Download THERMAL POLLUTION:INTRODUCTION AND ITS EFFECTS

THERMAL POLLUTION:INTRODUCTION AND ITS EFFECTS
SUBMITTED BY- JITENDRA MAURYA
STUDENT NO.-1121049
SERIAL NO. -043
B.TECH EN-E
SUBMITTED TO-Dr. P.DHAMA
ASSISTANT PROFESSOR OF
DEPARTMENT OF APPLIED SCIENCE
AND HUMANITIES
Thermal pollution is the degradation of water quality by any process that changes ambient
water temperature.
A common cause of thermal pollution is the use of water as a coolant by power plants and
industrial manufacturers. When water used as a coolant is returned to the natural environment at a
higher temperature, the change in temperature decreases oxygensupply, and
affects ecosystem composition. Urban runoff–stormwater discharged to surface waters
from roads and parking lots–can also be a source of elevated water temperatures.
When a power plant first opens or shuts down for repair or other causes, fish and other organisms
adapted to particular temperature range can be killed by the abrupt change in water temperature
known as "thermal shock."
Thermal Pollution, harmful increase in water temperature in streams, rivers, lakes, or
occasionally, coastal ocean waters. Thermal pollution is caused by either dumping hot water from
factories and power plants or removing trees and vegetation that shade streams, permitting
sunlight to raise the temperature of these waters. Like other forms of water pollution, thermal
pollution is widespread, affecting many lakes and vast numbers of streams and rivers in
the United States and other parts of the world. A temperature increase as small as 1 or 2 Celsius
degrees (about 2 to 4 Fahrenheit degrees) can kill native fish, shellfish, and plants, or drive them
out in favor of other species, often with undesirable effects.
The major sources of thermal pollution are electric power plants and industrial factories. In most
electric power plants, heat is produced when coal, oil, or natural gas is burned or nuclear fuels
undergo fission to release huge amounts of energy. This heat turns water to steam, which in turn
spins turbines to produce electricity. After doing its work, the spent steam must be cooled and
condensed back into water. To condense the steam, cool water is brought into the plant and
circulated next to the hot steam. In this process, the water used for cooling warms 5 to 10 Celsius
degrees (9 to 18 Fahrenheit degrees), after which it may be dumped back into the lake, river, or
ocean from which it came. Similarly, factories contribute to thermal pollution when they dump
water used to cool their machinery.
The second type of thermal pollution is much more widespread. Streams and small lakes are
naturally kept cool by trees and other tall plants that block sunlight. People often remove this
shading vegetation in order to harvest the wood in the trees, to make room for crops, or to
construct buildings, roads, and other structures. Left unshaded, the water warms by as much as 10
Celsius degrees (18 Fahrenheit degrees). In a similar manner, grazing sheep and cattle can strip
streamsides of low vegetation, including young trees. Even the removal of vegetation far away
from a stream or lake can contribute to thermal pollution by speeding up the erosion of soil into
the water, making it muddy. Muddy water absorbs more energy from the sun than clear water
does, resulting in further heating. Finally, water running off of artificial surfaces, such as streets,
parking lots, and roofs, is warmer than water running off vegetated land and, thus, contributes to
thermal pollution.
Waste Heat - A pollutant as dangerous to waters as more tangible of forms of waste Human
activity can change normal temperature: By altering environment of watercourse: Road building ,
logging, poundments, diverting flows for irrigation Adding or removing heat. On national scale,
industrial cooling waters is a first-order source of heat. Electro power generation uses 80% of
cooling waters. Best single index of thermal pollution lies in projecting future electric power
generation. Past experience has indicated that thermal pollution has not multiplied as fast as
power generation because of improvements in thermal plant efficiency and developement of
hydropower. Nulear plants - waste even higher proportion of heat than fossil-fuel plants. Heat
rejection is expected to increase nine fold by the year 2000. Problem is one of managing
tremendous amounts of waste heat in a manner that will maintain or enhance, physical, chemical
and biological nature of our water resources.
Effect of Thermal Pollution:
Warm water typically decreases the level of dissolved oxygen in the water. The decrease in levels
of dissolved oxygen can harm aquatic animals such as fish, amphibians and copepods. Thermal
pollution may also increase the metabolic rate of aquatic animals, as enzyme activity, resulting in
these organisms consuming more food in a shorter time than if their environment were not
changed. An increased metabolic rate may result in food source shortages, causing a sharp
decrease in a population. Changes in the environment may also result in a migration of organisms
to another, more suitable environment, and to in-migration of organisms that normally only live in
warmer waters elsewhere. This leads to competition for fewer resources; the more adapted
organisms moving in may have an advantage over organisms that are not used to the warmer
temperature. As a result one has the problem of compromising food chains of the old and new
environments. Biodiversity can be decreased as a result.
In the 1970s there was considerable activity from scientists in quantifying effects of thermal
pollution. Hydrologists, physicists, meteorologists, and computer scientists combined their skills
in one of the first interdisciplinary pursuits of the modern environmental science era. First came
the application of gaussian function dispersal modeling that forecasts how a thermal plume is
formed from a thermal point source and predicts the distribution of aquatic temperatures. The
ultimate model was developed by the U.S. Environmental Protection Agency introducing the
statistical variations in meteorology to predict the resulting plume from a thermal outfall.
Coal-burning power plants are known producers of thermal pollution in nearby bodies of water
that they use as cooling ponds. This research focused on the effects that thermal pollution caused
by the Marshall Steam Station had on Lake Norman, North Carolina. It was found that dissolved
oxygen in the steam station's discharge cove was decreased by approximately four mg/L as
compared to a site ten miles upstream, and was decreased by about three mg/L as compared to a
cove several hundred yards downstream. Temperatures of the surface water in the discharge
Elevated temperature typically decreases the level of dissolved oxygen (DO) in water. The
decrease in levels of DO can harm aquatic animals such as fish, amphibians and copepods.
Thermal pollution may also increase themetabolic rate of aquatic animals, as enzyme activity,
resulting in these organisms consuming more food in a shorter time than if their environment
were not changed. An increased metabolic rate may result in fewer resources; the more adapted
organisms moving in may have an advantage over organisms that are not used to the warmer
temperature. As a result one has the problem of compromising food chains of the old and new
environments. Biodiversity can be decreased as a result.
It is known that temperature changes of even one to two degrees Celsius can cause significant
changes in organism metabolism and other adverse cellular biology effects. Principal adverse
changes can include rendering cell walls less permeable to necessary osmosis, coagulation of
cell proteins, and alteration of enzymemetabolism. These cellular level effects can adversely
affect mortality and reproduction.
Primary producers are affected by warm water because higher water temperature increases plant
growth rates, resulting in a shorter lifespan and species overpopulation. This can cause an algae
bloom which reduces oxygen levels.
A large increase in temperature can lead to the denaturing of life-supporting enzymes by breaking
downhydrogen- and disulphide bonds within the quaternary structure of the enzymes. Decreased
enzyme activity in aquatic organisms can cause problems such as the inability to break
down lipids, which leads to malnutrition.
In limited cases, warm water has little deleterious effect and may even lead to improved function
of the receiving aquatic ecosystem. This phenomenon is seen especially in seasonal waters and is
known as thermal enrichment.... An extreme case is derived from the aggregational habits of
the manatee, which often uses power plant discharge sites during winter. Projections suggest that
manatee populations would decline upon the removal of these discharges.
Releases of unnaturally cold water from reservoirs can dramatically change the fish and
macroinvertebrate fauna of rivers, and reduce river productivity. In Australia, where many rivers
have warmer temperature regimes, native fish species have been eliminated, and
macroinvertebrate fauna have been drastically altered.
• cooling ponds, man-made bodies of water designed for cooling
by evaporation, convection, and radiation
• cooling towers, which transfer waste heat to the atmosphere through evaporation
and/or heat transfer
• cogeneration, a process where waste heat is recycled for domestic and/or industrial
heating purposes.
The government plays a very important role in prevention of air pollution. It is through
government regulations that industries are forced to reduce their air pollution and new
developments in technology are created to help everyone do their part in the prevention of air
pollution.
Legislation, such as the Clean Air Act, helps to make sure that the main culprits of air pollution
are properly regulated and mandatory laws are in place to ensure that air pollution prevention is
taken seriously. The government also helps by continuously making regulations stricter and
enforcing new regulations that help to combat any new found source of air pollution.
In water, thermal pollution(making the water warmer) can change the species of fish present in
the water (trout for instance prefer cold water) and other organisms both because of the heat and
the decreased oxygen in the water (warm water dissolves less oxygen). The warme water
increases algal growth and encourages migratory birds, like ducks, to over winter.
In air, thermal pollution is limited to the heat island effect caused by cites. Cities trap and radiate
more heat than forests and fields. The warmer air makes thermal currents in the air which can act
as a barrier to the normal wind patterns. This in turn affects the rainfall on the far side (down
wind) of the city.
In soil, theramal pollution is limited to the impact of climate on the types of plants that can grow
and the reduction of areas which have permafrost. The loss of permafrost impacts the solidarity of
the ground (impacting animal migration) and releases methane from the frozen decomposing
organic matter.
The primary effects of thermal pollution are direct thermal shock , changes in dissolved oxygen,
and the redistribution of organisms in the local community. Because water can absorb thermal
energy with only small changes in temperature, most aquatic organisms have developed enzyme
systems that operate in only narrow ranges of temperature. These stenothermic organisms can be
killed by sudden temperature changes that are beyond the tolerance limits of their metabolic
systems. The cooling water discharges of power plants are designed to minimize heat effects on
local fish communities. However, periodic heat treatments used to keep the cooling system clear
of fouling organisms that clog the intake pipes can cause fish mortality. A heat treatment reverses
the flow and increases the temperature of the discharge to kill the mussels and other fouling
organisms in the intake pipes. Southern California Edison had developed a "fish-chase" procedure
in which the water temperature of the heat treatment is increased gradually, instead of rapidly, to
drive fish away from the intake pipes before the temperature reaches lethal levels. The fish chase
procedure has significantly reduced fish kills related to heat treatments.
Small chronic changes in temperature can also adversely affect the reproductive systems of these
organisms and also make them more susceptible to disease. Cold water contains more oxygen
than hot water so increases in temperature also decrease the oxygen-carrying capacity of water. In
addition, raising the water temperature increases the decomposition rate of organic matter in
water, which also depletes dissolved oxygen. These decreases in the oxygen content of the water
occur at the same time that the metabolic rates of the aquatic organisms, which are dependent on
a sufficient oxygen supply, are rising because of the increasing temperature.
The composition and diversity of communities in the vicinity of cooling water discharges from
power plants can be adversely affected by the direct mortality of organisms or movement of
organisms away from unfavorable temperature or oxygen environments. A nuclear powergenerating station on Nanwan Bay in Taiwan caused bleaching of corals in the vicinity of the
discharge channel when the plant first began operation in 1988. Studies of the coral Acropora
grandis in 1988 showed that the coral was bleached within two days of exposure to temperatures
of 91.4°F. In 1990 samples of coral taken from the same area did not start bleaching until six days
after exposure to the same temperature. It appears that the thermotolerance of these corals was
enhanced by the production of heat-shock proteins that help to protect many organisms from
potentially damaging changes in temperature. The populations of some species can also be
enhanced by the presence of cooling water discharges. The only large population of sea turtles in
California, for example, is found in the southern portion of San Diego Bay near the discharge of
an electrical generating station.