Assessment of heavy metals in fly ash and groundwater

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/251881155

Assessment of heavy metals in fly ash and groundwater - A case study of ntpc badarpur thermal power plant, Delhi, India Article in Pollution Research · December 2010

CITATIONS

READS

3

228

4 authors, including: R K Singh

NC Gupta

Guru Gobind Singh Indraprastha University

Guru Gobind Singh Indraprastha University

17 PUBLICATIONS 25 CITATIONS

60 PUBLICATIONS 87 CITATIONS

SEE PROFILE

All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.

SEE PROFILE

Available from: R K Singh Retrieved on: 16 April 2016

Poll Res. 29 (4) : 685-689 (2010) Copyright © EM International

ASSESSMENT OF HEAVY METALS IN FLY ASH AND GROUNDWATER - A CASE STUDY OF NTPC BADARPUR THERMAL POWER PLANT, DELHI, INDIA REENA SINGH1, R. K. SINGH2, N. C. GUPTA2* AND B. K. GUHA3 1

Emergent Ventures India Pvt. Ltd. 5th floor Universal Trade Tower, Sec 49, Sohna Road, Gurgaon 122001, India. 2 University School of Environment Management, GGS Indraprastha University, Kashmere Gate, Delhi 110 403, India 3 Department of Chemical Engineering, IIT Delhi, Hauz Khas, New Delhi-110016, India ABSTRACT Fly ash is an industrial waste generated from the thermal energy sector. The environmental concerns regarding the potential contamination of soil, surface water and ground water due to the presence of heavy metals in the ash is of serious concern. Moreover, the use of low quality coal with high ash content results in large quantities of bottom and fly ashes for disposal. This study is carried out to analyze the heavy metals concentration of fly ash and pond ash from Badarpur thermal power plant located in Delhi. The current disposal methods of fly ash by the plant management are also studied. The samples of the fly ashes were analyzed for the presence of Chromium (Cr), Nickel (Ni) and Zinc (Zn) and the detectable levels of these metals were found in both fly ash and pond ash. The concentration of Ni was higher as compared to Cr concentration. The wet disposal method is used in the thermal power plant. The ground water samples of the ash pond were also analyzed and investigated for the presence of these heavy metals. The concentration of Zn was found in higher side while Ni concentration was very less and Cr was below detectable limit. No ash pond lining is employed in the construction of the ash pond; hence leaching of heavy metals is possible. Promotion of increased use of fly ash in construction activities, proper disposal practices with better management need to be undertaken to minimize the adverse impacts of fly ash on the surrounding environment.

KEY WORDS : Thermal power plant, Fly ash disposal, Heavy metals, Ground water contamination, Safe management. INTRODUCTION Coal is the most abundant available fossil fuel in India and provides a substantial part of energy needs of the country. About 69% of India’s total installed capacity of power generation is thermal, of which coal-based generation is 90% (balance 10% is diesel, gas, renewable etc.). Thus the power generation is predominantly coal based (Ministry of power, 2005-06). Indian coal used in thermal power plant predominantly has high ash content (35-45%) and is of lower quality (Mathur et al., 2003). The fly ash generation has increased from 40 million tones in 1994 to 112 million tones in 2004-05. At present, generation of fly ash is 150 million tones per year in the country. Such a huge generation of fly ash causes a considerable impact on the environment and

ecosystem. By the year 2012, it is predicted to increase to 170 million tones per annum (Rajamane, 2003). Worldwide, China is currently the largest producer of fly ash followed by Russia and USA. The European coal combustion products association member countries account for 90% of total coal combustion product in Europe, producing 37.14 million tones of fly ash and utilizing about 48% of it. In India, at present, major portion of the fly ash is unutilized and necessitates the disposal in ash ponds and landfills and only a small fraction of the ash is utilized (Bhattacharjee et al., 2002). In India, the utilization rate (13%) of fly ash is well below the global utilization rate of (25%) (Iyer and Scott, 2001). The production of fly ash in Delhi is nearly 1.5 million tones annually by the thermal power plants. Due to very fine particle size and presence of

*Corresponding author : Email: [email protected], [email protected]; Mobile: +91 9313983660

SINGH ET AL

potentially toxic elements like Arsenic, Chromium, Boron, Vanadium and Antimony, fly ash has been considered hazardous for living organisms. Some heavy metals leach out of the ash ponds and contaminate the surrounding soil, surface and groundwater. These heavy metals have been known to limit the survival and growth of plants and microbial population (Rai et al., 2004). The objective of this study is to analyze the concentration of heavy metals; Nickel, Chromium and Zinc in the fly ash and pond ash samples, collected from the NTPC Badarpur, thermal power plant and to determine the degree of contamination of these heavy metals in the groundwater near the ash pond area. Elemental concentration in fly ash from the present study is compared with the results from literature available on Indian fly ash. The study also looks at the handling, disposal methods and techniques adopted by the thermal power plant to manage their fly ash effectively.

Ground Water Samples 500 mL of well-mixed, acid-preserved sample was transferred to a beaker added with 5 mL of nitric acid was boiled and evaporated on a hot plate to the lowest volume (150-200 mL) before precipitation occurred. Heating and adding of conc. HNO3 was continued until digestion was completed as shown by light-colored, clear solution. After proper digestion volume was made up to 500 ml. RESULTS Analysis of Cr, Ni and Zn for fly ash samples and for ground water sample was carried out as per the standard methods (Standard Methods, 20th edition). The results for heavy metal analysis of fly ash and pond ash samples are given in Fig. 1 and results for groundwater analysis are presented in Fig. 2. 180 Concentration of elements (mg/kg)

686

Sampling and Analysis

0.9 0.8

Concentration (mg/l)

The NTPC Badarpur power station was commissioned in 1973 and is a 705 megawatt (MW) coal fired thermal power plant. The facility is equipped with electrostatic precipitator. The power plant uses most of the coal received mainly from Jharia coal fields located in eastern part of India. The fly ash and pond ash samples were collected from the selected sites. The fly ash samples were light grey in colour and fine. Pond ash samples were coarser and light grey in colour. Groundwater samples were collected from the bore well near the ash pond area. The collected samples were tested for the selected elements like Cr, Ni, and Zn by UVvisible spectrophotometer, Hach Model DR 4000. The method used for heavy metal analysis was APHA, Standard Methods for Examination of Water and Wastewater.

160 140 120 Fresh Fly ash

100 80

Pond ash

60 40 20 0 Cr

Ni

Zn

Trace element

0.7

Fig. 0.6 1. Concentration of elements in the fly ash and pond 0.5 ash sample from Badarpur Thermal Power Plant (unit mg/kg). 0.4 0.3 0.2 0.1 0 Cr

Ni

Zn Elements

Fly ash and Pond ash Samples Dry sample (0.6 gm) of fly ash and (1.2 gm) of pond ash was weighed into Teflon vessel. Five milliliters of 70% conc. HNO3 and 2 mL of HF were added to these vessels and kept for digestion in an autodigester called Multiwave Microwave Digestion System (MDS), for 20 minutes attaining a temperature of 280 0C and pressure 35 bars. After digestion the sample was filtered and transferred to a volumetric flask and the volume was made up to 50 mL.

Fig. 2. Concentration of elements in the ground water sample (unit mg/L)

DISCUSSION Concentration of Ni is found to be highest in both fly ash and pond ash samples. In general, the

ASSESSMENT OF HEAVY METALS IN FLY ASH AND GROUNDWATER concentration of elements in fly ash was higher as compared to pond ash and ground water. Difference between the fly ash and pond ash samples from the same power plant may be due to the leaching of elements taking place when the fly ash is disposed as dilute slurry. Elements having lower mass can be carried and precipitated with fly ash while elements having higher mass may settle rapidly after combustion and enrich in bottom ash. Some elements like, Ni, however show no such preference (Shivkumar et al., 1996). It has also been reported that the composition of trace elements in fly ash even from single coal fired power plant may vary measurably on a daily basis (Egeman and yurteri, 1996). The results from this study are compared with the ranges of heavy metals reported in the literature for fly ash from India and from other countries (Table 1). It can be observed that the values are within the range reported for Indian fly ash. It can be seen that heavy element Cr in Indian fly ash as reported in literature and analyzed in this study is found in lower concentration than in other countries. Ash Handling and Disposal Methods The power plant follows the wet disposal technique. The stacks at power plant are installed with electro static precipitators for the collection of fly ash of different particle size from the outgoing flue gasses. A major portion of the fly ash is collected in the form of wet slurry. The slurry is transported and disposed off in an ash pond. The overflow water from the pond is collected and discharged in the river or drain. The surface of the pond ash is sprinkled with the water treatment plant sludge. This has the advantage of controlling the fugitive emissions by forming a thin film on the surface; enhancing the fertility of ash for growth of vegetation and groundwater cover thus providing a disposal option for the water treatment plant sludge. A small portion of the fly ash is collected in the

687

dry from. The power plant has the facility to directly fill the fly ash into trucks, which can be sent to the user. The system has the flexibility of collecting graded dry fly ash from the different fields of ESP. As per the guidelines on the utilization of fly ash, pond ash and bottom ash, it is supplied free of cost to all types of users. The fly ash is used for brick manufacturing and for filling and embankment of roads and low-lying areas. Potential for Contamination from Trace Elements Leaching is the most likely path by which coal ash constituents would become mobile environmental contaminants (Fly ash report, 1997). The quantity of elements that will be available for leaching in an aqueous media will depend on the fixation of these elements on the ash particles and pH of the ashaqueous medium. In addition to this the other factors influencing leaching include ash source and leaching time. In general, under acidic conditions the rate and quantity of leaching is higher. Certain studies reveal that for most of the elements present in coal ash, a significant fraction, ranging from 8% in case of Ni to 17% in case of Cr is able to leach (Querol et al., 1993). Leaching tests have been commonly used to predict environmental impact associated with ash disposal. Comparison of ground water in the vicinity of a thermal power plant in Turkey with leaching tests revealed that certain leaching tests could be used to predict contamination from toxic elements in ash (Baba and Kaya, 2004). Serial batch leaching test done on some Indian fly ashes have shown that many elements like Mn, Zn, Ca, As and Mg show maximum concentration in the leachate at low L/S (Liquid solid ratio) of 4 and 8. Some elements like Cu and Pb were also present in the leachates but with insignificant levels, while other elements like Co, Cr and Ni did not leach at any L/ S ratio (Praharaj et al., 2002). Analysis of heavy metals in groundwater near a coal ash disposal site in Orissa, India showed that Zn, Cu and Pb were

Table 1. Heavy metals concentration obtained from fresh fly ash vs. those reported in literature (unit mg/kg) Elements

Locations Current Study

Cr Ni Zn n/r: not reported

14 166 124

India (average)

Orissa India

China

UK

Spain

120 150 n/r

145.75 56.50 69

n/r n/r n/r

n/r n/r n/r

134.2 87.9 221.3

Greece 110-160 n/r 59.6

688

SINGH ET AL

found in high concentration in tube well water located in the vicinity of ash pond while Cu, Mn, Pb and Zn were the major contaminants in ground water (Prahraj et al., 2002). Cr, Zn, Mn and Cu in Greek fly ash have exhibited an increase in leachates concentration with the reduction in leachant pH from 8 to 4. Pb exhibited maximum extractability at all pH values (Fytianos et al., 1998). Presently ash pond lining is not being followed in practice. Therefore, the possibility of leaching of heavy metals has increased. Since the soil below the impoundments is always saturated and under considerable hydraulic pressure, the inefficiently lined ponds may provide a great opportunity for ground water contamination to seep in. Therefore, the seepage from ash pond may be more compared to leaching from landfills and ash mounds (Theis et al., 1978). In addition to this, discharge of rainwater and run off from ash mounds areas to surface water bodies can also be a source of water pollution. Therefore, it is imperative to incorporate ash pond lining while designing the ash ponds. Planting of saplings having tolerance to warm slurry water and heavy metals can be considered to be the most ideal mitigation measure, since the biomass can also adsorb toxic metals as nutrients and can provide obstruction for wind blown particulates (Sahu, 1996). Plantation of saplings in an abandoned ash pond area is an important measure of pollution control. For improvement and enriching the ash surface in order to propagate and maintain vigorous vegetation growth, the selection of species have been successfully tried in various NTPC plants are Ipomea, Casurina equisetifolia, Accaia auriculoiformis, Eucalyptus, Pongamia glabra. Creation of greenbelt all around the ash disposal site is also a good mitigation measure (Datta, 2000). CONCLUSIONS Total concentration of Cr, Ni and Zn was investigated in fly ash and pond ash samples from the site of Badarpur thermal power plant. All elements were present within the detectable limits. In general the heavy metal concentration of Indian coal ash was less as compare to ash from different other parts of the world. Though, heavy metal concentration in groundwater samples was found to be very less but wet disposal technique using ash ponds without lining, makes surrounding more prone to heavy metals contamination. There is no definite conclusion available that the leachates of

Indian fly ash are polluting the ground water. The shift from wet collection to dry collection system would be a welcome step, as it will increase the potential of utilization of ash in various applications. One of the disadvantages of using this system is the cost involved, especially the transportation of fly ash to far-off places. A combination of suitable disposal technique and increased utilization is required to combat the environmental hazards associated with fly ash generation. ACKNOWLEDGEMENTS The authors are thankful to Prof. J. K. Garg, Dean, USEM, GGS Indraprastha University for his constant inspiration and support. The authors are also thankful to the staff of NTPC Badarpur for providing necessary logistics during the sampling work. REFERENCES Annual Report of Ministry of Power Govt of India, New Delhi, 2005-06. APHA, Standard Methods for Examination of Water and Waste Water. 20th Edition. American Public Health Association, Washington DC. Baba, A. and Kaya, A. 2004. Leaching characteristics of solid wastes from thermal power plants of western Turkey and comparison of toxicity methodologies. Journal of Environmental Management 73(3): 199-207 Bhattacharjee, U. and Kandpal, T. C. 2002. Potential of fly ash utilization in India. Energy 27(2) : 151-166. Datta, M. 2000. Environmental aspects of ash disposal in ponds and mounds. In management of ash ponds. Gandhi, S. R., Raju,V. S. and Kumar,V. editors Narosa Publishing House, New Delhi. Egemen, E. and Yurteri, C. 1996. Regulatory leaching tests for fly ash: A case study. Waste Management Resources, 14(1) : 311-325. Fytianos, K., Tsaniklidi, B. and Voudrias, E. 1998. Leachability of heavy metals in Greek fly ash from coal combustion.. Environment International 24(4): 477-486. Iyer, R. S. and Scott, J. A. 2001. Power station fly ash - a review of value-added utilization outside of the construction industry. Resource Conservation & Recycling 31(3) : 217228. Mathur, R., Chand, S., and Tezuka,T. 2003. Optimal use of coal for the power generation in India. Energy Policy, 31(3): 319331. Minnesota Department of Transportation. 1997. Fly ash report document. Praharaj, T., Powell, M. A., Hart, B. R. and Tripathy, S. 2002. Leachability of elements from sub-bituminous coal fly ash from India. Environment International 27(10): 609-615

ASSESSMENT OF HEAVY METALS IN FLY ASH AND GROUNDWATER Praharaj, T., Swain, S. P., Powell, M. A., Hart, B. R. and Tripathy, S. 2002. Delineation of groundwater contamination around an ash pond - geochemical and GIS approach. Environment International. 27(10): 631-638. Querol, X., Pares, J. M., Plana, F., Fernandez-Turiel, J. L. and Lopez, A. 1993. Fly ash content and distribution in lake sediments around a large power station: inference form magnetic susceptibility analysis. Environmental Geochemistry and Health, 15(4): 9-18. Rai, U. N., Pandey, K., Sinha, S., Singh, A., Saxena, R. and Gupta, D. K. 2004 Re-vegetating fly ash landfills with prosopis julifera: impact of different amendments and Rhizobium inoculation. Environment International 30(3) : 293-300. Rajamane, N. P., 2003. Making concrete green through use of

689

fly ash, Green Business Opportunity 9(4) : 23. Sahu, K. C. 1996. Environmental impacts of ash ponds and measures for pollution control. In ash pond and ash disposal systems, V. S. Raju editor, Narosa Publishing House, New Delhi. Shivkumar, D. S. and Datta, M. 1996.Assessment of groundwater contamination potential around ash pond through field sampling: a review. In Ash pond and disposal systems, Raju VS editor, New Delhi: Narosa Publishing House, 293-300 Theis, T. S., Westrick, J. D., Hsu, C. L and Marley, J. J. 1978. Field investigation of trace metals in ground water from fly ash disposal. Journal of Water Pollution Control Federation 24: 57-69.