise pollution
• Water pollution
• Soil pollution
• Thermal pollution
• Radiation pollution
AIR POLLUTION
Air pollution is a result of industrial and certain domestic activity. An ever increasing use of fossil fuels in power plants, industries, transportation, mining, construction of buildings, stone quarries had led to air pollution. Air pollution may be defined as the presence of any solid, liquid or gaseous substance including noise and radioactive radiation in the atmosphere in such concentration that may be directly and indirectly injurious to humans or other living organisms, plants, property or interferes with the normal environmental processes. Air pollutants are of two types (1) suspended particulate matter, and (2) gaseous pollutants like carbon dioxide (CO2), NOx etc.
Particulate
pollutants
Particulate matter suspended in air are dust and soot
released from the industrial chimneys. Their size ranges from 0.001 to 500 μm in diameter. Particles less than
10μm float and move freely with
the air current. Particles which are more than 10μm in diameter settle
down. Particles less than 0.02 μm form persisent
aerosols. Major source of SPM (suspended particulate matter) are vehicles, power plants, construction
activities, oil refinery, railway yard,
market place, industries, etc.
• Fly ash
Fly
ash is ejected mostly by thermal power plants as by products of coal burning
operations. Fly ash pollutes air
and water and may cause heavy metal pollution in water bodies. Fly
ash affects vegetation as a result of its direct
deposition on leaf surfaces or indirectly through its deposition on soil. Fly ash is now being used for making
bricks and as a land fill material.
• Lead
and other metals particles
Tetraethyl
lead (TEL) is used as an anti-knock agent in petrol for smooth and easy running
of vehicles. The lead particles coming out from
the exhaust pipes of vehicles is mixed with air. If inhaled it produces injurious effects on
kidney and liver and interferes with development of red blood cells. Lead mixed with water and food can
create cumulative poisoning. It has
long term effects on children as it lowers intelligence. Oxides of iron, aluminum, manganese, magnesium, zinc
and other metals have adverse effect
due to deposition of dust on plants during mining operations and metallurgical
processes. They create physiological,
biochemical and developmental disorders in plants and also contribute towards reproductive failure in
plants.
Gaseous
pollutants
Power
plants, industries, different types of vehicles – both private and commercial
use petrol, diesel as fuel and
release gaseous pollutants such as carbon dioxide,
oxides of nitrogen and sulphur
dioxide along with particulate matter in the form of smoke. All of
these have harmful effects on plants and humans.
Prevention
and control of air pollution
(i)
Indoor air pollution
Poor
ventilation due to faulty design of buildings leads to pollution of the
confined space. Paints, carpets,
furniture, etc. in rooms may give out volatile organic compounds (VOCs).
Use of disinfectants, fumigants, etc. may
release hazardous gases. In hospitals, pathogens present in waste remain in the air in the form of
spores. This can result in hospital acquired infections and is an occupational health hazard. In
congested areas, slums and rural areas burning of firewood and biomass results in lot of smoke. Children and
ladies exposed to smoke
may suffer from acute respiratory problems which include running nose, cough,
sore throat, lung infection, asthama, difficulty
in breathing, noisy respiration and wheezing.
(ii)
Prevention and control of indoor air pollution
Use
of wood and dung cakes should be replaced by cleaner fuels such as biogas,
kerosene or electricity. But
supply of electricity is limited. Similarly kerosene is also limited. Improved
stoves for looking like smokeless chullahs have
high thermal efficiency and reduced emission of pollutants including smoke. The house designs
should incorporate a well ventilated kitchen.
Use of biogas and CNG (Compressed Natural Gas) need to be encouraged.
Those species of trees such as baval (Acacia nilotica) which are least smoky
should be planted and used.
Charcoal is a comparatively cleaner fuel. Indoor pollution due to decay
of exposed kitchen waste can be reduced by
covering the waste properly. Segregation of waste, pretreatment at source, sterilization of rooms
will help in checking indoor air pollution.
(iii) Prevention and control of industrial pollutio
Industrial pollution can be greatly reduced by:(a) use of cleaner fuels such as liquefied natural gas (LNG) in power plants, fertilizer plants etc. which is cheaper in addition to being environmentally friendly
(b) employing environment friendly industrial processes so that emission of pollutants and hazardous waste is minimized.
(c)
installing devices which reduce release of pollutants. Devices like filters,
electrostatic precipitators,
inertial collectors, scrubbers, gravel bed filters or dry scrubbers are
described below:
(i) Filters – Filters remove
particulate matter from the gas stream. The medium of a filter may be made of fibrous materials like cloth, granular
material like sand, a rigid material like
screen, or any mat like felt pad. Baghouse filtration system is the most common
one and is made of cotton or synthetic fibres (
for low temperatures) or glass cloth fabrics
(for higher temperature up to 290oC).
(ii) Electrostatic
precipitators (ESP)- The emanating dust is
charged with ions and the ionized
particulate matter is collected on an oppositely charged surface. The particles
are removed from the collection surface by occasional shaking or by rapping the surface.
ESPs are used in boilers, furnaces, and many other units of thermal power plants,
cement factories, steel plants, etc.
(iii) Inertial
collectors –
It works on
the principle that inertia of SPM in a gas is higher
than
its solvent and as inertia is a function of the mass of the particulate matter
this
device
collects heavier particles more efficiently. ‘Cyclone’ is a common inertial
collector used in gas cleaning
plants.
(iv) Scrubbers – Scrubbers are wet
collectors. They remove aerosols from a stream of gas
either by collecting wet particles on a surface followed by their removal, or
else the
particles are wetted by a scrubbing liquid. The particles get trapped as they
travel from
supporting gaseous medium across the interface to the liquid scrubbing medium.
Gaseous
pollutants can be removed by absorption in a liquid using a wet scrubber and
depends on the type of the gas to be removed
e.g. for removal of sulphur dioxide alkaline solution is needed as it dissolves sulphur dioxide.
Gaseous pollutants may be absorbed on an activated solid surface like silica gel, alumina, carbon, etc.
Silica gel can remove water vapour.
Condensation allows the recovery of many by products in coal and petroleum
processing industries from their liquid
effluents.
Apart
from the use of above mentioned devices, other control measures are-
• increasing the height of
chimneys.
• closing industries which
pollute the environment.
• shifting of polluting
industries away from cities and heavily populated areas.
• development and
maintenance of green belt of adequate width.
(iv)
Control of vehicular pollution
• The emission standards
for automobiles have been set which if followed will reduce the
pollution. Standards have been set for the durability of catalytic converters
which reduce
vehicular emission.
• In cities like Delhi,
motor vehicles need to obtain Pollution Under Control (PUC)
certificate
at regular intervals. This ensures that levels of pollutants emitted from vehicle
exhaust are not beyond the prescribed legal
limits.
• The price of diesel is
much cheaper than petrol which promotes use of diesel. To
reduce
emission of sulphurdioxide, sulphur content in diesel has been reduced to 0.05%.
• Earlier lead in the form
of tetraethyl lead was added in the petrol to raise octane level for smooth running of engines. Addition of lead in
petrol has been banned to prevent emission
of lead particles with the vehicular emission.
