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Development Team Paper No: 5 Water Resources and Management Module: 29 Water Pollution-III (Thermal Pollution) Development Team Prof. R.K. Kohli Principal Investigator & Prof. V.K. Garg & Prof. Ashok Dhawan Co- Principal Investigator Central University of Punjab, Bathinda Dr Hardeep Rai Sharma, IES Paper Coordinator Kurukshetra University, Kurukshetra Dr. Hardeep Rai Sharma* and Ms. Anjali Malan, Content Writer Institute of Environmental Studies, Kurukshetra University, Kurukshetra Content Reviewer Prof. Asha Gupta, Guru Jambheshwar University of Science & Technology, Hisar Anchor Institute Central University of Punjab 1 Water Resources and Management Environmental Sciences Water Pollution-III (Thermal Pollution) Description of Module Subject Name Environmental Sciences Paper Name Water Resources and Management Module Water Pollution-III (Thermal Pollution) Name/Title Module Id EVS/WRM-V/29 Pre-requisites To understand causes and effects of thermal pollution as well as its control Objectives practices. Keywords Artificial lakes, cooling ponds, cooling towers, thermal pollution. 2 Water Resources and Management Environmental Sciences Water Pollution-III (Thermal Pollution) Pollution Thermal Pollution Sources Impacts Control Introduction Water is able to absorb large quantities of heat without changing from its liquid state. The high heat capacity means that it can be extensively used as a coolant in many industries. Heat can be considered a pollutant when its release into an environmental system adversely affects the optimal temperature ranges or indirectly alters other conditions that harm organisms, including humans. Thermal pollution can be defined as “an accumulation of unusable heat from human activities that disrupts ecosystems in the natural environment” or “as the degradation of water quality by any process that changes ambient water temperature.” One major physical stressor on aquatic ecosystems is thermal pollution; it is not only problematic in itself, but can also exaggerate the impacts of chemical pollution. Much of the heat produced by industries is in the form of condenser cooling water. The principal user of water as a coolant include the electricity generating industry, thermal power plants, 3 Water Resources and Management Environmental Sciences Water Pollution-III (Thermal Pollution) nuclear power plants, petroleum refineries, steel mills, chemical plants, paper and pulp mills etc. Future thermal stress on aquatic systems is likely to increase due to intensive use of water bodies as sources and sinks of anthropogenic heat as well as due to ongoing climate warming. The coolant water required by industry is drawn directly from water bodies, frequently rivers which after use, is often directly discharged back into the original water body, resulting in thermal pollution. The increase in heat contributes to the physical, chemical and biological changes in the receiving water bodies. Soil erosion and shoreline deforestation also contribute to thermal water pollution but to a limited extent. The soil erosion makes the water muddy, which in turn increases the light absorbed and thus the water temperature is raised. Deforestation of shorelines further contributes to the problem in two ways. First, it increases soil erosion and secondly, it increases the amount of light that strikes the water, both of which increase the temperature of water. Sources of thermal pollution: This pollution is caused due to release of waste heat into water bodies and sources of such kind are: 1. Nuclear power plants (NPPs): Nuclear power plants including drainage from hospitals, research institutions, nuclear experiments and explosions, discharge a lot of heat along with traces of toxic radio nuclides into nearby water streams. Emissions from nuclear reactors and processing installations are also responsible for increasing the temperatures of water bodies. Heated effluents from power plants are discharged at temperature 10˚C higher than the receiving waters and affect the aquatic animals and plants. The cooling water discharge from NPPs is among the greatest local sources of thermal pollution due to the high levels of energy produced per plant. In addition, nuclear power plants require 30–100% more cooling water than other types of plant with a comparable power output [Electric Power Research Institute (EPRI, 2008)]. The warm water discharge from the NPP superimposes the regional climate warming, which provides an additional heat stress at the water surface. For example river Mississippi receives the highest total amount of heat emissions (62% and 28% of which come from coal-fuelled and nuclear power plants, respectively) and presents the highest number of instances where the commonly set 3°C temperature increase limit is exceeded (Raptis et al. 2016). 4 Water Resources and Management Environmental Sciences Water Pollution-III (Thermal Pollution) 2. Coal-fired power plants: Water from nearby lakes or rivers is used to cool the condenser coils in coal fired power plants. That heated water is discharged into lakes and streams thereby raising the water temperature by 15˚C. Heated effluent decreases the dissolved oxygen content of water resulting in death of aquatic organisms. The sudden fluctuations in temperature also lead to "thermal shock" that can kill aquatic life. Globally, over 46% of the thermal emissions into rivers are due to coal-fuelled power plants and almost one third due to nuclear power plants. The countries like United States, China and France are with the highest combined rates of riverine thermal emissions, occupying shares of 26%, 16%, and 12% of the global thermal emission rate, respectively (Raptis et al. 2016). 3. Thermoelectric power plants: Thermoelectric power plants are one of the main causes of thermal pollution. Such plants pump water directly from rivers, lakes or the ocean, to cool the turbine condensers. During the process, which usually involves once-through cooling, the water becomes warmer than the source water, so that the wastewater is returned to its source at temperatures significantly higher than the freshwater that originally entered the electric generation station. 4. Industrial effluents: Industries like textile, paper, sugar and pulp manufacturing discharge large amounts of cooling water along with effluents into nearby water bodies. In urbanized watersheds, heat contained in effluents from wastewater treatment plants can also lead to significant increase in stream temperature (Kinouchi et al, 2007). Similar is the case with effluents of other industries. The water gets polluted by release of sudden and massive organic loads resulting in drop in levels of dissolved O2 which affect aquatic life. 5. Sewage: Domestic sewage is discharged into rivers, lakes, or streams with minimal or without any treatment. These wastes having a higher temperature and organic load leads to decrease in dissolved O2 content in the receiving waters. Eventually, this leads to the development of anaerobic and anoxic conditions resulting in sudden death of aquatic organisms. 6. Hydro-electric power: Generation of hydroelectric power sometimes leads to negative thermal loading in water systems. Dams may change a river habitat into a lake habitat by creating a reservoir (man-made lake) behind the dam. The reservoir water temperature is often colder than the original stream or river. On the contrary, downstream of dams and Hydropower Plants (HPPs) has generally warm water than upstream because of passing of water from pipelines, penstock, turbine and cooling system (Bobat, 2015). Despite the change in water temperature emerging from construction and 5 Water Resources and Management Environmental Sciences Water Pollution-III (Thermal Pollution) operation of HPPs not as high as that in fossil-fuel and nuclear power plants, it is too important to affect lifecycle and survival of aquatic organisms. 7. Soil erosion: Soil erosion is another major factor that causes thermal pollution. Consistent soil erosion causes water bodies to rise, making them more exposed to sunlight. The high temperature could prove fatal for aquatic biomes as it may give rise to anaerobic conditions. 8. Deforestation: Trees and plants prevent sunlight from falling directly on lakes, ponds or rivers. When deforestation takes place, these water bodies are directly exposed to sunlight, thus absorbing more heat and raising its temperature. Deforestation is also a main cause of the higher concentrations of green house gases i.e. global warming in the atmosphere. 9. Runoff from paved surfaces: Urban runoff discharged to surface waters from paved surfaces like roads and parking lots can cause warming of water. The pavement gets quite hot during summers, which creates warm runoff that gets into the sewer systems and water bodies. 10. Natural causes: Natural causes like volcanoes and geothermal activity under the oceans and seas can trigger warm lava to raise the temperature of water bodies. Lightening can also introduce vast amount of heat into the oceans. This means that the overall temperature of the water source will rise, having significant impacts on the environment. Effects of thermal pollution: There are many impacts of thermal pollution on physic-chemical properties of water as well as on the aquatic organisms. Some of these effects are as mentioned in Figure 1: 6 Water Resources and Management Environmental Sciences Water Pollution-III (Thermal Pollution) Fig 1 Effects of Thermal pollution (Vallero, 2011) Temperature influences the viscosity, density, vapour pressure,
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