Water Pollution Due to Ash Disposal and Control Measures

Large-scale combustion of coal is required to produce heat that is utilized in certain manufacturing/production processes. The residue of coal combustion, i.e., ash, mainly consists of (a) furnace bottom ash and (b) pulverized fuel ash. The Central Electricity Authority (CEA) prepares an annual report on fly ash generation at coal/lignite-based thermal power stations and its utilization. Methods of ash disposal in dry ash form, lean concentration slurry disposal (LCSD), high concentration slurry disposal (HCSD), and ash disposal in mine voids are commonly used, based on techno-economic feasibility. The Ministry of Environment, Forest, and Climate Change (MoEF&CC) has given directives for dry ash disposal and its utilization. The general scope for monitoring surface and ground water pollution due to ash ponds is discussed. A detailed study of ash ponds in the Singrauli region is presented to illustrate the pollution caused by ash ponds and possible mitigation measures. The study covers a brief description of coal and water availability and power plants in the region. Several thermal power plants and other industries have come up in the Singrauli region due to the abundant availability of coal and water. The rapid development of private and public sector thermal power plants in the region caused heavy pollution. In January 2010, MoEF&CC had declared Singrauli as a critically polluted area on the basis of the comprehensive environmental pollution index (CEPI) of Central Pollution Control Board (CPCB). Areas having aggregate CEPI scores of 70 are considered to be critically polluted. The CEPI score for the Singrauli region in 2018 was 83.24, with all three categories (i.e., air, water, and land environment) in the critical state. Mercury has been measured in ash, ash pond effluents, and surface and ground water bodies, but was found to be within permissible limits. Leaching tests have been carried out by erstwhile University of Roorkee and now IIT Roorkee. Standard leaching tests showed that under the worst case, leaching of heavy elements from the ash was very low due to the high pH of ash water (7–7.5) as well as huge dilution (ash water = 1:10) with a large quantity of natural water. IIT Roorkee, in its study during October 2017, found that the chances of contamination of ground water through the ash pond were meager, as the villages are situated on the upslope side of the water table. Human health-related impacts are discussed. The ash from thermal power plants and effluents from chemical industries have caused the pollution of the Rihand reservoir, resulting in adverse impacts on the health of the dam body. The reservoir area has been encroached upon, and overflow lagoons of the ash dikes have been constructed in the vicinity of the reservoir. Several measures have been proposed by NTPC, MoEF&CC, and CPCB. A brief description of these measures is provided, such as lining of ash disposal area, non-operating and abandoned ash pond, dry disposal of fly ash to avoid contamination of ground water, and phyto-remediation.