Modelling approaches to thermal pollution in inland aquatic systems and issues related to its environmental impacts

Guidelines for the safe discharge of thermal effluents in aquatic environmental systems both surface water and marine coastal out falls has become very relevant to Indian environmental conditions with its rich biodiversity. While aquatic ecology may form the basis for such guidelines, the need for regulatory approach to the related issues has become the prime mover in thermal discharge problems. This is more so since the impacts considered are under short term and long term exposure conditions where the bio acclimatization and thermal stress factors may come to cross roads. Constant temperatures and cyclic temperature elevations also causes differential thermal stress which could be site specific. The recent notification by the Ministry of Environment and Forest (MoEF) revising the temperature limit for discharge of condenser cooling water from thermal power plants into coastal areas using sea water from 5 deg to 7 degC over and above the ambient temperature of the receiving water bodies. Discussions on whether the limiting temperature is to be achieved at the point of discharge or within a specified zone of the thermal plume is currently being debated. The act also stipulates installation of cooling towers using water from rivers, lakes and reservoirs irrespective of the plant location and capacity. For existing thermal plants the rise in temperature of the condenser cooling water from inlet to the let of the condenser shall not be more than 10 degC. (author)