Read this essay to learn about Environmental Pollution. After reading this essay you will learn about:- 1. Meaning of Environmental Pollution 2. Types of Environmental Pollution 3. Sources 4. Effects 5. Control.
- Essay on the Meaning of Environmental Pollution
- Essay on the Types of Environmental Pollution
- Essay on the Sources of Environmental Pollution
- Essay on the Effects of Environmental Pollution
- Essay on the Control of Environmental Pollution
Essay # 1. Meaning of Environmental Pollution:
The word pollution is derived from a Greek word meaning “defilement”. A few decades back the word “pollution” meant the addition of filth or poison to water or air. It was also referred to as ‘resource misplaced’. Environmental pollution is defined as an undesirable change in the physical, chemical or biological characteristic of air, water or land that will be, or may be, harmful to human and other life, industrial processes, living conditions and cultural assets; or that may or will waste or deteriorate our raw material resources. A formal definition of pollution can be said as un-favourable modification of the environment by human activities.
Pollution is nothing new. It dates back to mid-1600s when burning of coal was recognised as the cause of air pollution which caused health problems in human. Pollution affects not only the individual organism directly by weakening or killing it, but it also affects the population and ecosystem.
In some instances pollution tolerant species may increase in number as its competitor has been harmed by the same pollutant. Such effects may change the structure of the community making it less diverse. Thus, pollution of one kind or another is an important factor in structuring the habitat.
Sometimes environmental pollution may result not due to human activity but by other natural factors. For example, the huge build-ups of bird droppings (gnano) at some sea bird colonies, where the concentrations of nutrients prevent almost any living organism from colonizing at those sites. However, such examples of natural pollution are rare.
Dr. Kurt Waldheim, Ex-Secretary General of United Nations, while addressing a conference in 1972 opined that pollution of environment is a problem “no nation, no continent, no hemisphere, no race, no system can handle alone”.
He further said that “the quality of our atmosphere can be nothing else but the by-product of the behavior of the nations’. The protection, preservation and enhancement of environment for the present and the future generation is the responsibility of all states.
Essay # 2. Types of Environmental Pollution:
Environmental pollution can be broadly classified into two types:
(a) Natural and
But commonly, environmental pollution is classified on the environmental basis as:
(i) Air pollution,
(ii) Water pollution,
(iii) Soil pollution, and
(iv) Noise pollution.
(i) Air Pollution:
Degradation of air quality and natural atmospheric conditions constitute air pollution. When, due to some natural processes or human activities, the amount of solid wastes or concentration of gases other than oxygen increase in the air which are harmful to man and his environment, then the air is said to be polluted and this process is referred to as air or atmospheric pollution.
Air pollution is one of the most dangerous and common kind of environmental pollution that is reported in most industrial towns and metropolitan cities of our country and abroad such as Delhi, Mumbai, Kolkata, Kanpur, Chennai, Hyderabad, Bhopal, Jaipur, Ahmedabad, Nagpur, Firozabad, Agra and also in London, New York, Tokyo, Pittsburg, etc.
The importance of air pollution can be estimated by a calculated fact that air constitutes nearly 80 per cent of man’s daily intake by weight. A man breathes about 22,000 times a day inhaling about 16 kg of air.
Classification of Air Pollutants:
Air pollutants may occur in gaseous or particulate form and may be organic or inorganic in nature. On the basis of origin of pollutants they can be classified as primary or secondary pollutants.
1. Primary Pollutants:
These are emitted directly from the point source (identifiable source) e.g. carbon monoxide (CO), oxides of nitrogen (NOx), oxides of sulphur (SOx), hydrocarbons, radioactive substances etc.
2. Secondary Pollutants:
These are formed by interaction of primary pollutant(s) with other primary pollutant(s) or with some natural constituents of atmosphere, e.g. ozone (O3), peroxyacetyl nitrate (PAN), Photochemical smog etc.
(ii) Water Pollution:
‘Water is life’ is a common saying because all organisms including man need water for various purposes; it is needed for various metabolic activities and some organisms use it as habitat as well; man needs water for several purposes like bathing, washing, cooking, irrigation, flushing away wastes, generating electricity, manufacturing different products in industries, navigation, etc.
However, during all these processes the wastes and undesirable substances are continuously added to the water sources. A general survey has revealed that nearly 70% streams and rivers in our country contain polluted water. Rivers of our country like Ganga, Jamuna, Hooghly, Godawari, Cauvery, etc., which were once very pure in their waters, are polluted to the extent of 70%.
Realizing the importance, the Government has now started several projects to clean the waters of these rivers in phases to make them free from pollutants. The term water pollution, therefore, refers to any type of aquatic contamination which affects the living organisms.
(iii) Soil Pollution:
Land and soil are very essential like air and water, either directly or indirectly for the survival and maintenance of living organisms including man. Soil supports vegetation on which every living animal depends. However, like air and water soil may also get polluted.
There are many natural and synthetic materials that can adversely affect the physical, chemical and biological properties of soil and seriously affect its productivity. Therefore, any substance that reduces the productivity of soil is called soil pollutant and such soil is referred to as polluted.
Soil gets polluted either directly by dumping and disposal of solid wastes or indirectly by air pollution.
The major soil pollutants are different types of biocides used in agricultural practices fertilizers, industrial wastes such as chemicals, flyash and cinders which are residues of combustion of solid fuels, garbage, discarded food, paper, plastics, rubbers, cloth leather asphalt tin iron, lead, copper, building materials, dead animals like cattle, dogs, cats, birds, and discarded goods like refrigerators and autos, etc.
Huge quantity of unwanted materials causes serious disposal problems. From these, the organic wastes decompose and befoul the air; others do not decompose, hence, cause a problem for their disposal.
Biocides such as pesticides, insecticides, larvaecides, herbicides reduce the population of undesired species as also of the desired microorganisms in the soil. Therefore, their uncontrolled use affects the structure and fertility of the soil. Several pesticides or their residues are absorbed by the plants that affect the entire food chains and food webs.
The excretory products of humans and livestock, and digested sewage sludge used as manure pollute the soil. In underdeveloped and developing countries the poor sanitary condition aggravates soil pollution. Several disease germs contained in such wastes contaminate the soil and vegetables causing severe health hazards for human beings and domestic animals.
Salination of soil also affects its productivity and degrades the quality of land. Intensive farming with poor drainage also results in salination of the soil. An estimate suggests that there are nearly six million hectares of saline land in our country. In Punjab alone nearly 6000-8000 hectares of farm land are becoming saline and unfit for agriculture. About one-sixth of the arid and semi-arid lands of the world have high salinity.
(iv) Noise Pollution:
It is expressed as a dimensionless unit, decibel (dB). The international reference pressure of 2 Ã— 10-5 Pa is the average threshold of hearing for a healthy ear. Decibel scale is a measure of loudness. Noise can affect human ear because of its loudness and frequency (pitch). The Central Pollution Control Board (CPCB) committee has recommended permissible noise levels for different locations as given in Table 29.6.
Essay # 3. Sources of Environmental Pollution:
Sources of Air Pollution:
1. Industrial chimney waste:
The main constituents are sulphur di-oxide, oxides of Nitrogen, dust, acid vapours and carbon di-oxide.
2. Thermal power stations:
The main pollutants emitted are fly ash, sulphure dioxide, hydrocarbons (Benzene, benzpyrene, and methane) and other gases.
Automobiles emit (hydrocarbons) carbon monoxide, oxide of Nitrogen, lead oxides, aldehydes, esters, ether, peroxides and ketones. Thick veil of smog observed in cities now-a-days are formed by photo-oxidation of oxides of nitrogen and hydrocarbons in the presence of ultra violet light from the sun.
Toxicants like arsenic (metal refining industries), asbestos (cement industries), Carbon tetrachloride and chloroform (refrigerant, propellant), mercury (fungicides, paints, cosmetics and paper pulp industries), zinc (smeltors and scrap zinc refineries) and cadmium (Electroplating, welding, pesticides and phosphate fertilizers) are regularly making air unsuitable for breathing.
This growing menace can be kept under control by the following measures:
1. Use of non-conventional sources of energy which are completely non-polluting like- Solar energy, Wind energy, Sea wave energy etc.
2. Judicious use of fossil fuel.
3. Strict legislation and implementation of environmental laws.
4. Make public transport cheap and efficient.
5. To create awareness about problems and its solution.
(ii) Sources of Water Pollution:
Sources of water pollution are of two types:
(i) Natural Sources:
Clay and silt from soil erosion, leaching of minerals, falling of organic matter from the banks constitute natural sources of water pollution.
(ii) Anthropogenic or Man-Made Sources:
Domestic waste, sewage, soaps and detergents, run-off from agricultural fields having fertilisers and pesticides, industrial wastes, wastes from animal sheds and slaughter houses, oil spills, etc., all constitute the man-made sources of water pollution. Due to all these human activities and pollutants generated by them all types of water-bodies are becoming polluted.
Categories of Water Pollutants:
Water pollutants are categorized as under:
(i) Point Source:
It refers to pollutants, which enters the water-body from a discrete or single which enters source.
(ii) Non-point Source:
It refers to pollutants, the water-body from a wide source.
Types of water Pollutants:
The water pollutants can be grouped in to three categories based on their source:
(i) Domestic sewage
(ii) Industrial wastes
(iii) Agricultural run off
It primarily contains biodegradable organic matter, which is decomposed by the microorganisms. It is released from every household on daily basis.
Domestic sewage from home and hospitals may also contain pathogens and cause disease like typhoid, cholera, jaundice, dysentery, etc. This trigger the growth of algae and other aquatic plants; that may result in algal bloom.
Which in turn causes the following problems:
i. Fish mortality.
ii. Secretion of chemicals that are highly toxic to humans and other animals.
iii. Deterioration in water quality.
These are released from petroleum, paper manufacturing, metal and chemical manufacturing industries, etc., into water-bodies.
The industrial effluents contain toxic heavy metals like mercury and variety of organic compounds leading to bio-magnification.
Oil spills and thermal wastewater are physical industrial pollutants, out of which, oil spills are physical pollutants of industrial wastes that are accidental discharges of petroleum from tankers, offshore oil drilling and oil refineries. The thermal wastewater eliminates the organisms, which are sensitive to high temperature that causes damage to the indigenous flora and fauna.
The run-off from agriculture land is polluted with pesticides and fertilisers. It enters our water sources by seeping through the soil to groundwater or entering streams as surface run-off.
(iii) Sources of Soil Pollution:
Different sources of soil pollution are:
1. Solid waste materials
2. Pollutants from atmosphere
3. Pesticides & Biocides
4. Artificial fertilizers
6. Radiostopes, and
7. Soil erosion.
1. Solid Waste Materials:
One of the major pollution problems in large cities is the disposal of solid waste materials such as garbage, ashes, building materials, rubbles, empty bottles & cans, industrial wastes, paper, card board, plastics, rubber, cloth, leather, metal and glass and discoarded manufactured old products. Huge quantities of unwanted material cause serious disposal problems.
These solid wastes are sometimes called the “third pollution”, and they are disposed in big cities by controlled tripping or the sanitary landfill. In this untreated waste is buried in layers, covered by at least 9 inches of earth. The surface can then be used for housing or sports fields.
2. Pollutants from Atmosphere:
Many atmospheric pollutants are washed out by rain or other means reaching the soil. Examples are lead, sulphur and radio-active minerals.
3. Pesticides and Biocides:
Among the thousands of man-made chemicals released into the environment, the most detrimental are pesticides and other biocides. Many of these like chlordane, DDT, Dieldrin, Heptachlor, Loxaphene etc. are non-biodegradable and alter the basic structure of soil. Biocides may prove lethal to essential soil organisms. They can also make the soil toxic for plant growth.
One of the dangers of using a chemical as a biocide is that it tends to become concentrated in soil. This phenomenon is known as biological amplification. Many pesticides present in soil, have a direct harmful effect on bacteria, important in crop production. Pesticides such as thiram and phygon inhibit the formation of root nodules in leguminous crops.
So atmospheric nitrogen become unavailable to the plants, hence crop yield decreases. DDT, a commonly used pesticide accumulates in animals, causing reduced reproductive ability in birds and many health problems in man.
4. Artificial Fertilizers:
Most inorganic fertilizers also spoil the quality of agricultural soils in the long run. But organic manures are highly beneficial to soil.
Some elements e.g. nitrogen, potassium, calcium, phosphorus, sulphur, magnesium, iron etc. present in soil are normal growth nutrients for various organisms. Others such as mercury, lead, arsenic and chlorinated hydrocarbons are toxic to one or the other components of biological food chain. Such chemicals occurring in soil are deleterious both to man and ecosystem.
Metallic mercury is released into the soil from industrial, medical and individual sources. It is relatively a nontoxic metal. However, some bacteria in soil and water are able to convert this heavy metal into more toxic methylmercury and alkyl-mercury compounds. Mercury poisoning in man results in blindness, insanity, co-ordination loss, memory loss, deafness and ultimately death.
6. Radio-active Isotopes:
Many radioisotopes such as Radium -226, Uranium-235 or 238. Thorium-232, Potassium-40 and Carbon-14 occur in rocks and soils. Exposure of man to radiation may cause cancer, genetic damage and infant mortality.
7. Soil Erosion:
Soil erosion is a negative pollution (excessive use and removal of a particular resource in soil). Loss of soil productivity due to erosion, unplanned irrigation, overgrazing, deforestation and other defective agricultural practices lead to formation of deserts.
Deserts cover nearly 40% of the land surface in world. But deserts are spreading in every continent destroying arable land, uprooting livestock and seriously threatening food supplies. In India the Thar desert spreads annually over 12,000 hectares of Productive land.
4. Sources of Noise Pollution:
The main sources of noise are various modes of transportation (like air, road, and rail- transportation), industrial operations, construction activities and celebrations (social/religious) functions, elections etc.) electric home appliances.
High levels of noise have been recorded in some of the cities of the world. In Nanjing (China) noise level of 105 dB has been recorded, while in some other cities of the world these levels are: Rome 90 dB, New York 88 dB, Kolkata 85 dB, Mumbai 82 dB, Delhi 80 dB, Kathmandu 75 db.
Essay # 4. Effects of Environmental Pollution:
(i) Effects of Air Pollution:
Air pollution has adverse effects on living organisms and materials.
1. Effects on Human Health:
Human respiratory system has a number of mechanisms for protection from air pollution. Bigger particles (> 10 Âµm) can be trapped by the hairs and sticky mucus in the lining of the nose. Smaller particles can reach tracheobronchial system and there get trapped in mucus.
They are sent back to throat by beating of hair like cilia from where they can be removed by spitting or swallowing. Years of exposure to air pollutants (including cigarette smoke) adversely affect these natural defenses and can result in lung cancer, asthma, chronic bronchitis and emphysema (damage to air sacs leading to loss of lung elasticity and acute shortness of breath).
Suspended particulates can cause damage to lung tissues and diseases like asthma, bronchitis and cancer especially when they bring with them cancer causing or toxic pollutants attached on their surface. Sulphur dioxide (SO2) causes constriction of respiratory passage and can cause bronchitis like conditions. In the presence of suspended particulates, SO2 can form acid sulphate particles, which can go deep into lungs and affect them severely.
Oxides of nitrogen especially NO2 can irritate the lungs and cause conditions like chronic bronchitis and emphysema. Carbon monoxide (CO) reaches lungs and combines with haemoglobin of blood to form carboxy haemoglobin. CO has affinity for haemoglobin 210 times more than oxygen. Haemoglobin is, therefore, unable to transport oxygen to various parts of the body. This causes suffocation. Long exposure to CO may cause dizziness, unconsciousness and even death.
Many other air pollutants like benzene (from unleaded petrol), formaldehyde and particulates like polychlorinated biphenyls (PCBs) toxic metals and dioxins (from burning of polythene) can cause mutations, reproductive problems or even cancer.
Many other hazardous material like asbestos, beryllium, mercury, arsenic and radioactive substances cause lung disease and/or affect other vital organs like kidney, liver, spleen, brain etc. and some may also cause cancer.
2. Effects on Plants:
Air pollutants affect plants by entering through stomata (leaf pores through which gases diffuse), destroy chlorophyll and affect photosynthesis. During the day time the stomata are wide open to facilitate photosynthesis. Air pollutants during day time affect plants by entering the leaf through these stomata more than night. Pollutants also erode waxy coating of the leaves called cuticle.
Cuticle prevents excessive water loss and damage from diseases, pests, drought and frost. Damage to leaf structure causes necrosis (dead areas of leaf), chlorosis (loss or reduction of chlorophyll causing yellowing of leaf) or epinasty (downward curling of leaf), and abscission (dropping of leaves).
Particulates deposited on leaves can form enerustations and plug the stomata and also reduce the availability of sunlight. The damage can result in death of the plant. SO2 causes bleaching of leaves, chlorosis, injury and necrosis of leaves NO2 results in increased abscission and suppressed growth. O3 causes flecks on leaf surface, premature again, necrosis and bleaching.
Peroxyacetyl nitrate (PAN) causes silvering of lower surface of leaf, damage to young and more sensitive leaves and suppressed growth. Fluorides cause necrosis of leaf-tip while ethylene results in epinasty, leaf abscission and dropping of flowers.
3. Effects on Aquatic Life:
Air pollutants mixing up with rain can cause high acidity (lower pH) in fresh water lakes. This affects aquatic life especially fish. Some of the fresh water lakes have experienced total fish death.
4. Effects on Materials:
Because of their corrosiveness, particulates can cause damage to exposed surfaces. Presence of SO2 and moisture can accelerate corrosion of metallic surfaces due to formation of sulfuric acid. Metal parts of buildings, vehicles, bridges, wires and metallic railway tracks are affected.
Sulfuric acid also damages buildings and causes disfigurement of statues made up of marble and limestone. Sulfuric acid formed by the atmospheric SO2 and water vapours damages the leather binding of books.
The pages of the books also become brittle. SO2 can affect fabric, leather, paint and paper. Ozone in the atmosphere can crack of rubber. Nylon stockings are weakened and ultimately damaged. Tyres of various vehicles area also damaged. These daysâ€™ chemicals are added to prevent damage to tyre rubber by ozone. Oxides of nitrogen and ozone can also cause fading of cotton and rayon fibres.
(ii) Effects of Water Pollution:
Some important effects of various types of water pollutants are:
1. Oxygen Demanding Wastes:
Organic matter which reaches water bodies is decomposed by micro-organisms present in water. For this degradation oxygen dissolved in water is consumed.
Dissolved oxygen (DO) is the amount of oxygen dissolved in a given quantity of water at a particular temperature and atmospheric pressure. Amount of dissolved oxygen depends on aeration, photosynthetic activity in water, respiration of animals and plants and ambient temperature.
The saturation value of DO varies from 8-15 mg/L. For active fish species (Trout and Salmon) 5-8 mg/L of DO is required whereas less desirable species like carp can survive at 3.0 mg/L of DO. Lower DO may be harmful to animals especially fish population. Oxygen depletion (deoxygeneration) helps in release of phosphates from bottom sediments and causes eutrophication.
2. Nitrogen and Phosphorus Compounds (Nutrients):
Addition of compounds containing nitrogen and phosphorus helps in the growth of algae and other plants which when die and decay consume oxygen of water. Under anaerobic conditions foul smelling gases are produced.
Excess growth or decomposition of plant material will change the concentration of CO2which will further change pH of water. Changes in pH, oxygen and temperature will change many physico-chemical characteristics of water.
Many wastewaters especially sewage contain many pathogenic (disease causing) and non-pathogenic micro-organisms and many viruses. Water borne diseases like cholera, dysentery, typhoid, jaundice etc. are spread by water contaminated with sewage.
4. Toxic Compounds:
Pollutants such as heavy metals, pesticides, cyanides and many other organic and inorganic compounds are harmful to aquatic organisms. The demand of DO increases with addition of biodegradable organic matter which is expressed as biological oxygen demand (BOD).
BOD is defined as the amount of DO required to aerobically decompose biodegradable organic matter of a given volume of water over a period of 5 days at 20Â°C. More BOD values of any water sample are associated with poor water quality. The non-biodegradable toxic compounds bio-magnify in the food chain and cause toxic effects at various levels of food chain.
Toxic substances polluting the water ultimately affect human health. Some heavy metals like lead, mercury and cadmium cause various types of diseases. Mercury dumped into water is transformed into water soluble methyl mercury by bacterial action. Methyl mercury accumulates in fish.
In 1953, people in Japan suffered from numbness of body parts, vision and hearing problems and abnormal mental behaviour. This disease called Minamata disease occurred due to consumption of methyl mercury contaminated fish caught from Minamata bay in Japan. The disease claimed 50 lives and permanently paralyzed over 700 persons.
Pollution by another heavy metal cadmium had caused the disease called Itai-itai in the people of Japan. The disease was caused by cadmium contaminated rice. The rice fields were irrigated with effluents of zinc smelters and drainage water from mines. In this disease bones, liver, kidney, lungs, pancreas and thyroid are affected.
Arsenic pollution of ground water in Bangladesh and West Bengal is causing various types of abnormalities.
Nitrate when present in excess in drinking water causes blue baby syndrome or methaemoglobinemia. The disease develops when a part of haemoglobin is converted into non-functional oxidized form.
Nitrate in stomach partly gets changed into nitrites which can produce cancer-causing products in the stomach.
Excess of fluoride in drinking water causes defects in teeth and bones called fluorosis.
Pesticides in drinking water ultimately reach humans and are known to cause various health problems. DDT, aldrin, dieldrin etc. have therefore, been banned. Recently in Andhra Pradesh, people suffered from various abnormalities due to consumption of endosulphan contaminated cashew nuts.
(iii) Effects of Noise Pollution:
Noise causes the following effects:
1. Interferes with Man’s Communication:
In a noisy area communication is severely affected.
2. Hearing Damage:
Noise can cause temporary or permanent hearing loss. It depends on intensity and duration of sound level. Auditory sensitivity is reduced with noise level of over 90 dB in the mid-high frequency for more than a few minutes.
3. Physiological and Psychological Changes:
Continuous exposure to noise affects the functioning of various systems of the body. It may result in hypertension, insomnia (sleeplessness), gastro-intestinal and digestive disorders, peptic ulcers, blood pressure changes, behavioural changes, emotional changes etc.
Essay # 5. Control of Environmental Pollution:
(i) Control of Air Pollution:
Air pollution can be minimized by the following methods:
i. Siting of industries after proper environmental impact assessment studies. By dilution of emission. This can be done by increasing the stack height (though up to permissible height), beyond inversion layer. Wind currents will disperse the pollutants.
ii. But this results in interstate dispute and is not considered to be solution for air pollution problem.
iii. Minimize activities which cause pollution like transportation and energy production.
iv. Modification of process and/or equipment’s.
v. Use of appropriate material.
vi. Using low sulphur coal in industries.
vii. Removing sulphur from coal (by washing or with the help of bacteria).
viii. Removing NOx during the combustion process and controlling the flow of air and fuel in industrial boilers.
ix. Vehicular pollution can be checked by regular tune-up of engines; replacement of more polluting old vehicles; installing catalytic converters; by engine modification to have fuel efficient (lean) mixtures to reduce CO and hydrocarbon emissions; and slow and cooler burning of fuels to reduce NOx emission (Honda Technology).
x. Using mass transport system, bicycles etc.
xi. Shifting to less polluting (clean) fuels (hydrogen gas).
xii. Using non-conventional sources of energy.
xiii. Using biological filters and bio-scrubbers.
xiv. Planting more trees.
xv. Reduction of pollution at source.
Reduction of Air Pollution:
1. Gaseous Pollutants:
Gaseous pollutants can be reduced by physical adsorption on porous solid materials like activated charcoal, silica gel, Fuller’s earth, etc. Effluent gases can be absorbed in liquid absorbent, e.g. SO2 absorbed in ammonia solution.
They can be removed by condensation which is carried out by cooling medium in tubes where the gases in contact condense and can be collected thereafter. Combustion can be used to reduce pollution by burning the pollutants in combustion equipment at optimal conditions of oxygen and temperature.
2. Particulate Matter:
Many devices are available now-a-days, choice of which depends on characteristics of particulate, flow rate, collection efficiency, costs, etc.
It consists of a cylinder with an inverted cone attached at the bottom. The gas with particles in it enters tangentially at the top of the cylinder and spins forming a vortex. Due to centrifugal force, the particles strike the wall of the cylinder. The particles then fall in the hopper due to gravity from where they are removed.
The spinning gas forms an inner vortex and leaves from the top. The cyclone is very efficient for larger particles. However, smaller particles which pose human health problems are not removed efficiently. Therefore, cyclones are employed before the use of other costly devices.
4. Bag House Filters:
A bag filter contains a large number of filter bags made of fabric. They are hung upside down in several compartments of bag house filter. Dirty gas is passed through the filter bags which leaves the bags through their pores. The dust particles get deposited on the inner surface of the bag filters and may form a cake which can be removed by shaking.
The device is efficient for removal of very small particles and is preferred in various types of industries. The bag house filters and expensive and cannot be operated for moist gases. Corrosive gases may damage the material of the bags.
Various types of materials, depending on the nature of the flue gases to be cleaned, are used for making the filter bags from the lower end get negatively charged (ionized) and are collected on the positively charged surface (plates/cylindrical body) while the clean gas leaves from the top.
The deposited dust particles fall down in the dust collector or are removed by scrapping or by liquids. Electrostatic precipitators utilize electric energy and can efficiently remove even submicroscopic particles.
(ii) Control of Water Pollution:
It is easy to reduce water pollution from point sources by legislation. However, due to absence of defined strategies it becomes difficult to prevent water pollution from non-point sources.
The following points may help in reducing water pollution from non-point sources:
(i) Judicious use of agro-chemicals like pesticides and fertilizers which will reduce their surface run-off and leaching. Avoid use of these on sloped lands.
(ii) Use of nitrogen fixing plants to supplement the use of fertilizers.
(iii) Adopting integrated pest management to reduce reliance on pesticides.
(iv) Prevent run-off of manure. Divert such run-off to basin for settlement. The nutrient rich water can be used as fertilizer in the fields.
(v) Separate drainage of sewage and rain water should be provided to prevent overflow of sewage with rainwater.
(vi) Planting trees would reduce pollution by sediments and also prevent soil erosion.
For controlling water pollution from point sources, treatment of waste waters is essential before being discharged. Parameters which are considered for reduction in such water are:
Total solids, biological oxygen demand (BOD), chemical oxygen demand (COD), nitrates and phosphates, oil and grease, toxic metals etc.
Waste waters should be properly treated by primary and secondary treatments to reduce the BOD, COD levels up to the permissible levels.
(iii) Control of Soil Pollution:
1. Transfer stations should be established at various places in a city for bulk transfer of refuge to ultimate discharge sites.
2. Pneumatic pipes should be used for collecting and disposing wastes.
3. Materials such as paper, plastics and glass should be recycled.
4. Animal refuge should be used for production of biogas for various domestic as well as industrial use.
5. Use of chemical fertilizers should be minimised by applying bio-fertilizers and manures.
6. Use of biocides should be minimised by adopting biological control methods.
7. Soil erosion can be checked by planting more trees and the process of deforestation should be checked.
(iv) Control of Noise Pollution:
(a) Reduction in sources of noise. Sources of noise pollution like heavy vehicles and old vehicles may not be allowed to ply in the populated areas.
(b) Noise making machines should be kept in containers with sound absorbing media. The noise path will be in interrupted and will not reach the workers.
(c) Proper oiling will reduce the noise from the machinery.
(d) Use of sound absorbing silencers. Silencers can reduce noise by absorbing sound. For this purpose various types of fibrous material could be used.
(e) Planting more trees having broad leaves.
(f) Through law. Legislation can ensure that sound production is minimized at various social functions. Unnecessary horn blowing should be restricted especially in vehicle- congested areas.