TVA
EPA
Tennessee
Valley
Authority
Energy Demonstrations and
Technology
rhattanooga, TN 37401
EDT-110
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/7-80-067
March 1980
of Coal Ash
in Water:
Trace Metal Leaching
and Ash Settling
Interagency
Energy/Environment
R&D Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-80-067
March 1980
Behavior of Coal Ash
Particles in Water:
Trace Metal Leaching
and Ash Settling
by
T.-Y.J. Chu, B.R. Kim, and R.J. Ruane
TVA Project Director
Hollis B. Flora II
Tennessee Valley Authority
1140 Chestnut Street, Tower II
Chattanooga, Tennessee 34701
EPA Interagency Agreement No. D5-E721
Program Element No. INE624A
EPA Project Officer: Michael C. Osborne
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
U.S. Em\mnmm^ Protection Agency
Regies V, Library
230 South Dearborn Street
Chicago, Illinois 60604
-------
DISCLAIMER
This report was prepared by the Tennessee Valley Authority
and has been reviewed by the Office of Energy, Minerals, and
Industry, United States Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the
Tennessee Valley Authority or the United States Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
ill
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ABSTRACT
At a TVA 1000-MW coal-fired power plant, approximately 700 tons
(635,040 kg) of ash residues (fly and bottom ashes) produced by burn-
ing coal must be disposed of daily. The chief determinants of amount
of ash produced are the type of coal burned, ash content of the coal,
and method of firing (type of boiler). Dry or wet handling and dis-
posal are employed, depending on the availability of water, proximity
of the disposal site, environmental regulations, and cost. The exist-
ing prevalent method for ash disposal is by wet sluicing to ash ponds
near the power plants. The average size of TVA ash ponds is about 180
acres--17 percent of the total area of the plant sites. This report
addresses six major areas of concern in wet ash disposal, namely the
(1) characteristics of ashes and ash pond effluents, (2) effects of
ash and raw water characteristics on the pH of ash pond water, (3)
methods for pH adjustment of ash pond effluents, (4) settling
characteristics of both fly ash and bottom ash, (5) leaching of
minerals from ashes, and (6) relationship of trace metals to pH and
concentration of suspended solids in ash pond effluents.
The chemical characteristics of ash pond effluents are affected by
the ash material and the quantity and quality of water for slucing. TVA
ash pond effluents vary from a pH of 3 to 12. The acidity and alkalinity
depend on the content of sulfur oxides and alkaline metal oxides in the
ash and on the buffering capacity of water used for sluicing. Methods
for adjusting the pH of ash pond effluents may include (1) controlling
the ash-to-water ratio for ash sluicing, (2) combining effluents with
other wastewaters within power plants, or (3) adding chemicals. Because
of high ash concentration during sluicing, 90 percent of fly ash par-
ticles follow hindered-zone settling behavior and settle faster than
those remaining ash particles, which follow discrete settling behavior.
Mathematical equations were developed to delineate the ash settling
behavior and to estimate the residual suspended solids concentration
in the effluent of a sedimentation basin or settling pond.
Mathematical analyses indicated the leaching of trace metals from
ash depends on the concentration of each trace metal in the ash matrix,
its chemical bonding in the ash, and particle size of ash. Laboratory
results showed that pH also influenced the leaching concentrations of
trace metals. A delineation of potential trace metal pollution result-
ing from ash disposal under various ash-to-water contacting ratios was
provided by laboratory studies. Trace metals in 14 ash pond effluents
were monitored quarterly. Several trace metals were found to occur in
potentially toxic quantities and some trace metals were present in both
dissolved and suspended forms. Adjustment of effluent pH between 6 and
9 and reduction of suspended solids concentrations to 30 mg/1 reduced
the total concentrations of many trace metals such as chromium, copper,
lead, and zinc. However, these measures did not appreciably reduce the
total concentrations of arsenic, boron, cadmium, iron, manganese, and
selenium. Iron was found mostly in suspended form.
IV
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CONTENTS
Abstract
Figures v
Tables ,x
Acknowledgment • Xli
1. Introduction 1
2. Conclusions and Recommendations 5
3. Literature Review 9
4. pH of Ash Sluice Water 15
Effect of ash characteristics 15
Effect of buffering capacity of sluicing
makeup water 18
Effect of ash-to-water ratio during sluicing 18
5. pH Adjustment of Ash Sluice Water 22
Neutralization of acidic ash pond effluents 22
Neutralization of alkaline ash pond effluents 22
Strong acid treatment 28
Carbonation 28
Combining streams 29
6. Ash Settling 34
Particle size distribution of ashes used
for settling tests 34
Ash settling character 37
7. Characteristics of Ashes 57
8. Leaching of Minerals from Ashes 62
9. Effect of pH and Suspended Solids on Trace
Metal Concentrations in Ash Pond Effluents 84
Study 1—Reducing suspended solids concentration to
30 mg/1 and then adjusting pH to 6 and 9 ... 86
Study 2—Spiking trace metals into composite
alkaline ash pond effluent and adjusting
pH to 9 and 7 95
Study 3—Adjusting acidic ash pond effluent
using lime and investigating suspended
trace metals settling 95
Study 4—Investigation of dissolved and
suspended trace metals in TVA ash pond
discharges 95
Summary 99
Arsenic 99
Boron 100
Cadmium ' • 1°°
Chromium 101
Copper 101
Iron 101
Lead 101
Manganese 102
Selenium 102
Zinc 102
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CONTENTS
(Continued)
References
Appendices
A. Effects of initial concentrations of suspended
solids on settling of ashes
B. Results of investigation of mineral leaching
rate of fly ashes 140
C. pH and conductivity of ash transport water
versus mixing time for various ash
concentrations 149
D. Percentage of trace element concentrations
in ash pond effluents equal to or greater
than various given concentrations 154
E. Water quality criteria for domestic water supplies 170
F. Analytical procedures 172
vi
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LIST OF FIGURES
Number Pa8e
1 Range and average of ash content in U.S. coals ....... 13
2 Relationship between the equilibrium (pH of ash/water
mixture and the mole ratio of CaO plus MgO to S03
contained in dry fly ashes . ............ ... 17
3 Relationship between pH and concentration ratios
of calcium to sulfate in effluents from combined
ash ponds .......... .............. 19
4 Seasonal variation of water quality parameters in
an ash pond effluent ................... 20
5 Relationship between equilibrium pH and the
concentration of ash in the sluice water ......... 21
6 Titration curves of acidic ash pond effluents
from TVA steam plants .................. 23
7 Titration curves of alkaline ash pond effluents
from TVA steam plants . . ................ 24
8 Neutralization of acidic ash sluice water with
base (ash-water contacted for 1 h and not
separated before neutralization) ............. 25
9 Neutralization of alkaline ash sluice water with
acid (ash-water contacted for 1 h and not
separated before neutralization) ............. 27
10 Neutralization of an alkaline ash pond effluent
with liquid carbon dioxide ....... . ..... ... 30
11 Neutralization of alkaline ash pond effluents
with once-through cooling water ............. 32
12 Particle size distribution curves of fly ashes
used for settling test .................. 36
13 Quiescent settling column with sampling ports ....... 39
14 Suspended solids concentration vs. settling
time (electrostatic precipitator fly ash
from plant J; initial suspended solids
concentration C = 48,000 mg/1) ... .......... 4°
vii
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LIST OF FIGURES
(continued)
Number Page
15 Suspended solids concentration vs. the reciprocal
of settling velocity (electrostatic precipitator
fly ash from plant J; initial suspended solids
concentration (C = 48,000 mg/1) 41
o
16 Suspended solids concentration vs. t - kz
(electrostatic precipitator fly ash from
plant J; initial suspended solids concen-
tration C = 48,000 mg/1) 43
17 Suspended solids concentration vs. the reciprocal
of settling velocity (electrostatic precipitator
fly ash from plant J; initial suspended solids
concentration C = 30,000 mg/1) 46
18 Suspended solids concentration vs. t - kz
(electrostatic precipitator fly ash from
plant J; initial suspended solids concen-
tration CQ = 30,000 mg/1) 47
19 Suspended solids concentration vs. the reciprocal
of settling velocity (electrostatic precipitator
fly ash from plant J; initial suspended solids
concentration C = 8900 mg/1) 48
20 Suspended solids concentration vs. t - kz (electro-
static precipitator fly ash from plant J; initial
suspended solids concentration C = 8900 mg/1) .... 49
21 Velocity of the hindered settling zone vs. the
initial suspended solids concentration of ash
settling 52
22 Suspended solids concentration vs. the reciprocal
of settling velocity (river water from the South
Chickamauga Creek; initial suspended solids
concentration C = 140 mg/1) 53
23 Suspended solids concentration vs. t - kz (river
water from South Chickamauga Creek; initial
suspended solids concentration C = 140 mg/1) .... 55
viii
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LIST OF FIGURES
(Continued)
Number page
>
24 pH and mineral leaching rate of 3 percent
electrostatic precipitator fly ash from
plant A * 65
25 pH and mineral leaching rate of 3 percent
electrostatic precipitator fly ash from
plant E 66
26 pH of ash transport water vs. mixing time
for various ash concentrations (electro-
static precipitator fly ash from plant A) 68
27 Conductivity of ash transport water vs.
mixing time for various ash concentrations
(electostatic precipitator fly ash from
plant A) 69
28 pH and leaching of principal constituents
from an alkaline fly ash sample from
plant E 73
29 Leaching of trace metals from an alkaline
fly ash sample from plant E 74
30 pH and leaching of principal constituents
from a neutral fly ash sample from Plant J 75
31 Leaching of trace metals from a neutral
fly ash sample from plant J 76
32 pH and leaching of principal constituents
from an acidic fly ash sample from plant A 77
33 Leaching of trace metals from an acidic fly
ash sample from plant A • 78
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LIST OF TABLES
Number
1 Chemical Effluent Guidelines and Standards,
Steam-Electric Power Generating Plants 2
2 Classification of Common Minerals Found in
Coal , iQ
3 Trace Inorganic Elements in Coal 11
4 Average Content (%) of Trace Metals in Coals 12
5 Relationships Between Plant Operation Condi-
tions and pH Values of Ash Pond Effluents
at TVA Coal-Fired Power Plants 16
6 Basicity and Cost Comparisons of Various
Alkaline Agents 26
7 Fly Ash Particle Size Analysis 35
8 Size Distribution of Bottom Ash from Plant J 38
9 Values of Constants for Settling Curves 50
10 Chemical Composition of Fly Ashes from TVA
Steam Plants 58
11 Percentage of Cenospheres in Fly Ashes 59
12 Chemical Composition of Cenospheres . . 61
13 Chemical Composition of Dry Fly Ashes
Used for Leaching Study 72
14 Characteristics of Once-Through Ash
Pond Discharges 80
15 Average Concentrations (mg/1) of Dissolved and
Suspended Chemical Species in Intake Water,
Ash Sluice Water, and Ash Pond Effluent 85
16 Concentrations of Dissolved and Suspended
Trace Metals in Tennessee River Water 87
17 Effect of pH Adjustment on Trace Metal Con-
centrations in Electrostatic Precipitator
Ash Transport Water of Plant A 88
x
-------
LIST OF TABLES
(Continued)
Number
18 Effect of pH Adjustment on Trace Metal Con-
centrations in Electrostatic Precipitator
Ash Transport Water of Plant E 89
19 Effect of pH Adjustment on Trace Metal, Con-
centrations in Ash Transport Water of Plant H 90
20 Effect of pH Adjustment on Trace Metal Con-
centrations in Ash Transport Water of Plant J 91
21 Effect of pH Adjustment on Trace Metal Con-
centrations in Ash Transport Water of Plant K 92
22 Effect of pH Adjustment on Trace Metal Con-
centrations in Ash Transport Water of Plant L 93
23 Composition of Dissolved and Undissolved Trace
Metals in Alkaline Combined Ash Pond Effluents 96
24 Effect of pH Adjustment Using Lime on Suspended
and Dissolved Solids and Trace Metals in Acid
Fly Ash Pond Effluents from Plant A 97
25 Trace Element Concentrations (mg/1) of Dissolved
and Suspended Fractions in Ash Pond Effluents
from Plants A Through L 98
xi
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ACKNOWLEDGMENT
This study was initiated by TVA as part of the project entitled
"Characterization of Effluents from Coal-Fired Utility Boilers" and is
supported under Federal Interagency Agreement No. EPA-IAG-D5-E721-BB
between TVA and EPA for energyrelated environmental research. Thanks
are extended to the EPA Project Officer, Michael C. Osborne, and the
TVA Project Director, Hollis B. Flora II. Appreciation is also extended
to Kenneth L. Ogle, Jerry D. Pierce, and James M. Wyatt for their
assistance in the project.
xii
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SECTION 1
INTRODUCTION
Coal ashes resulting from burning coal in steam electric utility
boilers consist of fly ash, bottom ash, and slag. Fly ash is a powdery
residue that is normally collected from the stack gas by mechanical
collectors and/or electrostatic precipitators. Bottom ash, which is
darker than fly ash, is collected in the bottom of the furnace section.
Slag is molten bottom ash, which turns black when quenched with water
in the wet-bottom boiler combustion process.
The major factors affecting the amount of ash materials collected
are the type of fossil-fuel used, ash content of the fuel, and methods
of firing.1*3 In general, 700 tons (635,040 kg) of ashes can be pro-
duced daily at a Tennessee Valley Authority (TVA) 1000-megawatt (MW)
power plant burning coal from the Appalachian and midwestern regions.
These ashes must be disposed of daily. In 1975, about 60 million tons
(5.4 x 1010 kg) of ashes were generated by U.S. electric utilities; only
about 16.3 percent of the total amounts of ash produced were used.4 The
current national emphasis on using coal to produce energy, coupled with
the expanded use of lignite and western coal, has caused the continuing
rise in ash production. Therefore, the problems associated with the
disposal of coal ashes will continue.
In October 1974, the U.S. Environmental Protection Agency (EPA)
established effluent guidelines to limit the discharge of pollutants
from existing and new point sources within the steam-electric power
generating category (Table 1). The limits set for oil and grease,
polychlorinated biphenyls, pH, and suspended solids for wet and dry
ash disposal are shown in Table 1. In June 1976, EPA launched a mas-
sive program aimed at controlling 129 priority pollutants discharged
by 21 major industrial categories, including the steam-electric power
generating industry. The proposed regulations will be published in 1980.
In addition to the Federal effluent guidelines, each state may also have
its own water quality and effluent standards for discharges into public
waters. The various states may establish discharge limitations more
stringent than those established by the EPA under the National Pollution
Discharge Elimination System (NPDES) permit issuing program.
Ash disposal siting and operation are major items of consideration
during licensing procedures for new coal-flirfed power plants. At exist-
ing plants, many utilities are being directed either to adopt corrective
procedures to relieve adverse public opinion, or to simply meet the
stricter regulations adopted or proposed by Federal and State agencies.
Nevertheless, economic consideration, in addition to the environmental
-1-
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TABLE 1.
CHEMICAL EFFLUENT GUIBELHSES AND STAKMEDS,
STEAM-ELECTBIC POWER GENERATING PLANTS
BPCTCA
July 1, 1977
All discharges
pH (except once-through cooling)
Polychlorinated biphenyls
Bottom ash transport water
Total suspended solids
Oil and grease
Fly ash transport water
Total suspended solids
Oil and grease
Low-volume sources
Total suspended solids
Oil and grease
Metal cleaning wastes
and boiler blowdown
Total suspended solids
Oil and grease
Total iron
Total copper
Cooling tower blowdown
Zinc
Chromium
Phosphorus
Other corrosion inhibitors
Free available chlorine
6.0-9
0
Average
daily
30
15
30
15
30
15
30
15
1.0
1.0
-
-
-
0.2
.0
Daily
maximum
100
20
100
20
100
20
100
20
1.0
1.0
-
-
-
0.5
BATEA
July 1, 1983
6.0-9.0
0
Average
daily
30-M2.5
15 T 12.5
30
15
30
15
30
15
1.0
1.0
1.0
0.2
5.0
Case-by-case
0.2
Daily
maximum
100 -:- 12.5
20 4- 12.5
100
20
100
20
100
20
1.0
1.0
1.0
0.2
5.0
Case-by-case
0.5
New Source
Standards
6.0-9.0
0
Average
daily
30 -^ 20
15 -f 20
Oc
Oc
30
15
30
15
1.0
1.0
None detectable
None detectable
None detectable
None detectable
0.2
Daily
maximum
100 4- 20
20 -r 20
Oc
Oc
100
20
100
20
1.0
1.0
Hone detectable
None detectable
None detectable
None detectable
0.5
Once-through cooling
Free available chlorine
Material storage and
construction runoff
Total suspended solids0
0.2
0.5
0.2
0.5
0.2
0.5
50
50
50
All units are in milligrams per liter. Allowable discharge is the quantity obtained by multiplying flow by standard in
milligrams tier liter.
b . V
Neither free available chlorine nor total residual chlorine may be discharged from any unit for more than 2 h in any one
day, and not more than one unit in any plant may discharge free available chlorine or total residual chlorine at any one
time unless the utility can demonstrate that the units in a particular location cannot operate at or below this level of
chlorination.
Limitations were remanded by the Fourth Circuit Court of Appeals in July 1976.
Source: U.S. Environmental Protection Agency. Development Document for Effluent Limitations Guidelines
and New Source Performance Standards for the Steam-Electric Power Generating Point Source
Category. EPA-l*l(-0/l-7lt-029-a, October 197^. 8kO p.
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considerations, is still an important factor for ash disposal. Thus,
the selection of ash ponds or landfill for ash disposal is site-specific,
depending on the comparison and evaluation of the environmental and
engineering-economic factors. Environmental factors include air quality,
aesthetics, aquatic ecology and water quality, land use, noise, public
health and safety, socioeconomic, and terrestrial ecology. Engineering
and economic factors include hydrology, site development, transportation
and access, geology, treatment equipment, land availability, and cost.
For instance, dry disposal of fly ash could be more desirable than wet
disposal for some new coal-fired power plants, particularly in arid
regions; whereas wet ash could be more economical than dry ash disposal
for plants located in regions with an abundant supply of water.
The prevalent method for ash disposal at existing plants is wet
sluicing of ash to settling ponds near the power plants. The ash pond
is usually designed for ultimate disposal of total ash produced during
a specified time period. Typical water requirements for sluicing coal
ashes generally range from 1200 to 40,000 gal of water per ton of fly
ash (5 to 167 liters per kg) and from 2400 to 40,000 gal of water per
ton of bottom ash (10 to 167 liters per kg).5 For TVA's 12 coal-fired
power plants, ash sluicing water requirements average about 11.5 x 106
gpd (43.5 x 106 liters per day) per 1000 MW capacity.7 In the United
States, about 40 percent of the water requirements for ash sluicing at
coal-fired power plants are greater than 10 x 106 gpd (37.9 liters per
day) per 1000 MW capacity.
The most significant potential problems associated with ash dis-
posal in ponds are (1) acidic or alkaline character of ash pond water
and quantities of suspended solids and trace metals in surface water
effluents and (2) quantities of trace metals in groundwater leachates.
To meet the "best available control technology economically achievable"
(BATEA) effluent guidelines, existing coal-fired power plants using ash
ponds generally have to either (l) separate the fly ash and bottom ash
disposal ponds and recycle or provide a higher degree of treatment for
removing suspended solids from bottom ash pond effluents or (2) achieve
for combined ash pond effluents a suspended solids concentration equal
to a weighted average of the limits for fly ash and bottom ash transport
water. New coal-fired power plants using ash ponds would have to
(1) recycle or provide a higher degree of treatment for removing suspended
solids from bottom ash pond effluents and (2) completely recycle fly ash
pond effluent. In all cases, the pH must be maintained between 6 and 9
for any surface water discharges.
It is important to determine how adjustments in pH and reduction of
suspended solids concentrations affect trace metal concentrations in ash
pond discharges.
The scope of this study involved field survey of ash ponds at 12
TVA coal-fired power plants and bench-scale tests on TVA ash pond dis-
charges. This report addresses six major areas of concern in wet ash
-------
disposal, namely, the (1) characteristics of ashes and ash pond efflu-
ents, (2) effects of ash and raw water characteristics on the pH of ash
pond water, (3) methods for pH adjustment of ash pond effluents, (4)
settling characteristics of both fly ash and bottom ash, (5) leaching of
minerals from ashes, and (6) relationship of trace metals to pH and
concentration of suspended solids in ash pond effluents.
This report is complementary to two other studies: "Design of a
Monitoring Program for Ash Pond Effluents" and "The Effects of Coal-Ash
Leachates on Ground Water Quality," which are part of a project entitled
"Characterization of Effluents from Coal-Fired Utility Boilers" supported
under EPA interagency energy-environment research and development program.
-4-
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
Eight specific conclusions can be drawn from this study:
1. At a TVA 1000 MW coal-fired power plant, approximately 700 tons
(635,040 kg) of ash residues (fly ashes and bottom ashes) pro-
duced by the burning of coal must be disposed of daily.
Nationally, the increased use of coal for power generation
will result in increased ash production, land requirements for
ash disposal, and potential for contamination of water supplies.
2. The options for ash disposal that are generally available are
ponding and landfill. The selection of ash disposal methods
is site-specific, depending on the evaluation and comparison
of the environmental, engineering, and economic factors. The
environmental factors include air quality, aesthetics, aquatic
ecology and water quality, land use, noise, public health and
safety, socioeconomics, and terrestrial ecology. The engineer-
ing and economic factors include hydrology, site development,
transportation and access, geology, treatment equipment, land
availability, and cost. The existing prevalent method for ash
disposal is by wet sluicing to ash ponds near the power plants
The average size of TVA ash ponds is about 180 acres (728,460
square miles), which is about 17 percent of the total area of
the plant sites.
3. The principal environmental problems in ash disposal are
acidic or alkaline character of the ash pile runoff and ash
pond effluent, quantities of suspended solids in the runoff
and effluent, and quantities of trace metals in leachate,
runoff, and effluent from the disposal sites.
4. The pH of the ash transport water depends on either the
buffering capacity of makeup water and the ratio of alkaline
metal oxides to sulfur oxides in the ashes or the ratio of
total dissolved alkaline metal ions to sulfate ion in the
transport water. The equilibrium pH value of water, after
being in contact with fly ash, was acidic if the mole ratio of
CaO plus MgO to sulfur oxides as S03 in ash was less than 5;
if the ratio is above 5, the ash transport water ranged from
neutral to alkaline. The pH of the ash pond effluent in-
creased with the increase of concentration ratio of dissolved
calcium to sulfate in the effluent. The ash pond effluent was
neutral (pH 7) if the concentration ratio of dissolved calcium
to sulfate (in milligrams per liter) was close to 0.4. Also,
it is interesting to relate the factors that affect the pH
-5-
-------
of ash transport water to coal sources, and types of boilers.
For the TVA power plants with circular, horizontal, opposed,
tangential, and vertical boilers that use pulverized coal from
western Kentucky, northern Alabama, and southern Illinois, the
ash pond effluents are alkaline. For those plants with tan-
gential boilers that use pulverized coal from eastern Tennessee,
eastern Kentucky, and Virginia, the ash pond effluents are
neutral or acidic. The pH of the effluents from plants with
cyclone furnace boilers is neutral or acidic, even though the
coal sources are western Kentucky and southern Illinois.
5. Methods for adjusting the pH of ash pond effluents may include
(1) controlling the ash-to-water ratio for ash sluicing, (2)
combining ash pond effluents with other wastewaters within
power plants, or (3) adding chemicals. The quantities of
chemicals such as lime, limestone, soda ash, and caustic soda
required for acid effluent neutralization were relatively
small. The amounts of chemicals such as strong acid and C02
for neutralizing alkaline effluents were relatively large,
especially in consideration of the large flow of ash pond
discharge. At some plants, neutralization of alkaline ash
pond effluent by routing it into condenser cooling water
intake or condenser discharge has many practical advantages
as well as the obvious economic value of eliminating the need
for costly chemical treatemnt of ash pond effluents.
6. About 90 percent of the fly ash particles, following hindered-
zone or flocculent settling behavior, settled faster than those
residual fine ash particles which follow discrete settling
behavior. The flocculent settling behavior was caused by the
high ash concentration during sluicing and settling. Mathe-
matical equations were developed to delineate the ash settling
behavior and to estimate the residual suspended solids con-
centration in the effluent of a sedimentation basin or
settling pond. The design of ash settling basins or ponds
should be based on laboratory settling analysis. Discharge of
cenospheres into settling pond effluents must be prevented at
some plants to meet the effluent limitation guidelines for
suspended solids.
7. Theoretical analyses of mass transfer rates of minerals from
ash into water indicated that the principal factors affecting
the mineral leaching rate of fly ash were the concentration
and form of chemical species in ash, molecular diffusivity,
particle size, and intensity of turbulence. Experimental
-6-
-------
results indicated that the dissolved'minerals that leached
from ash into sluice water (river water) at the afflbient
temperature reached their equilibrium concentrations within
4 h, and that the equilibrium concentration levels depended on
the ash concentration. However, ash deposited in the bottom
of the ash pond may continue to leach while the ash is in
contact with ground water if the surrounding environment is
changed to anaerobic and low-pH conditions. The determina-
tion of concentration levels of chemical constituents
leaching from ashes were analyzed mathematically. The amounts
of minerals leaching from ash depend on the concentration and
form of chemical species in ash, particle size of the ash,
and diffusivity of each individual species. Laboratory results
indicated that pH also influenced the leaching concentrations
of many chemical species. A delineation of potential trace
metal pollution resulting from ash disposal under various ash-
to-water contacting ratios was provided by both laboratory
testing and field monitoring at TVA's 12 coal-fired power
plants.
8. Several trace metals in the ash pond discharges were found to
occur in potentially toxic quantities, and some trace metals
were present in both dissolved and suspended forms. The dis-
tribution of specific trace metals between the dissolved and
suspended forms is site-specific, but it is important to
analyze the trace metals in both the dissolved and suspended
forms for monitoring trace metals in ash pond discharges.
Adjustment of acidic ash pond discharges up to pH 6 or
of alkaline ash pond discharges down to pH 9, and reduction of
suspended solids concentrations to 30 mg/1 reduced total
concentrations of many trace metals, such as chromium, copper,
lead, and zinc. However, adjustment of pH between 6 and 9 did
not appreciably reduce total concentrations of arsenic, boron,
cadmium, iron, manganese, and selenium. The solubilities of
arsenic, boron, and selenium are independent of pH. Dissolved
cadmium and manganese may be greatly removed at pH above 9 and
12, respectively. Because of the high iron content in the
suspended ash particles, total iron concentrations could not
be reduced to the 1 mg/1 level at neutral pH, even though
total suspended solids concentrations in some ash pond
effluents were reduced to 30 mg/1.
Six special areas needed for further research are recommended as
below:
1. The determination of the chemical formula of metallic oxides
and other important constituents such as sulfur oxides in fly
and bottom ashes.
2. The distribution of trace metals in the surface and bulk of
ash particles.
-7-
-------
3. The formulation of dynamic models on trace metal leaching
from ash into water including the considerations of rates of
chemical reaction, pH, temperature, and buffer intensity of
water.
4. The chemical speciation of trace metals in ash pond efflu-
ents to determine the oxidation states of trace metals,
especially for arsenic, chromium, and selenium.
5. A demonstration of reduction of trace metals in ash pond
effluents by practical treatment methods such as pH adjust-
ment, chemical precipitation, and coagulation; for example, a
reduction of arsenic in ash pond effluents to 0.05 mg/1
through the above conventional treatment methods.
6. The identification and analysis of toxic organic compounds
in ashes and ash pond effluents.
-8-
-------
SECTION 3
LITERATURE REVIEW
Coal is formed by the partial decomposition of vegetative matter
under anaerobic conditions and varying degrees of temperature and high
pressure. Organic matter composed of carbon, hydrogen, oxygen, nitro-
gen, and sulfur is the principal constituent of coal, inorganic matter
occurs partly in coal and primarily in ash. The major minerals present
in U.S. bituminous coals are listed in Table 2. Many trace elements are
also found in coal (Table 3). The average concentrations of some trace
elements in coal throughout the coal regions of the United States are
presented in Table 4.
Coal ash, the combustion byproduct from coal-fired power plants, is
derived primarily from the inorganic mineral constituents in coal. The
nature of the inorganic residual results from the geologic and geogra-
phic factors associated with the coal deposits. The ash content in U.S.
coals, as summarized in Figure 1, varies from one coal bed to another.
In general, these raw coals contained an average of 14 percent ash.
However, as coal consumption in the United States continues to increase,
the quality of coal being used is deteriorating and the ash content is
increasing.12"16 Some of the subbituminous and lignite coals now being
used contain 15 to 18 percent noncombustible mineral constituents.
During combustion of coal in the furnace, the distribution of fly
ash and bottom ash depends on method of firing and type of combustion
chamber.5 When pulverized coal is burned in a dry-bottom furnace, 70 to
95 percent of the ash material is released as fly ash, and the other 5
to 30 percent is released as bottom ash. On the other hand, when pul-
verized coal is burned in a wet-bottom furnace, about 50 percent of the
ash is released as fly ash, and the other 50 percent falls to the bottom
of the furnace as bottom ash or slag. With the cyclone furnace, 70 to
80 percent of the total ash is removed from the bottom of the furnace as
bottom ash or slag, and 20 to 30 percent is released as fly ash in the
flue gas.
Fly ash generally occurs as very fine spherical particles, ranging
in diameter from 0.5 to 100 yon or greater and having a specific gravity
of 2.0 to 2.9.17 Bottom ash and slag occur as angular- and porous-
surface texture particles, ranging in diameter from 0.05 to 50 mm and
having a specific gravity of 2.2 to 2.8.18 Some low-weight, hollow-
sphere particles called cenospheres are found in fly ash. The true
specific gravity of the cenospheres ranges from 0.4 to 0.6. The
cenospheres can be as much as 4 to 5 percent by weight, or 15 to 20
percent by volume, of the fly ash generated at coal-fired power plants.
-9-
-------
TABLE 2. CLASSIFICATION OF COMMON MINERALS FOUND IN COAL
SHALE GROUP (Group M)
Muscovite (KAL(AlSiO3Ow)(OH)2)
Hydromuscovite
Illite (K(MgAl,Si)(Al,Si3)O,o(OH)!,
Bravaisite
Montmorillonite
(MgAl)s(Si,O,o).,(OH)ln-12H,O
KAOLIN GROUP (Group K)
Kaolinite (Al2Si2O5(OH)()
Levisite
Metahalloysite
SULFIDE GROUP (Group S)
Pyrite (FeS2)
Marcasite (FeS2)
CARBONATE GROUP (Group C)
Ankerite CaCO.v(Mg,Fe,Mn)CO:,
Calcite (CaCO.,)
Siderite (FeCO3)
CHLORIDE GROUP (Group O)
Sylvite (KC1)
Halite (NaCI)
OXIDE GROUP (Group O)
Quartz (SiO2)
Hematite (Fe3O,)
Magnetite (Fe:O;,)
ACCESSORY MINERALS GROUP
Sphalerite (ZnS)
Feldspar (K, Na)2O'Al2O3-6SiO2
Garnet (3CaO-Al2O.,-3SiO2)
Hornblende (CaO-3FeO-4SiO2)
Gypsum (CaSO4-2H2O)
Apatite (9CaO-3P2O5-CaF2)
Zircon (ZrSiO,)
Epidote (4CaO-3Al2O3-6SiOi-H2O)
Biotite (K2O-MgO-Al2O.v3SiO2-H20)
Augite (CaO-MgO-2SiO2)
Prochlorite
(2FeO • 2MgO • A12O,- 2SiO. • 2H2O)
Chlorite
(Mg(Fe,Al)«(Si,Al)4Oi»(OH)8
Diaspore (A12O3-H2O)
Lepidocrocite (Fe2O3-H2O)
Barite (BaSO,)
Kyanite (Al2O3-SiO2)
Staurolite (2FeO-5Al2O3-4SiO2'H2O)
Topaz (AlF)sSiO.
Tourmaline HBAl^BOHJsSi^w
Pyrophyllite (Al2Si,O10(OH)2)
Penninite (5MgO-Al2O3-3SiO2-2H2O)
Source: Lucas, J. R., et al. Plant Waste Contaminants In:
Coal Preparation, J. W. Leonard and D. R. Mitchell, eds.,
The American Institute of Mining, New York, 1968.
pp. 17.1-17.54.
-10-
-------
TABLE 3. TRACE INORGANIC ELEMENTS IN COAL
Constituent
As
B
Be
Br
Cd
Co
Cr
Cu
F
Ga
Ge
Hg
Mn
Mo
Ni
P
Pb
Sb
Se
Sn
V
Zn
Zr
Al
Ca
Cl
Fe
K
Mg
Na
Si
Ti
Mean
Value
14.02
102.21
1.61
15.42
2.52
9.57
13.75
15.16
60.94
3.12
6.59
0.20
49.40
7.54
21.07
71.10
34.78
1.26
2.08
4.79
32.71
272.29
72.46
1.29
0.77
0.14
1.92
0.16
0.05
0.05
2.49
0.07
IT . Standard
untt: Deviation
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
17.70
54.65
0.82
5.92
7.60
7.26
7.26
8.12
20.99
1.06
6.71
0.20
40.15
5.96
12.35
72.81
43.69
1.32
1.10
6.15
12.03
694.23
57.76
0.45
0.55
0.14
0.79
0.06
0.04
0.04
0.80
0.02
Min imum
Value
0.50
5.00
0.20
4.00
0.10
1.00
4.00
5.00
25.00
1.10
1.00
0.02
6.00
1.00
3.00
5.00
4.00
0.20
0.45
1.00
11.00
6.00
8.00
0.43
0.05
0.01
0.34
0.02
0.01
0.00
0.58
0.02
Maximum
Value
93.00
224.00
4.00
52.00
65.00
43.00
54.00
61.00
143.00
7.50
43.00
1.60
181.00
30.00
80.00
400.00
218.00
8.90
7.70
51.00
78.00
5350.00
133.00
3.04
2.67
0.54
4.32
0.43
0.25
0.20
6.09
0.15
Source: Ruch, R. R., et al. Occurrence and Distribution of Potentially
Volatile Trace Elements in Coal. EPA 12-74-054, U. S. Environmental
Protection Agency, July 1974. 96 P.
-11
-------
TABLE 4. AVERAGE CONTENT (%) OF TRACE METALS IN COALS
Trace metal content (%) in coal
Metal
Antimony
Arsenic
Beryllium
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Thallium
Silver
Zinc
Appalachian
0.001a
0.0031°
0.0025s
NA
0.0013d
0.0015d
0.0009C
0.000015s
0.0014e
0.00018d
0.00008d
0.00082C
Interior
Eastern
NAb
0.0011d
0.0025s
NA
0.002s
0.00116
0.0011C
0.000013e
0.0015e
0.00007d
NA
0.0044s
Interior
Western
NA
NA
0.0015C
NA
0.0014C
0.0012C
0.0004e
0.000019s
0.0017a .
NA
NA
0.0193d
Great
Northern
Plains
NA
0.08C
0.0015s
NA
0.0007s
0.0015s
0.0007s
0.000007s
0.00072s
NA
NA
0.0059a
Southwestern
NA
0.0073s
0. 00006s
0.000003°
0.006a
0.0008C
0.0006d
0.000013°
0.0006d
NA
NA
0.0009d
Western
NA
0.00043
0.0015s
NA
0.00069d
0.00046d
0.0008°
0.000007s
0.00053d
0.00005d
NA
0.0025d
Product of average of the range of element percentages in ash and average ash content
of coal.
bNot available.
£
Based on average of the ranges of percentage of the element in coal.
Product of average value of element in coal and average ash content of
coal.
fin
Based on average percentage of element in coal as reported.
Sources:
Magee, E. M., et al. Potential Pollutants in Fossil Fuels. EPA-R2-73-249.
U.S. Environmental Protection Agency, June 1973. 151 p.
Wachter, R. A., and T. R. Blackwood. Source Assessment: Water Pollutants
from Coal Storage Areas. EPA-600/2-78-004m, May 1978. 106 p.
--
-------
NORTH APPALACHIAN
40 j-
30
H-
LU
20
10
EASTERN MIDWEST
SOUTH APPALACHIAN
ALABAMA
WESTERN MIDWEST
WESTERN
REGIONS OF UNITED STATE COALS
Figure 1. Range and average of ash content in U.S. coals.
Source: Cavallaro, J. A., et al. Sulfur Reduction Potential of the Coals of the United States.
Report No. 8118, Bureau of Mines, U.S. Department of the Interior, 1976. 323 p.
-------
The composition of fly ash and bottom ash varies greatly and
depends on the geographical area from which the coal is derived, com-
bustion conditions, and other factors such as the removal efficiency of
air pollution control devices. The primary constituents in fly ash and
bottom ash may be metal oxides such as alumina, calcium oxide, ferric
oxide, magnesium oxide, potassium oxide, silica, sodium oxide, and
titanium oxide, and other constituents such as sulfur oxides and carbon
residuals. Almost 40 percent of the ash component is silica, and
another 40 percent of the ash consists of alumina and ferric oxide.20
Fifteen years ago, two studies reported that a wide range of trace
contaminants, including 17 trace metals, were identified in fly ash from
coal-fired power plants.21"22 Recent studies of coal ashes23"34 have
indicated that virtually every mineral constituent accumulated along the
deposit of coal on the earth's surface can be found in coal ashes. The
elements contained in coal ashes can be divided into five groups:
alkali and alkali earth metals, refractories, transition metals, halo-
gens, and volatiles. Some recent studies27"35 have established that
many trace elements, particularly the more volatile ones, are richer in
fly ash than in raw coal, and the specific concentrations of many trace
elements in fly ash increase significantly with decreasing particle size
of fly ash. Also, the natural radionuclides have been reported in fly
ash and bottom ash from coal-fired power plants.36"40
Virtually all ash disposal and utilization techniques expose ash to
water at one time or another. The exposure ranges from complete immer-
sion of ash into water such as sluicing and ponding, or intermittent
percolation of water through ash landfill areas. Therefore, the water
quality problems of effluent and leachate from ash disposal depend on
the methods of ash disposal; e.g., the quantities of suspended solids
and trace metals depend on whether the ash is disposed of in ash ponds,
ash storage piles, or landfill sites. The water quality problems
associated with particular ash ponds have been reported extensively.41"53
-14-
-------
SECTION 4
pH OF ASH SLUICE WATER
The pH of water contacted with ash material may vary from acid to
alkaline, depending on ash characteristics and quality and quantity of
water used for sluicing. Primarily, the pH of ash sluice water is
affected by the amounts and concentrations of chemical species that
dissolve from ash into water.
EFFECT OF ASH CHARACTERISTICS
The pH of ash pond effluent relates to those factors affecting the
ash characteristics. The operating conditions for TVA's 12 coal-fired
power plants are summarized in Table 5. For the plants that use pul-
verized coal, the pH of the ash pond effluents is mainly affected by the
source of coal. Ash pond effluents from plants that receive coal from
western Kentucky and southern Illinois are alkaline, whereas those from
plants that receive coal from eastern Tennessee, eastern Kentucky, and
Virginia are neutral or acidic. However, the pH of the effluents from
the two plants with cyclone furnaces is neutral or acidic, even though
the coal source for both plants is western Kentucky and southern
Illinois.
The fly and bottom ashes are basically glass-like particles, and
fly ash is also coated with various oxides during the condensation
process after combustion.1 The composition of this coating varies
greatly from ash to ash, depending on the type of coal burned and
method of firing (type of boiler) . Most of the sulfur oxides and
alkaline metal oxides in ash are readily dissolved in water. The
alkaline metal oxides of calcium, magnesium, potassium, and sodium can
produce a basic reaction in water as
M 0 + yH20 -> x M X + 2yOH . (1)
The sulfur compounds dissolve in water and ultimately yield an acidic
reaction. One possibility for sulfur trioxide is:
-2 +
S03 + H20 •» S04 + 2H . (2)
Therefore, the pH of the ash sluice water depends on either the ratio
of alkaline metal oxides to sulfur oxides in ash or the ratio of total
dissolved alkaline metal ions to sulfate ion in sluice water. CaO and
MgO are the two principal alkaline metal oxides in ash. Figure 2 shows
-15-
-------
TABLE 5. RELATIONSHIPS BETWEEN PLANT OPERATION CONDITIONS AND pH VALUES
OF ASH POND EFFLUENTS AT TVA COAL-FIRED POWER PLANTS
1
t— '
1
Parameter
Coal sources
Method of
firing
Ash content in
the coala, %
Fly ash of
total asha, %
Bottom ash of
total asha, %
Sluice water-
to ash ratioa,
gal/ton
pH value of
raw watera
pH value of
ash pond
effluent3
Plant D Plant H
E. Kentucky Virginia
E. Kentucky
E. Tennessee
Tangential Tangential
15.5 15
75 67
25 33
10,770 11,425
7.5 7.0
8.6° 8.9C
Plant J Plant E
E. Kentucky W. Kentucky
E. Tennessee
Tangential Circular
tangential
19.1 15.3
75 67
25 33
9,520 9,585
7.6 7.0
6.3° ll.r
Plant F Plant G Plant I
W. Kentucky W. Kentucky W. Kentucky
S. Illinois
Opposed Tangential Tangential
horizontal
16.3 15.7 I**
80 80 70
20 20 30
19,1+90 12,31+5 1+2,1+30
7.4 7-3 7.1+
11.2° 9.6C 11.2°
Plant K
S. Illinois
W. Kentucky
Circular
15-6
75
25
17,265
7.6
10.8°
Plant L Plant B
W. Kentucky W. Kentucky
N. Alabama
Horizontal Vertical
tangential
16 14.8
75 50
25 50
15,370
7.5 7.5
9 8^
10.1° s!od
Plant C Plant A
W. Kentucky W. Kentucky
S. Illinois
Cyclone Cyclone
11 18.8
30 30
70 70
12,38ob
23,065 9,810°
7.1+ 7.7
k lib
7.1° 7'.2i
Based on average values during 1971+.
Fly ash pond only.
2
Combined bottom and fly ash pond.
Bottom ash pond only.
1 gal/ton = 4.2 x 10~3 I/kg
-------
EQUILIBRIUM pH (units)
pi
w
(0
CO
c
H
N5
fi»
fr,
fD
PJ
rt
(D
O
s
(D
H-
o m
rt rt
H- s!
O (0
ro
o o
o cr
$11 (D
O
fl>
13 ^5
M C
C H-
W !-•
O H-
w ta
o
10 o
Ml
O
O P
H-
3
(D
5-3
(D
o
o
+
OQ
O
CO
O
to
I-i
H-
O
ro
b
en
b
po
b
8
ro
b
ro
b
(30
O
O
b
O
O
O
-------
the relationship of pH to the mole ratio of CaO plus MgO to sulfur
oxides as S03 contained in fly ashes collected from seven TVA steam
plants. The equilibrium pH values of water, after contact with these
fly ashes, are acidic if the mole ratios of CaO plus MgO to sulfur
oxides as S03 are less than about 5. For a mole ratio greater than 5,
the ash sluice water can be neutral or alkaline depending on the dis-
solution of alkaline metal oxides and sulfur oxides from ash into water.
The pH values of ash pond effluents at 12 TVA steam plants vary from 3
to 12. Figure 3 illustrates the relationship between pH and the con-
centration ratio of calcium to sulfate in ash pond effluents. In
general, the pH increase is proportional to the increase of concen-
tration ratio of calcium to sulfate in ash pond effluents.
EFFECT OF BUFFERING CAPACITY OF SLUICING MAKEUP WATER
The importance of the buffering capacity of makeup water used for
sluicing is apparent at Plant J, where the pH of the ash pond effluent
varies seasonally from acidic in the winter and spring to slightly
alkaline in the summer and fall (Figure 4). The cause of this variation
is that the water used for sluicing consists of two separate river
waters—one, containing low alkalinity, is used for makeup water in
winter and spring; and another, containing relative high alkalinity, is
used for makeup water in summer and fall.
EFFECT OF ASH-TO-WATER RATIO DURING SLUICING
The equilibrium pH of ash sluice water is also affected by the
concentration of ash during sluicing as shown in Figure 5. Recently the
effect of ash-to-water ratio on the pH of ash transport water has been
dramatically demonstrated at two TVA alkaline ash ponds. At plant G,
the raw water flow for ash sluicing has increased from 10.6 x 106
to 16.4 x 106 gpd (40.1 x 106 to 62.1 x 106 liter per day) (the average
ash concentration of ash slurry during sluicing decreased from 19.4 to
12.6 g per liter) and the pH of ash pond water has dropped from 9.6 to
9- At plant I, the raw water flow for ash sluicing has increased from
14 x 10B to 21.6 x 106 gpd (53 x 106 to 81.8 x 106 liter per day) (the
average ash concentrations of ash slurry during sluicing decreased from
5.6 to 3.7 g per liter) and the pH of the ash pond water has dropped
from 11.2 to 9.3.
The effect of ash-to-water ratio on pH can be important for those
ashes that have pH values close to either 6 or 9; therefore, a slight
change in ash-to-water ratio during sluicing can shift the pH values
within the limitation range.
-18-
-------
Q_
14
12
10
~ 8
0
i 1 1
i 1 r
o =
i i i L
AVERAGE VALUES DURING
1973 and 1974 AT EIGHT
TVA COAL-FIRED POWER
PLANTS
J I I L
0.2 0.4 0.6 0.8 1.0
Ca(mg/l)/S04(mg/l)
12
Figure 3. Relationship between pH and concentration ratios of calcium
to sulfate in effluents from combined ash ponds.
-19-
-------
Total
Total
Total Total
ouapciiucu OUJLAUS uj.ssuj.vfc:u aux-tua aj.K.aj.j.nn:y hardness pH
(mg/D (mg/1) (mg/1 as CaC03) (mg/i as CaC03) (units)
Ml-'tsJ H1 to U> h-1 M
UiOUiOvOvDOOOO Oi 1— ' »-J Ui
t^j C5 i"_-> C? t'^j tji f~*i ^J^ f"*3 f^ (^/i t ^ i ^ji f~^ (jj .£•» ^«, ^j IQ
* * •••••• •• • •• • t f •••
o o ooooooooooooouiomo
. . | 1 1 1 ) 1 j JL | , 1 1 1 j 1 1 I i ,
*5 IV
o
'• ' '.
•• • 9
• * * *
'". . " '
k -" • • " •
-
l-J-j
era |_, •
% %
Vf J_j
'
T3 W
ftt (D
l-S So
m CO
3 0
0 g ^
1 (D (-* VO
ro i-{ -vj
O CO -< N)
H- H
3 H-
tu
:*' .
*. . • •. •
-.'
f ' -:l
?." •* •'
m 9 *
* *• • *
•'* ' "' ' s
.'*• "'•''
.' •
- • " • • . "
' . * * '
'*'• ''\
-*.'•" ." ' * *
* * •*
' ' • J
l:
• *•
' .V :'x.
s? /?*
(U S /. '.'.
co
CT1 O
l-h
T!
o s:
3 (» 1-
CL rt VO
• •• . '
• / ' • . •
* • * 8
• . • • • .
" 't ' • '
. /' • ••:. "'
fl> ^4 r
(0 ^ U)
f-h iJQ
M C
C P
(B 1—
3 H-
... . .
'• . .•
• * •
;•'' ' " • '.'
t * * * •* *
• * •
rt rt 1. . ' .- 1
M
^
*-
• .' •
' . • % f
• • ' ' '.
• . . • 1
• • • .'
• * 9g
t •
. • " •* " .
'•* '• °. • "
t ' .• °
'*' • ' ,' •"
•'.* ' ' "•••'.
'• *. •
- * • •
• • B ^ " ^ ^ ^ ^
*' f °** , 1 '
•, a*
^ "'». " ' : • .
" * • . t ' • '
f t .•'
/• '•' .
°* * '", *
f ' fS •.'"
.• •' ° ••/ • •"*'
' t ' ° '• *
•f' ' ',''•
% °, *•'
•\ s
!• '. '
a • f • a *
'• * ' ' '• ,
<° . °'f '•' . '
* • f *
f "*• I * *
V.
„ f f " s8 ,
' •" ** * 9 *
^ ^ 9" "
7 % * *
f.- •'/ ' • •' •
* . . '•. . '• .
;:C 1 ;'i:
* • ^ * • *
% * **
'• fl « *
« * i
:. '/ >•• :
* ^ . »
*s • » 9
' s • 9 ^ » a
• • • • e
• x „
• * . • .
• . •
»"* ^*o »"*
• ."• •! . *'•
' ' .'« .."'• '' i'
• • *• . ' ,'
•''•'.
*a ° 9 *
*• ..
•».{ / ' ' ,'••
\ ? • .
•:° / . '•
• . '••' S •• :'•
* « • * * •
- * .** „» fl
-------
-13-
FLY ASH CONCENTRATION (g/l)
O
o
o
3 (D
M
rt p>
rr rt
(D H«
o
W 3
M 0)
C Zf
M- H-
n "0
n>
cr
s; ro
ft) rt
rt f>
ro n>
H ro
• 3
rt)
*a
c
S3
a.
rt
s*
ro
n
o
3
r>
ID
3
rt
l-l
O
3
O
i-h
CD
(A
ff
X
C
00
>OD<
3212 IS 32
a a a a
3.3.3.3.
moc->
O
-------
SECTION 5
pH ADJUSTMENT OF ASH SLUICE WATER
The pH of ash pond effluents may be adjusted by (1) controlling the
ash-to-water ratio for ash sluicing, (2) combining ash pond effluents
with other waste streams within power plants, or (3) adding chemicals.
Various titration curves of acid and alkaline ash pond effluents
from TVA steam plants are shown in Figures 6 and 7. The quantity of
chemicals required for neutralization of acidic effluents is relatively
small, and the increase in the concentration of total dissolved solids
is insignificant (usually less than 60 mg/1). However, the amount of
chemicals required for neutralizing alkaline effluents is relatively
large, especially when considering the large volume of ash pond dis-
charges, and the increase in total dissolved solids concentration may be
as much as 300 mg/1.
NEUTRALIZATION OF ACIDIC ASH POND EFFLUENTS
The degree of acidity of ash sluice water is affected by the ash
concentration during sluicing. Therefore, the alkaline reagent require-
ment for neutralization is also affected. Figure 8 shows that the
caustic soda requirement for adjusting the pH of acidic ash sluice
water is related to the ash-to-water ratio.
The acidic pond effluents can be treated by a technique commonly
used for water and wastewater treatment throughout the industry. Lime,
limestone, soda ash, or caustic soda can be added to raise the pH of
acidic effluent to 6 and above. The choice of the alkaline reagent
depends on the volume of the effluent stream, variability of pH, and
price of the neutralizing alkali. The basicity and costs of the acid-
neutralizing methods and agents are compared in Table 6. Lime is used
most often, despite the frequent formation of precipitates or suspended
solids, which must be removed by sedimentation at the end of the flow
through ash ponds before the effluents are discharged to receiving
waters.
NEUTRALIZATION OF ALKALINE ASH POND EFFLUENTS
The acid requirement for neutralizing alkaline ash pond effluents
is also related to the ash-to-water ratio, as shown in Figure 9. Strong
acids or C02 can be used to neutralize the alkaline ash pond effluents.
-22-
-------
1.0
10-0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
PLANT J
PLANT A
SAMPLE VOLUME* 100ml
3.0% suspended solids
present in ash transport
• I I
0.0
1.0
2,0
3.0
4,0 5.0 6.0 7,0
8.0
VOLUME 0.023N NaOH (mt)
Figure 6. Titration curves of acidic ash pond effluents
from TVA steam plants.
-23-
-------
C
X
o.
-e-
11.0
10.0
9.0
8.0
70-
6.C-
5.0
4O-
30-
0.0
SAMPLE VOLUME = 100ml
3.0% suspended solids present in
ash transport water.
-o
PLANT
B
E
F
-0-
-D-
I (NORTH OUTFALL)
I (SOUTH OUTFALL)
K
L
2.0 4.0 6.0 8.0 10-0 12.0
VOLUME 0.02N H
14.0
(ml)
16.0 18.0 20.0 22,0
Figure 7. Titration curves of alkaline ash pond effluents
from TVA ste^m plants.
-------
12
i — i
W
'E
3
I
Q.
to
Ul
1
i — i r
(0.5)
Sample Volume = 100 ml
( ) = % suspended solids present
in ash transport water
(3.0)
Figure 8.
VOLUME O.O183N NoOH (ml)
Neutralization of acidic ash sluice water with base (ash-water contacted
for 1 h and not separated before neutralization).
-------
TABLE 6. BASICITY AND COST COMPARISONS OF VARIOUS ALKALINE AGENTS3
NaOH (76% Na20)
Na2C03 (58% Na 0)
MgO
High-calcium hydrated lime
Dolomitic hydrated lime
High-calcium quicklime
Dolomitic quicklime
High-calcium limestone
Dolomitic limestone
Cost, $/ton
(approx.)b
290
87
140
33
120
33
120
12
12
Basicity
factorb
0.687
0.507
1.306
0.710
0.912
0.941
1.110
0.489
0.564
Cost, $/ton
of basicity
422
172
107
46
132
35
108
25
21
aBased on 1978 cost quotations.
aV3ilable for neutralization (grams of equivalent
-26-
-------
I
NJ
CO
4J
•H
§
O,
Sample Volume = 100 ml
( ) = % suspended solids
present in ash transport
water
20 30
VOLUME 0.02N H2S04 (ml)
Figure 9. Neutralization of alkaline ash sluice water with acid (ash-water contacted
for 1. h and not separated before neutralization).
-------
Strong Acid Treatment
A common method of neutralizing alkaline wastes is to feed sulfuric
acid into the waste stream. Techniques and equipment are commercially
available to monitor the effluent pH and automatically control the
sulfuric acid feed. The sulfuric acid reduces the pH by reacting with
the hydroxide and carbonate ions present in highly alkaline water.
Neutralization by adding sulfuric acid is ecologically acceptable
because the reaction products are primarily sulfate compounds, which are
relatively innocuous to biota and are normally present in natural waters.
The chief disadvantage of using sulfuric acid is safety-related, (sul-
furic acid is a highly corrosive, strong oxidant that is hazardous to
handle). In the case of equipment malfunction, the pH of the effluent
stream could drop to extremely low values with the potential for adverse
environmental impact. The sulfuric acid storage facilities should also
be located within a diked area capable of retaining 110 percent of the
storage capacity.
Carbonation
An alternative method of neutralizing alkaline wastes is to add
carbon dioxide (C02) to the waste disposal pond. This process is more
acceptable from two standpoints: (1) In the case of equipment malfunc-
tion, the pH of the effluent stream will not drop below about 4.5, thus
minimizing ecological damage; and (2) the cost of treatment is somewhat
less. Carbon dioxide has been used by municipal water treatment plants
to recarbonate and neutralize water after the softening process. The
softening process involves the addition of excess lime, resulting in
conditions similar to the conditions to be expected in the ash disposal
ponds.
Two methods available for adding C02 to the ash pond are (1) onsite
generation of C02 by burning a fuel such as oil, natural gas, or coke,
and (2) the purchase of commercial C02 as a bulk liquid. The yield from
the combustion process varies from 12 to 18 percent C02, depending on
the type of system and fuel used. The combustion process involves more
equipment (generally a compressor and scrubber, drier, etc.) than does
the use of commercial C02. In addition to the cost of equipment for
onsite generation of C02, other problems remain. The gas provided by
combustion is corrosive and relatively impure, increasing the need for
equipment maintenance. Also, the nitrogen associated with the C02 from
the combustion process reduces the solubility rate, thereby requiring
greater water contact time in the basin.
Adjustment of C02 production in a generator is moderately diffi-
cult and time consuming. Considerable care must be exercised to main-
tain conditions that will assure complete combustion. Natural gas is
almost universally used for C02 generation. Current prices and availa-
bility without interruption during cold weather may require a more
expensive second or standby fuel supply. At best, generation of C02 for
Carbonation is a process that is difficult to control; it requires
-28-
-------
considerable operator attention and maintenance over the useful life of
the equipment. For these reasons, the use of commercially available
bulk liquid C02 appears to be a viable method for adding C02 to effluents.
An alternative method, similar to the onsite generation of C02,
is the use of plant stack gases as a source of C02 for neutralizing ash
pond effluents.
There are two general methods of carbonating water with bulk carbon
dioxide:
1. The most common practice is to admit C02 to the bottom of the
basin through 3/4- to 2-in.-diameter (1.9- to 5.1-cm-diameter)
piping. The gas is diffused by a distribution grid of per-
forated pipe with 1/16- to 3/32-in. (0.16- to 2.38-cm) holes
on 6- to 12-in. (15.2- to 30.5-cm) centers, with the holes
pointed downward to obtain a reasonable dispersion of the gas.
A line of porous ceramic tubing suitable for C02 diffusion is
also commercially available. Pipeline regulators are used to
reduce the receiver pressure of 240 to 300 psig (17.3 to
21.4 atm) to a flowmeter-calibrated pressure of 50 psig
(4.4 atm).
2. A more sophisticated technique of adding C02 to water entails
the use of a V-notch C02 feeder, which carbonates an auxiliary
stream of water, which is then piped to the basin. These
feeders are available in capacities of up to 1500 Ib (680.4 kg)
of C02 per day. Most models are suitable for modulating C02
flow in direct relationship to the water processing rate and
eliminate the need for diffusion grids in the basin.
Little information has been published on the efficiency of C02
absorption systems, and an estimate of the cost of C02 on a per-pound-
absorbed basis is difficult. An absorption efficiency of 98 to 99 per-
cent can be achieved in a recarbonation process by using liquid C02,
and absorption efficiencies in the range of 12 to 18 percent can be
achieved for combustion-generated C02 because of the low percentage of
C02 in the gas produced in the combustion process. Figure 10 shows the
laboratory result of neutralizing an alkaline ash pond effluent with
liquid C02•
Combining Streams
A third method of neutralizing the alkaline ash pond discharge at
TVA plants involves reaction of the ash pond effluent with the incoming
cooling water by feeding the ash pond effluent into the condenser cool-
ing water at the condenser inlet or discharge channel. The alkaline ash
pond effluent reacts with the carbon dioxide and bicarbonates naturally
present in cooling water, resulting in neutralization of the excess
alkalinity present in the ash pond effluent and a slight increase in
the pH of the cooling water. Ash pond effluents treated by this method
would meet the present water quality limitations.
-29-
-------
o
w
4J
•H
§
w
a.
10 20 30 40 50 60
INCREASED TOTAL CARBON DIOXIDE CONCENTRATION IN WATER (mg/1)
70
Figure 10. Neutralization of an alkaline ash pond effluent with liquid
carbon dioxide.
-------
In the case of combining ash pond effluents with condenser cooling
water, the ash pond effluents would meet all.the concentration-controlled
pollutant limitations (e.g., total suspended solids and oil and grease)
before it is introduced into the cooling stream. The only parameter
being affected is the pH, which is not controlled on a basis of con-
centration times flow. Although pH is not considered a pollutant as
such, it is controlled within a range that is not detrimental to biota
in the discharge area of the receiving waters.
Reuse of ash pond effluent by feeding it into the condenser inlet
or discharge has many practical advantages as well as the obvious eco-
nomic value of eliminating the need for costly chemical treatment of ash
pond effluents.
The mixing of alkaline ash pond effluents with cooling water does
not generate significant additional dissolved solids, as occurs in
chemical treatment, e.g., sulfuric acid and C02 treatment methods could
add as much as 300 mg/1 and 100 mg/1 of dissolved solids, respectively,
to existing concentrations in effluent streams. The chemical reactions
that occur when the streams are combined involve reactants already
present in the water and result in a slight increase in reaction pro-
ducts also already present in the cooling water. The primary reactions
that take place are shown by two equations:
2 OH" + C02 •» C03~2 + H20, (3)
and
OH" + HC03~ * CDs"2 + H20. (4)
As shown by the equations, the hydroxide ions in alkaline ash pond
water react with carbon dioxide and bicarbonate ions present in cooling
water to form carbonates. The neutralization of alkaline ash pond
effluents with once-through cooling water has been investigated through
bench-scale tests. The water quality of once-through cooling water is
the same as that of river water. The maximum necessary ratio of cooling
water to alkaline ash pond effluents from TVA steam plants was about 10
to 1 to reduce the pH of alkaline effluents from about 11 to 9 (Figure 11).
For a once-through cooling system, the cooling water available is adequate
to neutralize ash pond effluent. To reduce the pH of alkaline effluents
to 7.5, a reduction that may be needed to meet the quality criteria for
cooling system makeup water, the necessary blending ratio for a cooling
tower system would have to be greater than 50 to 1. Usually, the amount
of effluent from ash ponds is greater than that used for mixing with
cooling tower makeup water. Thus, only part of the alkaline effluent
could be reused in the cooling tower system.
Changing the pH of cooling water would affect the total C02 (car-
bonic acid, carbonate, and bicarbonate) concentration present in the
water. Fish and other aquatic life are sensitive to this balance in
-31-
-------
50°
u
Q
2
O
Q.
X
V)
cr
LJ
O
2
_J
O
O
o
X
o
Z)
o
K.
o
o
100 -
PLANT E
-- PLANT F
PLANT I
PLANT K
— PLANT L
9.0 9.5
pH (units)
10.0
10.5
11.0
Figure 11. Neutralization of alkaline ash pond effluents
with once-through cooling water.
-------
water. However, the actual effect of pH change in cooling water is a
small increase in the bicarbonate concentration and a small decrease in
the carbonic acid concentration. These small changes would not
measurably affect aquatic biota.
A small benefit may be derived from the reuse of ash pond effluent
because the change in pH and bicarbonate ion concentration may offset
the decrease in pH caused by chlorination of the condenser cooling
water, thus reducing the corrosion of condenser tubes and the release of
heavy metals such as iron, copper, nickel, and zinc. This effect would
be small, but nonetheless may be beneficial when the overall effect of
numerous installations is considered.
The major benefits of reusing the ash pond effluent in the feed to
the condenser are economic. The benefits of essentially eliminating
treatment costs and eliminating the need for adding treatment chemicals
to the discharge with no potential adverse ecological effects makes the
reuse of ash pond effluents as feed to the condenser cooling water the
most practical method available.
-33-
-------
SECTION 6
ASH SETTLING
In the course of treating ash sluice water, both "discrete particle
settling" and "flocculent settling" take place. Because of the gen-
erally high ash concentration in ash sluice water, with interaction and
agglomeration of the ash particles, flocculent settling first takes
place. Discrete particles settling then occurs for the remaining ash
particles and can be analyzed by means of the classic laws of sedi-
mentation formulated by Newton and Stokes.54 The terminal settling
velocity of discrete particles is a function of particle size and den^
sity. In the design of a settling pond, the usual procedure is to
select a particle with a terminal velocity and to design the basin so
that all particles that have a terminal velocity equal to or greater
than the specified terminal velocity will be removed. When flocculation
occurs, both overflow rate and detention time become significant factors
for design. Obviously, the degree of flocculation will be influenced by
the initial concentration of suspended solids. The design of ash settling
tanks or ponds should include laboratory ash settling analysis of both
discrete and flocculent settling behavior. In all cases, one has to
account for turbulence, short circuiting, and other interferences that
do not occur in the laboratory. Short circuiting in tanks or ponds can
be characterized by tracer techniques. The introduction of a plug of
dye, salt, or radioactive material into the inlet gives a concentration
distribution in the effluent stream that is characteristic of the flow
patterns.
PARTICLE SIZE DISTRIBUTION OF ASHES USED FOR SETTLING TESTS
At plants A and E, all the fly ash is collected by electrostatic
precipitators. At plant J, the fly ash is removed from stack gas by
mechanical collectors followed by electrostatic precipitators. Table 7
shows the size distribution and specific gravity of fly ashes that were
collected at these three different steam plants. The specific gravities
fall into the range of 2 to 3, except in the size fractions of large
particles. The reason for this low specific gravity of large particles
may be that the large particles contain some cenospheres. These ceno-
spheres do not settle, but float on the top surface of settling columns.
Removal of cenospheres was not considered in this settling study.
The cumulative particle size distribution of fly ashes used for
this study is shown in Figure 12. For fly ashes collected by electro-
static precipitators, there were more than 50 percent of the particles
less than 10}jm; however, for fly ashes collected by mechanical collec-
tors, there were about 50 percent of the particles greater than 40 |jm.
-34-
-------
TABLE 7.
Particle size (pra)
Plant J -
<6.4
6.4 - 9.2
9.2 - 12.9
12.9 - 17.3
17.3 - 23.5
23.5 - 27.3
27.3 - 38.0
>38.0
Plant J
<3.3
3.3 - 6.5
6.5 - 9.6
9.6 - 13.4
13.4 - 18.3
18.3 - 29.9
>29.9
Plant E
<3.1
3.1 - 5.9
5.9 - 8.9
8.9 - 11.8
11.8 - 16.1
16.1 - 21.1
21.1 - 23.1
23.1 - 44.0
>44.0
Plant A
<3.0
3.0 - 5.8
5.8 - 9.0
9.0 - 11.5
11.5 - 16.9
16.9 - 22.0
22.0 - 30.8
30.8 - 44.0
>44.0
FLY ASH PARTICLE SIZE ANALYSIS
Weight fraction Specific gravity
mechanical collector (cyclone)
0.044 2.28
0.047 2.43
0.089 2.34
0.128 2.40
0.109 2.31
0.032 2.35
0.033 2.55
0.518 1.63
- electrostatic precipitator
0.269 2.23
0.245 2.17
0.181 2.21
0.142 2.14
0.107 2.14
0.041 1.59
0.015 *
- electrostatic precipitator
0.237 2.56
0.134 2.67
0.103 2.60
0.096 2.80
0.073 2.77
0.062 2.85
0.022 2.58
0.056 2.66
0.196 1.80
- electrostatic precipitator
0.195 2.56
0.171 2.77
0.140 2.53
0.132 2.91
0.103 2.52
0.108 2.64
0.039 2.45
0.044 2.83
0.068 2.13
Not analyzed.
-35-
-------
100
c_>
I-H
H
O
CO
CO
a
o
CJ
A Plant E
Plant J
ICO
PARTICLE DIAMETER (pm)
Figure 12. Particle size distribution curves of fly ashes used for settling test.
-------
The fly ash collected by electrostatic precipitators at plant J was the
finest because most of the coarse particles were removed by mechanical
collectors ahead of electrostatic precipitators. The particle size dis-
tribution curves of fly ashes collected by electrostatic precipitators
at plants A and E were lower than that of fly ash collected by mechani-
cal collectors at plant J, because both coarse and fine fly ashes were
collected by electrostatic precipitators at Plants A and E.
A sample of bottom ash was obtained from plant J. Grab samples
were collected at the end of bottom ash sluice pipe at 5-s intervals
during sluicing; all samples were then combined. The particle size
distribution and specific gravity of the bottom ash were analyzed,
and the results are given in Table 8. The particle size distribution of
bottom ash from plant J ranged from about 0.075 to greater than 2 mm,
and the specific gravity was about the same as that for fly ash.
The fly and bottom ashes collected from plants A, E, and J were
used for the settling study.
ASH SETTLING CHARACTER
Settling studies were carried out by using a column with five
sampling ports, as shown in Figure 13. Fly ash collected from the
electrostatic precipitators or mechanical collectors was weighted
and soaked in tapwater in a bucket; it was then poured into the column,
where the tapwater was mixed by a stirrer. The ash-water mixture was
then mixed for a few minutes to achieve complete mixing, and samples
were taken from ports 1, 3, and 5 to determine the initial suspended
solids concentration. As soon as the stirrer was turned off, the
settling study started and the samples were taken from the five ports
at various time intervals. The time interval after the stirrer was
turned off is defined as t, the time of ash settling, and is independ-
ent of depth. The time intervals selected for this study generally
ranged from 10 minutes to approximately 9000 minutes.
A typical plot of settling curve of suspended solids concen-
trations at five different depths versus settling time is shown in
Figure 14. The sharp drop of suspended solids concentrations at the
initial period indicates a hindered-zone settling behavior at this
initial high concentration of suspended solids (48,000 mg/1). The
zone (defined as an interface between the flocculent particles and the
clarified supernatant) settled at a uniform velocity under conditions of
hindered settling, and the velocity is a function of the concentration.
Unfortunately, the interface between the particle-liquid zone was not
visible because of the very fine particles remaining in the clarified
zone, which made it impossible to monitor the position of the interface
to study the clarification capacity. Instead, a graphical method was
used to find the velocity of the interface, as shown in Figure 15, where
the suspended solids concentration was plotted as a function of the
reciprocal of the settling veolcity t/z (t is again the time of ash
settling and z is the vertical distance of ash settling measured from
the water surface). This figure clearly shows the settling behavior
-37-
-------
TABLE 9. SIZE DISTRIBUTION OF BOTTOM ASH FROM PLANT J
Ash size (pm)
>2000
2000-420
420-147
147-75
<75
Weight percent
45.6
40.4
9.4
2.6
1.8
Specific gravity
a
2.17
2.35
2.23
2.38
ntery heterogeneous as to size and porosity—specific gravity
not run.
-38-
-------
SAMPLING PORTS
51—
diameter
1 ft
Figure 13. Quiesent settling column with sampling ports
(1 ft = 30.48 cm).
-39-
-------
SUSPENDED SOLIDS CONCENTRATION (mg/1)
§3 3
o 3 <
3 H
CL O
£3
-3
C-1
°, O o > n ^
£- O O O O O
CO ?d ?3 53 ?u ?d
i-3 ;-3 H -3 H
O
2
00
n pco
j i i i i 111
DD>
0
D
<>
n
n 4p
coo
1 1 1 1 1 1 1
-------
SUSPENDED SOLIDS CONCENTRATION (mg/1)
CC < C/l
3! — ?.
•O O T3
(5 T O
3—3
C- I-T —
(,-. -! V.
O
n a; o
3-33
o,
a —
=• -3
3 «
rr o
rf
t-i rt
H- 3
a TO
— p—
1
h
1 — I — 1 1 1 II I
^r
P
i-
1 — I — 1 1 1 i 1 1
o
O
o
D
o >
. 7T
ll
o o
3 •
^-' ^
J_l
1_J 111!
i I I
-------
of the zone so that its settling velocity can be determined graphically
by finding an intersection point of two lines described in the figure.
Jn *oJ/- / t(2 31 this point ls denoted as k, which is 19 min/ft
(0.6234 mm/cm). The settling velocity of the zone is the reciprocal of
k at that point of 0.0526 ft/Bin (1.604 cm/min)..
in tJ*Jf?USPr?ed S^ldS fncentration of less than 30 mg/1 is desired
in the effluent from the sedimentation basin, this will depend on the
degree of fine ash particle settling after the zone settling. An
attempt was made to use concepts of discrete particle settling and floccu-
lent suspention, developed by Camp55 and O'Connor and Eckenfelder 56
respectively, to estimate the removal efficiency of sedimentation'
basins. This attempt was not successful because the concentration
gradient over depth was too shallow to get either a meaningful settling-
velocity analysis curve by Camp's method, especially at the low settling
velocity, or meaningful isoconcentration lines by the O'Connor and
Eckenfelder method. For low suspended solids concentrations (less than
luu fflg/lj, the slope of the settling-velocity analysis curve was too
fnr A.??.,** 8l°£eVf tlie isoconcentration lines were too steep to use
for estimating the fractional removal.
Therefore, a new approach was developed to interpret the fly ash
settling data in this study.
As the interface of settling zone passes a certain point, the
suspended solids concentration will change at this point at a drastic
rate, but will then rapidly slow down after the interface passes. The
profile of the suspended solids concentration versus settling time is
assumed to be a straight line. This assumption is accurate enough to
analyze the settling data and tire-dirt- th^ nov^/^ma^.,, ~* ~ «_j_- *.-*.•
nn -8 a? an Predl0t the P«*>»«ce of a sedimentation
tank, especially if the low suspended solids concentration range is of
prime interest. For low concentration of suspended solids, the rate of
ash settlin is ver
ash settling is very slow.
This concept was applied to the data in Figures 14 and 15 to gen-
erate Figure 16, where the suspended soldis concentration was plotted as
IfS!CS!n-°I Y6W T uaMe' t " kz> Which indicates the time measured
after the interface of hindered settling zone passed the settling depth z
Here k is a value obtained from Figure 15. Figure 16 clearly describes
a well-defined relationship for all of the data, which were obtained
from five different ports.
The theoretical retention time, t,, requirement for ash settling
can be determined by the following equation:
. DA
where d" Q
D = depth of sedimentation basin or pond,
A = area of sedimentation basin or pond, and
Q = flow rate of ash transport water into a sedimentation basin or
pond.
-42-
-------
00
6
g
§
O
z;
O
1-1
O
tn
Q
O
PH
1/1
10'
10
10
n 11 r~i—i—r
'0
0 PORT I
O PORT 2
n PORT 3
A PORT 4
O PORT 5
CQ • 48,000 mg/1
k - 0.6236 rain/cm
A
0L
LULL.L-J..
in
.J
10
II I. I I I J L_
2
M I I I I I L
10
10
t - kz (min)
Figure 16. Suspendc-d solids concentration vs. t - kz (electrostatic
preclpitator Tly ash from plant J; initial suspended solids
concentration CQ = 48,000 mg/1).
-43-
-------
In Figure 16, the data can be described by a straight line. The relation-
ship of instantaneous suspended solids concentration in effluent to any
instantaneous settling time t and vertical settling depth z can be
expressed as below:
In C = a In (t - kz) + In b, (6)
where
C = suspended solids concentration, mg/1
a,b - constants.
For these specific data, a and b are found to be -1.0546 and 31,000,
respectively. Then the average suspended solids concentration in the
effluent, C , over the whole depth of the settling basin or pond at a
retention time t, will be
d
Ceff = 5 4 Cdz = kDcfelJ tt/+1 - (td - kD)a+1],
where td > kD and a ^ -1.
This approach is also valid even for the case where the data follow
piecewise straight lines for concentrations of suspended solids below
100 mg/1.
For some cases where the data follow a straight line on a semilog
paper, the relationship of an instantaneous suspended solids concentra-
tion in effluent to any instantaneous settling time and vertical settling
depth can be expressed as
C = a In (t - kz) + b. (9)
Similarly, the average suspended solids concentration in effluent will
be
Ceff = 5 'o Cdz>
or
Ceff = b - £D C(td - kD) ln ™- (11)
-44-
-------
If the data do not follow the above mathematical equations,
the average suspended solids concentration in effluent still can be
estimated by segmenting the depth of sedimentation basin. If the
depth of basin is segmented by the positions where the sampling ports
are located in Figure 13, then the suspended solids concentration in
effluent can be approximated as
where
C. = average suspended solids concentration of C. and Ci+^ at
1 t = td, mg/1,
C.=: suspended solids concentration at z = z., mg/1.
i r 3-
C. is obtained from Figure 16 by reading C. and Ci+1 at (td - k.^z)
and (t. - k. ..z), respectively, after drawing a smooth curve to cover
the settling data.
To invesigate the effect of initial concentration of suspended
solids on settling, two additional experiments using different
initial concentration (C ) were performed and the results are shown
in Figures 17, 18, 19, aBd 20, Although all these cases yielded
straight lines in plots of suspended solids concentrations versus t - kz
(Figures 16, 18, and 20), it was not possible to determine any general
trend on the effect of C . A more extensive study is needed to deter-
mine this trend and express it in a mathematical relationship, which
will allow prediction of the settling performance for a given initial
suspended solids concentration. A qualitative analysis is described
later in this report.
Similar experiments were conducted for the ashes collected by the
electrostatic precipitators at plants A and E; the results and analyses
are shown in Figures A-l through A-12 in appendix A. The settling of
these ashes showed piecewise straight lines on plots of suspended solids
concentrations versus t - kz except in Figure A-12. Table 9 shows
the values of constants that were obtained from the graphical methods
and figures. These constants can be used to estimate the suspended
solids concentration in effluent from the sedimentation basin by using
Equations 7, 10, or 12.
-45-
-------
ff
o
M
H
O
u
o
en
Q
•s.
Hi
en
10'
u 11 i i ~i—i—r
10
10
- A
a
O
-i nil — i — i
O PORT 1
£] PORT 2
A POKT 3
O PORT 4
<£> PORT r)
C() = 30,000 mg/1
k - 0.4429 min/cm
A
A OO
i i i i i i i i
k = 13.5 min/ft
.4429 min/cm)
i i l i i
10
10
10
10
10
10
10
SETTI.INC; UMrc/SKmiNO DEPTH, t/z (min/ft)
Figure 17. SuHpondod solids concentration vs. the reciprocal of settling
velocity (electrostatic precipitator Ply ash from plant J; initial
.suspended solids concentration GO = 30,000 mg/1).
-46-
-------
Sfl
o
1
o
u:
tl
'^j
fj
o PORT 1
OVORT 2
Dl'ORT 3
APORT
APORT 5
CQ = 10,000 mg/l
k = 0.4429 mln/cm
t - kz (rain)
Figure 18. Suspended solids concentration vs t - kz (electrostatic precipitator
fly asli from plant J; Initial suspended solids concentration
C0 = 30,000 mg/l).
-47-
-------
io4
10
e
~
M
H
X
U
§ y
u io2
to
a
0
us
p
w
to
s~>
C - 8900 mg/1
— o
I k - 0.1969 min/cm ;
/
_
o
- n£
0 A /
n /
A R/
0 a AzXOf
r ^
a A
A OA
-o a° ^ 0
D 0
_
: O
-
- A
O
_
-
f
-
:
-
-
—
_
-
-
_
-
k = 6 min/ft
(0.1969 min/cm)
Ll.l. 1 1 1 1 1 | 1 1 1 I i I I II I i*i 1 1 1
u
10A
)
3
10
io2
10
1
io3 io2 10
SETTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure 19. Suspended solids concentration vs. the reciprocal of settling
velocity (electrostatic preclpitator fly ash from plant J;
initial suspended solids concentration Cfl = 8900 mg/1).
-48-
-------
10
10
10
•a,
o
g
O
V)
o
H
10
10
i i i i r 11 i i i i i i r
O PORT 1
APORT A
OPORT 5
C = 8900 mg/1
k *•• 0.198 ratn/cm
O
D
i I I I I ...I I I I I I I I I 1 L
10
10
10
10
10
t - kz (min)
Figure 20. Suspended solids concentration vs. t - kz (electrostatic precipitator
fly ash from plant J; initial suspended solids concentration CQ = 8900
mg/1).
-49-
-------
- TABLE 9. VALUES OF CONSTANTS FOR SETTLING CURVES
Plant
J — electrostatic
precipitator
E — electrostatic
precipitator
A — electrostatic
precipitator
J — mechanical
collector
South Chlckamauga
Creek
- — ~. •• _
*
R = t - kz.
C0
(mg/1)
48,000
30,000
8,900
35,000
35,000
22,000
22,000
5,800
5,800
31,000
31,000
18,000
18,000
6,000
30,000
30,000
17,500
17,500
4,500
140
Equation
used
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
(9)
=r
Range of R* k
(min) (rain/cm)
R>10
R>10
R>10
60.5>R>5
R>60.5
200>R>10
R>200
70>R>10
R>70
200>R>5
R>200
280>R>10
R>280
R>5
180>R>10
R>180
250>R>10
R>250
R>5
R>10
0.6234
0.4429
0.198
0.3117
0.3117
0.2364
0.2364
0.1101
0.1101
XJ.5414
0.5414
0.4593
0.4593
0.1773
0.2198
0.2198
0.1837
0.3837
0.16404
0.19685
**
Constant
a b
-1.0546
-0.9895
-0.8373
-0.5374
-0.2904
-0.8480
-0.0774
-0.6052
-0.2973
-0.8722
-0.5321
-0.9064
-0.424
-0.8466
-1.1431
-0.4175
-1.0524
-0.5222
-0.9798
18.559
31,000
5,300
1,950
770
275
2,100
35
850
230
9,100
1,500
11,000
720
2,600
17,200
3,900
11,200
590
8,700
174.9
**Units for constants a and b are mg/l-min and mg/1,respectively.
-50-
-------
\
Results of the settling studies on fly ash collected by mechanical
collectors or cyclones at plant J are shown in Figures A-12 through A-18.
The settling velocity of hindered zone of this fly ash was about twice
as fast as that collected by electrostatic precipitators at CQ = 30,000
mg/1 (compare k values in Figure 17 and A-13 and in Table 9). This
increased velocity is expected because the larger and heavier particles
are collected by cyclones. However, the mechanically collected fly ash
showed a slower settling behavior in the clarified zone (the zone behind
the hindered settling zone) than did the ash collected by the electro-
static precipitator (Figures 18 and A-14). This difference in settling
behavior is quite interesting if the wide differences in particle size
distribution (Figure 12) between the two ashes are considered.
The difference in settling behavior illustrates again that the very
fine particles play a major role for achieving a low suspended solids
concentration of the effluent from the clarification process, since the
relatively heavier particles are removed at the initial stage through
hindered-zone settling. In Figure 12, less than 30 percent of fly ash
particles collected by electrostatic precipitators are greater than
20 [Jm, whereas more than 60 percent of fly ash particles collected by
mechanical collectors are larger than 20 |Jm. The hindered-zone settling
of ash collected by the electrostatic precipitators seems to entrap more
fine particles than that of the ash collected by mechanical collectors,
thus leaving a lower concentration of suspended solids behind the zone.
This entrapment phenomenon could result from the fact that the coarser
particles of mechanically collected ashes had less chance of interaction
with the finer particles because of the fewer particles and the less
contact time, or settling time, than did the ashes collected by electro-
static precipitators. Examination of Figures A-14, A-16, and A-18 for
the settling of mechanically collected fly ash shows that the data do
not differ much, except for the low suspended solids concentration,
whereas data for the electrostatic precipitator fly ash vary signifi-
cantly. This may indicate that the hindered settling zone only minimally
affects the initial removal of fine particles in mechanically collected
ash, whereas it significantly affects the settling of ash collected by
electrostatic precipitators.
The velocity of hindered settling zone (reciprocal of k) decreased
with the increase of initial suspended solids concentration, as shown in
Figure 21.
To investigate the applicability of this graphical approach to the
settling of suspended solids in river water, a sample was collected from
the South Chickamauga Creek, Chattanooga, Tennessee, after a rainfall
and a settling study was conducted by placing the sample in a settling
column. The movement of hindered settling zone could hardly be observed
in this case, as shown in Figure 22. The rate of sedimentation was
relatively slow, probably because of the fine silt, clay materials, and
other low-density materials present; it took more than two days to
reduce the suspended solids concentration to 30 mg/1. By estimating
-51-
-------
14
12
•H
1C
O
N 8
i-i
H
j? 6
W
M
Pn
O
M
O o
o 2
FLY ASH
O Plant A - Electrostatic precipitator
A Plant E - Electrostatic precipitator
O Plant J - Electrostatic precipitator
Plant J - Mechanical collector
I
10 20 30 40 50
INITIAL SUSPENDED SOLIDS CONCENTRATION (g/1)
60
Figure 21. Velocity of the hindered settling zone
vs. the initial suspended solids concen-
tration of ash settling.
-52-
-------
10
I
Cn
CO
CO
Q
t-i
$
tn
W
Pu
CO
10
io2
10
1
1 1 1 1 1 Ml
E~ '
K
-
-
•
r-
"
k
(0.
1
1 1 1 1 1 1 II
5JH3^A^L^3-_
= 6 min/ft
1969 min/cm)
i i i i i i 1 I
n 1
[ 1 1 — 1 Mill
0
OA o
XV D°
OA n
OA
<
1 1 1 Mill
co
k
o
o
on o
C>A ° D
OA ° n
1 1 1 1 1 1 1.
0 PORT 1
D PORT 2 ~
O PORT 3
A PORT 4
O PORT 5
= 140 mg/1
» 0.1969 min/cm
o
o ___
1 1 1 1 1 1 1 1
2
10
10
1
o2 io3 10* ioj
SETTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure 22. Suspended solids concentration vs. the reciprocal of settling
velocity (river water from South Chickafflauga Creek; initial
suspended solids concentration Cn = 140 mg/1).
-------
the best k value (Figure 22), it was found that the suspended solids
concentration followed Equation 9, as shown in Figure 23. Whether this
slow settling resulted from the different nature of suspended solids
present or from the very low initial suspended solids concentration (140
mg/1), or both, is not clear. The constants for Equation 9 are shown in
Table 9, and the effluent concentration of the sedimentation basin can
be estimated by Equation 10.
The effect of initial concentration of suspended solids on the
behavior of zone settling was studied by conducting a series of experi-
ments on the lower initial suspended solids concentrations (390 to
3800 mg/1) of electrostatic precipitator fly ash from plant J. The
results are shown in Figures A-19 through A-24. The settling rate was
greater for the higher than for the lower initial concentrations of
suspended solids in this range (390 to 3800 mg/1); these results are
Opposite to the previous cases for which the initial suspended solids
concentration was high (8900 to 48,000 mg/1) (Figures 15 through 20).
The behavior of hindered zone settling seems to become less evident for
initial concentrations of suspended solids less than 8900 mg/1.
Examination of settling data over the concentration range of 390 to
48,000 mg/1 (Figures 15 through 20 and Figures A-19 through A-24) show
the degrees and changes of particle interaction for different initial
concentrations of suspended solids. Up to 8900 mg/1 the increase in
suspended solids concentration enhances the settling rate, probably
because of the flocculating type of interaction in which large particles
become even larger by colloiding with the small particles. However,
the suspended solids concentration is still not high enough to form
a hindered settling zone. As the suspended solids concentration
increases further, however, the settling rate is reduced because of the
increase in hindrance and the formation of a hindered zone. This is
shown in Figures 16 and 18 for suspended solids concentrations of 48,000
and 30,000 mg/1, respectively.
At this higher concentration of suspended solids, (greater than
8900 mg/1), more water is displaced by settling in the hindered zone.
Therefore, behind the hindered settling zone, the relatively high dis-
turbances induced by the flow of displaced water can prevent the residual
fine ash particles from settling. The poorer settling of fine particles
for very high and very low initial suspended solids concentrations indi-
cates that an optimum initial concentration gives the best settling.
For the case of electrostatically precipitated fly ash from plant J, the
optimum initial concentration for suspended solids seems to be about
8900 mg/1. This optimum initial concentration of suspended solids
appears to be a point at which the suspended solids concentration is
(1) high enough to provide the particle interaction necessary for
the formation of larger particles, and (2) low enough to reduce the
turbulence resulting from the rise of displaced water caused by the zone
settling at high concentrations of suspended solids.
-54-
-------
140
120
(100
80
1 1 till
T—I—I 1 11
u
CO
.J
«60
E
(X
K)
g
40
20
Ttr
J I I I I I
T—i—i i i » r
0 PORT 1
D PORT 2
O PORT 3
A PORT 4
O PORT 5
C0 = 140 mg/1
k = 0.1969 min/cm
O
I I I I
J I I I I 14
10
t - kz (rain)
Figure 23. Suspended solids concentration vs. t - kz (river water from South
Chickamauga Creek; initial suspended solids concentration CQ = 140 mg/1).
-------
A similar result was observed in settling of the mechanically
collected fly ash from plant J, as shown in Figures A-25 and A-26. The
degree of hindrance was reduced at an initial suspended solids concen-
tration of 3000 mg/1 (Figure A-25), as compared with the previous cases
where the initial suspended solids concentrations were 30,000 17 500
and 4500 mg/1 (Figures A-13, A-15, and A-17). At the initial suspended
solids concentration of 3000 mg/1, more fine particles escaped from
the hindered settling zone (Figure A-26) than in the previous cases
(Figures A-12, A-14, and A-16), probably due to the reason that was
discussed earlier.
Bottom ash settling tests were performed at two initial ash con-
centrations, 30,000 and 10,000 mg/1. Results of the ash settling tests
are presented in Figures A-27 and A-28. Bottom ash, due to its rela-
tively large particle size, settled much faster than the fly ash. Also,
the settling characteristics of bottom ash differed from that of fly
ash; that is, no distinction was found between the behavior of high and
low suspended solids concentrations in the hindered settling zone during
bottom ash settling. After about two minutes of bottom ash settling,
only the fine particles, representing about 2 percent of the initial ash
weight, were suspended in the water. However, these fine bottom ashes
behave like the fine fly ashes left behind the hindered zone.
-56-
-------
SECTION 7
CHARACTERISTICS OF ASHES
Coals contain various elements found in the earth's crust, inclu-
ding various rare elements (Table 3). The mineral in coal comes from
the (1) inherent matter in the plants from which the coal bed forms and
(2) extraneous matter that is deposited in the coal bed from outside by
mechanical means (e.g., dust deposited from the atmosphere or suspended
and dissolved material carried by water). Most of the mineral matter of
coal is extraneous. After combustion, many trace and rare elements have
been found concentrated in the ashes of coals27'29'31*35'39 despite the
different chemical properties of coals. The chemical characteristics of
ashes from individual pieces of coal may also vary widely, even when the
pieces are selected from closely adjacent places in the same seam.
Three mass balance studies have been conducted at three TVA steam
plants.24'29'58 Many toxic trace metals were found to be enriched to a
significant extent in the combined particulate and vapor phases of stack
gas. These toxic metals may leach into water when ash contacts water by
ponding or landfill.
The distribution of major elements in fly and bottom ashes is
approximately the same, but more trace metals are concentrated in fly
ash than in bottom ash. Fly ash has been characterized within TVA.
Table 10 presents the chemical properties of fly ashes from 11 TVA steam
plants.
Fly ash contains cenospheres, which are thin-walled hollow spheres,
20 to 200 |Jm in diameter, that float on water. Some coarse-size ceno-
spheres are either particles filled with smaller spheres (plerospheres)
or particles that have a thicker wall with a porous and irregular sur-
face. The formation of cenospheres is dynamic, and gases of C02 and
Ng are trapped inside the sphere.59 The proportion of cenospheres in
fly ash is probably affected by the nature of minerals in the coal being
burned,19'59 fusing temperature, type of boiler, and efficiency of fly
ash collection. Almost all coal-fired power plants produce cenospheres.
At some power plants, the cenospheres are sufficient to form a thick
layer of floating material on the surface of ash ponds. Laboratory
tests were conducted to determine the amounts of cenospheres produced at
several TVA steam plants, and the cenospheres were defined as those fly
ashes with a specific gravity less than one and floating on water for
more than three days. The results in Table 11 indicate that the con-
tents of cenospheres range from 0.02 to 0.13 percent by weight in fly
ash collected by electrostatic precipitators and from 0.1 to 0.42 percent
by weight in fly ash collected by mechanical collectors. To meet the
effluent limitations guidelines for suspended solids, discharge of
cenospheres into the ash pond effluent must be prevented at some ash
ponds.
-57-
-------
TABUS 10, CHEMICAL COMPOSITION OF ELY ASHES FROM TVA STEAM HAHTSa'b
Alumina (A1203), %
Calcium (CaO), %
Iron (Fe203), %
Magnesium (MgO), %
Potassium (KgO), %
Silica (Si02), %
Sodium (Na20), %
Sulfur (S03), %
Titanium (TiOg), %
Beryllium (Be), ppm
Cadmium (Ci), ppm
Chromium (Cr), ppm
Copper (Cu), ppm
Lead (Pb), ppm
Manganese (Mn), ppm
Nickel (Hi), ppm
Vanadium (v), ppm
Zinc (Zn), ppm
Specific gravity
Mean fly ash particle
diameter, ppi
Plant A
ESP
20.1*
1.8
21.1
0.9
2.9
1*7.1*
0.2
1.6
1.2
11*
5.3
170
160
120
285
150
150
965
2.69
11.1*
Plant C
ESP
22.7
1.7
H-3
0.93
-
1*7.6
2.7
-
-
-
8.0
300
ll*0
80
298
207
1*1*0
71*0
2.69
„
Plant D
ESP
29.6
0.8
3-8
0.9
2.7
57.5
0.7
0.1*
1.7
12
<1
180
195
69
51
115
130
97
2.13
10.1*
Plant E
ESP
16.2
5.1
23-0
1.1
2.3
1*7.6
0.6
1.1*
0.8
8.7
3.6
160
89
95
328
88
1*90
398
2.53
8.1*
MC
16.6
1*.6
29.0
1.0
2.1*
1*2.5
0.1*
1.2
0.8
8.1*
5.1*
135
91
1*9
395
100
235
1*35
2.66
9.8
Plant F
ESP
17.5
7.0
20.3
1.3
2.9
1*7.9
0.8
1.5
0.9
5.5
1.7
ll*C
89
53
635
81
235
395
2. US
13.3
Plant G
ESP
23.7
2.8
13-7
1.1
2.8
1*8.6
0.6
2.6
1.2
12
6.8
160
11*5
125
255
115
230
790
2.1*2
6.3
Plant H
MC
25.7
1.3
12.3
1.1
3-1
51.2
0.3
0.5
1.1
11
<1
11*5
11*5
31
2l*0
100
125
190
2.11
l!*.7
ELant I
ESP
2l*.7
1.9
12.9
1.3
3-3
51.8
0.1*
1.1*
1.1
13
5.1
130
150
105
250
115
160
550
2.6
3.8
MC
20.9
1.6
18.1*
1.0
2.6
51.5
0.2
0.1*
1.0
7.3
<1
120
76
15
255
91
115
11*0
2.3
13-5
Plant 3
ESP
26.5
1.1
12.2
0.9
2.8
1*8.7
0.2
0.7
1.2
8.5
<1
150
150
1*9
230
105
130
175
2.07
10.3
Plant K
ESP
25.1
2.1
12.1*
1.2
3-0
52.1*
0.9
1.0
1.1
12
9
170
230
105
70
115
130
920
2.1*5
5.2
MC
20.6
3.0
2l*.3
1.0
2.2
1*5.2
0.5
0.5
0.9
8
<1
ll*0
130
30
2l*5
97
120
310
2.1*
15.6
Plant L
ESP
21.6
2.3
1*.9
0.9
2.3
1*8.3
0.3
0.7
1.0
7.3
-------
TABLE ll.P||ganagEJ)F CENOSPHERES IN FLY ASHES
Cenospheres
Fly ashes in fly ashes (%)
Plant A—electrostatic precipitator 0.022
Plant C—electrostatic precipitator 0.034
Plant E—electrostatic precipitator 0.042
Plant E--mechanical collector 0.094
Plant H—electrostatic precipitator 0.037
Plant H—mechanical collector 0.422
Plant J—electrostatic precipitator 0.132
Plant J—mechanical collector 0.173
Plant K—electrostatic precipitator 0.092
Plant K—mechanical collector 0.101
Plant L--electrostatic precipitator 0.080
Plant L—mechanical collector 0.177
-59-
-------
Also, cenospheres were collected from two acid ash ponds and one
alkaline ash pond, and samples were analyzed for both the principal and
trace constituents. The results in Table 12 show that the chemical
composition of cenospheres is similar to that of fly ash, except that
the soluble constituents such as alkaline metals are lower in ceno-
spheres than in dry fly ash because those cenospheres have already been
in contact with water in the pond for several days. However, when
cenospheres enter the discharges, they can contribute to both suspended
solids concentration and total concentration of trace metals in ash
pond effluents.
-60-
-------
TABLE 12. CHEMICAL COMPOSITION OF CENOSPHERES
Constituent
Alumina (A1203) , %
Calcium oxide (CaO) , %
Iron oxide (Fe203) , %
Magnesium oxide (MgO) , %
Potassium oxide (F^O) , %
Silica (Si02), %
Sodium oxide (Na20) , %
Sulfur oxide (S03), %
Titanium oxide (Ti02) , %
Arsenic, yg/g
Cadmium, yg/g
Chromium, yg/g
Copper, yg/g
Lead, yg/g
Mercury, yg/g
Nickel, yg/g
Selenium, yg/g
Zinc, yg/g
Plant Aa
24.93
0.06
4.07
0.50
3.01
45.00
0.22
NA
1.50
45
<1
<5
45
140
<0.1
100
8
140
Plant Eb
20.73
14.91
6.59
0.98
4.22
41.90
0.69
0.19
1.22
10
<1
32.5
41
65
<0.1
140
8
120
Plant Jc
18.70
0.01
4.43
0.73
4.58
42.86
0.3
NA
1.63
94
<5
70
85
110
<0.1
80
<2
100
aAsh pond water—4.4 pH.
bAsh pond water—11.1 pH.
cAsh pond water—4.0 pH.
NA—Not Available.
-61-
-------
SECTION 8
LEACHING OF MINERALS FROM ASHES
Inorganic materials, including trace elements, present in coal ash
leach into water during ash sluicing and settling. Many trace elements
apparently are located on the surface of ash particles and thus cause
water quality problems at ash disposal sites. This section of the
report is on laboratory leaching tests to assess the levels of minerals
leached from ash into water and on mathematical analysis of mass trans-
fer of chemical species leached from ash.
The rate of mass transfer of any chemical species from ash into
water can be expressed as
»A"U <«!-«. 03)
^A = rate Of mass transfer' Per unit area, g-mole/sec-cm2,
km = coefficient of mass transfer between the surroundings and the
surface of solids, cm/sec,
C.^ - concentration of a species at the interface, g-mole/cm3,
C = concentration of a species in the bulk liquid, g-mole/cm3.
The concentration of a species at a given point of ash surface
varies with time during leaching. The mass transfer coefficient for a
single ash particle can be calculated by using the Chilton-Colburn
analogy,60 as
where
NSh s NSho
= Sherwood number (k Ly/D) ,
where
L = characteristic length dimension, cm,
y = mole fraction of a species in the bulk liquid,
D = volumetric molecular diffusivity, cm2/sec,
-62-
-------
SL, - Sherwood number for molecular diffusion from a sphere,
bflO
Nr, - Reynolds number (dVp/p) ,
Ke
where
d - diameter of a sphere, cm,
V s mean velocity, cm/ sec,
p = density of solvent, g/cm3,
V - viscosity, g/cm-sec,
N0 = Schmidt number (p/pD),
bC
a, m, n - constants.
The Nq, can be assumed to have a value of 2. Ranz and Marshall61
obtained tne°following correlation for mass transfer of a component of
mole fraction y in a fluid to free-falling solids:
' 2 + «•
When ash materials are sluiced into the ash ponds or when water
seeps into the ash landfills, correlations of the form of Equation 14
with or without Nq» can be used to describe forced-convection rates of
mass transfer only when the effects of free or natural convection are
negligible. The effects of free or natural convection are negligible
for Reynolds numbers that satisfy the expression,
NRe i °-4 "Or
where
N-, - Grashof number for mass transfer {p2agd (y. - y)/M2}>
br -L
where
a = concentration coefficient of volumetric expansion,
dimensionless ,
g - gravitational acceleration, cm/sec2,
y. = mole fraction of a species at the interface.
-63-
-------
Twelve different correlations of Equation 14, with or without N_, ,
have been presented by various workers62 for forced-convection mass
transfer from single spheres. Recommendation of one correlation rather
than another is somewhat difficult.
Reed et al.63 determined the mass transfer coefficient of calcium
ion from a Wyoming coal fly ash and produced the correlation equation,
NSho ~ 3'26 x 10~5 (w/Ps)-°-78 NRe°'21 Nsc°'33 » C17)
where
w - weight concentration of solids in solvent, g/cm3,
p = density of solids, g/cm3.
s
The mass transfer coefficient was calculated as ranging from 1.3 x 1(T3
to 8.3 x 10"5 cm/sec.
Based on the above theoretical analyses, many independent param-
eters in the dimensionless numbers can affect the mineral leaching rate
of fly ash. However, principal factors may be the concentration and
form of chemical species in ash, molecular diffusivity, particle size,
and corresponding bulk flow velocity normal to the solid surface (or
intensity of turbulence).
Kinetic studies were performed to investigate the mineral leaching
rate of fly ash. Acid, neutral, and alkaline fly ashes were collected
from TVA steam plants, and certain amounts of fly ash were put in beakers
and mixed with water with two-blade impellers. The result of mineral
leaching represented by conductivity and the corresponding pH for each
of the 10 fly ashes with 3 percent ash concentration are presented in
Figures 24 and 25 and Figures B-l and B-8 in appendix B. The kinetic
equilibrium curves of conductivity and pH for these ashes leveled off
between 10 and 240 min after the ash and water were in contact.
In general, the rate of mass transfer of minerals for these fly
ashes was rapid. This indicated that the dissolved material in the ash
can leach into water within a very short period of contact time. For
wet ash handling, most of the dissolved minerals will be leached out of
ash during sluicing and transporting ash into ash pond. However, the
ash in the bottom of the pond will continue to leach while the ash is in
contact with water if the surrounding environment is changed, such as
under anoxic and low-pH conditions. TVA has monitored ash pond leachate
at two coal-fired power plants.51 The interstitial water extracted from
several soil core samples collected underneath the ash ponds was found
to be acidic (pH about 4) even though the surface discharges of these
two ash ponds were alkaline.
-64-
-------
-S9-
"J
H-
00
n
N)
*-
5
0.
2
rt
ID
O
-o
n
H-
•O
M
§
•O
sr
a
rt
>
nH (units)
o
H
-{>—r"1-
q
M
0
o
o
o
o
CONDUCTIVITY (ymhos/cm)
-------
12.5
-2000
12.0
11.5 -
11.0
20
"O" - CONDUCTIVITY
-A- - T>H
40
60
80
100
120
140
160
180
200
220
MIXING TIME (min)
Figure 25. pH and mineral leaching rate of 3 percent electrostatic precipitator fly ash from plant E.
1800
-1600
-1400
1200
_1000
800
600
400
240
u
•-»
0)
O
s
HI
>
g
-------
Laboratory leaching studies were also conducted at four different
ash concentrations. The resulting kinetic equilibrium curves of con-
ductivity and pH in Figures 26 and 27 and Figures C-l through C-4 show
that the ash concentration has a major effect on the concentration level
of dissolved solids in water, but has little effect on the time of
mineral leaching. Obviously, the concentration level of trace metals
leaching to water significantly impacts water quality.
After the water has contacted the active sites on or in the ash
particle and dissolved the soluble chemical species, the mathematical
expression of the concentration of chemical species leaching from fly
ash can be derived by unsteady-state molecular diffusion in a sphere.
Therefore, three assumptions are made: (1) the concentration of solute
is uniform at C through the sphere at the start of diffusion (t = 0);
(2) the resistance to transfer in the medium surrounding the ash sphere
is negligible, so that the surface concentration of the ash sphere is
constant at C* and is in equilibrium with the entire water phase; and
(3) the diffusion is radial, there being no variation in concentration
with angular position, and physical properties are constant. The par-
tial differential equation for unsteady-state diffusion can be generally
expressed by
2 dC-. ftn\
5t = u ^* + r §^ ' (18)
The boundary conditions follow from the initial assumptions:
C(r,o) = CQ
C(r ,t) = C*,
O
lira C(r,t) = bounded,
r-»o
where r is the radius of the ash sphere.
s
Equation 18 can be solved by applying the methods of separating
variables and Fourier series:
n=l s
The total transfer up to time t is N,
where
8r3 CD
i . fllllL^. ,-Llli /I L."* fin\
— sin ( ) exp (—32 J • (1°)
C|k) dt s _» (c - C*) I ^ (1 - exp ( y u)) (20)
r r=r ° n=l n rs
s
-67-
-------
6-
20
SUSPENDED SOLID CONCENTRATION
3_% E% 1% 0.5%
30 40
MIXING TIME (min.)
50
O
60
6
-4
0
Figure 26. pH of ash transport water vs. mixing time for various ash concentrations
(electrostatic precipitator fly ash from plant A).
-68-
-------
1200
!000-
10
20
SUSPENDED SOLIDS CONCENTRATION
$%> 2% !%
O OO
30 40
MIXING TIME (min.)
50
200
000
800
600
Figure 27. Conductivity of ash transport water vs. mixing time for various ash
concentrations (electrostatic precipitator fly ash from plant A).
-69-
-------
A mass balance on the transfer up to time t is:
(Co - C) x f Ttr* = N, (21)
in which C is the average concentration throughout the ash sphere at t
ine fractional extraction from the ash sphere at time t may be defined
as follows and combined with Equation 20:
C - C
o _ 3N 6 °° 1 -Dn27t2t
CQ - C*~ 4nr*(C -C*) ~ l ~ & f ^ exP< - £2—)- (22)
Skelland62 indicated that the series in Equations 19 and 22 con-
verge rapidly only for large times or large values of Dt/r2 The
previous kinetic studies show that the rate of mineral leading from ash
is rapid, or that the value of Dt/r2 is small. Therefore, alternative
solutions useful for small times can be derived by use of the Laplace
transform. The results are in terms of an infinite series of error
functions and associated functions:
rs °° (2n+l)r -r (2n+l)r +r
C = Co + ^(C*-Co) I (erfc s - - erfc - - ^, (23)
n=0 2 VDt 2
and
( + 2 z ierfc ) - 3 2. (24)
o s V71 n=l ^5t rs
where
ierfcx = J^ erfc0d0 = -± exp(-x2)-x erfcx
Vn
Therefore, the amounts of chemical constituents leaching from fly
ash depend on the available concentration and form of chemical species
in ash, particle size of ash, and diffusivity of each individual species.
Laboratory studies were conducted to determine the level of mineral
concentrations in ash sluice water resulting from the different ratios
of ash to water in contact. The chemical composition of three fly ashes
-70-
-------
used for this study are shown in Table 13, and these compositions are
within the range of expected values reported in the literature. Repre-
sentative weight fractions of ash samples were mixed with water at 20 C
for 24 h and filtered. The soluble minerals leaching from ash into
water should reach equilibrium levels under these conditions. The
results of this study are plotted in Figures 28 through 33.
Results of the study indicated that .sulfur oxides and alkaline
metal oxides in the fly ash easily dissolved in water. The concen-
trations of sulfate and calcium built up rapidly in the water as ash
concentrations increased, but their maximum concentrations depended on
pH, carbonate alkalinity, and ionic strength of water. Potassium and
sodium also were released readily into the sluice water and were inde-
pendent of the pH value. Chlorides dissolved only slightly. The
concentrations of dissolved potassium and sodium were less than the
concentrations of calcium in sluice water, but the concentrations of
potassium and sodium can increase linearly at high ash concentrations
because of their high solubility limits. The leaching of magnesium and
silicon oxides were continuously released into water, even though the
silicon has a low solubility limit. However, neither magnesium nor
silicon was leached from the alkaline fly ash.
According to Tables 10 and 13, silica, alumina, and iron oxides are
the three major components of fly ash. The other principal components
are calcium, potassium, magnesium, sodium, titanium oxides, and sulfur
oxides. Among these principal components, iron and titanium were not
released into the neutral and alkaline sluice waters, but were released
into the acid sluice water. Aluminum was not released into the neutral
sluice water; it dissolved only slightly in the alkaline sluice water,
but dissolved greatly in the acid sluice water.
However, pH is not the only factor that governs the release of the
components in fly ash. The total amount of dissolved salts released
from fly ash also depends on (1) the content of elements in fly ash,
especially the quantity of alkaline oxides and sulfur oxides in ash,
and (2) the manner in which each element is held to the fly ash. These
particular studies indicated that the concentrations of total dissolved
solids and the conductivity in the acidic ash sluice water were higher
than those in the neutral and alkaline ash sluice waters, and the
concentrations of total dissolved solids and the conductivity in the
alkaline ash sluice water were higher than those in the neutral ash
sluice water.
The leaching of trace metals from ashes is of particular concern.
Leachability of trace metals from ash is governed by the surface con-
centration of each trace metal in the ash matrix,65 its chemical bonding
in the ash, and pH of water with which it comes in contact. In the
studies of neutral fly ash in contact with river water, chromium, lead,
-71-
-------
TABLE 13. CHEMICAL COMPOSITION OF DRY FLY ASHES
USED FOR LEACHING STUDY
Constituent
Alumina (A1203) , %
Barium oxide (BaO) , %
Calcium oxide (CaO) , %
Chloride (Cl) , %
Iron oxide (Fe^g) , %
Magnesium oxide (MgO) , %
Potassium oxide (K20) , %
Silica (Si02), %
Sodium oxide (Na20) , %
Sulfur trioxide (S03) , %
Titanium oxide (Ti02) , %
Arsenic, yg/g
Boron, yg/g
Cadmium, yg/g
Chromium, yg/g
Copper, yg/g
Lead, yg/g
Manganese, ug/g
Mercury, yg/g
Nickel, yg/g
Selenium, yg/g
Zinc, yg/g
Plant A
22.67
0.06
1.68
NA
20.02
0.62
0.27
44.91
0.35
0.85
1.17
72
NA
12
140
NA
460
250
0.15
280
4.8
1000
Plant E
18.52
0.22
5.74
0.25
20.79
1.23
3.37
46.28
0.66
1.55
1.07
55
1800
6
90
78
75
410
0.1
100
6
540
Plant J
31.19
0.16
1.82
0.35
8.76
1.53
4.34
49.70
0.32
0.40
1.27
170
400
<2
140
170
100
220
0.42
100
8
280
NA--Not Available
-72-
-------
I I I I I I ] I I I I I I I I I I I I I I
0
240 360 480
ASH CONCENTRATION (g/l)
Figure 28. pH and leaching of principal constituents from an
alkaline fly ash sample from plant V.
-73-
-------
CONCENTRATION (mo/1)
OQ
6
(D
10
Ml f
n n>
O Q3
I-1 E3
p> OQ
0
rt O
It
H
03
r>
n>
rt
to
CO
§
Pi
J?
(B
n»
(B
co
CO
1
P
CM O
CO
O> O
r
r
r
o
o
O
6
ODO
> g7
o O
00
o
o -
o
o
O
-------
Ui
H-
•5
i-i
n>
u>
o
CONCENTRATION (mq/l)
CONDUCTIVITY pH
(umhos/cm) units
_ ro cu
o o o
o o o
OO O O
I
o
o
m
-------
CONCENTRATION (mg/l)
-------
CONCENTRATION (mg/l)
pH
(units)
O O PO 4* CD CD O
-------
CONCENTRATION (mq/l)
00
c
CO
05
01 r1
03 n>
03
S o
1
(D S
00
Mi
ft O
O Hi
It
T3 H
l_i BJ
01 O
3 tD
rt
H"
0>
Ml
i-J
O
3
§
P>
o
H-
d.
H-
O
t-h
0)
-------
and mercury did not leach from the ash. This agrees with their solu-
bility limits at neutral pH. Concentrations of arsenic, barium, boron,
cadmium, copper, manganese, nickel, selenium, and zinc increased with
increasing concentrations of ash (Figure 31). Concentrations of arse-
nic, boron, cadmium, manganese, and selenium greatly exceeded the
quality criteria for water.66 Copper and zinc apparently would have
exceeded quality criteria for water if the ash concentration were
higher than 60 percent by weight. Although these criteria (appendix E,
Table E-l) are not applicable to ash pond effluents, they are used here
and elsewhere in this report as a screening process to identify water
quality constituents that may deserve environmental consideration.
Alkaline fly ash in contact with water did not release cadmium,
iron, lead, manganese, and mercury into alkaline water because of the
low solubilities of these trace metals. However, boron, barium, arse-
nic, chromium, copper, nickel, selenium, and zinc did leach into the
sluice water, but their concentrations quickly leveled off somewhat
(Figure 29). Concentrations of barium, boron, chromium, and selenium
exceeded quality criteria for water.66
When acidic fly ash was in contact with water, almost all the
metals mentioned above could have leached into the water (Figure 33).
Concentrations of arsenic, boron, cadmium, chromium, copper, iron, lead,
manganese, mercury, selenium, and zinc exceeded the quality criteria for
water.66 In addition, the concentration levels of boron, chromium,
copper, iron, manganese, nickel, and zinc in the acidic ash sluice water
were much higher than those in the alkaline and neutral ash sluice
waters. Therefore, according to these studies, low-pH water does favor
the leaching of most trace metals; however, the leaching of boron and
selenium does not depend significantly on pH. Of these trace metals,
arsenic, barium, cadmium, chromium, lead, mercury, and selenium are
toxic to humans, and boron is toxic to plants.
The rankings of trace metal concentrations resulting from leaching
from these three particular ashes were: B>Ba>Se>Cr>Zn>Ni>Cu>Se>As in
alkaline ash sluice water; B>As>Zn>Mn>Ni>Ba>Se>Cu>Cd in neutral ash
sluice water; and Al>Fe>B>Zn>Cu>Mn>Ni>Ti>Cr>As>Ba>Pb>Cd>Se>Hg in acidic
ash sluice water.
The laboratory testing results may provide a delineation of poten-
tial trace metal pollution resulting from ash disposal under various
ash-to-water contact ratios. Field characterizations of ash pond efflu-
ents have also been conducted at TVA's 12 steam plants since 1967. TVA
ash ponds are divided into three categories: (1) those that receive
only fly ash, (2) those that receive only bottom ash, and (3) those that
receive both types of ash. Table 14 lists data related to the chemical
composition of ash pond effluents from TVA's 12 steam plants.
-79-
-------
TABLE 14. CHAEACTKBISIICS OF ONCE-THROUGH ASH POHD DISCHABGES
Plant A
Sourcea
Flow, gpm
Total alkalinity, b
mg/1 as CaCO,
Phen. alkalinity, b
mg/1 as CaCOj
Conductivity, b
lamhos/cm
Total hardness,
mg/1 as CaCO^
pH, units b
1
00 .
O Dissolved solids, D
1 mg/1
Suspended solids,
mg/1
Aluminum, mg/1
Ammonia,
mg/1 as H
Arsenic, mg/1
Barium, mg/1
EFF
BW
EFF
HW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
Fly ash
pond
6667.3
6441.7
18.7
110
-------
Plant A
Beryllium, mg/L
Cadmium, mg/1
Calcium, mg/1
Chloride, mg/1
Chromium, mg/1
Copper, mg/1
jjg Cyanide, mg/1
t— •
Iron, mg/1
Lead, mg/1
Magnesium, mg/1
Manganese, mg/1
Mercury, mg/1
EFF
EW
EFF
EW
EFF
RW
EFF
BW
EFF
EW
EFF
RW
EFF
EW
EFF
HW
EFF
EW
EFF
EW
EFF
EW
EFF
EW
Fly ash
pond
0.01
<0.01
0.038
0.001
126
35
7
6
0.072
0.010
0.33
0.09
<0.01
2.3
2.7
0.066
0.021
14
6.1
0.49
0.13
0.0003
< 0.0002
Bottom ash
pond
<0.01
<0.01
0.001
0.001
3S
35
7
6
0.007
0.010
0.07
0.09
<0.01
5.2
2.7
0.017
0.021
6.0
6.1
0.17
0.13
0.0005
< 0.0002
Plant B
Fly ash
pond
<0.01
<0.01
0.001
0.004
152
19
6
5
0.013
< 0.005
0.03
0.02
<0.01
1.4
0.57
0.015
<0.01
3.6
0.12
0.06
0.0008
< 0.0002
Bottom ash
pond
<0.01
<0.01
0.002
0.004
50
19
7
5
0.009
< 0.005
0.06
0.02
<0.01
4.7
0.57
0.018
<0.01
6.2
4.3
0.40
0.06
0.0009
< 0.0002
Plant C
East
West
<0.01 <0.01
<0.01 <0.01
0.006
0.001
78
29
11
11
0.006
0.012
0.05
0.11
0.01
1.7
6.5
0.021
0.022
10
9.5
0.20
0.31
0.0034
0.0004
0.002
0.001
37
33
11
11
0.009
0.013
0.06
0.12
0.01
6.0
7.2
0.017
0.024
10
6.6
0.18
0.31
0.0070
0.0003
Plant 13
<0.01
<0.01
0.001
< 0.001
31
28
3
3
<0.005
0.005
0.03
0.07
<0.01
0.32
0.51
0.016
0.012
8.3
8.0
0.02
0.07
0.0002
0.0002
Plant E
<0.01
<0.01
0.001
0.001
126
17
6
5
0.017
< 0.005
0.08
0.05
<0.01
0.16
1.0
0.017
0.015
0.3
0.01
0.05
0.0002
< 0.0002
Plant F
<0.01
<0.01
0.001
0.001
107
27
5
4
0.033
0.006
0.03
0.05
<0.01
0.22
1.1
0.013
0.019
1.57
4.2
0.01
0.07
0.0003
0.0006
Plant G
<0.01
<0.01
< 0.001
< 0.001
73
20
4
4
0.011
0.005
C.05
0.07
0.01
0.53
1.3
0.014
0.019
2.4
4.0
0.02
0.10
0.0024
0.0049
Plant E
<0.01
<0.01
0.001
< 0.001
50
28
14
14
0.006
0.005
0.04
0.07
<0.01
0.56
1.1
0.015
0.019
7.4
7-4
0.06
0.14
0.0004
0.0003
Plant I
<0.01
<0.01
< 0.001
< 0.001
84
19
6
6
0.017
< 0.005
0.06
0.07
<0.01
0.26
1.7
0.012
0.15
1.2
3.3
0.05
0.01
0.0003
0.0002
Plant J
<0.01
<0.01
0.001
0.001
34
15
5
2
0.005
0.005
0.11
0.08
<0.01
2.4
0.7
0.015
0.010
6.7
4.5
0.38
0.07
0.0003
0.0003
Plant K
<0.01
<0.01
0.001
< 0.001
76
20
10
7
0.019
' 0.009
0.05
0.07
<0.01
0.39
1-9
0.017
0.01
1.6
4.3
0.02
0.10
0.0003
< 0.0002
Plant L
<0.01
<0.01
0.001
< 0.001
54
17
6
6
0.009
0.009
0.06
0.07
<0.01
0.56
1.03
0.017
0.016
2.6
3.9
0.03
0.07
0.0003
< 0.0002
-------
SABLE 14 (COHTHfUED)
Plant A
Fly ash Bottom ash
pond pond
Nickel, mg/l
Total phosphate,
mg/l as P
Selenium, mg/l
Silica, mg/l
Silver, mg/l
Sulfate, mg/l
I
OO Zinc, mg/l
1
EFF
RW
EFF
RW
EFF
RW
EFF
RW
EFF
RW
EFF
RW
EFF
RW
0.08
<0.05
0.03
0.07
0.002
< 0.002
13
5.6
<0.01
<0.01
346
21
1.4
0.09
0.06
<0.05
0.07
0.08
0.002
0.002
7.4
5.6
<0.01
<0.01
45
21
0.08
0.09
Plant B
Fly ash Bottom asl
pond pond
0.05
<0.05
0.06
0.02
0.015
< 0.002
7.1
5.4
<0.01
0.02
214
12
0.05
0.02
0.06
<0.05
0.06
0.02
0.007
0.002
6.4
5.4
<0.01
0.02
102
12
0.13
0.02
i Plant C
East
0.05
<0.05
0.04
0.22
0.010
0.002
7.4
6.1
0.01
0.01
158
23
0.13
0.08
West
0.06
0.05
0.12
0.25
0.003
0.002
6.7
6.2
0.01
0.01
99
49
0.14
0.08
Plant D
0.06
0.08
0.03
0.02
0.070
0.002
4.0
5.2
0.01
<0.01
57
16
0.03
O.o4
Plant E
<0.05
<0.05
0.01
0.07
0.007
< 0.002
7.0
4.7
0.01
<0.01
147
20
0.05
0.08
Plant F
0.05
<0.05
0.02
0.13
0.014
< 0.002
6.0
4.5
<0.01
<0.01
160
19
0.05
0.12
Plant G
<0.05
<0.05
0.07
0.09
0.010
0.002
4.4
4.4
•CO.Ol
<0.01
182
17
0.05
0.09
Plant H
0.05
<0.05
0.12
0.14
0.017
0.002
4.9
4.9
<0.01
<0.01
98
19
0.05
0.11
Plant I
0.05
<0.05
0.06
0.17
0.012
< 0.002
7.1
5.4
<0.01
<0.01
81
21
0.08
0.07
Plant J
0.05
<0.05
0.06
0.02
o.oo4
0.003
6.4
3-9
<0.01
<0.01
119
22
0.07
0.06
Plant K
0.06
<0.05
0.05
0.1C
0.010
0.002
6.7
4.6
<0.01
<0.01
83
20
0.05
0.07
Plant L
<0.05
<0.05
0.06
0.03
0.010
0.002
5 7
x« i
5.1
< 0.01
<0.01
80
13
0.0^4-
0.06
aEFF—ash pond effluent (data from 1973 to 1975); EW—raw water for ash sluicing (data from 1974 to 1975).
Average values of weekly grab samples; all other numbers are average values of ouarterly grab samples.
-------
The quantity of water for ash handling is generally high at TVA
steam plants because of the large available quantity of water in the
Tennessee Valley. Therefore, the ash concentrations in the ash trans-
port water during sluicing at TVA steam plants range from 5.6 to 25.2 g
per liter; these values are much lower than the nationwide range of 6 to
200 g per liter.5
Although the ash concentration in the ash transport water is low at
TVA steam plants, various trace metals were found to have concentrations
exceeding the water quality criteria. Based on quarterly ash pond
monitoring for a 3-year period, the percentage of each trace element
equal to or exceeding a given concentration are presented in Figures D-l
to D-15. Boron was not included in the monitoring, but the quantity of
boron in ash pond effluents would be high because the coal fly ash contains
significant levels of boron and the leaching of boron is not limited by
pH. The results from laboratory leaching tests and ash pond monitoring
indicate that many trace metals are present in ash pond effluents in
potentially toxic quantities.
-83-
-------
SECTION 9
EFFECT OF pH AND SUSPENDED SOLIDS ON TRACE METAL
CONCENTRATIONS IN ASH POND EFFLUENTS
Trace metals may occur in ash pond discharges in both dissolved and
suspended forms. The dissolved trace metals in the ash transport water
are governed by their leachability from the ash materials (see section 8)
The suspended trace metals in ash pond effluents may be associated with
unsettled ash and colloid particles which contain undissolved trace
elements.
A field survey was conducted at the plant E alkaline ash pond to
investigate the distribution of dissolved and suspended trace elements
in the intake water, ash transport water, and ash pond effluent. The
average concentrations of chemical species and their relative forms of
existence are presented in Table 15. The intake water, which was pumped
from the once-through cooling water discharge channel, contained very
low concentrations of total suspended solids (3 mg/1) as well as dis-
solved and suspended trace metals.
During the survey, the average ash sluicing times per day were 240
min for fly ash collected by electrostatic precipitators, 93 min for fly
ash collected by mechanical collectors, 20 min for bottom ash, and 44
min for pyrite.
The total suspended solids concentrations in ash slurries were
quite high, and trace metals were mostly in the undissolved forms. For
instance, 8.5 mg/1 suspended lead and 0.017 mg/1 dissolved lead were
found in fly ash slurry from electrostatic precipitators, 1.8 mg/1
suspended lead and 0.047 mg/1 dissolved lead were found in fly ash
slurry from mechanical collectors, 14.7 mg/1 suspended lead and 0.016
mg/1 dissolved lead were found in bottom ash slurry, and 0.12 mg/1
suspended lead and 0.02 mg/1 dissolved lead were found in pyrite slurry.
Because most of the ash particles settled in the ash pond and only 11
mg/1 suspended solids was found in ash pond effluent, the suspended
trace metals were not observed in significant quantities. Also the
dissolved trace metal concentrations were low in the alkaline effluent.
Concentrations of some trace metals, such as copper, iron, lead, and
zinc were found to be lower in the effluent than in the intake water.
Laboratory studies were conducted to investigate the effects of pH
adjustment between 6 and 9 and reduction of suspended solids concen-
tration to 30 mg/1 on the forms and concentrations of trace metals in
ash transport water after settling.
-84-
-------
TABLE 15. AVEBAGE CONCEHTEATIONS (mg/1) OF DISSOLVED AND SUSPENDED CHEMICAL SPECIES DJ IHTAKE WATEE,
CM
Flv ash slurry
Solids
Dissolved
Suspended
Aluminum
Dissolved
Suspended
Calcium
Dissolved
Suspended
Chromium
Dissolved
Suspended
Copper
Dissolved
Suspended
Iron
Di ssolved
Suspended
Magnesium
Dissolved
Suspended
Lead
Dissolved
Suspended
Zinc
Dissolved
Suspended
Silica
Dissolved
Suspended
Sulfate
Dissolved
Suspended
nH of water
104
3
0.3
0.5
27
6
< 0.005
<0.005
0.06
0.06
0.06
0.26
U.7
0.01
0.01
0.03
0.01
2.3
0.5
10
7.8
Electrostatic
precipitator
1*6,000
3.1
1*,330
500
1,330
0.022
0.01
3.1
0.1
323
0.017
8.5
0.02
29
1.3
10,030
360
260
12. U
Mechanical
collector
21,500
1.1
1,750
520 .
795
0.007
2.0
0.01
0.71
0.8
3,830
135
0.0^7
1.8
0.02
7.3
1.1
4,21*0
133
li*7
12.lt
Bottom ash
slurry
115,500
0.6
9,730
83
180
< 0.005
0.1
<0.01
5.6
-------
Study 1—Reducing Suspended Solids Concentrations to 30 mg/1 and Then
Adjusting pH to 6 and 9~ ~~ ~
Dry fly ash samples, representing acidic, neutral, and alkaline
characteristics, were collected from six TVA steam plants. Each ash
sample was weighed and then soaked in river water for about 3 h. The
water quality of the river water is shown in Table 16. Ash slurry
samples were prepared so as to contain 30 g/1 suspended solids, and each
slurry was poured into a column for settling tests, as described pre-
viously. The concentration of suspended solids in the supernatant was
determined by measuring the sample withdrawn from the top portion of the
settling column at various time intervals. When the suspended solids
concentration reached about 30 mg/1, a large quantity of sample was then
taken, and the sample was analyzed for dissolved and suspended trace
metals. All acid and alkaline samples were adjusted to pH 6 or 9 by
using sodium hydroxide or hydrochloric acid solution before they were
analyzed for dissolved and suspended trace metals. The results of the
effect of pH on the settled ash transport water are presented in Tables
17 through 22.
The electrostatical precipitator fly ash transport waters at two
plants (plants A and H) were originally acidic. For the acidic ash
transport water sample at plant A, containing 30 mg/1 suspended solids
(Table 17), total concentrations of boron, cadmium, iron, manganese, and
lead exceeded water quality criteria for domestic water supply and long-
term irrigation.66 The concentration of suspended iron, which is asso-
ciated with unsettled fly ash particles, was quite high (4.2 mg/1).
Although the concentration of suspended lead was not high, the concen-
tration of total lead exceeded the 0.05-mg/l level of water quality
criterion. A high concentration of dissolved aluminum was leached from
the fly ash, but aluminum is not regulated in the quality criteria for
water by EPA.
After the pH was raised to 6, most of the dissolved aluminum and
iron were transformed to their suspended forms as aluminum and iron
hydroxides. Other trace metals did not change significantly at pH 6.
After the pH of the water was raised to 9, the aluminum slightly
redissolved, and arsenic, boron, barium, cadmium, magnesium, and sele-
nium remained mostly in their dissolved forms. The other dissolved
trace metals were precipitated at pH 9. Therefore, for this particular
fly ash transport water, boron, cadmium, and manganese concentrations
exceeded the water quality criteria for domestic water supply and long-
term irrigation after pH had been adjusted to 6 and 9 and suspended
trace metals had been removed.
For the acidic ash transport water sample from plant H (electro-
static precipitator), containing 30 mg/1 suspended solids (Table 19),
the total concentrations of boron, cadmium, iron, and manganese exceeded
water quality criteria for domestic water supply. The concentration of
-86-
-------
TABLE 16. CONCENTRATIONS OF DISSOLVED AND SUSPENDED
TRACE METALS IN TENNESSEE RIVER WATER3
Trace metal
Aluminum
Arsenic
Boron
Barium
Cadmium
Chromium
Copper
Iron
Mercury
Manganese
Nickel
Lead
Selenium
Zinc
Concentrations
Dissolved
0.4
<0.005
0.16
<0.1
<0.001
<0.005
0.05
<0.05
<0.0002
0.01
<0.05
<0.01
<0.002
<0.01
(mg/l)
Suspended
0.3
<0.005
<0.1
<0.1
<0.001
<0.005
0.01
0.26
<0.0002
<0.01
<0.05
<0.01
<0.002
<0.01
apH of river water was 7.2.
-87-
-------
TABLE 17. EFFECT OF pH ADJUSTMENT ON TRACE METAL CONCENTRATIONS IN ELECTROSTATIC.
PRECIPITATOR ASH TRANSPORT WATER OF PLANT
Trace metal concentration (mg/1) in ash transport
water with varying pH
Trace metal
Aluminum
Arsenic
Boron
Barium
Cadmium
Chromium
Copper
Iron
Mercury
Manganese
Nickel
Lead
Selenium
Zinc
pH 3.
Dissolved
27
0.05
4.6
0.3
0.077
0.023
0.5
3
<0.0002
0.47
0.12
0.047
0.002
1.3
5
Suspended
1.6
<0.005
<0.1
<0.1
<0.001
<0.005
0.02
4.2
<0.0002
<0.01
<0.05
0.01
<0.002
0.03
PH
Dissolved
0.9
0.04
4.5
0.3
0.077
0.02
0.5
0.9
<0.0002
0.47
0.12
0.045
0.002
1.3
6
Suspended
27.7
0.01
0.1
<0.1
<0.001
<0.005
0.02
6.3
<0.0002
<0.01
<0.05
0.01
<0.002
0.03
PH 9
Dissolved
1.6
0.04
4.7
0.2
0.05
<0.005
<0.01
0.6
<0.0002
0.3
0.07
0.01
0.002
0.09
Suspended
27
0.01
<0.1
<0.1
0.02
0.02
0.5
6.5
<0.0002
0.1
0.05
0.04
<0.002
1.2
Before settling, the ash concentration of the slurry was 30 g/1. After
settling test, the suspended solids concentration of the collected water
sample was 30 mg/1 and the pH was 3.5. The pH of the unfiltered water
sample was then adjusted to pH 6 and 9 by adding sodium hydroxide.
-88-
-------
TABLE 18. EFFECT OF pH ADJUSTMENT ON TRACE METAL CONCENTRATIONS IN ELECTROSTATIC,
PRECIPITATOR ASH TRANSPORT WATER OF PLANT Ea
Trace metal concentration (mg/1) in ash transport
water with varying pH
Trace metal
Aluminum
Arsenic
Boron
Barium
Cadmium
Chromium
Copper
Iron
Mercury
Manganese
Nickel
Lead
Selenium
Zinc
PH
Dissolved
9.2
<0.005
7.1
0.3
0.002
0.07
<0.01
0.1
<0.0002
<0.01
<0.05
0.012
0.046
0.04
11.1
Suspended
2.4
<0.005
<0.1
<0.1
<0.001
<0.005
0.07
0.4
<0.0002
0.01
<0.05
<0.01
<0.002
0.02
pH
Dissolved
8.8
<0.005
7.2
0.4
0.002
0.04
<0.01
0.09
<0.0002
0.01
<0.05
0.01
0.04
0.04
9
Suspended
<0.8
<0.005
<0.1
<0.1
<0.001
0.03
0.07
0.4
<0.0002
<0.01
<0.05
<0.01
<0.002
0.02
pH 6
Dissolved
0.4
<0.005
6.7
0.4
0.002
0.07
0.07
0.15
<0.0002
0.01
<0.05
0.01
0.04
0.04
Suspended
11.2
<0.005
0.4
<0.1
<0.001
<0.005
<0.01
0.4
<0.0002
<0.01
<0.05
<0.01
<0.002
0.02
aBefore settling, the ash concentration of the slurry was 30 g/1. After
settling test, the suspended solids concentration of the collected water
sample was 30 mg/1 and the pH was 11.1. The pH of the unfiltered water
sample was then adjusted to pH 9 and 6 by adding hydrochloric acid solution.
-89-
-------
Trace metal concentration (mg/1) in electrostatical precipitator
ash transport water with varying pH
Trace metal
Aluminum
Arsenic
Boron
Barium
Cadmium
Chromium
Copper
Iron
Mercury
(^ Manganese
O
' Nickel
Lead
Selenium
Zinc
PH4.
Dissolved
13.6
0.039
2.2
0.2
0.037
0.013
0.48
1.8
< 0.0002
0.5
0.2
<0.01
0.007
0.73
3
Suspended
2.03
0.005
<0.1
<0.1
< 0.001
<0.01
<0.01
3.66
< 0.0002
<0.01
<0.05
<0.01
< 0.002
<0.01
PH
Dissolved
0.8
0.043
2.0
0.2
0.029
0.012
0.47
0.7
6
Suspended
14.8
0.005
<0.l
<0.1
< 0.001
<0.01
0.01
M
< 0.0002 < 0.0002
0.49 H
PH 9.
Dissolved
1.9
0.12
0.96
0.2
< 0.001
0.026
0.01
<0.05
< 0.0002
<0.01
<0.05
<0.01
0.014
<0.01
8
Suspended
3.59
0.05
<0.1
<0.1
< 0.001
0.008
<0.01
2.92
< 0.0002
0.01
<0.05
<0.01
< 0.002
<0.01
vK 9
Dissolved
1.8
0.11
0.98
0.2
< 0.001
0.024
0.01
<0.05
< 0.0002
0.01
<0.05
<0.01
0.016
<0.01
Suspended
3-6
0.05
<0.1
<0.1
< 0.001
0.008
<0.01
2.9
< 0.0002
<0.01
<0.05
<0.01
< 0.002
<0.01
pH 6
Dissolved
0.9
0.08
1.2
0.2
< 0.001
0.035
0.01
1.2
< 0.0002
0.02
<0.05
<0.01
0.016
<0.01
Suspended
2.8
0.06
<0.1
<0.1
< 0.001
< 0.005
<0.01
1.6
< 0.0002
<0.01
<0.05
<0.01
< 0.002
<0.01
Note: Before settling the ash concentrations of both slurries were 30 g/1. After settling test, the suspended solids concentrations of both collected water samples
were 30 ng/1; the pH of the electrostatical precipitator fly ash transport water was 4.3, and the pH of the mechanical collector fly ash transport water was 9.8
The pE of both water samples was then adjusted by adding sodium hydroxide or hydrochloric acid solution.
-------
TABLE 20. EFFECT OF pH ADJUSTMENT ON TRACE METAL CONCENTRATIONS IN ASH TRANSPORT WATER OF PLANT Ja
Trace metal concentration (mg/1)
in electrostatical precipttator ash Trace metal concentration (mg/1) in mechanical collector
transport water with varying pH ash transport water with varying pH
Trace
pH i
3 pH 9
metal Dissolved Suspended Dissolved Suspended
Aluminum
Arsenic
Boron
Barium
Cadmium
Chromium
Copper
Iron
Mercury
Manganese
Nickel
Lead
Selenium
Zinc
0.9
0.26
2
<0.1
0.001
0.026
0.05
0.19
<0.0002
0.01
<0.05
<0.01
0.048
0.04
4.9
0.005
<0.1
<0.1
<0.001
<0.005
<0.01
4.4
<0.0002
<0.01
<0.05
<0.01
<0.002
<0.01
1.8
0.23
1.8
<0.1
<0.001
0.025
0.02
0.2
<0.0002
0.01
<0.05
<0.01
0.068
0.02
3
0
<0
<0
0
<0
0
4
<0
<0
<0
<0
<0
0
.7
.005
.1
.1
.001
.005
.03
.0
.0002
.01
.05
.01
.002
.02
pH 9.3
pH <-.
)
pH (
>
Dissolved Suspended Dissolved Suspended Dissolved Suspended
1.7
0.11
0.57
<0.1
<0.001
<0.005
<0.01
<0.05
<0.0002
<0.01
<0.05
<0.01
0.021
<0.01
3.9
0.007
<0.1
<0.1
<0.001
0.01
0.01
3.5
<0.0002
0.02
<0.05
<0.01
<0.002
<0.01
1.6
0.12
0.54
<0.1
0.001
<0.005
<0.01
<0.05
<0.0002
0.01
<0.05
<0.01
0.023
<0.01
4.1
0.007
<0.1
<0.1
<0.001
0.01
0.01
3.5
<0.0002
0.01
<0.05
<0.01
<0.002
<0.01
0.7
0.06
0.7
<0.1
0.001
0.011
0.01
0.9
<0.0002
0.02
<0.05
<0.01
0.021
<0.01
4.8
0.009
<0.1
<0.1
<0.001
<0.005
<0.01
2.5
<0.0002
<0.01
<0.05
<0.01
<0.002
<0.01
aBefore settling, the ash concentrations of both slurries were 30 g/1. After settling, the suspended solids concentra-
tions of both collected water samples were 30 mg/1; the pH of the electrostatical precipitator fly ash transport water
was 8, and the pH of the mechanical collector fly ash transport water was 9.3. The pH of both water samples was then
adjusted to 9 or 6 by adding sodium hydroxide or hydrochloric acid solution.
-------
10
Trace metal concentration (mg/1) in electrostatical
precipitator ash transport water with varying pH
Trace metal.
Aluminum
Arsenic
Boron
Barium
Cadmium
Chromium
Copper
Iron
Mercury
Manganese
Nickel
Lead
Selenium
Zinc
pH 1O.8
Dissolved Suspended
1.9
0.16
5
<0.l
< 0.001
0.018
<0.01
<0.05
< 0.0002
<0.01
<0.05
<0.01
0.22
<0.01
3.6
0.1
<" n i
<0.1
< 0.001
0.005
0.01
2.56
< 0.0002
<0.01
<0.05
<0.01
< 0.002
0.03
T)H 9
1.7 3.7
0.18
•
"'
<0.1
< 0.001
0.018
<0.01
<0.05
< 0.0002
<0.01
<0.05
<0.01
0.16
0.01
0.1
<0.1
< 0.001
0.005
0.01
2.6
<0.0002
<0.01
<0.05
-H
Tfi 11.2
Dissolved Suspended
1.1 2.9
0.12
1.3
<0 1
< 0.001
< 0.005
<0.01
<0.05
< 0.0002
<0.01
<0.05
<0.01
0.029
<0.01
0.05
<0.1
<0 1
< 0.001
< 0.005
0.01
5-0
< 0.0002
0.01
<0.05
<0.01
< 0.0002
0.01
tfl Q
Tfl 6
Dissolved Suspended
1.0 3.0
0.11
1.5
< 0.001
< 0.005
<0.01
<0.05
< 0.0002
0.01
<0.05
<0.01
0.026
<0.01
0.05
<0.1
< 0.001
< 0.005
0.01
5.0
< 0.0002
<0.01
<0.05
<0.01
< 0.0002
0.01
Dissolved Suspended
0.6 3.1*
0.12
<0.1
0.001
0.005
0.01
0.8
< 0.0002
0.01
-------
TABLE ?? WFECT OF tiH ADJUSTMENT ON TBA.CE METAL CONCENTEATIONS IN ASH TRANSPORT WATEE OF PLANT L
a
Trace metal concentration (ag/1) in electrostatical
precipitator ash transport water with varying .pH
pH 11.7
VO
OJ
Trace metal
Aluminum
Arsenic
Boron
Barium
Cadmium
Chromium
Copper
Iron
Mercury
Manganese
Hickel
Lead
Selenium
Zinc
pH 9
pH 6
Trace metal concentration
ash transport
pH 10.4
Dissolved Suspended Dissolved Suspended Dissolved Suspended
1.1 4.3
0.074
7.1
<0.1
0.002
0.03
0.01
-------
total dissolved aluminum in the acid solution (13.6 mg/1) was higher
than any other trace metal concentration. Except for suspended aluminum
and iron, all other suspended trace metal concentrations were relatively
low and insignificant. After the pH was raised to 6, most of the dis-
solved aluminum and iron became suspended. Dissolved and suspended
concentrations of arsenic, boron, barium, and selenium did not change
after pH was adjusted to 6 and 9; but the other dissolved trace metals
were completely or partly changed to their suspended forms. However,
dissolved boron, cadmium, and manganese concentrations still exceeded
water quality criteria after pH adjustment.
The fly ash transport water at plant J (electrostatic precipita-
tor fly ash) was neutral (Table 20), and the concentrations of total
arsenic, iron, and selenium exceeded water quality criteria for domestic
water supply. The iron was mainly in suspended form and associated with
fly ash. This finding may indicate that suspended solids must be reduced
to a concentration of less than 30 mg/1 to decrease total iron concentra-
tion to 1 mg/1 or less. Raising pH from 8 to 9 resulted in little
change in dissolved and suspended forms of trace metals.
The other three electrostatic precipitator fly ash transport waters
(plants E, K, and L) and all four mechanical precipitator fly ash trans-
port waters (plants H, J, K, and L) were alkaline. In these alkaline
water samples containing 30 mg/1 suspended solids, concentrations of
total trace metals exceeding water quality criteria for domestic water
supply and long-term irrigation were boron, chromium, iron, and selenium
in transport water (electrostatic precipitator fly ash) of plant E;
arsenic, boron, iron, and selenium in transport water (mechanical collec-
tor fly ash) at plant H; and arsenic, iron, and selenium in transport
water (mechanical collector fly ash) of plant J. Also, in alkaline
water samples, the concentrations of total trace metals exceeding these
water quality criteria were arsenic, boron, iron, and selenium in trans-
port waters (electrostatic precipitator fly ash and mechanical collector
fly ash) of plant K; and arsenic, boron, iron, and selemium in transport
waters (electrostatic precipitator fly ash and mechanical collector fly
ash) of plant L.
Aluminum was also leached from alkaline fly ashes, but the amount
of aluminum leaching varied between ashes. After pH adjustments to 6
and 9 for those alkaline fly ash transport waters, the behavior of trace
metals was about the same as that after pH adjustment for acidic fly ash
transport water. The change of concentrations of arsenic, boron, and
selenium were not sensitive to the change of pH. Suspended iron remained
undissolved at pH 9 and 6, and dissolved chromium concentrations were
somewhat lower at pH 9 than either at pH 6 or at pH above 9. Therefore,
chromium in ash transport water may be in the trivalent form, because
solubility of hexavalent chromium is also pH-independent.
-94-
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Study 2—Spiking Trace Metals into Composite Alkaline Ash Pond
Effluent and Adjusting pH to 9 and 7
To investigate the behavior of trace metals in ash transport water
further, field samples of acidic and alkaline ash pond effluents were
collected from five TVA steam plants. The effluents from alkaline
combined ash ponds at 4 different plants were equally mixed, and the
mixture was spiked with 11 trace metals in the dissolved form 100 times
in excess of their analytical detection limits. The pH of the composite
was then adjusted to 11 using sodium hydroxide and subsequently reduced
to 9 and 7 by neutralizing with C02. The results are given in Table 23.
Of the 11 trace metals, cadmium, chromium, copper, iron, lead, nickel,
and zinc were generally found in undissolved forms at pH 11, 9, and 7.
These seven trace metals may be precipitated as metal hydroxides, except
the lead may be precipitated as lead carbonate at pH 9 and 7. Although
the spiked concentrations of these trace metals were quite high, only
the dissolved concentrations exceeded water quality criteria at pH 7,
whereas dissolved chromium, copper, iron, lead, and zinc were below
their water quality criteria. Arsenic, mercury, and selenium were found
in both dissolved and undissolved forms. Aluminum was found in dissolved
forms at pH 11 and 9 and in undissolved form at pH 7.
Study 3--Adjusting Acidic Ash Pond Effluent Using Lime and Investigating
Suspended Trace Metals Settling
The acidic ash pond effluent from plant A was neutralized by adding
lime from original pH 3.8 to 6, 7.3, 8.1, 9.0, and 10. After each pH
adjustment, a homogeneous sample was taken and analyzed for dissolved
and suspended cadmium, copper, iron, lead, and zinc. Then the mixture
was allowed to settle in the beaker, and the supernatant was carefully
sampled at several subsequent settling times to study the sedimentation
of metal precipitates. Examination of the data in Table 24 reveals that
suspended solids, as well as cadmium, copper, iron, lead, and zinc, are
removed best by adjusting pH to about 9 with lime and settling for
several hours. Therefore, some of the trace metals apparently were in
the forms of metal hydroxides or metal carbonates (not contained in fly
ash particles) and precipitated after several hours.
Study 4—Investigation of Dissolved and Suspended Trace Metals in TVA
Ash Pond Discharges
Because the pH of TVA ash pond effluents varies from acidic to
alkaline, grab samples were also collected from 14 ash pond discharges
at 12 steam plants to investigate the dissolved and suspended nature of
trace metals in ash pond discharges. The results are shown in Table 25.
The concentrations of mercury, nickel, and silver were less than the
general minimum detectable limits (0.0002, 0.05, and 0.02 mg/1, respec-
tively) in all samples and, therefore, are not listed in the table.
Boron was not included in the chemical analysis.
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TABLE 23. COMPOSITION OF DISSOLVED ATO ^DISSOLVED TRACE METALS
HT ALKALINE COMBIHED ASE POHD EFETOEHTSa
Ash Pond
Effluent
Plant E
Plant 7
Plant H
Plant L
1
•P Composite
Composite
Composite
Aluminum
^ Diss. Susp.
10.9 l.
10.7 0.
9.6 1.
9.1* 1.
11 18
9 16
7 0.
5 <0.2
5 <0.2
2 0.1*
5 0.1*
<0.2
-------
TABLE 2k.
EFFECT OF pH ADJUSTMENT USING LIME ON SUSPENDED AND DISSOLVED SOLIDS
AND TRACE METALS IN ACID FLY ASH POND EFFLUENT FROM PLANT A
pH
3.8
3.8
3.8
6.0
6.0
6.0
7.3
7-3
7.3
8.1
8.1
8.1
9.0
9-0
9.0
10.0
inn
10.0
CaO blank
Deionized
•water
blank
CaO
added
(mg/l)
0
0
0
36.2
36.2
36.2
1*1.9
1*1.9
1*1.9
1+6.1+
1+6.1+
1+6.1+
53.6
53-6
53.6
67.0
67.0
67.0
0
Settling
time
(h)
0
6
23
0
2.5
19
0
i*
20.5
0
3-5
20
0
3-5
19-5
0
,.
1Q
0
0
Solids
Suspended
8
1*
2
1+2
8
2
1+0
10
2
1+0
5
3
1*7
5
2
72
?
11
-
(mg/l )
Dissolved
600
580
610
560
570
530
580
570
580
580
570
570
580
570
580
560
CCS}
560
J>'~J'*s
120
-
Cadmium
Suspended
0.0008
0.0007
< 0.0001
0.0008
0.0001+
< 0.0001
o.oooi*
0.0013
0.0007
0.0336
0.0067
0.0015
0.0376
0.0021+
O.OC05
0.0371
0 . 0011
0.0008
0.0009
0.0013
(mg/l )
Dissolved
0.01*51
0.01*59
0.0507
0.01*28
0.01+01+
O.OtCc
0.0327
0.0197
0.0251
0.0090
0.001+5
0.0061
0.0009
0.0009
0.0023
0.0005
,- r^^-li.
n r.r^l
< O.C001
-------
TABLE 25. TEACE ELEMENT CONCENTRATIONS (mg/1) OF DISSOLVED AND SUSPENDED FRACTIONS
Planta pH
A-b
A-f
B
C
D
E
F
G
H-b
1 H-f
00 I
J
K
L
7.0
4.0
6.0
7.1
7.7
11.4
10.8
9-7
8.8
7.0
9-1
3.6
11.4
10.9
Susp.
solids
40
24
20
15
13
20
7
32
29
34
34
23
37
4
Arsenic
Diss. Suso.
< 0.005
< 0.005
0.045
< 0.005
0.04
< 0.005
< 0.005
0.050
O.ll+O
0.140
O.l4o
0.050
0.120
< 0.005
0.005
0.010
0.145
0.01
0.005
< 0.005
< 0.005
< 0.005
< 0.005
0.05
0.020
0.090
0.100
< 0.005
Cadmium
Diss. Susp.
< 0.001 < 0.001
< 0.001
-------
In the grab samples, concentrations of arsenic, cadmium, chromium,
iron, manganese, and selenium exceeded water quality criteria for
domestic water supply. Dissolved arsenic concentrations exceeded the
0.05-mg/l level at five ash ponds (bottom ash and fly ash ponds at plant
H and combined ash ponds at plants I, J, and K), and suspended arsenic
concentrations exceeded the 0.05-mg/l level at four ash ponds (fly ash
pond at plant H and combined ash ponds at plants B, J, and K). The high
concentrations of arsenic occurred in these ash pond effluents in spite
of the water being acid, neutral, or alkaline.
Dissolved cadmium exceeded the 0.01-mg/l level at one combined ash
pond (plant J), where the effluent was acidic (pH 3.6). Dissolved chro-
mium exceeded the 0.05-mg/l level at one fly ash pond (plant A), where
the effluent was also acidic (pH 4.0).
Dissolved iron exceeded the 0.3-mg/l level at one acid fly ash pond
(plant A) and at one alkaline combined ash pond (plant K). The pH of
this alkaline ash pond effluent was 11.4; at this pH, the dissolved
ferric iron is no longer at minimum solubility level. The suspended
iron exceeded the 0.3-mg/l level at 11 ash ponds (bottom ash and fly ash
ponds at plants A and H and combined ash ponds at plants B, C, D, E, I,
J, and K). The suspended iron may be associated with unsettled ash or
cenospheres in effluents, because the content of iron, one of the three
principal constituents (aluminum, iron, and silicon) in fly and bottom
ashes, in ash ranges from 5 to 30 percent.7
Dissolved manganese exceeded the 0.05-mg/l level at two fly ash
ponds (plants A and H) and four combined ash ponds (plants B, C, D, and
J). The pH of these six ash ponds was either acidic or neutral. Sus-
pended manganese exceeded 0.05 mg/1 at one bottom ash pond (plant A).
Dissolved selenium exceeded the 0.01-mg/l level at one combined ash pond
(plant D).
Summary
Based on the laboratory tests, field surveys, and literature
reviews, conclusions may be drawn from the data for the trace metals
that exist in significant amounts in ash pond effluents: arsenic,
boron, cadmium, chromium, copper, iron, lead, manganese, selenium, and
zinc.
ARSENIC
Arsenic exists in aquatic systems in the 3-, 0, 3-I-, and 5+ oxida-
tion states.67 The pentavalent state (H3As04, H2As04~, HAs042~) is
stable in aerated water, and elemental arsenic and arsine (AsHg) can
exist in highly reducing sediments or ashes. In more moderately
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reducing environments, the trivalent state (H3As03, H2As03-, HAs032~)
can exist.67 Although the pentavalent form is thermodynamically much
more stable in air-saturated water, about equal amounts of As (III) and
As(V) seem to occur in ocean water. The distribution of As(III) and
As(V) in ash pond effluents and ash pond leachate needs further inves-
tigation. However, the solubility of total dissolved arsenic is
independent of pH. For As(V), H2As04~ is the predominant species in
the pH range of 3 to 7; HAs042- is predominant in the pH range of 7 to
11.5; and As043~ predominates at pH above 11.5. For As(III), H3As03 is
the predominant species in the pH range of 0 to 9.2; H2As03~ is pre-
dominant in pH range between 9.2 to 12, and HAs032" predominates at pH
above 12.
Therefore, dissolved arsenic cannot be reduced to any great degree
by pH adjustment alone. Dissolved arsenic can be removed by complexa-
tion with polyvalent metal species, coprecipitation with metal hydroxide
adsorption onto a coagulant floe, sulfide precipitation, adsorption onto
activated carbon and alumina, and ion exchange.68'80 Some of these
processes for reducing arsenic from ash pond effluents need to be demon-
strated. Although removal of suspended solids could reduce suspended
arsenic, the suspended arsenic concentration may exceed 0.1 mg/1 when
total suspended solids concentration is 30 mg/1 (Table 24).
BORON
Boron(III) does not form a simple cation in solution.67 The
hydrolysis products of boric acid are B(OH)4-, B20(OH)5~, B303(OH)4-,
and B405(OH)42~. The solubility of boron is independent of pH, and
boron was found mostly in the dissolved form in ash pond water (Tables
17 to 22). Therefore, the boron content of an ash pond effluent cannot
be controlled by adjusting pH of the ash pond system. Reported treatment
methods for boron removal include evaporation, reverse osmosis, and ion
exchange.80
CADMIUM
Cadmium exhibits only the 2+ valence in aqueous solution. Mono-
nuclear hydrolysis products appear above pH 8, but the low solubility of
the hydroxide limits the concentration of cadmium (CdOH , Cd(OH)2) to
<10~5 M until pH 13 is reached. In the presence of carbonate ions, the
concentration of cadmium in solution is limited to even lower values by
the insolubility of CdC03. The formation of (Ca-Cd)C03 is to be
expected because Cd2+ and Ca*+ ions are nearly the same size.67 This
may be an important mechanism for the removal of trace concentrations of
cadmium from water in contact with CaC03. Cadmium cannot be greatly
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removed from ash pond effluents by adjusting pH and reducing suspended
solids unless the pH value is 9 or more (Tables 17 to 25). Suspended
cadmium can be readily settled within several hours (Table 24). Other
treatment processes for removing cadmium are coprecipitation with, or
adsorption on, iron or aluminum hydroxide, sulfide precipitation, ion
exchange, and reverse osmosis.80
CHROMIUM
Chromium occurs in the 2+, 3+, and 6+ oxidation states in water.
The divalent state is unstable with respect to evolution of hydrogen,
the trivalent state has broad stability, and hexavalent chromium
occurs under highly oxidized conditions.67 The minimum solubility of
hydrated Cr(OH)3 is in the pH range of 8 to 9,5, but chromium(VI) is^_
extensively hydrolyzed yielding species of HCr04~, Cr042~, and Cr207 ~.
Neutralization of acidic or alkaline ash ponds to a pH between 8 and 9
can cause chromium precipitation (Tables 17 to 22). Therefore, it is
likely that chromium(III) ions predominately exist in ash pond water.
COPPER
Only small amounts of copper(l) ion can exist in water unless it
is stabilized by complexing agents. The copper(II) ion at ordinary
concentrations begins to hydrolyze above pH 4 and precipitates the
oxide or hydroxide soon thereafter.67 The minimum solubility of Cu
occurs at pH between 8 and 11. Therefore, dissolved cupric ion can
be removed effectively by adjusting pH to neutral values (Tables
17 to 25) and precipitating in ash ponds (Table 24).
IRON
Iron in the 2+ and 3+ oxidation states is stable over broad
regions of potential and pH.67 In ash sluice water, the ferric
ion is probably predominant. The minimum solubility of the ferric
ion occurs at pH between 6 and 9. Therefore, neutralization of acidic
ash pond effluents can result in soluble iron converting to the sus-
pended form. However, because of the high iron content in coal ash,
reduction of suspended solids to 30 mg/1 might not reduce suspended
iron to the 1-mg/l level (Tables 17 to 25). The highest concentra-
tion of suspended iron was found as 5 mg/1 at a suspended solids
concentration of 20 mg/1 (Table 25).
LEAD
Lead(II) is the most common form of lead and has the most complex
hydrolysis behavior. The minimum solubility for hydrolyzed lead(II) is
at pH about 11. Lead carbonate is often the insoluble form of lead(II),
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-------
Neutralization of acidic ash pond effluents to pH between 8 and 9 may
precipitate dissolved lead(II) as Pb3(C03)2(OH)2, if sufficient carbonate
species is available in water.67'68
MANGANESE
Manganous ion, Mn2+, is the most stable aqueous oxidation state for
the element.67 The 3+ to 7+ states also occur in solution, but are not
likely to occur in ash pond water. The manganous ion is not readily
oxidized to the manganic form, other than at elevated pH. The +3 state
(manganic) is quite unstable, being easily reduced to Mn+2 or dispro-
portionating to Mn2+ and Mn02. The minimum solubility of manganous ion
is at a pH above 10. Adjustment of pH between 6 and 9 may not reduce
the concentration of manganese to a level of 0.05 mg/1 (Tables 17 to
22). The most common general approach seems to involve oxidation of the
soluble manganous form to insoluble manganous hydroxide or oxide at high
pH, with subsequent precipitation. Ion exchange treatment has proven
effective.80
SELENIUM
Selenium(IV) and selenium(VI) are very soluble in water.67 Sele-
nium(IV) may be the most common form of selenium in ash pond water. The
predominant species of selenium(IV) in water below pH 2 is H2Se03,
selenous acid. The anions HSe03- and Se032~ form at pH between 3 and 8,
respectively. Therefore, adjustment of pH for ash pond systems will not
remove selenium (Tables 17 to 23, and Table 25). Selenite ions can form
complexes with several metal ions. For removal from wastewater, iron
would be preferred as the precipitant.81 Selenium treatment by pre-
cipitation after adding a sulfide salt at slightly acid pH (pH 6.5) has
been suggested.79 The likely treatment mechanism involved is reduction
of the selenite ion, precipitating elemental selenium. Sulfide would be
cooxidized in the process. However, the cost-effective treatment pro-
cesses for removing selenium from ash pond effluents need further
investigation.
ZINC
Zinc(II) hydrolyzes only sparingly in acidic media to produce ZnOH+
and ZngOH3"1" before precipitation begins in the neutral region. In basic
media, Zn(OH)42" and perhaps Zn2(OH)62- are formed.67 The minimum solu-
bility of zinc(II) occurs between pH 9 and 11. Adjustment of pH to
about 9 may control the zinc in ash pond effluents (Tables 17 to 25).
-102-
-------
In summary, some trace metals in ash pond effluents were present in
both dissolved and suspended forms. The distribution of specific trace
metals between the dissolved and suspended forms is site-specific, but
it is important to analyze both forms for monitoring trace metals in
ash pond discharges. Adjustment of pH between 6 and 9 and reduction of
suspended solids concentrations to 30 mg/1 reduced total concentration
of many trace metals such as chromium, copper, lead, and zinc. However,
pH adjustment did not appreciably reduce total concentrations of arsenic,
boron, cadmium, iron, manganese, and selenium. The solubilities of
arsenic, boron, and selenium are independent of pH. Dissolved cadmium
and manganese can be greatly removed at pH above 9 and 12, respectively.
Total iron concentrations could not be reduced to the l»mg/l level at
neutral pH, even though suspended solids in some ash pond effluents were
reduced to 30 mg/1, because the high iron content in the suspended ash
particles.
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REFERENCES
1. Cooper, H.B. The Ultimate Disposal of Ash and Other Solids From
Electric Power Generation. In: Water Management by the Electric
Power Industry, E.F. Gloyna, et al., eds., The University of Texas,
Austin, Texas, 1975, pp. 183-195.
2. The Babcock and Wilcox Company. Steam/Its Generation and Use.
1972. 607 p.
3. Ruch, R. R., et al. Occurrence and Distribution of Potentially
Volatile Trace Elements in Coal. EPA/2-74-054, U.S. Environmental
Protection Agency, July 1974. 96 p.
4. Faber, J. H. U.S. Overview of Ash Production and Utilization. In:
Proceedings of the Fourth International Ash Utilization Symposium,
J. H. Faber, et al., eds. MERC/SP-76/4, U.S. Energy Research and
Development Administration, 1976. pp. 5-13.
5. U.S. Environmental Protection Agnecy. Development Document for
Effluent Limitations Guidelines and New Source Performance Stan-
dards for the Steam Electric Power Generating Point Source Category.
EPA-440/l-74-029-a, October 1974. 840 p.
6. Frascino, P. J., and D. L. Vail. Utility Ash Disposal: State of
the Art. In: Ash Utilization: Proceedings of the Fourth Inter-
national Ash Utilization Symposium, J. H, Faber, et al., eds.
MERC/SP-76/4, U.S. Energy Research and Development Administration,
1976. pp. 345-368.
7. Chu, T.-Y.J., et al. Complete Reuse of Ash Pond Effluents in
Fossil-Fueled Power Plants. In: Water 1976: I. Physical-Chemical
Wastewater Treatment, AIChE Symposium Series, No. 166, vol. 83,
1977. pp. 299-311.
8. Lucas, J. R., et al. Plant Waste Contaminants, In: Coal Pre-
paration. J. W. Leonard and D. R. Mitchell, eds., The American
Institute of Mining, New York, 1968. pp. 17.1-17.54.
9. Magee, E. M,, et al. Potential Pollutants in Fossil Fuels. EPA-
R2-73-249, U.S. Environmental Protection Agency, June 1973. 151 p.
10. Wachter, R. A., and T. R. Blackwood. Source Assessment: Water
Pollutants from Coal Storage Areas. EPA-600/2-78-004m, May 1978.
106 p.
11. Cavallaro, J. A., et al. Sulfur Reduction Potential of the Coals
of the United States. Report No. 8118, Bureau of Mines, U.S.
Department of the Interior, 1976. 323 p.
-104-
-------
12 Faber J. H., and P. 6. Meikle. Use and Disposal of Fly Ash.
Presented at the Association of Rural Electric Generating Cooper-
atives, Annual Plant Operators Conference, Lexington, Kentucky,
June 1970.
13 Brackett, E. E. Production and Utilization of Ash in the United
States. In: Ash Utilization: Proceedings of the Third Annual Ash
Utilization Symposium, J. H. Faber, et al., eds. Circular No. 8640,
Bureau of Mines, U.S. Department of the Interior, 1974. pp. 12-18.
14 Brackett, E. E. Production and Utilization of Ash in the United
States. In: Ash Utilization: Proceedings of the Second Inter-
national Ash Utilization Symposium, J. H. Faber, et al., eds.
Report No. 8488, Bureau of Mines, U.S. Department of the Interior,
1970. pp. 11-16.
15 Cockrell, C. E., et al. Production of Fly Ash-Based Structural
Materials. Report No. 69, Contract No. 14-01-0001-488, Office of
Coal Research, U.S. Department of the Interior, 1972.
16. Gartrell, F. E., and J. C. Barber. Environmental Protection—the
TVA Experience. J. Sanitary Engineering Division, Proceedings of
the American Society of Civil Engineers, 96, SA6, 1970.
pp. 1321-1334.
17 Hecht, N. L., nad D. S. Duvall. Characterization and Utilization
of Municipal and Utility Sludge and Ashes: Vol. II. Utility Coal
Ash. EPA-670/2-75-033c, U.S. Environmental Protection Agency, May
1975. 67 p.
18. Moulton, L. K. Bottom Ash and Boiler Slag. In: Ash Utilization:
Proceedings of the Third Annual Ash Utilization Symposium, J. H.
Faber, et al., eds. Circular No. 8640, Bureau of Mines, U.S.
Department of the Interior, 1974. pp. 148-157.
19. Pedlow, J. W. Cenospheres. In: Ash Utilization: Proceedings of
the Third Annual Ash Utilization Symposium, J. H. Faber, et al.,
eds. Circular No. 8640, Bureau of Mines, U.S. Department of the
Interior, 1974. pp. 34-43.
20. Capp, J. P., and J. D. Spencer. Fly Ash Utilization—A Summary of
Applications and Technology. Circular 3433, Bureau of Mines, U.S.
Department of the Interior, 1970. 78 p.
21. Cuffe, S. T., et al. Air Pollutant Emissions from Coal-Fired
Power Plants. Part 1, J. Air Pollut. Control Assoc., 14, 9, 1964.
pp, 353-362.
-105-
-------
22. Gerstle, R. W., et al. Air Pollution Emissions from Coal-Fired
Power Plants. Part 2, J. Air Pollut. Control Assoc., 15, 2, 1965
pp. 59-64. ' '
23. 0'Gorman, J V., and P. L. Walker, Jr. Mineral Matter and Trace
Elements in U.S. Coals. Report No. 62, U.S. Department of the
Interior, July 1972.
24. Bolton, N. E., et al. Trace Element Measurements at the Coal-Fired
Allen Steam Plant. Progress Report, June 1971-January 1973, Oak
Ridge National Laboratory. Report No. EP-43, National Science
Foundation, March 1975.
25. Kaakinen, J. W., and M. Jordan. Determination of a Trace Element
Mass Balance for a Coal-Fired Power Plant. Presented at the First
Annual Science Foundation Conference on Trace Contaminants, Oak
Ridge, Tennessee, August 1973.
26. Lee, R. E., Jr., and D. J. Von Lehmden. Trace Metal Pollution in
the Environment. J. Air Pollut. Control Assoc., 23, 10 1973
pp. 853-857. ' '
27. Davison, R. L., et al. Trace Elements in Fly Ash-Dependence of
Concentration on Particle Size. Environ. Sci. Technol., 8 13
1974. pp. 1107-1113. '
28. Von Lehmden, D. J., et al. Determination of Trace Elements in
Coal, Fly Ash, Fuel Oil, and Gasoline--A Preliminary Comparison of
Selected Analytical Techniques. Anal. Chem., 46. 2 1974
pp. 239-245. ' '
29. Cowherd, Jr., et al. Hazardous Emission Characterization of
Utility Boilers. EPA-650/2-75-066, U.S. Environmental Protection
Agency, July 1975. 175 p.
30. Kaakinen, J. W., et al. Trace Element Behavior in Coal-Fired Power
Plants. Environ. Sci. Technol., 9, 9, 1975. pp. 862-869.
31. Klein, D. H., et al. Pathways of Thirty-Seven Trace Elements
Through a Coal-Fired Power Plant. Environ. Sci. Technol 9
10, 1975. pp. 973-979. ' '
32. Lee, R. E., Jr., et al. Concentration and Size of Trace Metal
Emissions from a Power Plant, a Steel Plant, and a Cotton Gin
Environ. Sci. Technol., 9, 1975. pp. 643-647.
33. Magee, R. A., et al. Coal-Fired Power Plant Trace Element Study,
Vol. 1: A three Station Comparison. U.S. Environmental Protection
Agency, September 1975. 50 p.
-106-
-------
34. Natusch, D.F.S., et al. Characterization of Trace Elements in Coal
Fly Ash. In: Proceedings of the International Conference on Heavy
Metals in the Environment, Vol. II. Pathways and Cycling, 1975.
pp. 553-575.
35 Furr A. K., et al. National Survey of Elements and Radioactivity
in Fly Ashes. Environ. Sci. Technol., 11, 13, 1977. pp. 1194-1201.
36. Coles, D. G., et al. Behavior of Natural Radionuclides in Western
Coal-Fired Power Plants. Environ. Sci. Technol. 12, 4, 1978.
pp. 442-446.
37. Eisenbud, M., and H. C. Petrow. Radioactivity in the Atmospheric
Effluents of Power Plants That Use Fossil Fuels. Science, 144,
1964, pp. 288-289.
38. Martin, J. E., et al. Radioactivity from Fossil-Fuel and Nuclear
Power Plants. Presented at the IAEA Symposium on Environmental
Aspects of Nuclear Power Stations, New York, New York, 1969.
39. Hull, A. P. Comparing Effluent Releases from Nuclear and Fossil-
Fueled Power Plants. Nuclear Plants, April 1974. pp. 51-55.
40. Moore, H. E., et al. Sources of Polonium-210 in the Atmosphere.
Environ. Sci. Technol., 10, 6, 1976. pp. 586-591.
41. Grossman, J. S., et al. Aquatic Invertebrate Recovery in the
Clinch River Following Hazardous Spills and Floods. Report No.
VPI-WRRC-Bull-63, Water Resources Research Center, Virginia Poly-
technic Institute and State University, Blacksburg, Virginia,
December 1975.
42. Tenney, M. W., and W. F. Echelberger. Fly Ash Utilization in the
Treatment of Polluted Waters. In: Ash Utilization: Proceedings
of the Second Ash Utilization Symposium, J. H. Faber, et al., eds.
Circular No. 8488, Bureau of Mines, U.S. Department of the Interior,
1970. pp. 237-268.
43. Rohrinan, F. A. Analyzing the Effect of Fly Ash on Water Pollution.
44. O'Connor, J. T., et al. The Composition of Leachates from Combus-
tion Byproducts. Presented at the ASCE National Environmental
Engineering Division Conference, Symposium on Wastewater Effluent
Limits, The University of Michigan, Ann Arbor, Michigan, 1973.
45. Stephens, N. T., et al. Trace Metals in Effluents from Coal-Fired
Furnaces. Presented at the Fourth Annual Environmental Engineering
and Science Conference, University of Louisville, Louisville,
Kentucky, 1974.
-107-
-------
46. Weeter, D. W., et al. Environmental Management of Residues from
Fossil-Fuel Power Stations. Presented at the 47th Water Pollution
Control Federation Annual Conference, Denver, Colorado, 1974.
47. DiGioia, A. M., et al. Environmental Acceptable Coal-Ash Disposal
Sites. Civil Engineering American Society of Civil Engineers
December 1974. pp. 64-67. '
48. Guthrie, R. K., and D. S. Cherry. Pollutant Removal from Coal-Ash
Basin Effluent. Water Resour. Bull., 12, 5,' 1976. pp. 889-902.
49. Chu, T.-Y.J., et al. Characteristics of Wastewater Discharges from
Coal-Fired Power Plants. In: Proceedings of the 31st Purdue
Industrial Waste Conference, 1976, pp. 690-712.
50, Chu, T.-Y.J., et al. Characterization and Reuse of Ash Pond
Effluents in Coal-Fired Power Plants. J. Water Pollut. Control
Fed., 50, 11, 1978. pp. 2494-2508.
51. Milligan, J. D., et al. Characterization of Coal Pile Drainage
and Ash Pond Leachate. Presented at the 49th Water Pollution
Control Federation Annual Conference, Minneapolis, Minnesota,
October 3-8, 1976.
52. Theis, T. L., et al. Field investigations of Trace Metals in
Ground Water from Fly Ash Disposal. In: Proceedings of the 32nd
Purdue Industral Waste Conference, 1977. pp. 332-344.
53. Theis, T. L., and J. L. Marley. Environmental Considerations for
Power Plants Fly Ash Disposal. Presented at the ASCE Spring Con-
vention and Exhibit, Pittsburgh, Pennsylvania, April 24-28, 1978.
54. Rich, L. G. Unit Operation of Sanitary Engineering. John Wiley &
Sons, Inc., 1961. 308 p.
55. Camp, T. R. Sedimentation and the Design of Settling Tanks.
Trans. Am. Soc. Civil Eng., 111, 1946. pp. 895-958.
56. O'Connor, D. J., and W. W. Eckenfelder, Jr. Evaluation of Labora-
tory Settling Data for Process Design. In: Biological Treatment
of Sewage and Industrial Wastes, vol. 2: Anaerobic Digestion and
Solid-Liquid Separation, B. J. McCabe and W. W. Eckenfelder, Jr.,
eds. Reinhold Publishing Corporation, 1958. pp. 171-181.
57. Curtis, K. E., Trace Element Emissions from the Coal-Fired Gen-
erating Stations on Ontario Hydro. Report No. 77-156-k, Ontario
Hydro, Canada, 1977. 27 p.
58. Vandergriff, V. E. Characterization of Ashes at TVA Colbert Steam
Plant. Report, Division of Environmental Planning, Tennessee
Valley Authority, 1978. 97 p.
-108-
-------
59. Raask, E. Cenospheres in Pulverized-Fuel Ash. J. Fuel, 41, 1968.
pp. 339-344.
60. Chilton, T. H., and A. P. Colburn. Ind. Eng. Chem., 26, 11, 1934.
pp. 1183-1187.
61. Ranz, W. E., and W. R. Marshall. Chem. Eng. Prog., 48, 14,
1952. pp. 173-180.
62. Skelland, A.H.P. Diffusional Mass Transfer. John Wiley & Sons,
Inc., New York, 1974. 510 p.
63. Reed, G. 0., et al. Water Quality Effects of Aqueous Fly Ash
Disposal. In: Proceedings of the 31st Purdue Industrial Waste
Conference, 1976. pp. 337-343.
64. Crank, J. The Mathematics of Diffusion. Clarendon Press, Oxford,
England, 1956. 397 p.
65. Theis, T. L., et al. Sorptive Characteristics of Heavy Metals in
Fly Ash-Soil Environments. In: Proceedings of the 31st Purdue
Industrial Waste Conference, 1976. pp. 312-324.
66. U.S. Environmental Protection Agency, Quality Criteria for Water.
EPA-440/9-76-023, 1976. 501 p.
67. Baes, C. F., and R. E. Mesmer. The Hydrolysis of Cations: John
Wiley & Sons, Inc., New York, 1976. 489 p.
68. Cherkinski, S. N., and F. I. Ginzburg. Purification of Arsenious
Wastewaters. Water Pollut. Abstr., 14, 1941. pp. 315-316.
69. Buswell, A. M., et al. Water Problems in Analysis and Treatment.
J. Am. Water Works Assoc., 35, 1945. pp. 1303-1311.
70. Berezman, R. I. Removal of Inorganic Arsenic from Drinking Water
under Field Conditions. Water Pollut. Abstr,, 29, 1965. p. 185.
71. Logsdon, G. S., et al. Removal of Heavy Metals by Conventional
Treatment. In: Proceedings of the 16th Water Quality Conference,
vol. 16, University of Illinois, Urbana, Illinois, February 13-14,
1974. pp. 111-133.
72. Skripach, T., et al. Removal of Fluoride and Arsenic from the
Wastewater of the Rare Earth Industry. In: Proceedings of the 5th
International Conference on Water Pollution Research, vol. 2, 1971.
pp. 11-34.
-109-
-------
73. Rosehart, R., and L. Lee. Effective Methods of Arsenic Removal
from Gold Mine Wastes. Can. Mining J., June 1972. pp. 53-57.
74. Magnusen, L. M., et al. Arsenic in Detergents: Possible Danger
and Pollutions Hazard. Science, 168, 1970, pp. 389-390.
75. Irukayama, K. Discussion—Relation Between Black-Foot Disease and
the Pollution of Drinking Water by Arsenic in Taiwan. In: Pro-
ceedings of the 2d International Conference on Water Pollution
Research, vol. 1, 1964. pp. 185-187.
76. Shen, Y. S,, and C. S. Chen. Relation Between Black-Foot Disease
and the Pollution of Drinking Water by Arsenic in Taiwan. In:
Proceedings of the 2d International Conference on Water Pollution
Research, vol. 1, 1964. pp. 173-180.
77. Curry, N. A. Philosophy and Methodology of Metallic Waste Treat-
ment. In: Prbceedings of the 27th Purdue Industrial Waste
Conference, 1972. pp. 85-94.
78. Lee, J. Y., and R. G. Rosehart. Arsenic Removal by Sorption
Process from Wastewaters. Can. Mining Metall. (CIM) Bull., 65,
11, 1972. pp. 35-37.
79. Bellack, E. Arsenic Removal from Potable Water. J. Am. Water
Works Assoc., 63, 1971. pp. 454-458.
80. Patterson, J. W. Waste Water Treatment Technology. Ann Arbor
Science Publishers, Inc., Ann Arbor, Michigan, 1975. 265 p.
81. Hannah, S. A., et al. Removal of Uncommon Trace Metals by Physical
and Chemical Treatment Processes. J. Water Pollut. Control Fed.,
49, 11, 1977. pp. 2297-2309.
-110-
-------
APPENDIX A
EFFECTS OF INITIAL CONCENTRATIONS OF SUSPENDED SOLIDS
ON SETTLING OF ASHES
-111-
-------
10
10
-------
en
o
g
10"
10-
10
10
10J
in i i i—i [ill i i i i—i |iu i i i i—r
o PORT 1
O PORT 2
D PORT 3
A PORT 4
<^ PORT 5
CQ - 35,000 mg/1
k - 0.3117 min/cm
I i I
10
10"
10
t - kz (min)
Figure A-2. Suspended solids concentration vs. t - kz (electrostatic
preclpitator fly ash from plant E; initial suspended solids
concentration C0 - 35,000 mg/1).
-113-
-------
CO
E
10-
10-
10
Ul I I I I I I
ii 11 i i i—r
III I I I | T
o PORT 1
D PORT 2
A PORT 3
O PORT 4
O PORT 5
C0 - 22,000 mg/1
k - 0.2362 min/cm
A
D
oO
I I
""III
103
— 102
102
k = 7.2 rain/ft
(0.2362 min/cm)
* ' ' ' '
10
SETTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure A-3. Suspended solids concentration vs. the reciprocal of settling
velocity (electrostatic precipitator fly ash from plant E; initial
suspended solids concentration CQ - 22,000 mg/1).
-114-
-------
'£.
O
O
M
10-
10'
10
111 i i—i—r
11 I I | I I T
III I I I—I T
O PORT 1
O PORT 2
Q PORT 3
£ PORT 4
O PORT 5
C0 - 22,000 mg/1
k • 0.2360 min/cm
A ~
O
o
D
10"
10J
10
10J
10
10
t - kz (rain)
Figure A-A. Suspended solids concentration vs. t - kz (electrostatic
precipltator from plant E; Initial suspended solids
concentration C0 - 22,000 mg/1).
-115-
-------
10-
00
6
w
I
e
10'
10-
10
A
i Uu i i i
n i I i i i—
o PORT 1
C] TORT 2
A PORT 3
O PORT 4
O PORT 5
CQ - 5800 mg/1
k = 0.1099 mln/cm
III I I I I T
LDO
A O
103
III I I l i i i
102
10
SETTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure A-5. Suspended solids concentration vs. the reciprocal of settling
velocity (electrostatic precipitator fly ash from plant E; initial
suspended solids concentration CQ = 5800 mg/1).
-116-
-------
10=
10
10J
10
mrr—i—r
5
111 i i—i—r
T—i—r
PORT 1
PORT 2
PORT 3
PORT.4
PORT 5
o
o
•D
A
O
CQ - 5800 mg/1
k - 0.1101 min/cm
JJ.11 .1 1 L
LLU_J_
10
10J
10
10
t - kz (rnln)
Figure A-6. Suspended solids concentration vs. t - kz (electrostatic
preclpltator fly ash from plant E; initial suspended
solids concentration CQ = 5800 mg/1).
-117-
-------
'S.
o
I
§
O
Q
W
10
10'
10-
10'
10
i I I i—r
111 i i r
0 PORT 1
D PORT 2
A PORT 3
O PORT 4
O PORT 5
C0 - 31,000 mg/1
k = 0.5413 mJn/cm
D
A
D
A
MM I I I I I
103
I I
k - 16.5 mln/ft
>/| (0.5413 min/cm)
» II H i I I I i
10"
10J
10
10
SETTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure A-7. Suspended solids concentration vs. the reciprocal of settling
velocity (electrostatic precipitator fly ash from plant A; initial
suspended solids concentration C0 = 31,000 mg/1).
-118-
-------
o
M
H
W
U
§
u
s
10"
TTT~T — i — — m 1 1 n— i — r
° PORT 1
O PORT 2
Q PORT 3
A PORT 4
/\ PORT 5
CQ - 31,000 mg/1
k • 0.5414 rain/cm
10-
10'
10
JLL
i 111 i
mini—i—r
10J
10
10
t - kz (min)
Figure A-8. Suspended solids concentration vs. t - kz (electrostatic
precipitator fly ash from plant A; initial suspended
solids concentration Cn » 31,000 mg/1).
-119-
-------
10
s
u
a
I
10'
-------
oc
6
o
t~i
H
§
U
O
(SI
o
o
w
io5 u" i M i i — i - Mill i i — i — r
o PORT 1
O PORT 2
[-) PORT 3
A PORT 4
O PORT 5
C0 - 18,000 mg/1
k « 0.4593 min/cm
10-
10'
10
[II I I I I
O
O
11 I I I
O
o
o .
10"
10
10J
10
10
t - kz (min)
Figure A-10. Suspended solids concentration vs. t - kz (electrostatic
precipitator fly ash from plant A; initial suspended
solids concentration C0 = 18,000 mg/1).
-121-
-------
o
K
g
o
e
10
10
10
10
O
a A
o
111 i
10
o PORT 1
DPORT 2
APORT 3
OPORT /i
<>PORT 5
C0 = 6000 raB/I
k = 0.1.640 min/cm
D
A °O
LJ-LLL-L 1 I (
k_= 5.0 min/ft
(0.1640 mln/cm
mill i i
10J
10"
10
10
H)2 10
SKTTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure A-l1. SuHpcnded solids concentration vs. the reciprocal of settling
velocity (electrostatic precipitator fly ash from plant A; initial
suspended fsolicls concentration C = 6000 mg/1) .
-122-
-------
e
M
H
10
10
10
0 PORT 1
O PORT 2
D PORT 3
A PORT 4
OPORT 5
C(, = 6000 mg/1.
k = 0.1773 min/cm
D
O
In.
11 i
10
10
t - kz (rain)
10
10
A-12. Suspended solids concentration vs. t-kz (electrostatic
prt-cipi tator Cly ash from plant A; initial suspended
sol ids concentration CQ = 6000 mg/1).
-123-
-------
g
o
c.
M
^J
O
O
u
105
pi I I I
10'
10J
10
10
D
A
o
ii 11 i i i—r
o PORT 1
[] PORT 2
O PORT 3
A PORT 4
O PORT 5
CQ = 30,000 mg/l
k - 0.2198 min/cm
D
O AO
CO
D
O A
A
O
I I I i I—r
O
O A<>
1 II I I
I i I I I I I
k = 6.7 min/ft
(0.2198 mln/cml
liulT i i
10
10"
10
10
10
10
10 10
SETTLING TIME/SETTLING DEPTH, t/z (mln/ft)
Figure A-13. Suspended solids concentration vs. the reciprocal of settling
velocity (mechanical collector fly ash from plant J; initial
suspended solids concentration C0 = 30,000 mg/l).
-124-
-------
t/3
g
10-
10
10J
10
10
103
i—r
o PORT 1
O PORT 2
Q PORT 3
^ PORT 4
O PORT 5
C - 30,000 mg/1
k • 0.2198 min/cir
A
O
D
D
J L.
10
ii i i i i I L
10
t - kz (rain)
.0
Figure A-14. Suspended solids concentration vs. t - kz (mechanical
collector fly ash from plant J; initial suspended solids
concentration CQ - 30,000 mg/1).
-125-
-------
10J
SB
o
u
g
(J
e
e
10
10-
10'
10
0
D
A
O
O
[III I |"T
PORT 1
PORT 2
PORT 3
PORT 4
PORT 5
i—r
103
C0 - 17,500 mg/1
k = 0.1739 rain/cm
D
A
n A oO
o
A O
A
J L
LJ-LL.L..I
]k • 5.3 mln/ft
,(0.1739 min/cm)
II I il*l i I I
10J
104
10J
10
10* 10
SETTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure A-15. Suspended solids concentration vs. the reciprocal of settling
velocity (mechanical collector fly ash from plant J; initial
suspended solids concentration C0 « 17,500 mg/1).
-126-
-------
(X)
6
§
o
O
tn
Q
m—i—i rTTTT-n—i—i
o PORT 1
O PORT 2
PORT 3
PORT 4
PORT 5
C0 - 17,500 mg/1
k •» 0. 1837 min/cit
t - kz (rain)
Figure A-16. Suspended solids concentration vs. t - kz (mechanical
collector fly ash from plant J; initial suspended solids
concentration CQ » 17,500 mg/1).
-127-
-------
10*
;;- io3
1
O
t— 4
H
CONCENTR,
ts> 9
a 10
g
w
SUSPENDED
10
1
jT-rn-T—T i miii! i — i in in i i — i
o PORT 1
Q PORT 2
O PORT 3
A PORT 4
<> PORT 5
C0 - 4500 mg/1
k = 0. 1640 min/cm
o /
P
OA>
: T
: oA
n /.
0 DoQ^
Ap
V
r ° °A°
1 AO
0
o o
n OA 0
D
r°A°
i
-Mrl..' 1 .' ' 1 JJU.JL...L, ,1 1 1 1,LI._LJ.
o°A<> ~.
-
_
™
"
—
k - 5 min/ft -
(0.1640 min/cm)
4 . •
[O5
IO4
103
IO2
10
10^ _ J_
SETTLING TIME/SETTLING DEPTH, t/z (min/ft)
Figure. A-17. Suspended solids concentration vs. the reciprocal of settling
velocity (mechanical collector fly ash from plant J; initial
suspended solids concentration C0 = 4500 mg/1).
-128-
-------
10J
H
I
Cfi
o
0-
V.
10'
10
10
II I I I 1 1 III I I I IT
ri nil i (
0 PORT 1
O PORT 2
DPORT 3
A PORT k
VPORT 5
C, - 4500 mg/1
0
k * 0.1640 mln/cm
JJJ-i-I-J—L—--I— I I I I I I...J—1 1 11.1 I I ' '—I
10
10
10
t - kz (min)
10
10
Figure A-18. Suspended solids concentrations vs. t - kz (mechanical
collector fly ash from plant J-. inicial suspended solids
concentration CQ - 4500 mg/1).
-129-
-------
10-
o
V.
ST.
U
0,
10
10
TTTT-TT
" PORT 1
LJ PORT 2
A PORT 3
•0>PORT 5
ro • 3800 mg/1
k = 0.2297 rain/cm
O
-J——3 105
1., L
li I I l
k - 7 min/ft
(0.2297 rain/cm)
1..1..0 1.-I I , i
10
10J
1Q
10
SCTTI.IMC, TIME/SETTI,INC DEPTH, t/z (min/ft)
F-'iflure A-19. Suspended solids concentration vs. the reciprocal of
settling velocity (electrostatic precipitator fly ash
from plant ,1; initial suspended solids concentration
CQ - 1ROO rag/1).
•130-
-------
10
§
S io2
d
10
J 1 1 1 1 1 I ! 1 I I 1 ! 1 1 1 1 I
o PORT 1
O PORT 2
D PORT 3
A POST 4
- — O PORT 5
- C - 3800 rog/1
~ k - 0.2297 rain/cm
-
.
-
-
.
__
^
-
A-
0
o -
o _
1 6 «
nb
0 Qc
: 9
o
- o A
- D
- Q
1 1 i i i i i i 1 ii i i i i i i
10* 103
™
_
— I
M
.
-
•
102 ' ' ' !
lO
10
10
10
10
t - kz (mln)
Figure A-20. Suspended solids concentration vs. t - kz (electrostatic
precipitator fly ash from plant J: initial suspended
solids concentration C0 «= 3800 »g/l).
-131-
-------
10'
'(JIM
i r
TTTT7~T—I T
•.KIM i—r—r
10J
10'
0 PORT 1
D POUT Z
A PORT J
Q PORT A
/\ PORT 5
k - 0.3609 min/cm
10
^
c
8
v:
r.
~ * nO
-LJ
°n
n
AO
IS'
ID"
Uilil I. ! I
k = 11 min/ft
(0.3609 min/cm)
.1-1 I. I I I I
10
in
SI'TTMHC 'nMr./SETTI,TN6 nrT>T1l, t/z (min/ft)
A-2! . Suspended solids concentration vs. thr recinrocal of
settling velocity (electrostatic precipltator fly ash
from plant .T: initial suspended solids concnetration
C0 « 1600 mR/1).
-132-
-------
10-
10
IO3
K-l
c
IT;
10
F-n
O
o
- A
-A
en
1CT
0 PORT 1
O PORT 2
Q PORT 3
A PORT 4
O PORT 5
C - 1600 mg/1
k - 0.3609 rain/cm
10J
10
10
io
10
t - kz (mln)
Figure A-22. Suspended solids concentration vs. t - kz (electrostatic
preclpltntor fly ash frora plant J; Initial suspended solids
concentrntion C « 1600 mp,/l).
-133-
-------
10
10
i 10
§
a
I
,J
O
C
UJ
o
a
(X
K.
1C
ll-U,
10
n 1 1 i i
0 PORT 1
D PORT 2
A PORT 3
O PORT 4
<^> PORT 5
CQ - 0.6234 mg/1
k " 0.6234 min/cm
"Mil I
/
k " 19 min/ft
,(0.6234 min/cm)
III I I I I I
10
10
io
10
10
10
SETTMNO TIME/SETTLING DEPTH, t/z (mln/ft)
Figure A-23. Suspended solids concentration va. the reciprocal of
settling velocity (electrostatic precipitator fly ash
from plant J: initial suspended solids concentration
C0 - 390 mg/1).
-134-
-------
5
io4
/-v
Cl 3
I 10
§
H
1
u
W3
o
1 2
g 10
to
i
tn
£
10
1
i i i i l l l 1 1 i i l i i 1 l | 1 I i i i 1 1 1
° PORT 1
Q PORT 2
D PORT 3
A PORT A
O PORT 5 :
C0 • 390 mg/1 "
k • 0.6034 min/cra
;— —
-
_
D Ao
x^" °^
v^
— O o —
: ^o !
o
o ® °
A
r ^>
o
i t-i iri i il i 1 i i i l i i i i 1 i i i i i i l i
O3
0*
O3
102
10
1
10*
10J
t - kz (rain)
10
Figure A-2A. Suspended solids concentration vs. t - kz (electrostatic
precipltator fly ash from plant .1; Initial suspended
solids concentration Co - 390 mg/1).
-135-
-------
SUSPENDED SOLIDS CONCENTRATION (mg/1)
-------
1Q3U I I | I I—I 1 II I I I ' I
o PORT 1
O PORT 2
- PORT 3
10
10
o
in
s
10
10
A PORT 4
O PORT 5
C - 3000 mg/1
k • 0. 1148 mln/ctn
Illl I I—T
i i i i___j I
10
10J
10
10
10
10
Illl i i
10
t - kz (min)
.Figure A-26. Suspended solids concentration vs. t - kz (mechanical
collector fly ash from plant J; initial suspended solids
concentration CQ - 3000 mg/1).
-137-
-------
10
4-4
sf 10'
§
K
I
M
Q
M
$
m 102
S
&.
VI
g
10
O PORT i
Q PORT 2
A PORT 3
^ PORT 4
O PORT 5
CQ - 30,000 mg/1
-
-
: ^xx
X
X
8 A
u o °
S
"Mil 1 1 IMI 1 , , ,
10
10' 10
SETTLING TIME (mln)
Figure A-27. Suspended solids concentration vs. settling time
(bottom ash from plant L; Initial suspended solids
concentration 0.. " 30,000 mg/1).
-138-
-------
10"
10 J
8
10'
10
8
8
O PORT 1
U PORT 2
A PORT 3
-------
APPENDIX B
RESULTS OF INVESTIGATION OF MINERAL LEACHING RATE
OF FLY ASHES
-140-
-------
-w-
(units)
R
S
n
w
s-
rt
n
£
o
o
n
rt
o
•s-
S-
o
H
§
O
o
o
N>
o
o
o
o
CONDUCTIVITY (ymhos/cm)
-------
•& & A-
- CONDUCTIVITY
310
290
270
250
210
190
70
50
fc
1-1
»
-------
pH (units)
5
o-
o
•a
»
IT
O
CONDUCTIVITY (vmhos/cm)
-------
pll (units)
so
i
a.
I
H«
a
09
n
a
I 2
3- 3
S §
H
S
3 ^
i-1 a
M H-
m 3
r> '-'
n
3-
CONDUCTIVITY (ynhos/cm)
-------
1000
*•>
on
i
10
50 'id 70
MIXING TIME (min)
90 100
110
800
120
Figure B-5. pH and mineral leaching rate of 3 percent electrostatic precinitator fly ash from plant K.
-------
A—A—A
O
o
A
A- - PH
-Q_ - CONDUCTIVITY
_L
J_
_L
900
800
700
600
500
400
300
200
o
I
8
10
20
30
40
50
60
70
80
90 100 110 120
MIXING TIME (rain)
Figure B-6. pH and mineral leaching rate of 3 percent mechanical collector fly ash from plant K,
-------
t
h-'
.p-
12
50
90
100
60 70 80
MIXING TIME (rain)
Figure B-7.. pH and mineral leaching rate of 3 percent electrostatic precipitator fly ash from plant L.
_ 1700
1500
- 1300
C!
ce
o
f.
e
>
M
g
- 100
110 120
-------
500
oo
12 t-
11
10
J_
10
_L
20
_L
J_
J_
J_
_L
_L
_L
30
40
80
90
O
PH
CONDUCTIVITY
50 60 70
MIXING TIME (min)
Figure B-8. pH and mineral leaching rate of 3 percent mechanical collector fly ash from plant t.
100
110
1°
•A 00
300
200
B
M
CJ
O
O
100
120
-------
APPENDIX C
pH AND CONDUCTIVITY Of ASH TRANSPORT WATER VS. MIXING TIME
FOR VARIOUS ASH CONCENTRATIONS
-149-
-------
Ul
o
SUSPENDED SOLID CONCENTRATION
3% 2% J% Q.5%
A DVD
12
_L
_L
0
20 40 60 80 100 120
MIXING TIME (min.)
140
160
180
Figure C-l.
time for various ash concentrations (electorstatic precipitator
-------
-IST-
CONDUCTIVITY (jjmho / cm)
§o
o
8
"j
H*
OQ
n 3
o o.
H- C
•a o
Hi O
r-* H>
•4
01 cr
(I) rt
3
era
8-
X
z
CD
3-
n
H-
o
8
s
O
CO
o
-------
10
8-
X
Q.
6-
D ~~
SUSPENDED SOLIDS CONCENTATION
3% 2% 1% 0.5%
D
o
_L
10
20 40 60 80 100 120
MIXING TIME (min.)
140
160
180
Figure C-3. pH of ash transport water vs. mixing time for various ash concentrations (electrostatic precipitator
fly ash from plant J).
-------
-esi-
CONDUCTIVITY (^mho/cm)
til ^J OO CO
ag-
-e R
H- rt
ft H-
V <
n H-
O rt
•< -^
Hi O
» a"
y
rt
hti 1
O S
S 0}
•o
•O O
f ft
X
3
H- g>
g- m
(X)
ft i.
B P
o
H
g
1
H-
O
g
Hi
8-
i
o
3
CO
OC
w
OSS
m
o
D^oR
^5
C/)
o
Op |
m
p
0 tn
01
CO
10
-------
APPENDIX D
PERCENTAGE OF TRACE ELEMENT CONCENTRATIONS IN ASH POND EFFLUENTS
EQUAL TO OR GREATER THAN VARIOUS GIVEN CONCENTRATIONS
-154-
-------
100 F-
1
1
1
1
1
(
(
1
rrr^
10
O.I
0.01
n
At (•)
Fe (O)
pH(A)
Zn(A)
-O
—D Cu (D)
Cr (•)
Pb (*)
Ni (•)-
Cd (T)
As (V)
Be (•)
__ __ - - -O Se (O) -
0.001
Hg (CO E
0.0001
1
1
1
1
1
1
1
100 90 80 70 60 50 40 30 20
PERCENT OF TRACE ELEMENT CONCENTRATIONS OR pH EQUAL TO
OR GREATER THAN A GIVEN VALUE (%)
10
Figure D-l. Percent of trace elements concentrations in fly ash pond effluent
at plant A equal to or greater than various given concentrations.
-155-
-------
:>
D
5
3
0
b
o
— i — i i i 1 1 1 1 r
O
CONCENTRATION (mg/1) OR pH (UNIT)
E _ 6
.
o
o
V)
ft
tt>
a
o n> >T3
O Hi (B
S i-h ft
n t-> n
fl) C fl>
a n> 3
rt 3 rr
1 rr
(b o
rt D> i-h
H- rr
O rr
0 T3 n
0) r-> (b
• 8) O
a ro
rr
ID
rt O
O O
9
O n
ft tt>
00 rr
ft ft
fl> P>
fb rr
rr H-
(B O
ft 3
(o
rt
jr H.
g 3
cr
< o
a> rt
i-( rt
r* O
CO B)
CO
OQ 3"
H-
< TJ
n o
3 3
CL
O
o
(0
o
P3
H
OS
"H -^
eg °
pa
W
f
M
>8 en
o z o
< n
^M O
3 §
w
52 CM
^ °
33
•2 ro
P °
H
O
-------
100 p-
10
•a
m
o
S3
O
8
0.01
0.001
p Fe(O)
pH (A) -
Al (•)
Mn(O) I
Zn(A) g
CuO
Ni
Se(0)
As(V)
Hg(Q)
Cr(W
Cd(T)
0.0001
I I I I I I I
I I I
100 90 80 70 60 50 40 30 20 10 0
PERCENT OF TSACE ELEMENT CONCENTRATIONS OR pH EQUAL TO
OR GREATER THAN A GIVEN VALUE (%)
Figure D-3. Percent of trace elements concentrations in bottom ash pond
effluent at plant B equal to or greater than various given
concentrations.
-157-
-------
Ui
oo
i
00
o
M »
01 9
3 ff
rt
O
ea M,
O M
(B
O 3
>"< (6
OQ rt
1 CO
ft
01 O
n o
ft a
fl O
«
rt 3
3* r»
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3 (tt
r»
< H.
a, o
1 3
1* 01
o
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M- »-•
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3 -O
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3 a.
0» i-h
rt M,
M. M
O C
3 ft
0) 3
• rt
n
H
W
50
W
="8
o Z
1-1 n
< M
M 2
Z H
c o
K a
C/J
^^
S-8 O
H
O
Q
b
o
o
p
o
o
p
b
CONCENTRATION (mg/1) OR pH (UNIT)
"1—I I I Mill
I I I I III
1—I I I III
I I I Mil
O
O
CD
O
00
O
H o
h
o
Q.
I 1 I M Mill 1 I I I Hill ml || iii, i,M
-------
^ O CONCENTRATION (mg/1) OR pH (UNIT)
I 8 i 2
1 1 1 I Illl
1 1 — ! 1 1 1 Illl
I 1 — TTT1 1 1 1
1 1 1 II III li
0 C
l
Ui
3
7
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3 «> O
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3 C rt
rt » i-«
H 3 »
p> rt o
rt fl>
H. W
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rt rt
(0
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c o
SB (I)
(-• 3
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3- PI
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< w
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8
ro
O
o
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1
1
_ 1
I
1
1
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l
1
r__^
N
313!
mill
_L_L
IQ
' I I I Mil
-------
ON
O
I
D
D 0
D 0 0
5QO
i i i i I 1 1
CONCENTRATION (mg/1) OR pH (UNIT)
^ _ 0 C
1
1 1
Ml"| 1 1 Mllll II | ITTTT] 1 1 | Mllll
H-
30
"-C
00 /""* *T5
H- z; »
< e> n
it 01 n
v^ 3
n
3 i-*i O
(I) !->
3 C rt
rt rt o
rt re
H- 0>
O rt (!)
3 (->
w ^ ro
• i * at
01 (D
3 3
rt rt
O 0
oncent rations .
equal to or gi
n> 3
to
rt o
n> o
11 g-
3* 3
B) n>
3 CL
B> 09
n 3"
H-
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C O
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O.
TJ
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i-3
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^ ™
£4 EB
="8
HCENTRATIONS 01
SIVEN VALUE C%5
•a
M
JO
t
H
O
O
(£>
0
CD
0
OJ
0
ro
o
O
—
1
1
- 1
1
1
— 1
I
- e
O
cp >OTJ:T>ZO
CD tQ "^ ^r «Q «> — c
0)
I ' ' ' "Mil 1 I I I Mill 1 I I Mllll I i I I i i i i mil i i i i mil
-------
-, O CONCENTRATION (mg/1) OR pH (UNIT)
\ 8 § 8 - 5
1 1 1 1 till
1 1 1 1 INI
1 1 1 1 Mil
1 1 1 1 1 111
1 | I 1 I ill
O
0
00
O It TJ
O i-h fl>
3 i-h H
n (~> o
men
ana
it 3 rr
>-( rt
B) O
rt pi i-h
t* rr
O r»
3 TJ H
01 I— ' to
• V O
a ID
rr
fl)
n> 3
ja n
c a
0) re
i-"
O
rf O
O 9
O
o n>
>1 3
rt
on n
H S«
re 3
ft (0
3* 3
A)
< a
01 O*
>-( H-
H- 3
o n
c a.
DO (n
H- y
n •«
3 §
O.
PJ
8
M
o
50
o
H
1
o z
M O
< M
w a
55 H
o
!/l
o
pa
EC
W
-------
100
10
X
tx
CO
e
I o.i
O
O
0.01 -
0.001 —
0.0001 I—
pH (A).
Al (•)
Fe (O)
m
Cu (D)
Zn (A)_
Mn (O)
Cr (•)
Se
r~-*r> V As (V)_
Cd (V) -
c
^ —
1
1
1
1
1 1 1
1
1
l_l
i.y
VI
100 90 80 70 60 50 40 30 20
PERCENT OF TRACE ELEMENT CONCENTRATIONS OR pH EQUAL TO
OR GREATER THAN A GIVEN VALUE (%)
10
0
Figure D-8. Percent of trace element concentrations in combined ash pond
effluent at plant E equal to or greater than various given
concentrations.
-162-
-------
^ -^ Ovl'ViiJ*-'' A*-****- J-V/A* \.*U£}/ JU
^ § o
2 o Q P
1 1 1 Mill
1 1 1 1 Illl
1 — 1 1 1 Illl 1 I
j vsj.v if*-*- \ *•»*• •*-•*-/
_ C
_ o c
1 1 1 III) 1 1 1 Mill! "
1 1 IIMI
CO
I
00
IB
\0
n a
• 91 O
3 to
fl>
O 3
wo n
C 3
(a ft
n
ft o
O 3
o
o m
K 3
OQ M
1 SB
(D rt
a> H-
ft O
n 3
H| 01
ft H-
3* 3
3 O
O
P- 3
O (0
oo 10
O "O
3§
o.
-------
3 § O CONCENTRATION (mg/1) OR pH (UNIT)
2 Q Q P _
1 1 1 1 1 1 III 1 TT7 I 1 1 1
1 1 1 1 1 1 II I 1 1 1 1 III 1 1
0 C
1 1 1 1 1 1 1 III ITTT
o
n A 13
o H» n
3 i"ti ^
§ si
rt- 3 rt
•1 rt
9, o
rt so HI
O rt
£3 13 ^
• st n
3 A
n
A
osr
5§
s s
o
rt o
O 3
o
O A
H 3
rt
00 1
to H-
rt O
A 3
it w
3" 3
P>
3 O
O
< 3
•^ H-
H- 3
O A
C O.
OQ CO
H. B*
A 13
3 O
a.
13
M
H
O
O
> M
H
M PI
to f
PI
> O
O Z
M O
^ w
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o
en
o
•3
w
I
H
o
J
I Mill I ' ' ' Hill I I I i INI
-------
100 E~
10
Ou
O
§ O.I
H
25
w
O
a
o
O
0.01
0.001
0.0001
Or
-0--0-
.XT
.-o-o-
--0-
-0—0—0
—Or'
.AT
----—A-A PH(A)
Al
.O Fe (O).
As
Zn
Cu
Mn (O)E
Ni
Pb (093
Se (O)
Cr (•)_
Cd W
Hg (0)
1
1
1
100 90 80 70 60 50 40 30 20 10 0
PERCENT OF TRACE ELEMENT CONCENTRATIONS OR pH EQUAL TO
OR GREATER THAN A GIVEN VALUE (%)
Figure D-ll. Percent of trace element concentrations in combined ash pond
effluent at plant H equal to or greater than various given
concentrations.
-165-
-------
100
10
BE!
a..
t>0
E
O.I
0.01
0.001
0.0001 I—
A—
A- ---- A ------- A pH(Al_
AI (•)
cr
Fe
Zn (A)
As (V)
Cu (D)_
Se (O)
Pb (*)
Cr (•)
Mn (O)
Cd
P Hg O_
1
1
1
1
1
1
_J
1
100 90 80 70 60 50 40 30 20 10
PERCENT OF TRACE ELEMENT CONCENTRATIONS OR pH EQUAL TO
OR GREATER THAN A GIVEN VALUE (%)
Figure D-12. Percent of trace element concentrations in combined ash pond
effluent at plant I equal to or greater than various given
concentrations.
-166-
-------
100 p-
10
•a
cri
O
00
e
O.I
w
O
§
O
0.01
0.001
0.0001
pH (A)
Al (•)
Fe (O)
Zn (A) _
As (V).
Ni (+)
Pb (•)
Se (O)
Cr (•)
Cd (V)
Hg (Q)
Q
____.—O
--cr'
1
1
1
1
1 1
100 90 80 70 60 50 40 30 20
PERCENT OF TRACE ELEMENT CONCENTRATIONS OR pH EQUAL TO
OR GREATER THAN A GIVEN VALUE (%)
10
Figure D-13. Percent of trace element concentrations in combined ash pond
effluent at plant J equal to or greater than various given
concentrations.
-167-
-------
D P CONCENTRATION (mg/1) OR pH (UNIT)
3 O P
2 Q O P
1 1 I I 1 1 1 1
i I l l I III
1 1 1 1 Mil
1 1 II III! I I
5 1
1 1 1 1 i i i 1 1 1 1 r
OQ
o
o
CO
I
n to <-a
O l-Tt fit
n t-> n
n> c %
3 ffl S
rr 3 rr
n rt
to o
rr p> MJ
O
S
M
1-8
W
• P> O
S fl>
ro
*->
(0
e 3
B> rr
n
rr o
O 3
O
O ft)
rt 3
rr
ao £
fl> rr
B> H.
rr O
(D 9
r| 0>
sr s
3 O
O
O ID
g °"
fi>
00 CO
H- P"
ffl -a
9 o
3
Ou
CD
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13
M
S
n 00
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S^ o
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w rd
50 S CD
si °
> 2
< M
M Z
Z H
s o OJ
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13
I
^"^
D
i mil
O
a.
-------
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30
c
n>
a
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3 HI H
o M n
ro c »
3 fl> 3
rt 3 rt
i-( rr
50 o
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3 T3 H
CD t-1 OJ
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3 rt>
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f9
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n
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n
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r+ O
(B 3
P< 00
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111
3 O
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11 H-
H. 3
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C 0.
3)
W
(X) 0)
H- 3"
(B 13
3 O
3
o.
0
o
0
o
p
o
o_
CONCENTRATION (mg/1)
P
OR pH (UNIT)
I I 1 1 1 1
O
O
[
1
-a
M
50
M
25
H
O
O T)
w o
> M
H
C1! W
50 r1
M
H 2
="8
o z
n O
< M
§3
g§
C O
W 2
cn
*-"N
5^ O
M
O
s
O
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(0
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00
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s
g
8
9
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R
t?
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l|>
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f
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*
^
i
{
I
i
I i I mil I I I I Mill
-------
APPENDIX E
WATER QUALITY CRITERIA FOR DOMESTIC
WATER SUPPLIES
-170-
-------
TABLE E-l. WATER QUALITY CRITERIA FOR DOMESTIC WATER SUPPLIES3
Parameter (mg/1. unless otherwise noted)
Concentration
Aluminum b
Arsenic 0.05
Boron b
Beryllium b
Calcium b
Cadmium 0-01
Chromium °-05
Copper J--0
Iron ° • •*
Lead °-05
Magnesium "
Manganese 0.05
Mercury °-002
Nickel b
pH, standard units 5-9
Selenium °-01
Sulfate 25°
Sulfide b
Total dissolved solids 250
Zinc 5.0
aU.S. Environmental Protection Agency. Quality Criteria for
Water. EPA-440/9-76-023, Washington, DC, 1976. 501 p.
Not applicable.
-171-
-------
APPENDIX F
ANALYTICAL PROCEDURES
-172-
-------
APPENDIX P
ANALYTICAL PROCEDURES
Parameter
Alkalinity,
total (pH 4.5)
mg/1 as CaCO
Alkalinity,
phenolphthalein
mg/1 as CaCO
Aluminum
Mg/1 Al
Antimony
Mg/1 Sb
Arsenic
Mg/1 As
Procedure
Titrimetric -
electrometric
(Orion Model 701)
Titrimetric -
electrometric
(Orion Model 701)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Digestion and
colorimetric
SDDC (Beckman Model B)
Atomic absorption -
gaseous hydride (Tech-
tron Model AA-5 or
1200)
Reference
SM, p. 278
SM, p. 278
EPA, pp. 81, 92
EPA, pp. 81, 94
SM, pp. 62, 65
EPA, pp. 81, 95
Minimum
detectable
amount
200
100
-------
Parameter
Barium
M8/1 Ba
Beryllium
Mg/1 Be
Boron
MS/1 B
Bromide
M8/1 Br
Cadmium
H8/1 Cd
Procedure
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Colorimetric -
cur cumin
(Beckman Model DB-Gt)
Titrimetric
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Reference
EPA, pp. 81, 95,
EPA, pp. 81, 99
SM, p. 287 and
EPA, pp. 13, 81
EPA, p. 14
EPA, pp. 81, 101
Minimum
detectable
amount
97 100
10
100
2
10
Calcium
mg/1 Ca
Atomic absorption -
extracted (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
EPA, pp. 81, 89, 101 1
EPA, pp. 81, 103
-------
01
i
Parameter
Procedure
Reference
Minimum
detectable
amount
Chemical
oxygen demand
mg/1 COD
Chloride
mg/1 Cl
Chromium
Mg/1 Cr
Cobalt
Mg/1 Co
Conductance,
specific
Mmhos/cm at 25 C
Titrimetric -
dichromate reflux
Colorimetric-automated
ferricyanide
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
extracted (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
extracted (Techtron
Model AA-5 or 1200)
Kohlrausch bridge
with carbon
conductance cell
(Lab-Line Mark IV)
EPA, p. 20
SM, p. 613
EPA, pp. 81, 105
EPA, pp. 81, 107
EPA, p. 275
50
EPA, pp. 81, 89, 105 5
100
EPA, pp. 81, 89, 107 5
0.5
-------
Parameter
Procedure
ON
I
Copper
MgA Cu
Cyanide, total
mg/1 Cn
Fluoride
mg/1 F
Hardness, total
mg/1 as CaCO
J
Iron, total
Mg/1 Fe
Iron, ferrous
Mg/1 Fe
Reference
Atomic absorption -
Direct (Techtron
Model AA-5 or 1200)
Distillation and
colorimetric
(Beckman model B)
Specific ion
electrode (Orion
Model 101)
Distillation and
specific ion electrode
(Corning Model 101)
Calculation from
Ca and Mg values
Atomic abosrption -
direct (Techtron
Model AA-5 or 1200)
Colorimetric -
phenanthroline
(Beckman Model B)
EPA, pp. 81, 108
EPA, p. 40
EPA, p. 65
SM, pp. 388, 391
SM, p. 201
EPA, pp. 81, 110
SM, p. -;:08
Minimum
detectable
amount
10
0.01
0.1
0.1
50
10
-------
Procedure
Reference
Minimum
detectable
amount
Lead
MgA
Magnesium
mg/1 Mg
Manganese
Mn
Manganese,
filterable
Mg/1 Mn
Mercury
Mg/1 Hg
Nickel
Mg/1
Atomic absorption -
direct (Techtron Model
AA-5 or 1200)
Atomic absorption -
extracted (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
membrane filter filtra-
tion (Techtron Model
AA-5 or 1200)
Digestion and flameless
atomic absorption
(Coleman Model MAS-50)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
extracted (Techtron
Model AA-5 or 1200)
EPA, pp. 81, 112 100
EPA, pp. 81, 89, 112 10
EPA, pp. 81, 114 0.1
EPA, pp. 81, 116 10
EPA, pp. 81, 116 10
EPA, p. 118 0.2
EPA, pp. 81, 141 50
EPA, pp. 81, 89, 141
-------
oo
t
Parameter
Nitrogen,
ammonia
mg/1 N
Minimum
detectable
Procedure Reference amount
Colorimetric - EPA, p. 168 0,01
automated phenate
(Technicon Auto-
Analyzer II)
Nitrogen, nitrate
plus nitrite
mg/1 N
Oil and grease
mg/1
PH
standard units
Phenols
Mg/1 phenols
Phosphate, total
mg/1 P
Colorimetric -
automated cadmium
reduction (Technicon
AutoAnalyzer II)
Separatory funnel
extraction and gravi-
metric (Mettler Model
H51)
Potentiometric
(Orion Model 701)
Distillation and
colorimetric -
4-AAP (Beckman
Model B)
Colorimetric -
automated digestion
and single reagent
(Technicon Auto-
Analyzer II)
Colorimetric -
manual digestion and
automated ascorbic acid
reduction (Technicon
AutoAnalyzer I)
EPA, p. 207
EPA, p. 232
EPA, p. 239
SM, p. 577 and
EPA, p. 241
EPA, p. 249 -
with TVA
modifications
EPA, p. 256
0.01
Not
Applicable
1
0.01
0.01
-------
!t
Procedure
Reference
Minimum
detectable
amount
Potassium
mg/1 K
Residue, total
filterable
mg/1
Residue, total
nonfilterable
mg/1
Selenium
Mg/1 Se
Silica
mg/1 SiO,
Silver
pg/1 Ag
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Gravimetric - glass
fiber filtration
(Mettler Model H51)
Gravimetric - glass
fiber filtration
(Mettler Model H51)
Atomic absorption -
gaseous hydride
(Techtron Model
AA-5 or 1200)
EPA, pp. 81, 143
EPA, p. 266
EPA, p. 268
EPA, p. 145
Colorimetric - automated EPA, p. 274
molybdosilicate
(Technicon Auto-
Analyzer I)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
extracted (Techtron
Model AA-5 or 1200)
automated
by TVA
EPA, pp. 81, 146
EPA, pp. 81, 89, 146
0.1
10
0.1
10
-------
oo
o
Parameter
Sodium
mg/1 Na
Sulfate
mg/1 S04
Sulfide, total
mg/1 S
Sulfite
mg/1 S03
Tin
Hg/1 Sn
Titanium
Mg/1 Ti
Procedure
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Turbidimetric
(Hach Model 2100)
Colorimetric -
methylene blue
(Beckman Model B)
Titrimetric -
iodine
Titrimetric -
iodide-iodate
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Minimum
detectable
Reference amount
EPA, pp. 81, 147 0.1
EPA, p. 277 1
SM, p. 503. 0.02
EPA, p. 284 1.0
EPA, p. 285 2
EPA, pp. 81, 150 <1000
EPA, pp. 81, 151 1000
Turbidity
Jackson units
Model AA-5 or 1200)
Nephelometric -
formazin
(Hach Model 2100)
EPA, p. 295
-------
Parameter
Vanadium
M8/1 V
Zinc
Mg/1 Zn
Procedure
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Atomic absorption -
direct (Techtron
Model AA-5 or 1200)
Reference
EPA, pp. 81, 153
EPA, pp. 81, 155
Minimum
detectable
amount
500
10
i
i-1
00
(-»
i
Abbreviations of references:
EPA - U.S. Environmental Protection Agency. Methods for chemical analysis of
water and wastes. EPA, Water Quality Office, Cincinnati, Ohio. 1974.
298 p.
SM - American Public Health Association.
of water and wastewater. 14 ed., American
New York, N.Y. 1975. 1193 p.
Health
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
2.
1. REPORT NO.
EPA-600/7-80-067
4. TITLE AND SUBTITLE
Behavior of Coal Ash Particles in Water: Trace
Metal Leaching and Ash Settling
7. AUTHOR(S)
T.-Y.J.Chu, B.R. Kim, andR.J. Ruane
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Tennessee Valley Authority
1120 Chestnut Street, Tower H
Chattanooga, Tennessee 34701
8. PERFORMING ORGANIZATION REPORT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
15. SUPPLEMENTARY NOTES
919/541-2547. TVA
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
March 1980
6. PERFORMING ORGANIZATION CODE
10. PROGRAM ELEMENT NO
INE624A
• 1. CONTRACT/GRANT NO.
EPA Interagency Agreement
D5-E721
3. TYPE OF REPORT AND I
Final; 5/75-11/79
3. TYPE OF REPORT AND PERIOD COVERED
4. SPONSORING AGENCY CODE
EPA/600/13
"IB. ABSTRACT Tne report giyes results Qt- stud f th b h
water a study of importance to coal-fired power planteiTa10M-
of danv°D?h reSl£lT & ^ b°tt0m ^ fr°m Coal
abmtv SS^7'^ W hand/mg and diSp°Sal are used' ^pending on water
effluent ^ J P f proximity, environmental regulations, and cost. Ash pond
effluent limitations for suspended solids can be met by properly designing; ash oonds
fn tin?,PO?dS- B6CaUSe °f h^h ^ con'cen'traLn durrggs^Lg
*°11™ the hindered-zone settling behavior, and settle faster thaS
ChemiCal characteristics of ash pond
ter Tv hnnH f u the quantity ** quality of slu^ing wa-
and aLIfin? rnSdn5iUe PS ^ fr°m 3 tO 12' dePendinS ™ the content of SOx
ter A^klunP ££ °XldeS|im the *?* and on the buffering capacity of the sluicing wa-
r» ««oS? P. In haS a ratio of concentration (in terms of ng/1) of dissolved
of^ach S™ °' \ ^ac?limetal leach^ fro^ the ashes dlpends on the con-
metal m the ash matrix' its chemical bonding in the ash
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Pollution
Water
Coal
Ashes
Particles
Leaching
Settling
Waste Disposal
Ponds
Suspended Sediments
Sluices
3. DISTRIBUTION STATEMENT
Release to Public
EPA Form 2220-1 (9-73)
b.lDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
Coal Ash
Trace Metals
19. SECURITY CLASS (ThisReport)
Unclassified
20. SECURITY CLASS (Thispage)
Unclassified
c. COSATI Field/Group
13B
07B
21D
2 IB
14B
07D,07A
08H
21. NO. OF PAGES
194
22. PRICE
-182-
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