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Thermal Pollution

Thermal pollution is the act of altering the temperature of a natural water body, which may be a river, lake or ocean environment. This condition chiefly arises from the waste heat generated by an industrial process such as certain power generation plants. The concept is most frequently discussed in the context of elevating natural water temperature, but may also be caused by the release of cooler water from the base of reservoirs into warmer rivers. Elevated river temperatures can also arise from deforestation or urbanization that can reduce stream shading. 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.

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Sources Of Thermal Pollution

MAJOR SOURCES

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.

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Major Sources Of Thermal Pollution

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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. 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.

Sources Of Thermal Pollution

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Side Effects Of Thermal Pollution

Ecological Effects — Warm WaterElevated 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.

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Side Effects Of Thermal Pollution

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.

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Side Effects Of Thermal Pollution

Ecological effects — Cold WaterReleases of unnaturally cold water from reservoirs can dramatically change the fish and macro invertebrate fauna of rivers, and reduce river productivity. E.g. In Australia, where many rivers have warmer temperature regimes, native fish species have been eliminated, and macro invertebrate fauna have been drastically altered.

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Impact Of Thermal Pollution On Living Organisms

Thermal Water Pollution and Aquatic Ecology

Like other species, aquatic animals and plants have evolved with biological systems that can function best within a certain temperature range. The sudden discharge of heated water to lakes, rivers and oceans causes damage to the habitats of aquatic organisms by affecting their metabolic functions; the oxygen dissolving ability of hot water decreases and thus, as the water temperature rises significantly, it disrupts the food web by killing fish and other heat-sensitive living organisms.

Most animals living in water are cold-blooded by nature and cannot maintain their body temperatures; therefore, a temperature rise in their natural surroundings has serious implications upon their biological functions. For instance, thermal shocks of mild intensity can result in reproductive disorders among fish, thereby affecting the biodiversity of aquatic ecosystems.

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Impact Of Thermal Pollution On Living Organisms

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 ).

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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.

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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 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.

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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.

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Prevention & Control Of Thermal Pollution

Control of thermal pollution

Industrial 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

cogeneration, a process where waste heat is recycled for domestic and/or industrial heating purposes.

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Cooling of Industrial Waste Water

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.

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Mount Storm Lake Cooling Pond For A Power Plant In Grant County, West Virginia.

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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.

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Hyperboloid Cooling Tower

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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.

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Manado Combined Heat And Power Station Manado, Denmark

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Control Of Thermal Pollution

Urban Runoff

During warm weather, urban runoff can have significant thermal impacts on small streams, as stormwater passes over hot parking lots, roads and sidewalks. Stormwater 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

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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 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.

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Bioretention System

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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.

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Infiltration Basin

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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.

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Retention Basin Pinnau, Germany

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Case Study-Thermal Pollution

• The Severity of the Pollutant and its Effects:• The severity of thermal pollution is indicated by a plume( form of effluent in water)• of warm water from the outflow pipe of the power station. The impact on the receiving water is limited to the

plume and its surrounding area, although the direction and distribution of the plume is dependent upon the physical conditions of the receiving area e.g. tidal currents, weather conditions and the ecological features exposed to the elevated temperatures.

• Thermal pollution has a greater impact in temperate environments due to the greater difference between the temperature of the cooling water and the ambient water temperatures. This is especially so during the winter period when energy demands are at their highest and thus the power production and amount of cooling water are greatest. In tropical regions, there is little fluctuation experienced in power demand or the local sea temperature.

• Thermally polluted water often undergoes biological and chemical changes that render it less valuable for drinking, recreational, habitat and industrial purposes. The main impacts of thermal pollution include:

• The inhibition of plant growth leading to a change in character of the plant communities within the vicinity of the warm-water outfalls

• A change in the behavior of migratory fish if temperature is used as a trigger for migration.

• Reduced O2 levels in the water column as the oxygen carrying capacity of seawater decreases with increasing temperature.

• Interference with enzyme function and physiology of marine organisms for example increased temperatures increasing metabolic rate in aquatic organisms. Increased respiration at higher temperatures can alter an organisms energy budget if food is limiting.

• The introduction of non-native species which are suited to living in warmer water. These species may then out-compete the native species for the local resources such as food, breeding areas etc.

• Interference with the life-cycles and reproductive physiology of marine organisms that live within the vicinity of the plume

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Case Study-Thermal Pollution

• Example: Most marine organisms rely on temperature thresholds as a trigger for spawning. Angulus Tenuis (the “thin tellin”), a marine bivalve, is a summer spawner and therefore spawns when the water temperature reaches a certain level. An increased water temperature around the out-fall pipes of a power station encourage A. tenuis to spawn earlier and for longer in the year. This can cause problems to their populations if the preferred food for their larvae is not available.

Tellin

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Case Study-Thermal Pollution

• Turkey Point Nuclear Power Generating Station, South Florida

• Turkey Point nuclear power station is situated on the Atlantic coast of Florida, and serves more than 7 million people in the Florida area. This power station removes water from Biscayne Bay then passes it through the condensers. The output water with an increased temperature of up to 15°C above ambient is then pumped back into the receiving water. An area of nearly 40 hectares is affected by cooling water discharged from this power station.

• The cooling water at Turkey Point is discharged into a shallow soft-bottomed area which is dominated by turtle grass, Thalassia.

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Thalassia - Turtle Grass

• Turtle grass is the largest and most robust seagrass in Florida and the Caribbean. Its leaves are about 1.2cm wide, which can grow up to 35cm long. Turtle grass will grow in water up to 25m deep, however it prefers shallow water of less than 10m deep. Turtle grass forms complex shallow water communities. The water temperature around the outfall pipe at Turkey Point is 30-35°C and a further temperature increase of 5°C would be detrimental to the turtle grass community. It is estimated that about 9.3 hectares of Thalassia has been destroyed around this outfall, with a further 30 hectares showing reduced growth rates.

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Assignment

Explain Cold Water Pollution.

Write a S.N. on Thermal pollution mentioning, sources, effects & preventive measures.

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Reduce Thermal Pollution

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