Assessment of ground water contamination for heavy metals in the proximity of ash ponds

1. “Assessment of ground water contamination for
heavy metals in the proximity of ash ponds”
Raj Kishore Singh

2. INTRODUCTION
 India uses coal as a major fuel for power generation. 59.2 percent of
electricity production is based on coal in the country.
 At present in India more than 90 coal based thermal power plants
are producing about 170 million tonnes of fly ash every year.
 In National Capital Territory (NCT) of Delhi alone the production of
fly ash were nearly 1.33 million tonnes annually by two thermal
power plants.
 Indian coal with high ash contents(35-45%) results in the formation
of huge quantities of both fly ash as well as bottom ash.

3.  The toxic elements scavenged in fly ash may leach out when
environmental conditions are changed as a result of weather or
other anthropogenic activities.
 Leaching of toxic elements and compound from fly ash can
contaminate soil and water.
 The leaching of coal fly ash during disposal is of concern for
possible contamination, especially for the aquatic environment when
ash is in contact with water.
 The surface of a fly ash particle is only microns in thickness and can
contain leachable heavy metals which have condensed on the
surface.

4. CLASSIFICATION OF FLY ASH
 There are two types of fly ashes produced from coal combustion as
defined by American Society of Testing Materials (ASTM) C618.
 The classification of these fly ash are based on lime contain in it.
These are type ‘F’ and ‘C’ fly ash.
 Type ‘F’ is produced when anthracite, bituminous coal is burnt and is
low in lime and contains more silica, alumina and iron oxide.
 Type ‘C’ comes from lignite, sub-bituminous coal and contains more
lime.

5. CLASS ‘F’
 This fly ash is pozzolanic in nature.
 Contains less than 20% lime (CaO).
 In Class ‘F’ fly ash, total calcium typically
ranges from 1 to 12 percent,
CLASS ‘C’
 This fly ash in addition to having pozzolanic
properties, also has some self-cementing
properties.
 Class ‘C’ fly ash generally contains more
than 20% lime (CaO).
 Class ‘C’ fly ashes have reported calcium
oxide contents as high as 30 to 40 percent.

6. PHYSICAL PROPERTIES
CHEMICAL PROPERTIES
EXPRESSED AS PERCENT BY WEIGHT
 Fine, powdery particles
 Spherical in shape
 Glassy (amorphous) in nature
 Particle size is less than 0.075 mm
 Sub bituminous coal fly ashes are generally
slightly coarser than bituminous coal fly ashes.
 Specific gravity ranges from 2.1 to 3.0
 Specific surface area may range from 170 to
1000 m2/kg.
 Colour vary from tan to gray to black,
depending on the amount of unburned carbon
in the ash.
Component Bituminous Sub bituminous Lignite
SiO2
20-60 40-60 15-45
Al2O3
5-35 20-30 10-25
Fe2O3
10-40 4-10 4-15
CaO 1-12 5-30 15-40
MgO 0-5 1-6 3-10
SO3
0-4 0-2 0-10
Na2O 0-4 0-2 0-6
K2O 0-3 0-4 0-4
LOI 0-15 0-3 0-5

7.  The lighter the color, the lower the carbon content.
 Lignite or sub bituminous fly ashes are usually light tan to buff in
colour.
 This indicate relatively low amounts of carbon as well as the
presence of some lime or calcium.
 Bituminous fly ashes are usually of gray shade.
 With the lighter shades of gray generally indicating a higher quality
of ash.

8. FLY ASH GENERATION AND UTILIZATION IN DELHI
S.N. Name
of TPP
FLY ASH GERNERATION AND ITS UTILIZATION MODE OF UTILIZATION
Coal
Consumed
Ash Content Installed
Capacity
Fly Ash
Generation
Fly Ash
Utilization
Utilization Cement Bricks Road,
Embankments
, Ash Dyke
Reclamation
MTPA % MW MTPA MTPA % MTPA MTPA MTPA MTPA
1. RPH 0.70 33.78 135.50 0.23 0.20 86.95 0.15 --- 0.05 ---
2. BTPS 3.68 30.00 705.00 1.10 0.99 90.00 0.19 0.00 0.76 0.03
*Source: Central electricity authority

9. OBJECTIVES
 Laboratory batch leaching tests on fly ash samples with periodic
analysis of leachate to determine the maximum amount of
contaminants that can be leached from fly ash.
 Estimation of solutes in the supernatant of a wet disposal system
and measurement of the concentration versus time profile for solute
extracted from fly ash.
 Study for the concentration of trace elements in ground water
samples in surrounding area of the thermal power plant and to
examine the impact of fly ash on surface and ground water.
 To assess compliance with regulatory criteria for the safe disposal of
fly ash from thermal power plants.
Cont……

10. BADARPUR THERMAL POWER STATION
 The BTPS was commissioned in
1973
 Capacity: 705 megawatt (MW)
 The supernatants from NTPC
Badarpur power station were
discharged into a receiving
system and finally discharged
into river Yamuna

12. FLY ASH DISPOSAL IN ASH PONDS
 Primarily, the fly ashes are disposed off using either dry or wet
disposal scheme.
 In dry disposal, the fly ash is transported by truck, chute or conveyor
at the site and disposed off by constructing a dry embankment
(dyke).
 In the wet disposal system, the fly ash is transported as slurry
through pipe and disposed off in impoundment called as "ash pond".

13. FLY ASH GENERATION AND DUMPING IN ASH PONDS
0
20
40
60
80
100
120
140
Quantity
of
Fly
Ash
(Million
Tonnes)
Year
Fly ash generation
Fly ash dumping
*Source: Central electricity authority

14. QUANTITY OF UN-UTILIZED FLY ASH
0
100
200
300
400
500
600
700
800
900
1000
Un-utilized
fly
ash(Million
Tonnes)
Year
*Source: Central electricity authority

15. LEACHING METHODS
 For this study ASTM Method D-3987, Standard Test Methods for
Shake Extraction of solid waste with water (ASTM, 1995) were
employed.
 This method is a procedure for rapidly generating leachate from
solid waste.
 This method is an agitated extraction method that uses reagent
water as the leaching fluid.
 The final pH of the leachate is to reflect the interaction of the
leaching fluid with the buffering capacity of the waste.
 The method calls for testing a representative sample of the waste,
and as a result, it does not require particle size reduction

16. SAMPLING
 10 Kg samples of fly ash from
each thermal power plants
were collected from the
hopper of units.
 Ground water samples from
the nearby area and
discharge of ash ponds were
collected during study period.
 The surface water samples
from the river Yamuna at
different location were
collected during study period.

17. EXTRACTION MEDIUM
 The extraction fluid is prepared by mixing 5.70ml glacial acetic acid
(CH3CH2OOH) with 500ml double distilled water. 64.3ml of 1N
Sodium Hydroxide (NaOH) solution is added with the solution and
volume is diluted to 1000ml.
 Double distilled water is taken as aqueous solution.
 The buffer solution is prepared by mixing 0.1N Sodium Hydroxide
(NaOH) solution drop wise in double distilled water until the pH of
the solution is reached around 10.

18. SHAKE TEST AND ANALYTICAL METHOD
 L/S ratio of 20:1
 Test performed for varying period of
time.
 The rotation of the extraction apparatus
is controlled by rpm controlling switch.
 After specific time the supernatant was
collected, filtered and analyzed.
 After extraction, the bottles were left for
5 minutes for settling.
 The aqueous phase were separated
from the solid phase by filtration
through 0.45 μm fiber filters.
 The pH of the leachate was measured
immediately, and was acidified.
 The instrument used for analysis of
heavy metals is AAS (Perkin Elmers,
Model No. AAnalyst 700).

19. LEACHING OF DIFFERENT ELEMENTS IN AQUEOUS SOLUTION
0
0.05
0.1
0.15
0.2
0.25
0.3
1 week
(pH-8.10)
2 week
(pH-7.40)
3 week
(pH-7.30)
4 week
(pH-7.40)
Concentration
(mg/L)
Leaching Period
Aqueous Solution-I
Iron
Copper
Lead
Cadmium
Chromium
Nickel
0
0.05
0.1
0.15
0.2
0.25
0.3
1 week
(pH-8.00)
2 week
(pH-7.50)
3 week
(pH-7.50)
4 week
(pH-7.40)
Concentration
(mg/L)
Leaching Period
Aqueous Solution-II
Iron
Copper
Lead
Cadmium
Chromium
Nickel
0
0.05
0.1
0.15
0.2
0.25
1 week
(pH-8.20)
2 week
(pH-7.40)
3 week
(pH-7.40)
4 week
(pH-7.30)
Concentration
(mg/L)
Leaching Period
Aqueous Solution-III
Iron
Copper
Lead
Cadmium
Chromium
Nickel
LEACHING TEST RESULTS

20. LEACHING OF DIFFERENT ELEMENTS IN BUFFER SOLUTION
0
0.1
0.2
0.3
0.4
0.5
1 week
(pH-10.50)
2 week
(pH-10.20)
3 week
(pH-10.30)
4 week
(pH-10.30)
Concentration
(mg/L)
Leaching Period
Buffer Solution-I
Iron
Copper
Lead
Cadmium
Chromium
Nickel
0
0.1
0.2
0.3
0.4
0.5
1 week
(pH-10.60)
2 week
(pH-10.30)
3 week
(pH-10.20)
4 week
(pH-10.40)
Concentration
(mg/L)
Leaching Period
Buffer Solution-II
Iron
Copper
Lead
Cadmium
Chromium
Nickel
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
1 week
(pH-10.40)
2 week
(pH-10.00)
3 week
(pH-10.10)
4 week
(pH-10.00)
Concentration
(mg/L)
Leaching Period
Buffer Solution-III
Iron
Copper
Lead
Cadmium
Chromium
Nickel

21. LEACHING OF DIFFERENT ELEMENTS IN EXTRACTION SOLUTION
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1 week
(pH-6.10)
2 week
(pH-5.50)
3 week
(pH-5.60)
4 week
(pH-5.60)
Concentration
(mg/L)
Leaching Period
Extraction Solution-I
Iron
Copper
Lead
Cadmium
Chromium
Nickel
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1 week
(pH-6.10)
2 week
(pH-5.70)
3 week
(pH-5.60)
4 week
(pH-5.70)
Concentration
(mg/L)
Leaching Period
Extraction Solution-II
Iron
Copper
Lead
Cadmium
Chromium
Nickel
0
0.1
0.2
0.3
0.4
0.5
0.6
1 week
(pH-6.20)
2 week
(pH-5.90)
3 week
(pH-5.60)
4 week
(pH-5.70)
Concentration
(mg/L)
Leaching Period
Extraction Solution-III
Iron
Copper
Lead
Cadmium
Chromium
Nickel

22. CONCENTRATION OF SELECTED ELEMENTS IN GROUND WATER
SAMPLES NEAR BTPS
0.01
0.1
1
10
Concentration
(mg/L)
Location
Nickel
Copper
Iron
Chromium
Lead
Cadmium
0.01
0.1
1
10
Concentration
(mg/L)
Location
Nickel
Copper
Iron
Chromium
Lead
Cadmium
0.01
0.1
1
10
Concentration
(mg/L)
Location
Nickel
Copper
Iron
Chromium
Lead
Cadmium

23. DISCUSSIONS
 It is observed that when the ash is shaken with either of the extraction
solution (pH~5.0), aqueous solution (pH~ 7) or buffer solution (pH~10-
11), the pH of the leachate increases after one week of leaching,
followed by progressive decrease or increase.
 Trace metals present on the surface of fly ash particles are the most
immediately available candidates for release into the aqueous
environment.
 Liberation of the heavy elements from fly ash surface depends on the
pH of the aqueous media.
 It is observed that at the low pH value maximum metals are released
from the surface of the ash into leachate. As the pH increases the
dissolution of metals from ash surface decreases.
 It is observed that Pb concentration in leachant has crossed the
prescribed standard limit of drinking water quality (IS: 10500).
 The concentration of lead was found to increase considerably with the
leaching period.

24. LEACHING OF IRON LEACHING OF COPPER
 Iron becomes soluble at pH ≤ 1.5
Seidel and Zimmels, 1998), but
releases are of little significance
in relation to the concentration in
the ash.
 In this study, the leaching of iron
in fly ash fluctuates over time
with extraction fluid, buffer
solution and aqueous solution.
 The leachability does not reach
stability in the leaching process
in all three extraction solution. It
was slightly higher when the fly
ash is mixed with the extraction
solution.
 Cu shows some degree of
mobility in an acidic environment,
regardless of the mode of
occurrence.
 The leaching of copper studied in
the fly ash with aqueous solution
increase significantly with time.
 The leachability does not reach
stability in the leaching process
in buffer solution and extraction
fluid. The relationship of
leachability of Cu with three
leachants medium is LExtraction
>LBuffer> LAqueous.

25. LEACHING OF LEAD LEACHING OF CADMIUM
 Being an element associated
with sulphides in coal, a marked
surface association of Pb in ash
might be expected. Around 50-
60% Pb is estimated to be in
surface association in fly ash
(Spears and Martinez-Tarrazona,
2004).
 Acidic conditions slightly
enhance Pb leaching (Jones,
1995).
 The leachability of Pb fluctuates
over time for the entire leaching
medium.
 The environmental concerns
over Cd arise from its potential
solubility and toxicity in aquatic
systems.
 The leachability of Cd in all three
leachants is not stable and has
no significant difference in
leaching in different solution.

26. LEACHING OF CHROMIUM LEACHING OF NICKEL
 The leaching pattern of Cr
displays a marked pH
dependence, reaching the lowest
values at near-neutral pH.
 The leachability of Cr rises
significantly with the time.
 The relationship of leachability of
Cr with three leachants is
LExtraction >LBuffer> LAqueous.
 The solubility of Ni is markedly
sensitive to pH and covers a few
orders of magnitude.
 Up to 10% Ni was removed when
using pH ~ 1 leachant (Kim et al.,
2003).
 Whether the fly ash leaching with
aqueous solution, buffer solution
or extraction fluid, the leachability
of Ni increases substantially with
time.
 The relationship of leachability
of Ni with three leachants is
LExtraction >LBuffer> LAqueous.

27.  Irregular pattern of six heavy metals released have been obtained in
leachates. The leaching of these metals show their presence in the
fly ash sample from the thermal power plants.
 Presently ash pond lining is not being followed, therefore the
possibility of leaching of heavy metals has increased.
 The soil below the impoundments is always saturated and under
considerable hydraulic head. Therefore, the inefficiently lined ponds
provide a great opportunity for groundwater contamination to seep
in.

28. GROUND WATER
•WHO guidelines
P : Permissible limit E : Excessive limit.
BTPS : Badarpur Thermal Power Station
Parameter BIS (1991) Average concentration of trace elements in
ground water samples near ash ponds
P(mg/l) E(mg/l) BTPS
Iron 0.3 1 1.432
Chromium 0.05 0.05 0.054
Copper 0.05 1.5 0.032
Cadmium 0.01 0.01 0.019
Lead 0.05 0.05 0.062
Nickel 0.02* 0.02 0.024

29.  The average concentration of trace elements found in the ground water
samples from the nearby area of ash ponds, shows that almost all the
metals are crossing the prescribed limit of drinking water. This may be
due to leaching of these trace elements from the fly ash deposits in
nearby areas.
 The dissolved toxic elements in the samples collected from the nearby
area of the ash pond sites of the thermal plants can endanger public
health and the environment by contaminating surface water as well as
groundwater used for drinking purposes.
 The surface water contamination also takes place due to surface run off
from ash ponds.