The thermal pollution It occurs when some factor causes an undesirable or harmful change in the ambient temperature. The environment most affected by this pollution is water, however it can also affect air and soil.
The average temperature of the environment can be altered both by natural causes and by human actions (anthropogenic). Natural causes include unprovoked forest fires and volcanic eruptions.
Among the anthropogenic causes are the generation of electrical energy, the production of greenhouse gases and industrial processes. Likewise, refrigeration and air conditioning systems contribute..
The most relevant thermal pollution phenomenon is global warming, which implies an increase in the average planetary temperature. This is due to the so-called greenhouse effect and the net contributions of residual heat by humans..
The activity that generates the most thermal pollution is the production of electricity from the burning of fossil fuels. Burning coal or petroleum products diffuses heat and produces CO2, the main greenhouse gas.
Thermal pollution causes physical, chemical and biological changes that have a negative impact on biodiversity. The most relevant property of high temperatures is its catalytic power and includes the metabolic reactions that occur in living organisms..
Living beings require certain conditions of amplitude of variation of temperature determined to survive. That is why any alteration of this amplitude may imply the decrease of populations, their migration or their extinction..
On the other hand, thermal pollution directly affects human health causing heat exhaustion, heat shock and aggravating cardiovascular diseases. Additionally, global warming causes tropical diseases to expand their geographic range of action..
Preventing thermal pollution requires modifying the modes of economic development and the habits of modern society. This in turn implies implementing technologies that reduce the thermal impact on the environment..
Some examples of thermal pollution are presented here, such as the Santa María de Garoña nuclear power plant (Burgos, Spain) that operated between 1970 and 2012. This power station dumped hot water from its cooling system into the Ebro river, increasing its natural temperature by up to 10 ºC..
Another characteristic case of thermal pollution is provided by the use of air conditioning devices. The proliferation of these systems to reduce the temperature increases the temperature of a city like Madrid by up to 2 ºC.
Finally, the positive case of a margarine producing company in Peru that uses water to cool the system and the resulting hot water is returned to the sea. Thus, they managed to save energy, water and reduce the contribution of hot water to the environment.
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Thermal pollution is derived from the transformation of other energies since all energy when deployed generates heat. This consists of the acceleration of the movement of the particles of the medium.
Therefore heat is a transfer of energy between two systems that are at different temperatures..
Temperature is a quantity that measures the kinetic energy of a system, that is, the average movement of its molecules. Said movement can be translational as in a gas or vibrations as in a solid.
It is measured by a thermometer, of which there are several types, the most common being the dilation and the electronic.
The expansion thermometer is based on the coefficient of expansion of certain substances. These substances, when heated, stretch and their rise marks a graduated scale..
The electronic thermometer is based on the transformation of thermal energy into electrical energy translated on a numerical scale.
The most common scale used is the one proposed by Anders Celsius (ºC, degrees Celsius or centigrade). In it, 0 ºC corresponds to the freezing point of water and 100 ºC to the boiling point..
Thermodynamics is the branch of Physics that studies the interactions of heat with other forms of energy. Thermodynamics contemplates four fundamental principles:
- Two objects with different temperatures will exchange heat until they reach equilibrium.
- Energy is neither created nor destroyed, it only transforms.
- One form of energy cannot be fully transformed into another without loss of heat. And the heat flow will be from the hottest medium to the least hot, never the other way around.
- It is not possible to reach a temperature equal to absolute zero.
These principles applied to thermal pollution determine that every physical process generates heat transfer and produces thermal pollution. In addition, it can be produced either by increasing or decreasing the temperature of the medium..
The increase or decrease in temperature is considered a pollutant when it goes outside the vital parameters.
Temperature is one of the fundamental aspects for the occurrence of life as we know it. The range of temperature variation that allows most of the active life ranges from -18ºC to 50ºC.
Living organisms can exist in a latent state at temperatures of -200 ºC and 110 ºC, however they are rare cases.
Certain so-called thermophilic bacteria can exist at temperatures of up to 100ºC as long as there is liquid water. This condition occurs at high pressures on the seabed in areas of hydrothermal vents..
This tells us that the definition of thermal pollution in a medium is relative and depends on the natural characteristics of the medium. Likewise, it is related to the requirements of the organisms that inhabit a given area..
In humans, normal body temperature ranges from 36.5ºC to 37.2ºC, and homeostatic capacity (to compensate for external variations) is limited. Temperatures below 0 ºC for long periods of time and without any artificial protection cause death..
Likewise, temperatures consistently above 50 ºC are very difficult to compensate in the long term..
In water, thermal pollution has a more immediate effect as the heat dissipates more slowly here. In the air and on the ground, thermal pollution has less forceful effects because the heat dissipates more quickly..
On the other hand, in small areas the capacity of the environment to dissipate large amounts of heat is very limited..
Heat has a catalytic effect on chemical reactions, that is, it accelerates these reactions. This effect is the main factor by which thermal pollution can have negative consequences for the environment..
Thus, a few degrees of temperature difference can trigger reactions that would not otherwise occur..
The Earth has gone through cycles of high and low average temperatures throughout its geological history. In these cases, the sources of the increase in the planet's temperature were of a natural nature such as the sun and geothermal energy..
Currently, the global warming process is associated with human activities. In this case, the main problem is the decrease in the dissipation rate of said heat towards the stratosphere..
This occurs mainly due to the emission of greenhouse gases by human activity. These include industry, vehicular traffic and the burning of fossil fuels..
Global warming represents the largest and most dangerous thermal pollution process that exists today. In addition, the heat emission from the global use of fossil fuels adds additional heat to the system..
A thermoelectric plant is an industrial complex designed to produce electricity from fuel. Said fuel can be fossil (coal, oil or derivatives) or a radioactive material (uranium for example).
This system requires cooling of the turbines or reactors and for this water is used. In the cooling sequence, a large volume of water is drawn from a convenient, cold source (a river or the sea).
Subsequently, the pumps force it through tubes that are surrounded by the hot exhaust steam. The heat passes from the steam to the cooling water and the heated water is returned to the source, bringing excess heat to the natural environment..
Forest fires are a common phenomenon today, being in many cases caused directly or indirectly by human beings. The burning of large forest masses transfers enormous amounts of heat mainly to the air and the ground.
Air conditioning devices not only alter the temperature of the indoor area, but cause imbalances in the outdoor area. For example, air conditioners dissipate to the outside 30% more than the heat they extract from inside.
According to the International Energy Agency there are around 1,600 million air conditioners in the world. Likewise, refrigerators, refrigerators, cellars and any equipment designed to lower the temperature in a closed area generate thermal pollution..
In fact, all industrial transformation processes involve the transfer of heat to the environment. Some industries do so at particularly high rates such as those dedicated to gas liquefaction, metallurgy and glass production.
The regasification and liquefaction industries of various industrial and medical gases require refrigeration processes. These processes are endothermic, that is, they absorb heat by cooling the surrounding environment..
For this, water is used that is returned to the environment at a lower temperature than the initial one..
Blast smelting furnaces emit heat into the environment, as they reach temperatures above 1,500 ºC. On the other hand, the materials cooling processes use water that re-enters the environment at a higher temperature..
In the melting and molding processes of the material, temperatures of up to 1,600 ºC are reached. In this sense, the thermal pollution generated by this industry is considerable, especially in the work environment..
Incandescent lamps or spotlights and fluorescent lamps dissipate energy in the form of heat to the environment. Due to the high concentration of lighting sources in urban areas, this becomes a source of significant thermal pollution.
Internal combustion engines, like those in cars, can generate around 2,500ºC. This heat is dissipated to the environment through the cooling system, specifically through the radiator..
Taking into account that hundreds of thousands of vehicles circulate daily in a city, it is possible to infer the amount of heat transferred.
In practice, a city is a source of thermal pollution due to the existence in it of many of the factors already mentioned. However, a city is a system whose thermal effect forms a heat island within the framework of its environment..
Albedo refers to the ability of an object to reflect solar radiation. Beyond the caloric contribution that each element present (automobiles, homes, industries) can make, the urban structure exerts a significant synergy.
For example, materials in urban centers (mainly concrete and asphalt) have a low albedo. This causes them to get very hot, which together with the heat emitted by activity in the city enhances thermal pollution.
Various investigations have shown that the generation of heat by human activities during a warm day in a city can be very high.
For example, in Tokyo there is a net heat input of 140 W / m2, equivalent to an increase in temperature of approximately 3 ºC. In Stockholm, the net contribution is estimated at 70 W / m2, equivalent to a 1.5 ºC increase in temperature.
The increase in water temperature as a result of thermal pollution causes physical changes in it. For example, it decreases dissolved oxygen and increases the concentration of salts, affecting aquatic ecosystems..
In bodies of water subject to seasonal changes (winter freezing), adding hot water alters the natural freezing rate. This in turn affects living beings that have adapted to that seasonality..
In the cooling systems of thermoelectric plants, exposure to high temperatures produces a physiological shock for certain organisms. In this case, phytoplankton, zooplankton, plankton eggs and larvae, fish and invertebrates are affected..
Many aquatic organisms, especially fish, are very sensitive to water temperature. In the same species, the ideal temperature range varies depending on the acclimatization temperature of each specific population..
Due to this, temperature variations cause disappearance or migration of entire populations. Thus, the discharge water from a thermoelectric plant can increase the temperature by 7.5-11 ºC (fresh water) and 12-16 ºC (salt water).
This heat shock can lead to rapid death or induce side effects that affect the survival of populations. Among other effects, heating the water decreases the dissolved oxygen in the water, causing hypoxia problems..
This phenomenon seriously affects aquatic ecosystems, even causing the disappearance of life in them. It begins with the proliferation of algae, bacteria and aquatic plants as a result of artificial contributions of nutrients to the water.
As the populations of these organisms increase, they consume the dissolved oxygen in the water, causing the death of fish and other species. The increase in water temperature contributes to eutrophication by reducing dissolved oxygen and concentrating salts, favoring the growth of algae and bacteria..
In the case of air, temperature variations affect physiological processes and the behavior of species. Many insects decrease their fertility at temperatures above certain levels.
Likewise, plants are sensitive to temperature for their flowering. Global warming is causing some species to expand their geographic range, while others see it restricted.
Unusually high temperatures affect human health, so-called thermal shock or heat stroke can occur. This consists of acute dehydration that can cause paralysis of various vital organs and even cause death..
Heat waves can cause hundreds and even thousands of people as in Chicago (USA), where in 1995 approximately 700 people died. Meanwhile, the heat waves in Europe between 2003 and 2010 have caused the death of thousands of people.
On the other hand, high temperatures negatively affect the health of people with cardiovascular diseases. This situation is especially serious in cases of hypertension..
Sudden variations in temperature can weaken the immune system and make the body more susceptible to respiratory diseases.
Thermal pollution is an occupational health factor in some industries, for example metallurgy and glass. Here workers are subjected to radiant heat that can cause serious health problems.
Although safety measures are obviously taken, thermal pollution is significant. Conditions include heat exhaustion, heat shock, extreme radiated heat burns, and fertility problems.
The increase in global temperature causes that diseases hitherto restricted to certain tropical areas expand their radius of action.
In April 2019, the 29th European Congress of Clinical Microbiology and Infectious Diseases was held in Amsterdam. In this event it was pointed out that diseases such as chikungunya, dengue or leishmaniasis can spread to Europe.
Similarly, tick-borne encephalitis can be affected by the same phenomenon..
It is about reducing the net contributions of heat to the environment and preventing the heat produced from being trapped in the atmosphere.
Thermoelectric plants cause the greatest contribution of thermal pollution in terms of net heat transfer to the atmosphere. In this sense, to reduce thermal pollution it is essential to replace fossil fuels with clean energies.
Solar, wind (from wind) and hydroelectric (from water) energy production processes make very low residual heat inputs. The same happens with other alternatives such as wave energy (waves) and geothermal energy (heat from the earth),
Thermoelectric plants and industries whose processes require cooling systems can employ closed-loop systems. Mechanical heat diffusion systems can also be incorporated to help reduce the water temperature..
Cogeneration consists of simultaneously producing electrical energy and useful thermal energy such as steam or hot water. For this, technologies have been developed that allow to recover and take advantage of the residual heat generated in industrial processes..
For example, the INDUS3ES project funded by the European Commission is developing a system based on a “heat transformer”. This system is capable of absorbing low temperature residual heat (70 to 110 ºC) and returning it to a higher temperature (120-150 ºC).
More complex systems may include other dimensions of energy production or transformation.
Among these we have trigeneration, which consists of incorporating cooling processes in addition to the generation of electricity and heat. In addition, if mechanical energy is additionally generated, we speak of tetrageneration.
Some systems are CO2 traps, in addition to producing electricity, thermal and mechanical energy, in which case we speak of four-generation. All these systems also contribute to reducing CO2 emissions..
Since global warming is the phenomenon of thermal pollution with the greatest impact on the planet, its mitigation is necessary. To achieve this, the main thing is to reduce greenhouse gas emissions, including CO2..
Reducing emissions requires a change in the pattern of economic development, substituting fossil energy sources for clean energy. In fact, this reduces the emission of greenhouse gases and the production of waste heat..
An alternative used by some thermoelectric plants is the construction of cooling ponds. Its function is to rest and cool the waters derived from the cooling system before returning them to their natural source..
Nuclear power plants produce electrical energy from the decomposition of radioactive material. This generates a lot of heat, requiring a cooling system.
The Santa María de Garoña nuclear power plant (Spain) was a BWR (boiling water reactor) type power generation plant inaugurated in 1970. Its cooling system used 24 cubic meters of water per second from the Ebro river.
According to the original project, the wastewater returned to the river would not exceed 3 ºC with respect to the river temperature. In 2011, a Greenpeace report, corroborated by an independent environmental company, found much higher temperature increases.
The water in the area of the spill reached 24ºC (from 6.6 to 7ºC of natural river water). Then, four kilometers downstream from the spill area, it exceeded 21 ºC. The plant ceased operations on December 16, 2012.
In cities there are more and more air conditioning systems to reduce the ambient temperature in the hot season. These devices work by extracting hot air from inside and diffusing it outside.
They are generally not highly efficient, so they diffuse even more heat outside than they extract from inside. These systems are therefore a relevant source of thermal pollution.
In Madrid, the set of air conditioning devices present in the city raise the ambient temperature by up to 1.5 or 2 ºC.
Margarine is a substitute for butter obtained by hydrogenating vegetable oils. Hydrogenation requires saturating vegetable oil with hydrogen at high temperatures and pressures.
This process requires a water-based cooling system to capture the waste heat generated. Water absorbs heat and raises its temperature, being then returned to the environment.
In a Peruvian margarine-producing company, a flow of hot water (35ºC) caused thermal pollution in the sea. To counteract this effect, the company implemented a cogeneration system based on a closed cooling circuit.
Through this system it was possible to reuse the hot water to preheat the water entering the boiler. In this way, water and energy were saved and the flow of hot water to the sea was reduced..
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