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ENVIRONMENTAL POLLUTION AIR POLLUTION

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Title: ENVIRONMENTAL POLLUTION AIR POLLUTION


1
ENVIRONMENTAL POLLUTIONAIR POLLUTION
2
Air Pollution
  • Air
  • Necessary for Existence
  • Colorless, odorless mixture of gases
  • Quality of air varies in different environments
  • Urban vs. Rural
  • Emission of Particulate Matter from
  • Anthropogenic (Man-made) Sources (Industry)
  • Natural Sources (Volcanoes, Forest Fires, Pollen)

3
Composition of Air
  • Five Substances
  • Nitrogen (N2) 78.1(v/v)
  • Oxygen (O2) 21.0(v/v)
  • Carbon Dioxide (CO2) 0.033(v/v)
  • Argon (Ar) 0.93(v/v)
  • Water (H2O) varies
  • Other trace components 0.007(v/v)

4
POLLUTION
  • Pollution is the effect of undesirable changes in
    our surroundings that have harmful effects on
    plants, animals and human beings.
  • This occurs when only short-term economic gains
    are made at the cost of the long-term ecological
    benefits for humanity.
  • No natural phenomenon has led to greater
    ecological changes than have been made by
    mankind.
  • During the last few decades we have contaminated
    our air, water and land on which life itself
    depends with a variety of waste products.

5
  • Pollutants include solid, liquid or gaseous
    substances present in greater than natural
    abundance produced due to human activity, which
    have a detrimental effect on our environment.
  • The nature and concentration of a pollutant
    determines the severity of detrimental effects on
    human health. An average human requires about 12
    kg of air each day, which is nearly 12 to15 times
    greater than the amount of food we eat.
  • Thus even a small concentration of pollutants in
    the air becomes more significant in comparison to
    the similar levels present in food.

6
  • Pollutants that enter water have the ability to
    spread to distant places especially in the marine
    ecosystem.
  • From an ecological perspective pollutants can be
    classified as follows
  • Degradable or non-persistent pollutants These
    can be rapidly broken down by natural processes.
    Eg domestic sewage, discarded vegetables, etc.
  • Slowly degradable or persistent pollutants
    Pollutants that remain in the environment for
    many years in an unchanged condition and take
    decades or longer to degrade. Eg DDT and most
    plastics.
  • Non-degradable pollutants These cannot be
    degraded by natural processes. Once they are
    released into the environment they are difficult
    to eradicate and continue to accumulate. Eg
    toxic elements like lead or mercury.

7
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8
What is Air Pollution?
  • Air pollution occurs due to the presence of
    undesirable solid or gaseous particles in the air
    in quantities that are harmful to human health
    and the environment.
  • Air may get polluted by natural causes such as
    volcanoes, which release ash, dust, sulphur and
    other gases, or by forest fires that are
    occasionally naturally caused by lightning.
  • However, unlike pollutants from human activity,
    naturally occurring pollutants tend to remain in
    the atmosphere for a short time and do not lead
    to permanent atmospheric change.

9
  • Pollutants that are emitted directly from
    identifiable sources are produced both by natural
    events (for example, dust storms and volcanic
    eruptions) and human activities (emission from
    vehicles, industries, etc.). These are called
    primary pollutants.
  • There are five primary pollutants that together
    contribute about 90 percent of the global air
    pollution. These are carbon oxides (CO and CO2),
    nitrogen oxides, sulfur oxides, volatile organic
    compounds (mostly hydrocarbons) and suspended
    particulate matter.
  • Pollutants that are produced in the atmosphere
    when certain chemical reactions take place among
    the primary pollutants are called secondary
    pollutants. Eg sulfuric acid, nitric acid,
    carbonic acid, etc.
  • Carbon monoxide is a colourless, odorless and
    toxic gas produced when organic materials such as
    natural gas, coal or wood are incompletely burnt.
    Vehicular exhausts are the single largest source
    of carbon monoxide. The number of vehicles has
    been increasing over the years all over the
    world. Vehicles are also poorly maintained and
    several have inadequate pollution control
    equipment resulting in release of greater amounts
    of carbon monoxide. Carbon monoxide is however
    not a persistent pollutant.

10
  • Natural processes can convert carbon monoxide to
    other compounds that are not harmful. Therefore
    the air can be cleared of its carbon monoxide if
    no new carbon monoxide is introduced into the
    atmosphere. Sulfur oxides are produced when
    sulfur containing fossil fuels are burnt.
  • Nitrogen oxides are found in vehicular exhausts.
    Nitrogen oxides are significant, as they are
    involved in the production of secondary air
    pollutants such as ozone. Hydrocarbons are a
    group of compounds consisting of carbon and
    hydrogen atoms. They either evaporate from fuel
    supplies or are remnants of fuel that did not
    burn completely.
  • Hydrocarbons are washed out of the air when it
    rains and run into surface water. They cause an
    oily film on the surface and do not as such cause
    a serious issue until they react to form
    secondary pollutants. Using higher oxygen
    concentrations in the fuel-air mixture and using
    valves to prevent the escape of gases, fitting of
    catalytic converters in automobiles, are some of
    the modifications that can reduce the release of
    hydrocarbons into the atmosphere.

11
  • Particulates are small pieces of solid material
    (for example, smoke particles from fires, bits of
    asbestos, dust particles and ash from industries)
    dispersed into the atmosphere. The effects of
    particulates range from soot to the carcinogenic
    (cancer causing) effects of asbestos, dust
    particles and ash from industrial plants that are
    dispersed into the atmosphere. Repeated exposure
    to particulates can cause them to accumulate in
    the lungs and interfere with the ability of the
    lungs to exchange gases.
  • Lead is a major air pollutant that remains
    largely unmonitored and is emitted by vehicles.
    High lead levels have been reported in the
    ambient air in metropolitan cities. Leaded petrol
    is the primary source of airborne lead emissions
    in Indian cities.
  • Pollutants are also found indoors from
    infiltration of polluted outside air and from
    various chemicals used or produced inside
    buildings. Both indoor and outdoor air pollution
    are equally harmful.

12
NATURAL SOURCES OF AIR POLLUTION
  • Natural Fires - Smoke
  • Volcanoes - Ash and acidic components
  • Sea Spray - Sulfur
  • Vegetation - Volatile organic compounds
  • Bacterial Metabolism - Methane
  • Dust
  • Pollen
  • Viruses and Bacteria

13
Air pollution sources and effects
  • Source type refers to natural and anthropogenic
    sources as well as to additional sub
    classifications within each group.
  • Natural sources include windblown dust, pollen,
    sea salt nuclei, volcanic ash and gases, smoke
    and trace gases from forest fires, and terpenes
    from forests. Anthropogenic sources cover a wide
    spectrum of types. Table includes a list of major
    anthropogenic air pollution sources and their
    characteristics emissions.

14
Classification of anthropogenic air pollution
sources
Source type Category Important Sources Typical Pollutants
Combustion Stationary Power plants, industrial boilers, diesel generators, municipal or industrial incineration,refuse burning Oxides of sulphur, NOX, CO, smoke, flyash, trace metal oxides
Combustion Mobile Motor vehicles, air craft CO, hydrocarbons, OX, SO2 particles
Roasting and heating process Nonferrous metallurgical Roasting smelting and refining operations Dust, Smoke, metal fumes (Cu, Pb and Zn) oxides of sulphur
Roasting and heating process Ferrous metallurgical Materials handling, ore sintering and pelletising, coke, ovens blast furnace, Steel furnaces Smoke, fumes, CO, Odours, H2S, organic vapour, fluorides
Roasting and heating process Nonmetallic minerals Crushed stone, gravel, and sand processing, cement, glass,refractories and ceramics manufacture, coal cleaning Mineral and organic particulates, SO2,NOX dust fumes
15
Chemicals, Petroleum, pulp and paper Petroleum refining Boilers, process heaters, catalyst regenerators, flares, reactors, storage tanks, compressor engines Oxides of sulphur hydrocarbons, NOX, particulate matter, CO, aldehydes ammonia, odours
Chemicals, Petroleum, pulp and paper Inorganic chemicals Sulphuric acid plants, fertilizer manufacture, nitric acid and ammonia plants, phosphoric acid manufacture SO2, HF, H2S, NOX, NH3, particulate matter, H3PO4, etc.,
Chemicals, Petroleum, pulp and paper Organic chemicals Plastics, paint and varnish manufacture, synthetic rubber, rayon, insecticide, soap and detergent manufacture, methanol, phenol, etc., Particulate matter, odours,SO2,CO,organic intermediates, product gases and vapours, solvent vapours, etc.,
Chemicals, Petroleum, pulp and paper Pulp and paper (Kraft process) Digester blow system, pulp washers, recovery furnace, evaporators, oxidation towers Particulate matter, odorous sulphur compounds (H2S, methyl mercaptan, dimethyl sulphide) and SO2 (sulphite process)
Food and Agriculture Food processing Drying, preserving, packaging Vapours, odours, dust
Food and Agriculture Crop spraying and dusting Pest and weed control Organic phosphates, chlorinated HC, arsenic, lead
Food and Agriculture Field burning Refuse burning Smoke, flyash and soot
16
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17
  • Types of Particulates

Term Meaning Examples
Aerosol General term for particulates suspended in air Sprays from pressurized cans
Mist Aerosol consisting of liquid droplets Sulfuric acid mist
Dust Aerosol consisting of solid particles that are blown into the air or are produced from larger particles by grinding them down Dust storm
Smoke Aerosol consisting of solid particles or a mixture of solid and liquid particles produced by chemical reactions such as fire Cigarette smoke, smoke from a burning garbage
Fume Generally means the same as smoke but often applies specifically to aerosols produced by condensation of hot vapors of metals. Zinc/lead fumes
Plume Geometrical shape or form of the smoke coming out a chimney
Fog Aerosol consisting of water droplets
Smog Term used to describe a mixture of smoke and fog
18
Major toxic metals and their effects
Element Sources Health effects
Lead Auto exhaust (from gasoline), paints, storage batteries, pipes Neurotoxin, affects blood system, behavioral disorders, death
Cadmium Coal, zinc mining, incineration of plastic containers, refining of metals, tobacco smoke Cardiovascular disease and hypertension, interference with zinc and copper metabolism, kidney damages
Nickel Combustion of coal, diesel and residual oils, tobacco smoke, chemicals and catalysts, steel and non ferrous alloys manufacture Respiratory symptoms, lung cancer (as nickel carbonyl)
Mercury Combustion of fossil fuels, evaporation from ore mining, exhausts from metal smelters, chloralkali cells, paints, pharmaceuticals Nerve and brain damage, kidney damage
19
HUMAN-CAUSED AIR POLLUTION
  • Primary Pollutants - Released directly from the
    source.
  • Secondary Pollutants - Modified to a hazardous
    form after entering the air and mixing with other
    environmental components.
  • Fugitive Emissions - Do not go through
    smokestack.
  • Dust from human-activities.

20
Conventional Pollutants
  • Clean Air Act designated seven major
    (conventional or criteria) pollutants for which
    maximum ambient air levels are mandated.
  • Sulfur Dioxide
  • Nitrogen Oxides
  • Carbon Oxides
  • Particulate Matter
  • Metals and Halogens
  • Volatile Organic Compounds

21
Conventional Pollutants
  • Sulfur Compounds
  • Natural sources of sulfur in the atmosphere
    include evaporation from sea spray, volcanic
    fumes, and organic compounds.
  • Predominant form of anthropogenic sulfur is
    sulfur-dioxide from fossil-fuel combustion.
  • Annual Emissions 114 million metric tons

22
Conventional Pollutants
  • Nitrogen Compounds
  • Nitrogen oxides are reactive gases formed when
    nitrogen is heated above 650o C in the presence
    of oxygen, or when nitrogen compounds are
    oxidized.
  • Annual Emissions 230 million metric tons

23
Conventional Pollutants
  • Carbon Oxides
  • Predominant form of carbon in the air is carbon
    dioxide.
  • Increasing levels due to human activities.
  • Annual Emissions 7-8 billion metric tons
  • Carbon monoxide is a colorless, odorless, toxic
    gas produced by incomplete fuel combustion.
  • Annual Emissions 1 billion metric tons

24
Conventional Pollutants
  • Particulate Matter
  • Atmospheric aerosols (solid or liquid)
  • Respirable particles smaller than 2.5 micrometers
    are among most dangerous.
  • Anthropogenic particulate emissions amount to
    about 362 million metric tons annually.

25
Conventional Pollutants
  • Metals
  • Many toxic metals occur as trace elements in
    fuel.
  • Lead Emissions 2 million metric tons.
  • Mercury
  • Bioaccumulation in aquatic ecosystems.
  • Nickel, beryllium, cadmium, arsenic
  • Halogens (Fluorine, Chlorine, Bromine)
  • CFCs

26
Conventional Pollutants
  • Volatile Organic Compounds
  • Organic chemicals
  • Generally oxidized to CO and CO2.
  • Plants are largest source.
  • Photochemical Oxidants
  • Products of secondary atmospheric reactions
    driven by solar energy.
  • Ozone formed by splitting nitrogen dioxide.

27
Unconventional Pollutants
  • Aesthetic Degradation
  • Noise, odor, light pollution.
  • Reduce quality of life.

28
EFFECTS OF AIR POLLUTION
  • Human Health
  • EPA estimates each year 50,000 people die
    prematurely from illnesses related to air
    pollution.
  • Likelihood of suffering ill health is related to
    intensity and duration of exposure.
  • Inhalation is the most common route, but
    absorption through the skin and consumption via
    food can also occur.

29
Human Health
  • Bronchitis
  • Persistent inflammation of airways in the lung
    that causes mucus build-up and muscle spasms
    constricting airways.
  • Can lead to emphysema - irreversible chronic
    obstructive lung disease in which airways become
    permanently constricted and alveoli are damaged
    or destroyed.

30
Plant Pathology
  • Chemical pollutants can directly damage plants,
    or can cause indirect damage by disrupting normal
    growth and development patterns.
  • Certain environmental factors have synergistic
    effects in which the injury caused by the
    combination is more than the sum of the
    individual exposures.
  • Pollutant levels too low to cause visible effects
    may still be damaging.

31
Acid Deposition
  • pH and Atmospheric Acidity
  • pH scale ranges from 0-14.
  • 7 Neutral lt7 Acidic gt7 Basic
  • Unpolluted rain generally has ph of 5.6.
  • Carbonic acid from atmospheric CO2.
  • In industrialized areas, anthropogenic acids in
    the air often outweigh natural sources of acid.

32
Acid Deposition
  • Forest Damage
  • Air pollution and depositions of atmospheric
    acids are believed to be important causes of
    forest destruction in many areas.
  • Buildings and Monuments
  • Limestone and marble are destroyed by air
    pollution at an alarming rate.
  • Corroding steel in reinforced concrete weakens
    buildings, roads, and bridges.

33
Effects of Air Pollution
  • Adverse effect of air pollution may be divided
    into two classes
  • Acute effects
  • Chronic effects
  • Acute effects manifest themselves immediately
    upon short-term exposure to air pollutants at
    high concentrations.
  • Chronic effects become evident only after
    continuous exposure to low levels of air
    pollution. The Chronic effects are very difficult
    to demonstrate and or consequently less obvious.
  • The chief causes of deaths and causalities were
    vomiting, violent coughing, eye infections
    (chemical conjuctivitis), suffocation, cardiac
    failure and pulmonary disorders. The full
    consequences are not yet known.
  • Pollutants may enter the body by a number of
    ways. The can cause eye and skin irritation
    certain particulates may be swallowed as a result
    of internal respiratory cleaning action or
    certain pollutants could even be ingested. But
    the primary mode of pollutant transfer into the
    human body is through the respiratory system.

34
Effects of Air Pollution on Living Organisms
  • Our respiratory system has a number of mechanisms
    that help in protecting us from air pollution.
    The hair in our nose filters out large particles.
    The sticky mucus in the lining of the upper
    respiratory tract captures smaller particles and
    dissolves some gaseous pollutants.
  • When the upper respiratory system is irritated by
    pollutants sneezing and coughing expel
    contaminated air and mucus. Prolonged smoking or
    exposure to air pollutants can overload or
    breakdown these natural defenses causing or
    contributing to diseases such as lung cancer,
    asthma, chronic bronchitis and emphysema.
  • Elderly people, infants, pregnant women and
    people with heart disease, asthma or other
    respiratory diseases are especially vulnerable to
    air pollution.

35
  • Cigarette smoking is responsible for the greatest
    exposure to carbon monoxide. Exposure to air
    containing even 0.001 percent of carbon monoxide
    for several hours can cause collapse, coma and
    even death. As carbon monoxide remains attached
    to hemoglobin in blood for a long time, it
    accumulates and reduces the oxygen carrying
    capacity of blood. This impairs perception and
    thinking, slows reflexes and causes headaches,
    drowsiness, dizziness and nausea.
  • Carbon monoxide in heavy traffic causes
    headaches, drowsiness and blurred vision. Sulfur
    dioxide irritates respiratory tissues. Chronic
    exposure causes a condition similar to
    bronchitis. It also reacts with water, oxygen and
    other material in the air to form
    sulfur-containing acids. The acids can become
    attached to particles which when inhaled are very
    corrosive to the lung. Nitrogen oxides especially
    NO2 can irritate the lungs, aggravate asthma or
    chronic bronchitis and also increase
    susceptibility to respiratory infections such as
    influenza or common colds.
  • Suspended particles aggravate bronchitis and
    asthma. Exposure to these particles over a long
    period of time damages lung tissue and
    contributes to the development of chronic
    respiratory disease and cancer. Many volatile
    organic compounds such as (benzene and
    formaldehyde) and toxic particulates (such as
    lead, cadmium) can cause mutations, reproductive
    problems or cancer. Inhaling ozone, a component
    of photochemical smog causes coughing, chest
    pain, breathlessness and irritation of the eye,
    nose and the throat.

36
  • Effects on Plants
  • When some gaseous pollutants enter leaf pores
    they damage the leaves of crop plants.
  • Chronic exposure of the leaves to air pollutants
    can break down the waxy coating that helps
    prevent excessive water loss and leads to damage
    from diseases, pests, drought and frost. Such
    exposure interferes with photosynthesis and plant
    growth, reduces nutrient uptake and causes leaves
    to turn yellow, brown or drop off altogether.
  • At a higher concentration of sulphur dioxide
    majority of the flower buds become stiff and
    hard. They eventually fall from the plants, as
    they are unable to flower.
  • Prolonged exposure to high levels of several air
    pollutants from smelters, coal burning power
    plants and industrial units as well as from cars
    and trucks can damage trees and other plants.

37
  • Effects of Air Pollution on Materials
  • Every year air pollutants cause damage worth
    billions of rupees.
  • Air pollutants break down exterior paint on cars
    and houses.
  • All around the world air pollutants have
    discoloured irreplaceable monuments, historic
    buildings, marble statues, etc.

38
  • Effects of Air Pollution on the Stratosphere
  • The upper stratosphere consists of considerable
    amounts of ozone, which works as an effective
    screen for ultraviolet light. This region called
    the ozone layer extends up to 60 kms above the
    surface of the earth.
  • Though the ozone is present upto 60 kms its
    greatest density remains in the region between 20
    to 25 kms. The ozone layer does not consist of
    solely ozone but a mixture of other common
    atmospheric gases. In the most dense ozone layer
    there will be only one ozone molecule in 100,000
    gas molecules. Therefore even small changes in
    the ozone concentration can produce dramatic
    effects of life on earth.
  • The total amount of ozone in a column of air
    from the earths surface upto an altitude of 50
    km is the total column ozone. This is recorded in
    Dobson Units (DU), a measure of the thickness of
    the ozone layer by an equivalent layer of pure
    ozone gas at normal temperature and pressure at
    sea level. This means that 100 DU1mm of pure
    ozone gas at normal temperature and pressure at
    sea level.

39
  • Ozone is a form of oxygen with three atoms
    instead of two. It is produced naturally from the
    photodissociation of oxygen gas molecules in the
    atmosphere. The ozone thus formed is constantly
    broken down by naturally occurring processes that
    maintain its balance in the ozone layer.
  • In the absence of pollutants the creation and
    breakdown of ozone are purely governed by natural
    forces, but the presence of certain pollutants
    can accelerate the breakdown of ozone.
  • Though it was known earlier that ozone shows
    fluctuations in its concentrations which may be
    accompanied sometimes with a little ozone
    depletion, it was only in 1985 that the large
    scale destruction of the ozone also called the
    Ozone Hole came into limelight when some British
    researchers published measurements about the
    ozone layer.
  • Soon after these findings a greater impetus was
    given to research on the ozone layer, which
    convincingly established that CFCs were leading
    to its depletion. These CFCs (chloro-flurocarbons)
    are extremely stable, non-flammable, non-toxic
    and harmless to handle.

40
  • This makes them ideal for many industrial
    applications like aerosols, air conditioners,
    refrigerators and fire extinguishers. Many cans,
    which give out foams and sprays, use CFCs. (eg
    perfumes, room fresheners, etc.) CFCs are also
    used in making foams for mattresses and cushions,
    disposable Styrofoam cups, glasses, packaging
    material for insulation, cold storage etc.
    However their stability also gives them a long
    life span in the atmosphere.
  • Halons are similar in structure to the CFCs but
    contain bromine atoms instead of chlorine. They
    are more dangerous to the ozone layer than CFCs.
    Halons are used as fire extinguishing agents as
    they do not pose a harm to people and equipment
    exposed to them during fire fighting.
  • The CFCs and the halons migrate into the upper
    atmosphere after they are released. As they are
    heavier than air they have to be carried by air
    currents up to just above the lower atmosphere
    and then they slowly diffuse into the upper
    atmosphere. This is a slow process and can take
    as long as five to fifteen years.

41
  • In the stratosphere unfiltered UV-radiation
    severs the chemical bonds releasing chlorine from
    the rest of the CFC. This attacks the ozone
    molecule resulting in its splitting into an
    oxygen molecule and an oxygen atom.
  • Despite the fact that CFCs are evenly distribute
    over the globe, the ozone depletion is especially
    pronounced over the South Pole due to the extreme
    weather conditions in the Antarctic atmosphere.
  • The presence of the ice crystals makes the Cl-O
    bonding easier. The ozone layer over countries
    like Australia, New Zealand, South Africa and
    parts of South America is also depleted. India
    has signed the Montreal Protocol in 1992, which
    aims to control the production and consumption of
    Ozone Depleting Substances.

42
  • Ozone Depletion-What Does it Do?
  • Changes in the ozone layer have serious
    implications for mankind.
  • Effects on human health Sunburn, cataract, aging
    of the skin and skin cancer are caused by
    increased ultra-violet radiation. It weakens the
    immune system by suppressing the resistance of
    the whole body to certain infections like
    measles, chicken pox and other viral diseases
    that elicit rash and parasitic diseases such as
    malaria introduced through the skin.
  • Food production Ultra violet radiation affects
    the ability of plants to capture light energy
    during the process of photosynthesis. This
    reduces the nutrient content and the growth of
    plants. This is seen especially in legumes and
    cabbage. Plant and animal planktons are damaged
    by ultra- violet radiation. In zooplanktons
    (microscopic animals) the breeding period is
    shortened by changes in radiation. As planktons
    form the basis of the marine food chain a change
    in their number and species composition
    influences fish and shell fish production.

43
  • Effect on Materials
  • Increased UV radiation damages paints and
    fabrics, causing them to fade faster.
  • Effect on Climate
  • Atmospheric changes induced by pollution
    contribute to global warming, a phenomenon which
    is caused due to the increase in concentration of
    certain gases like carbon dioxide, nitrogen
    oxides, methane and CFCs. Observations of the
    earth have shown beyond doubt that atmospheric
    constituents such as water vapour, carbon
    dioxide, methane, nitrogen oxides and Chloro
    Fluro Carbons trap heat in the form of infra-red
    radiation near the earths surface. This is known
    as the Greenhouse Effect. The phenomenon is
    similar to what happens in a greenhouse. The
    glass in a greenhouse allows solar radiation to
    enter which is absorbed by the objects inside.
    These objects radiate heat in the form of
    terrestrial radiation, which does not pass out
    through the glass. The heat is therefore trapped
    in the greenhouse increasing the temperature
    inside and ensuring the luxuriant growth of
    plants.

44
Green House Effect
45
  • There could be several adverse effects of global
    warming.
  • With a warmer earth the polar ice caps will melt
    causing a rise in ocean levels and flooding of
    coastal areas.
  • In countries like Bangladesh or the Maldives this
    would be catastrophic. If the sea level rises by
    3m., Maldives will disappear completely beneath
    the waves.
  • The rise in temperature will bring about a fall
    in agricultural produce.
  • Changes in the distribution of solar energy can
    bring about changes in habitats. A previously
    productive agricultural area will suffer severe
    droughts while rains will fall in locations that
    were once deserts. This could bring about changes
    in the species of natural plants, agricultural
    crops, insects, livestock and micro-organisms.
  • In the polar regions temperature rises caused by
    global warming would have disastrous effects.
    Vast quantities of methane are trapped beneath
    the frozen soil of Alaska. When the permafrost
    melts the methane that will be released can
    accelerate the process of global warming.

46
AIR POLLUTION CONTROL
  • Reducing Production
  • Particulate Removal
  • Remove particles physically by trapping them in a
    porous mesh which allows air to pass through but
    holds back solids.
  • Sulfur Removal
  • Switch from soft coal with a high sulfur content
    to low sulfur coal.
  • Change to another fuel (natural gas).

47
Air Pollution Control
  • Nitrogen Oxides
  • Best method is to prevent creation.
  • Staged Burners
  • Selective Catalysts
  • Hydrocarbon Control
  • Use closed systems to prevent escape of fugitive
    emissions.

48
Control Measures for Air Pollution
  • Air pollution can be controlled by two
    fundamental approaches
  • Preventive Techniques and Effluent control.
  • One of the effective means of controlling air
    pollution is to have proper equipment in place.
    This includes devices for removal of pollutants
    from the flue gases though scrubbers, closed
    collection recovery systems through which it is
    possible to collect the pollutants before they
    escape, use of dry and wet collectors, filters,
    electrostatic precipitators, etc.
  • Providing a greater height to the stacks can help
    in facilitating the discharge of pollutants as
    far away from the ground as possible.
  • Industries should be located in places so as to
    minimize the effects of pollution after
    considering the topography and the wind
    directions.
  • Substitution of raw material that causes more
    pollution with those that cause less pollution
    can be done.

49
Air Pollution Control
  • Raw Material Changes
  • If a particular raw material is responsible for
    causing air pollution, use of a purer grade of
    raw material is often beneficial and may reduce
    the formation of undesirable impurities and
    byproducts or may even eliminate the troublesome
    effluent. A typical example of this approach is
    the use of low-sulphur fuel in place of
    high-sulphur ones.
  • Fuel desulphurization is an attractive
    alternative, but removal of sulphur from fuels
    such as coal posses formidable technical
    problems. The most promising way of using coal in
    combustion processes with minimum air pollution
    appears to be through coal gasification because
    sulphur and some other unwanted materials can be
    removed from the gas much more readily than from
    solid coal

50
  • Process Changes.
  • Process changes involving new or modified
    techniques offer important ways of lowering
    atmospheric pollutant emissions. Radical changes
    in chemical and petroleum refining industries
    have resulted in minimizing of the release of
    materials to the atmosphere. The volatile
    substances are recovered by condensation and the
    non-condensable gases are recycled for additional
    reactions. Hydrogen sulphide, which was once
    flared in refineries, is now recycled and used in
    Claus process to recover elemental sulphur.
  • Equipment Modification or Replacement
  • Air pollutant emissions can be minimized by
    suitable modification or replacement of process
    equipment. For example, the unburnt carbon
    monoxide and hydrocarbons in the cylinders of an
    automobile engine, which are otherwise emitted
    into the atmosphere through the tail pipe can be
    burnt by injecting air into the hot exhaust
    manifold of the engine. Similar results can be
    obtained by suitable modifications in the
    carburetion and ignition systems.

51
  • Cleaning of Gaseous Effluents.
  • The Technology for the removal of gaseous
    pollutant emissions after their formation has
    probably received the maximum attention. The
    cleaning techniques are applied to those cases
    where emissions of pollutants cannot be prevented
    and pollution control equipment is necessary to
    remove them from the main gas stream.
  • Normally, it is more economical to install the
    control equipment at the source where the
    pollutants are present in the smallest possible
    volume in relatively high concentrations rather
    than at some point away from the source where the
    pollutants are diluted by other process gases or
    air.

52
  • The size of equipment is directly related to
    their volume being treated, and equipment cost
    can be drastically reduced by decreasing the
    exhaust volume. At the same time, the equipment
    is more efficient for the handling of higher
    concentrations of pollutants. Gas cleaning
    technique used alone, or in conjunction with
    source correction methods form the basis of
    present-day air resource management concepts. The
    method are often integrated into chemical
    processes, which eliminate pollutant discharges
    and conserve materials in the same unit
    operation.
  • Emission control equipment may be classified into
    two general types particulate control type, and
    gases and odours control type.
  • The basic mechanisms of removing particulate
    matter from gas streams may be classified as (1)
    Gravitational settling (2) Centrifugal impaction
    (3) Inertial impaction (4) Direct interception
    (5) Diffusion (6) Electro static precipitation.

53
  • Equipment presently available, which make use of
    one or more of the above mechanisms, fall into
    the following five broad categories
  • Gravitational settling chambers
  • Cyclone separators
  • Fabric filters
  • Electrostatic precipitators
  • Wet collectors (scrubbers)

54
Gravitational Settling Chambers
  • Gravitational settling chambers are generally
    used to remove large, abrasive particles (usually
    gt 50 ?m) from gas streams. They offer low
    pressure drop and require simple maintenance, but
    their efficiencies are quite low for particles
    smaller than 50 ?m.

55
Cyclone Separators
  • Cyclone separators utilize a centrifugal force
    generated by a spinning gas stream to separate
    the particulate matter from the carrier gas. The
    centrifugal force on particles in a spinning gas
    stream is much greater than gravity
  • Cyclones are effective in the removal of much
    smaller particles than gravitational settling
    chambers, and require much less space to handle
    the same gas volumes

56
Cyclone Separators
57
Fabric Filter Systems
  • Fabric filter systems typically consist of
    tubular bag or an envelope, suspended or mounted
    in such a manner that the collected particles
    fall into a hopper when dislodged from the
    fabric. The structure in which the bags hang is
    known as bag house. Generally, particle-laden gas
    enters the bag at the bottom and passes through
    the fabric while the particles are deposited on
    the inside of the bag.

58
Fabric Filter Systems
59
Electrostatic Precipitators (ESP)
  • The electrostatic precipitators are extensively
    used in removal of flyash from electric utility
    boiler emissions. The use of this collector is
    growing rapidly because of the new strict air
    quality codes.
  • The dust-laden gas is passed between oppositely
    charged conductors and it becomes ionized as the
    voltage applied between the conductors is
    sufficiently large (30,000 to 60,000 volts
    dependent on electrode spacing).
  • As the dust-laden gas is passed through these
    highly charged electrodes, both negative and
    positives ions are formed, the latter being as
    high as 80. The ionized gas is further passed
    through the collecting unit, which consists of a
    set of vertical metal plates. Alternate plates
    are positively charged and earthed.
  • The dust removed from the plates with the help of
    shaking motion is collected in the dust hoppers.

60
  • As the alternate plates are grounded, high
    intensity electrostatic field exists between the
    plates. When the charged dust particles are
    passed between the plates. The deposited dust
    particles are removed from the plates by giving
    the shaking motion to the plates with the help of
    cam driven by external means

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Advantages and disadvantages of electrostatic
precipitator
Advantages Disadvantages
1. Pressure drop and hence power requirement is small compared to that in other devices economical and simple to operate 1.Relatively high initial cost and large space requirement
2. 99 percent efficiency obtainable very small particles can be collected wet or dry 2. Sensitive to variable particulate loadings or flow rates
3. Can handle both gases and mists for higher volume flow 3. Safeguard of operating personnel from high voltage is necessary
4. Few moving parts can be operated at high temperatures and pressures 4. Collection efficiency can deteriorate gradually
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Wet Scrubbers
  • Wet precipitations the principal mechanisms by
    which atmospheric particles are removed by
    nature. This idea has been exploited by industry
    to develop a variety of liquid scrubbing
    equipment.
  • Wet collectors have a number of advantageous over
    dry collectors, such as simultaneous removal of
    particles and gaseous pollutants but suffer from
    the problems of corrosion and liquid waste
    disposal.

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Advantages and disadvantages of wet collectors
Advantages Disadvantages
1. Simultaneous removal of gases and particulates 1. Relatively high-energy costs
2. Effective performance over a wide loading range 2. Problem of wet sludge disposal
3. Equipment occupies only a moderate amount of space compared to dry collectors such as bag houses 3. Corrosion problem
4. Hazards of explosive dust-air mixtures are reduced 4. Visible wet fumes, reduction in buoyancy
5. Indifference to the temperature and moisture content of gas 5. Very small particles (sub-micron sizes) may not be captured
6. Corrosive gases my be neutralized
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CLEAN AIR LEGISLATION
  • Clean Air Act (1963) - First national air
    pollution control.
  • Clean Air Act (1970) rewrote original.
  • Identified critical pollutants.
  • Established ambient air quality standards.
  • Primary Standards - Human health
  • Secondary Standards - Materials, environment,
    aesthetic and comfort.

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Clean Air Act (CAA)
  • First passed in 1970
  • Amended in 1977 and 1990
  • Places strict limits on emission of pollutants
    from
  • Point sources
  • Factories
  • Power plants
  • Mobile sources
  • Motorized vehicles
  • Plain English guide to CAA on the web
  • http//www.epa.gov/oar/oaqps/peg_caa/pegcaain.html

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Clean Air Act
  • Revision (1990) - Included provision for
  • Acid Rain
  • Urban Smog
  • Toxic Air Pollutants
  • Ozone Protection
  • Marketing Pollution Rights
  • Volatile Organic Compounds
  • Ambient Ozone
  • Nox Emissions
  • Revision (1997) - Stricter standards

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Assessing Air Quality
  • EPA developed the Air Quality Index (AQI)
  • Definition of AQI There are six categories
  • 0 - 50 Good
  • 51 - 100 Moderate
  • 101 - 150 Unhealthy for Sensitive Groups
  • 151 - 200 Unhealthy
  • 201 - 250 Very Unhealthy
  • 251 - 300 Hazardous

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Assessing Air Quality
  • So AQI of 100 is the level EPA has set to protect
    public health
  • Example A carbon monoxide concentration of 9 ppm
    would result in an AQI of 100 for CO
  • AQI is set to most offending pollutant (i.e.
    pollutant with largest AQI

69
Air Quality - Particulates
  • Another quality index for particulates is called
    a particulate matter index (PM index)
  • PM10 index total concentration of all particles
    lt 10 µm diameter
  • PM2.5 index total concentration of all particles
    lt 2.5 µm diameter
  • Units of PM index µg/m3
  • That is, micrograms of particulate matter per
    cubic meter of air
  • Remember, one cubic meter air 1000 liters air

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Indoor Air Quality
  • Clean Air Act focuses on outdoor pollution.
  • Much of our time spent indoors
  • Quality of inside air depends on how well inside
    air is exchanged for outside air
  • Pollutant concentrations typically larger inside
    than outside

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Indoor Air Quality
72
Indoor Air Pollutants
  • Pollutant
  • Carbon Monoxide
  • Ozone
  • Formaldehyde
  • Nitrogen Oxides
  • Source
  • Faulty furnace, cigarette smoke
  • Electric Arcing
  • Furniture, plywood/pressboard adhesives, new
    carpet
  • Gas furnace

73
Water Pollution
74
Water Pollution
  • Water is the essential element that makes life on
    earth possible.
  • Without water there would be no life.
  • We usually take water for granted. It flows from
    our taps when they are turned on. Most of us are
    able to bathe when we want to, swim when we
    choose and water our gardens. Like good health we
    ignore water when we have it.
  • Although 71 of the earths surface is covered by
    water only a tiny fraction of this water is
    available to us as fresh water.
  • About 97 of the total water available on earth
    is found in oceans and is too salty for drinking
    or irrigation. The remaining 3 is fresh water.
    Of this 2.997 is locked in ice caps or glaciers.

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  • Thus only 0.003 of the earth total volume of
    water is easily available to us as soil moisture,
    groundwater, water vapour and water in lakes,
    streams, rivers and wetlands.
  • In short if the worlds water supply were only
    100 litres our usable supply of fresh water would
    be only about 0.003 litres (one-half teaspoon).
    This makes water a very precious resource.
  • The future wars in our world may well be fought
    over water.
  • By the middle of this century, almost twice as
    many people will be trying to share the same
    amount of fresh water the earth has today.
  • As freshwater becomes more scarce access to water
    resources will be a major factor in determining
    the economic growth of several countries around
    the world.

76
  • Water Availability on the Planet
  • Water that is found in streams, rivers, lakes,
    wetlands and artificial reservoirs is called
    surface water.
  • Water that percolates into the ground and fills
    the pores in soil and rock is called groundwater.
  • Porous water-saturated layers of sand, gravel or
    bedrock through which ground water flows are
    called aquifers. Most aquifers are replenished
    naturally by rainfall that percolates downward
    through the soil and rock. This process is called
    natural recharge.

77
  • If the withdrawal rate of an aquifer exceeds its
    natural recharge rate, the water table is
    lowered.
  • Any pollutant that is discharged onto the land
    above is also pulled into the aquifer and
    pollutes the groundwater resulting in polluted
    water in the nearby wells.
  • India receives most of her rainfall during the
    months of June to September due to the seasonal
    winds and the temperature differences between the
    land and the sea. These winds blow from the
    opposite directions in the different seasons.
  • They blow into India from the surrounding oceans
    during the summer season and blow out from the
    subcontinent to the oceans during the winter.
  • The monsoon in India is usually reasonably stable
    but varies geographically. In some years the
    commencement of the rains may be delayed
    considerably over the entire country or a part of
    it. The rains may also terminate earlier than
    usual. They may be heavier than usual over one
    part than over another.

78
  • All these may cause local floods or drought.
  • However in India even areas that receive adequate
    rainfall during the monsoon suffer from water
    shortages in the post monsoon period due to lack
    of storage facilities.
  • When the quality or composition of water changes
    directly or indirectly as a result of mans
    activities such that it becomes unfit for any
    purpose it is said to be polluted.
  • Point sources of pollution When a source of
    pollution can be readily identified because it
    has a definite source and place where it enters
    the water it is said to come from a point source.
    Eg. Municipal and Industrial Discharge Pipes.
  • When a source of pollution cannot be readily
    identified, such as agricultural runoff, acid
    rain, etc, they are said to be non-point sources
    of pollution.

79
Sources of Pollution
80
Causes of Water Pollution
  • There are several classes of common water
    pollutants.
  • These are disease-causing agents (pathogens)
    which include bacteria, viruses, protozoa and
    parasitic worms that enter water from domestic
    sewage and untreated human and animal wastes.
  • Human wastes contain concentrated populations of
    coliform bacteria such as Escherichia coli and
    Streptococcus faecalis. These bacteria normally
    grow in the large intestine of humans where they
    are responsible for some food digestion and for
    the production of vitamin K. These bacteria are
    not harmful in low numbers.
  • Large amounts of human waste in water, increases
    the number of these bacteria which cause
    gastrointestinal diseases.

81
  • Other potentially harmful bacteria from human
    wastes may also be present in smaller numbers.
    Thus the greater the amount of wastes in the
    water the greater are the chances of contracting
    diseases from them.
  • Another category of water pollutants is oxygen
    depleting wastes. These are organic wastes that
    can be decomposed by aerobic (oxygen requiring)
    bacteria. Large populations of bacteria use up
    the oxygen present in water to degrade these
    wastes. In the process this degrades water
    quality.
  • The amount of oxygen required to break down a
    certain amount of organic matter is called the
    biological oxygen demand (BOD). The amount of BOD
    in the water is an indicator of the level of
    pollution. If too much organic matter is added to
    the water all the available oxygen is used up.
    This causes fish and other forms of oxygen
    dependent aquatic life to die. Thus anaerobic
    bacteria (those that do not require oxygen) begin
    to break down the wastes. Their anaerobic
    respiration produces chemicals that have a foul
    odour and an unpleasant taste that is harmful to
    human health.

82
  • A third class of pollutants are inorganic plant
    nutrients. These are water soluble nitrates and
    phosphates that cause excessive growth of algae
    and other aquatic plants. The excessive growth of
    algae and aquatic plants due to added nutrients
    is called eutrophication. They may interfere with
    the use of the water by clogging water intake
    pipes, changing the taste and odour of water and
    cause a buildup of organic matter. As the organic
    matter decays, oxygen levels decrease and fish
    and other aquatic species die.
  • The quantity of fertilizers applied in a field is
    often many times more than is actually required
    by the plants. The chemicals in fertilizers and
    pesticides pollute soil and water. While excess
    fertilizers cause eutrophication, pesticides
    cause bioaccumulation and biomagnification.
    Pesticides which enter water bodies are
    introduced into the aquatic food chain. They are
    then absorbed by the phytoplanktons and aquatic
    plants. These plants are eaten by the herbivorous
    fish which are in turn eaten by the carnivorous
    fish which are in turn eaten by the water birds.
    At each link in the food chain these chemicals
    which do not pass out of the body are accumulated
    and increasingly concentrated resulting in
    biomagnification of these harmful substances.

83
  • One of the effects of accumulation of high levels
    of pesticides such as DDT is that birds lay eggs
    with shells that are much thinner than normal.
    This results in the premature breaking of these
    eggs, killing the chicks inside. Birds of prey
    such as hawks, eagles and other fish eating birds
    are affected by such pollution. Although DDT has
    been banned in India for agricultural use and is
    to be used only for malaria eradication, it is
    still used in the fields as it is cheap.
  • A fourth class of water pollutants is water
    soluble inorganic chemicals which are acids,
    salts and compounds of toxic metals such as
    mercury and lead. High levels of these chemicals
    can make the water unfit to drink, harm fish and
    other aquatic life, reduce crop yields and
    accelerate corrosion of equipment that use this
    water.
  • Another cause of water pollution is a variety of
    organic chemicals, which include oil, gasoline,
    plastics, pesticides, cleaning solvents,
    detergent and many other chemicals. These are
    harmful to aquatic life and human health. They
    get into the water directly from industrial
    activity either from improper handling of the
    chemicals in industries and more often from
    improper and illegal disposal of chemical wastes.

84
  • Sediment of suspended matter is another class of
    water pollutants. These are insoluble particles
    of soil and other solids that become suspended in
    water. This occurs when soil is eroded from the
    land. High levels of soil particles suspended in
    water, interferes with the penetration of
    sunlight. This reduces the photosynthetic
    activity of aquatic plants and algae disrupting
    the ecological balance of the aquatic bodies.
    When the velocity of water in streams and rivers
    decreases the suspended particles settle down at
    the bottom as sediments. Excessive sediments that
    settle down destroys feeding and spawning grounds
    of fish, clogs and fills lakes, artificial
    reservoirs etc.
  • Water soluble radioactive isotopes are yet
    another source of water pollution. These can be
    concentrated in various tissues and organs as
    they pass through food chains and food webs.
    Ionizing radiation emitted by such isotopes can
    cause birth defects, cancer and genetic damage.

85
  • Hot water let out by power plants and industries
    that use large volumes of water to cool the plant
    result in rise in temperature of the local water
    bodies. Thermal pollution occurs when industry
    returns the heated water to a water source. Power
    plants heat water to convert it into steam, to
    drive the turbines that generate electricity. For
    efficient functioning of the steam turbines, the
    steam is condensed into water after it leaves the
    turbines. This condensation is done by taking
    water from a water body to absorb the heat. This
    heated water, which is at least 15oC higher than
    the normal is discharged back into the water
    body. The warm water not only decreases the
    solubility of oxygen but changes the breeding
    cycles of various aquatic organisms.
  • Oil is washed into surface water in runoff from
    roads and parking lots which also pollutes
    groundwater. Leakage from underground tanks is
    another source of pollution. Accidental oil spill
    from large transport tankers at sea have been
    causing significant environmental damage. Though
    accidents such as the Exxon Valdez get worldwide
    attention, much more oil is released as a result
    of small, regular releases from other less
    visible sources. Nearly two thirds of all marine
    oil pollution comes from three sources runoff
    from streets, improper discharge of lubricating
    oil from machines or automobile crankcases and
    intentional oil discharges that occur during the
    loading and unloading of tankers. Oil tankers
    often use sea water as ballast to stabilize the
    ship after they have discharged their oil. This
    oil contaminated water is then discharged back
    into the sea when the tanker is refilled.

86
Types of Water Pollutants and their Effects
  • The problem of water pollution due to discharge
    of domestic and industrial wastes into aquatic
    systems has already become a serious problem in
    the country. Nearly 75 to 80 of Indias
    population is exposed to unsafe drinking water
  • To aid in a systematic discussion of water
    pollutants, they have been classified into nine
    categories as described below

87
Oxygen Demanding Wastes
  • Dissolved Oxygen (DO) is essential for sustaining
    the plant and animal life in any aquatic system.
    For example, warm-water fish requires a minimum
    DO level of at least 5 mg/l (5 ppm). If the DO
    level drops below the level necessary to sustain
    normal life, then the aquatic system is
    classified as polluted
  • There are four processes which actually affect
    the DO content in the Water reaeration,
    Photosynthesis, respiration and the oxidation of
    wastes
  • Reaeration is the process by which oxygen in
    fresh water at saturation point decreases with an
    increase in temperature
  • Photosynthesis requires solar radiation. During
    the process, the green plants such as algae
    utilize carbon dioxide and the inorganic
    nutrients present in the water to synthesize
    organic materials and liberate oxygen. Since the
    process occurs only in the presence of sunlight,
    the DO level in the water increase during the day

88
  • At night the algae and the microorganisms compete
    with each other for both dissolved oxygen and
    organic compounds. This bacterial and algal
    respiration is responsible for the production of
    carbon dioxide and subsequent depletion of
    dissolved oxygen.
  • Combination of the three effects of respiration,
    photosynthesis and reaeration results in the
    diurnal variation in dissolved oxygen
    concentration from the values that may far exceed
    saturation during the day to much lower values or
    depletion at night.
  • The primary cause of deoxygenation of aquatic
    systems is the presence of organic substances
    collectively called oxygen-demanding wastes. When
    these substances enter a waterway, dissolved
    oxygen is consumed in their breakdown by
    microorganisms, so the organic substances can be
    said to exert a demand on the availability of
    dissolved oxygen. The more the oxygen is required
    for the breakdown of the substance, the greater
    will be the deoxygenation of the waterway.
    Pollution results when the oxygen demand exceeds
    the available oxygen.

89
  • Although some inorganic substances are found in
    the category of oxygen demanding wastes, most of
    them are organic in nature. For example
    pollutants in this category typically come from
    such sources as sewage, food processing plants,
    pulp and paper mills, tanning operations, and
    other organic waste producing activities. These
    waste, in addition to depleting the DO levels,
    produce-annoying odours, impair domestic and
    livestock water supplies by affecting its taste,
    odour and colour.

90
Biochemical Oxygen Demand
  • The biochemical oxygen demand (BOD) is a measure
    of the oxygen utilized by microorganisms during
    the oxidation of organic materials. It is the
    most widely known measure for assessing the water
    pollution potential of a given organic waste. On
    an average, the demand for oxygen is directly
    proportional to the amount of organic waste.
    Hence, BOD is a direct measure of oxygen
    requirements and an indirect measure of
    biodegradable organic matter

91
Disease Causing Agents
  • Water is a potential carrier of pathogenic
    microorganisms these pathogens are carried into
    the water bodies by sewage and wastes from farms
    and various industries, specially tanning and
    meat packaging industries. Contact with the
    pathogens can be made by drinking the water or
    through other activities involving contact with
    water.
  • Some bacteria are water-borne and these include
    those responsible for causing cholera, typhoid,
    amoebic dysentery and gastroenteritis. Viruses
    are also found in water including strains, which
    are responsible for polio, infectious hepatitis,
    and Coxsackies fever. Water may also contain
    some animal parasites including the round worm,
    and the pork tapeworm. All these types of
    organisms occur in faeces, and so present in
    sewage. Water also plays an indirect but vitally
    important role in the transmission of disease
    like malaria, yellow fever, filariasis, and
    schistomiasis

92
Synthetic Organic Compounds
  • These include pesticides, synthetic organic
    chemicals and detergents. These compounds, in
    contrast to the organic wastes, are not
    biodegradable and may persist for long periods.
  • These are great concern to environmentalists
    because most of the synthetic compounds are
    accumulative toxic poisons and ultimately may
    reach objectionable levels in water or in aquatic
    life.

93
Plant Nutrients
  • Nitrogen and phosphorous are essential elements
    which are required by plants and animal for
    maintaining their growth and metabolism. Small
    amount of nitrates and phosphates occur in all
    aquatic systems and these are sufficient to
    maintain a balanced biological growth.
  • In wastewaters, these nutrients are present in
    abundance as phosphates, nitrates, and ammonia or
    combined organic nitrogen. These compounds may
    enter the water bodies directly from the
    manufacture and use of fertilizers, and from the
    processing of biological materials such as food
    and textiles, or via domestic sewage treatment
    plants.
  • When unusually large concentrations of nutrients
    are present in water bodies, an excess growth of
    algae, known as and algal bloom appears. This
    produces an unsightly green slime layer over the
    surface of the water body and subsequently leads
    to eutrophication.

94
  • The slime layer reduces light penetration and
    restricts atmospheric reoxygenation of the water.
    The dense algal growth eventually dies and the
    subsequent biodegradation produces an oxygen
    deficit, which can result in foul-smelling
    anaerobic conditions.
  • Birds feeding on the algae are killed by the
    powerful toxin produced by the anaerobic
    bacterium Clostridium botulinum, which flourishes
    in the environment.
  • Other problems resulting from heavy algal growth
    are the clogging of filters in water treatment
    plants and slowing down of stream flow by
    filamentous weeds can trap solid particles
    carried by a stream and if they are organic, a
    large decaying mass accumulates which exerts a
    high oxygen demand.
  • High concentrations of nitrate in drinking water.
    When it enters the blood stream it becomes
    attached to hemoglobin, forming
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