Thermal Pollution
Thermal Pollution
Introduction: The word thermal means “related to heat”. Thermal pollution means the unwanted changes
occurring in the environment due to higher temperatures in the ambient atmosphere. It is generally related to
the water bodies, which receive heated discharges of the spent water released through manufacturing industries, power housed and oil refineries etc. In India, there are more than 75 thermal power plants, and several nuclear power plants, industrial belts across the country on the banks or in the vicinity of the bank of several river systems.
A/c to the report of Nidhivan Foundation, “During the 1980’s one-sixth of the river systems in the USA were affected.”
Definition of Thermal Pollution:-
The ‘thermal pollution’ or ‘thermal discharge’ is defined as “unwanted discharge or introduction of undesirable waste, heat, generated by anthropogenic activities, into the water bodies like rivers, lakes streams, thereby causing the rise of average ambient temperature of the water bodies, thus affecting the aquatic flora and fauna.”
or
Thermal pollution is defined as “the warning up of an ecosystem to the plant where the aquatic regine consisting of flora and fauna are adversely affected”.
Causes of Thermal Pollution:-
(i) Power Plants-
• Coal-based Power Plant- The water is very efficient and cheap sink for beat engines and is commonly used in electricity generation stations. The power plants generally emanate a lot of thermal discharge. In coal-fired power plants, the major requirement of the cold water is met from nearby water bodies, which is passed through the power plants, for cooling the condenser coils located in the power plants. The heated water is sent out into the same water body from which the water was withdrawn. It causes the raise in the temperature of water bodies to the tune of about 15°C. The sudden fluctuation of temperature causes “thermal shock” to aquatic life and it eventually dies.
• Nuclear power plants- The power generation unit requires large amounts of water to maintain low sink temperature and high thermal efficiency. Nuclear power plants discharge a lot of heat mainly because of operation of power reactors and nuclear fuel processing units. The heated effluents along with spent water coming from power plants are discharged at 10-15°C higher than the receiving waters affecting the ambient temperature of the aquatic bodies, in which the discharges are made.
• Hydroelectric power plants- The generation of hydroelectric power sometimes leads to negative thermal loading in water systems. Apart from electric power industries, various factories with cooling requirement contribute to thermal loading.
(ii) Manufacturing Industries- The textile, chemical, paper, pulp, sugar and other manufacturing industries generate huge amounts of effluents along with heat energy, which are discharged into nearby natural water bodies. The waters polluted by such dumping of thermal discharge may increase the level of pollution beyond threshold levels, resolting in the deleterious impact on the aquatic bodies.
(iii) Domestic Sewage- The domestic sewage from the city drainage system is generally discharged into aquatic bodies with partial treatment or even without any treatment. These effluents of sewage system have a higher organic load and also higher organic temperature. The sewage effluents may have temperature 5-10°C higher than the aquatic bodies, in which it is discharge. It leads thereby creating anaerobic conditions and releases foul and odious gases in water.
(iv) Other causes-
• Soil Erosion- Soil erosion can cause greater exposure of water bodies to sunlight thereby raising temperature.
• Deforestation- Removal of trees and vegetation from alongside rivers, lakes, ponds can increase the exposure to sunlight.
• Runoff from paved surfaces- In urban areas the surfaces of pavements, roads and parking areas make water warm and such water when discharged into surrounding water bodies or sewer systems causes thermal pollution.
Effects of Thermal Pollution:-
(i) Ecological effects of thermal pollution-
• Thermal shock- Generally the aquatic fauna can withstand variations in the temperature. But, wide fluctuations in the temperatures may cause thermal shocks to the animals; and it may happen by the increase of 1-2°C of temperature causing the animals to die.
• Reduces Dissolved Oxygen (DO)- Concentration of dissolved oxygen decreases with rise in temperature of water, which can hold less oxygen than the cold water. A rise of 10°C in temperature reduces the solubility of the oxygen by 20%. This condition creates suffocation and asphyxiation in the aquatic fauna.
• Lower Reproduction- Breeding activities of aquatic life forms are governed by temperature Nest building, spawning, hatching, migration and reproduction take place in a certain temperature range. These are inhibited by higher temperatures because the rise in temperature makes spawning difficult.
• Replacement of the species- When there is increase in the temperature, it is congenial for the growth of blue-green algae (35-40°C) over the green algae (30-35°C). The blue-green algae is not a good source of food and also increases some kind of obnoxious toxic substances harmful to the aquatic fauna, avian-fauna and human beings.
• Food Storage for Fish- Abrupt variations in temperature changes the availability of proper food for fish and other aquatic fauna.
(ii) Increase in Toxicity- The rising temperature increase the toxicity levels of the chemicals present in water. A 10°C increase in temperature of water doubles the toxicity effect of certain chemicals.
(iii) Loss of Biodiversity- Thermal pollution is directly responsible for mortality of aquatic organisms. Increase in temperature of water leads to exhaustion of micro-organisms, thereby shortening the life span of fish. Above a certain temperature, the fish dies due to failure of respiratory system and nervous system.
Measures to Control Thermal Pollution:-
(i) Cooling Towers- The cooling towers are the devices used for the cooling of the thermal discharges before being discharged into a water body. Here, the temperature of the discharge is reduced. These towers transfer waste heat into the atmosphere by evaporation or heat transfer and sometimes by both the processes. The cooling towers employ a system of coiled pipes kept in a tower; and the hot water released by any industry is allowed to pass through the coiled pipes, over which the cool air is allowed to flow, lowering the temperature of the effluents within the coils so that the effluents coming out of the tower may have lower temperatures.
(ii) Cooling Ponds- The cooling ponds are the wide ponds excavated in the adjoining areas of the industries, where ample land is available. The thermal discharges are released into these cooling ponds, where the hot effluents are stored for some time and cooled by natural evaporation resulting in temperature reduction. Thereafter, these effluents are discharged from the cooling ponds into the water bodies. Hence, less thermal pollution is possible.
(iii) Spray Ponds- The spray ponds are the structures especially designed; and the thermal discharges released from the industries are discharged into these ponds, not directly but through a series of sprayers with nozzles, which make water into fine water droplets, the heat is dissipated into atmosphere and the temperature of the collected discharge is reduced.
(iv) Artificial Lakes- The artificial lakes are very large water bodies created by man artificially; and these Lakes function as the supply source of cool water for any industry from one side. The heated effluent discharges are released into the same lake from the other side of the lake. During the course of time, the hot effluent gradually become cool, because of dissipation of heat into the atmosphere.
(v) Cogeneration (Recovery of waste heat)- Cogeneration is a process in which the heat generated in thermal pollution is utilized for the heating purpose in domestic as well as industrial use. In this, there is a simultaneously production of multiple forms of useful energy is integrated approach. Waste heat of medium and high temperatures can be used for the generation of electricity or mechanical work. It is also known as the recovery of waste heat. This type of waste recovery method may be applied in places like hotels, hospitals and mall, etc.
