| Abstract |
Disposal of hot wastewater from a standard steam cycle power plant directly into an existing natural waterway inevitably leads to an increase in temperature. This changes various physical–chemical properties of water, such as density, viscosity, surface tension and solubility of gases. The influence of heating on aquatic ecosystems is ambiguous, and at different levels of heating it may be both positive and negative. The most important ecological factor is then to limit excessive heat dumping which will exceed the buffer capacity of the aquatic ecosystem. Of the many environmental factors influencing an ecosystem probably none exerts a more profound influence than temperature. Nesjavellir geothermal co-generation power plant in SW-Iceland utilizes high temperature geothermal fluid for production of electricity and hot water for district heating. The plant wastewater is either pumped into shallow drill holes or disposed off in a stream, which finds its way into a freshwater Lake. Result of water temperature measurements done to determine the extent of thermal influence show that large volume of geothermal effluent (40.9°C - 84.0°C) disposed of has caused a rise in both summer and winter temperature at lake shoreline outflow sites. Summer temperature was in the range of 11.7°C - 27.3°C with definite outflow sites temperature being in the range 23.4-27.3°C. During winter temperature at Varmagja varied from 0.6°C on the ice edge to 26°C at the mouth. To minimize local effects deep reinjection of geothermal wastewater and further cooling of the condensed steam was recommended. |