Heavy metals release from ash pond to soil water environment: A simulated technique

Environment International, Vol. 18, pp. 283-295, 1992 Printed in the U.S.A. All rightsreserved.

0160-4120/92 $5.00 + .00 Copyright © 1992 Pergamon Press Ltd.

HEAVY METALS RELEASE FROM ASH POND TO SOIL WATER ENVIRONMENT: A SIMULATED TECHNIQUE

M.H. Fulekar* and J.M. Dave Pollution Monitoring Laboratory, School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, 110067 India

E19005-069M (Received 7 May 1990; accepted 5 October 1991)

A column experiment was set up to provide an environment in which certain heavy metals leach from impounded ash, then enter ground water by percolation through soils, a condition that is prevailing in an ash pond. Percolation of 1 L and 2 L ash effluent per d. up to a period of 40 d., through 60 cm depth of the alluvial soil resulted in an increased pH, electrical conductivity (E.C.), and levels of heavy metals like Cr, Mn, Ni, and Pb in leachates as well as in layers of soils. The heavy metals content in leachates was found increased with increased percolation of ash effluents.The pH of the soil was found to increase from 7.4 to 8.1. The pH of the soil was regulating the available and total metals content. It had lower available and higher total metals concentrations in alkaline soil at the top while higher available and lower total metals concentrations in acidic soil at the middle of the treated soil columns. The sorption and retention of heavy metals in the soil layers were also found to be dependent on the following in order of importance, based on soil texture: level of organic matter, cation exchange capacity, sorption/precipitation, and mobility of these metals in soil.

well as the depth of the ground water table (EPA 1980; Naik et al. 1983 ; Fulekar and Dave 1986). The texture of a soil is important in the mechanism of leaching and percolation of heavy metals. Christopherson et al. (1980) have constructed a mathematical model based on ion exchange and demonstrated that the fluid passing through smaller pores moves so slowly that equilibrium is reached, while fluid passing through larger pores moves so quickly that equilibrium is virtually unchanged. The concentration of heavy metals is expected to be higher in smaller pores than in larger ones because of the residence time of the percolating water. Bolter (1977) has reported that a uniform distribution of heavy metals can occur only if the organic matter is

INTRODUCTION In India, an estimated 8.14 Gg of fly ash is produced by coal-fired power plants in a year. This ash is mixed with water and discharged into impounded ponds, lagoons, rivers, or the sea (Sharma et al. 1989; Fulekar and Dave 1990). Heavy metals, leached from fly ash over a long period of time into an ash pond or lagoon, percolate through soil and may enter the ground water. Percolation of ash effluents is affected by the physico-chemical characteristics of the soil as

*Present address: Dr. M.H. Fulekar, Deputy Director (Industrial Hygiene, Central Labour Institute, Sion, Bombay, 400 022 India.

283

284

M.H. Fulekar and J.M. Dave

high and uniformly distributed throughout the soils. The extent to which heavy metal ions bind varies with the solution pH, concentration of competing cations, nature of the organic material, and the complexing power of any ligands present. The sorptive capacity of organic matter for metal ions was found greater than that of many clays and varied more with pH changes (Jennet and Foil 1979; Gerritse et al. 1982). Braunstein et al. (1977) have reported that water percolating through the soil is undergoing a mixing process and that some elements are relatively more mobile in the soil. The mechanism by which heavy metals are sorbed/retained in the soil and released into the ground water by infiltration of ash effluents through soil is of growing interest to researchers. The present study has been designed to investigate the effect of percolation of ash effluent water at the rate of 1 L and 2 L/d, up to a period of 40 d, through 60 cm deep alluvial soil bed. A lysimeter was used as a simulated technique for the condition prevailing in an ash pond. Characteristics of the leachates as well as mechanisms by which heavy metals such as Cr, Mn, Ni, and Pb sorbed on the soil at different depth are examined.

c

.-~ll

-. ~ ! ! ! I

EXPERIMENTAL SET-UP A lysimeter was designed to make use as a simulated technique to study the effect of heavy metals release from an ash pond to soil water environment, a condition that is prevailing in an ash pond (Fig. 1). The lysimeter consists of a column, bottom collection, and dosing at the top. Five such lysimeters were used for the present study. Each lysimeter was made up of a perspex sheet (20 x 20 c m x 91 cm length) having a percolated plate at the bottom for water outflow. For soil testing, three sampling points I, II, and III (each 10 mm in diameter) were made on both sides of each column at distances of 60 cm, 40 cm, and 20 cm, respectively, from the bottom of the soil column. The sampling points were kept closed with corks during the percolation period. A typical Delhi soil of an alluvial type was selected from the village Mehrauli, near Delhi, which is about 6 km from Jawaharlal Nehru University (JNU). About 200 kg of the surface soils (0 to 15 cm) were collected and used for percolation of the ash effluent water. Soil samples were air dried and crushed to pass through a 2 mm sieve. As evident from Table 1, selected physical and chemical parameters of the soil were studied. Gravel, initially washed, was packed at the bottom above the perforated plate in each column which attained a 5 cm height of the column from the

,I

Fig. 1. Lysimeter.

bottom. Similarly, sand initially washed several times, was packed above the gravel in each column which attained a 5 cm height from the gravel. A measured soil sample of 30 kg was packed into each column which attained about a 60 em height from the sand. Water was then introduced into each column from the top. As soon as the soil surfaces became slightly ponded, the inflow was stopped. The soil was allowed to equilibrate for a one-week period. About 500 L ash effluent (supernatant water) were collected from the ash pond located near a coal-fired power plant in New Delhi and used for the percolation experiment. Selected physical and chemical parameters of the ash effluent were studied (Table I).

Heavy metals release from ash pond

285

Table I. Some properties of alluvial soil and ash-effluent used for column experiment.

Characteristics

Soil

Ash effluent

Particulate size distribution Sand (%)

62.5

Silt (%)

25.5

Clay (%)

12.0

pH Electrical Conductivity (Siemen s)

0.16

Cation Exchange Capacity (meq I00 g-I )

15.2

Organic Matter (%)

0.78

0.95

Total Cr

20.30

Available Cr Total Mn

7.6

7.4

.

0.020

**

0.012

* **

0.098 0.028

* **

0.590 0.104

*

0.224

**

0.042

0.020 260.00

Available Mn

14.00

Total Ni

40.55

Available Ni Total Pb

Available Pb

0.808 14. 250

1.224

Soil I metal concentration (~tglg), average; * Ash effluent / digested sample (rag/L); ** Ash effluent / undigested sample (rag/L).

Per day, I L ash effluent water was allowed to percolate through each of the two soil columns (IA and IB), and 2 L ash of effluent water per day were allowed to percolate through each of the other two soil columns (IIA and IIB); while the remaining soil column, B, served as a control where 2 L/d of double-distilled water were added. Ash effluent water was added slowly (drop by drop, within 3-4 h) in each column from the top by a rubber tube attached to the aspirator bottle. First, a water layer was formed at the top of

the soil in each column which took about 16 h to percolate gradually through the ponded soils. After a 24 h interval, the leachate was collected in a collector from the bottom of each column; and samples were analysed for pH, electrical conductivity (E.C.), and heavy metals such as Cr, Mn, Ni, and Pb. The experiment was continued up to a period of 40 d. After an interval of 8 d, three soil samples (small quantities), each from sampling points I, II, and III from both sides of each column, were collected; and composite

286

M.H. Fulekar and LM. Dave

Table 2. Analytical procedure employed. Element pH

Procedure Glass

Reference

Electrode

APHA (1975); Dewis and Freitas (1970)

Electrical Conductivity (E.C)

Conductivity Cell

Organic Carbon

Titrimetric

Walkley and Allan(1935)

Cation Exchange Capacity (C.E.C.)

Titrimetric

Piper (1950)

Particle Size

Mechanical Analysis

Dewis and Freitas (1970) i

Available Cr, Mn, Ni

DTPA Method

Phung e t a l .

and Pb

Flame Atomic

(O.M.)

(1979)

Absorption Spectro-

Lindsay and Norvell

photometer (Perkin

(1978)

Elmer - 703) Total Cr, Mn, Ni

Atomic Absorption

Rhung et al. (1979)]

and Pb

Spectrophotometer

APHA (]975);

(Perkin Elmer-703)

Jackson (]973)

soil samples were made and analysed for pH, E.C., cation exchange capacity (c.e.c.), organic matter (O.M.) available, and total Cr, Mn, Ni, and Pb. Methods employed for the analysis of the above parameters are given in Table 2. The average value of the parameters from columns IA and IB (i.e., 1 L ash effluent water applied soil columns); and IIA and IIB (i.e., 2 L ash effluent water applied soil columns) are presented in the following.

RESULTS Physico-chemical properties of ash effluent and alluvial soil used for the experiment are presented in Table 1. Ash effluent percolation at the rate of 1 L and 2 L/d, up to a period of 40 d, through 60 cm depth of soil in a lysimeter (like the conditions prevailing in an ash pond), resulted in the following. The pH, E.C., and heavy metals in leachates Results obtained (Fig. 2(a) and 2(b)) indicate the higher level of pH and B.C. in the leachates of treated

columns (i.e., 1 L and 2 L ash effluent/d applied columns). Fig. 3(a), 3(b), 3(c), and 3(d) demonstrate that concentrations of Cr, Mn, Ni, and Pb in the leachates of the control column were less than 0.008 mg, 0.10 mg, 0.075 rag, and 0.028 mg, respectively. Columns applied with 1 L ash effluent/d resulted in the increase in levels of these metals to 0.016 mg, 0.115 mg, 0.155 mg, and 0.055 mg, respectively; while percolation of 2 L/d ash effluent increased these levels to 0.024 mg, 0.135 mg, 0.28 mg, and 0.090 mg, respectively. The pH, E.C., and heavy metals in layers of soil

Ash effluent percolation through soil resulted in an alkaline pH at the top (sampling Point I) and an acidic pH in the middle (sampling Point II) of the soil bed (Fig.4). The build-up of heavy metals in the soil was found to vary with the depth of the soils. Fig. 5(a), 5(b), 5(c), and 5(d) illustrate higher total and lower available heavy metal concentrations in alkaline soil and lower total and higher available

Heavy metals release from ash pond

287

H 2L DDW H 1Lash-effluent o-..o 2 L a s h - e f f l u e n t

Ash effluent-soil

leaching

(Leochote pH)

9"0

8'0 •

~

~ ' ~ " ~ - o - ~ - ~ - o - ~

~

,,, ,/ ,',l,,I,,,,,i,l,ll 1.8

1"6

"~

•

ll,,,,,I,,,,

2 ( a / e - e 2L DDW H 1L. a s h - e f f l u e n t o--o 2 L a s h - e f f L u e n t

"~'.~-.

~

',''',1

Ash effluent-soiL

leaching

( Leachote

E.C.)

1"4

•

**

0.8-

0"4 0"2 O!

I I I

I I I

0\2(b)/

II

il

J

~o

I

= *

I

i

,

a

I I I

i

t

II

,

20 Days

J a

I

,

=

,

~

30

**

i

,

,

= I

40

Fig. 2. 2(a) and 2(b) The pH and electrical conductivity of successive leachates from aUuvial soils in relation to ash effluent application.

Ash effluent- soil [eczching e H o 0030

8 >~

o 2LDDW 1LEffluent o 2LEffluent

l

00200"010 0~

10

20 Days

30

40

Fig. 3(a). Concentrations of chromium in successive leachates from alluvial soils in relation to ash effluent application.

288

M.H. Fulekar and J.M. Dave

Ash e f f l u e n t - s o i l

0"20

o

o

2 LDDW

H o

o

1LAsh 2LAsh

leaching

effluent effluent

C~ O L

C~ C~

0"10

E

0

'''

''

'''

'1~)''''

'''

' 'J0''

' '''

'''3'0'

' ''''

'''410

Days Fig. 3(b). Concentrations of manganese in successive leachates from alluvial soils in relation to ash effluent application.

Ash efft, u e n t - s o i l

leaching

0"30 e---e 2 L D D W H 1LAsh

effluent ent

c~ 0"20 O

(D > O

E

0"10

0

10

20 Days

30

40

Fig, 3(c). Concentrations of nickel in successive leachatcs from alluvial soils in relation to ash effluent application.

Heavy metals release from ash pond

289

effluent-soil

Ash

1.0

teaching

o

e

2LDDW

H c

o

| LAsh 2LAsh

effluent effluent

A

C7~ 0 Cb

E

0"05

0

10

20 Doys

30

40

Fig. 3(d). Concentrations of lead in successive leachates from alluvial soils in relation to ash effluent application.

Soil 2L D DW

pH =

Soil E.C. :I

(60o'n)

2L DDW

==I 60c~1 o--o I (/,acre) Ill (20cm)

o---o II (/.,l:]cm) III (20cn'0

_

,12

07

I

I

2Lash

I

I

I

I

effluent

2Lash

I

I

I

effluent

•0~ t'@ •11 ~

d 0 7 uJ

I

I

I

I

I

I

1L a s h - e f f [ u e n t

I

1L a s h

I

I

effluent

"01 "11

D7 ~

.o

I

I

I

I

16

24

32

40

I

I

I

I

8

16

24

32

Days Fig. 4. The pH and E.C.in layers of soils in relation to ash effluent application.

-01 40

290

M.H. Fulekar and J.M. Dave

Availalable'Cr'in

: I (60cm) o--o l l ( 4 0 c m ) o--o IlI(20cm)

2L DDW

O0

s0il

:

Total " C r ' i n

soil

21 DDW

.--4, I ( 6 0 c m )

o - o II (40cmJ- 22 III (20cm)

0"02

21 -

-

I E ~ I : ~ : ~ ~ _ _

_ ~

_ ___ %

~

_

~

_"

_

0"01 - -

I

En O I,,.

o

> O

20

I

2Lash

I

I

I

I

effluent

I

I

2Lash

0"03

I

9

effluent

22

c~ O > O

002

21 _

_~__ __ ~ . . . . . ~

_~

0"01 --

20

I

I

1Lash

I

I

I

I

effluent

I

1Lash

003

I

I

19

effluent

22

DO 2

21 v

A

(YO

1 --

v

120

I

I

I

I

I

I

I

i

i

B

16

24

32

40

8

16

24

32

Days Fig. 5(a). Distribution of chromium (available and total) in layers of soils in relation to ash effluent application.

19

40

c~

291

Heavy metals release from ash pond

Avoiloble "Mn" in soil 2 L DDW

T o t a l "ME in

H I (60cm) o--o II (40cm) e--e Ill (20cm)

14-1

2L DDW

soil

I (60cm) o--.o II(40cm) -- 262 Ill (20 cm)

H

14"0

--

13'9

ol:n O o

260

I

13.1~

261

I

I

2L ash

I

I

effluent

I

I

I

2Lash

I

259

effluent -- 262

14"1

0J c~ oJ

"~ 14.0

-

261

O

C~

13.9

I------e--~--~

I

13"8

1Lash

I

I

I

I

effluent

- -

I

I

I

1Lash

effluent

i

- ~

260

I

259

1/,-1

-- 262

14"0

--

13-9

13"8

261

260

I

I

I

I

I

I

I

I

I

8

16

24

32

40

8

16

24

32

259 40

Days Fig. 5(b). Distribution of manganese (available and total) in layers of soils in relation to ash effluent application.

292

M.H. Fulekat and J.M. Dave

Available'Ni" in soil 0"9

2L DDW

Total'Ni'in 2L DDW

I (60cm) o--o o---o

soil

I (60cm) o-.-o ll(40cm) IIl(20cm)

II(40cm) III (20cm)

42 41

0-8 _-~----~---,~--

-

--1~1-

-

-

v

0.7

0"6i

40

--

I

I

2Lash

I

I

I

effluent

I

I

I

I

2Lash effluent

39~ - 42c~ O

0.9 >

0-8 0.7

0.( 0.!

-

I

I

I

!

I

I

!

I

40

I

39

1L ash effluent

1L ash effluent

42

0~

.41

0-7 ~'0.6

I

I

I

I

I

8

16

24

32

40 8 Days

I

140

I

I

16

24

I 32:

39 40

Fig. 5(c). Distribution of nickel (available and total) in layers of soils in relation to ash effluent application,

293

Heavy metals release from ash pond

Available 2L 1"3

DDW

--

Lead

in

Total

soil

H I (60cm) o---o II (40cm) o I I I (20cm)

Lead

2L DDW

in

soil

H I (60cm) o--o II ( 4 0 c m ) - 16 o o Ill (20cm~

1-2--

15

1-1--

I

1"0

I

I

I

I

2L ash e f f l u e n t

I

I

I

2L ash

I

13

effluent

1'3 -

16

~-Z..~

Cl

---~

O

1"2-

15

c~ tT~ (:n

> c~ c7~

1'1-

:t

:¢.

I

1.0

I

I

I

I

1L a s h e f f l u e n t

I

I

1Lash

I

I

13

effluent

1"3--

16

1"2--

15

1"1--

14

1"C

I

I

I

i

8

16

24

32

I 40 Days

I

I

I

I

8

16

24

32

13 40

Fig. 5(d). Distr/bution of lead (available and total) in layers of soils in relation to ash effluent application.

294

M.H. Fulekar and J.M. Dave

CEC meq/1OOgm I ] H

16 - -

2L

DDW

I (60cm)

o---olI(40cm) o--o III(20cm)

14

LOoM. °/0~

2L DDW

I (60cm} o--oli (40cm)'- 1'10 o---o III ( 2 0 c ~ ) - 1.0

_

0"80 12

I 16

I

I

I

I

I

2 L osh e f f l u e n t

I

I

I

2L osh e f f l u e n t

0"60 1.10

:

1.0

E

o

LU

U

14

C 0

0"80

k,.

0

12

m

I 16

-

-

I

I

I

I

IL osh e f f l u e n t

I

I

1Losh

I

I

0"60 1"0

effluent

m

14

0"80 B

12

- 0.60

B

I

I

I

I

8

16

24

32

I

I

40 8 Doys

I

I

I

16

24

32

40

Fig. 6. Cation exchange capacity and organic matter in layers of soils in relation to ash effluent application.

heavy metal content in acidic soil of the treated columns. At the end of the experiment, the average concentrations of available Cr, Mn, Ni, and Pb remaining in the soil (average of sampling point I, II, and III) of the control column were less than 0.0148, 13.931, 0.745, 1.206 Ixg/g, respectively. Percolation of 1 L ash effluent/d through soil, up to a period of 40 d, increased the average levels of the available content of these metals in soil to 0.0188, 13.933, 0.76, 1.22 Ixg/g, respectively. Whereas the percolation of

2 L ash effluent/d increased these levels up to 0.0198, 13.948, 0.785, and 1.233 I.tg/g, respectively. At the end of the experiment, the average concentrations of total Cr, Mn, Ni, and Pb remaining in the soil (average of sampling points I, II, and III) of the control column were less than 20.233,259.916, 40.483, and 14.166 ~tg/g, respectively. Percolation of 1 L ash effluent/d through the soil, up to a period of 40 d, resulted in the build-up of total heavy metals in the soil to the levels of 20.25,260.06, 40.816, and 14.45 lxg/g, respectively, while the build-up of these heavy metals in the soil due to the percolation of 2 L

Heavy metals release from ash pond

295

ash effluent/d resulted in the increase up to 20.3, 260.116, 41.283, and 14.566 ~tg/g, respectively.

pond, keeping in view the conditions prevailing in the actual environment.

Cation exchange capacity (C.E. C) and organic matter (O.M.) in layers of soils

Acknowledgment

The C.E.C. and O.M. were found varied with depth and even from sample to sample for the small quantities of soil samples used in the study (Fig. 6). Mass balance calculation shows that only 49.58% of Cr, 58.83% of Mn, 65.61% of Ni, and 54.58% of Pb (soluble) were recovered in the leachates of 1 L ash effluent applied columns; whereas 2 L ash effluent applied columns resulted in the recovery of 56.56% of Cr, 60.60% of Mn, 76.14% of Ni, and 64.82% of Pb. This was attributed to sorption/retention of these heavy metals in the soil under control conditions. DISCUSSION

The shape and position of the peak or maximum concentration provides information on the concentrations of Cr, Mn, Ni, and Pb in the leachates, the mobility of these metals, and the flow characteristics of the alluvial soil. Results obtained indicate that heavy metals content in leachates increases with increased quantity of ash effluent percolation. Ash effluent percolation through soil also caused unfavourable changes in the soil system including increases in the pH, E.C., and heavy metals content. The pH of the soil was increased from 7.4 to 8.1 due to infiltration of alkaline ash effluent (EPA 1980; Sharma et al. 1989). An alkaline pH at the top of the soil (Sampling Point I) resulted in a decrease in the concentration of available metals and an increase in the concentration of total metals. However, when the pH of the soil was acidic at the middle of the treated columns (Sampling Point II), the pH of the soil and the available heavy metals content were inversely related (Gerritse et al. 1982; Fulekar 1983). At the same time, total heavy metal content varied with the O.M. and C.E.C. of the soil at different depths (Bolter 1977; Jennett and Foil 1979; Christopherson et al. 1980). The variation in the concentration of sorbed/retained heavy metals in soil layers may also be explained by the mobility of some elements in soil as the ash effluent percolation through the soil system undergoes a mixing process in a lysimeter (Braunstein et al. 1977). The data of this study may be carefully interpreted and used for the discharge of ash effluents in an ash

~ The financial assistance rendered by the Council of Scientific and Industrial Research is gratefully acknowledged. Thanks to the Fulekar family and Dr. (Mrs.) Kalpana M. Fulekar for the help and cooperation received.

REFERENCES APHA (American Public Health Association), American Water Works Association, and Water Pollution Control Federation. In: Standard methods for the examination of water and waste water, 14th Edition.; 1975. Available from: APHA, New York. Braunstein, H.M.; Copenhaver, E.D.; Pfuderer, H.A., eds. In: Environmental, health and control aspects of coal conversion: An information overview, ORNL EIS-95, Vol. I and II. Oak Ridge, TN: Oak Ridge National Laboratory; 1977. Boher, E.A. Soils and geochemistry studies. In: Wilson, B.G., ed. The Missouri lead study, chapter 5. A report of the inter-disciplinarF lead belt team. Columbia: Univ. of Missouri; 1977. Christopherson, N; Scip, H.M.; Njos, A. Simulation of flow patterns and ion-exchange in soil percolation experiments. Water, Air, Soil Pollut. 14:159-170; 1980. Devis, J.; Freitas, F. Physical and chemical methods of soil and water analysis. Rome: Food and Agriculture Organisadon of the United Nations; 1970: 275. EPA (U.S. Environmental Protection Agency) Report. Element flow in aquatic systems surrounding coal-fired power plants (EPA-600/3-80-076, July 1980). Cincinnati, OH: EPA; 1980. Fulekar, M.H. Release and behaviour of selected trace elements in soil-water environment caused by coal-fired power plants flyash disposal. Ph.D. Thesis, Jawaharlal Nehru University, New Delhi; 1983. Fulekar, M.H.; Dave J.M. Disposal of fly-ash - An environmental problem. Int. J. Environ. Stud. 26:191-215; 1986. Fulekar, M.H.; Dave, J.M. Environmental impact assessment of fly-ash from coal-fired power plants. Ecology 4 (8):25-34; 1990. Gerritse, R.G; Vriesema, R; Dalenberg, J.W.; De Ross, H.P. Effect of sewage sludge on trace element mobility in soils. J. Environ. Quality 11 (37):359-364; 1982. Jackson, M.L. Soil chemical analysis. New Delhi: Prentice Hall; 1973:452. Jennett, J.C.; Foil, J.L. Trace metal transport from mining, milling, and smelting water sheds. J. Water Pollut. Control Federation; 51:378-404; 1979. Lindsay, W.L; Norvell, W.A. Development of a DTPA soil test for zinc, iron, manganese, and copper. Soil Sci. Soc. Am. J. 42:421428; 1978. Naik, D.S.; Fulekar, M.H.; Dave, J.M. Pbysicochemical characteristics of sluicing water in an ash pond. Chem. Era 19 (2):2831; 1983. Piper, C.S. Soil and plant analysis. New York, NY: Interscience Publications Inc.; 1950:368. Pbung, H.T.; Lund, L.J.; Page A.L.; Bradford G.P. Trace elements in fly-ash and their release in water and treated soils. J. Environ. Qual. 8:171-175; 1975. Sharma, S; Fulekar, M.H.; Jayalakshmi, C.P. Flyash dynamics in soil-water system, CRC, Critical Reviews in Environ. Control 19:251-275; 1989. Walkley, A.. An examination of methods for determining organic carbon and nitrogen. J. Agri. Sci. 25:598; 1935.