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Thermal pollution and its remedies BY MS. SNEHA PARAB

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Page 1: Thermal Pollution Project

Thermal pollution and its remedies

BY

MS. SNEHA PARAB

Thermal pollution

Page 2: Thermal Pollution Project

Introduction

Thermal pollution is basically the form of water pollution that refers to

degradation of water quality by any process that changes ambient water temperature. It is

the act of altering the temperature of a natural water body, which may be a river, lake or

ocean environment. While a degree or two of difference may sound minor, warming of an

aquatic or marine environment even by a small amount can result in devastating

alterations to the habitats of fish, insects, plants, and animals. Increases in ambient water

temperature also occur in streams where shading vegetation along the banks is removed

or where sediments have made the water more turbid . Both of these effects allow more

energy from the sun to be absorbed by the water and thereby increase its 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 (a) decreases oxygen

supply, and (b) affects ecosystem composition. Urban runoff--storm water discharged to

surface waters from roads and parking lots--can also be a source of elevated water

temperatures. Thermal pollution is one parameter of the broader subject of water

pollution. There can be significant environmental consequences of thermal pollution with

respect to surface receiving waters such as rivers and lakes; in particular, decrease in

biodiversity and creation of an environment hospitable to alien aquatic species may

occur.

Illustration of thermal pollution

Sources

Page 3: Thermal Pollution Project

There are several main causes of thermal pollution, each contributing to what some

environmental experts call a possible environmental catastrophe. Two major sources that

lead to thermal pollution can be given as

Electric power plants and use of water as a cooling agent

deforestation of the shoreline

1. Electric power plants and use of water as a cooling agent

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.

A major example of that proves this point is the Coal-burning power plants that 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

Deforestation Of The Shoreline

Page 4: Thermal Pollution Project

The second major cause of thermal pollution which is much more widespread is deforestation of the shoreline. 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 stream sides of low vegetation. 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.

EFFECTS OF THERMAL POLLUTION

Page 5: Thermal Pollution Project

1. Ecological Effects — Warm Water

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 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

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 enzyme metabolism.

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 down hydrogen-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 (Sea Cow), which often uses power

plant discharge sites during winter. Projections suggest that manatee populations would

decline upon the removal of these discharges.

Page 6: Thermal Pollution Project

2. Ecological effects — cold water

Releases of unnaturally cold water from reservoirs can dramatically change the

fish and macro invertebrate fauna of rivers, and reduce river productivity. In Australia,

where many rivers have warmer temperature regimes, native fish species have been

eliminated, and macro invertebrate fauna have been drastically altered.

3. Impact Of Thermal Pollution On Aquatic Ecology

All plant and animal species that live in water are adapted to temperatures within

a certain range. When water in an area warms more than they can tolerate, species that

cannot move, such as rooted plants and shellfish, will die. Species that can move, such as

fish, will leave the area in search of cooler conditions, and they will die if they can not find

them. Typically, other species, often less desirable, will move into the area to fill the

vacancy.

In general, cold waters are better habitat for plants and animals than warm ones

because cold waters contain more dissolved oxygen. Many freshwater fish species that

are valued for sport and food, especially trout and salmon, do poorly in warm water.

Some organisms do thrive in warm water, often with undesirable effects.

As water temperature rises, the rate of photosynthesis and plant growth also increases.

More plants grow and die. As plants die, they are decomposed by bacteria that consume

oxygen. Therefore, when the rate of photosynthesis is increased, the need for oxygen in

the water (BOD) is also increased.

The metabolic rate of organisms also rises with increasing water temperatures, resulting

in even greater oxygen demand. The life cycles of aquatic insects tend to speed up in

warm water. Animals that feed on these insects can be negatively affected, particularly

birds that depend on insects emerging at key periods during their migratory flights.

Most aquatic organisms have adapted to survive within a range of water temperatures,

Some organisms prefer cooler water, such as trout, stonefly nymphs, while others thrive

Page 7: Thermal Pollution Project

under warmer conditions, such as carp and dragonfly nymphs. As the temperature of a

river increases, cool water species will be replaced by warm water organisms. Few

organisms can tolerate extremes of heat or cold.

Temperature also affects aquatic life's sensitivity to toxic wastes, parasites, and disease.

For example, thermal pollution may cause fish to become more vulnerable to disease,

either due to the stress of rising water temperatures or the resulting decrease in dissolved

oxygen.

The hot waste water released from power plants and industries disrupts the biodiversity

of aquatic ecosystems by disturbing metabolic functions of living organisms. In addition,

sever thermal shocks distort the food web by killing fish and other animals. All plant and

animal species that live in water are adapted to temperatures within a certain range. When

water in an area warms more than they can tolerate, species that cannot move, such as

rooted plants and shellfish, will die. Species that can move, such as fish, will leave the

area in search of cooler conditions, and they will die if they can not find them. Typically,

other species, often less desirable, will move into the area to fill the vacancy. In general,

cold waters are better habitat for plants and animals than warm ones because cold waters

contain more dissolved oxygen. Many freshwater fish species that are valued for sport

and food, especially trout and salmon, do poorly in warm water. Some organisms do

thrive in warm water, often with undesirable effects. Algae and other plants grow more

rapidly in warm water than in cold, but they also die more rapidly; the bacteria that

decompose their dead tissue use up oxygen, further reducing the amount available for

animals. The dead and decaying algae make the water look, taste, and smell unpleasant.

(Eutrophication ).

4.Physical and chemical effects

Water is naturally constituted of chemical components (metals, salts, trace elements,

gases, carbonates,) in balance. A change in temperature can modify it and accelerate

chemical and biochemical reactions: it is a catalyst. For example, the hotter the

Page 8: Thermal Pollution Project

temperature of rejected water is, the more its effects on benthic organizations are

harmful.

An increase in temperature can also cause a reduction of solubility. It's an important

consequence because the amount of dissolved oxygen (DO) in water decreases. This

makes it more difficult for fish and other aquatic organisms to obtain the necessary

oxygen for cellular respiration. But, in the first part, we could see that the seaweeds rate

increase, so, they use up more O2: there is a lack of oxygen so aquatic living beings are

asphyxiated. Another repercussion of this phenomenon is taste and odor. In fact, products

which are in water become more volatile, it is why there are impacts on the surrounding

air.

Salinity is an important measurement in biology because salt is dissolved in the bodily

fluids of all living things. The level of dissolved salts in a fluid controls many of the

processes of life. Most animals are adapted to a narrow range of salinity and cannot live

in water that is outside that range. But, when the temperature of water increases, salinity

decreases so, there are important repercussions on aquatic life.

 

       A particular problem is the stratification in lakes. Because of density difference,

layers of different temperature are formed in accordance with the depth of water. So the

temperature of water changes suddenly with the depth. These have consequences on

fauna and flora, which modifies the landscape.

Increase in temperature = Reduction of solubility

Increase in temperature = Change of salinity

Page 9: Thermal Pollution Project

Stratification in lakes

5. Biological effects of this pollution

Temperature is an important factor for life. So, an increase, or a reduction, of this one can

destroy ecologic niches, which are very sensitive to little variation of their environment.

Their disappearance is followed by that of the fauna and flora living there.

Producing or catching heat in or from a source of water can involve the death of micro-

organisms by thermal shock. This problem also affects other living beings that feed on it,

and so on and so forth. So, the tropic chain is broken.

       

We have presented you the problem of the destruction of nature, but this pollution can

also generate the proliferation of bacteria that occupy the niches of other types of living

beings. So, almost the same result is achieved through another way ... Secondly, with a

higher temperature, algae grow much more rapidly. They use up dissolved oxygen (DO)

in water, block the sunlight from getting to the submerged aquatic vegetation (SAV), and

the entire ecosystem suffers.

Change in temperature = Stratification

Increase \ reduction in temperature = Destruction of fauna and flora

Page 10: Thermal Pollution Project

Proliferation of algae

Measure Of Thermal Pollution

Guidelines for testing for thermal pollution vary from place to place. One way to test

thermal pollution in water is to measure the difference in the water temperature between

the entry site and a point 1 mi upstream. A change of 0°C to 2°C is evaluated as

excellent. A change of 2.2°C to 5°C is evaluated as good. A change of 5.1°C to 9.9°C is

fair, and more than 10°C difference is considered poor.

Prevention & Control Of Thermal Pollution

There are a number of ways to minimize the harmful effects of Thermal Pollutions:

Prevention

Following are the means to reduce thermal pollution:

Theoretically, when efficiency of any heat engine is equal to 1.0 then it will

convert 100% of heat energy to mechanical energy. So there will be no loss of

heat to the environment. This is practically impossible. Rather, we should aim at

Increase in temperature = Proliferation of bacteria \ reduction of O2

Page 11: Thermal Pollution Project

maximizing the efficiency of heat engines (steam, IC, nuclear etc) so that heat

loss is minimum.

Reduce mechanical friction in any rotating parts.

Avoid consuming energy more than necessity. Burn less coal, oil or gas.

Temperature signal conditioners accept outputs from temperature measurement

devices such as resistance temperature detectors (RTDs), thermocouples, and

thermostats. They then filter, amplify, and/or convert these outputs to digital

signals, or to levels suitable for digitization.

Industrial fans and industrial blowers and commercial fans and blowers are

designed to move air and/or powders in industrial and commercial settings.

Typical applications include air circulation for personnel, exhaust or material

handling

Limiting the amount of heated water discharged into the same body of water.

Control By Dilution

Returning the heated water at a point away from the ecologically vulnerable shore

zone.

Transferring the heat from the water to the atmosphere by means of wet or dry

cooling towers.

Discharging the heated water into shallow ponds or canals, allowing it to cool,

and reusing it as cooling water. This method is useful where enough affordable

land is available.

Control of thermal pollutionIndustrial wastewater

Thermal pollution from industrial sources is generated mostly by power plants,

petroleum refineries, pulp and paper mills, chemical plants, steel mills and smelters.

Heated water from these sources may be controlled with:

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

Page 12: Thermal Pollution Project

cogeneration, a process where waste heat is recycled for domestic and/or

industrial heating purposes.

Cooling pond:

A cooling pond is a man-made body of water primarily formed for the purpose of

supplying cooling water to a nearby power plant or industrial facility such as a petroleum

refinery, pulp and paper mill, chemical plant, steel mill or smelter. Cooling ponds are

used where sufficient land is available, as an alternative to cooling towers or discharging

of heated water to a nearby river or coastal bay, a process known as "once-through

cooling." The latter process can cause thermal pollution of the receiving waters. Cooling

ponds are also sometimes used with in large buildings as an alternative to cooling towers.

Air conditioning systems The pond receives thermal energy in the water from the plant's

condensers and the energy is dissipated mainly through evaporation. Once the water has

cooled in the pond, it is reused by the plant. New water is added to the system ("make-

up" water) to replace the water lost through evaporation. Many such ponds have

secondary outdoor recreational purposes that include fishing, swimming, boating,

camping and picnicking. The warm waters are frequently used as a fish hatchery.

Cooling Tower

Cooling towers are heat removal devices used to transfer process waste heat to the

atmosphere. Cooling towers may either use the evaporation of water to remove process

heat and cool the working fluid to near the wet-bulb air temperature or in the case of

"Close Circuit Dry Cooling Towers" rely solely on air to cool the working fluid to near

the dry-bulb air temperature. Common applications include cooling the circulating water

used in oil refineries, chemical plants, power stations and building cooling. The towers

vary in size from small roof-top units to very large hyperboloid structures that can be up

to 200 metres tall and 100 metres in diameter, or rectangular structures that can be over

40 metres tall and 80 metres long. Smaller towers are normally factory-built, while larger

ones are constructed on site. They are often associated with nuclear power plants in

popular culture. A hyperboloid cooling tower was patented by Frederik van Iterson and

Gerard Kuypers in 1918.

Page 13: Thermal Pollution Project

Cogeneration (Combined heat and power, CHP)

Cogeneration (Combined heat and power, CHP) is the use of a heat engine or a

power station to simultaneously generate both electricity and useful heat. All power

plants must emit a certain amount of heat during electricity generation. This can be

released into the natural environment through cooling towers, flue gas, or by other means.

By contrast CHP captures some or all of the by-product heat for heating purposes, either

very close to the plant, or as hot water for district heating with temperatures ranging from

approximately 80 to 130 °C. This is also called Combined Heat and Power District

Heating or CHPDH. Small CHP plants are an example of decentralized energy.

In the United States, Con Edison distributes 30 billion pounds of 350 °F/180 °C steam

each year through its seven cogeneration plants to 100,000 buildings in Manhattan—the

biggest steam district in the United States. The peak delivery is 10 million pounds per

hour (corresponding to approx. 2.5 GW). This steam distribution system is the reason for

the steaming manholes often seen in "gritty" New York movies. Cogeneration is a

thermodynamically efficient use of fuel. In separate production of electricity some energy

must be rejected as waste heat, but in cogeneration this thermal energy is put to good use.

Bioretention systems and infiltration basins

Storm water management facilities that absorb runoff or direct it into

groundwater, such as bioretention systems and infiltration basins, can reduce these

thermal effects. Retention basins tend to be less effective at reducing temperature, as the

water may be heated by the sun before being discharged to a receiving stream

Bioretention System

Bioretention is the process in which contaminants and sedimentation are removed

from stormwater runoff. Stormwater is collected into the treatment area which consists of

a grass buffer strip, sand bed, ponding area, organic layer or mulch layer, planting soil,

and plants. Runoff passes first over or through a sand bed, which slows the runoff's

velocity, distributes it evenly along the length of the ponding area, which consists of a

Page 14: Thermal Pollution Project

surface organic layer and/or groundcover and the underlying planting soil. The ponding

area is graded, its center depressed. Water is ponded to a depth of 15 cm (5.9 in) and

gradually infiltrates the bioretention area or is evapotranspired. The bioretention area is

graded to divert excess runoff away from itself. Stored water in the bioretention area

planting soil exfiltrates over a period of days into the underlying soils.

Infiltration Basin

An infiltration basin (also known as a recharge basin or in some areas, a sump), is

a type of best management practice (BMP) that is used to manage stormwater runoff,

prevent flooding and downstream erosion, and improve water quality in an adjacent river,

stream, lake or bay. It is essentially a shallow artificial pond that is designed to infiltrate

stormwater though permeable soils into the groundwater aquifer. Infiltration basins do

not discharge to a surface water body under most storm conditions, but are designed with

overflow structures (pipes, weirs, etc.) that operate during flood conditions. It is

distinguished from a detention basin, sometimes called a dry pond, which is designed to

discharge to a downstream water body (although it may incidentally infiltrate some of its

volume to groundwater); and from a retention basin, which is designed to include a

permanent pool of water.

Retention Basin

A retention basin is a type of best management practice (BMP) that is used to

manage stormwater runoff to prevent flooding and downstream erosion, and improve

water quality in an adjacent river, stream, lake or bay. Sometimes called a wet pond or

wet detention basin, it is an artificial lake with vegetation around the perimeter, and

includes a permanent pool of water in its design. It is distinguished from a detention

basin, sometimes called a dry pond, which temporarily stores water after a storm, but

eventually empties out at a controlled rate to a downstream water body. It also differs

from an infiltration basin which is designed to direct stormwater to groundwater through

permeable soils. Wet ponds are frequently used for water quality improvement,

groundwater recharge, flood protection, aesthetic improvement or any combination of

these. Sometimes they act as a replacement for the natural absorption of a forest or other

natural process that was lost when an area is developed. As such, these structures are

designed to blend into neighborhoods and viewed as an amenity.

Page 15: Thermal Pollution Project

Conclusion

Thermal pollution is a problem that we have to deal with more and more. This

pollution is principally located in rivers and waterways nearby industries. Even if we

can't see immediately the effects of thermal pollution it has an impact on our

environment. So, scientists have to research solutions to reduce it (heat!!).

When prevention is inefficient, industries use some techniques to solve thermal

pollution. The first technique is the control by dilution; it consists in diluting warm water

in cool water to decrease the impact on water life. Another solution is to use cooling

towers to transfer heat from water to the atmosphere. The last one is the discharging of

heated water in shallow ponds and canals. The last two are very much used even if the

last one is the least costly.

References

Brown, Richard D.; Ouellette, Robert P.; and Chermisinoff, Paul N. (1983). Pollution

Control at Electric Power Stations: Comparisons for U.S. and Europe. Boston:

Butterworth-Heinemann.

Langford, Terry E. (1990). Ecological Effects of Thermal Discharges. New York:

Elsevier Applied Science.

Slovic, Paul. (2000). The Perception of Risk. London: Earthscan Publications Ltd.

 

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