RADIONUCLIDE AND TRACE ELEMENT CONTAMINATION FROM COAL COMBUSTION FROM KOLAGHAT THERMAL POWER PLANT, INDIA

One of the major environmental problems associated with the use of coal as fuel in thermal power plants is the production of ash. This problem is particularly important for Indian power stations because most of the power stations use poor quality coal with 5–50% ash yielding about 100 million tons of ash per annum. Owing to its relatively small size and, hence, large surface area, the ashes have a greater tendency to absorb trace elements and radionuclides that are transferred from coal to waste products during combustion.

Major, minor and trace element analyses of the coal and ash from a major thermal power plant of India located at Kolaghat document predominance of silica and alumina. The coal-ash is significantly enriched in the trace elements Pb, Cu, Ni, As, Cd, Cr, V, Mo etc. Radiometric analysis of the ash shows that the radionuclides (U238, Th232) are enriched 3-5 times in the coal ash as compared to their crustal average. The average absorbed gamma dose rates at 1m above the ground from the ash ponds due to the presence of Th, U 40K is 160 nGy h^-1 which is ~4 times higher than the world average(43nGyh^-1)as reported by UNSCEAR (2000).Chemical analysis of the water samples show siginificant concentration of the trace elements (Al, Ni, Fe, As, Zn, Co, V, Mo, Ba, Rb, Pb V, Cr, Cu, Cd, Mn and Sr) whose distribution is mainly controlled by the ash deposited in the area. Among these elements, Al, As, Zn, Mo, Ba, V, Mo, Cd, Mn, and Pb exceed the WHO guidelines for drinking water in the tube well waters, near the ash pond than those of the neighbouring villages implying significant input from the ash pile. Chemical and radiometric analysis of the soil samples show enrichment of the trace elements Mo, As, Cr, Mn, Cu, Ni, Co, Zn, by a factor of (2-5) than the crustal values.

Combustion of coal thus causes serious environmental concern due to the release of the toxic trace elements and the radionuclides in the ash, thus contaminating the top soil and the subsurface aquifer. People living near the ash ponds are subjected to a high radiation dose from the ash ponds and the soil cover, which is ~ 2.6 times higher than the world average.