Thermal pollution by power plants

An important by-product of most chemical technologies, in the broad sense, is heat. Few industrial processes are carried out without heat being rejected at some point in the process stream, even if the net energy balance is endothermic. Historically, it was more convenient and less costly to reject such waste heat to the environment than to attempt significant recovery. Although energy scarcities and high costs and stimulating innovative heat-recovery schemes, the low temperatures of waste heat in relation to process requirements often make reuse impractical and disposal the only attractive alternative. Concern over heat rejection arose when the quantities at localized sites rose dramatically as the electric utility industry shifted to water-cooled, thermal-electric generating stations of high unit capacity in the 1950s, particularly in the UK and the US. Concern was further heightened by a planned shift to nuclear fission reactors as the energy source, which entailed both a further increase in localized generating capacity because of economics of scale and a higher percentage of rejected heat compared to useable electrical energy. It was estimated that perhaps 25% of the total available freshwater runoff in the entire nation would be needed for cooling purposes by 1980. The term thermal pollution took on fearsome portents among aquatic scientists, fishery managers, and eventually water-pollution control agencies. Topics discussed include environmental risks, minimizing the risks, thermal effects, preventing mortality, preventing stressful high temperatures over long periods, maintaining ecosystem structure, biocides, entrainment, gas balance, and aquaculture. 35 references, 8 figures, 1 table