INTRODUCTION

In recent years the global energy demand has increased with the advances in industrialization and this has been largely met by fossil fuels. Coal meets 29.6% of global primary energy needs and its share in the world's electricity generation is about 42% (World coal association, 2011). India with an installed electricity generating capacity of 190 GW caters to a population of 1.21 billion.  Coal combustion from thermal power plants contributes to 55.32% of the total electricity generation in India (Ministry of Power, 2012). Apart from dwindling stock indigenous coal resources are unable to supplement the increasing energy demands. Conventional generation of electricity from fossil fuel based sources like coal results in serious environmental problems (pollution of air, water and land) with far reaching local and global implications (global warming and changes in the climate regime). Major pollutants due to coal based power generation include sulfur dioxide, carbon and nitrogen compounds, non-combustible hydrocarbons, heavy metals and fly ash.

Major environmental problems associated with the use of coal as fuel in thermal power plants are the likely contamination of air, water and land environment affecting the livelihood of the local people. The disposal of fly ash from coal fired power generation, and its possible impacts on the environment, has been a serious environmental problem. The fly ash is disposed of either by dry methods of disposal in landfills or by wet methods of disposal where the ash is mixed with water and removed as slurry for settlement in ponds. The supernatants are discharged into a receiving system and the final effluents discharged into a natural aquatic drainage system like a river. Both these methods of fly ash disposal result in metal contamination of surface and groundwater resources and hence can transfer these contaminants into the food chain (Mehra et.al, 1998).

The major part of fly ash is disposed off in unmanaged landfills or lagoons, leads to environmental pollution in the area through fly ash erosion and leachate generation (Gupta et.al, 2002). Heavy metals like Arsenic, Lead, Nickel, Cobalt, Chromium, Boron and Antimony found in fly ash are hazardous for living organisms. These elements released to the soil, surface water, and groundwater by leaching processes affects the biota in an ecosystem.

The leaching potential of ash ponds is higher due to diurnal and seasonal variations in temperature, moisture and other parameters (Praharaj et.al, 2002). Leaching of soluble ions from ash ponds into the ground water was reported near Vijayawada Thermal Power Station (Suresh et.al, 1998). Leachability of metals such as cadmium, chromium, zinc, lead, mercury, and silver (cations) increases with decreasing pH or under acidic conditions (Dwivedi et.al, 2008). Al, Fe, Mn and Pb are the major contaminants contributed from the ash pond effluent to the river water in Orissa and their enrichment with respect to the respective prescribed limits confirmed  that the river water is contaminated to varying degrees and therefore not potable (Tripathy et.al,  2002).

Bio-accumulation of heavy metals in plants lead to increased elemental composition that eventually enters the food chain. An investigation of fly ash contaminated areas in Uttar Pradesh, India showed the bio-accumulation of heavy metals like Fe, Zn, Cu, Mo, B, Si, Al, Cr, Pb, Cd, Hg and As in native aquatic, terrestrial and algal species in the vicinity (Rajarshi et.al, 2009).

he effluents discharged by thermal power plants (TPP) require treatment, before they are discharged into the fresh water streams. Effluents from thermal power plants include thermal discharges, wastewater effluents (e.g., cooling tower blow down; ash handling wastewater; wet FGD system discharges; material storage runoff; metal cleaning wastewater; and low-volume wastewater), and sanitary wastewater. There is also the release of ash pond decant into the local water bodies from the coal-based industries. Such release of ash pond decant tends to deposit ash all along its path thereby causing fugitive dust nuisance when it dries up. Also when such water mixes with a water body, it increases the turbidity of the water body thereby decreasing the primary productivity. This is harmful to the fisheries and other aquatic biota in the water body. The effect of Tuticorin Thermal Power Plant effluents on Tuticorin coastal water reveal an elevated temperature of coolant water resulted in suppression of phytoplankton, zooplankton, fishes and shell fishes (Selvin et.al, 2010). The effect of Tuticorin Power plant on the Tuticorin Bay is evident from the enhanced water temperature upto 2 km from discharging point apart from the decline of depth of Bay and increased ash layer and turbidity due to sustained discharge of ash slurry (Selvaraj et.al in 2000) leading to eutrophication with higher Biological Oxygen Demand (BOD) and reduced levels of Dissolved Oxygen (DO). The physical (pH, TDS, TS and TSS) and chemical (BOD, DO, CO₂, CL2, H2S, SO4 and PO4 etc.) constituents of a water body help to understand the extent of water pollution (Dwivedi, and Pandey, 2002). These constituents decide the biotic assemblages and distribution pattern in any water body. In recent years cases related to surface and ground water pollution have increased due to the inadequate environmental protection measures in coal mining and related industries as well as the presence of active and abandoned coal mines, waste dumps, coal washeries, coking coal plants, thermal power plants, steel fertilizer and cement plants (Amita Kiran & Arvind Kumar Jha, 2011). Overexploitation of ground water has resulted in drying up of wells, salt intrusion in coastal areas and depletion of water resources.

A coal-based thermal power project (with the installed capacity of 1200 MW) is setup in Udupi District, Karnataka State in the Coastal Region of India (Figure 1). The region is sandwiched by Western Ghats in the east and Arabian Sea in the West. The river Shambhavi, a tributary to river Mulki flows nearly 4 km south of the Yellur village.  The phase 1 of this power plant (600 MW) achieved commercial operation from June 2010. The water for condenser cooling water system is pumped from Arabian Sea at a distance of 6 km. A re-circulating type natural draft cooling tower has been installed, and the sea water is returned after cooling in the cooling towers. The liquid effluents from the Thermal Power Plant are being released to nearby streams.  The objective of this study is to analyze the environmental impacts of effluent discharge on the surrounding environment focusing on the surface and ground water quality in the vicinity of thermal power plant.