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Thermal pollution from coal plants

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This article is part of the Coal Issues portal on SourceWatch, a project of CoalSwarm and the Center for Media and Democracy. See here for help on adding material to CoalSwarm.

Thermal pollution is the degradation of water quality by any process that changes ambient water 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 impacts organisms by (a) decreasing oxygen supply, and (b) affecting ecosystem composition.[1]

When a power plant first opens or shuts down for repair or other causes, fish and other organisms adapted to particular temperature range can be killed by the abrupt rise in water temperature known as 'thermal shock': most aquatic organisms have developed enzyme systems that operate in only narrow ranges of temperature, and can be killed by sudden temperature changes that are beyond the tolerance limits of their metabolic systems.[1]

Ecological effects

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 food source shortages, causing a sharp decrease in a population. Changes in the environment may also result in a migration of organisms to another, more suitable environment, and to in-migration of fishes that normally only live in warmer waters elsewhere. This leads to competition for 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.[1]

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 rates and reproduction.[1]

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 the oxygen levels in the water. The higher plant density leads to an increased plant respiration rate because the reduced light intensity decreases photosynthesis. This is similar to the eutrophication that occurs when watercourses are polluted with leached agricultural inorganic fertilizers.[1]

A large increase in temperature can lead to the denaturing of life-supporting enzymes by breaking down Hydrogen bond 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.[1]

Control of thermal pollution

"The case for fish-friendlier power: A Watershed Moment for the EPA"

In 2011, the Chicago Tribune accessed industry reports through the Freedom of Information Act, and discovered that numerous older power plants have been exempted from environmental regulations designed to prevent enormous industrial fish kills. These older plants, employing "once-through" cooling, pump massive amounts of water from lakes and rivers through the screens of water intake systems - some so powerful they could fill an Olympic swimming pool in less than a minute - and sucking up multiple fish. Dozens of older power plants that ring the Great Lakes kill hundreds of millions of fish each year as a consequence of employing outdated processes to cool their equipment.[2]

The FirstEnergy Bay Shore Plant on the Maumee River shoreline near Toledo, Ohio, kills an estimated 46 million adult fish annually, as well as 2.4 billion eggs, larvae and young fish. Not far away, at the mouth of another important Lake Erie tributary, the Monroe Power Plant in Michigan kills more than 25 million fish and almost a half-billion fish eggs and other organisms each year. FirstEnergy's Bay Shore power plant also withdraws more than 749 million gallons of water per day from Lake Erie, using vast quantities of "once-through" water used to cool equipment exits, and creating prime growing conditions for bacteria that harm native fish habitat.[3] According to the EPA, in the United States thermal pollution from industrial sources is generated mostly by power plants, but also petroleum refineries, pulp and paper mills, chemical plants, steel mills and smelters.[4] [5] 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.[6]

Some facilities use once-through cooling (OTC) systems which do not reduce temperature as effectively as the above systems. For example, Mirant Corporation's natural gas-powered Potrero Generating Station in San Francisco, which uses OTC, discharges water to the San Francisco Bay approximately 10° C (20° F) above the ambient bay temperature.[7] Groups like Hudson Riverkeeper advocate closed-cycle cooling systems, mandated by the Clean Water Act, to lessen the water used and the fish harmed (see video).

US Regulations

Section 316(b) of the Clean Water Act (CWA) requires the EPA to ensure that the location, design, construction, and capacity of cooling water intake structures reflect the best technology available (BTA) for minimizing adverse environmental impacts, including thermal pollution. The EPA has been in the process of developing a rule that will define how States will establish standards for cooling water intake structures at large power plants, expected to be published in the Federal Register in September 2010. The rule would apply to large existing power plants that withdraw 50 million gallons per day or more, and that use at least 25 percent of their withdrawn water for cooling purposes only - an estimated 422 fossil-fueled and 38 nuclear power plants representing over 308 and 52 GW of existing capacity, respectively.[8] The rule has been repeatedly challenged by industry lawsuits[8], prompting states like CA to move forward with their own regulations.[9]

In July 2010, the U.S. Court of Appeals for the Fifth Circuit granted EPA's request to take back part of a rule on cooling water intake structures relating to existing facilities so it can consider what might be appropriate requirements (ConocoPhillips v. EPA, 5th Cir., No. 06-60662, 7/23/10). Industries are particularly concerned about the requirements because of the high costs associated with retrofitting cooling towers. According to a 2010 report, "Special Reliability Scenario Assessment: Resource Adequacy Impacts of Potential U.S. Environmental Regulations" by the North American Electric Reliability Corp., an estimated 33 gigawatts to 36 gigawatts of generating capacity could be forced to be retired, depending on how stringent the cooling tower rule might be.[10] A 2010 study by The Brattle Group, "Potential Coal Plant Retirements Under Emerging Environmental Regulations" found that 11,000 to 12,000 MW of coal power could retire if cooling towers are mandated. According to the report, if scrubbers and cooling towers are required, it could shut down every merchant coal plant (plants that sell power into competitive wholesale markets) in the Texas ERCOT region.[11]

Overall water use in U.S.

A 2011 Union of Concerned Scientists report, "Freshwater Use by U.S. Power Plants: Electricity’s Thirst for a Precious Resource," calculated the available water in every major watershed in the U.S. and measured that against the water used by power plants in each watershed. The report found that every day in 2008, on average, water-cooled thermoelectric power plants in the United States withdrew 60 billion to 170 billion gallons of freshwater from rivers, lakes, streams, and aquifers, and consumed 2.8 billion to 5.9 billion gallons - coal plants were responsible for 67 percent of those withdrawals, and 65 percent of that consumption.

Plants in the East generally withdrew more water for each unit of electricity produced than plants in the West, because most have not been fitted with recirculating, dry cooling, or hybrid cooling technologies. Freshwater withdrawal intensity was 41 to 55 times greater in Virginia, North Carolina, Michigan, and Missouri than in Utah, Nevada, and California.[12]


Related SourceWatch articles


  1. 1.0 1.1 1.2 1.3 1.4 1.5 "Thermal Pollution" Pollution Issues, accessed November 2009
  2. Michael Hawthorne, "Millions of Great Lakes fish killed in power plant intakes: Industry resists alternative cooling equipment that would protect species," Chicago Tribune, June 17, 2011.
  3. Doug Schmidt, "'Huge' fish kill, power plants linked: Toll at U.S. generating station water intakes called astronomical", The Windsor Star June 18, 2011.
  4. U.S. Environmental Protection Agency (EPA). Washington, D.C. "Cooling Water Intake Structures - Basic Information." EPA Website, accessed November, 2009
  5. "Technical Development Document for the Final Section 316(b) Phase III Rule. Chapter 2." EPA Website, accessed November 2009
  6. "Profile of the Fossil Fuel Electric Power Generation Industry." EPA Report EPA/310-R-97-007: p. 24, 1997
  7. California Environmental Protection Agency,"Waste Discharge Requirements for Mirant Potrero, LLC, Potrero Power Plant." San Francisco Bay Regional Water Quality Control Board Website, Order No. R2-2006-0032; NPDES Permit No. CA0005657. May 10, 2006.
  8. 8.0 8.1 "Criteria and Standards for Cooling Water Intake Structures" EPA Website, accessed July 2010.
  9. Cassandra Sweet, "California Rules Restrict Power Plants' Marine Water Use" The Wall Street Journal, May 5, 2010.
  10. Andrew Childers, "Electric Companies Said to Need Time to Implement Environmental Rules" Air and Waste Management Association, 2010.
  11. "EPA rules could spark $180bn in upgrades, 67,000 MW of coal-fired retirements" Power-Gen, Dec. 8, 2010.
  12. Averyt, K., J. Fisher, A. Huber-Lee, A. Lewis, J. Macknick, N. Madden, J. Rogers, and S. Tellinghuisen, "Freshwater Use by U.S. Power Plants: Electricity’s Thirst for a Precious Resource," The Union of Concerned Scientists' Energy and Water in a Warming World initiative, November 2011 Report.

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