Office of
Research and
Development
Municipal Environmental Research
Laboratory
Cincinnati, Ohio 45268
EPA-600/7-77-11!
December 1977
DATA BASE FOR
STANDARDS/REGULATIONS
DEVELOPMENT FOR
LAND DISPOSAL OF
FLUE GAS CLEANING SLUDGES
Interagency
Energy-Environment
Research and Development
Program Report
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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 reJate 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.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-77-118
December 1977
DATA BASE FOR STANDARDS/REGULATIONS
DEVELOPMENT FOR LAND DISPOSAL OF
FLUE GAS CLEANING SLUDGES
by
Dallas E. Weaver
Curtis J. Schmidt
John P. Woodyard
SCS Engineers
Long Beach, California 90807
Contract No. 68-03-2352
Project Officer
Donald E. Sanning
Solid and Hazardous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati , Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This document, prepared by SCS Engineers, is a report to the
Office of Research and Development, Environmental Protection
Agency of their research efforts funded by that Office under con-
tract. It has been published exactly as received. The mention
of trade names or commercial products does not constitute en-
dorsement or recommendation for use. The conclusions, recommen-
dations and other contents of this report do not necessarily re-
flect the present views and policies of the U.S. Environmental
Protection Agency as stated by the Office of Solid Waste:
"The Office of Solid Waste believes that scrubber sludge
should not be landfilled unless the sludge is solid. This
will normally require chemical treatment of the sludge
except in special situations (such as a desert) where the
sludge will dry out. If the sludge remains wet indefinite-
ly, the disposal area will be useless for additional use
and this should not be acceptable. Long term land degrada-
tion that is reasonably avoidable should not be a tradeoff
of air pollution control."
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FOREWORD
The Environmental Protection Agency was created because of
increasing public and government concern about the dangers of
pollution to the health and welfare of the American people.
Noxious air, foul water, and spoiled land are tragic testimony
to the deterioration of our natural environment. The complexity
of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in
problem solution and it involves defining the problem, measuring
its impact, and searching for solutions. The Municipal Environ-
mental Research Laboratory develops new and improved technology
and systems for prevention, treatment, and management of waste-
water and solid and hazardous waste pollutant discharges from
municipal and community sources, for the preservation and treat-
ment of public drinking water supplies, and to minimize the ad-
verse economic, social, health, and aesthetic effects of pollu-
tion. This publication is one of the products of that research;
a most vital communications link between the researcher and the
user community.
This report presents a decision tree approach to the formu-
lation of guidelines and limitations for Flue Gas Cleaning (FGC)
sludge management which takes into account site specific geo-
graphical and hydrological considerations. The information is
applicable to the problem of safely disposing of wastes on land.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
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ABSTRACT
This study addresses the problem of flue gas cleaning (FGC)
sludge disposal to the land. It considers the problem from a
potential regulatory approach, looking at the various aspects
which could play a part in determining the best practical control
technology currently available. Factors that were taken into
consideration include: (1) the origin of the FGC sludge problem
(character of the fuel, combustion process, gas cleaning, and
sludge management); (2) criteria for the evaluation of sludge
disposal options (sludge characteristics, health, ecological,
safety, and aesthetic considerations; (3) applicable, existing
or proposed standards/regulations (solid waste, hazardous waste,
drinking water, and air pollution regulations); and (4) impacts
of applying existing standards/regulations to the disposal of
flue gas cleaning sludges (cost aspects). The report presents
14 conclusions supporting the need for FGC sludge disposal regu-
lations and suggests a decision tree approach to the formulation
of guidelines and limitations for FGC sludge management which
takes into account site specific geographical and hydrological
considerations. The report contains 179 references and an
Appendix on The Equations of Mass Transport.
The report was submitted in fulfillment of Contract No.
68-03-2352 by SCS Engineers of Long Beach, California. The work
was completed July 22, 1977.
i v
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CONTENTS
Page
Foreword iii
Abstract jv
Figures v i i i
Tables x
I Co inclusions 1
11 Recommendations 1 1
III Introducti on 13
Purpose and Authority "13
Objective and Approach 14
General Background 16
Projections 17
IV Industry Categorization 20
Description of Power Generation Facilities 20
Description of Industrial FGD Users 21
Location of FGD Users 21
Existing FGD Systems and Sludge Disposal
Operations 24
Rationale for Subcategorization 24
V Sulfur Oxide Control Technology 38
Introduction 38
State-of-the-Art 38
FGD Systems with Sludge Generation 40
By-Product Recovery Systems that Produce a
Marketable Product 47
Regenerable FGD Systems 48
Other Non-Scrubbing Desu1furization Options 62
VI Waste Characterization 69
Parameters which Determine Sludge
Characteristics 69
Chemical, Physical, and Biological
Characteristics of FGD Sludge 72
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CONTENTS (continued)
Pag
VII Treatment and Disposal Technology 91
FGD Sludge Treatment Technology 91
Sludge Transport 127
FGD Sludge Disposal Technology 131
FGD Sludge Utilization 142
VIII Environmental Considerations 143
Disposal Site Characteristics 143
Health Effects 157
Safety 169
Ecological Considerations 170
IX Selection of Chemical and Physical Regulating
Parameters 181
Rationale for Chemical Regulating Parameters 181
Rationale for Physical Regulating Parameters 182
X The Cost of FGD Sludge Disposal 187
Introduction 187
Published Cost Analyses of FGD Sludge Disposal 188
Forthcoming Cost Analyses of FGC Sludge Disposal 194
XI Applicable Existing Standards/Regulations 197
Introduction .197
Solid Waste Disposal 198
Hazardous Waste Disposal 208
Wastewater Disposal 225
Water Quality Criteria for Various Beneficial
Uses 228
Air Pollution Regulations 236
WasteDisposaltoOceans 237
Waste Disposal to Mines 238
Case Study: The Commonwealth of Pennsylvania 240
XII Acknowledgements 246
XIII References 247
XIV Glossary 262
Abbreviations 262
Conversion Table - English to Metric 264
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CONTENTS (continued)
Page
Appendix A - Available Technology and Regulatory
Options 266
Appendix B - The Equations of Mass Transport 278
VI 1
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FIGURES
Page
1. Decision Tree Approach to Disposal Site
Categorization 9
2. Location of Industrial and Utility Plants in the
United States Utilizing Sludge Generating FGD Units 23
3. Scrubber Addition of Limestone 43
4. Double Alkali Process Variation - Sodium Scrubbing
with Lime Regeneration 46
5. Chiyoda Thoroughbred 101 Flow Diagram 50
6. Wellman-Lord Process Schematic 52
7. MgO Slurry Process for Flue Gas Free of Particulate
Matter 54
8. Citrate Process 56
9. Particle-Size Distribution of FGD Sludge 79
10. Bulk Density Versus Moisture Content for Selected
Sulfate (Mohave) and Sulfite (Shawnee) FGC Sludges 81
11. FGD Sludge Load Bearing Strength 87
12. Viscosities of FGD Sludges 89
13. Thickener Sizing vs Solid-Phase Sulfite Predominance 95
14. Leachate Analyses from EPA/TVA Shawnee Untreated
Limestone Waste: Anaerobic Conditions 114
15. Leachate Analyses from EPA/TVA Shawnee Treated
Limestone Waste (Chemfix): Anaerobic Conditions 115
16. Projected Mass Loading of TDS to Subsoil for Various
Disposal Modes of Treated and Untreated FGC Wastes,
Based on Theoretical Considerations I19
VI 1 1
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FIGURES (continued)
Page
17. Leachate pH for Untreated and Treated Residues 120
18. Poz-0-Tec from Aerospace Shawnee Pond Leachate
IDS vs Wash No. 126
19. Simplified Pathway Chart for Contaminants in
Coal Reaching Man 159
20. Comparison of FGD Sludge Contaminant Pathways to
the Envi ronment 1 72
21. Salt Tolerance of Major Crops Grown in the
Colorado River Basin 177
22. Stepwise Approach to the Proposed Regulatory
System 268
23. Decision Tree Approach to Disposal Site
Categorization 272
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TABLES
Page
1. Current FGD Waste Management Practices in the
U.S. (June 1977) 3
2. Comparison of FGD Sludge Production with
Production of Other Waste Materials 18
3. Committed and Projected Non-Regenerabl e
Capability, 1975-1985 (MW) 19
4. Industrial FGD Applications and Their Sludge
DisposalMethods 22
5. Description of Operational Utility FGD Systems 25
6. Description of Utility FGD Sludge Management
Systems 29
7. Summary of Operational Flue Gas Desul f uri zation
Systems 39
8. Sludge Utilization Schemes 58
9. State of Development of Typical Low BTU Gasification
Process 68
10. Composition of Sludge from Operating S02 Scrubbers 74
11. Levels of Chemical Species in FGC Sludge Liquors
and El u tri ates 75
12. Sludge Properties and their Relation to Sludge
Disposal 76
13. Physical Properties of Selected Raw FGD Sludges 77
14. True and Bulk Densities of FGC Sludge Solids 82
15. Permeabilities of Untreated FGC Sludges 84
16. Thickener Diameter Required as a Function of
Calcium Sulfate Oxidation and Generating Capacity 86
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TABLES (continued)
Page
17. Current FGC Waste Management Practices in the U.S.
(June 1977) 92
18. Dewatering Performance by Selected Scrubber Sludge
Treatment Systems 94
19. Clarifier Surface Area Reported for Various Sludges 96
20. Description of Processes Used by WES to Stabilize
FGD Sludge Samples 104
21. Permeability of Raw and Commercially Stabilized FGD 107
22. Mix Consistencies with Various Additives for
Lakeview Gas Scrubber Sludge Containing 65 Percent
Solids 109
23. Effect of Treatment on Bulk Density 110
24. Comparison of the Leachate Constituents from
Eastern Limestone Sludge and Chemfix Treated Sludge 116
25. Case Studies for Calculating Mass Loading of
Leachate Constituents into Subsoil 118
26. Poz-0-Tec Leachate from Successive Shake Tests 123
27. Runoff Test Data on Stabilized and Unstabilized
Materials 125
28. Description of Several Commercial Slurry Pipelines 129
29- Pond Liner Material Characteristics 134
30. Liner Materials 136
31. General Mine Characteristics 141
32. Relative Effects of Variables on Mass Transport of
Contaminants from Disposal Site to Groundwater 147
33. Metals in the Environment and their Toxicity 163
34. Summary of Leachate Data from Several Studies of
FGD Sludge Chemistry 164
35. Effect of Increased Concentrations of Fluorine in
Drinking Water on Teeth 168
xi
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TABLES (continued)
Page
36. Permissible Limits for Concentration of Boron in
Several Classes of Water for Irrigation 178
37. Chemical Contaminant Relationships in FGC Sludge
Liquid Phase 183
38. Model Plant Parameters Given in Recent FGD Sludge
Disposal Cost Studies 189
39. Summary of FGD Sludge Disposal Systems Cost Data
Base 190
40. Computation of Unlined Ponding Costs from
Available Information 192
41. Summary of FGD Sludge Disposal Systems Cost Data
Base, Including Unlined Ponding 193
42. State Solid Waste Regulations Pertaining to
Selected FGD Systems 207
43. Chemical Composition of Phosphate Slimes Solids 209
44. Excerpts from Chapter 17-9 of the Florida Rules
of the Department of Pollution Control 212
45. AMD Treatment Process Aerator Slurry Analyses 213
46. Results of AMD Dewatering Research 214
47. Effluent Limitations for Treated Acid Mine
Drainage 216
48. Composition of Typical By-Product Calcium Sulfates
from Different Rock Sources 217
49. Chemical and Physical Characterization of Selected
Coal Preparation Plant Wastes 220
50. Power Plant Coal Ash Compositions 223
51. National Interim Primary Drinking Water
Regulations - Maximum Contaminant Levels for
Inorganic Chemicals 230
52. Limits of Pollutants for Irrigation Water
Recommended by EPA 231
XT
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TABLES (continued)
53. State of New York Groundwater Contaminant Limits
54. State of Missouri Groundwater Contaminant Limits
55. Proposed Categorization of FGC Disposal Sites
Page
233
235
271
xi
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SECTION I
CONCLUSIONS
1. Existing air pollution control regulations limit the
quantity of SOX that can be discharged by fossil fueled power
plants and other industries. One option available for SOX
removal is flue gas desu1furization (FGD) processes, in which
various designs of scrubbers use calcium or other sorbants to
react with the SOX. These scrubbers generate large quantities of
FGD sludge, and the proper management of this sludge is of
national environmental concern.
2. Based upon an estimated 0.5 million t/1000 MW capacity
(at 70 percent load factor) of FGD sludge generation, projected
FGD sludge quantities are:
Year
1975 1980 1985
Number of FGD scrubber units 14 64 72
Total power capacity, MW 2,500 23,000 27,000
FGD sludge generated annually
in thousand metric tons of
dry solids 1,225 11,200 13,300
An additional 10 percent (approximately) of the installed
FGD systems use supplementary processes to convert the recovered
wastes into marketable by-products. Unfortunately, the economic
feasibility is currently unfavorable in the U.S., so throwaway
sludge methods are expected to dominate industries.
3. Consideration was given to the subcategorization (for
regulatory purposes) of plants generating FGD sludge. The
physical and chemical characteristics of raw FGD sludge are
influenced by many, often interrelated, in-plant variables,
including:
• Fuel type and composition
• Boiler type, design, and operation
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• Fly ash and bottom ash removal systems and their relation
to sludge disposal
• FGD system type, design, and operation
• FGD reagent and input water quality
The effectsof these variables upon the characteristics of
the raw FGD sludge generated are complex and difficult to
predict. In addition, plants may often change fuel and/or opera-
tional procedures, thereby changing the FGD sludge characteris-
tics. Therefore, it is deemed impractical to regulate FGD sludge
disposal on the basis of type of plant or in-plant process. As
stated later in these conclusions, regulation for FGD sludge
treatment and disposal should be based, instead, upon analysis of
disposal site characteristics.
4. The physical and chemical characteristics of FGD sludge
are important to effective management and are the subject of most
disposal-related research efforts to date. Biological character-
istics of the sludge are expected to be of limited importance
since the waste is inorganic; research in this area is lacking.
FGD sludge solids typically contain four major constituents:
calcium sulfate dihydrate, calcium sulfite hemihydrate, unreacted
sorbent, and fly ash. The solid phase of FGD sludge also con-
tains a variety of trace metals and mixed sulfite/su1 fate
crystals. The liquid phase of FGD sludge usually contains ions
of sulfate, sulfite, calcium, and various trace chemical species.
The total dissolved solids (TDS) concentration in the liquor is
a function of the equilibrium levels of solids in the scrubber
system. TDS concentration in closed-loop operations is typically
15,000 to 20,000 ppm.
Physical characteristics of FGD sludge vary widely depending
primarily upon:
• The ratio of sulfate to sulfite in the FGD sludge;
• The size and shape of the crystals; and
• The quantity of fly ash and/or bottom ash contained in
the FGD sludge.
Predominantly sulfite sludges ar*e more unstable (often
thixotropic) and difficult to dewater than predominantly sulfate
sludges. The addition of fly ash and possibly bottom ash can
improve the stability of sulfite sludges, sometimes by one or
two orders of magnitude.
5. Current FGD sludge treatment and disposal practices are
listed in Table 1. The typical operations are:
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TABLE 1. CURRENT FGD WASTE MANAGEMENT
PRACTICES IN THE U.S. (JUNE 1977)
Process
Treatment
Dewatering
No. of Operating Units
Industrial Utility
Clarifier/thickener
Vacuum filter
Centrifuge
Stabil ization
Commercial
Other*
Transportati on
Pipe
Truck/rai 1
Disposal
Pond (unlined)
Pond (lined)t
Landfill
Mine
6
6
0
2
1
6
1
1
6
0
32
10
4
6
5
35
7
6
22
8
1
* Either continuous or intermittent codisposal with fly ash
and/or bottom ash after dewatering mechanical
"*" With either natural low permeability material or similar
"foreign" materials
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• Initial dewatering in a clarifier thickener;
a Secondary dewatering with a vacuum filter or centrifuge;
9 Stabilization by addition of ash (with dewatering) and/or
commercial additives;
0 Pipeline transportation to the disposal site; and
• Disposal into a pond or landfill.
Initial dewatering is virtually universal because it reduces
sludge volume, conserves water, and improves handling character-
istics. Secondary dewatering is generally used if it is desired
to further reduce volume prior to truck transport or commercial
stabilization treatment.
The stabilization of sludge is designed to improve struc-
tural stability and decrease contaminant mobility. Stabilization
can be performed by one of several commercial processes or by
addition of ash, soil, or some other stabilizing additive.
Sludge is usually transported to the disposal site by pipe-
line. Truck transport of sludge is used when:
• The sludge is too thick to pipe, which is the case after
secondary dewatering or stabilization;
0 The sludge is removed to a distant disposal site; or
0 Less expensive alternatives are otherwise infeasible.
Existing FGD sludge disposal methods include the use of
ponds (lined or unlined) or landfills to contain the sludge. To
date, most power plants have used ponds, while most other indus-
tries have used landfills because their sludge volumes are
relatively low. Ocean and mine disposal are under study but are
not being practiced.
6. Important considerations when evaluating the potential
health effects of sludge contaminants are: (1) the pathways to
man, and (2) the concentrations at the point of exposure. The
pathways of interest are groundwaters and surface waters. The
transport of contaminants via groundwater is a complex mechanism,
involving a storage function in the soil and dilution in the
aquifer. Each contaminant has its own time constant for trans-
port based upon the two previously mentioned considerations.
Surface water contamination can be caused by either intentional
liquor discharge (although not practiced) or accidental release
of sludge suspensions.
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Limited studies of sludge leachate and surface water dis-
charges have concluded the following:
• All studies agree that the total dissolved solids in the
sludge liquors exceed drinking water standards;
• All studies indicate that the selenium concentration
commonly exceeds drinking water standards;
• Some data indicate that fluoride concentrations may be
high;
• All studies indicate that arsenic, lead, and mercury
(among other) concentrations can exceed drinking water
standards in some instances, although these concentra-
tions are typically below standards and are readily
attenuated by most soils.
7. Important disposal site characteristics are: present
and projected land use, topography, hydrogeology, and meteor-
ology. Projected land use is an important consideration,
particularly in urban areas where land value is high. Treatment/
disposal techniques that utilize less land space and/or generate
a fill material with adequate bearing strength are often cost
effective in urban areas.
Topography of the disposal area influences the potential
impact of the disposal operation. Sludge retention structures
(dikes, dams, etc.) should be fail-safe in areas where sludge
could flow to nearby surface waters. The relative elevation of
the pond surface, the pond bottom, and the groundwater affect
mass transport of sludge contaminants and dissolved solids.
Site hydrogeology is of major concern to regulatory
agencies, as it controls the mass transport of contaminants to
the surrounding environment. Important hydrogeologic parameters
are site permeability, hydraulic potential, and groundwater
characteristics. These parameters, coupled with estimates of
attenuation and ion exchange in the soil, can provide an estimate
of contaminant mass transport rate and mixing with the ground-
water.
Local meteorology interacts with the disposal technique
through the evaporation/precipitation ratio and wind erosion
potential. The evaporation/precipitation ratio controls the
concentration of salts in the leachate and the hydraulic
potential above the groundwater.
8. Safety considerations associated with the disposal of
FGD sludges can be directed toward: (1) workers employed at
the site; (2) the general public; and (3) livestock and wild
animals. These safety considerations relate to the unstable
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properties of certain FGD sludges. Safety problems can be alle-
viated by worker awareness and limited access to the disposal
area.
9. Ecologically, if the sludge should accidentally be
discharged in large quantities to flowing water courses, it could
have a catastrophic effect upon surface water biota. Since
sulfite-bearing sludges have a high COD, the contents of a large
pond could theoretically deplete the oxygen in a major waterway
for a considerable distance.
10. The aesthetic impact of an FGD sludge disposal site is
site specific. The impact is highly dependent upon the proximity
of the site to the public, which determines whether the operation
can be seen and heard. It is presumed that local ordinances can
sufficiently regulate heavy construction work. After decommis-
sioning of the site, proper soil cover and landscaping should be
implemented.
11. Parameters that regulate chemical and physical charac-
teristics of the FGD sludge were evaluated. The significant
chemical characteristics are the liquid phase concentrations of
TDS, boron, fluoride, mercury, lead, and selenium. The selection
of a regulating parameter from among these components should
satisfy the following criteria:
• Accurate correlation with environmental impacts;
• Usefulness as an indicator of the migration of many
contaminants, aside from itself;
• Simplicity of measurement;
• High measurement accuracy and reproducibi1ity ; and
• Low analytical cost.
Of the contaminants listed, TDS provides the best indication
of overall contaminant migration, due to limited attenuation and
ion exchange. TDS is also the simplest and least expensive
contaminant to measure. In view of these considerations, it is
concluded that TDS is the best chemical regulating parameter for
FGD sludge disposal. While TDS should be used to monitor con-
taminant migration, concentrations of other contaminants should
also be measured in the leachate to confirm the mass transport
calculations.
The physical properties of FGC sludges are important to
the following disposal site considerations:
• Future land use;
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• Rate of mass transport of contaminants from the site, as
a factor of in-place sludge permeability; and
• Sludge flow during accidental release (particularly to
a f1owi ng stream).
Physical characteristics relating to these considerations
include load-bearing strength, viscosity, and permeability. How
many, if any, of these characteristics are important to a partic-
ular site are site-dependent.
It was concluded that characteristics of FGD sludge set need
for regulation. Regulations should allow for site-specific
factors as well as sludge characteristics.
12. Only fragmented disposal cost information was available
for inclusion in this report. In some instances, the information
was based on minimal actual engineering cost estimates. Studies
presenting cost estimates thus far have concentrated upon stabil-
ization costs, transport costs, and costs of final disposal
operations. Detailed engineering cost information on FGD sludge
disposal should be available in mid 1977 from a recently com-
pleted study by TVA.
13. State solid waste disposal and water quality standards
have most frequently been applied to FGD sludge disposal on
state and local levels. State solid waste disposal regulations
often include consideration of: (1) groundwater protection;
(2) protection of the site from floods; (3) rainfall runoff
control; and (4) site reclamation.
Quantitative specifications applicable to FGD sludge
disposal for control measures are available from other state
and federal regulations, such as those concerning:
Hazardous waste disposal;
Wastewater disposal;
Water quality criteria for various beneficial uses;
Comprehensive air quality criteria;
Waste disposal to oceans; and
Waste disposal to mines.
Several hazardous waste disposal regulations and guidelines
are particularly applicable to FGD sludge disposal. Dam con-
struction guidelines for phosphate slime ponds are enforced by
the state of Florida, where most phosphate mining is performed.
Similarly, acid mine drainage sludge ponds are subject to
federal regulations for impounding structures. The disposal of
gypsum from phosphoric acid manufacture is similar to that of
FGD sludge; applicable regulations include runoff control and
impoundment construction.
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14. Consideration was given to development criteria for
guidelines for F6D sludge disposal. Based upon the data base
compiled in this study, it was concluded that potential environ-
mental impacts from FGD sludge disposal can be identified, and
a conceptual approach to their control can be developed.
The most appropriate regulatory approach may be one that
takes into account the site variables and their effect on
environmental impact. The suggested approach consists of:
(1) Establishment of environmental resources to be pro-
tected and beneficial uses (if any) of the disposal
site;
(2) Determination of the degree of regulation necessary to
protect the environmental resources;
(3) Categorization of treatment/disposal system capability
to provide necessary environmental protection; and
(4) Establishment of monitoring, control, and reporting
procedures.
When defining beneficial uses of a site, the regulatory
agency determines the environmental resources to be protected.
These resources may include groundwater resources underlying the
site, surface water resources, and future land use.
The acceptability of the proposed disposal site is
estimated, based upon natural site characteristics and sludge
characteristics. A simplistic system of subcategorizing sites
as a function of their beneficial uses is presented in Figure 1.
This "decision tree" uses the following site variables as
decision points:
• Possible future land use;
• Groundwater resources;
• Evaluation of natural protection to groundwater resources
afforded by site geology and hydrology;
• Surface water protection from catastrophic events; and
• Si te meteorology.
The output of this decision tree is an assigned site
category that defines what control technology is necessary to
protect the given environmental benefits. The numbers selected
for the decision points are subjective, due to the nebulous
legal definitions of degradation and the future value of land.
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CATEGORY 1
UNSTABLE
CATEGORY 2
UNSTABLE , HIGH
RELIABILITY DIKE
CATEGORY 6
LOW FLOW, HIGH
RELIABILITY DIKE
CATEGORY 5
LOW FLOW
SITE
CHARACTERISTICS
SLUDGE
CHARACTERISTICS
IS GROUNDWATER
USEFUL?
CATEGORY 3
STADLE
IS GROUNDWATER
MASS
TRANSPORT
MODEL
MASS
TRANSPORT
MODEL
IS FLOW
<0.3 M/YRT
IS FLOW
<0. 3 M/YR?
IS EVAP/
PRECIP > 17
IS FLOW
<3 M/YR?
WILL
GROUNOWATER
A TDS > 10*7
WILL
GROUNDWATER
4 TDS >10X7
MODIFY SITE TO
LOWER MASS
TRANSPORT
MODIFY. SITE TO
LOWER MASS
TRANSPORT
WILL
GROUNDWATER
TDS > 10X7
WILL
GROUNDWATER
A TDS > 10X7
STABLE, LOW FLOW
IS SURFACE
WATER
ENDANGERED?
CATEGORY 7
UNACCEPTABLE
Figure 1. Decision Tree Approach to Disposal Site Categorization
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Once the disposal site has been subjected to the above
criteria, it becomes operational under the appropriate category
and its restrictions. Monitoring, control, and reporting pro-
cedures should be specified. The most important groundwater
monitoring technique is one that measures the rate at which
leachate moves through soil. This technique would confirm or
refute the theoretical calculations performed during site cate-
gorization. Spill monitoring and prevention procedures are
available from several specialized waste disposal and handling
systems, such as phosphate slimes and oil. Disposal regulations
based upon stability or other specific physical parameters alone
are not sufficient unless they are consistent with the projected
use of the completed disposal site.
10
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SECTION II
RECOMMENDATIONS
1. Substantial additional FGD research is currently under
way or planned by both EPA and industry programs. The data base
presented in this report should be periodically updated to
include new research results.
2. A key conclusion of this report is that characteristics
of FGD sludge set need for regulation. Regulations allow for
site-specific factors. In order for state and local regulatory
officials to regulate properly, specific information will be
required:
(a) Geohydrological survey of proposed disposal site
locations;
(b) Mass transport of contaminants from the disposal site
into groundwater under various conditions of geology,
hydrology, FGD sludge characteristics, disposal site
design, climate, and other factors;
(c) Engineering design standards for retention structures,
secondary retention safeguards, drainage structures,
and accessories associated with FGD disposal ponds;
(d) Sludge characteristics required as a function of future
use for the site. Guidelines are required to correlate
future stability, bearing capacity, etc. of various
types of in-place FGD sludge with desired future land
uses;
(e) Techniques to allow monitoring of contaminant mass
transport from the disposal site through the underlying
soil; and
(f) Value analysis of allowable groundwater degradation vs.
disposal operation cost; e.g., is a rise in groundwater
TDS concentration of 20 mg/£ in x m^ of water accept-
able in exchange for a savings of $5/ton in FGD sludge
disposal cost? Consideration must be given to the
time scale involved and the impossibility of zero
di scharge.
11
-------
Aspects of the above listed guidelines are being researched.
3. Detailed study is suggested specifically to identify the
various disposal advantages and disadvantages of calcium sulfite
and calcium sulfate in terms of the various environmental impact
criteria set forth under "Conclusions."
4. If regulations are deemed necessary, the site-specific
regulatory approach shown in Appendix A is suggested. This
approach is based upon (1) a preliminary assessment of potential
environmental impacts from all disposal aspects, followed by (2)
a monitoring program to cross-check this assessment against
actual events.
In cases where a particular disposal operation will not
degrade local groundwaters or surface waters due to their already
poor quality, it is important that baseline "normal and reason-
able" disposal precautions be established and practiced nonethe-
1 ess.
12
-------
SECTION III
INTRODUCTION
PURPOSE AND AUTHORITY
On December 23, 1971, the U.S. Environmental Protection
Agency, under the authority of the Clean Air Act of 1970, promul-
gated regulations on standards of performance for new stationary
sources of air pollution. The regulations provided air pollution
emission limits for a variety of stationary source categories,
and called upon the states to establish compliance schedules
using emission limits at least as stringent as the federal
standard.
Specifically, subpart D established Standards of Performance
for Fossil-Fuel Fired Steam Generators of more than 63 million
kcal per hour heat input (250 million Btu per hour). These
standards became effective on August 17, 1971. Section 60.43
established the standards for sulfur dioxide emissions at (1)
1.4 g per million cal heat input (0.8 Ib per million Btu)
derived from liquid fossil fuels and (2) 2.2 g per million cal
heat input (1.2 Ib per million Btu) derived from solid fossil
fuels.
On September 10, 1973, the U.S. Court of Appeals for the
District of Columbia remanded to EPA certain of the new source
standards as they apply to power plants. In particular, the
court stated that EPA had not satisfactorily addressed the
problem of by-product sludge disposal from wet scrubbing flue
gas desulfurization (FGD) systems. These lime, limestone, and
double alkali slurry scrubbing processes were denoted as the
anticipated "best system" for standard compliance by high sulfur
fuel users. The major areas of concern were (1) the necessity
of disposing of large quantities of solid wastes; (2) possible
surface and groundwater contamination; and (3) possible degrada-
tion of large areas of land by certain untreated sludges. In
its response to remand (November 12, 1974), EPA recognized the
problem of FGD sludge disposal and the care which must be taken
in selecting an environmentally acceptable disposal method.
Chemical treatment of FGD sludge was recommended as most environ-
mentally acceptable.
13
-------
Beginning in 1972, EPA initiated a major study program aimed
at fully assessing the extent of the FGD sludge disposal problem.
This report is the product of a one-year study of related
research findings generated by the EPA study program.
OBJECTIVE AND APPROACH
The primary objective of this study is to organize the
existing data base to assist the future development of disposal
regulations/standards and to suggest research needs in related
areas. The purpose is: (1) to establish a data base reflecting
the present state of knowledge for the environmentally-acceptable
disposal of FGD sludges, and (2) to evaluate the completeness of
this data base to support the formulation of related regulations/
standards for the disposal of FGD sludge. The data base includes
the environmental aspects of sludge disposal, state-of-the-art
disposal technologies, proposed or existing standards/regulations
which could have a bearing on FGD sludge disposal, and the impact
of applying these standards/regulations. The data base evalua-
tion is intended to provide a basis for assessing the potential
for environmental degradation imposed by desulfurization sludges,
and for determining the extent to which existing technologies
can cope with or avert this problem.
This study is one of 17 currently under way as part of the
EPA's Energy Research Program entitled "Control of Waste and
Water Pollution from Flue Gas Cleaning Systems." The major aims
of the program are: (1) to establish an understanding of the
environmental impact associated with sludge disposal, and (2) to
evaluate the available technology and associated economics
necessary to limit degradation of the environment. The following
is a list of current projects and the organizations responsible
for each:
Environmental Assessment of FGD Waste Disposal
1. FGC Waste Characterization, Disposal Evaluation and Transfer
of FGC Waste Disposal Technology (Aerospace Corporation).
2. Shawnee FGD Waste Disposal Field Evaluation (Tennessee Valley
Authority (TVA)).
3. Louisville Gas and Electric Evaluation of FGD Waste Disposal
Options (Louisville Gas and Electric).
4. Lime/Limestone Wet Scrubbing Waste Characterization (TVA).
5. Lab and Field Evaluation of First and Second Generation FGC
Waste Treatment Processes (U.S. Army Corps of Engineers -
Waterways Experiment Station (WES)).
14
-------
6. Characterization of Effluents from Coal - Field Power Plants
(TVA).
7. Ash Characterization and Disposal (TVA).
8. Studies of Attenuation of FGC Waste Leachate by Soils (U.S.
Army Materiel Command).
9. FGC Waste Leachate-Liner Compatibility Studies (WES).
10. Establishment of Data Base for FGC Waste Disposal Standards
Development (SCS Engineers).
11. Environmental Effects and Control of Various Flue Gas
Cleaning (FGC) Sludge Disposal Options (SCS Engineers).
FGD Waste Disposal Economics
1. Conceptual Design/Cost Study of Alternative Methods for
Lime/Limestone Scrubbing Waste Disposal (TVA).
2 . Shawnee FGD Waste Disposal Field Evaluation (Tennessee
Valley Authority (TVA)).
3. Environmental Effects and Control of Various Flue Gas
Cleaning (FGC) Sludge Disposal Options (SCS Engineers).
Alternate Disposal Methods
1. Evaluation of Alternative FGD Waste Disposal Sites (A. D.
Little, Inc.).
2 . Environmental Effects and Control of Various Flue Gas
Cleaning (FGC) Sludge Disposal Options (SCS Engineers).
FGD Waste Utilization
1. Gypsum By-Product Marketing Studies (TVA).
2. Fertilizer Production Using Lime/Limestone Scrubbing
Wastes (TVA).
3. Lime/Limestone Scrubbing Waste Conversion Pilot Studies
(currently under negotiation).
Power Plant Water Use
1. Assess/Demonstrate Power Plant Water Reuse/Recycle (Radian
Corporation).
This study was approached in two phases, as dictated by its
dual purpose. Phase I was establishment of the environmental,
15
-------
technological, and legal data base, and consisted of four
principal tasks: (1) development of a detailed work plan for
EPA approval; (2) establishment of the criteria necessary to
evaluate existing disposal options; (3) compilation of existing
or proposed standards/regulations which could have a bearing on
the disposal of FGD sludges; and (4) evaluation of the impact of
applying Task 3 standards/regulations to the present sludge
disposal problem. The Phase II effort organized Phase I results
into an information base for the future development of standards
and consisted of the following tasks: (1) development of a
detailed work plan for EPA approval; (2) analysis of the inter-
relationships between environmental effects and regulatory
approaches; (3) development of a technical basis for future
standards development; and (4) identification of research and
development needs.
GENERAL BACKGROUND
The combustion of sulfur-bearing compounds to produce by-
product sulfur oxides (S02, SOs) occurs on a large scale in
several industries including petroleum refining, non-ferrous
metal smelting, sulfur and sulfuric acid manufacture, and fossil
fuel combustion to produce steam and electric power. Of these
sources, fossil fuel (particularly coal) combustion most often
encounters the problem of throwaway sludge disposal.
The alternatives available for compliance with air emission
standards are: (1) to burn fuels of sufficiently low sulfur
content, (2) to burn higher sulfur fuels and remove the sulfur
oxides from the exhaust gas, or (3) to use alternative combustion
technologies. Selection of the first alternative precludes the
need for FGD. The second alternative permits the use of a wide
variety of fuels, but usually necessitates the use of some type
of wet scrubbing FGD system. The third alternative is only now
achieving commercial availability.
Flue gas desu1furization (FGD) refers to any system, wet or
dry, which removes sulfur oxides from exhaust gases. This is
contrasted with flue gas cleaning (FGC), which for the purposes
of this study refers to any system which removes particulate
and/or gaseous air pollutants from exhaust gases. The FGC
systems of interest here are those which collect: (1) sulfur
oxides alone, or (2) sulfur oxides and fly ash simultaneously.
For this reason, FGD and FGC are often used interchangeably
throughout this report.
The technology of flue gas cleaning for SOX control has
advanced rapidly in the last ten years. Consequently, a variety
of wet scrubbing systems have become available for the removal
of S02 from power plant flue gas. Sorbents commonly used in
wet scrubbing include lime, limestone, and sodium salts. The
choice of a sorbent is dependent on several considerations
16
-------
including: cost, reactivity, amount of preparation required, and
dissolution rate. Lime and limestone are both effective and
inexpensive and currently most popular. Other alkali sorbents
are gaining favor.
FGC throwaway sludges are most easily classified as sulfate,
sulfite, or double alkali. Calcium sulfate and calcium sulfite
are the predominant components of the first two, while the third
contains a fractional amount of sodium sulfate loss from the
regeneration system. All three types may contain varying amounts
of fly ash, depending upon particulate control equipment removal
effici ency.
Table 2 displays the relative amounts of fly ash, bottom
ash, and FGD sludge generated and disposed of at a hypothetical
1,000-MW power plant.
PROJECTIONS
Table 3 displays the total existing (1975) and projected
non-regenerabl e FGD capability in the U.S. through 1985. These
figures are based upon information in the December 1976 PEDCO
summary report of FGD systems (Ref. 123). "Committed" systems
are those plants which have at least signed a letter of intent
to install FGD. Regenerable FGD systems presently account for
less than 10 percent of the total installed capacity and should
continue at this level through 1985.
More detailed projections of FGD installations are presented
later in this report.
17
-------
TABLE 2. COMPARISON OF FGD SLUDGE PRODUCTION WITH
PRODUCTION OF OTHER WASTE MATERIALS
CO
Waste
FGD Sludge
Fly Ash
Bottom Ashr Slag
Municipal Refuse
Municipal Sewage
SI udge
Phosphate Rock SI ime
Acid Mine Drainage
SIudge
Gypsum from Ferti-
1i zer Manufacture
Percent
Solids
25
50
25
100
25
100
75
0.1-20.0
4-6
1-5
85-90
Total Tonnage,
1 ,000 MW Power Plant*
250,186
125,093
117,734
29,433
1 ,059,609
264,902
Total Annual Production
(year)**
64,000,000 (1980)
95,000,000 (1980, 80% solids)
360,000,000 (1973)
55,000,000 (1980)
760,000,000 (1970)
8,200,000 (1973)
28,000,000 (1973)
*Model Plant Assumptions
Coal: 3% S
12% Ash
Boiler Type: Cyclone
Load Factor: 70%
Scrubber Efficiency: 85%
Sludge Production: 0.082 metric tons sludge/metric
ton coal
0.4 Kg coal/kwh
Fly ash production = 12 kg/metric ton coal
**Ref. 129.
-------
TABLE 3. COMMITTED AND PROJECTED NON-REGENERABLE
FGD CAPABILITY, 1975-1985 (MW)*
Lime Limestone Lime/ Double Total Total
Scrubbing Scrubbing Limestone Alkali Committed Projected
1975 475 ( 2) 1,954 ( 9) 20 (2) 32 (1) 2,481 (14)
1980 9,445 (23) 12,695 (35) 270 (3) 902 (4) 23,312 (65) 35,000
1985 11,515 (28) 13,445 (37) 797 (4) t 26,659 (73) 100,000
* Numbers in parenthesis indicate number of scrubber units
t None committed beyond 1980
Ref. 123
-------
SECTION IV
INDUSTRY CATEGORIZATION
DESCRIPTION OF POWER GENERATING FACILITIES
In 1977, there are 1040 fossil fuel fired power plants
operating in the United States, possessing a combined generating
capacity of more than 320,000 megawatts. By 1994, 200 more
plants with an additional 111,041 megawatts of generating
capacity are projected to become operational. Of this 1994
capacity, 66 percent will fire coal exclusively. The remainder
will use oil, natural gas, or a combination of oil and coal
(Ref. 138). Oil will decline in popularity because of both
uncertainty of supply and expected rising costs from foreign
sources. Domestic coal use will increase due to its ready
availability and autonomy from foreign control. Coal use will
also rise due to the current administration policy on energy.
Under the federal Clean Air Act, power plants are respon-
sible for emission control. For control of sulfur oxide
emissions, the two most widely used methods are:
(1) The use of a natural low sulfur fuel or partially
desulfurized high sulfur fuel; and
(2) Flue gas desulfurization (FGD).
Existing oil-fired plants can convert with relative ease
to low sulfur oil if it is available. Coal-fired boilers,
however, have difficulty in converting to low sulfur coals due
to differences in heating value, percentage ash, and other fuel
characteristics.
Most coal-fired generating plants are in the heavily
populated eastern sector of the United States. Coal supplies in
these regions are for the most part high sulfur bituminous and
subbituminous varieties. The scarcer low sulfur eastern coals
are in great demand for metallurgical use, and hence are more
expensive than higher sulfur coal. Long distance transport of
low sulfur western coal may be less economically feasible than
FGD installation. Consequently, the majority of installed FGD
units are in the eastern United States. However, stringent
state SOX standards in the west may also cause increased FGD use
in that area.
20
-------
Non-regenerable processes account for approximately 90
percent of those FGD systems which are either operational or
under construction. Lime and limestone systems are the most
prevalent, with 75 percent of the scrubbers projected to be
operational by 1980 utilizing these processes (Ref. 65).
The sodium-lime double-alkali systems thus far have been
installed primarily on industrial fossil fuel fired boilers.
However, interest in the double-alkali process is increasing due
to difficulty with mist-eliminator pluggage in certain lime/
limestone systems. Recently, Gulf Power Company completed test-
ing of a double-alkali system on a 20-MW plant at its Scholz
Station. Central Illinois Public Services' 600-MW Newton plant
will be operating the only utility scale double-alkali system
when it comes on line in December 1977. Louisville Gas and
Electric is building a 250-MW system at Cane Run under partial
EPA sponsorship.
Scrubber systems regenerating sulfur or sulfuric acid have
not yet gained very much acceptance in the United States. Only
four full-scale projects are still in the active planning stages,
while two others were shut down due to acid marketing problems.
These are:
• WeiIman-Lord/Al1ied Chemical process at the San Juan
station of New Mexico Public Service
• EPA's demonstration project with Wellman-Lord/Al1ied
Chemical process at the Mitchell station of Northern
Indiana Public Service
• United Engineers magnesia oxide process at the Phila-
delphia Electric Eddystone station
DESCRIPTION OF INDUSTRIAL FGD USERS
Many non-utility industrial scale fossil fuel fired steam
generators are also regulated by the new source standards. Most
smaller boiler units are equipped for firing a variety of fuels
and have achieved compliance by use of low sulfur fuels.
A total of eight non-regenerable industrial scale FGD
systems will be on line by June 1977 in the United States. As
seen in Table 4, non-regenerable double-alkali FGD is the system
prevalent for industrial steam generators. The table also shows
that landfill is the most common means of sludge disposal by
industrial FGD users.
LOCATION OF FGD USERS
Figure 2 displays the locations of operational non-regener-
able FGD systems (both utility and industrial) in the United
States as of June 1977.
21
-------
TABLE 4. INDUSTRIAL FGD APPLICATIONS AND
THEIR SLUDGE DISPOSAL METHODS*
ro
System Operator
FMC
Modesto, CA
Green River, WO
General Motors
Parma, OH
Caterpillar Tractor Co.
Joliet, IL
East Peoria, IL
Mossville, IL
Fi restone
Pottstown , PA
Alyeska
Valdez, AK
* As of June 1977
MW or
Equivalent
10
150
32
20-30
100
45-55
3
13
**FDS - Fl
FGD
Doubl e
Sodium
Doubl e
Doubl e
Doubl e
Doubl e
Doubl e
Sodium
o o d Disc
Process
Al kal i
Carbonate
Alkali-
Alkali
Al kali
Alkali
Alkali
Carbonate
Scrubber
Scrubber
Type
Packed
bed
FDS**
Adsorber
trays
Venturi
Ventur i
Venturi
Venturi
FDS**
Disposal
Method
Landf ill
Lined pond
Unl i ned pond/
Landfill
Landf 11 1
Landfill
Landfill
Landfill
-------
A Industrial
• Utility
Figure 2. Location of Industrial and Utility Plants in the United
States Utilizing Sludge Generating FGD Units
-------
EXISTING UTILITY FGC SYSTEMS AND SLUDGE DISPOSAL OPERATIONS
As of June 1977, there will be 41 operational FGD units
installed on utility scale boilers in the United States. Table 5
locates and describes these systems. Table 6 gives the details
of their associated FGD sludge management systems. The informa-
tion contained in the table was obtained from both the July-
August 1976 report by PEDCO Environmental Specialists (Ref. 123)
and an SCS phone survey of selected power utilities in November-
December 1976. Systems are subject to changes in fuel type,
scrubber bed packing, recirculation loop status, and the extent
of sludge dewatering.
RATIONALE FOR SUBCATEGORIZATION
General
The purpose of subcategorization within an industry category
was to take into account basic differences in waste generation,
treatment technology, and economics between plants.
When discussing subcategorization for FGD sludge disposal
regulation purposes, some of the same factors that entered sub-
categorization during effluent guideline development should be
considered, but with several important differences.
The most important difference is that FGD sludge is disposed
to land disposal sites and the characteristics of the specific
disposal site are the most important factor in protection of the
environment. For this reason, it is more logical to subcate-
gorize FGD sludge disposal on the basis of variations between
disposal sites than on the basis of variations between the plants
which generate the FGD sludge.
The second major consideration in FGD sludge disposal sub-
categorization is that the power industry is a utility and its
economics are regulated by governmental agencies. Cost increases
are passed on to the consumer. Therefore, there is no rationale
for subcategorization by differences in micro-economic impact.
Each disposal operation must be designed on the basis of the
most cost-effective method which will provide adequate protection
to the environmental resources at the specific disposal site
being considered. It would be a disservice to the power utility
consumer to create an arbitrary subcategorization on the basis
of "ability to pay," which has been necessary in some other
industries to prevent economic inequities and plant closures.
An elaboration on the use of disposal site variables for
implementing regulatory controls for FGD sludge disposal is
provided in Appendix A.
24
-------
TABLE 5. DESCRIPTION OF OPERATIONAL UTILITY FGD SYSTEMS
Power Station
Utility
Unit
Plant
Size
MW
Fuel Characteristics
Type
BTU/lb
of r
/a O
% Ash
Participate
Control
Device
FGD Process
Sorbent
Scrubber
Arizona PU
Service
Arizona PU
Service
Arizona PU
Service
Central 111.
Light Co.
Columbus & So.
Ohio Elec.
Commonwealth
Edison Co.
Detroit Edison
Duquesne
Light Co.
Duquesne
Light Co.
Gulf Power Co.
Cholla No. 1
Cholla No. 2
4 Corners
No. 5A
Duck Creek
No. 1A
Conesville
No. 5
Will County
No. 1
St. Clair
No. 6
Elrama
Phillips
Scholz Nos.
IB & 2B
115
250
160
100
400
167
180
510
410
23
Coal
Coal
Coal
Coal
Coal
Coal
Coal
Coal
Coal
Coal
12,146
8,750
10,300-
10,500
10,600
9,463
11,300
11,000
11,000
12,400
0.44-1
0.44-1
0.7
2.5-3.0
4.5-4.9
2.1
3.7
1.0-2.8
1.0-2.8
3.0-5.0
12.3
10
22
9-10
17
10
16
18.2
18.2
14
Mech.
ESP
ESP
ESP
ESP
ESP Venturi
ESP
Mech., ESP
Mech., ESP
ESP Venturi
Limestone
Limestone
Lime
Limestone
Lime
Limestone
Limestone
Lime
Lime
Dilute
acid
FGD , packed
tower
FSS1, packed
tower
Horizontal
Venturi rod
TCA
Spray tower
Tray tower
Venturi
Venturi
Spray trays
Packed tower
1
FDS = Flooded Disc Scrubber
-TCA = Turbulent Contact Adsorber
-------
Table 5 (continued)
Power Station
Utility
Unit
Plant
Size
MW
Fuel Characteristics
Type
BTU/lb
at c
h o
% Ash
Participate
Control
Device
FGD Process
Sorbent
Scrubber
cr>
Kansas City
Pwr. & Light
Kansas City
Pwr. & Light
Kansas City
Pwr. & Light
Kansas City
Pwr. & Light
Kansas City
Pwr. & Light
Kentucky
Utilities
Key West
Utility Brd.
Louisville
Gas & Elec.
Louisville
Gas & Elec.
Montana
Power Co.
Hawthorne
No. 3
Hawthorne
No. 4
LaCygne No. 1
Lawrence
No. 4
Lawrence
No. 5
Green River
No. 1 & 2
Stock Island
Cane Run
No. 4
Paddy's Run
No. 6
Col strip
No. 1
140
100
820
125
430
64
37
178
70
360
Coal
Coal
Coal
Coal
Coal
Coal
Oil
Coal
Coal
Coal
9,800-
11,500
9,800-
11,500
9,000
10,000-
12,000
10,000-
12,000
11,000
11,500
11,500
8,800
0.6-3.0 11-14
0.6-3.0 11-14
5.2 25
0.6-3.75 10-12
0.6-3.75 10-12
3.8 15-25
2.4-2.75
3.5-4.0 11-12
3.5-4.0 13
0.8 8.83
Absorber
tower
Absorber
tower
Venturi
Absorber
tower
Absorber
tower
Mech.
Mech.
ESP
ESP
None
Limestone
Limestone
Limestone
Limestone
Limestone
Lime
Limestone
Lime
Lime
Lime/alka-
line ash
Marble bed
Marble bed
Sieve tray
Marble bed
Marble bed
TCA2
Venturi
Scrubbing
trains
Marble bed
Venturi
2FDS = Flooded Disc Scrubber
TCA = Turbulent Contact Adsorber
-------
Table 5 (continued)
Power Station
Utility
Unit
Plant
Size
MW
Fuel Characteristics
Type
BTU/lb
% S
% Ash
Particulate
Control
Device
FGD Process
Sorbent
Scrubber
IN3
—i
Montana
Power Co.
Nevada Power
Co.
Nevada Power
Co.
Nevada Power
Co.
No. Indiana
PU Serv.
No. States
Power Co.
No. States
Power Co.
Penn. Power
Co.
Penn Power
Co.
Philadelphia
Elec. Co.
Col strip
No. 2
Reid Gardner
No. 1
Reid Gardner
No. 2
Reid Gardner
No. 3
Mitchell
No. 11
Sherburne
No. 1
Sherburne
No. 2
Bruce Mans-
field No. 1
Bruce Mans-
field No. 2
Eddystone
No. 1A
360
125
125
125
115
710
680
835
835
120
Coal
Coal
Coal
Coal
Coal
Coal
Coal
Coal
Coal
Coal
8,700
12,450
12,450
12,450
11,000
8,300
8,300
11,900
11,900
12,100
0.8/.7
0.5-1.0
0.5-1.0
0.5-1.0
3.2-3.5
0.8
0.8
4.3
4.3
2.3
8.83
8
8
8
10
9
9
12.5
12.5
None
Mech. ,
Venturi
Mech.,
Venturi
Mech.,
Venturi
ESP
Fixed-rod
Venturi
Fixed-rod
Venturi
Adjustable
Venturi
Adjustable
Venturi
Mech. ESP
Scrubber
Lime/a! ka-
li ne ash
Sodium
carbonate
Sodium
carbonate
Sodium
carbonate
Sulfite/
Wellman-
Lord
Limestone/
Alkaline ash
Limestone/
Alkaline ash
Lime
Lime
Magnesium
oxide
Venturi
Wash tray
Wash tray
Wash tray
Spray trays
Packed tower
Marble bed
Marble bed
Fixed-throat
Venturi
Fixed-throat
Venturi
Venturi -rod
= Flooded Disc Scrubber
TCA = Turbulent Contact Adsorber
-------
Table 5 (continued)
Power Station
Utility
Unit
Plant
Size
MW
Fuel Characteristics
Type
BTU/lb
o/ o
h o
% Ash
Particulate
Control
Device
FGD Process
Sorbent
Scrubber
Pub. Serv.
of Colorado
Rickenbacker
AFB
S. Carolina
Publ Serv. Aut.
Springfield
City Util.
rv> Tenn. Valley
00 Authority
Tenn. Valley
Authority
Tenn. Valley
Authority
Texas Util.
Co.
Utah Power
& Light Co.
Valmont No. 5
Rickenbacker
Winyah No. 2
Southwest
No. 1
Shawnee No.
10 A
Shawnee No.
10 B
Widows Creek
No. 8
Martin Lake
No. 1
Huntington
No. 1
100
20
140
200
10
10
550
793
415
Coal/ 10,780
gas
Coal
Coal 12,500
Coal 12,000
Coal
Coal
Coal 10,000
Coal 7,000
Coal 12,000
0.75
3.6
1.08
3.5
2.9
2.9
4-4.5
1.0
0.55
6-7 Absorber
tower
Mech.
17.2 ESP
13 ESP
Absorber
tower
Venturi
25 Mech.
Venturi
10-14 ESP
8.8 ESP
Limestone
Lime
Limestone
Limestone
Lime/
1 imestone
Lime/
limestone
Limestone
Limestone
Lime
TCA^
Spray tower
Venturi
Modified TCA2
TCA2
Venturi
Spray tower
Modified TCA2
Spray tower
Vertical
spray tower
,FDS = Flooded Disc Scrubber
"TCA = Turbulent Contact Adsorber
-------
TABLE 6. DESCRIPTION OF UTILITY FGD SLUDGE MANAGEMENT SYSTEMS
Power Station
Utility
Unit
FGD Sludge Disposal
Dewater
Transport
Treatment
Disposal
Fly Ash Disposal
Scrubber
Liquor
Circulation
Loop
Status2
Arizona PU
Service
Arizona PU
Service
Arizona PU
Service
Central 111.
Light Co.
Columbus & So.
Ohio Elec.
Commonwealth
Edison Co.
Detroit
Edison
Duquesne
Light Co.
Duquesne
Light Co.
]CL = Clarifier
F = Vacuum Fil
C = Centrifuge
Cholla No. 1
Cholla No. 2
4 Corners
No. 5A
Duck Creek
No. 1A
Conesville
No. 5
Will County
No. 1
St. Clair
No. 6
Elrama
Phillips
tration
None
None
CL
None
CL,
CL,
None
CL
CL
2OP =
UC =
Pipe
Pipe
Pipe
Pipe
F
F Pipe,
cement
tank
Pipe
Truck
Truck
None
None
None
None
IUCS
fixation
Chicago
fly ash
fixation
None
IUCS
fixation
IUCS
fixation
Operational
Under Construction, due to
Unlined
pond
Unlined
pond
Unl ined
pond
Landfill
Landfill
Lined
pond
Landfill
Landfill
go on line
Mixed in pipe w/
sludge
Mixed in pipe w/
sludge
Disposed in
closed coal mine
Disposed w/sludge
in common pond
Added to sludge
in fixation
Added to sludge
in fixation
Mixed w/sludge in
fixation
Collected w/S02
by 6/77.
Open
Open
Closed
Closed
Closed
Closed
Closed
Closed
Closed
OP
UC
OP
UC
UC
OP
OP
OP
OP
-------
Table 6 (continued)
Power Station
Utility
Unit
FGD Sludge Disposal
Dewater
Transport
Treatment
Disposal
Fly Ash Disposal
Scrubber
Liquor
Circulation
Loop
Status2
1
CL = Clarifier
F = Vacuum Filtration
C = Centrifuge
"OP = Operational
UC = Under Construction, due to go on line by 6/77.
Gulf Power Co.
Kansas City
Pwr. & Light
Kansas City
Pwr. & Light
Kansas City
Pwr. & Light
to Kansas City
0 Pwr. & Light
Kansas City
Pwr. & Light
Kentucky
Utilities
Key West
Utility Brd.
Louisville
Gas & Elec.
Scholz Nos.
IB & 2B
Hawthorne
No. 3
Hawthorne
No. 4
LaCygne
No. 1
Lawrence
No. 4
Lawrence
No. 5
Green River
No. 1 & 2
Stock Island
Cane, Run
No. 4
CL3 F
CL
CL
None
None
None
CL
CL
CL, F
Pipe
Pipe
Rubber
1 i ned
pond
Pipe
Pipe
Pipe
Pipe
Truck,
pipe
pH adj.
None
None
None
None
None
None
None
None
Ash pond
Un lined
pond
Unlined
pond
Unlined
pond
Unlined
pond
Unl ined
pond
Unlined
pond
Unlined
pond
Landfill
Intermittent
collecting W/S02
Collected w/or
added to sludge
Collected w/or
added to sludge
Ponded w/sludge
Collected w/S02
Collected W/S02
Collected w/502
Collected W/S02
Mixed w/sludge
on-site
Closed
Closed
Closed
Closed
Closed
Closed
Open
Open
Closed
OP
OP
OP
OP
OP
OP
OP
OP
OP
-------
Table 6 (continued)
Power Station
Utility
Unit
FGD Sludge Disposal
Dewater
Transport
Treatment
Disposal
Fly Ash Disposal
Scrubber
Liquor
Circulation
Loop
Status2
Louisville
Gas & Elec.
Montana
Power Co.
Montana
Power Co.
Nevada Power
Co.
Nevada Power
Co.
Nevada Power
Co.
No. Indiana
PU Serv.
No. States
Power Co.
]CL = Clarifier
F = Vacuum Fil
C = Centrifuge
Paddy's Run
No. 6
Co Is trip
No. 1
Col strip
No. 2
Reid Gardner
No. 1
Reid Gardner
No. 2
Reid Gardner
No. 3
Mitchell
No. 11
Sherburne
No. 1
tration
CL
CL
CL
CL
CL
CL
CL
2OP
UC
Pipe None
Pipe None
Pipe None
Pipe pH adj.
Pipe pH adj.
Pipe pH adj.
Pipe None
= Operational
= Under Construction, due
Landfill
Unl ined
pond
Unl ined/
1 i ned
pond
Unl ined
pond
Unl ined
pond
Unl ined
pond
Clay-
1 i ned
pond
Collected or Closed
added to sludge
Collected w/ Closed
sludge in
scrubber
Collected w/ Closed
sludge in
scrubber
Collected w/ Open
common liquor
Collected w/ Open
common liquor
Collected w/ Open
common liquor
Disposed in pond Closed
Collected w/S02 Closed
OP
OP
OP
OP
OP
OP
UC
OP
to go on line by 6/77.
-------
Table 6 (continued)
Power Station
Utility
Unit
FGD Sludge Disposal
Dewater
Transport
Treatment
Disposal
Fly Ash Disposal
Scrubber
Liquor
Circulation
Loop
Status2
Penn. Power
Co.
Penn Power
Co.
Philadelphia
Elec. Co.
Pub. Serv.
of Colorado
PO Rickenbacker
AFB
S. Carolina
Pub. Serv. Aut.
Springfield
City Util.
Tenn. Valley
Authority
Tenn. Valley
Authority
Bruce Mans-
field No. 1
Bruce Mans-
field No. 2
Eddystone
No. 1A
Valmont
No. 5
Rickenbacker
Winyah No. 2
Southwest
No. 1
Shawnee No.
IDA
Shawnee No.
10B
CL
CL
CL, C
CL
CL
CL
CL, F
CL, F,
C
CL, F,
C
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Truck
Pipe
Pipe
Dravo
fixation
Dravo
fixation
N/A
None
None
None
None
None
None
Unl ined
pond
Unl ined
pond
Acid
plant
Unl ined
pond
Lined
pond
Lined
pond
Landfill
Unl ined
pond
Unl ined
pond
Added to sludge
in fixation
Added to sludge
in fixation
Pond
Collected w/S02
Disposed in
separate pond
Mixed w/sludge
Collected w/S02
Collected w/S02
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
OP
UC
OP
OP
OP
UC
UC
OP
OP
1
CL = Clarifier
F = Vacuum Filtration
C = Centrifuge
OP = Operational
UC = Under Construction, due to go on line by 6/77.
-------
CO
CO
Table 6 (continued)
Power Station
Utility
Unit
FGD Sludge Disposal
Dewater
Transport
Treatment
Disposal
Fly Ash Disposal
Scrubber
Liquor
Circulation
Loop
Status2
Tenn. Valley
Authority
Texas Util.
Co.
Utah Power
& Light Co.
Widows Creek None Pipe None
No. 8
Martin Lake CL, C Railcar None
No. 1
Huntington F Truck None
No. 1
Unlined Disposed w/sludge Closed UC
pond in common pond
Landfill Mixed w/sludge Closed UC
Landfill Mixed w/sludge Closed UC
CL = Clarifier
F = Vacuum Filtration
C = Centrifuge
"OP = Operational
UC = Under Construction, due to go on line by 6/77.
-------
The following variables were considered as rationale for
subcategorization:
1. Size, age of plant, and financial strength;
2. Type of plant or fuel;
a. power boiler, steam boiler, metallurgical furnace;
b. coal, coke, oil fuel;
c. boiler design - tangential, wall fired, grate fired,
etc.
3. Type of air pollution control and FGD equipment:
a. particulate dontrol - electrostatic, venturi
scrubbers, mechanical collectors, etc.;
b. FGD equipment - venturi, packed bed, horizontal
spray, mobile bed, tray tower, etc.;
c. reagent process type - lime, limestone, double
alkali, etc.;
d. operating variables - unsaturated operating mode,
scrubber L/G ratio, method and time of reagent
addition, etc.
4. Untreated (raw) waste characteristics:
a. chemical characteristics;
b. physical characteristics;
5. Disposal site characteristics:
a. present and future land values and possible uses;
b. groundwater resources - quantity and quality;
c. disposal site hydrology and mass transport
potential - permeabilities, hydraulic gradients,
impurity attenuation, flooding potential, etc.;
d. disposal site meteorology - evaporation and precipi-
tation rates, etc.;
e. local ecology;
f. geographic location;
34
-------
g. amount of degradation which is acceptable.
The following is a brief analysis of each rationale as it
applies to FGD sludge disposal subcategorization.
Size, Age of Plant, and Financial Strength
The use of size, age, or financial strength as variables for
subcategorization is not recommended for the following reasons:
• The economics of scale associated with FGD disposal
operations are minimal in the range required for utility
plants;
• The age of the plant has little effect upon FGD disposal
operations. It is probable that few old plants will be
equipped with FGD equipment since (1) most will choose
to utilize low sulfur fuel, (2) many old plants are used
for peaking purposes where the economics of FGD are
prohibitive, and (3) the impetus for FGD falls primarily
under the New Source Performance Standards.
• The financial strength of the plant is not a logical
reason for subcategorization because power utility
industry rates are government regulated. FGD disposal
costs will be passed on to the consumer, which makes it
important that each plant be free to select the most
cost effective method of disposal that affords acceptable
environmental protection.
t The cost of FGD sludge disposal is significantly less
than the cost of the FGD system producing the sludge and
does not affect plant location. The FGD sludge disposal
cost makes only a small contribution to decisions
regarding plant closures or location, installation of
FGD equipment, use of low sulfur fuel, etc.
Type of Power Plant and Fuel
Obviously, the type of plant and the fuel used have an
influence upon the quantity and characteristics of the FGD sludge
produced. However, the interrelationships are very complex among
many of the variables (e.g., boiler design, efficiency, excess
air used, type of FGD equipment, etc.). The complexity of
assessing and defining the quality of a FGD sludge according to
coal type and boiler configuration is such that subcategorization
from these parameters is infeasible.
Type of Air Pollution Control and FGD Equipment
Subcategorization with respect to FGD and particulate
control equipment is not practical. The type and efficiency of
35
-------
participate control equpment are indeed major determinants of the
amount of fly ash available for collection by the desulfurization
equipment. The size distribution of the ash being removed with
the sulfur oxides has an influence on the chemical composition
of the sludge. However, solubility relationships rather than
total solid phase concentrations of contaminants in the sludge
often control their transport rate from the disposal site. The
physical properties of the sludge are partially determined by
the details of the scrubber design, which affect nucleation and
crystal growth kinetics and sulfite/su1fate ratios (oxidation
rates). These interactions are very complex and not fully under-
stood .
Untreated (Raw) Waste Characteristics
F6D sludge waste characteristics may vary widely with time.
The chemical properties of FGD sludge also vary with the time and
composition of coal fired. Certainty of consistent supply of a
specific coal type to a plant for its expected useful lifetime
is not always realistic. The range of chemical properties is
such that normal variations in coal type could shift the subcate-
gorization of certain FGD system users. This situation is not
desirable from the regulatory viewpoint.
The physical properties of the sludge can impact on both the
future land use and airborne dust problems. The physical proper-
ties desired at any given site will depend upon site-controlling
variables and their requirements. Since the physical properties
depend upon so many interrelated factors, it does not appear that
any single property or combination of properties would be suit-
able for categorization purposes.
Disposal Site Characteristics
It is recommended that FGD disposal regulations be based
upon disposal site characteristics. As discussed in Appendix A,
disposal site characteristics include:
• Environmental resources requiring protection;
• Ability of the disposal site to protect these environ-
mental resources, either naturally or through changes
made in sludge characteristics and/or site improvements
(liners, dikes, etc.); and
• Site monitoring.
Any subcategorization system should satisfy the following
criteria:
• The basic variables should be measurable and easily
specified.
36
-------
• They should be the dominant basic variables influencing
the controlling considerations.
• The basic variables used for subcategorization should be
constant with time.
Disposal site basic variables satisfy the above subcategor-
ization criteria. The disposal site variables are measurable and
easily specified. Standard methods exist for determining and
reporting permeabilities, hydraulic gradients,evaporation/preci-
pitation rates, etc. The disposal site variables are the
ultimate influence upon the control variables. Mass transport
rates of contaminants are controlled by disposal site permeabil-
ity, contaminant attenuation, hydraulic gradients, etc. The
degree of reliability required for retaining dams or impoundments
is a function of local ecology, geographic location, etc. The
disposal site variables are constant with time. For the pro-
jected duration of FGD sludge disposal operations at a certain
site, the basic disposal site variables are not expected to
change appreciably.
The reader is referred to Appendix A where disposal options
based upon site characteristics is presented.
37
-------
SECTION V
SULFUR OXIDE CONTROL TECHNOLOGY
INTRODUCTION
Utilities and other industries burning fossil fuels can
select from three general categories of control systems to
achieve compliance with standards
FGD systems with sludge generation
FGD systems that produce a marketat
Control systems that do not general
• FGD systems that produce a marketable product
t Control systems that do not generate a sludge
It is outside the scope of work of this report to discuss
in detail the technical and cost factors involved in selecting
in-plant sulfur oxide control systems. General considerations
include:
Capital requirements for FGD system construction
Annual FGD operation and maintenance costs
Full-scale operating experience
Land avai1abi1ity
Types and costs of available fuel
Available by-product markets
Energy requirements
Sustained capability to meet pollution control standards
This section will concentrate upon those aspects of the
various in-plant control systems that affect the volume and
character of the waste sludge generated.
STATE-OF-THE-ART
As of June 1977, 49 FGC systems will be in commercial opera
tion in the U.S. Of these, 41 will be installed on utility
plants and 8 on industrial fossil fuel-fired steam generators.
Table 7 differentiates the number and capacity of these opera-
tional systems by FGD process. This table shows that the lime/
limestone systems acc.ount for 34 utility scale systems and for
more than 90 percent of the total scrubbing capacity. Double
alkali systems currently dominate the industrial scale FGD
market, although several of these smaller systems were conceived
as pilot or demonstration facilities.
38
-------
TABLE 7. SUMMARY OF OPERATIONAL FLUE GAS
DESULFURIZATION SYSTEMS*
Number in Total MW
FGD Process Operation Capacity
Uti1i ty Seale
Lime scrubbing
Lime 12 3,897
Lime/alkaline ash 2 720
Limestone scrubbing
Limestonet 18 4,267
Limes tone/alkaline ash 2 1,390
We!Iman-Lord scrubbing 1 115
Dilute acid scrubbing 2 23
Sodium carbonate scrubbing 3 375
Magnesiumoxidescrubbing 1 120
Industrial Scale
Double alkali scrubbing 7 243
Sodium carbonate scrubbing 1 150
For fossil fuel-fired steam generators as of June 1977
At TVA Shawnee's Nos. 1OA and 10B power plants
(20 MW total), FGD is alternated between lime and
limestone scrubbing for experimental purposes.
These plants (both the number of them in operation
and their megawatt capacity) are included under lime-
stone scrubbing for convenience.
39
-------
Projections through the year 1985 indicate that lime/lime-
stone systems will continue to dominate the FGD field. However,
several large-scale double alkali systems are expected to go on
1i ne before 1990.
The majority of plants throughout the utility industry are
presently achieving compliance with emission standards through
the use of low sulfur fuels. Other plants face compliance
schedules calling for the use of either low sulfur fuel or FGD.
In addition, at several utility plants, the applicability of
sulfur oxide control requirements is embroiled in litigation.
It has been estimated that due to the scarcity of low sulfur
fuels, 65,000 MW of existing coal-fired generating capacity will
need to select FGD systems (Ref. 129). Including high sulfur
oil users, this figure is expected to exceed 100,000 MW by 1980.
Consequently, the demand for FGD systems will continue to exceed
the supply beyond 1985.
FGD SYSTEMS WITH SLUDGE GENERATION
Primarily nonregenerable FGD systems are employed by
industries and utilities. Available options for nonregenerable
FGD systems are:
® Lime scrubbing (tail end)
® Limestone scrubbing (tail end)
9 Double alkali scrubbing (sodium, ammonia)
® Sodium carbonate scrubbing
Lime Scrubbing (Tail End)
The 12 lime scrubbing units presently in operation have
accumulated over eight years of intermittent operational experi-
ence. The chemistry of the lime scrubbing process proceeds in
two stages: (1) the absorption of S02 and C02 gases by the
solution and their subsequent hydrat ion to SOs =, or oxidation
to S04~ and C03~; and (2) the reaction of these anions with the
calcium cation to form calcium sulfite, calcium sulfate, and
calcium carbonate precipitates.
The reaction mechanisms associated with each stage are as
follows: (Ref. 100)
Stage I
CaO + H20 5ca(OH)2 (s)
Ca(OH)2(s) tCa(OH)2(aq)
Ca(OH)2(aq)£Ca++ + 20H"
40
-------
S0«(g) + S0~(aq
£- L.
S02(aq) + H20~«
HSO: JH+ + so"
o 3
so3 + Jg02 ?so4
C02(g) ?C02(aq)
C02(aq) + H20 ? I
HCO~
Stage II
Ca + + +
Ca + + +
Ca + + +
SO" + %H70 ?C
O ^1
SO" + 2 H90 ?
4 2
C03 ?CaC03(s)
The pH of the lime scrubbing slurry ranges between 7 and 11
depending upon the amount of slurry reci rcul ated . Reaction
kinetics favor the formation of the hemihydrated sulfite, as high
pH limits sulfite oxidation to sulfate. The use of high sulfur
coal further reduces sulfate formation by forcing reduced reten-
tion time of slurry in the scrubber circuit and by lowering the
oxygen/S02 ratio in the flue gas.
Because of the high reactivity of lime with S02, the
required stoichiometric ratio of CaO/S02 is low. Typical ratios
are in the range of 1.1 to 1.2, although lower values have been
used effectively in certain systems.
Equipment designs that are prevalent with industrial users
are the packed-bed and horizontal scrubbers which utilize large
surface areas; adjustable or fixed-throat Venturis, which utilize
high turbulence; and mobile bed contactors; e.g., UOP's Turbulent
Contact Absorber (TCA), which have both large surface areas and
high turbulence. Lime scrubbers are followed by a filter or
impaction device ("Chevron" design) for demisting entrained
aerosol s .
The major problem encountered with lime scrubbing is scaling
within the system. The scale restricts flows in the scrubbing
units, and consequently lowers sulfur oxides removal
41
-------
efficiencies. The most prevalent cure for the scaling problem is
the use of a subsaturated scrubbing solution. By careful slurry
control, scaling can be minimized while maintaining scrubbing
efficiencies.
The 12 full-scale lime scrubbing systems have reported
operating time availabilities between 43 and 100 percent (Ref.
PEDCO Jan-March 77).
Limestone Scrubbing (Tail End)
Flue gas desu1furization using a limestone scrubbing solu-
tion has widespread application. There are 18 such full-scale
units presently in operation in the United States and several
others being used overseas. Over ten years of cumulative operat-
ing experience has been logged by American plants. Tail-end
limestone scrubbing involves the absorption of dilute sulfur
dioxide gas through turbulent contact with a slurry of limestone
and reaction products. The wet gas collectors most often
incorporated for limestone scrubbing, to date, are the spray
tower, the sieve tray, the packed bed, and the mobile bed
contactor designs. Figure 3 presents the typical process flow
for a limestone scrubbing system.
The chemistry of the limestone process can be summarized in
two stages: first, the absorption of the S02 gas by the solution
and its subsequent hydrolysis to S03 = and oxidation to S04 =,
and second, the reaction of these sulfite ions with the calcium
cation to form dihydrated calcium sulfate and hemihydrated
calcium sulfite. The reaction mechanisms generally are as
fo11ows:
Stage I:
S09(g) + S09(aq)
L. L.
S02(aq) + H20 H2S03?HS03" (aq) + H +
HS03 tH + + S03
so3 = + %o2 + so4=
CaC03(s) + CaC03(aq)
CaW^(aq) £Ca++ + CO"
O 3
HC03" + H+ + H20 + C02 (g)
42
-------
GAS TO STACK
STACK \
GAS /
SCRUBBER
CA
C°3
\
REAC-
TION
TANK
SETTLER
'
CAS03 4
CASO, SLUDGE
TO WASTE
Figure 3. Scrubber Addition of Limestone
-------
Stage II:
Ca++ +
Ca + + +
Ca + + +
SO,
3
so4
C00
+ 2H2o5caS04 • 2H20(s)
C03~ ?CaC03(s)
In the limestone system, the input liquor pH is approxi-
mately 5 to 5.5. Reaction kinetics favor the formation of the
dihydrated sulfate complex at low pH, e.g., a decrease in pH from
seven to four increases the sulfite oxidation rate up to ten
times (Ref. 176). The oxidation rate is also influenced by
other system parameters such as oxygen availability and sulfite
concentration. This makes the sulfate/sulfite ratio difficult
to predict.
The stoichiometric ratio of calcium ion concentration to
absorbed sulfur dioxide gas is generally somewhere between 1.3
and 1.5, although some advanced systems have effectively
approached a stoichiometric ratio of 1.0. Several pilot plants
have demonstrated S02 collection efficiencies in excess of 90
percent, while full-scale units are currently operating in the
70-90 percent removal range.
In addition to the gas-liquid contractor, most scrubber
systems include a demister and a reheater. Demisters remove
entrained aerosols from the scrubbed flue gas and usually
consist of an inertial impaction device. Impaction plates are
washed periodically to prevent clogging and buildup of solids.
At various FGD installations, reheaters are used when atmospheric
conditions or operational efficiencies indicate the need to
impart buoyance to the cooled exhaust gas. These reheaters
consist of either steam-heated tubes or direct fossil fuel
heating.
Limestone scrubbing systems have experienced several
operational problems in the past, most of which have been recti-
fied through trial and error procedures. Typical problems
include solids deposition on the flue gas reheater and demister
surfaces, surface metal erosion, and acid corrosion. FGD system
availability at a majority of the limestone scrubbing units has
been limited due to the startup status of the systems. However,
the systems that have been on line for a few years have reported
availabilities approaching 95 percent (Ref. 122).
Double Alakli Scrubbing (Sodium)
In the United States, the majority of double alkali systems
are installed on industrial boilers. There are currently no
operational full-scale utility double alkali systems. However,
a. A.
-------
one is under construction at the 575-MW Central Illinois Public
Service Newton No. 1 plant, and two other contracts have been
awarded elsewhere. In Japan, there are several oil-fired utility
plants using double alkali systems.
To date, research on double alkali scrubbing has concen-
trated on tail-end scrubbing of the flue gas with a liquor of
sodium salts, followed by treatment with hydrated or calcined
lime or limestone. Other processes utilizing ammonium or
magnesium scrubbing liquor have been investigated, but none has
been developed into full-scale systems. Figure 4 displays the
process flow for sodium scrubbing with lime regeneration.
The chemistry of the sodium/lime double alkali system can
be summarized in two physically distinct stages: (1) a gas
absorption and reaction stage, and (2) a precipitation and
regeneration stage. The related overall reaction mechanisms
proceed as follows:
Stage I (col 1ection )
Na2S03 + S02 + H20 +2NaHS03U)
Stage II (regeneration)
2NaHS03 + Ca(OH)2 tNa2S03 + 3/2 H20 + CaS03 ' %H20
The clear sodium sulfite liquor is recirculated, while the
calcium sulfite is precipitated and drawn off for disposal. A
variation of this system is being investigated at the General
Motors Chevrolet plant in Parma, Ohio. This variation employs
sodium hydroxide as the reactant and hydrated lime as the addi-
ti ve.
Pilot plant SO;? collection in excess of 99 percent has
been achieved. Efficiency can be enhanced by maintaining the
liquor pH between six and seven. A pH below six is avoided
because of increased S02 vapor pressure in the collector. A
pH above nine tends to cause scale formation. Various scrubbing
devices have been used in pilot plants.
The scrubber effluent treatment stage appears to be the
most critical for operational success. The stoichiometric ratio
of calcium additive to collected S02 is generally kept between
1.0 and 1.1.
Pilot plants operated to date have used settling and filtra-
tion to remove solids from the treated liquor. Filter cake
washing is done both to recover dissolved sodium salts for
45
-------
SCRUBBED
GAS
SCRUBBER
FLUE I
GAS
BY-PASSJ
en
FLUE GAS
FEED
H2O.
CA(OH).
FEED
RECYCLE
SCRUBBER
SCRUBBER
EFFLUENT
1 -
MIXING
TANK
1
CAUS'
VACUUM) WASTE
CALCIUM
SALTS
MAKE-UP
NA2C03
OR
HOLDING
TANK
NAOH
Figure 4. Double Alkali Process Variation - Sodium Scrubbing with Lime Regeneration
(Ref. 28).
-------
recycle to the scrubber and to reduce their concentration in the
throwaway sludge (Ref. 163).
The major reported problem associated with double alkali
scrubbing has been the loss of sodium salts to the filter cake.
The loss of some soluble sodium salts with the sludge is unavoid
able, but the loss can be limited by washing the filter cake.
Sodium Carbonate Scrubbing
Sodium carbonate FGD scrubbing is currently employed on
three 125-MW utility boilers at the Nevada Power Company Reid
Gardner Station, as well as on one industrial boiler. This
process, due to the soluble salts concentrations in scrubber
liquors, is most practicable in areas where high TDS liquors can
be disposed with little environmental hazard. Currently, the
process has found application in areas of low humidity or areas
with a high evaporation/precipitation ratio.
The system chemistry is based on the following reactions:
Na2S03 + S02 + H2O. 2NaHS03
Under proper pH conditions, the first reaction predominates so
that there is little NaHSOs in the scrubber effluent. The second
reaction is limited if a pH of 5 to 7 is maintained. It has been
reported that 0.8 to 0.9 mole of Na2C03 is required per mole of
S02 removed (Ref. 71).
BY-PRODUCT RECOVERY SYSTEMS THAT PRODUCE A MARKETABLE PRODUCT
There are three factors affecting the feasibility of
generating marketable by-products from FGD systems. These are:
t Technology availability
• Consumer/ institutional acceptance of the by-product
• Economics and markets
Regenerable FGD technology producing elemental sulfur or
sulfuric acid has a proven commercial market in certain areas.
Marketing and utilization of FGD sludges or gypsum is currently
under investigation by the EPA and other public and private
organi zations .
FGD by-products must meet with customer approval in order
to gain market acceptance. Since these by-products result from
pollution control, regulatory and consumer institutions may
require proof that the product is safe to both human health and
the environment. Institutional constraints also relate to
47
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market specifications and governmental rules and regulations.
These parameters must be considered for successful utilization
of FGD by-products.
Another important consideration for successful by-product
utilization is competition in the marketplace. Economic viabil-
ity is determined by the relative costs of secondary and virgin
materials. As virgin materials become increasingly scarce and
therefore more expensive, the value of related secondary
materials increases. The virgin materials competing with FGD
by-products are currently in plentiful supply, but regional
shortages and demand growth may render by-product utilization
economically attractive in some areas of the country. Utilities
are in business to market power. Most utilities balk at the
idea of developing sellable FGD by-products in an uncertain
marketpl ace.
Regenerable flue gas cleaning systems have found acceptance
for cleaning process gases from heavy industry, e.g., petroleum
refineries, sulfur acid plants and non-ferrous smelters. In
most cases, the by-product can be added to existing products
within the plant without additional marketing efforts. Regener-
able systems have been installed on a few power plants with some
degree of success.
Regenerable processes may eventually become the predominant
scheme for sulfur oxide control. These processes can yield
gypsum elemental sulfur and sulfuric acid, all of which have
proven market value.
The current market for nonregenerable FGD sludge is very
limited, and disposal is generally more cost effective than
recovery. Potential markets for FGD sludge include use as
gypsum, structural landfill, synthetic aggregate, mine void
backfill, soil amendment, and acid mine drainage control or
treatment. Research has shown these alternatives to be tech-
nically feasible under proper conditions of treatment and
control .
FGD by-product recovery can therefore be classified as
either (1) regenerable FGD with recovery of gypsum or sulfur
values or (2) use of FGD throwaway sludge. The following sub-
sections discuss these alternatives.
REGENERABLE FGD SYSTEMS
Regenerable FGD systems can have as their by-products
gypsum, hydrogen sulfide, sulfur dioxide, sulfur and sulfuric
a c i d .
Hydrogen sulfide and sulfur dioxide are gases with rela-
tively little commercial value, while gypsum, elemental sulfur,
48
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and sulfuric acid are readily marketable. Certain FGD systems
that remove and concentrate sulfur dioxide can either oxidize to
sulfuric acid or reduce to elemental sulfur. Other systems
directly produce sulfur or sulfuric acid. Currently, the most
popular systems are:
• Dilute and scrubbing
• WeiIman-Lord scrubbing
• Magnesium oxide scrubbing
• Citrate scrubbing
Dilute Acid Scrubbing
The only commercially demonstrated dilute acid scrubbing
system is the Chiyoda "Thoroughbred 101" process, which uses
dilute sulfuric acid as the absorbent liquid. Oxidation of
H2S03 to H2S04 is accomplished by using a soluble Fe2(S04_
catalyst. A portion of the resulting H2S04 is reacted witl
limestone to form gypsum. The remainder of the ^$04 is
recycled to the absorber. This process is composed of five
operations: (1) prescrubbing, (2) absorption, (3) oxidation,
(4) crystallization, and (5) by-product handling/disposal.
Figure 5 illustrates the basic process flows for the
Chiyoda process. The prescrubber cools the incoming flue gas
to its saturation temperature and removes entrained fly ash and
chlorides. Sulfur dioxide is then removed in a countercurrent
scrubber (fixed bed absorber) using a weak sulfuric acid solu-
tion. The absorption yields sulfurous acid, which is air
oxidized to sulfuric acid in the oxidizer using a ferric ion
catalyst. The solution is then passed to the crystallizer and
reacted with limestone to form gypsum crystals. Clarified liquor
is then recycled to the absorber.
The Chiyoda process was originally designed for oil-fired
systems. There are 13 such systems currently in operation in
Japan. A 23-MW demonstration plant started treating flue gas
February 1975, at the coal-fired Gulf Power Company Scholz
plant near Sneads, Florida. The demonstration program was com-
pleted on March 22, 1977. Chiyoda and Gulf Power are currently
preparing a comprehensive report on the program. Coal utilized
at the Scholz plant has a 3 percent sulfur content; SO? removal
efficiencies in excess of 80 percent have been obtained. The
plant did not operate in the closed-loop mode. Spent acid
liquor discharges from the prescrubber average approximately 20
gpm. The liquor is neutralized with limestone and piped to a
lined settling pond where fly ash, gypsum, unreacted limestone,
and Fe(OH)3 are removed by sedimentation. Concentrations of
total dissolved solids, iron, mercury, and fluoride in the
supernatant liquor currently exceed state water quality standards
for a surface receiving water. This liquor was routed to the
Scholz plant ash pond, which ultimately discharges into nearby
surface waters.
49
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Limestone
Silo
en
O
Waste
Disposal
Waste
Disposal
Mother
Liquor
Tank
Gypsum
Figure 5. Chiyoda Thoroughbred 101 Flow Diagram (Ref. 30).
-------
Dewatering of the Scholz sludge by centrifugation has pro-
duced an 80 to 85 percent solids filter cake. The gypsum was
being disposed of in a lined pond equipped with underdrainage.
Permeability of the filtered sludge has been calculated at
between 10"^ to 10"6 cm/sec. Rain water percolated through the
gypsum is routed from the underdrain to the ash pond.
Various minor problems limited the unit's availability
during the first few months of operation. These problems
included (1) maintaining chloride concentrations in the absorp-
tion/crystallization section below 200 ppm to prevent corrosion
in the stainless steel vessels; and (2) obtaining particulate
collection ahead of the absorber to reduce dust and fly ash
contamination of the mother liquid and gypsum. However, from
October 17, 1976, through program completion, the process
utilization was greater than 99 percent.
WeiIman-Lord Scrubbing
This process, patented by Davy Powergas, Inc., is a proven
method of flue gas desulfurization designed for ultimate recovery
of S02- The many such systems presently on line in Japan are
reported to have a low percentage of downtime and high collection
efficiencies. Recently, the WeiIman-Lord system was applied to
a coal-fired boiler unit at the D. H. Mitchell Station of the
Northern Indiana Public Service Company.
Figure 6 shows the typical process flow diagram for this
system. The principle of the Wellman-Lord process involves
scrubbing the flue gas with a sodium sulfite solution. The
bisulfite by-product is then heated, which regenerates the
sulfite and produces SO? for further processing to sulfuric acid
or elemental sulfur. Trie reaction mechanisms involved in the
scrubbing and regenerative steps are as follows (Ref. 164):
Stage I (scrubbing)
Na2S03 + S02 + H20 ?2NaHS03
Stage II (regeneration)
2NaHS03 ?Na2S03(s) + S02(g) + H20
Following regeneration, the S02 is transported to a sulfur
production unit where the concentrated S02 is reduced to
elemental sulfur using methane gas. It is also possible to
convert to liquid S02 or sulfuric acid from the recovered S02.
There has been little experience with coal-fired units
using the Wellman-Lord process; however, several major
51
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NAOH
MAKEUP
en
ro
DESULFURIZED
STACK GAS
REHEATER AND
BLOWER
ABSORBER
NAHS0
PRESCRUBBER
H20
DISSOLVER
NAHS0
SLURRY
REUSE
SO,
CONDENSER
EVAPORATIVE
CRYSTALLIZER
LOW PRESSURE
STEAM
PURGE TO WATER TREATMENT
FLUE GAS
Figure 6. WeiIman-Lord Process Schematic (Ref. 163)
-------
operational difficulties have been encountered with oil-fired
units. One problem is the generation of large quantities of
purge solids - particularly sodium sulfate - which are difficult
to dispose of properly. Sulfate formation is undesirable as it
wastes valuable sodium feedstock. The formation mechanisms are
primarily $03 absorption, sulfite oxidation, and disproportion-
ation (Ref. 163). Inhibiting additives and initiating process
modifications have been successful in preventing oxidation, and
low pH oxidation has been used to reduce effluent oxygen demand.
This treatment, however, has done little to reduce TDS in the
purge discharge.
A second problem with the Wellman-Lord process involves the
high steam demand for the dissociation of sodium bisulfite to
regain the SC^ gas. Power plants applying this process to SO?
control can expect a derating of between three and six percent
of rated generating capacity (Ref. 163).
The use of methane in the production of sulfur is a draw-
back because of the natural gas scarcity. Vendors whose
reducing systems rely on methane availability have been research-
ing alternate methods of converting SC^.
Most of the operational Wellman-Lord scrubbing units have
maintained $63 collection efficiencies of around 90 percent.
Operating time availability has been high in most cases,
attributable to the simplicity of the process. All existing
units use an absorption tower and employ either sieve plates or
packed beds (saddles) as the contactor.
Magnesium Oxide Scrubbing
Magnesium oxide scrubbing is designed as a closed-loop
operation, regenerating the magnesia used in the slurry and
collecting S02 for conversion of sulfuric acid or elemental
sulfur. Three such systems have been installed to date. Two
plants - PEPCo Dickerson No. 3 and Boston Edison Mystic No. 6 -
were shut down when the acid plant regeneration site was forced
to discontinue operations. The third plant, Philadelphia
Electric's Eddystone No. 1A, has been temporarily shut down
while its acid regeneration system is being relocated. In no
case have technical difficulties been the major reason for
process conversion or shutdown.
A typical flow diagram of this process is shown in Figure 7
In magnesium oxide scrubbing, an aqueous solution of MgO,
magnesium sulfite, and magnesium sulfate contacts the flue gas
in a venturi absorber unit, collecting the S02 and forming
several magnesium-sulfur compounds. The scrubber effluent is
dewatered to retain the solids and then recirculated. The dry
sludge cake, composed primarily of hydrated magnesium sulfite,
is transported to a processing facility. There it is thermally
53
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FLUE GAS
^CONTAINING SO
AIR
MGO
TANK
Figure 7. MgO Slurry Process - for Flue Gas Free of Particulate Matter (Ref. 11)
-------
dehydrated and calcined for reuse in the slurry. The S02 gas is
processed into salable by-products.
The majority of operating experience with magnesium oxide
scrubbing was acquired at the Boston Edison Mystic oil-fired
unit and PEPCo's coal-fired Dickerson station. Problems
encountered at the Mystic plant included high percentages of
unbound moisture in the filter cake, subsequent occlusion in
the dryer drum, inactivity of the recycled magnesium oxide when
slurried, and dust control during the drying step. Problems at
Dickerson can be traced to off-specification construction
materials and extended boiler shutdowns. There was no continu-
ous slurry bleed at any of the power plants.
Citrate Scrubbing
The Citrate Process, pioneered by the U.S. Bureau of Mines
(USBM), is designed for the regeneration of elemental sulfur.
Pilot plant operations have been constructed by both the Bureau
of Mines and Peabody Engineering Systems. To date, no full-
scale plants have been installed. However, a joint effort
between the USBM and the EPA has initiated construction of a
53-MW demonstration system at St. Joseph Minerals in Pittsburgh,
Pennsylvania.
Figure 8 is a schematic diagram of the Citrate Process
(Ref. 166). This process proceeds in six steps: (1) cleaning
the gas of particles and subsequently cooling the gas below 50°C;
(2) scrubbing with a solution of citric acid and sodium carbonate
(pH - 3.8-4.5); (3) precipitating the elemental sulfur by
bubbling h^S through the spent liquor; (4) dewatering the sulfur
by centrifuging; (5) melting the sulfur via an autoclave; and
(6) regenerating the H 2 S.
Aside from the obvious advantage of regeneration, the
Citrate Process is somewhat unique in its buffering capability.
A solution buffered with citric acid shows superior S02 solu-
bility compared to other potential agents, thereby reducing the
liquid/gas ratio necessary for a given efficiency. The optimal
pH values for the Bureau of Mines and Peabody (Citrex) processes
are 3.8 and 4.5, respectively; a higher pH would likely increase
solubility of $62, but increased formation of in-situ thio-
sulfates would reduce the recovery efficiency by increasing
input H2S and acid requirements (Ref. 163).
Although the two processes claim to produce minimal
oxidation of SCU, this is known to be a problem under certain
operating conditions. The oxidated product can be removed
from the scrubber loop through the use of additives (such as
SrC03), but the sulfate salt generated is difficult to dispose
of properly and results in additional expenditures for feedstock.
55
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MAKEUP
WATER
CLEAN
WASTE GAS
MAKEUP
CHEMICALS
GLAUBER1S
SALT CRYSTALS
FLUE GAS
Q— -
en
CTl
GAS
CLEANING
&
COOLING
so2
REMOVAL
SODIUM
SULFATE
CRYSTALIZER
PRECIPITATED
SULFUR
SEPARATION
FLY ASH
TO PIT
SULFUR
MELT &
DECANT
REGENERATION
REACTION
REDUCING
GAS (H2S)
GENERATOR
-O
MOLTEN
SULFUR
Figure 8. Citrate Process (Ref
REDUCING AGENT
(NATURAL GAS ETC. )
166)
-------
Pilot units in operation have been using either sieve-plate
or packed-bed tower absorbers for the scrubbing process. Removal
efficiencies in excess of 95 percent have been achieved with an
L/G ratio of less than ten. By-product sulfur purities of 99
percent or above are common. Citrate losses are attributed to
spills or oxidation. Peabody reports losses from pilot plant
studies of 6 to 7 Ib/ton of sulfur recovered.
The future of citrate scrubbing is unclear. Although pilot
studies have indicated that the process may be less costly than
other methods, scale-up of certain system components may be
difficult, thus reducing its cost effectiveness. Consideration
of oxidation kinetics and cost factors indicates that citrate
scrubbing will be used primarily to treat flue gases with high
concentrations of S02-
Lime/Limestone Sludge Utilization
In order to avoid the problems associated with FGD sludge
disposal, research has been in progress in the area of nonregen-
erable sludge utilization. Technical developments for FGD
sludge reuse have largely followed precedents established for
the utilization of fly ash. Table 8 lists both present and
proposed uses for FGD sludge. Current and past sludge utiliza-
tion investigations include:
• Autoclaved products, brick, and aerated or foamed
concrete and concrete materials, by the Coal Research
Bureau of West Virginia University;
• Use as an aggregate in highway construction by the
Gillette Company Research Institute.
Under EPA sponsorship:
• Elemental sulfur and calcium carbonate recovery, by the
PulIman Kel1ogg Co.;
• Use as a filler material and source of sulfur in
fertilizer, by TVA;
• Use of FGC gypsum in Portland cement manufacturing, by
Santee Portland Cement Corp. and South Carolina Public
Service Authority;
• Recovery of minerals, sulfur, alumina, and dicalcium
silicate, by TRW.
Presently, the most feasible utilization schemes appear to
include sludge conversion to gypsum, for use as a building
material, structural landfill, synthetic aggregate, mine
void backfill, soil amendment, and control of acid mine drainage.
57
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TABLE 8.
SLUDGE UTILIZATION SCHEMES*
Construction Materials
Pavement
Pavement base
Cement manufacture
Concrete admixture
Mineral aggregate
Sinter bricks
Autoclaved bricks
Autoclaved concrete blocks
(poured and aerated)
PI aster
Wai 1 board
Mineral wool
Lightweight aggregate
Environmental Uses
for land
Structural fill
recovery
Structural fill
tary landfill
Structural fill
subsidence control
Fill for fire control in
abandoned mines
Neutralization or prevention
of acid mine
Reclamation of
1 akes
Filter aid for
sludge
Tertiary
sewage
Soil amendment
Soil stabilization
for s a n i -
for mine
drai nage
pol1uted
sewage
Mineral Recovery
Sulfur
Aluminum
Lime or limestone
Magnesium oxide
Iron
Ti tani urn
Silicon
Rare earths
Fillers for Manufactured
Products
Glass
Fertilizer
Pai nt
Plastic
Rubber
Mi seellaneous
Cerami-c materials
Sand blasting grit
Porous pipe
Metal coatings
Grouting agent for wells
dewa teri ng
treatment of
Ref. 13
58
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The technologies for these utilization schemes are already
developed. Although these products are in many ways equal to
existing materials, utilization has been limited because (Ref.
129):
t Sludge is produced in a wet state and must be thoroughly
dewatered for many uses;
t Sludge properties can be highly variable, creating
potential quality control difficulties;
• Sludge use in sintered products manufacture causes the
release of sulfur dioxides;
• The contaminant content (e.g., salts and heavy metals)
of sludge presents a potential problem of water pollution
for certain applications, such as soil amendment and acid
mine-drainage neutralization;
• Severe competition exists from current virgin material
suppli es;
• General apathy of industry to the utilization of
secondary materials;
• High capital investments are necessary to produce auto-
clave products, e.g., bricks or blocks; and
• Technology for mineral recovery is undeveloped or very
costly.
Gypsum--
Gypsum produced from scrubber waste would have to compete
with a sautrated virgin gypsum market in the United States.
Japan is the only country in which gypsum is produced from FGD
and marketed primarily for wallboard and portland cement.
Japan's scrubber systems are in many cases equipped with sulfite
oxidizing units, which produce gypsum containing as little as
10 percent moisture- The high cost of oxidation has until
recently been offset by gypsum's high market value in Japan.
Since 1975, however, gypsum supply has exceeded demand and has
forced many power plants to store the excess in place of
disposal.
The purity and consistency in composition of gypsum
produced from FGD sludge is expected to be met with skepticism
in the United States. However, Chiyoda gypsum from the Gulf
Power Company's Scholz plant was tested and judged suitable for
wallboard manufacture (Ref. 131).
59
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Agricultural utilization of FGD gypsum is a possibility
for the amelioration of natric or solonetzic soils (Ref. 149).
The gypsum could act as a calcium source for plants or calcium
deficient soils. Chiyoda gypsum is under investigation by the
University of Florida Agricultural Research Center for use on
peanuts and soybeans (Ref. 133). It has also been noted (Ref.
141) that FGD gypsum combined with fly ash has the ability to
improve the texture and drainage characteristics of some soils.
Another potential advantage is that the FGD gypsum slurry may be
sprayed directly on the soil iwthout the need for prior drying.
Fertilizer Production--
The use of lime and limestone scrubber wastes as a filler
material and source of sulfur in granular fertilizers is being
evaluated by the Tennessee Valley Authority. Qualitative field
tests on rye grass have shown no apparent detrimental effects
from the addition of FGD sludge-based fertilizer. Quantitative
field tests have not b-e^n completed to assess either trace metal
or toxic material effects and/or concentration in the plants,
along with their rates of leaching.
There have been both physical and chemical problems with
fertilizer manufacture. Physical difficulties have been caused
by excess moisture in the sludge adversely affect ing granulation,
The fertilizer has also shown a high propensity for rewatering.
A major chemical problem has occurred in the preneutra1izer,
in which low pH (from phosphoric acid addition) causes high
solubilization of calcium sulfite and consequential loss of
sulfur dioxide to the atmosphere.
Sulfur losses ranged from 78 to 90 percent by weight of
the total sulfur added, while ammonia losses ranged between 34
and 61 percent by weight of the ammonia added (Ref. 133).
A procedure has been proposed for elimination of these
unwanted reactions. This procedure would promote either the
oxidation of calcium sulfite to calcium sulfate before feeding
to the preneutralizer or neutralization of the phosphoric acid
before it comes into contact with the sludge. Testing of these
procedures has not yet been completed at TVA (Ref. 130).
Aggregate in Construction--
Laboratory investigations were reported in 1975 by the
Gillette Company Research Institute to evaluate the performance
of FGD sludge use in construction (Ref. 149). Various mixtures
of water with lime, fly ash, and sludge were tested for use as
filler material in road building operations and as aggregate
particles in Portland cement and asphaltic concrete mixtures.
From the results of engineering tests, the following conclusions
were made:
60
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• When properly proportioned, compacted, and cured, the
sludge mixtures produced a strong, stiff material that
may be suitable for use in embankments, subgrades, and
subbases and bases for pavements.
• The durability of these mixtures when tested by freeze-
thaw and wet-dry tests was insufficient after seven days
of 23 C curing. Durability was still insufficient, but
had improved after a 28-day 23°C, curing period. The
study suggests that the use of lime-fly ash-sludge
mixtures for pavement components in cold climates should
be considered with caution.
• Selected mixtures were relatively impervious and might
be employed in dikes, lagoons, and levees.
• Compacted lime-fly ash-sludge mixtures were normally
lighter in weight than compacted soils. This feature
would be advantageous where soft, compressible ground is
to be crossed by an embankment.
• Initial effluent leachate concentrations of TDS were
high as soluble lime and gypsum materials were leached.
Leachate TDS concentrations showed approximately a 75
percent decrease after a 28-day period.
The use of lime-fly ash-sulfate mixture as an aggregate for
Portland cement and asphaltic concrete was evaluated. The major
conclusions were:
• Tests of concrete mixtures indicated acceptable strength
values for specialized applications, but unacceptable
durability factors for prolonged exposure to cyclic
freezing and thawing environments. These results
suggest that concrete mixtures may perform satisfactorily
in warm climates not subject to freezing and thawing.
• Admixtures normally used to enhance pozzolanic reactions
were found to have little effect on strength development.
• Aggregate used in concrete and cement mixtures had high
absorption characteristics and did not pass either
standard soundness tests or the Los Angeles abrasion
test.
0 Apparent leaching of the aggregates occurred during the
freeze-thaw testing, depositing an unidentified white
material in the regions of surface cracks.
In summary Gillette recommended that curing time be
increased to between six and nine months and that adequate
protection from freezing and thawing be provided; this would
61
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afford a stronger, more resistant aggregate particle capable
of selected construction applications.
OTHER NON-SCRUBBING DESULFURIZATION OPTIONS
The high cost of wet scrubbing techniques has prompted many
public and private institutions to seek alternate means for
reducing S02 emissions. Some of these techniques are:
• Fuel switching from high sulfur coal to natural gas,
oil, or low sulfur coal
0 Coal cleaning
• Fluidized bed combustion
0 Coal gasification
Many of the techniques are still in the developmental
stages, but accelerated research may in a few years promote
them to commercially available status. Alkalized alumina,
activated carbon, and catalytic oxidation were discussed in
previous subsections.
Low Sulfur Fuel
A reduction in sulfur dioxide emissions can be accomplished
by switching to a low sulfur fuel, i.e., a fuel low enough in
sulfur content to meet federal or state emission standards. The
use of low sulfur coal to meet emission standards is technolog-
ically simple, but may be difficult to justify economically. A
coal switch requires only a tnodera-te capital investment (for
particulate collection and plant conversions), but power plants
that were originally designed to burn one type of coal may
experience operational difficulties in burning another type.
For example, the replacement of high sulfur western coal with
western lignite and subbituminous coals - which are low-Btu,
low sulfur, high ash varieties - may double the ash disposal
requirements while also derating the boiler. The use of eastern
low sulfur coal does not present these problems, but supply-
demand pressures have forced the price up substantially. The
capital cost of a coal switch has been estimated at between
$5 to $15/KW (Ref. 129).
Use of a low sulfur distillate oil as the primary fuel is
common among plants that were originally equipped to use oil as
a standby fuel. The.major drawback to its use is price. Fuel
oil prices have increased rapidly since 1974, and the installa-
tion of large oil storage capacities is difficult to justify
under such unstable market conditions. A switch to oil firing
is a valid interim solution to the S02 emission problem, but
future cost uncertainties make long-range planning difficult for
62
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management. Recent statements by the Federal Energy Administra-
tion (FEA) and the Administration have stressed decreasing
dependence on imported oil and development of United States
coal reserves.
In order to comply with ambient SOp regulations, several
eastern power plants employ low sulfur fuels only when meteoro-
logical conditions might hinder pollutant dispersion. Inter-
mittent controls are a highly sophisticated art, employing
complex predictive modeling of atmospheric dispersion to deter-
mine when and to what degree boiler operation should be
modified. Typical of intermittent control systems are the
"Sulfur Dioxide Emission Limitation" (SDEL) by TVA and "Dynamic
Emission Controls" (DEC) by the Department of Commerce; neither
is endorsed by EPA except as an interim control measure. The
major criticism of intermittent controls is that they do little
to reduce total SOX and heavy metals loading to the biosphere
over the long range.
Tal1 Stacks
Stacks as high as 1,000 ft have been constructed to direct
power plant exhaust away from the local environment. The gases
are released so high that they are sufficiently dispersed in
any weather conditions, thereby meeting ambient standards. Like
intermittent controls, the relationship between stack height and
meteorological conditions has been studied in detail and is used
to determine the proper height for specific site conditions.
Although regulatory agencies consider tall stacks only an
interim solution to the S02 problem, power plants continue to
build them. Even if additional air pollution control equipment
is installed, it is considered desirable to have the dispersion
capability in case of control system failure.
Coal Cleaning
In 1977, 40 to 60 percent of the coal mined in the U.S.
will be cleaned of impurities for use in steelmaking operations.
The conventional cleaning systems are designed to remove mineral
matter, not to remove sulfur. During recent years, however,
substantial research has been directed toward developing
techniques for removing sulfur from coal.
There are several obstacles to desu1furization of coal,
which generally relate to the type of sulfur and how it is
situated in the coal matrix. Inorganic pyritic sulfur, con-
tained as FeSo, is a physically distinct portion of the coal and
can be removed by physical means. Organic sulfur is bound to
the various hydrocarbons in the coal matrix, and this sulfur
cannot be physically separated.
63
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Physical separation techniques include screening, froth
flotation, air classification, magnetic separation, and dense
media separation. These techniques utilize the difference in
physical properties between coal and pyrite.
Where pyritic sulfur comprises a majority of the sulfur
present, physical separation alone is often sufficient to
reduce total sulfur to acceptable levels. However, it is
estimated that only 16 to 17 percent of all coal mined in the
U.S. can be sufficiently cleaned of sulfur by physical means to
meet air standards when burned.
Chemical removal is being investigated with some success.
TRW has developed a process for leaching the sulfur with ferric
sulfate. The resulting solution of ferric sulfate, sulfuric
acid, and sulfur is volatilized to remove the elemental sulfur
and regenerate the original solution. Ledgemont Laboratories
is developing a process that applies oxygen directly to oxidize
the sulfur. Although some coal is lost to oxidation, this is
balanced by the reputed 90 percent sulfur removal; legal
problems have delayed process implementation.
Organic sulfur can also be removed by several techniques,
all of which are still on a laboratory scale. Both the Bureau
of Mines and Battelle are investigating sodium hydroxide
leaching, with preliminary results indicating up to 70 percent
organic sulfur removal. The KVB Corp. is developing an oxida-
tion process using a gaseous mixture of Ho, 02, and N03;
laboratory results have been encouraging (Ref. 31).
Fluidized Bed Combustion
Fluidized bed combustion (FBC) is still developmental, but
experts project that it will have a significant future impact on
the power generation field starting in the early to mid 1980s.
other
bed
This technique uses a bed of limestone (or dolomite) that is
suspended, or "fluidized," by underfire air jets; coal (or o
fuel) is injected into this bed for combustion. The high be
turbulence characteristic of FGC is an aid to more complete
combustion at lower operating temperatures. The optimum repyi L
combustion temperature for FBC is in the range of 750 to 950 C,
while temperatures as high as 1400 to 1500°C are commonly used
•I V^ rtlll\//-»V»T-T*-\«~l ^/-v-^l r* f^ W\ U. i i f -t~ ^ n v+
reported
in pulverized coal combustion.
While combustion efficiency is the primary consideration,
the potential for reduced air pollution emissions is also
attractive. Nitrogen oxide emissions from FBC are inherently
low, which makes FBC superior in this respect. Sulfur dioxide
emissions are also reduced due to the presence of the limestone
bed, which acts as an adsorbent. Unlike the relatively ineffi-
cient method of limestone injection into a conventional boiler,
FBC enhances adsorption through greater turbulence, good
64
-------
gas/solids contact, and long sorbent residence time in the bed,
while remaining at temperatures below the "dead burning" level
of limestone or dolomite. Eventually all coal ash is entrained
in the flue gas as particulate matter. The amount of sorbent
bed lost to the flue gas is dependent on gas velocity.
The United States is concentrating on FBC research through
a number of public (EPA, ERDA, and TVA) and private (EPRI)
institutions. In the past few years, laboratory and pilot scale
operations have been constructed, which operate at both atmo-
spheric and higher pressures. The state-of-the-art in FBC is
rapidly advancing toward full-scale operational status.
Recently, a 30-MW boiler operating at atmospheric pressure was
started up by ERDA at Rivesville, West Virginia. Other facili-
ties ranging from a 100,000-lb steam/hr commercial boiler to a
200-MW utility plant are in the design stages.
Many operational problems are anticipated with FBC,
although premature troubleshooting has, in the opinion of some,
slowed the advancement of the art. Potential problems include
the fol1owi ng:
t Solids handling; i.e., feed coal distribution and bed
material size control;
• Erosion of internal parts due to higher turbulence and
particulate loading; and
• Limestone regeneration (reuse is known to be a problem) •
moderate feedstock losses are anticipated in large-scale
systems, although the existing regeneration technology
is presently being studied for improvement (Ref. 7).
Coal Gasification
A promising technology for the use of high sulfur coal
involves low BTU coal gasification. Gasification has two
advantages over FGD. First, the gas is produced under reducing
conditions so the sulfur is converted to more easily removed
H 0 S. Second, the process can be performed at high gas pressures
allowing for use of combined power cycles with higher efficien-
cies. However, there are many unanswered environmental and
technical questions that need to be resolved. In addition, the
costs for coal gasification are high compared to conventional
fuel firing.
Three basic reactors have been developed for the gasifica-
tion of coal. These are fixed-bed (or moving-bed), fluidized-
bed, and entrained (or suspension) reactors. Gasification of
coal in molten-iron and molten-salt baths has also been studied.
In a fixed-bed reactor, the gasifying medium is passed counter-
current to the coal with ash removal from the bottom and coal
65
-------
addition at the top. The bed is fixed in that, ideally, condi-
tions remain constant with time throughout the bed. If the
velocity of the gasifying agent and the size of the coal
particles are such that the bed behaves as a fluid, the system
is called a fluidized bed. An entrained system operates with
pulverized coal particles carried by the gasifying agent (Ref.
84). Examples of commercially available coal gasification
systems are the Lurgi, Kopper-Totzek, and Winkler processes.
The Lurgi dry-ash gasifier is a fixed bed, pressurized
generator that is made up of three main parts: the coal hopper,
the reactor, and the coal ash lock. Coal is fed from the top of
the generator through the coal hopper and into the reactor. In
the reactor, the coal contacts a mixture of oxygen and steam (or
air and steam) counter-currently. The oxygen and steam are
injected into the lower region of the gasifier. The mixture is
proportioned to control the temperature in the reactor so that
the formation of clinkers, due to the fusion of ash, can be
avoided. A mechanical stirrer keeps the coal and ash separated.
The ash is continuously removed from the bottom through the ash
lock after being separated by a revolving grate. The fuel bed
is heated by the rising gases, and the volatile compositions of
coal are vented as part of the raw gas from the top of the
gasifier. Required operating conditions include a pressure
range from 240 to 315 N/cm , a temperature range from 620 to
760 C, and a residence time of almost one hour. The crude gas
leaves the gasifier at a temperature of 370 to 595°C and con-
tains tars, oil, naphtha, phenols, sulfides, and ammonia along
with coal and ash dusts and a variety of other chemical com-
pounds .
In the Kopper-Totzek process, a well-mixed feed of coal and
oxygen is injected from both sides of the reactor. The opposite
jet configuration creates a high degree of turbulence that
increases the reaction rate significantly. The combustion
reaction takes place very close to the injection point, while
the reduction reaction continues in the remaining space. Due
to the concurrent flow of the reactants, the hydrocarbons
produced at low temperatures are passed into a very high temper-
ature zone where they decompose rapidly. As a result, there is
no coagulation of coal particles. Some unreacted carbon and
about 50 percent of the ash, entrained in the hot gas (980 to
1260 C), leave the gasifier. This gas passes through the waste
heat boiler, the dust collector, the wet scrubbing tower, and
the disintegrator. The gas can be used directly or compressed
for future use or further processes. The remaining ash in the
gasifier is slagged and gets tapped off from the bottom of the
reactor.
The Kopper-Totzek process is very versatile. It can gasify
many types of fuel, including petroleum coke, tars, heavy
residual oils, and all ranks of coal; the transfer from solid to
66
-------
liquid fuel requires only a change in the burner head. A
second advantage is that the process is very low in air pollu-
tion generation.
The Winkier process is presently the only commercially
available fluidized bed gasifier. There are currently 36 Winkler
installations operating at 16 plants. This process can be used
to gasify a variety of solid fuels, including brown coal, brown
coal-char, semicoke, caking, and, most commonly, subbituminous
coal or its coke. The Winkler reaction is a fluidized bed,
operating at or near atmospheric pressure and from 800° to
1000°C. The temperature is varied to suit the reactivity of the
fuel, with maximum temperature limits being set by the ash
sintering temperature (Ref. 106).
Combined cycles power plants have been proposed for pres-
surized gasifiers. In this type of system, the high pressure
fuel gas is expanded through a turbine-generator and then burned
in a boiler to produce steam; the use of both steam and fuel
gas to generate electricity improves system efficiency. The
only pressurized gasifier that is commercially available is the
Lurgi process; its limited capacity would make multiple units
necessary to generate sufficient quantities of gas and electric
power to replace existing boiler equipment.
Table 9 shows the developmental stage of the various coal
gasification concepts. The cost of coal gasification is said
to compare favorably to conventional solid fuel-fired installa-
tions. One source quotes a new installation cost at $280/kW,
and retrofit costs have ranged from $110 to $498/kW (Ref. 161).
67
-------
TABLE 9.* STAGE OF DEVELOPMENT OF TYPICAL LOW BTU
GASIFICATION PROCESSES
CT>
co
£cyti$
8i-Gas
Hydra ite
COj Acceptor
Kopperi Toizek
Urgj
Molten Salt
Synthans
v-tes
Union Csrbld©
fctellman Galuslvg
Westinghouse
Kinkier
Concept
1
X
X
X
X
X
X
X
X
X
X
s
8
1
2
X
X
*
g
X
X
*
X
8
*
I
X
I
Bench
Const.
3
X
X
X
*
X
1
£
X
1
i
S
X
S
Test
4
X
X
X
X
X
£
£
X
s
1
1
1
z
Pilot
Const
5
X
X
X
X
X
X
i
1
1
X
Test
6
X
8
I
X
2
X
Demo,
Const.
7
X
x
a
x
Test
&
X
X
X
I
Commercial
Const.
9
X
2
I
I
Test
10
X
X
I
X
Coal
Condition
Caking
X
X
X
X
*
X
X
1
X
X
M
Non-Caking
X
X
X
X
X
X
X
X
X
X
X
X
HHV*
100-200
300-500
100-200
300-500
300-500
300-500
300-500
100-200
300-500
300-500
100-200
300-500
100-2CO
300-500
1CO-200
300-50Q
100-200
1CO-20C
500-60C
Type of Reactor
-a
3 T>
r— 41
f- tf!
Mol
X
X
Mol
X
X
£
X
X
c
••- -o
«J OJ
1- CO
4->.
C XI
uj qj
en- in
X
X
en-sa
Cn
C
s* ~o
£ .?
n bdtii
X
t bstii
X
Operating Pressure
0-15
32 ig
X
X
X
ii
100-500
psig
X
X
X
X
X
1000-
1500
psig
X
X
X
X
Wifihtr Hastif'3
"(Btu/scf )
*Ref. 106
-------
SECTION VI
WASTE CHARACTERIZATION
PARAMETERS WHICH DETERMINE SLUDGE CHARACTERISTICS
The physical and chemical properties of FGC sludges are
influenced by many interrelated parameters. These interrela-
tionships and the relative importance of each under a given
set of conditions are not completely understood. However,
general statements can be made about the various parameters and
how they interact. The chemical composition of the solid and
liquid phases is a function of the following parameters:
• Fuel type and composition
t Boiler type, design and operation
• Fly ash and bottom ash removal systems and
their relation to sludge disposal
t FGC system type, design and operation
• FGC reagent and input water
The physical properties of the sludge depend primarily upon
the same parameters but with a different functional dependence.
Fuel Type and Composition
The composition of the fuel is a primary factor in deter-
mining the concentration of trace elements in the sludge and
the amount of sludge generated. Generally, an increase in the
concentration of a particular trace element in the fuel results
in an increase in its concentration in the sludge. Sulfur
concentration in the fuel will obviously directly affect the
quantity of sludge solids generated, since a largely stoichio-
metric reaction occurs between the sulfur oxides and the sorbent.
The relationship between excess combustion air and coal sulfur
content combined with pH is most important. Due to the pre-
dominance of high sulfur coal-based FGD systems, most FGD
sludges have a sulfate/sulfite ratio of less than unity. The
few systems generating a predominantly sulfate sludge are
either (1) located in the western U.S. and burn low sulfur
coals, or (2) employing some method of forced oxidation.
69
-------
Coal is generally the primary source of trace metals in
FGD sludge liquors. Certain of the trace metals condense on
the surface of fly ash particles and are readily available for
subsequent dissolution in the sludge. The more volatile trace
metals encountered (arsenic, selenium, and mercury in parti-
cular) may not condense readily within the flue gas cleaning
system; their presence in the sludge liquor is strongly depen-
dent upon the particulate collection efficiency of the scrub-
bers .
Boiler Type, Design, and Operation
Boiler type, design and operation influence the parti-
tioning of various fuel impurities between the bottom ash, fly
ash and vapor phases. Chemical form, e.g., oxidation state,
etc., of specific impurities and their location in the ash
particles (within or upon the surface of the particle) depends
upon the time-temperature profile, flame chemistry, and ash
characteristics. These interactions are not well understood
at the present time.
Fly Ash and Bottom Ash Addition
Co-disposal of fly ash and bottom ash with FGC sludge
will affect both the chemical and physical properties of the
sludge. Addition of ash can improve physical properties for
subsequent disposal because the resulting sludge is more stable,
has higher load-bearing strength, and is more erosion resistant.
Since fly ash contains a large percentage of the trace
metals from the fuel, the amount and size distribution of the
fly ash entering the sludge will affect the chemical properties.
If all fly ash were removed ahead of the scrubber, the concen-
tration of many impurities would be reduced. The exceptions
are those impurities which either can exist in the vapor phase
at the scrubber or those impurities originating in the sorbent
or makeup water. The oxidation rate of sulfite to sulfate in
the scrubber system depends primarily upon the sulfur/oxygen
ratio in the flue gas. Although certain metallic ions act
as catalysts for this oxidation, very complex interactions will
also occur between the fly ash entering the sludge and the
nucleation and growth of calcium sulfite and sulfate crystals.
These interactions are not well understood at the present time.
FGD System Type, Design and Operation
The design and operation of the FGD system will affect the
sludge characteristics in various ways, just as the efficiency
of particulate collection in the scrubber will affect the
chemistry of the sludge. The details of system design (e.g.,
liquid to gas ratio, holding tank design, and method and loca-
tion of reagent addition) will affect the nucleation and growth
70
-------
of crystalline phases. In particular, the amount of super-
saturation at the point of reagent addition will affect the
nucleation and size distribution of the resulting crystals,
which in turn will affect both the permeability and load bear-
ing strength of the resulting sludge. Some understanding of
these interactions is being developed through present E P A -
sponsored test programs.
Operational variables in conjunction with fuel character-
istics and scrubber design will have an impact on the sulfate/
sulfite ratio. Decreasing the pH will generally increase the
ox-idation rate. In practice, the range of these operating
variables is limited by possible internal corrosion and scaling.
The ratio of calcium sulfate to calcium sulfite (better
known as sulfate/sulfite ratio) in the solid phase is important
to certain physical properties of the sludge. Sulfate is formed
by oxidation of sulfite, usually occurring within the scrubber
loop. Although a certain amount of sulfite oxidation occurs
in all lime/limestone systems, sulfate sludges are generally
formed in scrubbers with one or more of the following charac-
teristics :
• Low concentrations of sulfur dioxide in the inlet flue
gas, resulting in a high oxygen/sulfur dioxide ratio;
t The presence of oxidation catalysts, such as metals
from fly ash;
• Long gas retention times in the scrubber system (e.g.,
deep bed, multiple stages, etc.);
• An added oxidation stage, such as a special aerator;
• A low pH in the scrubber liquor.
Fly ash collection in FGD-equipped power plants is some-
times accomplished with the same scrubber or a second scrubber
in series using a common liquor reservoir; plants of this type
generate sludge with a high fly ash content. Fly ash is
typically a major source of trace metals found in FGD sludge.
Fly ash may also be added to the sludge if collected dry, there-
by improving sludge handling characteristics by increasing
the solids content of the disposed mixture.
Unreacted lime and limestone are often present in signifi-
cant amounts in FGD sludge. Limestone due to its low reacti-
vity, is often used in higher stoichiometric quantities (1.2 to
1.5). Lime systems and double alkali systems which incorporate
lime to regenerate sodium both operate at a near-stoichiometric
ratio with sulfur, thereby wasting little lime in the sludge
discharge.
71
-------
Whether the system is operated in an open or closed loop
mode makes a significant difference in the chemical properties
of the sludge, particularly the high soluble salt content
characteristics of a closed loop operation (continuous recir-
culati on).
FGC Reagent and Input Water Quality
The input water and sorbent are sources of impurities
which will affect the chemical composition of the sludge. In
general, the makeup water quality requirements for FGC equipment
are lower than for other systems in a power plant. Any water
reuse in a power plant would probably use the FGC system as the
water sink. Depending upon the cost and value of internal water
reuse, certain plants use low quality water for scrubber makeup.
The use of cooling towers blowdown for makeup water is one
common example; if the scrubber system is operated in a closed-
loop mode, all the salts entering the cooling tower with the
freshwater makeup will end up in the scrubber sludge. Even in
cases where some of the impurities in the input water are
removed by water treatment, the resulting sludge may be carried
over to the scrubber and thus transfer the impurities from the
input water to the scrubber sludge.
In a similar manner, the scrubber sorbent material can
affect sludge characteristics through trace metal inclusion and
the characteristic pH of the slurry. The lime systems generally
produce a higher sulfite content sludge than limestone systems.
The concentration of trace metals in the sorbent is specific
to each sorbent and its source.
Conclusion
From the above discussion it is clear that many factors
affect the chemical and physical characteristics of FGD sludge.
Several of these factors can be controlled with proper plant
operation. This might be construed to mean that sludge charac-
teristics can be modified to suit the disposal method and
specific site characteristics. However, the power plant
and associated gas cleaning equipment costs are generally much
greater than sludge disposal costs. Overall system cost mini-
mization will therefore generally require designs which minimize
the FGC system cost rather than optimize the sludge character-
istics.
CHEMICAL, PHYSICAL, AND BIOLOGICAL CHARACTERISTICS OF FGD SLUDGE
The physical and chemical characteristics of FGD sludge
are important to an effective disposal operation and have
been the subject of most disposal-related research efforts to
72
-------
date. An extensive data base is becoming available. Biological
characteristics are of limited importance since the waste is
inorganic; research in this area is currently lacking.
Chemical Characteristics
The by-products of non-regenerabl e FGD systems are
typically composed of four major constituents: calcium sulfate
hemihydrate and/or dihydrate (due to mixed crystal 1 i zation)^
calcium sulfite hemihydrate, unreacted sorbent, and fly ash.
The relative amounts of these constituents are determined by
the various scrubber and plant operating parameters discussed
in the previous section. Table 10 shows the wide variation
in sludge solid phase composition encountered in different FGD
systems .
The solid phase of FGD sludge can also contain a variety
of trace metals. These metals can come from several sources,
including fly ash, sorbent, makeup water or vapors in the flue
gas itself. The metals which are contained in fly ash generally
remain in the solid phase. Those which form on the ash surface
are often dissolved in the waste slurry and enter the liquid
phase; from there they may precipitate either as pure compounds
or with the sul fate/sul f i te crystals.
The liquid phase of FGD sludges is important due to its
potential as leachate. The sludge liquors typically contain
ions of sulfate, sulfite, chloride, calcium, magnesium, and
various trace chemical species. The total dissolved solids
(TDS) concentration in FGD sludges is a function of their
equilibrium levels in the scrubber system, with TDS concentra-
tion in excess of 20,000 ppm being quite common in closed-loop
operations. Table 11 lists the typical range of values for
various species concentrations in the liquid phase.
Physical Characteristics
The physical characteristics of FGD sludge solids are
important to treatment process operations, disposal methods,
and potential environmental effects. Of special interest are
crystal morphology, bulk density, viscosity, and compressi-
bility. Environmental considerations include permeability,
settling characteristics, and load bearing strength. Table 12
summarizes the importance of various sludge properties to
FGD sludge disposal operations and Table 13 lists some typical
values for those and other related parameters.
Crystal Morphology--
or--
Crystal morphology has perhaps the strongest influence on
FGD sludge physical characteristics. Calcium sulfite hemi-
hydrate is the predominant solid phase in most sludges.
73
-------
TABLE 10.*
COMPOSITION OF SLUDGE FROM OPERATING S02 SCRUBBERS
Fac i 1 i ty
Lawrence
Hawthorn 3
Hawthorn 4
Will County 1
Stock Island
La Cygne
Choi la
Paddy's Run 6
Mohave 2
Shawnee 1
Shawnee 2
Phillips
Parma
Scholz 1A
Utah
C o 1 s t r i p
Scrubber
Sorbent
Limestone
L imestone
L i me stone
Limestone
Limestone
Limestone
Limestone
Lime
Limestone
Limestone
Lime
Lime
Dual Alkali
Dual Alkali
Dual Alkali
Lime/Al kal i ne
Sludge Compos i
CaS03'JsH20
10
20
17
50
20
40
15
94
2
19-23
50
13
14
65-90
0.2
Ash 0-5
tion (dry
CaS04'2H20
40
25
23
15
5
15
20
2
95
15-32
6
19
72
5-25
82
5-20
basis) ,
CaC03
5
5
15
20
74
30-
0
0
0
4-14
3
0.2
8
2-10
11
0
wt percent
Fly Ash Comment
45
50
45
15
1 Oil fired
1 5
65 14% CaS203-6H20
4
3
20-43
41
60 9.8% CaS30]0
7
0
9
40-70 5-30% MqS04
*Ref.96, 129
-------
TABLE 11.* LEVELS OF CHEMICAL SPECIES IN FGC SLUDGE LIQUORS AND ELUTRIATES
Species
Antimony
Arsenic
Beryl 1 i urn
Boron
Cadmium
Cal c ium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Mol ybdenum
Nickel
Selenium
Sodium
Zi nc
Chi ori de
Fluoride
Sulfate
TDS
PH
Eastern Coal s
Range in
Liquor (ppm)
0.46-1 .6
<0. 004-1. 8
<0. 0005-0. 05
41
0.004-0.1
470-2600
0.001-0. 5
<0. 002-0.1
0.002-0.4
0.02-0. 1
0.002-0.55
<0. 01-9.0
0.0009-0.07
5.3
0.03-0.91
<0. 005-2. 7n *
36-20,000^ ' ;
0.01-27
470-5000
1.4-70 m
720-30,000^ \\ x
2500-70,000^ ' '
7.1-12.8
Median
(ppm)
1 .2
0.02
0.014
41
0.023
700
0.02
0.35
0.015
0.026
0.12
0.17
0. 001
5.3
0. 13
0.11
118
0.046
2300
3.2
2100
7000
—
Western Coal s
Range in
Liquor (ppm)
0.09-0.22
<0. 004-0. 2
0.0006-0. 14
8.0
0.011-0.044 m
420-(-45,000) { '
0.024-0.4
0.1-0.17
0.002-0.6
0.42-8. 1
0.0014-0.37
0.007-2. 5
<0. 01-0.07
0.91
0. 005-1 .5
<0. 001-2. 2 m
1650-(~9,000) v ;
0.028-0.88 m
1 700-43, Q00{ '
0.7-3.0 m
2100-18,500 '
5000-95, 000^'
2.8-10. 2
Median
0. 16
0.009
0.013
8.0
0.032
720
0.08
0.14
0.20
4.3
0.016
0. 74
0.01
0. 91
0.09
0.143
0. 18
--
1 . 5
3700
12,000
(1)
(2)
Levels of soluble sodium salts in dual alkali sludge (filter cake) depend strongly on
the degree of cake wash. The highest levels shown reflect single measurements on an
unwashed dual alkali filter cake.
Levels of soluble chloride components in sludges are dependent upon the chloride-to-
sulfur ratio in the coal. The highest levels shown are single measurements for a
western limestone scrubbing system.
Ref.
139
-------
TABLE 12. SLUDGE PROPERTIES AND THEIR
RELATION TO SLUDGE DISPOSAL
Physi cal
Property
Crystal
Morphology
Buik Density
Permeabi1i ty
Sett!ing
Characteristics
Compressi bi1i ty
Vi scosi ty
Importance to Disposal
Determines to some extent the settling,
dewatering, and water retentive character-
istics of the sludge; also regulates the
thixotropic behavior typical of some sludges.
Determines disposal capacity and transpor-
tation requirements.
Determines the rate at which liquid will
flow through the sludge; rate-controlling
step in leaching when the sludge permeability
is less than that of underlying soil.
May affect rate of release of leachate to
surrounding soil, as well as mechanical
dewatering capability.
Reclamation of the disposal site as well as
increasing site design capacity.
Gives some indication of the flow properties
of the sludge, although sludges are non-
Newtonian fluids and are subject to addi-
tional flow considerations.
76
-------
TABLE 13.* PHYSICAL PROPERTIES OF SELECTED RAW FGD SLUDGES
Sampl e
No.
1
2
3
4
5
6
7
8
9
Spec
gra
2.
3.
3.
2.
2.
2.
3.
2.
2.
•3
ifica
vi ty
45
27
99
73
90
67
00
82
95
Bui k
d e n s i
( kg/m
828.
1017.
2518.
1010.
837.
1425.
889.
1 030.
759.
h
U
ty
2)
2
2
1
8
8
6
0
0
3
Oven-d
unit
( kg/m
800.
679.
2452.
978.
754.
1374.
815.
919.
725.
h
ryb
wt
2)
9
2
4
7
5
4
3
5
6
Wa
con
(
3
49
2
3
11
3
9
12
4
K
ter°
tent
%}
. 3
.6
.7
.2
. 0
. 7
.1
.1
.6
Poro
(
67
79
38
64
74
48
72
67
75
,
s i ty
^ )
.3
.2
.5
.2
. 0
.5
.8
.4
.4
h
Void0
ratio
2. 059
3.81 5
0.627
1 . 789
2.844
0.943
2.679
2. 067
3.065
Value determined from one specimen.
Average value determined from three specimens.
GDisintegrated during first cycle.
Tangent of "straight" portion of stress-strain curve.
*Ref. 104
-------
Sulfite crystals usually form in single flat plates, although
spherical aggregated forms are also observed. In contrast,
calcium sulfate dihydrate solidifies in blocky crystals. A
limited amount of sulfate is soluble in the sulfite crystals,
thereby making an unsaturated mode of operation possible.
The sulfite crystaline species is generally described by
the formula:
(CaS03)x . (CaS04)y .
where x is much greater than y, and z approaches 0.5 (Ref. 28).
Research at TVA has shown that the scrubber sorbent can
affect the resulting crystal form (Ref. 28). Sulfite crystals
formed in limestone systems are generally of the flat plate
variety, although aggregated forms ("rosettes") are also ob-
served. The length-width-thickness ratio of these crystals is
approximately 25:20:1 and varies only by a factor of 2 or 3
between samples. In contrast, sulfite crystals formed in lime
systems are almost exclusively spherical and show no variation
in crystal size within a sample.
FGD sludge crystals are typically between 1 and 200 microns
in diameter. FGD sludges have been classified for study pur-
poses as silt (ML) under the Unified Soil Classification System
and as silt and silt loam under the U.S.D.A. systems (Ref. 106).
Figure 9 displays the typical range of grain sizes for FGD
si udges .
Other solid phases encountered in FGD sludges include fly
ash and mixed sul fate/sul f i te crystals. Fly ash is typically
formed in spheres from submicron to more than 1,000 microns in
size; sulfite crystal growth on fly ash is rarely encountered.
The impact of crystal morphology on sludge treatment and
disposal, as well as on other physical characteristics, is
discussed in the following subsections and Section VII.
Bulk Density--
The bulk density of FGD sludges is another important
physical characteristic. Bulk density determines such disposal-
related parameters as compressibility, landfill volume require-
ments, permeability, and to some extent, compaction strength.
Bulk density by definition refers to the weight per unit
volume of a bulk granular solid material; true density is the
density of the individual particles composing the material.
Because calcium su 1 fate/sul fi te is denser than water, dewatering
to a certain point will increase the density of the overall
sludge. Beyond that point, interstitial water is replaced by
78
-------
loo -
80 -
60~
CD
cc
HI
M 40 -
20 -
0 -
00 001
0.005 0.01
0.05
0. 1
0.5
Figure 9.
Grain size (mm)
Particle-size distribution of FGD sludges (Ref. 106)
-------
air voids which cause a decrease in density. The point at
which maximum (bulk) density can be achieved by compression is
termed the "optimum moisture content."
Figure 10 displays the relationship between moisture con-
tent and bulk density for two FGD sludges, a high sulfate sludge
from SCE Mohave and a high sulfite sludge from TVA Shawnee.
This figure indicates that the sulfite sludge has a higher
optimal moisture content than the sulfate sludge.
Table 14 compares the true densities with the bulk densi-
ties of several sludge samples; also shown is the effect of
dewatering on the density of the sludges. Note that only the
Mohave sulfate sludge exceeded the maximum bulk density follow-
ing mechanical dewatering; this low dewatering effectiveness is
typical of most full-scale mechanical dewatering operations.
Permeabi1i ty--
Permeability, another important physical parameter, is
related to the rate of flow of liquids through the material
under a hydraulic driving force. This parameter enters into the
calculation of the mass transport rate of contaminants from the
disposal site to the groundwater as discussed in Appendix B.
Before discussing the reported values of the permeability of
either untreated or treated sludges, it is useful to discuss
the techniques of measurement and their potential applicability
to field situations under various conditions.
Permeability data as reported in this document is based
upon laboratory experiments of either falling head or constant
head permeability tests under saturated flow conditions. In
this type of experiment, a sample of the material is placed in
a container with a bottom drain. A head of water is applied
above the sample with the rate of flow being measured either
at constant head or falling head. These flow rates are related
to the permeability of the specimen through the appropriate
equations.
This type of measurement is quite accurate. The values of
permeability are independent of hydraulic head for course
grained materials which do not compact under the applied hydrau-
lic head. For very fine grained materials which are subject
to compaction, the measured permeability depends upon the
hydraulic head applied.
When measuring very low permeabilities in solid materials,
edge effects (where most of the measured flow is around the
sample rather than through the sample) can be a significant
source of error in the measurements if not accounted for in the
design. Cracks in solid samples can also create non-reproduc-
able resul ts.
80
-------
CO
1.8
m
o
01 1.6
to
Z
LJ
O
_J
D
OQ
1.4
1.2
1.0
SULFITE
SULFATE
10 15 20
MOISTURE CONTENT, percent
25
30
35
Figure 10
Bulk density versus moisture
sulfate (Mohave) and sulfite
content for selected
(Shawnee) FGD sludges
*Ref. 96
-------
TABLE 14.* TRUE.AND BULK DENSITIES OF FGC SLUDGE SOLIDS
oo
Plant
Location
Eastern
Eastern
Eastern
Western
Western
Eastern
Western
Process
Limestone
Lime
Lime
Limestone
Limestone
Dual Alkali
Dual Alkali
Flyash
(*)
20
40
36
60
59
3
7
9
True
Density
(g/cc)
2.48
2.45
2.53
2.50
2.53
2.53
2.45
2.60
Dry Bulk
Density
(g/cc)
1.20
1.21
1.02
1.12
1.33
1.46
1.30
1.16
Settled
Density % Solids
1.45
1.52
1.34
1.40
1.39
1.65
1.26
1.29
45.0
52.9
43.4
47.6
46.7
66.6
40.0
37.4
Drained
Density % Solids
1.51
1.53
1.37
1.47
1.44
1.67
1.39
1.30
51.7
58.3
45.3
54.2
50.9
67.2
43.9
37.8
Filtered
Density % Solids
1.65
1.70
1.55
1.52
1.48
1.78
1.57
1.38
65.0
65.9
56.0
57.0
53.4
80.3
57.8
43.1
Centrifugation
Density % Solids
1.56
1.56
1.37
1.47
1.60
1.86
1.40
1.54
55.8
63.3
49.9
57.2
60.9
75.0
50.9
62.2
Saturation
Density % Solids
1.73
1.73
1.62
1.67
1.80
1.87
1.76
1.71
70
70
63
67
74
78
74
67
* Ref. 2
-------
When attempting to use permeability data in a mass trans-
port model, differences between saturated and unsaturated flow
must be accounted for. When the specimen is not initially
saturated with water, the void space is filled with air. When
water tries to flow through the sample, the air may be displaced
or trapped in some of the voids. Depending upon the hydrophilic
or hydrophobic nature of the internal surfaces of the sample,
drastically different results may be obtained. On one extreme,
a fine grained, hydrophobic material would measure zero permea-
bility for low hydraulic heads. By applying sufficient hy-
draulic head, the material would become saturated and the
surface tension forces would be overcome; in this case the
permeability would increase to the saturated value after all
the air is forced out of the specimen.
For strongly hydrophilic materials, the capillary tension
can make an unsaturated material behave as though it has a
very high permeability until it becomes saturated. The above
factors must be considered when translating laboratory data to
field situat ions.
FGD sludge permeability is dependent both upon size dis-
tribution and particle shape. Settled sulfite sludge is
generally less permeable than sulfate sludge do to the irre-
gular shape of the sulfite crystal aggregates. Settled and
drained FGD sludges exhibit permeabilities of 10~3 to 10~4
cm/sec; light compaction will decrease this to 10-5 cm/sec, and
even lower permeabilities have been attained on the laboratory
scale using greater compaction and more extensive dewatering.
The presence of fly ash will decrease sludge permeability.
The smaller fly ash particles fill in the sludge interstices,
thereby blocking the movement of fluid through the media.
Permeabilities of about 10~6 cm/sec have been achieved for a
sulfite sludge mixed with fly ash; this is thought to be the
minimum permeability achievable with untreated sludge. Table
15 lists the permeabilities of several FGD sludge samples.
Compressibili ty--
The compressibility, or compatibility, of FGC sludge is
an important parameter when planning for site reclamation. The
amount of compaction which can be achieved is dependent upon
moisture content, crystal morphology, and compaction force as
mentioned before, the optimum moisture content is that at which
the sludge can be compacted to the greatest extent (corres-
ponding to maximum compacted bulk density).
Studies of FGD sludge compressibility are documented in
literature; one found that a sludge with equal quantities of
sulfate and sulfite could be compacted to 1.3 g/cm3 at 77
percent solids but only 1.2 g/cm3 at 72 percent solids.
83
-------
TABLE 15.* PERMEABILITIES OF UNTREATED FGC SLUDGES
Samp! e
Location Process No.
Eastern Limestone 1
2
Eastern Lime 1
2
3
^ Western Limestone 1
2
3
Eastern Dual Alkali 1
2
Western Dual Alkali 1
VR
1 .
2.
1 .
1 .
1 .
0.
1 .
0.
5.
2.
2.
T
1
53
07
83
65
25
96
20
75
11
19
77
Sett
CP
1 .
3.
1 .
6.
1 .
3.
1 .
8.
7.
2.
9.
led
o
( cm/sec )
02
37
74
01
28
25
85
3
81
46
8
X
X
X
X
X
X
X
X
X
X
X
10"
10"
10"
10"
10"
10"
10"
10"
10"
10"
10"
4
5
4
5
4
5
5
4
5
4
4
VR
1 .
1 .
1 .
1 .
0.
0.
1 .
0.
4.
1 .
2.
Compa
T
1
27
56
68
42
97
63
20
50
17
95
61
CP
7.
1.
5.
1 .
7.
1 .
1 .
9.
2.
8.
1 .
cted
2
(cm/sec )
78
11
27
07
4
44
11
1
51
06
33
X
X
X
X
X
X
X
X
X
X
X
10"
10"
10"
10"
10"
10"
10"
10"
10"
10"
10"
5
5
5
5
5
5
5
5
5
5
4
1
Void Ratio
Coefficient of Permeability
*Ref. 1
-------
Similarly, a study of double alkali sludge achieved 1.15 g/cm3
at 75 percent solids. Another study dealing with the effects
of sulfate versus sulfite on compressibility as shown in Table
16 found that higher sulfate concentrations in the solid phase
reduced compressibility significantly (Ref. 64).
Laboratory experiments by the Aerospace Corporation have
achieved compacted bulk densities in excess of 1.44 g/cm3;
this represents a volume reduction of 25 percent for pure sul-
fite sludge but only 7 percent for sulfate sludge (Ref. 96).
This study also estimated the optimum moisture contents to be
10 and 20 percent for sulfate and sulfite sludges, respectively.
The actual field compaction of the two sludge types will not
result in such a marked difference in compaction due to varying
compaction efficiencies and compacting loads.
Load Bearing Strength--
Load bearing strength is a partial function of compressi-
bility, but also depends heavily upon the moisture content of
the sludge. The Aerospace studies have shown that sulfate
sludge compaction strength increases rapidly from 2.0 x 10^ to
2.0 x 106 dynes/cm2 below 35 percent moisture content. Since
this moisture content can be achieved by mechanical dewatering,
sulfate sludge can be made to support men and equipment if
compacted. Japanese experience with high sulfate sludge
(gypsum) production also indicates that this material will
readily support grading equipment (Ref. 139).
The load bearing strength of TVA sulfite sludge at Shawnee
was shown to increase gradually with decrease in moisture
content. At 30 percent moisture content, the strength begins
to increase markedly corresponding to the peak viscosity. The
load bearing capacity at this point was 2.1 to 2.4 x 10° dynes/
cm2. Even at low moisture content, however, the sludge will
liquify if jarred or vibrated. Figure 11 displays the results
of the Aerospace strength tests (Ref. 139).
Despite the variation in FGD sludge load bearing strength
between sludges, certain generalities can be made. Light
compaction will result in only a small improvement of strength.
Settlement is unavoidable even after heavy compaction, although
landfilled sludge settlement may be less than that of many
common soils under these circumstances. Unconfined compressive
strength is quite low, typically in the range of 7 to 14 x 105
dynes/cm2.
Settling Characteristies--
The settling and dewatering characteristics of FGD sludge
have been observed to be related to sulfite content. During
the first stage of settling, referred to as clarification, the rate
85
-------
TABLE 16.* THICKENER DIAMETER REQUIRED AS A FUNCTION OF
CALCIUM SULFATE OXIDATION AND GENERATING CAPACITY
Generating
Capaci ty
(MW)
150
500
1000
SI udge
Production**
( tons/day)
53
178
356
R e q u i
10% Oxid.
25
46
65
red Diameter
50% Oxid.
25
47
66
(ft)
80% Oxid.
27
49
69
* Ref. 64
**Based on 130 tons/MW year.
86
-------
25 j,
oo
o
c\j
s
u
N
c/>
OJ
z
LU
ce
h-
to
a:
<
LD
CO
Q
<
a
MOHAVE
(SULFATE SLUDGE
WITHOUT FLY AS,-!)
SHAW.NEE
(SULFITE SLUDGE
WITH FLY ASH)
35 40
MOISTURE CONTENT, WEIGHT PERCENT
11. FGD sludge load bearing strength.
*Ref. 128
-------
at which particles settle out of suspension is dependent upon
crystal size and shape. Fully hydrated gypsum is the superior
settling crystal due to its blocky structure. The flat plate
structure of sulfite crystals results in water retention and a
slower settling rate-
In the last two stages of settling, zone settling and
compression, sulfite sludge does not settle well due to the
lower solids concentration. Overall, sulfite sludges will
settle to 25 to 40 percent solids while sulfate sludges settle
to 60 to 65 percent solids. Free drainage will increase the
solids content of either sludge by about 10 percent.
A study of sulfate/sulfite settling and the associated
design considerations has concluded that the percent sulfite
oxidation to sulfate has little effect on the required thickener
diameters, provided the higher final moisture content can be
tolerated when preparing for vacuum filtration (Ref. 64). The
primary difference in sulfite sludge settling rates is in the
crystal plate size. Smaller plates entrap more liquor during
the compression stage due to a higher incidence of inner-
particle touching; thicker sulfite slurries take longer to reach
the compression stage. Table 16 demonstrates the effect of
oxidation on thickener diameter.
Viscosi ty--The viscosity of FGD sludge is important both in
terms of flow characteristics and load bearing properties. FGD
sludge viscosity is a function of moisture content, crystal
morphology, and amount of fly ash present. Figure 12 displays
the relationship between solids content and viscosity for 9
selected siudges .
FGD sludges, particularly sulfite sludges, are often said
to exhibit "thixotropic" behavior. Strictly speaking, a
thixotrophic solid is one which liquifies under an applied shear
force and resolidifies when the force is removed. Dewatered
sulfite sludges do liquify under applied force but tend to
remain in a liquid-like state. They, therefore, cannot properly
be considered strictly thixotrophic.
Nonetheless, studies by Aerospace have found sulfite
sludges to behave in a quicksand-like fashion. For the TVA
Shawnee sludge, viscosity was shown to drop from 120 to 20
poise, when water content was increased from 40 to 50 percent.
Higher solids contents gave erroneously low results, due to the
rapid release of the viscometer disc, as thixotropicity was
induced; this characteristic is important to handling considera-
tions (Ref. 139).
In a manner typical of other sulfate sludges, the viscosity
of the SCE Mohave sludge was found to increase with decreasing
water content, starting at close to 10 poise at 38.5 percent
88
-------
• CURVE
SOURCE
DATE FLY ASH, %
CD ARIZONA CHOLLA LIMESTONE
(2) SCE MOHAVE LIMESTONE
(D TVA SriAWNCE LIMESTONE
(4) TVA SHAWNEE LIMESTONE
(5) TVA SHAWNEE LIMESTONE
® DUQUESNi. PHILLIPS LIME
© TVA SHAWNEE LIME
® UTAH GADSBY DOUBLE ALKALI
(9) GM PARMA DOUBLE ALKALI
4/1/74
3/30/73
7/11/73
6/15/74
2/1/73
6/17/74
3/19/74
8/9/74
7/18/74
58.7
3.0
40.9
40.1
20.1
59.7
40.5
8.6
7.4
70
60 50
SOLIDS CONTENT. WEIGHT %
40
Figure 12.* Viscosities of FGD sludges.
* Ref. 96
89
-------
water and increasing to approximately 46 poise at 36.5 percent
water. Because the sulfate sludge stiffens and settles rapidly
at lower water content, viscosity measurements above 50 poise
could not be made. All sludges, whether sulfate or sulfite,
demonstrated a rapid change in viscosity at the solids content
characteristic of each particular sludge. Solids content
changes which occur as the various power plant and scrubber
operating parameters change, make solidification of the sludge
in pipes a potential problem, when pipes are used to transport
high solids sludge.
A high fly ash content generally serves to lower viscosity
and reduce the "thixotrophic" tendencies of FGD sludges. An
explanation for this phenomenon is not currently available.
Biological Characteristics--
FGD sludge generating processes operate with inorganic
reagents, caustic solutions and high temperature exhaust gases.
These do not create an environment conducive to biological
activity. Consequently, studies on the biological aspects of
sludge have not been deemed necessary by EPA. Current research
on biological properties of FGD sludge has focused on the
speculated toxic effects of sludge and leachate upon ecosystems
and human health. This topic is discussed in Section VIII,
Environmental Considerations.
90
-------
SECTION VII
TREATMENT AND DISPOSAL TECHNOLOGY
Table 17 shows FGC sludge management practices for utilities
and industrial plants currently operating FGC systems. The
table is divided into treatment (including both dewatering and
stabilization), transportation, and disposal practices. Each of
these operations is described in detail in this section.
As can be seen in the table, FGC waste management operations
may include (1) initial dewatering in a clarifier/thickener;
(2) secondary dewatering with a vacuum filter or centrifuge;
(3) stabilization by addition of ash (with dewatering) and/or
for commercial additives; (4) pipeline transport to the disposal
sites; and (5) disposal into a pond or landfill.
FGD SLUDGE TREATMENT TECHNOLOGY
Dewateri ng
Dewatering reduces the volume of sludge, removes and recir-
culates water, and improves sludge handling characteristics.
Dewatering processes with demonstrated or potential applica-
bility to scrubber sludges are:
C1 a r i f i e r s
Centrifuges
Vacuum filters
Solar evaporation ponds
Bed dryers
Thermal dryers
The first four processes listed above have been applied
to scrubber sludges, and operating experience is documented.
The other processes listed have not been applied to scrubber
sludges but have been used successfully for other types of
industrial and municipal sewage sludges. The following subsec-
tions review applicability of the above dewatering techniques
to FGC sludges.
Clarifiers--
Clarifiers (also referred to as settling tanks and gravity
thickeners) are a standard unit treatment process on most
91
-------
TABLE 17. CURRENT FGC WASTE MANAGEMENT
PRACTICES IN THE U.S. (JUNE 1977)
No. of Operating Units
Process
Treatment
Dewatering
Cl arif ier/thickener
Vacuum filter
Centrifuge
Stabilization
Commercial
. Other*
Transportation
Pipe
Truck/rai 1
Disposal
Pond (unlined)
Pond (1 i ned )
Landfil 1
Mine
Industrial I
6
6
0
2
1
6
1
1
6
0
Jti 1 ity
32
10
4
6
5
35
7
6
22
8
1
Either continuous or intermittent codisposal with fly ash
and/or bottom ash after mechanical dewatering
With either natural low permeability material or similar
"foreign" materials
92
-------
full-scale scrubber sludge treatment installations. They are
used to reduce sludge volume prior to disposal, secondary
dewatering, or stabilization. In addition, clarifiers sometimes
function as mixing or preparation basins for recirculated
scrubber feedwater.
Clarifiers are a cost-effective means of dewatering FGD
sludge and are used even where further dewatering is done by
filtration or centrifugation. Clarification reduces the cost of
a second dewatering stage by reducing the volume and increasing
the solids content of the sludge.
Clarifier design is based primarily on the settling charac-
teristics of the sludge, which in turn are largely dictated by
sludge constituents and particle size. Scrubber sludges, par-
ticularly those generated by lime or limestone processes, exhibit
fair settling characteristics compared to most solids encountered
in the chemical processing industry. Laboratory-scale investi-
gations have shown that dilute slurries of lime/limestone
scrubbing effluent have a particle settling rate of 30 cm/hr,
with more concentrated suspensions settling more slowly (Ref.
129) .
Table 18 displays a cross-section of scrubbing operations
and their associated sludge flow. These figures are only
examples and are by means standard for the given scrubber con-
figuration. Note that the clarifier underflows are in the range
of 1.9 to 7.2 £pm/MW, or about .06 to .12 dry metric tons/MWh.
The data base for the design of FGD sludge clarifiers is
only now becoming available. Table 19 relates clarifier surface
area to type of sludge, as obtained from the literature.
Fly ash alone thickens better than most FGD sludges. The
settling rate for flocculated fly ash is about 1.0 M2/jPD for
fine ash from eastern coals; western coal fly ash is coarser and
generally settles better. The differences in the settling pro-
perties of various FGD sludge solids are typically attributed
to differences in crystal morphology. Figure 13, although
derived from only six data points, demonstrates the apparent
settling superiority of sulfate versus sulfite sludges. The
underflow design point for this data is about 22 percent solids,
with a coagulant concentration of 1 to 2 ppm. In the underflow,
it has generally been found that the higher the sulfate content
in the solid phase, the higher the underflow solids concentra-
tion -- up to 50 percent solids. Studies by Humenick (Ref. 64)
did not demonstrate such a marked dependence of settling rate
on percent sulfite oxidation (see Table 16). No explanation for
disparity could be found in the literature, although the
Humenick study did not incorporate a coagulant, as did the
studies referenced by Cornell (Ref. 27).
93
-------
TABLE 18*. DEWATERING PERFORMANCE BY SELECTED SCRUBBER SLUDGE TREATMENT SYSTEMS
Scrubber To Clarifier Clarifier Underflow Filtrate System modeled
Configuration £pm/MW+
Two-stage Venturi 23.7
Venturi/spray tower 18.2
TCA scrubber 15.6
FDS absorption tower 151.4
% Solids £pm/MW % Solids £pm/MW after:
4 1.9 38 -- Duquesne-Phillips
(2.0% S coal)
8 7.2 18 5.3 TVA-Shawnee
(3.4% S coal)
8 3.1 40 -- TVA-Shawnee
(3.4% S coal)
2.0 15 — APS-Cholla
(0.5% S coal)
* Ref. 12
+ £pm/MW = liters per minute per megawatt
-------
60
UD
cn
O
Q_
Lu
O
UJ
tr
UJ
h-
t-H
z
UJ 20
-------
TABLE 19. CLARIFIER SURFACE AREA REPORTED
FOR VARIOUS SLUDGES
Type of FGD Process
Clarifier Area
2
m /metric ton/day
Reference
Lime scrubbing
Limestone
Double alkal i w/f*
Double alkali wo/f
Limestone w/c+
Limestone w/c w/fly ash
Lime w/f
Lime w/f w/fly ash
Lime and limestone
2.0 - 2.5
0.7 - 2.3
1.0 - 2.5
3.0 - 6.0
1.2 - 1.5
0.8 - 1 .2
1.3 - 1.7
1 -0
3.5 - 6.0
27
27
27
27
60
60
64
64
64
* With flocculation
+ With coagulation
96
-------
Reactor-Clarifiers--
Reactor-clarifiers are finding increased application in
FGD sludge dewatering, particularly in double alkali systems.
These units employ a combination drive to rotate the rake arm
at a slow rate and the recirculation pump at a faster rate,
resulting in a more thorough mixing than that provided by a con-
ventional clarifier. FGD systems that can best utilize the
reactor-cl arifier are double alkali systems (which need good
mixing for sorbent regeneration) and lime/limestone systems
employing a coagulant. A series of reactor-clarifiers , such as
those used at the General Motors Parma plant, can also reduce
the calcium ion concentration in the double alkali return
liquor, thereby reducing scaling in the scrubber.
Centrifuges--
The use of centrifuges for sludge dewatering has had labora-
tory and pilot scale analysis and widespread use in Japan. Cen-
trifugation is an efficient technique for removing unbound mois-
ture from wetted solids; however, it entails comparatively high
power-consumption and maintenance requirements.
Diverse centrifuges are available commercially, which differ
primarily in the design of the collection surface and of the feed
and discharge mechanisms. Bowl-type centrifuges have been
applied to scrubber sludges.
Generally a centrifuge is employed for slurry dewatering
when (1) the solids tend to attain a crystalline shape, and when
(2) the solids will not cause severe abrasion of the removal
screw used in the solid-bowl type centrifuge normally employed
for slurry dewatering. Severe abrasion, and consequential high
maintenance costs, are endemic to centrifuge applications in
FGD sludge treatment. This problem encourages use of a vacuum
filter instead of a centrifuge. Also, the shape of calcium
sulfite crystals does not lend itself well to centrifuge applica-
tion (Ref. 27).
Dravo, TVA, and EPA investigated separately the use of cen-
trifuges to dewater scrubber sludges. Dravo, using lime sludge
from the Duquesne Light Company's Phillips Station, achieved
only moderate dewatering efficiencies using a continuous cen-
trifuge. The TVA results using limestone sludges were better,
leaving as 1ittle as 37 percent moisture in the centrifuge cake.
The use of a centrifuge to dewater sludge from the Chiyoda
process (high su1fate/sulfite ratio) resulted in a 10-15 percent
moisture cake (Ref. 133).
The Aerospace Corporation study (Ref. 139) analyzed the
comparative dewatering properties of sludges with varied sulfate/
sulfite ratios. Using clarifier bottoms with equal water
97
-------
contents, it was observed that high sulfate sludge dewatered to
less than 35 percent moisture using a lab centrifuge, while the
high sulfite sludge was reduced to 44 percent moisture. It was
concluded that crystal morphology caused the disparity in
results .
Vacuum Filtration--
The vacuum filter process appears to be the best secondary
dewatering technique for most FGD sludges. Both the revolving
drum and belt filter designs yield better overall performance
(when reliability is considered)than the centrifuge. Like
other dewatering methods, however, process effectiveness is
highly dependent on sludge characteristics and is subject to
operating difficulties.
Sludge variables that are known to affect filter performance
are concentration and nature of solids, viscosity, temperature,
and compressive strength. Operating variables are vacuum
strength, filter media, drum speed, degree of drum submergence,
and amount of fluid agitation. Problems encountered include
cake cracking and difficulties with cake removal from the filter
media, both of which resulted in temporary shutdown of experi-
ments .
The filtration rate is partially dependent upon the sulfate/
sulfite ratio. Filtration rates for high sulfate limestone
sludges are typically between 730 and 1220 kg/hr/m2 of filter
area (Ref. 27).
High sulfite lime scrubbing sludges are reported to filter
at rates of 250 to 300 kg/hr/m2- The optimal filtration rate
is a function of the specific sludge and should be determined
i ndividually.
Double alkali systems have recorded the most FGD sludge
vacuum filtration experience. Double alkali sludge often con-
tains undesirable amounts of purged sodium salts. To alleviate
this problem, the cake is usually washed on the filter. The
amount wash time required may overshadow the filtration rate
itself and should be determined first through laboratory studies.
Although double alkali crystals are coarse and filter well, the
wash time generally places the overall filtration rate near that
of a high sulfite lime system.
EPA investigations at the TVA Shawnee plant showed that a
55 to 70 percent solids filter cake could be achieved, using a
flow rate of 2,000 to 2,200 £/hr/m2 and a feed of unknown
sulfate/sulfite ratio. Further investigations by Dravo using
a high sulfite sludge yielded a cake with 45 to 55 percent
solids (60 percent with cake manipulation). The comparative
study done by Aerospace for EPA found that sludges of varying
98
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sulfite content filtered equally well (65 percent solids), but
that vacuum release caused the sulfite portion to rewater (Ref.
129).
The Louisville Gas and Electric Company's Paddy's Run No. 6
FGD system employs twin rotary drum vacuum filters. Each has a
cloth area of 13.9 sq m (150 sq ft) and can handle 11 t/hr of
the high sulfite sludge. The input sludges contain 22-24 percent
solids, and the filter cake is generally between 35 and 40
percent solids. No precoat is used on the filter. Paddy's Run
No. 6 is a peak load unit for LG&E, and the filters are operated
intermittently for several months at a time (Ref. 60).
The Gulf Power Scholz #1 double alkali unit has logged over
a year of vacuum filtration experience. The filter was con-
structed of fiberglass instead of stainless steel to avoid
chloride corrosion. The following problems have been encountered
with this unit:
• Erosion of fiberglass scraper blade, resulting in
jagged edges that tear the cloth;
• Erosion of the bridge valve due to solids carried
through cloth holes;
• Loss of vacuum due to cracks in the internal drum
trunni on tubes ;
• Cracking of the plastic caulking strips, allowing
retention ropes to loosen and releasing the cloth
panels ;
• Failure of the fiberglass rocker arm used to agitate
the slurry in the filter tub.
The Gulf power unit achieved 50 to 55 percent solids in
the cake with 2 to 12 percent soluble solids on a dry cake
basis. The sludge is predominantly sulfite containing only 15
to 25 percent sulfate in the sulfur-bearing salts (Ref. 83).
The Caterpillar Corp. plant in Joliet, Illinois, operates
two vacuum filters, each capable of handling the total solids
load. The filter belts, woven of multifi1ament polypropylene,
had failed frequently due to clogging, until higher pressure
spray jets were installed. The system vendor is currently
experimenting with other materials and weaves to optimize the
operation (Ref. 83) .
Another double alkali system, at the GM Chevrolet plant in
Parma, Ohio, also employs two vacuum filters. The filter belts
were originally made of polypropylene cloth but were changed to
nylon to improve cloth release. However, the nylon appears to
99
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wear more rapidly due to fly ash abrasion. Modification in the
washing system is expected to alleviate this problem (Ref. 52).
Solar Evaporation Ponds--
Use of solar energy to evaporate unbound moisture is the
basic principle of sludge ponding. The prerequisites for an
effective solar drying pond are (1) a net evaporation/precipita-
tion ratio in excess of unity, and (2) a pond liner or lining
soil that minimizes permeation through the pond bottom. Liners
available include clay, asphalt, cement, plastic, or synthetic
rubber. When protection of the groundwater resource is already
sufficient, unlined ponds may be allowed.
Many solar evaporation ponds -- some of which double as
clarification/recirculation units -- have been installed
throughout the United States for scrubber sludge drying.
In areas of favorable climate, ponding is the most eco-
nomical means for drying sludge. The mechanics of pond design
and operation are discussed in detail later in this section.
Bed Drying--
Dewatering scrubber sludge by solar drying on a bed with
porous underdrainage has been investigated to a small extent on
the laboratory scale. A bed dryer uses a granular bed for
drainage and an open-air space above the bed for surface moisture
evaporation. The bed media is graded, with granular size in-
creasing from small sand at the contact surface to large gravel
at the bottom adjacent to the drainage ports. Bed thicknesses
vary depending on sludge requirements; however, 12-24 in is
common for municipal sewage sludges.
Bed drying of scrubber sludges was studied by the Aerospace
Corporation using sludges with varied sulfate/sulfite ratios.
Using a column simulator, sulfate sludge dewatered to 50 percent
solids; sulfite sludge dewatered to only 35 percent solids.
Exposure to water caused the drained sludges to rewater readily
(Ref. 139). In addition to the rewatering problem, sufficient
bed capacity for a full-scale operation would require a very
1arge area.
Thermal Drying--
Thermal drying is a proven dewatering method for municipal
sewage sludges, and experiments have been conducted to test
its application to scrubber sludge. The types of dryers
commonly used are rotary drums and atomizing spray dryers. Most
thermal dryers use hot air. The rotary drum configuration
passes air through or around the drum, while spray dryers
100
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circulate hot flue gas through atomized sludge. Multiple hearth
dryers are available in several configurations, including a
hollow screw conveyor that transfers the heated air along its
axis of rotation while in contact with the sludge.
Koch Engineering has developed an atomizing system for
use in conjunction with a limestone or double alkali wet-scrub-
bing unit. The spent scrubber slurry is atomized into droplets
and injected into a low-temperature flue gas stream (149°C);
moisture is evaporated in the stream, and the dry powdered
solids along with fly ash are collected at the bottom. Dewater-
ing efficiencies in excess of 90 percent have been demonstrated
on a pilot scale (Ref. 129).
Thermal drying can conceivably dewater sludge to any mois-
ture content desired; the major drawback is the associated
high rate of energy consumption. Unlike sewage sludge, which
can be burned to provide drying heat, scrubber solids must
depend on other fuel sources or hot flue gases for the drying
operation. In areas where other techniques of drying are not
practical, or where land is at a premium, thermal drying may
be a feasible alternative for sludge dewatering.
Stabi1i zati on
General--
Stabilization refers to the addition of fly ash, bottom
ash, and/or chemicals to the FGD sludge for the purpose of: (1)
improving the load-bearing properties of the disposal sludge
and/or (2) decreasing the mass transport rate of contaminants
leaching out of the sludge. An increasing number of commercial
stabilization processes and services are being offered for FGD
sludge treatment. These commercial stabi1ization processes are
sometimes called fixation processes. To avoid confusion, only
the term stabi1i zati on will be used herein. For additional
clarity, commercial stabilization will be used for proprietary
processes being marketed, and noncommercial stabilization will
indicate nonproprietary stabilization performed by the utilities
themselves. By contrast, untreated siudge will refer to FGD
sludge that has not been stabilized.
Stabilization techniques employed thus far have incorporated
such power plant wastes as fly ash and bottom ash, thereby
consolidating several waste disposal activities into one
activity. Stabilization can reduce the volume required for
disposal through the mechanical dewatering operations included
in some systems. Since pozzolanic stabilization improves the
load-bearing and handling characteristics of sludge, such
materials can be used as a fill material for road base, berms,
embankments, and dams (Ref. 76). In addition, stabilized sludge
often has less pollution potential than raw sludge. This is
101
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because the stabilization process normally restricts the movement
of water through the sludge and/or chemically binds the contami-
nants so they are less readily dissolved by permeating water.
Status of Stabilization Processes--
In June 1977, approximately 11 power plants (see Table 5)
will stabilize their FGD sludge under the definition of stabili-
zation used herein. The stabilization operations are categorized
as fol1ows:
• Commercial stabilization -- 6 sites
• Noncommercial stabilization, landfill disposal -- 7
si tes
Some of the above noncommercial stabilization processes are
haphazard in that they are largely a simple codisposal of FGD
siudge and ash.
A variety of commercial stabilization processes and
services are available for FGD sludge treatment. Several of
these services use a proprietary additive or process. IU Con-
version Systems (IUCS) offers a patented treatment procedure
using the lime-fly ash reaction to produce a structurally stable
and low-permeability material. Dravo Lime Co. offers a stabili-
zation service utilizing a proprietary additive, CalciloxR,
which after a curing 2-4 weeks will solidify either in a landfill
or under water. Both of the above commercial services are under
long-term contracts with one or more utilities.
Research into FGD Sludge Stabilization--
Each type of stabilization process results in a material
with a different set of physical and chemical properties.
Research has been under way for several years to evaluate exis-
ting stabilization processes and to develop new processes.
Thus far, the most extensive studies of stabilized sludge and
its properties have been completed by the Aerospace Corporation
for EPA (Ref. 96), the Army Corps of Engineers Waterways Experi-
ment Station for EPA (Ref. 104) and IU Conversion Systems, Inc.
(Ref. 158, 165) .
A major emphasis has been placed upon the leaching of con-
taminants from stabilized FGD sludge. Four approaches to simu-
lating sludge leachate generation have been employed thus far:
1. Pressurized flow of small volumes of water or leaching
solution through stabilized sludges, with results
giving some indication of soluble salts depletion as a
function of pore volumes leached (Ref. 96);
102
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2. Surface Washing of stabilized sludge in a packed column,
representing rainwater and groundwater washing of the
sides of a sludge monolith, such as a stable landfill
(Ref. 103);
3. Agitated washing of a sludge plug, representing surface
runoff from a stable landfill (Ref. 112);
4. Elutriation of crushed, stabilized sludge, representing
the solubility limits of the various sludge contaminants
Ref. 96).
Approaches 1 and 4 are representative of convective leaching
of stabilized sludge, while 2 and 3 represent diffus ion-1imited
leaching. The latter approaches most closely represent the
mechanics of leaching within a stabilized mass.
The Aerospace Corporation (Ref. 96) recently completed a
broad-based, ongoing study to determine environmentally sound
disposal of solid and liquid wastes produced in FGD processes.
The tasks associated with evaluating stabilization of FGD
sludges include (1) evaluation of chemical treatment or condi-
tioning techniques needed to achieve environmentally sound
disposal; (2) identification and technical evaluation of environ-
mentally sound disposal methods including landfill design and
associated costs; and (3) planning and support of an EPA FGD
waste-disposal, field-evaluation program.
Studies are being conducted by the U.S. Army Engineer
Waterways Experiment Station (WES) in Vicksburg, Mississippi
(Ref. 104), to evaluate chemical treatment (stabilization) and
environmental effects associated with the disposal of FGC wastes.
The program, which also studies a number of industrial wastes,
has been divided into three areas encompassing the following
tasks:
• Assessment of the pollution potential of the leaching
of untreated and chemically fixed FGC wastes;
• Site survey and environmental assessment of existing
solid waste disposal sites;
• Evaluation of existing FGC waste fixation technology.
Table 20 display the stabilization processes used by WES
in this investigation.
IUCS has performed an extensive in-house evaluation of
FGD sludge properties after stabilization by their proprietary
"Poz-0-Tec" process. IUCS is currently under contract with
five utilities to provide stabilization and disposal services
for FGD sludge and fly ash. Both physical and chemical
103
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TABLE 20.* DESCRIPTION OF PROCESSES USED BY WES TO
STABILIZE FGD SLUDGE SAMPLES+
Stabilization Processes
Code Letter Description
A Fly ash and lime mixed to produce
pozzolan product"1"
B Two additives mixed with sludge to pro-
duce soil-like material; hardness is
a function of mix proportions*
C Organic resin* mixed with other addi-
tives and sludge to produce rubber-
1i ke materi al
D Encapsulation of a sludge-resin mixture
with .25-in plastic jacket
E Two readily available additives used
with sludge to produce concrete-like
mixture
F Additive"1" mixed with sludge at optimum
pH, cured 30 days with supernatant
G Sludge mixed with waste product of a
certain manufacturing process and pH
adjusted using a second waste product
Sludge Samples Used in Study
s
s
s
s
s
s
s
s
s
s
1
1
1
1
1
1
1
1
1
1
udge
udge
udge
udge
udge
udge
udge
udge
udge
udge
100 =
200 =
300 =
400 =
500 =
600 =
700 =
800 =
900 =
1000 =
FGD,
Elec
Nic
FGD
FGD
FGD
Ino
Chi
Cal
FG
1 ime process ,
troplating
ea
stern
coal
kel/cadmium battery
5
,
,
limestone proc
doubl e al kal i
1 imestone proc
es
s,
ea
process
es
s,
we
stern coal
, eastern
stern coal
coal
rganic pigment
0
c
D
rine production
i u m fluoride
, double alkali
»
»
bri
wes
ne
si udge
tern coal
* Ref 104
+ Patented or proprietary
104
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properties of the pozzolan-type stabilization product have
been studied. These properties include (Ref. 147).
Physical Chemical
Density 48 hour shake test
Compression strength Runoff test
Permeability Chemical analysis
Reslurrying tendency Crystal morphology
As the disposal of the Poz-0-Tec product is a landfill
operation, leaching tests by IUCS have concentrated on simulating
runoff conditions.
Physical Properties of Stabilized Materials--
The previously mentioned studies have evaluated such phy-
sical characteristics as permeability, compressive strength/
compressibility, bulk density, and porosity. Their findings are
summarized below.
Permeabi1i ty--The permeability of stabilized FGD sludge has
been investigated in all of the previously mentioned studies.
Both commercial and noncommercial stabilization processes were
used to prepare samples. Differences between study approaches
consisted primarily of emphasis on either in-place permeability
or disturbed/pulverized/compacted sludge permeability. In-
place (also "undisturbed") permeability is valuable to the
pozzolanic types of stabilization, ordinarily the product of
which would not be remolded. Compacted permeability would be
valuable to a landfill disposal operation for soil-like
stabilization products, where landscaping or compaction is
important.
Sludge permeability along with rate and degree of satura-
tion and hydraulic head, determines the rate of contaminant
transport from the site to the surrounding environment. When
the site has a relatively high permeability, the sludge is
saturated, and there exists some standing water on the sludge,
the sludge may require treatment in order to serve as the rate
limiting step for mass transport. The actual degree of permea-
bility decrease due to stabilization has therefore been a major
research subject. The permeability of untreated sludge is
discussed in Section 6.
The Aerospace results suggest that the commercial processes
tested decrease sludge permeability by as much as a factor of a
thousand. The permeability coefficients for raw sludge were
7 x 10-4 cm/sec to 1 x 10-$ cm/sec; coefficients for treated
sludges were 7 x 10-4 cm/sec to 4 x 10-5 cm/sec for remolded
samples, and 5 x 10-5 cm/sec to 5 x 10-8 cm/sec for undisturbed
bamnles. However, the small samples tested does not provide
105
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statistically conclusive proof of the exact magnitude of this
decrease in permeability.
The results of the Aerospace permeability evaluation are
shown in Table 21. The Chemfix process used in the study is
a proprietary stabilization process, producing a soil-like
material from the reaction of the sludge with soluble silicates
and silicate setting agents. The pulverized samples were packed
into columns to simulate landscaping or remolding, while the
undisturbed samples represented cores taken from the TVA Shawnee
experimental site. Except under unusual circumstances, an FGD
disposal site would be undisturbed and would reflect undisturbed
permeabi1i ties.
The permeabilities of the WES materials were in close agree
ment with the Aerospace results. Untreated compacted sludges
demonstrated permeability coefficients ranging from 6.04 x 10~5
cm/sec to 1.07 x 10~5 cm/sec. Only processes A and E decreased
the permeability by more than two orders of magnitude.
Commonwealth Edison studies (Ref. 96) of treated sludge
permeability indicated a much lower in-place permeability than
the WES and Aerospace results using noncommercial processes.
These studies demonstrated permeability coefficients of 10~7
cm/sec and less for undisturbed samples. Again, permeability
alone does not dictate the mass transport rate; degree of sludge
saturation, hydraulic gradient, and complexing effects of the
matrix must also be considered.
The important primary conclusion that can be drawn from
the results of the three major studies is that the pozzolan
type of stabilization processes substantially reduce sludge per-
meability over that of untreated sludge and soil-like products
when not disturbed.
Compressive Strength--
Stabilization, by definition, improves the structural
stability of raw FGD sludges. All commercial stabilization
processes improve the compressive strength of sulfite sludges.
Only pozzolan-type stabilization processes appear to improve
sulfate sludge compressive strength.
The Commonwealth Edison study (Ref. 52) evaluated the
compressive strength of over 270 test samples. The samples were
cured at various temperatures and stabilized with an assortment
of admixtures. It was concluded from these data that lime-fly
ash and Portland cement-fly ash admixtures gave the most satis-
factory results. It was also concluded that low temperatures
(22°F) significantly delayed hardening for the mixtures tested.
06
-------
TABLE 21.*
PERMEABILITY OF RAW AND COMMERCIALLY STABILIZED FGD
Sample Sample
Source Treatment
Shawnee Untreated
limestone
IUCS
Dravo
Chemf ix
Shawnee Untreated
lime IUCS
Mohave Raw
IUCS
Duquesne Untreated
Dravo
Fractional Void
Condition Volume
. Column packed as slurry
. Compacted wet
. Pulverized++
. Solid, undisturbed
. Pulverized++
. Solid, undisturbed
. Pulverized++
. Solid, undisturbed
. Compacted wet
. Solid, undisturbed
. Column packed as slurry
. Pulverized++
. Pulverized, compacted wet++
. Pulverized+
. Pulverized, compacted wet++
0.58
0.55
0.69
0.54
0.78
0.75
0.68-0.70
0.72
0.72-0.75
0.57
0.34-0.47
0.55-0.65
0.53
0.49-0.68
0.70-0.78
0.76
Permeabil ity
Coefficient, cm/sec
8.5xlO~j? - 2.3xlO"4
5.9x10";
2.2x10-4
5.5x10""
3.2x10',:
6.9xlO~D q
4.1-4.7x10";?
1.5-2.1x10"^
8.1xlO~j?-2.5xlO~4
5.5x10 , 5.5x10
1.6-7.5xlO"4 &
7.9x10-5-7.4x10"
1 .9x10-4
7.4xlO"5-1.3xlO"4
3.8-4.9x10-4
2.1x10-4
* Ref. 96
+ Shawnee samples collected with fly ash
++ For test purposes only; does not reflect actual disposal conditions
-------
The WES studies found the solidified material (processes A,
F, and G) to exhibit unconfined compressive strengths of 70
to 350 N/cm2 (100 to 500 Ibs/in2). Sludge treated with process
E to demonstrated strengths of nearly 3,500 N/cm2 (5,000 lb/in2).
Process B material, with strengths ranging from 14 to 350 N/cm2
(20-50 lb/in2), was only slightly greater in strength than un-
treated sludges. Compaction tests performed on process B
materials indicated that field compaction of certain fixed
sludges might create some difficulties. Several samples actually
decreased in density after compaction, while others showed no
change.
Studies performed by Ontario Hydro (Ref. 96) at their
Lakeview test facility evaluated the compactibi1ity of sludge
stabilization admixtures. Table 22 describes the mix consistency
and compactibi1ity for various proportions of admixture. Mix-
tures that exhibited the greatest compactibi1ity contained a
high percentage of fly ash combined with small amounts of lime
or cement.
The EPA Shawnee Field Evaluation (Ref. 140) tested the
IUCS, Chemfix, and Dravo stabilized FGD sludges for wet and dry
compaction strength. The IUCS material consistently demonstrated
unconfined compressive strengths in excess of 280 N/cm2 (400
lb/in2), while the other two processes (oven-dried samples)
never exceeded 114 N/cm2 (163 lb/in2) and 32 N/cm2 (45 lb/in2),
respectively.
Bulk Density — The change in FGD sludge bulk density as a
result of stabilization has also been studied, but not to
the same extent as permeability and strength. The WES investi-
gations observed bulk densities of 0.8 to 1.7 g/cm3 for five
treatments used; the specific densities for each sludge and
process are shown in Table 23. With the exception of process
G, stabilization increased the bulk density of raw sludges.
Results from the EPA field evaluation showed a lower range
of bulk densities for commercially stabilized sludges. The dry
densities ranged from a high of 1.08 g/cm3 for the IUCS solid
mass to a low of .59 g/cm3 for the Dravo material (under-
water). The difference between the WES and Aerospace studies
is due to the use of remolded samples by Aerospace and as-cast
samples by WES.
It can be concluded from these results that pozzolanic
processes produce a higher density material than other admix-
tures or processes producing a soil-like product. The latter
would therefore be expected to consolidate more under load, as
in a landfill operation or reclamation of the disposal site.
108
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TABLE 22.* MIX CONSISTENCIES WITH VARIOUS ADDITIVES FOR LAKEVIEW
GAS SCRUBBER SLUDGE CONTAINING 65 PERCENT SOLIDS
Mix Proportions
Consistency of Mix
Remarks on Compactability
Sludge + 5% Lime
Sludge + 10% Lime
Sludge + 5% Cement
Sludge + 10% Cement
Sludge + 15% Cement
Sludge + 52% Fly Ash
Sludge 4- 39% Fly Ash + 5% Cement
Sludge + 39% Fly Ash + 15% Cement
Sludge + 65% Fly Ash
Sludge + 15% lime
Sludge + 39% Fly Ash + 5% Lime
Sludge + 65% Fly Ash + 5% Cement
Sludge + 65% Fly A sh + 15% Cement
Sludge + 65% Fly Ash + 5% Lime
Sludge + 39% Fly Ash + 15% Lime
Sludge + 65% Fly Ash + 15% Lime
Soft and wet
Firm and wet
Firm and moist
Firm and dry
Powdery and dry
Both lime mixes were too wet
to compact, even after 1 week
of retention. The cement mixes
were too wet to compact ini-
tially but were compactable
after 24 hours .
All mixes were too wet, although
some only slightly, causing
some slumping of specimens
after removal from mold
Ideal mix combinations for
compaction
Slightly drier than above mixes,
but compactable
Too dry and powdery for proper
compaction
* Ref. 96
-------
TABLE 23.*
EFFECT OF TREATMENT ON BULK DENSITY
Location
Eastern
Eastern
Eastern
Western
Western
Process
Lime
Limestone
Double alkali
Limestone
Double alkali
Untreated
0,83
1.01
0.84
1.42
0.76
Process A
1.60
1.73
1.53
1.75
1.55
Bulk Density
Process B
1.23
1.42
1.45
1.27
1.30
(g/cm3)
Process E Process F Process G
1.62
1.32 1.00
1.59 0.84
1.77 1.30 0.91
1.32 1.01
* Ref. 104
+ Refer to Table VII-5 for code
-------
Particle Size--Data on the particle size distribution of
treated sludge is important when describing physical behavior,
particularly properties such as permeability and bulk density.
This is expecially important for the soil-like materials, as
the solid pozzolans behave as a constant mass and are not inten-
ded for remolding.
A comparison of particle size distributions in raw sludge
and in soil-like stabilized products (such as Chemfix) was
performed as part of the WES effort. Sludge stabilized by pro-
cess B proved to be much like raw sludge in texture and was
given a similar U.S.D.A. classification of loam or fine sandy
loam. The particle size distribution remained approximately
the same as that of raw sludge, although both finer and coarser
gradations were observed for certain sludge types (Ref. 104).
These soil-like products can therefore be expected to behave
much like sandy loam in their bulk density, permeability, and
compressi bi1i ty.
The particle size distribution of solid stabilized sludge
(pozzolanic or other cementitious products) is not important
except as it affects the void ratio of the matrix.
Chemical Properties of Stabilized Materials--
Stabilization, as well as providing a structurally improved
product, may also reduce the rate of mass transport leaching
of soluble contaminants from the FGD sludge. This can be
accomplished through a reduction in permeability/porosity and
through chemical bonding of contaminants within the stabilized
matrix.
Several of the previously named studies have been involved
in characterizing the leachate from stabilized sludge. Some
of these findings, as they relate to existing water quality
standards, are discussed in Section VIII under "Health
Considerations." The principal difficulty in evaluating the
study results has been to properly assess the applicability of
the various leaching tests being used. The following is a sum-
mary of the results compiled to date.
Leaching experiments conducted by Aerospace examined lea-
chate from treated FGD wastes under both aerobic and anaerobic
conditions. Two sets of leaching experiments were conducted.
In the first set, three laboratory columns were packed with
process wastes obtained from the TVA Shawnee limestone, the
Arizona Cholla limestone, the Duquesne Phillips lime, the GM
Parma double alkali, and the Southern California Edison Mohave
limestone scrubbing systems. The chemically treated sludge
was dried and pulverized before it was packed into the leaching
column, for the purpose of maximizing surface contact area to
obtain an indication of potentially available contaminants.
Ill
-------
Leaching water (unbuffered) adjusted to pH 4, 7, and 9, with
either HC1 or NaOH, was used in each set of columns. The leach-
ing water and the leachate were allowed to react with air in
order to stimulate aerobic conditions. A second set of leaching
experiments was conducted under anaerobic conditions. These
experiments duplicated the first experiments except that the
leaching water and leachate were protected from interaction with
the atmosphere. Also, leaching water with a pH 7 was used,
because no discernible effect had been noted in the aerobic
columns as a result of differences in the initial pH of the
1eachi ng waters.
The Shawnee FGD Waste Disposal Field Evaluation (Ref. 96,
141) was initiated to evaluate and monitor the field-site
disposal of untreated and treated FGC wastes. Its purpose is
to determine the effects of several scrubbing operations, waste
treatment methods, disposal techniques, soil interactions, and
field operation procedures. Test samples of treated and untrea-
ted wastes, groundwater, standing water, leachate (both ground
and surface), and soil cores are being analyzed in order to
evaluate the environmental acceptability of current disposal
technology.
The disposal evaluation site consists of five disposal
ponds, each occupying approximately 0.1 ac near the TVA
Shawnee Power Station at Paducah, Kentucky, approximately 1 mi
south of the Ohio River. All the ponds were filled between
October 7, 1974 and April 23, 1975 to a depth of about 3 ft.
Two of the ponds contain untreated wastes; each of the remaining
ponds contains wastes chemically treated by one of the three
commercial contractors.
The Chemfix-treated material was fractured and contoured
by a backhoe; the Dravo-treated material represents curing and
disposal under water where high strength is not necessarily
required; and the lUCS-treated material was not compacted by
placement vehicles that would be used in a full-scale operation.
Therefore, comparisons between processes are neither attempted
nor implied in the evaluations for the purpose of this document.
Within each pond is a leachate well for sampling water
that collects at the waste-soil interface. A groundwater well
is located on a berm of each pond, between the sludge and the
river. Groundwater wells are located approximately 100 ft
south of each pond (away from the river) to provide for the
monitoring of background water quality. The disposal sites
are also being monitored periodically for leachate, supernate,
and groundwater quality; soil chemistry changes; and treated
waste chemical and physical qualities.
The laboratory studies by Aerospace revealed a similarity
in leaching profiles between untreated sludges and stabilized
112
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(both pulverized and undisturbed) sludges. The principal dif-
ferences are in (1) the lower concentrations of IDS and major
chemical species in treated sludge leachate, and (2) the more
gradual decrease in concentration observed for treated sludge
leachate contaminants. Aerospace tests included elutriation of
pulverized pozzolanic stabilized sludge as a worse case, which
is not indicative of actual field conditions. The decrease in
surface area contacted through a stabilized sludge matrix will
result in a decreased rate of mass transport.
In the leaching of untreated waste, a higher rate of
decrease in concentration was observed under anaerobic condi-
tions. In assessing the results obtained from the leaching of
commercially stabilized wastes, it was concluded that the type
of conditions -- i.e., aerobic vs. anaerobic -- would not be
a significant factor in the selection of a particular chemical
treatment process .
Based on the results, Aerospace concluded that chemical
treatment generally improves leachate quality. The degree of
improvement is dependent on the specific waste and the specific
chemical process used. The concentration of the major chemical
species in the leachate from the chemically treated waste was
observed to be approximately 1/4 to 1/2 the concentration in
the leachate from untreated waste. When the results are examined
for effect on trace metals, it was not concluded that chemical
treatment of FGD waste improved the leachate quality (Ref. 96).
Another significant result of the Aerospace investigation
concerns the comparative rates of decrease in concentration
for the various leachate components. Figures 14 and 15 demon-
strate this relationship for untreated and Chemfix stabilized
sludges under anaerobic conditions. Actual data extend through
30 to 50 pore volumes of pulverized sludge. These data seem to
indicate that TDS, Pb, and $04 concentrations represent the
minimum rate of decrease among contaminants examined. Once
initial concentrations of the contaminants are known for a
given sludge, one or more of these three species would serve
as a worst case indicator of leachate quality. Again, results
obtained for trace metals other than those shown were too
dispersed to draw similar conclusions. Table 24 compares the
composition of leachate constituents for both raw sludge and
Chemfix treated sludge. Of the contaminants shown, only Cu
achieved a slower rate of decrease in concentration than TDS.
The primary value of this data is to identify one or more tracer
ions which can serve as monitoring parameters to indicate pollu-
tant migration from FGD sludge disposal sites.
13
-------
10
10 20 30 40 50
PORE VOLUME DISPLACEMENTS
60
70
80
Figure 14.
Leachate analyses from EPA/TVA
Shawnee untreated limestone
waste: anaerobic conditions.
114
-------
1.0
o
o
Q_
o;
IT
O
o
I—
<
0.1
0.01
o
o
0.001
10
LITERS
10 20 30 40 50 60
PORE VOLUME DISPLACEMENTS
70
80
Figure 15.
Leachate analyses from EPA/TVA
Shawnee treated limestone
waste (Chemfix): anaerobic conditions
115
-------
TABLE 24.* COMPARISON OF THE LEACHATE CONSTITUENTS FROM
EASTERN LIMESTONE SLUDGE AND CHEMFIX TREATED SLUDGE
As
Cd
Cr
Cu
Pb
Hg
Se
Zn
Cl
F
so4
TDS
PH
Sludge
1st Pore Vol .
0.14
0.003
0.09
0.01
0.25
<0.05
0.08
0.20
2300
6.2
10,000
15,000
8.3
- Aerobic
50th Pore Vol .
0.01
<0.001
0.003
0.010
0.01
<0. 00005
0.006
0.045
120
<0.2
1200
2400
5.0
Chemfix
1st Pore Vol .
0.04
0.003
0.04
0.05
0.35
<0.005
0.01
0.5
1400
0.9
3000
7000
4.70
- Aerobic
50th Pore Vol.
0.006
<0.001
<0.001
0.005
<0.001
<0.0005
0.002
0.065
60
0.2
650
1500
6.01
* Ref. 96
116
-------
Laboratory leaching studies for treated sludge samples from
Shawnee showed that the IDS concentration decreased rapidly
during the first five pore volume displacements in Chemfix
treated sludge. After that, the IDS concentration appeared to
be controlled by the solubility of major contaminants such as
sulfate, sulfite, and chloride. These data were then applied
to five hypothetical case studies and extrapolated in terms of
yearly mass loading to site subsoil. The results are shown in
Table 25 and Figure 16. This information demonstrates the ad-
vantages of low sludge site permeability and limited water per-
colation through the sludge, in terms of mass transport from
the disposal site.
WES has been performing leaching column studies (Ref. 104)
for 162 samples of untreated and stabilized sludge since January
1975. The molded sludge cylinders are placed in polypropylene
pellets. The fluid velocity down the sides of the cylinder
is maintained at about 10-5 cm/sec. This configuration simulates
(1) groundwater flow along the bottom and sides of a landfill,
and (2) flow through a crack in the material as placed. Under
these conditions, the leachate quality for treated and untreated
sludge would be expected to be similar for the initial wash.
Once diffusion, and not solubility, becomes limiting, the
leachate from the solid mass would improve in quality. However,
the time required to achieve diffusion-limited mass transport
is approximately 10 years.
In assessing the pollution potential of the wastes, seven
chemical fixation processes were used to treat the selected
wastes (Table 20). The processes are being evaluated by means
of leaching column studies as well as physical and chemical
testing of untreated and fixed wastes.
Analysis of leachate pH by sludge category and stabilization
process is being performed by WES. Figure 17 demonstrates the
change in leachate pH due to the various stabilization processes.
In general, raw sludges with a slightly basic leachate pH were
subject to an increase in pH due to stabilization. This concept
for the metals that are less mobile at a high pH due to forma-
tion of insoluble hydroxides. The effect of stabilization upon
leachates is more complex than stated above, but the pH effect is
one that could be documented by observed data. The stability
of pH is important because of its impact on the longevity of the
contaminant immobilization. WES data indicate that the pH of
leachates from several stabilized materials was initially higher
than that of untreated sludge but is tending to converge with
time.
117
-------
oo
TABLE 25.* CASE STUDIES FOR CALCULATING MASS LOADING OF LEACHATE
CONSTITUENTS INTO SUBSOIL
Disposal
Case Method
1 Lake*
2 Lake#
3 Pond
4 Pond
5 Landfill
FGC Waste, Five-Year Fill
Surface Waste Depth Permeability
Water Condition ft cm/sec+
Constant Untreated 30 10~4
supernate
Constant Treated 30 10"5
supernate
10 in/yr Untreated 30 10~4
recharge
10 in/yr Treated 30 10~5
recharge
1 in/yr Treated 30 10"5
recharge
Fractional
Pore
Volume
0.67
0.67
0.67
0.67
0.67
* Ref. 96
+ For all cases, subsoil permeability = 10 cm/sec
# Assumed maximum hydraulic head of 6 ft during filling, including depth of wastes;
1 ft constant water cover thereafter
-------
1000
CNJ
o
CO
o
uo
oo
Q
O
100
10
CASE 1
CASE 2
A END OF 5th PORE VOLUME
I I I I I I I A I
20 40 60 80 100 120 140 1300
YEARS
Figure 16.* Projected mass loading of IDS to subsoil for
various disposal modes of treated and untreated
FGC wastes, based on theoretical considerations.
*Ref. 96
119
-------
PH
7
10 II
12 13
RESIDUE
CATEGORY
100
200
300
400
500
600
700
800
900
IOOO
RAW SLUDGE
FIXATION PROCESS
1 1
V
C
V
D
V
A
V
C
1 1
V V
A F
V
B
B
V
E
V
B
V
A
V V
BE
V V
E B
V
A
V
B
V
A
V
B
^4
V V
E B
Figure 17. Leachate pH for untreated and treated residues.
-------
The conductivity of the leachates from untreated and
stabilized sludge samples was used as an indicator of dissolved
solids concentration. The conductivities for untreated sludges
were highly variable but were classified as "stable" for six
samples and as "decreasing with time" for the other four. The
conductivities for stabilized sludges, on the other hand, were
all generally decreasing, indicating a decreasing availability
of soluble material. Conductivities for six of the samples
tested were similar for treated and untreated sludge.
To analyze the effect of experimental design upon leachate
behavior, the data from a selected residue, 100, were subjected
to an analysis of variance. The design used included all
replicates for six time periods, two leaching solutions, and four
sludge treatments (one raw and three fixed). The results of the
analysis for pH indicated that residue, treatment, time, and
several interactions were significant sources of pH variance. It
was also noted that variation in leaching solution pH from pH
4.7-7.7 had no effect on the resulting leachate pH. Since most
of the untreated and fixed residues demonstrate a strong buf-
fering capacity, the effect of pH in the leaching solution upon
column effluent is small and would support the practice of leach
testing with one solution. A wider range of solution pH might
increase the significance of this effect.
A similar analysis for conductivity showed that treatment,
time, and treatment-time interaction effects are significant.
This indicates that stabilization indeed affects the conduc-
tivity of the leachate, and the effect is a function of time.
Again, leaching solution pH was not shown to be a significant
factor in determining leachate conductivity.
Analyses for sulfate and copper concentrations were also
included in the WES leachate characterization. Data indicate
that stabilization is effective at retarding sulfate leaching.
Leaching from the stabilized sludges was characterized by an
initially high sulfate concentration followed by a rapid decrease
in concentration, indicating early leaching of the more soluble
forms of sulfate. Few generalizations can be made about copper
leaching. All stabilized sludges leached copper to some extent,
several producing higher concentrations than the associated raw
sludge leachate. Several stabilized sludges actually showed
increased copper leach rates with time, a fact that was corre-
lated with the simultaneous decrease in pH. Definite trends
could not be identified at the time of the initial report.
In general, it was concluded from the WES data generated
thus far that the leaching and performance of fixed FGD sludges
is strongly dependent on the type of scrubber and, for the lime-
stone scrubbers, is dependent on the source of coal (initial
sulfur content). The double alkali scrubbers tend to produce
more soluble sulfate compounds, and thus their leaching behavior
121
-------
is affected by fixation to a greater degree. IUCS data (Ref.
147) indicate that the IDS concentration in untreated double
alkali sludge runoff can be reduced by more than 60 percent by
Poz-0-Tec stabilization. The limestone scrubbers produce less
soluble sulfate compounds, and fixation of these sludges affects
the leaching of sulfate to a lesser degree. Within the limestone
scrubber sludges, the amount of sulfate available appears to be
proportional to the initial sulfur content of the coal utilized
(Ref. 104). It was also shown that leachate quality improvement
from stabilization was more pronounced for double alkali sludges
than for lime/limestone sludges. This improvement is due to the
higher solubility of certain double alkali waste products. WES
and IUCS results have shown that contaminant transport from
stabilized sludge occurs primarily during rainwater runoff, and
could remain solubility-limited if disposed of in a properly
managed 1andfi11.
Commonwealth Edison (Ref. 96) 'Studied several samples of
sludge stabilized using different proportions of admixture. The
results are not reported here, as the elutriation test used is
not representative of actual field conditions.
IUCS used a variety of leaching tests for stabilized FGD
sludge. These include shake tests, runoff tests, permeability
tests, and diffusion tests (Ref. 158).
In the shake test, a material with known weight and surface
area is placed in contact with a specified amount of deionized
water. The water and material are contacted in a shake apparatus
for 48 hours. The water is removed for analysis, and the
material is exposed to fresh water. That process is repeated
for a total of 5 shakes. Each sample of water is analyzed for
total dissolved solids, with full chemical analysis and heavy
metal analysis on the first and fifth wash.
In the runoff test, a fresh sample of material is placed
into a box, the bottom of which is covered with graded aggre-
gate to the depth of approximately one inch. The surface of the
material to be tested is exposed to various degrees of simulated
rainfall for any amount of time one may desire. Runoff is
collected and analyzed. The amount of water absorption per each
simulated rainfall may be measured by weighing the box before
and after water contact. Permeate which results from the water
contact with the surface of the material is collected from the
bottom of the box and subsequently analyzed.
The results of a typical shake test for Poz-0-Tec are shown
in Table 26. These results, from five consecutive 48 hour
washes, indicate that an apparent equilibrium situation for TDS
is reached after the third wash. Leaching would then become
diffusion limited. The observed range of .01-.05 grams of
Teachable material/in? of sludge surface exposed is important
122
-------
TABLE 26.* POZ-0-TEC LEACHATE FROM SUCCESSIVE SHAKE TESTS
TDS
(ppm)
974
338
268
194
214
Grams
Leached
1 .948
.676
.536
.388
.428
Grams/
in2
.046
.015
.012
.009
.010
Surface area: 42.4 in2
Dilution ratio (in2/L): 21.2:1
*Ref. 158
123
-------
in a landfill situation. It indicates that the Teachable
material is an insignificant fraction of the total available
soluble material originally contained in the untreated sludge.
Several unstabilized and stabilized mixes were subjected
to runoff tests at various curing periods up to 28 days. Tests
were run simulating 2 in rainfall per hour. The runoff water
from each test was collected and analyzed. Any water permeating
through a test pad during the experiment was also collected and
analyzed. Table 27 summarizes such data for two unstabilized
mixes and two stabilized Poz-0-Tec materials. Runoff water from
Poz-0-Tec materials show lower TDS and TSS contents. TDS
typically start at about 2,000 ppm and diminish concentrations to
between 50 ppm and 600 ppm after several washings (Ref. 147).
Runoff and shake tests were performed using the Poz-0-Tec
product from the EPA Shawnee field study landfill. The results
of the shake tests are shown in Figure 18, using both solid and
broken cores. It is evident from this figure that diffusion-
limited leaching occurred within three to five washings for
both samples, but the surface washing phase was completed sooner
for the broken piece due to the higher surface area (Ref. 158).
Further work is required before conclusions can be drawn
from the sludge leaching data base established thus far in these
and other studies. The WES and Aerospace studies indicate at
this stage that TDS concentrations in the sludge leachate are
initially lower than concentrations in raw sludge and tend to
decrease with time. Similar conclusions have been drawn regar-
ding the major dissolved components such as sulfate.
It has also been concluded from IUCS research that a pro-
perly managed stabilized sludge landfill (limited contact with
groundwater or rainfall) will limit leaching to a slow surface
washing mechanism. Uncontrolled contact with water would
increase the leach rate until diffusion or permeation (assuming
saturation of the mass) becomes controlling.
Combining Waste Streams
It can be advantageous to dispose of FGD sludge with other
liquid and solid wastes generated at a power plant. Combinations
that are being used or studied include:
• Sludge and fly ash and/or bottom ash
o Sludge and mine tailings or overburden
• Sludge and acid mine effluent (drainage)
FGD Sludge Combined with Fly Ash and/or Bottom Ash--
FGD sludge combined with fly ash and/or bottom ash is the
most widely used method of combined waste disposal. Currently,
124
-------
TABLE 27.* RUNOFF TEST DATA ON STABILIZED AND UNSTABILIZED MATERIALS
IN3
en
Placement Pad
Sludge No
and fly
Sludqe No
Sludqc No
aUa.ll)
snd fly
Sludqe No
. 2 filter-cake
ash mix
. 2 Poz-0-Tec
, 1 (double
flltercake
ash mix
. 1 Poz-0-Tec
Aqe
Immediate
7 days
28 days
Immediate
7 days
28 days
Immediate
7 days
28 days
Immediate
7 days
20 days
PH
7.7
7.6
8.3
10.0
0.8
8.2
11.5
9.2
9.0
11.6
9.6
9.1
Runoff Water
TOS
(ppm)
2102
2396
1800
2210
50fl
439
1392
1GM
2902
1116
1010
1180
Analysts,
TS5
(ppm)
75,821
123,190
17,131
29,936
1,299
709
130
567
7.613
107
1,198
900
Permeate Water Analysis
TOS TSS
pH (PPm) (ppm)
7.8 1010 060
7.6 2560 5120
10.9 0361 308
11.2 21,270 175
*Ref. 147
-------
TDS
(ppm)
3000 -
Figure 18.
Poz-0-Tec from Aerospace Shawnee pond
leachate TDS vs. wash no. (Ref. 158).
2000 -
1000 -i
- Solid Piece
O - Broken Piece
SHORT TERM
DIFFUSION EFFECT
WASH NO.
126
-------
33 utility plants either continuously or intermittently add to
or collect fly ash with scrubbed SO;?- The pozzolanic reactions
of fly ash with unreacted lime or limestone in the FGD sludge
produces a more stabilized waste product. This reaction was
detailed in the previous discussion on stabilization.
Several power plants also dispose of bottom ash/slag with
FGD sludge. Bottom ash contributes silicates and lime to the
pozzolanic reaction, although these constituents are not as
available as they are in fly ash, due to the larger particle
size and relative insolubility of the slag matrix. Those plants
that do combine slag with sludge during disposal have observed
that the slag aids in preventing wind erosion and associated
fugitive dust emissions. One potential stabilization process
includes a material similar to boiler slag, blast furnace slag,
as a major ingredient.
FGD Sludge Combined with Mine Tailings or Overburden--
The combination of FGD sludge with mine waste is feasible
for the reclamation of strip mines. One codisposal alternative
might consist of dumping the sludge, followed by the mine waste,
directly into the pit. However, the resulting site would have
questionable foundation strength unless the sludge is adequately
stabilized prior to disposal. The preferable method of combina-
tion might be to mix the mine waste and the FGD sludge before
replacement in the mine. This mixing procedure would also sup-
press the generation of acid mine drainage.
FGD Sludge Combined with Acid Mine Drainage (AMD)--
Traditionally, virgin materials such as limestone, sodium
carbonate, hydrated lime, and caustic soda have been used for
neutralization of acid mine drainage. Recent investigations
have emphasized combining the FGD sludge with AMD for acid and
soluble iron control. This procedure would depend on the
unreacted alkali species in the FGD sludge for neutralization;
consequently, a larger amount of FGD sludge than virgin reagents
would be required. This factor renders the use of FGD sludge
for control of acid mine drainage highly site specific, depending
upon reagent availability. Questions have also been raised
concerning possible detrimental environmental effects of sludge
utilization, such as the formation of SO^ and the presence of
high levels of trace metals. No commercial operations of this
sort exist today.
SLUDGE TRANSPORT
The proper choice of a transport mode is a function of
sludge characteristics, transport distance, costs, capacity,
and other factors. Methods of sludge transport presently being
utilized or considered are:
127
-------
Sluicing by pipeline
Sluicing by channel
Truck
Conveyor or bucket elevator
Barge or rail
Pipe transportation of sludge is the most common mode among
existing wet scrubber systems. The major areas of concern when
designing a sludge piping system are the critical velocity, the
flow properties of the sludge, the distance to be traversed, and
any right-of-way impediments.
Predicting the flow properties of scrubber sludge is dif-
ficult. Aside from the readily measurable properties such as
solids content, composition, and particle size, certain sludges,
if not sufficiently dilute, exhibit thixotropic and rheopectic
behavoir. These types of behavior will cause a change in fluid
viscosity during transport and hence will affect the pumping
capacity of the system.
Typical high flow velocities encountered in sludge piping
can result in corrosion and erosion of pipes and appurtenances
by sludge solids. Many of the existing lime/limestone systems
thus incorporate rubber-lined pipes for protection. Due to
limited operating experience, the exact nature and extent of
corrosion and erosion from sludge piping are not well known and
require further investigation. Table 28 describes existing
commercial slurry pipelines.
To date, lined open channels have not been used for the
transport of FGD sludges. However, if topography is favorable,
open channels could have several advantages over closed pipe-
lines: decreased abrasion, a wider choice of construction
materials, reduced operating and maintenance costs, and decreased
possibility of clogging due to sludge variations.
Truck transport of sludge is used when (1) the sludge is
too thick to pipe, as is the case after secondary dewatering or
fixation; (2) the sludge is removed to a distant disposal site,
or (3) no cheaper alternative is feasible. The cost of truck
transport is specific to the area in question; related variables
include wage rates, distance, load limits, cycle times, and
terms of existing truck. The operating variables associated with
FGD sludge trucking are not fully known because of the differences
in sludge character, but investigations are presently under way
in this area. Technology transfer from studies of sewage sludge
truck transport (e.g., Los Angeles and Orange Counties,
California) appears relevant.
Several years ago, Combustion Engineering assessed the
handling characteristics of untreated FGD sludge. Two truckloads
(flat bottom and round bottom) were driven nonstop from the
128
-------
TABLE 28.* DESCRIPTION OF SEVERAL COMMERCIAL SLURRY PIPELINES
Pipeline
Consol idation
Coal
American
Gilsonite
Rugby Cement
Colombia
Cement
South Afri-
can Companies
Savage River
Mines
Black Mesa
Pipeline, Inc.
Hyperion
Wastewater
Treatment
Plant
Mogden
Wastewater
Treatment
Plant
*Ref. 129
tAs of 1971
Location
Ohio
Utah
England
Colombia
South
Africa
Tasmania
Arizona
Los
Angeles
England
Material
Coal
Gilson-
ite
Lime-
stone
Lime-
stone
Gold
tailings
Iron con-
centrate
Coal
Digested
sewage
sludge &
effluent
Digested
sewage
sludge
Length
(miles)
108
72
57
9.2
21.5
54
273
7.5
7
Diameter
(inches)
10
6
10
5
6 & 9
9
18
22
12
Throughput
(million tons
per year)
1.30
0.38
0.70
0.35
1.05
2.25
5.70
^Commercial operation ceased in 1963 for
Now maintained in stand hv rnnHit-inn
Solids
(specific
gravity)
1.40
1.05
2.70
2.70
2.70
4.90
1.40
1.80
1.80
Weight
(percent
solids)
52
46
61
55
50
60
50
1.0
4.0
Years in
Operation
or Statust
6*
11
5
25
14
2
In start
phase
11
33
-up
non-technical reasons.
-------
TABLE 28* (Continued)
Pipeline
Easterly
Pollution
Control
Center
CAPCO
Bruce
Mansfield
Location
Cleve-
land,
Ohio
Penna. ,
W. Va.
Material
Raw
Length
(miles)
13
Diameter
Cinches)
12
Throughput
(million tons
per year)
_
_
Solids
(specific
gravity)
1 .80
Weight
(percent
solids)
2.5
Years in
Operation
or Status^
32
sludge
FGD
7
12
6
.5
--
7.5
1
sludge
_, *Ref. 129
w fAs of 1971
-------
Kansas Power and Light Lawrence Station to Dulles Airport in
Washington, D.C. The sludge, which had been stored in a set-
tling pond for six months, was dredged up and drained for 24
hours prior to loading. No leakage other than water was obser-
ved during the trip. Final unloading of the flat-bottom trailer
required the aid of a backhoe, while the sludge slid readily
from the round-bottom trailer (Ref. 100).
Sludge treated by the Dravo fixation process has been
trucked from the Duquesne Light Company's Phillips Station to a
nearby landfill with no major problems. Dravo has concluded,
however, that the large volume of sludge that would be genera-
ted at a typical power plant would not lend itself to economical
truck transport, since as many as 40 trucks per hour would be
required for complete removal. Dravo has since switched
emphasis to piping of a thickened slurry -- a mode of transport
also in use at the CAPCO Bruce Mansfiled plant (Ref. 157).
Sludge filter cake from the Paddy's Run No. 6 (LG&E) FGD
system is trucked 1/2 mi to a borrow pit for disposal, at a
cost of $.55/t (Ref. 129).
The use of conveyors and bucket elevators to transport
dried or dewatered sludge should find increased application as
the number of large-scale fixation and dewatering processes
increases. Solids content is critical to the feasibility of
belt conveyors, while bucket elevators are somewhat more versa-
tile. Belt conveyors have been employed at several FGD opera-
tions, including Paddy's Run No. 6 and Caterpillar Tractor's
Joliet pilot plant. The automated conveyor at Caterpillar
(double alkali, 54-62 percent solids cake) has performed well,
although periodic cleaning has been required to remove sludge
from the idlers during cold weather (Ref. 52).
The feasibility of rail or barge transport of sludge is
site specific. Barge transport, probably the most economical
mode, is dependent on accessibility to navigable waterways.
Rail transport is competitive with trucking for long distance
hauls and is more widely accessible. Neither mode has been
used to date for FGD sludges. Loading/unloading problems may
be encountered with treated or mechanically dewatered sludges;
primary dewatering produces a sludge with a viscosity compara-
ble to that of certain commercial fuel oil grades that are
readily pumpable.
FGD SLUDGE DISPOSAL TECHNOLOGY
The disposal of FGD sludges has been the subject of much
research in recent years. A primary concern has been the poten-
tial for environmental degradation from the sludge and its
constituents, both at the disposal site and in the surrounding
ecosystem. Forty-eight FGD systems have been implemented sludge
131
-------
disposal systems are presently on line. Selection of these
systems has been dependent primarily on cost and land availa-
bility.
The general categories of available disposal options
include:
® Ponding (lined or unlined)
« Landfill
@ Disposal to oceans
® Disposal to mines
The following is a discussion of these alternatives as
they are practiced today.
Ponding
The use of ponds for waste disposal has been practiced
by many industries, including fertilizer manufacturing, phos-
phate and coal mines. The design and operation of disposal
ponds is well documented, as are the guidelines and standards
used by these industries.
Ponding research has centered around two areas of study:
(1) the actual degree of leaching encountered from lined and
unlined ponds; and (2) the most effective means of containing
contaminants within the disposal area.
Unlined Ponds--
The use of unlined disposal ponds is typically the least
expensive method of sludge disposal. This technique, however,
has been subject to criticism, primarily due to the potential
for sludge contaminants to enter the groundwater. Nonetheless,
20 of the FGD sludge disposal systems in operation use unlined
ponding for either intermediate clarifying or ultimate disposal.
The use of unlined ponds for sludge disposal is expected to
continue pending regulation of the practice.
The degree of leaching of contaminants from the pond is
dependent on several factors: the hydrostatic head in the
pond, which forces percolation through the pond bottom; the
nature of the sludge -- primarily the permeability and the
solubility of contaminants it contains; and finally, the
characteristics of the soil beneath the pond, which are very
important.
Lined Ponds--
The use of liners for sludge disposal ponds has recently
received much attention. Liners serve both to reduce pollutant
mobility and to retain water for recycle. A major deterrent
132
-------
thus far has been the high cost and questionable longevity of
available liner materials. For the purposes of this report,
"liner" refers to any material which is not native to the
disposal site and is used to decrease the rate of mass trans-
port.
The following criteria are considered important when
selecting a pond liner material (Ref. 129):
t High strength and elasticity
• Good weatherabi1ity and long life expectancy
t Resistance to bacterial and fungous attack
• Ease of repair
In addition to an acceptable liner, the pond design may
include a leakage detection system. One such system consists of
underbed drainage channels which collect the leakage in a
visible sump for periodic observation. Other methods of
visible detection include standpipes and wells. Techniques
of measuring ground resistivity have been developed and may
also be used for this purpose.
A variety of liners for sludge ponds are commercially
available. Synthetic liners use various polymeric materials,
e.g., plastic or rubber; other liners include clay, stabilized
sludge, admixed and asphaltic materials. Table 29 summarizes
the characteristics of available pond liners (Ref. 139).
Detailed characteristics of the various pond liners have
been discussed in several other studies (Ref. 129, 139). It
appears that most liners, particularly those of the synthetic
flexible variety, are superior to clay in permeability. Some
controversy exists, however, with regard to material longevity.
While some clays are thought to be longer lasting than synthetic
liners, studies have shown accelerated deterioration of clay
through extended ion exchange. Further investigation of liners
is necessary before selection criteria can be properly formu-
lated.
Results have been reported (Ref. 59) on the current evalu-
ation of liner materials exposed to typical landfill leachate.
After one year of exposure it was reported that:
• No significant change in water permeability was noted
in any of the 1iners;
• The admix materials, particularly the soil asphalts,
generally lost compressive strength;
• The asphalt liners absorbed some leachate but otherwise
changed little during exposure;
133
-------
TABLE 29.* POND LINER MATERIAL CHARACTERISTICS
CO
Material
Flexible
Polyethylene
Polyvinyl chloride
Hypalon
Chlorinated polyethylene
Petromat fabric
Butyl rubber
EPDM rubber
Polyester fiberglass
Nonflexible
Soil cement
Concrete
Clay
Asphalt concrete
Gunite
Pozzolan stabilized base
* Ref. 139
^Commonly used
Protection from ultraviol
.See Section 7.1
Superior to clay
Thickness
mil
10
10-20
30
30
- 1/1
30
30
65
_
-
- Up
-
_
-
et rays
^Affected by wet/dry and hot/cold cycl
Subject to sulfate attack
PAerospace Corp. estimates
Possible breakdown due to
a
5
in.
-
-
-
-
6-1/8
-
-
-
6
6
to 18
6
3
2-6
Permeability,
cm/sec
d
d
d
d
d
d
d
d
About 10~6
About 10-8
ID'5 to 10-8
d
d
10-5 to 10-7
Life expec-
tancy, yr
20
20
20+
20+
20+
20
20
20+
20+
50+9
50+9
50+9
20+9
50+9
Dirt
cover'3
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
No
To convert
es
from
sq yd
mil
in.
to
sq m
cm
cm
Average
installedc
Cost ,$/Sq yd
0.70
1.10-1.50
3.25
3.25
2.00
2.80
4.00
4.75
1.00
3.75-4.75
1.00-6.00
4.00
6.30
3.85
Multiply
by
0.8361
0.00254
2.54
Notes
e,f
e,f
e,h
e
e,f
ion exchange
-------
• The polymeric membranes swelled to varying degrees (by
absorption of leachate)
• Swelling of polymeric membranes can increase membrane
permeability to water and possibly to dissolved com-
ponents ;
• The polymeric membranes showed a decrease in tensile
strength and hardness but generally retained puncture
and tear strengths;
It should be noted that the sanitary landfill leachate used
in this study is not identical to FGD leachate. However, the
study may yield insight into compatibility of FGD leachate and
pond liners. Polymeric, admix, and asphaltic materials were
used as liners.
The U.S. Army Corps of Engineers Waterways Experiment
Station (WES) is conducting a program to (1) determine the
compatibility of 18 liner materials with flue gas cleaning
(FGD) wastes and associated liquors and leachates; (2) estimate
the length of life for the liners; and (3) assess the economics
involved with purchase and placement (including disposal area
construction) of various liner materials. A review of the
literature was made to evaluate potential liner materials,
including admixed materials (e.g., soil cements, asphalt
cements, stabilized FGC waste), flexible materials (e.g., poly-
vinyl chloride, polyethylene), and sprayed-on materials (e.g.,
plastics, asphalts, sulfur).
A total of 18 liner materials was selected for use in
the experiment; these are shown in Table 30. Each liner
material is being exposed to two different sludges, one being
a lime-scrubbed FGD waste from the Duquesne Light Company
Phillips Station and the other a limestone-scrubbed waste from
the Commonwealth Edison Will County Station. The liners will
remain exposed to the sludge for two years under a simulated
sludge depth of 30 feet. Physical property tests were performed
on each liner material upon receipt and after one year (March
1977). Results of the one-year test are not yet available. A
final report is expected to be issued in the spring of 1978.
(Ref. 96).
Landfill
FGC sludges are used as landfill in several locations. For
the purposes of this study, a sludge is classified as landfill
material only if (1) it is stabilized to a solid without a
head of water, or if (2) the sludge is dewatered mechanically
or thermally to a solid material. Both dewatering and stabili-
zation were discussed in a previous section of this report.
135
-------
TABLE 30.* LINER MATERIALS
Material
Material Type
Manufac tu re r
Sprayon Type
DCA-1295
Dynatech Formulation 267
Uniroyal
Aerospray 70
AC 40
SSK
Polyvinyl acetate
Natural rubber latex
Natural latex
Polyvinyl acetate
Asphalt cement
Slow setting cationic
emulsified asphalt
Union Carbide
Dynatech Research and Development Co.
Uniroyal, Inc.
American Cyanamid
Globe Asphalt
Globe Asphalt
Admixes
Cement
Lime
Fly Ash
Cement with Lime
Cement with Fly Ash
Lime with Fly Ash
M179
Guartec (UF)
Analine, Furfural
Asphalt Concrete Paving
Dundee Cement Co.
Williams Keith Lime Co.
Amax Fly Ash Co.
Polymer bentonite blend
A light grey powder
Dowell Div. of Dow Chemical
General Mills
GAF Corp (Analine) and General Mills (furfural)
Local Contractors
Prefabricated Membranes
Liner
T-16
Elasticized polyolefin
_(30 mil)
Black neoprene-coated
nylon-reinforced fabric
The Goodyear Tire and Rubber Co.
Reeves Brothers, Inc.
*Ref. 96
-------
Dewatering for landfill disposal is currently practiced
at six utility FGD systems. For example, at the Louisville Gas
and Electric Paddy's Run Station, clarifier underflow is vacuum
filtered to between 40 and 60 percent solids and trucked to a
nearby borrow pit for disposal. At the pit, the sludge is
mixed with fly ash and compacted with a bulldozer. Although
the sludge solids contain as much as 98 percent calcium sulfite,
rewatering of the sludge has not been a problem (Ref. 142).
Industrial FGC system users have favored landfilling of
dewatered sludge. In the U.S., six of the eight industrial
plants are currently utilizing this disposal scheme. In Japan,
mechanical dewatering is necessary if gypsum is to be generated
and sold from the FGC installations. Current marketing diffi-
culties have forced Japanese utilities to establish temporary
landfill operations.
Structural stability is an important consideration in
proper landfill operation and site reclamation. While some
FGD sludges can provide sufficient load-bearing strength to
support equipment and light construction, others may require
some type of stabilization to meet these requirements. Chemical
treatment of FGD sludge is presently practiced at several power
plants, including Duquesne Light Co., Phillips and Elrama
Stations (Pittsburgh, Pennsylvania), and Commonwealth Edison,
Will County Station (Chicago, Illinois). The need for stabili-
zation has generally been dictated by the value of local land
and by state and local laws regarding land reclamation.
The leaching of salts and trace metals from a sludge
landfill can be minimized through proper design and operation.
Although the lack of a hydraulic driving force is a primary
advantage of landfill over ponding, rewatering of the sludge
can yield a mass with the same potential for groundwater con-
tamination as raw sludge. Consequently, landfilled dewatered
sludge must be protected from liquid infiltration. For the
disposal of hazardous wastes, infiltration of the site is con-
trolled either by covering the material periodically with a
low-permeability soil (sanitary landfill) or encapsulating the
disposal site after decommissioning with a low-permeability
material such as a plastic liner, asphalt, or high clay-content
soil .
Ocean Disposal
Ocean disposal of FGD sludges is an option that is
perhaps available to throw away system users with economic
access to the ocean. New ocean disposal initiatives are
discouraged by regulatory agencies. Arthur D. Little, Inc.
(ADL), in a study sponsored by EPA, is currently investigating
the feasibility of ocean disposal of FGD sludges.
137
-------
There are two alternative ocean areas for sludge
di sposal:
• Shallow ocean (on the continental shelf)
• Deep ocean (off shelf)
Each area has a distinctly different ecosystem and is
therefore subject to a different set of criteria for evaluating
environmental impact.
The continental shelf is mainly a euphotic zone and is
rich in ecological diversity. It is, therefore, the major
ocean site for biomass production that is important to man.
A system of such magnitude is quite fragile and highly suscep-
tible to interference from foreign sources. In contrast, the
deep ocean is a relatively barren area of low productivity and
high resistivity to change. This would be the ideal area for
sludge disposal.
Transportation of sludge for ocean disposal can be
accomplished either by ship, barge, or pipeline. The mode
of transportation with the lowest projected costs (not con-
sidering regulatory constraints) is the conventional bottom
dump barge.
The A.D. Little study identified the following as potential
environmental concerns when disposing of FGD sludge to oceans
(Ref. 78):
"1. Ocean-floor sedimentation - The particle (crystal)
sizes of most untreated FGC wastes are much smaller than the
coarse-grained sand particles of the ocean floor, which are
most conducive to the marine life found on the continental
shelf. Therefore, deposition of these wastes in large quanti-
ties may have an undesirable effect in the relatively shallow
continental shelf area, particularly if disposal results in
"paving" of the ocean floor.
2. Solids suspended in the water column - Settling of
disposed FGC wastes toward the ocean floor through the water
column, as well as resuspension of solids from the ocean floor,
would expose various types of marine life to elevated concen-
trations of suspended sediments. The effects of sediments vary
from minimal to serious, depending on the organism involved.
3. Sulfite-rich wastes - Many FGC wastes contain signifi-
cant quantities of calcium sulfite hemihydrate, presenting a
potential problem of sulfite toxicity to marine life and a
potential chemical oxygen demand (COD) problem if oxidation
to sulfate occurs. The actual impacts of sulfite toxicity,
dissolution and oxidation will require further investigation.
138
-------
4. Trace contamination in wastes-Untreated and treated
FGC wastes may contain several trace elements in concentrations
in excess of acceptable levels for the marine environment.
Significant dilution of the wastes with seawater (i.e., disper-
sion) may be necessary for ocean disposal to be acceptable."
The alternative ocean disposal schemes being evaluated
by A. D. Little include:
t Dispersed dumping on the continental shelf
• Dispersed dumping off the continental shelf
• Concentrated dumping of treated sludge
• Conventional dumping off the continental shelf
The State University of New York (SUNY), Stony Brook cam-
pus is studying use of stabilized FGD sludge blocks (IUCS Poz-
0-Tec) to create artificial reefs for marine habitats. The
research funded by the New York State ERDA and Public Service
Commission, is being performed in two stages. The first stage
consists of a laboratory investigation into the chemical and
physical reactions of the sludge with seawater and marine flora
and fauna. The second stage is a field evaluation of a sludge
artificial reef in a bay near the SUNY campus.
The laboratory tests are nearing completion. Published
results are expected by October 1977. After one month of
kinetic studies, rapid initial solubi1ization of calcium and
certain other species has been noted. The rates of solubiliza-
tion slowed as equilibrium conditions were reached. No
appreciable trace metal leaching was noted. The explanation
put forth for this phenomenon is that the oxidized surface of
the sludge prevents migration of seawater into the blocks. It
was also noted that the sludge compressive strength increased
as the duration of exposure to the seawater increased.
The second stage was initiated in May 1977 and is expected
to continue for two to five years. One cu ft FGD sludge blocks
and a control cement block were placed ten feet under water
in a marine bay near the SUNY campus. Physical and chemical
reactions within the blocks will be studied. After two weeks of
submersion, rapid attachment of benthic macroorganisms to the
blocks was noted irrespective of their composition.
Mine Disposal
The feasibility of FGD sludge disposal to mines is of
interest particularly to the many mine-mouth, coal-fired power
plants. Sludge disposal to mines has the advantages of (1)
minimal transportation requirements, when a mine is nearby;
(2) minimal incremental land use; (3) possible mine reclamation;
and (4) serving as a pH amendment for mine tailings. The
principal concerns are possible interruption of mining
139
-------
operations, contamination of ground or surface waters, and
fugitive emissions and runoff. Several studies are currently
under way to evaluate the feasibility of various mine disposal
alternatives.
Arthur D. Little, Inc. is also evaluating the feasibility
of mine disposal of FGD sludges. A review of six selected
mine categories has suggested that the most promising sites
are surface area strip mines, underground room and pillar lime-
stone mines, and load-zinc mines. Table 31 lists the evaluation
of various mine types and the feasibility of sludge disposal in
the mines (Ref. 4).
The most promising surface mine disposal sites appear to
be located in the midwestern United States. These mines have
substantial capacity for receiving FGD wastes, and disposal
within existing mining operations appears to be technically
feasible. The disadvantage to surface mine disposal in the west
is the limited amount of rainfall available to dilute FGD
sludge leachate. In any instance, FGD sludge disposal within
surface mines will assist in returning the land to its original
elevation after covering with overburden (Ref. 78).
Eastern and midwestern room and pillar coal mines were
also determined to be promising disposal sites. Although
injection of FGD sludge into deep mines could complicate
onging mining operations, it has two distinct advantages:
(1) the long-term control of mine subsidence if dewatered and/or
stabilized, and (2) the prevention of acid mine drainage and
neutralization of acid which is generated (Ref. 78).
Both surface mine and underground mine disposal of FGD
sludge can prevent the potential for groundwater contamination
by sludge leachate. This is particularly true for untreated
sludge. Stabilization, although desirable for subsidence
control, leaching control, and backfill material, is more
expensive than simple untreated sludge disposal. The feasibi-
lity of FGD sludge disposal to mines is strongly dependent
on the hydrogeology of the surrounding area.
Radian Corporation has been studying the physics of mine
subsidence and its impact on the use of FGD sludge as backfill.
It has been determined that there is a trade-off between
viscosity of the sludge and allowable settlement in the mine
using untreated FGD sludge. The optimal range for both para-
meters is a function of the sludge and its behavior at various
solids contents. The study has concluded that sludge combined
with coal waste can provide the best means of preventing mine
subsidence while disposing of waste. The detailed study results
should be available in late 1977 (Ref. 78).
140
-------
TABLE 31.* GENERAL MINE CHARACTERISTICS
Rainfall/Evap.
Mine Type (Region)
Area strip coal mine
(Interior province)
Area strip coal mine
(Western province)
Room & pillar coal mines
(Eastern) 1)
(Eastern) 2)
(Interior & mountain) 3)
Longwall coal mines
(Eastern &
mountain)
Room & pillar load zinc mines
(Interior)
Room & pillar limestone mines
(Interior - actually in 12 states)
Room & pillar salt mines
(Eastern & interior)
Old iron ore pits
(Interior)
/yr.
40/36
15/42
40/32
40/32
40&15/36&42
40/32
15/42
40/36
40/36
40/36
40/32-36
30/24
Mine
Water Quality
Neutral/basic
Neutral
None
Acid (pH 3-5)
Neutral
None
Acid (pH 3-5)
Alkaline (pH-8)
None
Alkaline
None
Neutral/Alk.
(pH 7-8)
Sludge
Type
Dry +
Dry
Dry or
Slurry
Slurry
Dry
Dry or
Slurry
Dry or
Slurry
Slurry
Dry
Dry or
Slurry
Sludge
Disposal
Easy
Easy
Difficult
Difficult
Difficult
Difficult
Difficult
Easy
Easy
Difficult
Easy
*Ref. 103
+ Dry means any sludge that can be handled as a dry solid. The sludge can contain moisture and is best
if it is moist (<40 percent moisture according to sludge morphology).
-------
The Pennsylvania Department of Environmental Resources
has recently received a grant from EPA to assess the feasibility
of using FGC wastes to prevent mine subsidence and reduce acid
drainage. Results of that study are not expected before 1978.
FGD SLUDGE UTILIZATION
Sludge utilization is a desirable alternative to sludge
disposal. It relieves the FGD user of the burden of sludge
accumulation and disposal. In addition, utilization can
provide the user with a marketable commodity from an otherwise
expendable by-product. A discussion of current and proposed
sludge utilization practices was presented in Section V.
142
-------
SECTION VIII
ENVIRONMENTAL CONSIDERATIONS
DISPOSAL SITE CHARACTERISTICS
The disposal site characteristics which influence the
environmental impact, of FGC waste disposal include:
• Present and projected land use
• Topography
• Hydrology and geology
• Meterology
These site characteristics when combined with the sludge
characteristics, economics, and other disposal variables, will
determine the optimal solution to the disposal problem. The
variety of these relationships indicates that no general solu-
tion is appropriate to all areas. Some disposal sites may have
little significant environmental impact regardless of sludge
characteristics and disposal management variables. Other sites
may be very sensitive to the type of disposal operation employed
or to sludge characteristics.
The environmental impacts associated with each of the site
characteristics will be examined in the following subsections.
In addition, a discussion of the mass transport phenomenon
associated with contaminants transmitted from the disposal site
to the general environment through the groundwater will be
included in the section on hydrology and geology.
Present and Projected Land Use
The present and potential future land use of a proposed
disposal site will influence the disposal technique to be
utilized. A primary distinction can be made between urban and
rural land uses. Typically in urban locations, property values
are higher than in rural areas. Therefore, techniques which
utilize less land and/or generate a fill material of adequate
bearing strength would be cost-effective in urban, areas.
Potential land use will be at least partially determined
by present methods of FGD sludge disposal. For example, de-
pending upon sludge characteristics, the use of pond disposal
of unstabilized sludge may result in a site with virtually no
143
-------
bearing strength. In urban locations, this lack of mechanical
stability would prevent future use of the site for anything
more than the lightest duty applications (e.g., if suitable
cover material were provided, such a site could support a park)
On the other hand, the disposal of stabilized materials might
maintain the potential for future site use.
The optimum disposal scheme will be strongly influenced by
economic factors. Trade-offs between the cost of stabilizing
the fill area would be considered as opposed to the use of an
unstabilized pond which would drastically reduce property
values .
It should be noted that the property tax structure of most
metropolitan areas will introduce distortions into any economic
calculations. Property taxes are often based upon the value
of the land for its highest potential use. If the disposal
site is used for unstabilized sludge, the site would have an
essentially zero value for any other purpose; after decommis-
sioning, it would be taxed at a very low rate. If the site
receives structurally stable or fixated sludges, it will have
a higher potential value and be subject to correspondingly
high property taxes.
Rural locations are generally characterized by relatively
low land values. At most rural sites, land value is, to a
large degree, a reflection of its productivity. For example,
prime agricultural land may sell for somewhere in the range of
$500 to $2,000 per acre; grazing land may range from a few
dollars to $100 an acre.
At most rural sites, the land cost of disposed sludge is
down in the few cents per ton category. These low relative
costs make property tax and direct land purchase costs insig-
nificant terms when determining the optimum disposal technique
for a particular site.
Topography
Topography of the disposal site and adjacent areas influ-
ences the potential environmental impact of the disposal
operations in four ways, as follows:
• Drainage structures should be designed to prevent the
intrusion of rainwater runoff into the disposal area;
• FGD sludge retention structures (dikes, dams, etc.)
should be designed more securely when topography would
allow sludge release by retention structure failure to
flow to nearby surface waters;
144
-------
• As discussed in a later subsection, the relative
elevations of the disposal pond surface, pond bottom
and groundwater have a strong influence upon the mass
transport of FGD contaminants to the groundwater; and
• Proper use of topography can minimize the unaesthetic
visual impacts of the disposal site operation.
Retention structure failure and subsequent release of
large volumes of sludge to surface waters (rivers, lakes, etc.)
would have catastrophic effect upon the surface water biota.
When possible, disposal sites should be located so that acci-
dental sludge release would not flow to nearby surface waters.
If such a desirable location is not available, the retention
structures should be designed to high safety standards, includ-
ing back-up structures (e.g. a double dike system).
Hydrology and Geology
Generally, the impact of the FGD disposal site upon the
groundwater resources below the site is of major concern to
regulatory agencies. Of interest is the mass transport of
contaminants form the FGD sludge to the groundwater in a
pathway which includes:
1. Quality and quantity of leachate generated by the
in-place sludge;
2. The rate at which leachate permeates through the
retention structure (usually a pond liner), if a
1i ner is insta11ed ;
3. The rate at which individual contaminants in the
leachate which escapes the retention structure travel
through the underlying soil; and
4. The effect of the contaminants which reach the ground-
water aquifer upon the quality of the groundwater.
This subsection discusses the hydro logical and geological
factors involved in 3 and 4, above.
Groundwater quality can range from highly desirable drink-
ing water to water that is nonpotable. These variations in
existing groundwater quality can be of natural or artificial
orifin. In many areas of the southwest, it is common to find
shallow, highly saline water due to concentration by evapora-
tion or a preponderance of exchangeable cations. The water
quality in many of these areas may be worse than the quality of
the leachate generated in a disposal site. Where poor ground-
water underlies a disposal site, the question of groundwater
pollution from contaminant mass transport is perhaps academic.
145
-------
Where potentially useful water underlies a disposal area,
it is necessary to consider the mass transport of contaminants
from the site to the water table in order to evaluate the poten-
tial environmental significance of any given disposal practice.
The term "mass transport" as it is used here, refers to the
movement of contaminants from a disposal site to the surrounding
environment. The rate of mass transport is perhaps the^ most
important factor in estimating groundwater pollution potential.
This rate is a function of many variables, including:
• The concentration of contaminants in the leachate (c)
• The permeability of the sludge or the underlying soil
(whichever is lower), (k)
• The hydraulic gradient, (vH)
• The ion exchange capacity of the underlying material
• Other possible attentuation mechanisms in the soil
(adsorption, etc.)
The equations which determine flow rates through soils
are mathematically similar to equations found in other areas
of science. They incorporate most of the above-named variables
(attenuation and ion exchange being incorporated into the
"retardation factor," R). The specifics of mass transport
theory are discussed briefly in Appendix B and in the literature
(Ref . -134, 172) .
The effect of various disposal techniques and the asso-
ciated site variables on the overall mass transport of contami-
nants are summarized in Table 32. This summary table provides
information on the relative effects of various disposal
techniques and site variables on the overall mass transport of
the contaminants from the site.
As can be seen from Table 32, different disposal techniques
or site variables affect the mass transport by changing para-
meters. For example, clay liners in the bottom of ponds will
reduce the flow rate through the bottom of the pond by decreas-
ing the permeability; while locating a pond in a high water
table, low horizontal hydraulic gradient area will decrease the
mass transport by decreasing the hydraulic gradient. This will
also decrease the flow rate. Locating the disposal site above
clay and/or organic soils which have high cation exchange capa-
city will increase the retention factor. This will decrease
the mass transport of some contaminants by slowing cation
movement.
While research has been concerned with mass transport,
long term predictability of mass transport from a disposal site
146
-------
TABLE 32. RELATIVE EFFECTS OF VARIABLES ON MASS TRANSPORT OF CONTAMINANTS
FROM DISPOSAL SITE TO GROUNDWATER
Mass Transport = (C, kso1l> ly^, v-H, Rso1l)
Variable C (mg/1) k so11(cm/sec) kf1l1(cm/sec) v-H( ^jj)
Disposal Technique . .
. unllned pond -- 10" 10" 10
7 n
. clay lined pond -- 10" -10"
. membrane lined pond — * -- -- 0.0
. stabilization
. high k product Decrease
. _
. low k product May decrease — 10" -10"
Site Variables 7 „
. low k ,. - 10"'-10"B
bU 1 1
. soil w/h1gh 1on
exchange
. hydrology 9 ,
. high watertable — — — 10" -10~J
low horizontal
gradient
. low watertable -- -- -- 10-20
, meteorology
. high evap. rate May Increase -- -- Decreases
vs. predplta- for semi-
tlon rate dry fill
Long Term
Predlct-
R ability
1 for anlons
10 for cations
Fair
Poor
Fair
Fair
May decrease Good
for cations
1 -,anioos Fair
10"J-10~* cations
Excel-
lent
Excel-
lent
Good
Reduction
Factor
-1-
«J M
10-10*
00
1-103
f
10-106
O A
10-10*
Breakthru
phenomenon
1 A
10-10*
.5-1
l-«
Overall Effect on Mass
Transfer/Comment
. Base line case*
. Depends upon k decrease
. Depends upon long-term
Integrity of Uner
. Depends upon decreased
solubility within fill
. Effects of kfjii decrease only
significant If kfn] «kso1l
. Limits flow rate by low Lo1i-
only significant when
. oipends upon cation exchange
capacity
. Minimizes hydraulic gradient
. Provides maximum flow rate
but provides time delay (on
the order of one year)
. Decreases transport of
solubility limited compounds
by reducing liquid flow rate
(only significant when evap.
rate >perculat1on rate
-- = no change from base line C3S6
* unllned pond above relatively
permeable soil with deep water table.
where: C • liquid phase concentration of leachate
k • permeability coefficient
vH = gradient of the hydraulic potential
R = retardation factor related to adsorption of Impurities on surfaces
-------
is limited to purely physical parameters. Those effects which
are dependent upon subtle chemical interactions and may change
rapidly with time are far less predictable. The following is
a discussion of several important physical parameters and their
relation to sludge disposal.
Di ffusi on--
The intrinsic diffusion rate of various soluble species in
water is fairly well known. Even in cases where experimental
measurements of diffusion coefficients in water are unavailable,
theoretical methods for calculating such diffusion coefficients
are reasonably well developed. Present theoretical descrip-
tions, based upon molecular parameters, will usually provide
a diffusion coefficient within a factor of 2 of the measured
value. It should be noted that the value range for diffusion
coefficients of soluble species in water is on the order of
10~5 to 10~4-4 cm2/sec depending upon the specific impurity in
question. A more complete discussion of diffusion coefficients
in liquid and of calculation techniques can be obtained from
"Diffusion" by W. Jost. (Ref. 81).
Mass transport of ions through water tables and strate
underlying a disposal site involves distances of many meters,
usually in the 100 meter range. An idea of the extent of ion
mass transport over these distances can be obtained by con-
sidering a problem in one dimension. Such a problem can be
represented by a mixed pond in which a constant concentration
of a particular ion sitting on top of the stationary layer of
soil is in turn resting on top of a very porous layer of very
fast moving underground water. Assuming further that the flow
rates through this layer are zero in order to isolate the
effects of the diffusion term, the problem appears as a classic
barrier permeation experiment.
In this experiment, a known concentration of the species
of interest is placed on one side of a barrier. The time rate
of change of concentration on the other side of the barrier is
zero. It begins to increase at some later time as the contami-
nants diffuse through the stagnant layer. There is a charac-
teristic mathematically defined time for measuring the contami-
nant flow through the membrane and its appearance on the other
side. This characteristic time is related to the diffusion
coefficient as follows:
X2 = 6 D t1
where:
X = membrane thickness
D = dispersion coefficient
t1 = time for contaminant to flow across membrane
148
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Using values of 10 meters for the thickness of the soil layer
under the pond and a value for the dispersion coefficient
of 10~6 cm^/sec (including the corrections for the void fraction
and path length changes in translating liquid measurements into
our multi-based system of soils and water), a value on the order
of 5,300 years is obtained for this characteristic time. In
other words, if a salt solution is placed on one side of a 10
meter thick layer of non-absorbing soil (such as fine sand)
with fresh water on the other, it would take approximately
5,000 years before the salts diffuse to the other side.
The preceding discussion indicates that the dispersion
terms in the overall mass transport equation are insignificant
for realistic distances under conditions of no velocity or
hydraulic head. From an environmental standpoint, even after
the 5,000-year period, the rate of diffusive mass transport
will be insignificant. This is due to the large distances
involved and reflects the fact that these distances enter the
solutions of mass transport equations as the distance squared.
If distances on the order of 100 meters - the more probable
distances to any drinking water well - are considered, the
time delay would be increased by a factor of 100. This results
in a characteristic time on the order of five hundred thousand
years.
Convection--
There can be no significant mass transport from the site
independent of the variables associated with sludge composition
or disposal technique without convection terms. The convective
flow term in the mass transport equation (Appendix B) involves
the retardation factor, the velocity of the flowing fluid, and
the concentration of the particular ion in question. Velocity
is determined by both the permeability and hydraulic conducti-
vity of the material at the point in question, and the gradient
of the hydraulic permeability potential.
The permeabilities of flue gas cleaning sludge are rela-
tively uniform throughout the sludge mass. The permeabilities
in the surrounding area, however, may vary considerably. When
combined with the associated hydraulic gradients, these same
permeabilities in the soil provide analysis of the groundwater
flow including both natural groundwater and the leachate from
the disposal site.
In general, stabilization processes decrease the permea-
bility of FGD sludges (see Section VII). Stabilization in this
sense is crucial when the sludge permeability becomes less
than that of the underlying soil (i.e., becomes the rate con-
trolling step). If the soils underlying the site are less
permeable than the stabilized material or even with the same
149
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order of magnitude, the stabilization of the material will
change the overall flow rate from the site only if the material
is saturated. Proper site management is therefore essential
in preventing saturation. The only advantage of the fixation
process would then be the resulting decrease in concentration
of many ions, which is often related to pH changes occurring
during stabilization.
Since permeability is highly variable and depends upon a
detailed understanding of the underground strata, a detailed
solution to the mass transport equation is not usually possible
for three-dimensional flow. Nonetheless, the effect of changes
in various parameters entering the mass transport equation can
be estimated without a detailed calculation.
The use of clay lined FGD sludge ponds will affect the
overall rate of mass transport by creating an artificial low
permeability layer beneath the site. This low permeability
layer will decrease the overall mass transport from the site.
The use of clay as a liner material will also tend to cause a
temporary decrease in the retention factor R. The use of
impermeable liner materials such as hypalon, polyvinylchloride,
and similar impermeable membranes arrest mass transport of
contaminants from the site by stopping downward movement of the
leachate. Most of the materials being used for liners are
specified for temporary duty and have a useful life limited to
at most a few decades.
Hydraulic Potential--This is the basic driving force for
convective liquid phase mass transport. In simple terms, the
mass transport rate for leachate leaving the pond area depends
upon the difference in elevation between the free liquid level
in the pond and the surrounding water table. For two otherwise
identical disposal situations (characterized by the same soil
properties, permeabilities, sludge characteristics, and pond
design), significantly different mass transport rates can be
calculated for two different depths of water tables. In areas
with deep water tables, where density differences are favorable,
the leachate can migrate straight down to the water table and
then spread out, possibly mixing with the groundwater. In
very high water table areas, the driving force for vertical
movement is limited to diffusive mass transport. The hydraulic
potential will be small. Most sites with suitable high water
tables are located in low-lying areas which may be subject to
flooding. It would be necessary to surround the pond with
dikes in order to prevent surface water flow over the site in
the event of flooding. Since all material would actually be
disposed of below the water table in the pond, no hydraulic
forces would be exerted on the dikes themselves under normal
non-flooded conditions. If it is assumed that the water level
in the pond is maintained exactly equal to the height of the
water table in the surrounding areas, the only driving force
150
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for leachate movement will result from the possible small
density differences between the leachate and the surrounding
water. These driving forces would be very small; with any
regularly encountered permeability of the soils, the overall
mass transport rate for contaminants leaving the site would be
negl i gi ble .
The idea of protecting the groundwater supply by disposing
of the materials below the water table and actually in the
groundwater itself may seem to go against intuition. A
thorough evaluation of the appropriate mass transport equations
makes it clear that such an engineering solution is not only
feasible but optimal in terms of preventing groundwater contami-
nation. The key to practical application of this technique is
control of convection from the site to the groundwater, caused
by vertical or horizontal hydraulic gradients. Horizontal
hydraulic gradients can be controlled by engineering design.
One such design would involve cutting a trench extending well
down into the water table around the outside of the pond area.
Such a trench, completely surrounding the pond, would effect-
ively eliminate any horizontal hydraulic gradients. For the
vertical gradients, the pond level need only be kept below
that of the surrounding groundwater to inhibit leachate migra-
tion. The major drawback to this approach is the high cost of
excavating below the water table-
The above discussion of sludge disposal below groundwater
is intended to serve only as a limiting case. It does show
the dependence of mass transport on convection, and how
limiting convection can significantly reduce mass transport.
Limiting convection is also important to landfill opera-
tion. Although stabilized or dewatered and compacted FGD sludge
has a low permeability (10~5 - 10~6 cm/sec), the resulting
landfill may eventually become saturated due to capillary
action, rainwater percolation, or simple groundwater flow.
The control of runoff there becomes important to reducing the
vertical gradient. Without convection, diffusion of contami-
nants in and out of a sludge landfill will contribute negligible
amounts to the groundwater as demonstrated in a variety of
leaching tests being used (see Section VII under "Stabiliza-
tion").
Estimating Mass Transport Rates--
While the mass transport equations discussed here and in
Appendix B can be solved, their solution is far too complex for
day-to-day use in site selection and monitoring. "Rules of
thumb" are therefore important to properly assessing potential
environmental impact from sludge contaminant migration. These
estimates can be used to determine the acceptability of the
151
-------
site, and monitoring results can be checked against these
projections as a safeguard.
The site parameters which affect the mass transport are
permeability, hydraulic head, and distance to the groundwater
table. These parameters are all related to convection, as
diffusion is assumed negligible in comparison. The rate of
contaminant migration, a function of these parameters, is
expressed as follows:
V - K AH
Vs - K
where:
Vs = superficial velocity, cm/sec
K = coefficient of permeability, cm/sec
AH = hydraulic head, cm
AX = distance from pond to groundwater, cm
icroscopic rate of migration, or pore velocity (Vp)
itermined from the following expression:
The mat
would be determined from the following expre:
Vp = Vs/e
where e is the void fraction of the underlying soil. Based
upon the calculated pore velocity, the time to reach the
groundwater could then be determined from the thickness of the
soil layer. The time required for contamination to show up in
the monitoring wells would then be determined from the rate and
distance of groundwater flow.
As an example, consider a disposal site with the following
character!' sties :
• Location:
Arizona, less than 500 people within 50 Km radius - no
cities greater than 10,000 population within 75 Km
« Meteorology:
Net evaporation area, periods of high winds
• Hydrology and Geology:
- 10 meters of clay (permeability coefficient of 10"^
cm/sec) overlaying 20 meters of sand aquifer with a
water quality of 6,000 ppm TDS. Below this aquifer
152
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is another 10 meter clay layer (.30 void fraction)
with a deep fresh water aquifer under this second
clay 1ayer .
- Distance to nearest navigable waters from disposal
site 5 Km with an elevation drop of 20 meters
a 20 meter total hydraulic head to bottom of clay layer
(i.e. 10 m deep pond)
• Computing:
superficial velocity = Vs = K-ti- = 2 x 10~8 cm/sec
where K = permeability cm/sec
H - hydrauli c head
X = thickness of clay layer
The pore velocity Vp = Vs/void fraction
= 2 x 10-8/.30 = 6.6 x 10'8 cm/sec
=2.1 cm/yr
This flow rate would then be applied to the total acreage
involved and the contaminant concentration in the leachate to
compute mass flow. This mass flow rate would be added to the
groundwater flow to determine the change in water quality (if
any) .
As a second example, consider a site with the following
character is tics:
Location: Northeast coastal site
Meteorology: 3 meters of precipitation/year
Hydrology and Geology:
Abandoned sand and gravel quarry - 30 m deep and 20
Ha in area
Permeability - 10~2 cm/sec
Aquifer is 2 meters thick above clay layer
Velocity in aquifer is 1,000 m/yr
153
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Velocity in aquifer is 1,000 m/yr
Void fraction is 0.25
Water quality is 100 IDS
Also assume the sludge is stabilized and possess a permeability
coefficient of 10-6 cm/sec. The material is 25 meters deep.
If the drainage was poor, a unit hydraulic head would
exist on the material (hard to avoid with this rainfall) and a
flow rate into the aquifer on the order of 10~6 cm/sec over a
20 Ha area, or a total flow of 2 I/sec. This flow from the
fixated material could contain 2,000 ppm TDS, which could
contaminate 378 £/s or 12 x lO^nH/yr of the fresh water flowing
under the site beyond the 10 percent level considered pre-
viously. With a flow velocity of 1,000 m/yr, a total of
approximately 9 x 10^ m^/yr of fresh water would be flowing
under the site. If our 2 £/s of leachate mixed with this
water, we would have a concentration in the mixed plume of
227 ppm TDS, which is well over a 100 percent increase in TDS.
Considering the soft nature of some waters and the high
calcium hardness of FGC sludge leachate, the increase in water
hardness would be even greater.
Meteorology
Local meteorology can interact with the disposal technique
being employed through two primary mechanisms. The first of
these relates to the characteristic evaporation/precipitation
ratio at the site, and the second to the effects of wind
erosion on the surface of the site if the site is dried.
Evaporation/Precipitation--
In areas with high evaporation rates relative to preci-
pitation rates (again, as in most of the southwest United
States), significant amounts of water can be evaporated from an
evaporation pond. The net evaporation over precipitation rate
can vary from a matter of a fraction of a meter per year to
up to 2.5 meters annually. Standard meteorological evaporation
pan data may show evaporation rates up as high as 3 meters a
year, but when translated to actual field conditions, signi-
ficantly less total evaporation will occur. A high evaporation
rate allows certain types of solutions to disposal problems
that are not feasible in low evaporation rate areas. Under
such climatic conditions, contaminated leachate can be disposed
of through evaporation.
Whether the evaporation rate of an area can be effectively
utilized depends upon the detailed design of the disposal
system. If the disposal area contains a totally impermeable
154
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liner, the site can eventually evaporate to dryness. All
leachate will be dried by evaporation, leaving a salt residue
in the bottom of the pond. However, evaporation also concen-
trates the leachate before drying it, thereby actually increas
ing the mass transport rate for the same site permeability.
Potential salt leakage from the disposal pond can be
estimated from the following equation:
i + evaporation rate > n
Leak rate
Rc = concentration ratio, species solubility product
species solution concentration
By definition RC will always be 21 1 • If the equation is
not satisfied, soluble salts will escape the pond.
For example, many of the soluble salts (such as sodium
chloride) are several orders of magnitude below their sol
bility limits. This would yield a Rc of approximately 1
Therefore, for a pond which has a net evaporation rate of two
meters per year, a leak rate of less than two centimeters per
year would retain the sodium chloride. If the leak rate
exceeds 2 cm/yr for a single pond installation, the salts would
leave the confined area of the pond and enter the underlying
soils. Whether these salts would then migrate down into the
water table will depend on hydraulic considerations. However,
the main point is that the salts have now left the site and can
no longer be controlled.
If the object of the disposal technique is to minimize the
amount of salt leaving the site, it is possible to retain a
significant portion of the salt even though the leak rate may
be higher than the specified 2 cm/yr. This can be achieved by
using a series of ponds rather than a single pond for solar
evaporation. The benefits of series operation can be seen if
a hypothetical series of seven ponds is considered. An input
concentration for the first pond of l/100th of the saturated
concentration for the salt in question will be assumed. If
each pond evaporates to the point where the concentration is
double its inlet concentration before passing it along to the
next pond, the leakage out of the first pond will be a rela-
tively dilute solution of l/50th the saturated concentration.
The leakage out of the second pond will be l/25th of the
saturated concentration, and so on. The area required for the
second pond is only half of the area of the first pond. By
the time the water reaches the last pond, it will exceed the
solubility product and the salts will begin to precipitate out.
The leakage from the end pond is saturated with respect to the
soluble salts, although the total area required for this last
155
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evaporation pond may be only
for the single pond system.
0.8 percent of the area required
For a very dry area, where the evaporation rate is not a
function of the salt in the water and with a 2 cm/yr leak rate,
this hypothetical series-pond would retain about 93 percent of
the salts. Under the same conditions, however, none of the
salts would remain in a single pond with the same leak rate.
Under actual conditions, the problem involves multiple salts
with different solubility limits. This hypothetical example
illustrates in broad outline the anticipated impact of series
versus parallel operation for solar evaporation disposal ponds.
In areas with very high precipitation rates, significant
volumes of water may enter the site every year from normal
rainfall. This water can leave the site through either surface
water or groundwater flows. After decommissioning the plant,
it is clear that water would not be returning to it. If this
water leaves the site via the groundwater system, it must have
passed through the disposal materials and would, therefore,
contribute to the total leachate flow leaving the site. In
this case, added precipitation could stand on the site and
increase the hydraulic head, thereby increasing the total
leachate mass transport from the site. If the rainwater is
allowed to leave through surface runoff, it may carry materials
from the site. This can be partially controlled by engineering
designs which allow sufficient amounts of settling. Allowing
surface runoff would cause less total contamination than per-
mitting leachate to enter the groundwater. The surface water
which enters the site from precipitation only comes in limited
contact with the fill material. It would not necessarily flow
through the material. Therefore, the concentration of contami-
nants found in surface runoff is usually much less than the
concentration in the leachate.
In areas without the very low relative humidities charac-
teristic of the southwest desert areas, the operation of solar
evaporation ponds in series rather than parallel produces the
additional advantage of a higher net evaporation rate. This
is due to the fact that the initial series evaporation ponds
contain relatively dilute solutions and have correspondingly
higher evaporation rates than a single pond containing a very
concentrated solution.
In summary, areas of net evaporation and net precipitation
pose different problems to engineers designing FGD sludge
disposal systems. Net evaporation areas tend to concentrate
sludge liquors, thereby increasing salt concentrations in the
leachate. Net precipitation increases both the hydraulic head
on a pond and the incidence of landfill infiltration by rain-
water. Engineering solutions are available for each of these
problems.
156
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Wind Erosion--
The second effect of local meteorological conditions is
caused by surface wind erosion. If the disposal site dries out
and is not supporting vegetative cover, wind can erode the
surface material and remove it from the site. The importance
of this phenomenon will vary from area to area. Wind erosion
can be prevented by stabilizing the surface of the material.
Effective engineering solutions must aim at surface stabiliza-
tion.
Even so, stabilization processes are not altogether
effective at reducing wind erosion potential. Studies by WES
(Ref. 104) have shown that some stabilized sludges break down
to some extent under wet-dry and freeze-thaw cycling. While
this may only be a surface effect in a deep landfill, it none-
theless presents a possible wind erosion problem. This has
occurred at the Duquesne Light Company Phillips Station, where
a series of hot, dry summers has resulted in substantial
fugitive dust emissions from the compacted surface of the
stable landfill. An extensive sprinkler system has been
installed surrounding the site for use during dry, windy con-
ditions (Ref. 142) .
Covering a site with topsoil or using similar techniques
which allow establishment of a vegetative cover will help
stabilize the site, as is doen with dry ash disposal. Obser-
vations of fly ash disposal sites located in the southwest
areas of the United States indicate that the surface can also
be stabilized by bottom ash. When both fly ash and bottom ash
are disposed of at the same site, the wind erodes the loose
fly ash from between themixture of fly and bottom ash, leaving
a surface covered only by bottom ash. Bottom ash particles
tend to be too large for wind erosion. Once this bottom ash
surface is formed, the site is stabilized against further wind
erosion. Engineering solutions are therefore available for the
wind erosion problem at FGD sludge Inadfills. The proper
selection of cover materials is certainly preferable to
sprinklers and other dust control methods due to limited main-
tenance. Several sludge disposal systems have adopted co-dis-
posal of fly ash, bottom ash, and sludge and found that the
surface stabilizers help (see SEction VII). Since bottom ash
mixtures need cover only the top few feet of the site to pre-
vent erosion, it can be added before the site is closed.
HEALTH EFFECTS
The dissolved salts, trace metals, and other contaminants
contained in FGD sludges are all found in man's natural
environment. Through evolution man has acquired a tolerance
for these contaminants and requires many of them in his diet
for good health. A typical biological response curve would
157
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show an increasingly beneficial effect with increasing con-
taminant concentrations up to a certain optimum level. Beyond
this level there is a tolerance region beyond which benefits
decrease, injurious effects begin, and finally a lethal con-
centration is reached. The goal of FGD sludge management is
not to reduce contaminant levels to zero but rather to ensure
that the concentrations of the contaminants which could even-
tually return to man and other biota are not at harmful levels.
The purpose of this section is to put the health effects
of FGC sludge contaminants in perspective by identifying (1)
the possible contaminant pathways to man, and (2) the potential
contaminant concentrations at the point of consumption or
exposure. Related information is contained in Section VI which
discusses the range of contaminant concentrations in the liquid
phase of FGC sludges, and in Section XI which discusses drink-
ing-water quality standards.
Contaminant Pathways
The potential health problems posed by sludge disposal
can be approached by examining contaminant pathways to man in
Figure 19. It can be seen that adding an FGC system to a
power plant effectively removes trace contaminants from the
atmospheric pathway to man and places the contaminants instead
into drinking water. This converts a regional atmospheric
pollution problem into a potential local water pollution
problem.
Groundwater--
The major potential pollution problem in FGC sludge
disposal is the transport of leachate contaminants from the
disposal site into local potable groundwater supplies. Pre-
dicting the potential mass transport of specific contaminants
to man via this pathway is complex and involves the following
major variables:
• The flow rate of the leachate from the disposal site
into the aquifer, which is dependent upon such factors
as permeability of the soils and liner (if any) under-
lying the disposal site, and the hydrostatic head force
upon the leachate;
• The concentration of the specific contaminants con-
tained in the leachate generated by the disposal site,
and the changes occurring in these concentrations due
to attenuation effects by the soil during passage of
the leachate to the aquifer;
t The capability of the aquifer through actual replenish-
ment to dilute the leachate reaching it, i.e., the
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FUEL
FGC SYSTEM
SOREENT
MAKE-UP
WATER
AIR
en
i-D
Figure 19. Simplified pathway chart for contaminants
reaching man.
in coal
-------
relative volumetric rate of (1) the leachate reaching
the aquifer, (2) the replenishment by natural sources
such as horizontal groundwater migration, (3) the rate
of water supply withdrawal, and finally (4) the extent
of the mixing which occurs in the aquifer between
leachate and natural source water; and
• The contaminant concentrations of the natural source
water in the aquifer and their relation to concentra-
tions of similar contaminants in the leachate reaching
the aquifer.
The above listed variables are often interrelated, complex,
and difficult to measure accurately. Considering, however, the
large size and costs involved in FGD sludge treatment and dis-
posal, the effort to evaluate these factors should be cost
effective in designing the best sludge management system for a
particular site. It is outside the scope of this report to
delve comprehensively into each variable potentially effecting
health effects. However, a brief discussion follows.
Two storage functions are shown in Figure 19. The first of
these is associated with the storage capability of FGD sludge
itself after ultimate disposal. Several of the contaminants of
interest are either coprecipitated with the sludge crystals or
contained in the fly ash. As a result, they are retained
indefinitely within the disposal site. For chemically stabi-
lized sludges, new solid phases are created which often immo-
bilize impurities which would normally be in the liquid phase.
Another part of the site storage function is a delaying
action created by artificial or natural low permeability liners
underlying the disposal site- The long-term effectiveness of
various liners is being tested. However, it is possible that
most liners will eventually deteriorate or be bypassed. There-
fore, on a geological time scale such storage is temporary and
control over the rate of release of contaminants is the major
advantage.
A second storage function is associated with the soil
system. As contaminants are leached from the disposal site,
they can be retained by the soil. At least three mechanisms
are involved. One mechanism involves the precipitation of some
of the contaminants. A second storage mechanism involves ion
exchange within the soil. Soils which are high in organic and
clay contents have considerable cation exchange capability, as
well as limited anion exchange capability. Physical adsorption
of the impurities on the surfaces of the soil particles is a
third mechanism delaying their migration. Most elemental con-
taminants are readily adsorbed by soils. Of those contaminants
found in the sludge, only fluoride, boron, chloride, selenium,
160
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and arsenic are not easily absorbed by most soils, due to their
an ionic nature.
The soi1/groundwater system provides a delaying action for
contaminant release. In the process, the system limits the
concentration of impurities in the aquifers. The actual delay
time associated with the system depends upon the chemistry of
both soils and leachate, and the associated liquid flow rate.
Even in soils with relatively high permeabilities, it is pos-
sible that certain contaminants may migrate only a few feet over
a period of centuries. For contaminants which are not readily
absorbed by the soil, the storage times may be very short.
Contaminant concentrations which may reach man are influ-
enced by these storage times. When the storage time is sub-
stantially greater than the useful life of the power plant and
its sludge disposal system, the storage system reduces the rate
of release of contaminants to a level where their addition to
the groundwater system may be of little or no consequence to
human health. When the storage time for a given contaminant is
short in comparison to the life of the facility, the contaminant
will enter the groundwater system at or near its original con-
centration and be quickly dispersed. The proper selection of a
storage function, provided by either FGD sludge or the soil/
groundwater system, can control the rate of release of contami-
nants to an environmentally acceptable level.
Surface Waters--
A second pathway by which contaminants contained in FGD
sludge may reach man is by way of surface waters. In this
case, pond supernatant enters a nearby water course, which in
turn is used as a drinking water supply. Considering the
initial concentrations of the contaminants in question and the
dilution capabilities of the surface waters adjacent to many
power plants, the levels of contaminant reaching man from this
source will be strongly site-specific. However, good engineer-
ing practice can render this practically nil.
Atmosphere--
The atmosphere provides a third pathway by which these
contaminants may reach man. Even those power plants equipped
with FGD systems and high efficiency particulate removal do not
collect all contaminants. Once in the atmosphere, these con-
taminants will be inhaled by living beings or deposited on the
local terrain. Pollutants which settle out may reach man
through food crops or surface water runoff to drinking water
supplies. Atmospheric dispersion results in a lower concen-
tration of contaminants. As a consequence of this dispersion,
surface waters and soil concentrations would therefore also be
1ower.
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Health Significance of Sludge Contaminants
The health effects of metals and their compounds are often
difficult to quantify. Some are necessary to life in small
concentrations but toxic at high concentrations. Others react
differently within the body depending upon the chemical state.
Of the heavy metals found in FGC sludge, five elements
(arsenic, lead, mercury, fluoride and selenium) represent known
hazards to human health, based on existing evidence. Lead,
mercury, and cadmium are particularly insidious because they
can be retained in the body for relatively long periods of time,
thus functioning as cumulative poisons (Ref. 145).
Table 33 provides a comprehensive summary of the presence
of metals in the environment, their toxicity to humans, and
their half life in the body. As can be seen from the table, the
most toxic of these metals are antimony, arsenic, cadmium, lead
and mercuric salts.
In the liquid phase, trace element concentrations are
important in determining the potential health hazards of leach-
ing or of surface water discharge. Since each of these studies
involved different power plants, results are not directly com-
parable. A summary of these concentration ranges is given in
Table 34. This table includes trace contaminants which are
considered important to health or the ecology.
The range of data shown in the table for sludge leachates/
elutriates represents a wide variety of power plants and scrub-
ber systems. While the data do not always agree between sources,
virtually every drinking water standard is exceeded by at least
one sample value between the three sources.
More importantly, further analyses of these data indicate
that only a few parameters consistently exceed drinking water
standards (i.e., the standard value falls just inside or outside
the lower end of the sample range). These parameters are TDS,
arsenic, lead, mercury, fluoride, and selenium. Their potential
effects are discussed below.
Total Dissolved Solids--
The TDS concentration of FGD sludge has in some instances
been as high as 95,000 mg/ (Ref. 104). The amount of TDS
depends primarily upon the mode of scrubber operation. For
example, if the scrubber is operated in a very tight, closed-
loop mode, the soluble salt concentration will accumulate to a
much higher level than that experienced in a more open-loop
operation. Double alkali sludge liquors may contain large quan-
tities of dissolved solids, depending upon the effectiveness
of the sludge cake washing techniques employed. Insufficient
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TABLE 33. METALS IN THE ENVIRONMENT AND THEIR TOXICITY
cr>
Metal
Antimony
Arsenic
Barium
Beryl 1 i urn
Cadmium
Chromi urn
Copper
Iron
Lead
Manganese
Mercury
Ni ckel
Selenium
Silver
Tin
Zinc
* Ref. 1
b. Copper
Average daily intake
/ it \
Food and Water Air
100 1.7
400-900
735 30
Oral dose
producing
toxicity (mg)
100
5-50
200
12 0.04
160 7.4
245 1.1
1 ,325 11.4
15,000 84
300 46
4,400 28.8
25
600 2.3
62
60-80
3
200
50-250
--
--
not known
--
6
5
60
Fatal
dose
( i n g e s t i o n )
100-200 mg
1 20 mg
1 9
not known
not known
5 g
10 gb
5-10 gc
0.5 g
20 mg - 1 gd
--
2 gf
7,300 0.6 2,000
14,500 16.8
45
sul f ate
10 g9
Total
body content
(mg)
7.9
15-20
22
0.3
50
1 .8
72
4,200
120
12
10
14.6
1
17
2,300
Whole body
half-1 ife
(days)
38
280
65
180
200
616
80
800
1 ,460
17
70e
667
11
5
35
933
c. A two-yr old child
d . Mercur
e. Methyl
f . Silver
i c salts
mercury
nitrate
g. Zi nc/sulfate
-------
TABLE 34. SUMMARY-OF LEACHATE DATA FROM SEVERAL STUDIES OF FGD SLUDGE CHEMISTRY
CTl
-£=>
Range 1n Liquids
Element
or
'Item
TDS
PH
As
Ba
Be
B
Cd
Cr
Cu
F
Ge
Hg
Pb
Mn
Mo
N1
Se
Sb
V
Zn
Range in sol id
sludge
mg/kg
--
4-15
<20-4,400
1.5-4.0
41-210
.4-25
1.6-15
39-104
260-1017
<.l-6
<.01-2
1-290
56-340
8-81
<12-75
2-18
4.3-7.5
<100
14-2,000
FGD Sludg'e
Leachate
Ref. 12
3200-15,000
3.04-10.7
.004-. 3
--
.002-14
8.0-46
.004-. 11
.01-. 5
.002-. 2
.07-10
--
.0004 -.07
.01-. 4
.09-2.5
.91-6.3
.05-1.5
.001-2.2
--
.001-. 67
.01-. 35
FGD'SLudge
Leachate
Ref. 131
--
8.4-9.7
<.002-.03
<.3-2
.001 -.002
.96-6.3
.0005-. 002
<.001-.011
<.005-.045
7.6-31.5
<.01-.02
.0005-. 001
.003-. 006
<.002
.006-. 007
<.05
.01-. 045
.013-. 035
<0.1
.005-. 045
rng/1
FGD Sludge
Elutriate
Ref. 101
2,600-7,000
--
.006-. 019
--
.0005-. 01
--
.014-. 032
.002-. 08
.004-. 3
--
--
.01-. 03
.0029-. 06
.01-9.0
--
.007-. 03
.005-. 13
--
--
.024-. 88
Frame of Reference Values
Fly Ash
Solids
mg/kg
Ref. 131
--
--
3.2-74
700-15,000
5.2-13
179-1040
.39-5.3
3.6-28
43-238
84-2880
1.2-25
<.01-.146
4-27
157-374
6-12
34-108
1.7-16.4
1.-4.4
<100
92-854
Coal Ash
Leachate
mg /I
Ref.
2,200
13
<.002-.084
<.3-40
.0006-. 003
.03-17
<.001-.0025
<.001-.21
<.005-.092
1.4-17.3
<.01
.0003-. 015
.0027-. 024
<.002
.01-. 7
.015-. 05
<.0005-.47
.006-. 033
<.l
<.005-.038
Primary
Drinking
Water
Standards
Ref.
500
--
.05
1.0
--
--
.01
.05
1.0
1.4-2.4
--
.002
.05
.05
--
--
.01
--
--
5.0
Sanitary
Waste
Effluent
mq/1
Ref.
—
--
.013
--
--
--
.013-. 2
__
.08
--
--
.002
.08
--
--
_-
_-
--
--
.23
Landfill
Leachate
mg/1
Ref.
1 ,500-9,200
—
__
--
--
--
.007-. 05
.053-. 33
.17-. 45
--
--
.003-. 03
.09-. 29
--
--
-_
.02-. 077
--
—
--
Soils
mg/kg
Ref. 93
--
--
__
--
--
--
.01-7
--
2-100
--
--
--
2-200
100-4000
__
10-1000
-_
—
_-
10-300
-------
washing can result in significant sodium, potassium, or other
salt concentrations in the sludge liquor.
Ionic species typically contained in the leachate are
sodium, calcium chloride, sulfate, and limited amounts of sul-
fite (due to low solubility). The calcium component of IDS can
be absorbed by the soils, but mass balance and conservation of
charge relationships require the release of some other cation
presently contained in the soils, normally sodium. The absorp-
tion of the soils will tend to shift the sodium/calcium ratio,
although the total number of equivalents per liter would remain
relatively constant. If the leachate is to meet the potable
water standard for TDS (500 mg/£), the required dilution would
ordinarily be 4:1 to 30:1.
Arsenic--
The fatal dose of arsenic is 0.1 to 0.3 g. Organic arseni-
cals, such as arsphenamine and dimethylarsinic acid, release
slowly and are therefore less likely to cause acute poisoning.
The manifestations of arsenic poisoning appear to vary with
ethnic background, with blackfoot disease, pulmonary disease,
and gastrointestinal disturbances predominating. The principal
arsenic poisoning is hemolysis.
Arsenic presumably causes toxicity by combining with
sulfhydryl (-SH) enzymes and interfering with cellular metabo-
lism. Arsenic is suspected to be a carcinogen but not tumori-
genic. Arsenic was also suspected to be associated with in-
creased incidence of hyperkeratosis and skin cancer when arsenic-
contaminated water (0.3 mg/a) was consumed. Chronic exposure
to arsenic in drinking water (2.2 mg/a) was reported to cause
gangrene of the lower limbs (Ref. 145).
Table 34 shows that typical arsenic concentrations in FGD
sludge leachate are well below drinking water standards. Only
at one location were leachate arsenic levels at or near the 0.5
mg/£, standard (Ref. 12). Considering the possible forms of
arsenic and the attenuation/dilution potential at the site,
arsenic contamination of surrounding waters should not present
a significant health problem.
Lead--
Although lead is a cumulative poison, not all of it is
absorbed or retained by the body. Most of it is absorbed into
the blood and later excreted in the urine so that blood lead
does not rise to acute levels, except in cases of prolonged
exposure at high concentrations. A small portion of this daily
lead intake gradually accumulates in bones where it is normally
insoluble and harmless. But under certain conditions, such as
periods of high calcium metabolism in feverish illness, cortisone
165
-------
therapy, and old age, this accumulated lead can be released
suddenly into the blood at toxic levels.
American citizens have the highest average blood levels of
lead in the world. Although these blood levels are significant,
they fall well below the toxic threshold level for classical
lead poisoning. Because the general population is already
exposed to dangerously high levels of lead through food and air,
however, lead levels in water should be kept at a minimum.
Up to 100 cases of lead poisoning, with an average of ten
fatalities, are reported yearly. Most of these fatalities are
in children who lived in homes built before 1940 and can be
traced to lead based paint. Seven cases of lead poisoning from
drinking water in Australia in 1973 were reported. The well
water they used contained a soluble lead content of about 14
mg/£ (Ref. 145).
Lead levels are typically well below the drinking water
standard of 0.05 mg/£ in FGD sludge leachate. Only the Aero-
space analyses at Shawnee (Ref. 12) have shown lead concentra-
tions at or above the standard. As lead is readily attenuated
in soils with any ion exchange capacity, contamination of
groundwaters by lead contained in FGD sludge leachates is not
expected to be a problem.
Mercury--
The fatal dose of mercuric salts is 20 mg to 1 g. The
biological half-life of inorganic mercury compounds is estimated
to be about 70 (30 to 100) days. Ingested metallic mercury is
not toxic since it is not absorbed. Mercurous chloride and
organic mercurials such as acetomeroctol , ammoniated mercury,
merbromin, mercocresol , and mercury protoiodide are not likely
to cause acute poisoning because they also are poorly absorbed.
The single fatal dose of these compounds is three to five times
the fatal dose of soluble mercury salts. The mercurial diure-
tics (mersalyl, meralluvide, mercurophyl1ine , mercumati1 in ,
mercaptomerin, chlormerodrin , and merethoxyl1ine) are almost as
toxic as mercury salts. Volatile diethyl and dimethyl mercury
are ten times as toxic as mercuric chloride (Ref. 145). It is
therefore crucial to determine the chemical forms of mercury in
the leachate when evaluating potential health effects.
Since the leachates under consideration generally contain
both sulfite and sulfate ions in solution, a well-defined oxi-
dation/reduction potential exists. Thermodynamic calculations
based upon realistic S03/S04 ratios indicate that the mercury
will exist in one of the reduced states, either as elemental
mercury or possible mercurous chloride. In these insoluble
forms the mercury mobility and the potential for consequent
deleterious health effects are reduced.
166
-------
However if disposal site characteristics vary from those
favoring the existence of insoluble forms of mercury (such as
increased oxidation potential or acid leachate), soluble mercury
compounds would be formed. Mercury, when exposed to anaerobic
aquatic environments also methylates, thereby becoming even more
toxic.
The high attenuation capacity of most soil for mercury
coupled with the typically high pH of most FGD sludges would
seem to relegate mercury to a non-critical status at the leachate
concentrations shown. Nonetheless, this attenuation capacity is
a site characteristic; this capacity should be documented for
each site before mercury can be dismissed from being a potential
hazard.
Fluoride--
Fluorides are not considered toxic at even the highest
concentrations found in FGD sludge liquors. While several
studies have not analyzed the fluoride concentration in sludges,
the high fluoride content indicated by certain of the EPRI/
Radian Corporation data (Ref. 134) would cause severe mottling
of children's teeth. The amount of fluoride necessary to cause
this mottling is indicated in Table 35.
Fluorides, like many other an ionic species, are not atten-
uated in most soils. Because fluorine is beneficial to man at
the concentrations noted in most of the leachate samples shown,
fluorine may not be a problem when dilution and other site
characteristics are taken into account. Fluoride migration in
leachate occurs in much the same fashion as TDS and can there-
fore be correlated with TDS monitoring results (see Section IX).
Selenium--
Recent measurements indicate that selenium emissions from
the burning of coal account for 62 percent of total industrial
emissions of selenium in relation to natural sources (Ref. 22).
Both selenium-deficient and selenium-rich areas exist in the
United States and throughout the world. Selenium in low con-
centrations is beneficial and in high concentrations is a toxi-
cant. In regions deficient in selenium the propensity of
organismal bioaccumulation will be greater than in regions where
selenium is prevalent. The only reported case of human selenium
toxicity from water supplies was the result of a three-month
exposure to well water containing 9 mg/£ (Ref. 145). This level
is higher than that found in the worst sludge leachate by more
than an order of magnitude.
Selenium enters the FGC system in the form of elemental
selenium. The existence of sulfite in the sludge will affect
the oxidation reduction potential, preventing oxidation of
167
-------
TABLE 35. EFFECT OF INCREASED CONCENTRATIONS OF
FLUORINE IN DRINKING HATER ON TEETH*
<1.0 rng/1 Increased possibility for dental caries
1 mg/1 Optimum concentration for dental health
^ 1.7 mg/1 Mottling in 40 to 50% of the children
oo
2.5 mg/1 Mottling in 80% of the children; one-fourth of
which are severe
4.6 mg/1 100% mottling with a marked increase in severity
Ref. 55
-------
selenium to a more soluble form, selenite (Se02~^) or selenate
(SeO^-2). These forms are uptaken by organisms (Ref. 22).
Selenium occurring as inorganic selenides or in the elemental
form is very insoluble and not readily absorbed (Ref. 22).
The current USEPA drinking water standard for selenium
is 0.01 mg/ £ . In virtually every case, FGD sludge liquor
selenium concentrations were shown to exceed this standard
(typically by a factor of 1 to 4). As selenium is an anion and
behaves much like fluoride in passing through soils, this para-
meter is one which needs to be controlled during disposal.
Summary--
The following conclusions can be made regarding the health
significance of leachate and surface water discharges from dis-
posal systems:
• All studies agree that the total dissolved solids in
the sludge liquors exceed drinking water standards;
• All studies indicate that the selenium concentration
commonly exceeds drinking water standards;
• The EPRI/Radian data indicate that in some instances
fluoride concentrations may be high;
• All studies indicate that arsenic, lead, and mercury
(among others) can exceed drinking water standards in
some instances, although typically below standards and
readily attenuated by most soils.
SAFETY
Safety considerations associated with the disposal of FGC
sludges can be directed toward three groups: (a) workers
employed at the site; (b) the general public; and (c) livestock
and wild animals. These safety considerations relate to the
physical rather than the chemical properties of the sludge.
The safety of the workers at the plant is determined by
their awareness of the potential dangers associated with the
disposal site and material handling equipment. Each safety
hazard is specific to the plant in question; at present, the
safety of the materials handling equipment and operating proce-
dures is regulated by OSHA and MESA guidelines (see Section XI).
The thixotropic nature of certain FGD sludges poses an
unusual safety hazard. A pond filled with such material may
develop an apparently solid surface crust. This crust, however,
may liquify on impact (such as a person jumping or a vehicle
braking on the surface). Whether 1iquification will threaten
169
-------
men or machinery will depend upon the thickness of the crust.
Certain other industrial wastes, such as drilling muds, also
exhibit this property.
The answer to the safety problems associated with the
sludge disposal area lies in worker awareness of the associated
hazards. This is best achieved through the development and
implementation of standard safety procedures. These procedures
should include the use of a lifeline if onw person is attempting
to work on a dried pond, as well as appropriate warning signs
and barriers in plant and disposal areas.
Stabilized sludges are more structurally sound than raw
sludge and are not thixotropic in nature. The safety hazards
are therefore reduced to those of conventional materials hand-
ling and heavy equipment operation. It should be noted that
some of the stabilizing additives are caustic and must be hand-
1ed carefully.
The safety hazards to the general public are also a factor
of the load supporting characteristics of the sludge. Potential
dangers can be averted by fencing the site and by posting appro-
priate warning signs.
The dangers to animals and livestock is also determined by
the load supporting properties of raw sludge. Limiting access
is the best defense against this problem. In dry areas, wild
animals and livestock may be tempted to cross a crusted pond to
reach the wet area for drinking water. Once the animal becomes
mired in the material, his chances of escape would be minimal
unless aided by man.
ECOLOGICAL CONSIDERATIONS
FGD sludge disposal operations have potential for adverse
impact on the surrounding ecosystem. Of primary concern are:
« The aquatic environment;
• The terrestrial environment;
• Irrigated agriculture and livestock.
This discussion will evaluate the accessibility of FGD
sludge and its contaminants to the above listed ecosystems.
Aquatic Environment
Sludge disposal may affect the aquatic environment through
either accidental release to a waterway or through intentional
discharge to surface or groundwater. Surface and groundwater
discharge is generally continuous; accidental discharge is a
random, possibly catastrophic event.
170
-------
Catastrophic Events--
Figure 20 illustrates the change in the sludge contaminant
pathway due to catastrophic sludge release. Since large volumes
of cooling water are required to operate a fossil fuel-fired
power plant, most plants are located near a large body of water.
Installation of FGD units on these power plants entails a large
number of pipes to carry the slurries around the scrubber and
associated materials handling systems. Pipelines also usually
carry the sludge to disposal areas. Depending upon system
design, a pipeline break could result i& the accidental dis-
charge of the slurry into a watercourse. Dike failure at a
disposal pond may release several years' supply of sludge into
a waterway in only a few hours, producing a truly devastating
event.
Pipe failure — The consequences of a major pipe failure can
be suggested by outlining the effects of accidental sludge
release into a major river with a flow rate of approximately
5,000 cfs. This flow rate is comparable to that of the Colorado
River as it flows across Colorado/Utah border. The solubility
of oxygen in water is on the order of 7 ppm; the river would be
transporting roughly 1 kg/sec of oxygen past any particular
point. A 1,000 megawatt power plant using 3 percent sulfur
fuel with an 85 percent FGD efficiency would produce 7.5 kg/sec
of calcium sulfite hemihydrite, or approximately .93 Ibs/sec of
COD. Under these conditions, a sludge released into the adja-
cent river during a pipeline failure would effectively absorb
all the oxygen in the water, and kill all aquatic life in the
vici ni ty.
The impact on aquatic life forms from suspended solids will
vary but are experted to be minimal. The flow rates character-
istic of such a pipe break are relatively small in comparison
to the total flow rate of the river. Most aquatic organisms
can endure relatively high concentrations of suspended solids
for short periods of time. Fish are able to clear their gills
of suspended sediments, but this requires metabolic energy and
stresses the fish. This is usually not fatal until suspended
solids levels exceed several thousand ppm. In the case of a
pipe break, from 10 to 100 ppm suspended solids could be
expected depending on the amount of ash contained in the sludge.
The site-specific nature of any accident requires that
each plant and its associated water course be individually
evaluated. Estimations of potential hazards should include the
flow rate of the river, the potential oxygen transfer capabili-
ties of the river system, and the probably flow rates and sul-
fite content of the sludges in question. The severity of an
accidental sludge discharge from pipe failure may be reduced if:
171
-------
ATMOSPHERE
POWER
PLANT
SO SCRUBBER
ACCIDENTAL
RELEASE OF
SLUDGE
CATASTROPHIC EVENT
SLUDGE
HANDLING
SLUDGE
DISPOSAL
SURFACE
WATER
GROUNDWATER
STORAGE
AQUATIC
ENVIRONMENT
TERESTIAL
ENVIRONMENT
IRRIGATED
AGRICULTURE
LIVESTOCK
Figure 20. Comparison of FGD sludge contaminant pathways
totheenvironment.
-------
• The water velocity is sufficiently low to permit rapid
settling of the calcium sulfite crystals;
• The river flow is non-uniform, so that there are pockets
in the river where the fish can escape the reduced oxy-
ten conditions;
t The calcium sulfite crystals through the water column
are more highly concentrated at the bottom, with very
low concentrations at the surface; this provides a thin
layer of surface water where the fish can survive.
When estimating the effects of pipeline breaks, it should
be noted that the required oxygen levels for fish vary according
to species. The more sensitive species, trout and salmon,
require oxygen levels about 5 ppm; severe metabolic stress is
experienced below 4 ppm. Some of the more hearty warm water
species such as carp, can survive in as little as 2 ppm oxygen.
Fish are capable of searching for high oxygen areas when
they are being stressed by a low oxygen environment. Even
bottom-dwelling fish such as catfish may be seen at the surface
of water bodies whenever the oxygen level drops below 4 mg/ .
In a fash-flowing river maintaining undissolved calcium
sulfite in suspension, oxygen depletion might extend many miles
downstream from the point of discharge before reaeration from
the atmosphere could oxidize all the sulfite to sulfate and
reoxygenate the water. A smaller river or stream would, of
course, be more severely impacted.
The potential impact of the accidental release of sulfite
sludge into a water course can also be estimated by examining
oxygen depletion in rivers receiving sanitary waste. In terms
of oxygen depletion, an accidental sludge discharge from a
1,000 megawatt power plant would have roughly the same effects
as the discharge directly into a watercourse of raw sanitary
waste from a city of about 300,000 people. In other words, an
accidental FGD sludge spill will have about the same impact on
the oxygen levels of a receiving water as the discharge into
the same waterway of untreated municipal waste from one third
of the population being served by that power plant.
Dike failure--If sludge is disposed of in ponds the pos-
sibility of dike failure and spill into surface waters exists
whenever the elevation of the pond is greater than that of the
local watercourse- Kike failure of FGD sludge disposal ponds
has not yet occurred. However, dikes have failed in ponds con-
taining other waste materials, such as acid mine drainage sludge
and phosphate slimes.
73
-------
Dikes can fail for a number of reasons. Many signs of
impending failure have unique visible characteristics which
can aid in diagnosis. These include rotational slips, surface
slips, and flow type slides in addition to other slope movements
such as creep and backsapping (a concentrated areas of erosion
which continues to progress up the slope, the product of an
intermittent flow of water on the downstream face).
General factors affecting embankment stability include:
• Size factors: height, width, volume;
» Slope steepness;
• Slumping, sloughing, sliding (superficial or deepseated);
• Cracks parallel to the embankment crest or to stream
direction;
• Seepage: location, volume, carrying solids;
• Freeboard;
• Soils and downstream tow area;
• Bank erosion;
• Embankment vegetation;
• Phreatic surface.
These factors are related to the materials, methods of dike
construction, and the types of underlying soils.
Accidental release of FGD sludge would produce an immediate
physical impact on an adjacent watercourse. Once the sludge
wave had dissipated, the total suspended solids and chemical
oxygen demand would continue to devastate the surrounding area.
The total suspended solids loading would wither smother or bury
aquatic life forms until sufficient percentage of the material
had settled out. Beyond that point, the remaining suspended
solids (10,000 to 100,000 ppm) would continue to absorb oxygen
from the water. As long as the flow velocity was fast enough
to maintain the remaining material in suspension, all aerobic
aquatic life forms would suffocate. This action would last
until the calcium sulfite crystals settled out or oxygen demand
was satisfied. As long as calcium sulfite existed in large
quantities on the river bottom, an increase in flow velocity
could stir it up. Resuspended, it could exert an oxygen demand
on the entire water column. As a result, it could be very
difficult to successfully stock a river with fish for a long
time after such an event.
174
-------
It is estimated that the COD in one 300 hectare-meter
sulfite sludge pond would be sufficient to remove all the dis-
solved oxygen from virtually any lake or several hundred miles
of a large river. However, in a lake-type environment, rapid
settling of the sludge would limit the impact to that of the
immediate area of discharge.
Considering the number of dikes and ponds in use and the
comprehensive regulations governing their construction, the
probability of dike failure is low. Should such accidents occur,
however, the environmental consequences could be severe.
Surface and Groundwater Discharges--
In addition to accidental discharges to surface waters,
water from an FGD sludge pond can enter the aquatic environment
through (1) an intentional direct discharge to surface waters
or (2) percolation of pond water through underlying soils to
groundwater supplies. The possibility of a direct surface
discharge depends upon details of disposal site design. At
this time, no existing FGD system discharges pond water to sur-
face waters on a continuous basis; they are currently all
designed to produce no direct discharge. Percolation rates will
depend upon local site characteristics and disposal techniques.
Important discharge charcteristics include the concentra-
tions of total dissolved solids and trace contaminants.
Relatively small flow rates are involved. Flow rates from
an S02 scrubber are generally more than an order of magnitude
less than the discharge flow rates from a cooling tower. At
once-through cooling plants, the cooling water dominates all
flows in the facility. Therefore, considering the total flow
rate in most power plants, any surface water discharge could be
diluted by other plant flows.
Although sludge liquors may contain as much as 15,000 ppm
TDS, many fresh water fish commonly found in the United States
could easily tolerate these conditions. Adronomous species of
fish are able to tolerate salt concentrations several orders of
magnitude greater than that of typical sludge liquors. Trout,
for example, can tolerate the salinity of full strength seawater,
or 3.5 percent TDS. Most aquatic plants are equally tolerant
of slat concentrations up to several thousand ppm. It seems
likely, then, that high dissolved solids concentrations will
have a minimal effect on aquatic life forms.
Specific elemental contaminants contained in the sludge
might have some impact on the aquatic ecology. In general, the
heavy metal tolerance of fish increases with TDS tolerance. The
metal of primary concern is mercury. Mercury has certain
special properties; in the leachate entering surface water
175
-------
supplies it may be absorbed by the sediments in the water body.
Bacteria in the sediments convert elemental mercury or other
insoluble mercury compounds to methyl mercury, the 'most toxic
form of mercury. Moreover, as a consequence of its nonpolar
nature, it can accumulate in the biological system.
In summary, the low concentrations of most trace metals in
FGD sludge leachate would not appear to present a problem to
nearby aquatic life forms through groundwater discharge. Direct
exposure to the IDS levels present in sludge leachate could
harm certain aquatic life forms. Accidental release of sludge to
surface waters could suffocate nearby aquatic life and stress
fish life due to the expected high levels of suspended solids.
Irrigated Agricultural Considerations
When estimating the potential impact of FGD sludge leachate
or liquor on irrigated agriculture, the most important con-
taminants are IDS, selenium, and boron. None of these is readily
absorbed by soils. These contaminants can therefore enter the
ground or surface waters. After leaving the site, these impuri-
ties may enter an irrigation system. The adverse impact of
these components on agricultural lands is documented. A high
TDS concentration in irrigation water requires modification of
irrigation practices in order to prevent high salinity in the
root zone of the plants. The impact of saline irrigation on
crop yields has been extensively studied, particularly in the
southwestern U.S., where the problem is most prevalent.
The effects of salinity on various crops grown in the
southwest are shown in Figure 21. This figure includes the
range of values found in typical FGD sludge liquor, and shows
that it would be unreasonable to use the undiluted liquors for
irrigation on a majority of crops.
The salt loading by irrigated agriculture in the upper
Colorado basin can be compared to the total potential salt
loading of all flue gas desulfurization systems installed by
1985. If all of these FGD systems were to utilize unlined
ponds, and had an underlying soil permeability on the order of
10-6, the total salt loading from FGD pond leachate by 1985
would still comprise only an insignificant amount of the salt
loading contributed at present by irrigated agriculture in the
upper Colorado basin (Ref. 170).
Boron is also of concern to irrigated agriculture. Dif-
ferent crops have different sensitivities to boron in irrigation
water and soil. The effects of boron on sensitive, semi-toler-
ant, and tolerant crops is shown in Table 36. A boron concen-
tration of over 3.75 mg/£ is unsuitable even for the most
tolerant crops. Boron concentrations in FGD sludge liquors
range from 0.1 to 6.3 mg/jj, . Leachates falling within the low
176
-------
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16
18
ELECTRICAL CONDUCTIVITY OF SOIL SATURATION EXTRACT, MILLI MHOS/CM, 25°C
Fi gure 21 .
Salt tolerance of major crops grown in the
Colorado River basin (Ref. 170)
-------
TABLE 36. PERMISSIBLE LIMITS FOR CONCENTRATION OF
BORON IN SEVERAL CLASSES OF WATER FOR IRRIGATION*
CO
Class of Water
Excel 1ent
Good
Permissi ble
Doubtful
Unsui table
Concentration of Boron in mg/£
for crops that are:
Sensitive
Less than 0.33
0.33-0.67
0.67-1 .0
1.0-1.25
Over 1.25
Semi to!erant
Less than 0.67
0.67-1.33
1 .33-2.0
2.0-2.5
Over 2.50
Tolerant
Less than 1.0
1.0-2.0
2.0-3.0
3.0-3.75
Over 3.75
Ref. 101
-------
end of this range would be acceptable for even the most sensi-
tive crops. Concentrations of boron in the sludge itself can
range from 41 to over 200 mg/£ , depending on the ash content
of the sludge. Boron will be contained in the sludge for poten-
tial leaching over a very long period of time.
Selenium is a unique case, as was mentioned earlier in this
chapter. Selenium can be a nutrient at low concentrations or a
toxicant at high concentrations.
With the exceptions of selenium and boron, the other
elemental contaminants contained in the liquid effluent and
leachate from FGD sludge disposal systems are of no agricultural
significance at the concentrations typical of FGD sludge lea-
chate. In fact, studies are underway to investigate the use of
dewatered sludge as a fertilizer additive of filler material
in certain agricultural areas.
Li vestock
The effects of FGC sludge liquor consumption on livestock
could conceivably be a local problem under unusual circum-
stances. The salt tolerance limits of domestic livestock are
specific to each animal, although generally between 3,000 to
12,000 ppm. As FGD sludge is ordinarily at the low end of this
range, minimal dilution would render the leachate or superna-
tant harmless in terms of TDS.
The metals and toxic anions noted previously under Health
Effects are equally important here. Metals such as lead and
mercury are accumulated in animals and man alike, and could
present a problem with livestock. The available chemical form
of each element is important, but further investigation of
speciation and effects on livestock is necessary.
Well water used for livestock consumption would probably
be affected only by selenium and fluoride from FGD sludges.
Mercury again would generally be absorbed by the soil before
the leachate reached the well. Selenium would also be absorbed
to some degree, but fluoride would migrate through the soil at
approximately the same rate as the TDS.
Aesthetics and Land Use
The aesthetic impact of an FGD sludge disposal operation is
strongly site-specific. Local variables include public proxi-
mity, appearance of the operation, and site reclamation poten-
tial. Untreated sludge ponds resemble other common ponding
operations, e.g., ash ponds, sewage lagoons, raw water supplies,
storage reservoirs, etc. Obviously, disposal site location,
grading, landscaping, and access roads should be designed to
minimize public view and proximity to this site.
179
-------
The appearance of the disposal operation will also be
affected by the mode of sludge transport and the treatment of
small spills. Pipeline transport is a relatively clean opera-
tion. Truck, rail, and barge transport are likely to produce
a certain amount of spillage during loading and transit. These
problems can be minimized through selection of appropriate
equipment and operating procedures.
After site decommissioning, cover material which will
support vegetation should be considered. Revegetation to im-
prove the appearance of a disposal site, however, may conflict
with the design objective of minimizing leachate generation.
Vegetation of a covered site will reduce the surface water
runoff rate, permitting more water to percolate through the fill
material into the underground aquifer. Since stabilized sludges
generally have significantly different physical properties than
untreated sludges, vegetation and landscaping can be promoted
with minimal pollution problems. A recent study of public
reaction to solid waste disposal practices (Ref. 172) reported
that more than half of those citizens who object to landfill
disposal would find it acceptable if the site were to be
recalimed as a recreation area.
180
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SECTION IX
SELECTION OF CHEMICAL AND PHYSICAL
REGULATING PARAMETERS
RATIONALE FOR CHEMICAL REGULATING PARAMETERS
Various rationale are available for establishing chemical
regulating parameters for FGC sludge disposal. Under normal
disposal conditions, the important environmental considerations
related to chemical characteristics are groundwater and surface
water protection. Hence, the chemical regulating parameters of
interest would be those associated with the liquid phases of the
sludge rather than the solid phases.
The chemical regulating parameters selected should satisfy
the following criteria:
0 Accurate correlation with environmental impacts
• Usefulness as an indicator of the migration of many
contaminants aside from itself
• Simplicity of measurement
t High measurement accuracy and reproducibi1ity
• Low analytical cost
Section VIII discussed the chemical parameters of major
concern when assessing FGC sludge environmental impact. The
following chemical parameters could possibly have adverse
environmental impacts at the disposal site:
Total dissolved solids (TDS)
Boron
Fluoride
Mercury
Lead
Selenium
the
If large volumes of sludge accidently enter a water course
COD concentration will also be important.
181
-------
Generally, the regulating agency will not be concerned with
the chemical contaminant concentrations of the FGD sludge liquid
phase itself, but rather will concern itself with the rate of
escape of these contaminants from the disposal site into the
surrounding environment. As discussed in Appendix A, differing
rates of chemical contaminant escape will be acceptable for
different sites, depending upon the specific site conditions.
The problem then is selection of the chemical parameters which
are best for measuring the rate of escape of chemical contami-
nants from the site.
Groundwater monitoring programs should be designed to warn
of contamination by a disposal site in time for corrective action
to be taken. Both concentrations of contaminants in leachate and
the rate of leachate migration are important. The rate of con-
taminant movement through a soil varies according to soil
composition and other site conditions. Of the chemical
parameters which are useful indicators of leachate migration,
TDS concentration is the simplest to measure. Sodium and calcium
salts are the major components of TDS in FGC sludge liquors.
Under normal soil conditions, cation exchange sites on soil
particles are occupied by sodium and calcium ions. This would
preclude ion exchange reactions with sludge leachate TDS,
allowing the TDS profile to penetrate the soil faster than most
other measurable parameters.
In view of these considerations, the TDS concentration is
the best chemical regulating parameter for groundwater monitor-
ing of FGD sludge disposal sites. A review of Section VI "Waste
Characterization" shows that the relationship between the liquid
phase TDS concentration and the concentrations of the other
chemical contaminants of concern are as shown in Table 37. By
regulating the TDS contaminant escape, control of all the other
contaminant of concern is also achieved.
It would, of course, be necessary to periodically measure
the liquid phase concentrations of all the contaminants of
possible concern listed in Table 37 to verify that the ratios
between TDS and each contaminant were remaining sufficiently
high to ensure that TDS was a reliable "indicator." Such
periodic liquid phase analysis would warn of unusual situations
where the ratio of TDS to concentration of other contaminants
was lowered by dilution, and limits upon TDS mass transport
from the site might require appropriate modification.
RATIONALE FOR PHYSICAL REGULATING PARAMETERS
The physical properties of FGC sludges are important to the
following disposal site considerations:
« Future 1 and use
• Rate of mass transport of contaminants from the site
182
-------
CO
oo
TABLE 37. CHEMICAL CONTAMINANT RELATIONSHIPS
IN FGC SLUDGE LIQUID PHASE.
Contaminant
Total Dissolved
Solids (TDS)
Boron (B)
Fluoride ( F )
Mercury (Hg)
Lead (Pb)
Selenium (Se)
Typical Co
Range
Low
2500
8
0.7
.001
.001
.001
ncentration
. mg/1
High
95000
41
70
.07
.55
2.7
Ratio o
C o n t a m i
Low
1 :1
300:1
3600:1
2.5M:1
2.5M.-1
2.5M:1
f TDS to
nant
High
1 :1
2300:1
1300:1
135K:1
172K:1
35K:1
Drinking Water Standards
TDS/Contaminant*
1 :1
250:1**
500:1
250K:1
10K:1
10K:1
* Federal Register, p. 59570, December 24, 1975, assume 500mg/l
** Assumed Limit of 2.0mg/l Boron (Irrigation Water Quality).
M = 106
K = 103
TDS standard
-------
• Sludge flow during accidental catastropic release.
The relevant physical properties for untreated and stabil-
ized sludges were discussed in Sections VI and VII, respectively.
Load bearing strength is the physical property most often
associated with land use restrictions. In areas where construc-
tion is anticipated, a structurally stable sludge is often
necessary. However, engineers can design foundations to compen-
sate for variations in site characteristics. Buildings have
been built on soft clays, thixotropic clays, sanitary landfills,
and other equally poor structural conditions.
Load bearing strength of the closed disposal site should be,
at a minimum,sufficient to support recreational uses. Once
these minimum criteria are met, light construction would
probably present little problem on a closed and reclaimed pond
or landfill of normal depth (5 to 20 meters). Actually load
bearing strength is often correlated with high compression and
the low permeability often accompanying it. This could create
problems in residential developments when trying to cultivate
lawns, shrubs, and trees. Load bearing strength should there-
fore be used as a regulating parameter only in tandem with the
specific proposed use of the reclaimed site and the desired
permeability for groundwater protection.
For agricultural use, the reclaimed disposal site should
have the following physical characteristics:
• Good site drainage;
• High rain water input through the sludge surface to
flush out the soluble salts;
• Little or no sulfite content or COD;
0 Soft structure with high void volume.
If the sludge is first stabilized before disposal, the
feasibility of using the site for agricultural purposes is
actually reduced. Most commercially available processes reduce
the sludge permeability and increase the pH, both of which
decrease the availability of plant nutrients such as phosphorus,
iron, and zinc. Even covering the site with top soil may not
work without adequate planning for drainage of the added soil.
Conversely, the chemical properties of raw sludge would also
make the reclaimed site unsuitable for agricultural use (TDS,
pH, and boron contents).
Establishing a physical regulatory parameter for FGD sludge
disposal in agricultural areas is therefore of little value due
to this dichotomy.
184
-------
One physical characteristic of certain FGD sludges which
can strongly affect the range of potential site reclamation
schemes is their thixotropic nature. This property allows the
sludge to change state from a solid to a liquid upon heating,
vibration, or other loadings without a change in moisture
content. This phenomenon depends upon the specific sludge and
its moisture content. It is a hazard to buildings and other
objects on the site unless accounted for through stabilization
or proper foundation design.
Thixotropic sludges are also a potential hazard during
impoundment failure. The vibration accompanying the catastrophic
release of supernatant may be sufficient to liquify the settled
material. Sulfite sludges in particular exhibit this behavior;
these sludges also exert high COD, therefore compounding the
problem. With non-thixotropic sludges, the amount of solids
which would exit through a dike break would be much smaller.
Re suspension of settled solids would be minimal in comparison
to the 1iquificat ion of the solid mass.
The physical properties of FGD sludge which affect the mass
transport of contaminants are sludge permeability and hydraulic
head. For a given hydraulic head, the lowest permeability
between the sludge and the underlying soil will determine the
.rate of leachate movement. Similarly, a large hydraulic head
will drive leachate through even low permeability sludge. These
two physical parameters should certainly be employed as evalua-
tion criteria, but the overall rate of mass transport from the
disposal site is the real regulating parameter. It is a function
of both physical and chemical parameters of the sludge and the
site. The rate of mass transport is determined using a chemical
regulating parameter.
Based on the above discussion, it appears that no one
physical parameter can be used to regulate FGD sludge disposal
in an absolute fashion. As load bearing strength and thixotropy
are the most important physical characteristics to a disposal
operation, the best physical regulating parameter is stability
as it relates to load bearing strength. Stability is a qualita-
tive measure of a materials load supporting properties, based
both upon present strength and changes in physical properties
with time.
Stability as it is used here is a relative measure. There
is no absolute division between stable and unstable sludge for
all applications, only for each individual disposal situation.
Stability can therefore be redefined as necessary for each
application.
Evaluation criteria for stability should be specific to
each site, with the principle criteria being (1) the eventual
use of the land, and (2) the expected time before that use will
185
-------
begin. For example, an urban sludge disposal site should be
stable immediately upon closure so that reclamation and use can
begin, with the degree of stability being dependent upon the
expected land use. A rural, non-agricultural site on the other
hand might not require immediate stability. Land use projections
would be needed, as well as some estimate of the stabilization
rate (e.g., natural dewatering, oxidation, compaction, etc.).
In other words, the physical properties of FGD sludge should be
regulated based on when the disposal site will support a reuse
function at some time in the future. That time and that function
are si te specific.
It appears that research is required to place quantitative
values upon the in-place stability over time of FGD sludge of
various compositions, both untreated and treated. Research to
date has not provided a sufficient data base for assessing in-
place stability for FGD sludge of a specific composition.
186
-------
SECTION X
THE COST OF FGD SLUDGE DISPOSAL
INTRODUCTION
The cost information presented in this section is based
upon data derived from other reports - data that were fragmented
and, in some instances, based upon minimal actual operating or
engineering cost information. This is understandable, since
none of the completed studies had cost analysis as a primary
objective. Several newer, as yet uncompleted studies, however,
are focusing on the development of comprehensive cost analyses;
these studies will become available during 1977 and 1978.
In light of the constraints imposed by limited data, this
section should be viewed as a digest of preliminary cost informa
tion available in late 1976, not as a definitive cost analysis
of FGD disposal alternatives.
A utility faced with control of an SOX emissions problem
has to make economic decisions in the following broad areas,
many of which are interrelated:
• Whether to convert to a low sulfur fuel, entirely
eliminating the need for an FGD system;
• If it is decided to install an FGD system that produces
throwaway sludge, the kind of scrubber units to use
(which, of course, affects the volume and character of
the raw FGD sludge generated);
• Pretreatment of the raw FGD sludge, e.g., dewatering
and filtration (which again affects the volume and
character of the FGD sludge to be disposed);
• Mode of FGD sludge transport;
• Stabilization of the FGD sludge by noncommercial or
commercial processes;
• Method of final disposal.
This section provides cost information for the last two
economic decision areas, i.e., stabilization and final disposal.
187
-------
Reliable cost information in the other areas is not yet avail-
able.
PUBLISHED COST ANALYSES OF FGD SLUDGE DISPOSAL
Costs of lime/limestone throwaway sludge disposal have been
included in the following reports:
0 Solid Waste Disposal (Radian Corp., Ref. 135)
0 Disposal of By-Products from Non-Regenerable Flue Gas
Desulfurization Systems: Initial Report (Aerospace
Corp., Ref. 139)
0 Disposal of Flue Gas Cleaning Wastes: EPA Shawnee Field
Evaluation, Initial Report (Aerospace Corp., Ref. 47)
0 Sulfur Oxide Throwaway Sludge Evaluation Panel (SOTSEP),
Technical Discussion (Princiotta, NERC/EPA, Ref. 129).
These reports, due to their general nature, could not
include many site-specific variables in their analyses. The
assumptions made were necessarily broad in nature, and the only
sludge disposal alternatives considered were the following:
0 Stabilization using commercial systems offered by I U
Conversion Systems, Inc., Dravo Corp., and Chemfix Corp.
(Carborendum). Although these are not the only
commercially available processes, they received the most
attention in 1972-1976 EPA research.
0 Final disposal into lined ponds. Cost estimates for
unlined pond construction, although not provided by the
reports, were derived from the data presented, for use
in this analysis.
A review of the existing cost literature on FGD sludge
disposal revealed that each study defined a model plant upon
which to. base estimates. Variations of interest between plants
included the coal characteristics (percent sulfur and ash), the
power plant size and load factor, and sludge generation rate
based upon these other parameters. Table 38 lists the important
model plant parameters given by each study. These parameters
were used to derive FGD sludge disposal cost figures which could
be compared between studies.
Comparison of Cost Estimates
Table 39 summarizes the results of the cost data survey.
The table begins with the date of report and sludge generation
estimate per MWh from each data source. This information is
followed by an estimate of disposal costs per ton of dry sludge
188
-------
TABLE 38. MODEL PLANT PARAMETERS GIVEN IN
RECENT FGD SLUDGE DISPOSAL COST STUDIES
Parameter*
Date of Report
% Sulfur of Coal
% Ash of Coal
Plant Capacity in MW
Hours of Operation/Year
Million Tons Coal/Year
Tons Coal/MWh
Tons Dry Sludge/Ton Coal
Million Tons Dry Sludge/Year
Tons Dry Sludge/MWh
Radian
(Ref. 135)
May 1974
5/74
3
12
1000
6400
.4
.71
Aerospace
(Ref. 139)
May 1974
5/74
3
12
1000
6400
.65
Aerospace
(Ref. 141)
Aug. 1974
8/74
3
12
1000
4560
.46
Aerospace
(Ref. 47)
July 1975
7/75
1000
4380
.40
.28
SOTSEP
(Ref. 126)
Apr. 1975
4/75
3.5
12
1000
6400
.40
.69
*A11 tons are metric
-------
TABLE 39. SUMMARY OF FGD SLUDGE DISPOSAL SYSTEMS COST DATA BASE
UD
O
Disposal
Technique
Lined Ponding
**
IUCS
Stabil ization
Dravo
Stabil ization
Chemfix
Stabil ization
Tons dry sludge/MWh*
$ per Ton Dry Sludge
mills/kWh
$ per Ton Dry Sludge
mills/kWh
$ per Ton Dry Sludge
mills/kWh
$ per Ton Dry Sludge
mills/kWh
Radian
(Ref. 135)
May 1974
.111
—
1.65-2.76
.18-. 31
2.75-8.25
.30-. 91
11.00
1.20
Aerospace
(Ref. 139)
May 1974
.102
4.42-14.24
.45-1.43
3.30-5.52
.32-. 54
3.30-6.62
.32-. 67
11.02
1.12
Aerospace
(Ref. 141)
Aug. 1974
.102
5.00-9.00
.51-. 92
8.00-10.00
.82-1.02
4.00-12.00
.41-1.22
8.00-10.00
.82-1.02
Aerospace
(Ref. 47)
July 1975
.113
--
7.20-9.20
.82-1.04
5.80-8.80
.66-1.00
8.50-11.50
.97-1.30
SOTSEP
(Ref. 129)
Apr. 1975
.108
5.00-9.00
.54-. 97
8.00-10.00
.86-1.08
7.40-10.00
.80-1.08
8.00-10.00
.86-1.08
*A11 tons are metric
**Includes fly ash disposal
-------
and disposal costs in mills per kWh for each of the five alter-
nate means of disposal. It should be noted that estimates of
generated tons of dry sludge are similar in all studies. More-
over, the technique of presenting data from each study and for
each disposal alternative in terms of disposal cost per ton dry
sludge and disposal cost/kWh allows (1) comparisons between
references for a particular disposal alternative and (2) compari-
sons between alternatives for a given study. On the basis of
such comparisons, it appears that cost estimates for the various
disposal options may be increasing over time and are also
developing more narrowly defined ranges. These trends are con-
sonant with general cost inflation and with developing under-
standing of technology requirements for disposal implementation.
Appendix A of this report discusses conditions under which
unlined ponding may be environmentally acceptable; it is a fact
that most FGD sludge is disposed into unlined ponds. Cost
estimates for this disposal alternative were not explicitly
developed by the three studies that discussed artificially lined
ponds. However, Table 40 presents a method for obtaining unlined
ponding estimates from the liner cost information provided by
these studies. The first six items in Table 40 are merely
restated from Table 39 or from the preceding discussion of each
data source.
The estimated liner costs in terms of dollars per ton dry
sludge and mills per kWh are derived from the preceding items
in the table. That is, the liner cost per ton dry sludge is the
product of liner cost per ton processed and tons processed per
ton dry sludge. Similarly, mills of disposal costs per kWh is
the product of the liner cost per ton dry sludge and tons of dry
sludge per MWh. The last two items in Table 40 were derived by
subtracting the appropriate estimates of liner costs from the
published estimates of lined ponding disposal costs.
With these estimated disposal costs for unlined ponding,
it is now possible to summarize, in Table 41, the available cost
information for the state-of-the-art in FGD sludge disposal
alternatives. The table does not include cost estimates for
such disposal alternatives as mine or ocean; the feasibility of
such alternatives is highly site-specific. The costs of ocean
and mine disposal are currently being developed by A. D. Little,
Inc., as part of the EPA FGD Waste and Water Program, and the
State University of New York.
In Table 41, it appears that unlined ponding is approxi-
mately $3 to $10 less expensive per ton of dry sludge and
approximately .3 to 1.0 mills less expensive/kWh than lined
ponding. Moreover, Table 41 appears to show that both unlined
and lined ponding is less expensive than commercial stabiliza-
tion for power stations that have a choice under current
191
-------
TABLE 40. COMPUTATION OF UNLINED PONDING COSTS FROM AVAILABLE
INFORMATION*
Disposal
Item
Lined
Ponding
Estimates
of Pond
Liner Costs
(Installed)
Estimated
Unlined
Ponding Costs
Source
Data
Tons Dry Sludge/
MWh
$/Ton Dry Sludge
Mills/kWh
Tons Processed/
Ton Dry Sludge
$/Ton Processed
$/Ton Dry Sludge
Mills/kWh
$/Ton Dry Sludge
Mills/kWh
Aerospace
(Ref. 139)
May 1974
.102
4.42-14.24
.45- 1.45
2
1.38- 5.01
2.76-10.02
.27- 1.02
1.66- 4.22
.17- .43
Aerospace
(Ref. 141)
Aug. 1974
.102
5.00-9.
.51- .
2
1.50-2.
3.00-5.
.31- .
2.00-3.
.20- .
00
92
75
50
56
50
36
SOTSEP
(Ref. 129)
April 1975
.108
5.00-9.00
.54- .97
2
1.50-2.75
3.00-5.50
.32- .59
2.00-3.50
.22- .38
* All tons are metric
-------
TABLE 41. SUMMARY OF FGD SLUDGE DISPOSAL SYSTEMS COST DATA BASE,
INCLUDING UNLINED PONDING*
V£>
Di sposal
Technique
U n 1 i n e d
Ponding
Lined
Ponding
IUCS**
Fixation
Dravo
Fixation
Chemf i x
Fixation
Disposal
Costs
$/Dry
Mills/
$/Dry
Mills/
$/Dry
Mills/
$/Dry
Mills/
$/Dry
Mills/
Ton Sludge
kWh
Ton Sludge
kWh
Ton Sludge
kUh
Ton SI udge
kWh
Ton Sludge
kWh
Radian Aerospace
(Ref. 135) (Ref. 139)
May 1974 May 1974
1.66-
.17-
4.42-1
.45-
1 .65- 2.76 3.30-
.18- .31 -28-
2.75- 8.25 3.30-
.30- .91 .28-
11 .00 11 .02
1 .20 1.12
4.22
.43
4.24
1 .43
5.52
.46
6.62
.55
Aerospace Aerospace
(Ref. 141 ) (Ref. 47)
Aug. 1974 March 1976
2.00-
.20-
5.00-
.51-
8.00-1
.82-
4.00-1
.41-
8.00-1
.82-
3.
•
9.
•
0.
1 .
2.
1 .
0.
1 .
50
36
00
92
00 7.20- 9.20
02 .82- 1.04
00 5.80- 8.80
22 .66- 1.00
00 8.50-11.50
02 .97- 1 .30
SOTSEP
(Ref. 1
April
2.00-
.22-
5.00-
.54-
8.00-1
.86-
7.40-1
.80-1
8.00-1
.86-
29)
1975
3
9
0
1
0
•
0
1
.50
.38
.00
.97
.00
.08
.00
08
.00
.08
* All tons are metric
** Includes fly ash disposal
-------
regulations. In addition, it appears that noticeable cost
differentials also exist between the commercial stabilization
processes.
Table 41 cannot be used to predict (except in very general
terms) the actual cost ranking of alternatives that a given
power station will experience. These cost estimates were
developed for a hypothetical 1,000-MW power station; they provide
only a slight indication of how changes in plant size or location
would affect the hierarchical ranking of the alternative cost
estimates. An option that appears to be relatively inexpensive
for the hypothetical 1,000-MW plant might very well prove to be
more expensive for a smaller system, when scaled down to the
requirements of the smaller system. In addition to scale
economies, many other site-specific variables, such as land costs
of availability of input raw materials, will determine the
disposal regimes actually available to a given utility. Stabil-
ization processes such as IUCS which include fly ash disposal
will show an economic credit for normal ash disposal operations.
FORTHCOMING COST ANALYSES OF FGC SLUDGE DISPOSAL
The preceding section summarized currently available cost
information for FGC sludge commercial stabilization and pond
disposal. Several more detailed economic studies are presently
in progress. Two of these studies are:
• Conceptual Design and Cost Studies of Alternative
Methods for Lime and Limestone Scrubbing Waste Disposal
(Tennessee Valley Authority, Interagency Agreement No.
D5-E-721)
• Environmental Effects and Control of Various Flue Gas
Cleaning FGC Sludge Disposal Options (SCS Engineers,
EPA Contract No. 68-03-2471)
TVA: Conceptual Design and Cost Analysis of FGC Sludge Disposal
In this study, the Tennessee Valley Authority, Muscle
Shoals, Alabama, will use its extensive knowledge of the lime-
limestone scrubbing process and a cost-oriented computer model
to perform detailed economic evaluation of several FGC waste
treatment and disposal options. Iterative runs of the computer
model will use the following parameter variations:
• Power station size - 200, 500, and 1,500 MW;
t Power station age - new, 5, 10, and 15 years old, with
30 year 1 ife span;
• Coal sulfur - 2, 3.5, and 5 percent;
194
-------
• Coal ash - 12, 16, and 20 percent;
• Fly ash removal, separate and combined with S02
scrubbing;
t Sludge solids prior to disposal - 15, 35, and 60 percent;
• Lined and unlined ponding;
• Commercial stabilization - Dravo, IUCS, and Chemfix
processes; and
• Transport to disposal site - 1, 3, 5, and 10 mi.
The outputs of each scenario should provide a detailed
analysis of the various direct and indirect disposal costs over
each year of the remaining life of the power station and disposal
site. Study results are expected in late 1977.
SCS Engineers: Economic Assessment of FGC Sludge Disposal
The primary objectives of this project are:
Phase I. To develop a better understanding of the thermo-
dynamics and kinetics of chemical speciation in FGC sludge and
sludge 1iquors.
Phase II. To assess the economic impact of various FGC
sludge disposal regulatory approaches on the utility industry.
Phase II will involve the development of a detailed economic
impact document for national FGD sludge disposal regulations. A
family of cost curves will be developed relating disposal costs
to the goals of the ultimate disposal operation (i.e., reduced
permeability, increased load bearing strength). These costs will
be exemplified by several model power plants and a subsequent
analysis of regulatory impact on FGC sludge disposal operations.
Specifically, the following tasks are to be completed in
this study:
t Compile and evaluate information on the available sludge
disposal options and their associated regulatory
approaches;
• Standardize current cost information into unit cost
estimates for creation of typical sludge management
systems;
• Use these typical systems to generate a preliminary
assessment of the economic impact of regulatory compli-
ance on the u ti1i ty i ndu s try;
195
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• Verify the analysis inputs with a committee of industry
experts.
This study will utilize the information presented earlier
in this section and data from other economic studies completed
before mid-1 978.
196
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SECTION XI
APPLICABLE EXISTING STANDARDS/REGULATIONS
INTRODUCTION
The regulation of sludge disposal from flue gas desulfuriza-
tion (FGD) operations has not been uniform to date. Pending the
promulgation of specific guidance from federal regulatory
agencies, state and local agencies have generally relied upon
existing standards/regulations designed for the disposal of
other forms of waste.
Regulations that have been or could be applied to FGD
sludge disposal practices fall under one or more of the following
classifications:
Sol id waste di sposal
Hazardous waste disposal
Wastewater disposal
Water quality criteria for various beneficial uses
Comprehensive air quality criteria
Waste disposal to oceans
Waste disposal to mines
In implementing a sludge disposal plan, some FGD-equipped
power plants have had to comply with one or more of the above
regulations.
The major environmental problems potentially associated
with FGD sludge disposal include:
• Groundwater and surface water contamination from leaching
of trace metals and dissolved solids;
• Future beneficial use of the disposal areas;
• Failure of the sludge pond retaining structure and sub-
sequent discharge to surface waters;
• Floods or other extraordinary conditions that might
cause the sludge to enter the biosphere.
These potential problems may fall under several jurisdic-
tions in some states and go unregulated in other states. The
197
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purpose of this chapter is to summarize the applicability of
existing and/or proposed standards/regulations to the sludge
disposal techniques currently available. The applicability
criteria will in most cases regard the four potential environ-
mental problems listed above.
SOLID WASTE DISPOSAL
The predominant methods of solid waste disposal in the U.S.
are landfill and incineration. Other techniques account for only
a small percentage of the waste. Regulations governing the
disposal of solid wastes typically apply to specific waste
classifications such as municipal refuse, brush and tree wastes,
demolition and construction debris, sewage sludge, and bulky
wastes such as abandoned automobiles and appliances. Other solid
waste categories, specifically certain industrial sludges, are
sometimes mentioned as being similar to FGD sludge. These
categories are discussed in the subsection of this section
entitled "Hazardous Waste Disposal."
Of the four potential environmental concerns associated with
FGD sludge disposal, all but dike failure are used to evaluate
land disposal practices for solid waste. The percolation of
water through landfills has been shown to leach various organic
and inorganic contaminants from solid waste with the potential
of polluting ground and surface waters. Landfill sites are
generally situated outside of flood plains to avoid flooding and
severe erosion of the waste and cover material. Site reclama-
tion, although once considered unsafe, is now a common practice;
many recent landfill designs have predestined sites for use as
parks, golf courses, etc.
Regulatory agencies usually require that leachate and
flooding dangers be accounted for and that reclamation plans
be specified in the landfill design. The following is a summary
of federal and state solid waste disposal criteria as they may
apply to FGD s1udges.
Federal Solid Waste Regulations
In the past, regulation of solid waste disposal activities
in the U.S. has fallen under the jurisdiction of state and local
agencies. Until October 1976, federal agencies served only to
provide guidelines and technical assistance for solid waste
disposal, under authority of the Solid Waste Act of 1965. On
October 21, 1976, the Resource Conservation and Recovery Act
of 1976 was signed into law. This act, built on the Solid Waste
Disposal Act of 1965 and the Resource Recovery Act of 1970, by
statute establishes the Office of Solid Waste within EPA to
guide the implementation of the law, and establishes a federal/
state/local government partnership to share the implementation.
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The regulations which will be promulgated in April 1978
will define hazardous wastes and set forth a management control
system for these wastes. The effect of these regulations on the
generation and disposal of FGC wastes is as yet uncertain.
Should any portion of these wastes be defined as hazardous wastes
by either EPA or any of the states, a state permit system would
then be effected according to generation, transportation,
storage, and disposal criteria.
The U.S. EPA has formulated general guidelines and
recommended procedures for the land disposal of municipal solid
waste (Federal Register, 39(158):29327-37). Included under
"Requirements and Recommended Procedures (Subpart B)" are evalu-
ation criteria for potential groundwater contamination, flooding,
and site reclamation.
Recommended design considerations to protect water quality
at a land disposal site include specification of:
Groundwater elevation and movement
Initial quality of surrounding water resources
Soil and geological conditions
Potential for leachate generation
Location of monitoring wells
Testing procedure (24.204-2(a))
It is also suggested that leachate collection systems be
provided where necessary and that compliance with water quality
protection provisions be required.
With regard to flooding dangers, it is recommended that land
disposal sites "be protected against at least the 50-year design
flood by impervious dikes and other appropriate means" (241.204-
2(b)).
Site reclamation procedures should include a proper amount
of cover material and vegetative growth. Final cover should be
applied to completed areas or areas that will remain idle for
over a year and should be at least 2 ft thick (241.209-3(c)).
Vegetative growth should be promoted "as promptly as possible to
. . . improve (the) appearance of idle and completed areas"
(241.209-2(c)).
State Solid Waste Regulations
Examination of the solid waste regulations for each of the
50 states revealed some notation of groundwater protection,
flood plain consideration, and site reclamation in almost every
case. The degree of specificity varied significantly, however,
as many states prefer a permit system and reserve the right to
evaluate criteria on a site-specific basis.
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Many of the power plants employing FGD were subject to
disposal site approval by state solid waste agencies. Site
evaluation was usually limited to a soils analysis, including
permeability and chemical analysis. Contact with the state
agencies revealed that FGD site evaluation criteria were gener-
ally excerpted from applicable landfill requirements, since
specific FGD sludge disposal site evaluation criteria were not
available. As an example, the Pennsylvania Department of
Environmental Resources (PDER), Division of Solid Waste Manage-
ment, accepted monitoring responsibility for the fixated sludge
pond at the Duquesne Light Company's Phillips Station, yet they
referred the associated untreated sludge lagoons to another
division of PDER.
The following subsections specify detailed passages from
selected state solid waste management regulations that could be
excerpted to apply to FGD sludge disposal.
Leachate from Sludge Disposal--
Most states have adopted the federal recommendation for
protecting groundwater quality beneath solid waste disposal sites
without significant extrapolation. Some, however, have specified
modified restrictions which might be pertinent to site design
and location. Excerpts from nine such state regulations follow:
Iowa Solid Waste Title IV 27.1(5)(g). An acceptable landfill
site is:
1. So situated as to obviate any significant, predictable
lateral leakage of leachates from the landfill to shallow
unconsolidated aquifers that are in actual use or are deemed
to be of potential use as a water resource.
2. So situated that the base of the proposed landfill is
at least five feet above the high water table unless a
lesser separation is unlikely to have a significant effect
on ground and surface waters.
3. .Not in significant hydrologic subsurface or surface
connection with standing or flowing surface water.
4. Not situated in an unconsolidated sequence that will
permit more than 0.004 cubic foot of liquid per day per
square foot of area downward leakage into a subcropping
bedrock or alluvial aquifer if such an aquifer is present
beneath or adjacent to the proposed site. . .
5. At least 1,000 feet from any well in existence at the
time of application for the original permit. . .
6. At least one mile from a public water supply or well
or a public water supply water intake from a body of
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static water or one mile upstream or 1,000 feet downstream
from a riverine intake.
Indiana (SPC 8, Chapter III, Section 6).
c. In no case shall solid waste be deposited within an
aquifer. A barrier of undisturbed soil shall be maintained
between the lowest portion of deposited refuse and the
aquifer of a thickness to be determined by the Board based
upon permeability and ion exchange properties.
Maine (Title 38, M.R.S.A. 1302 406.1 Site Approval).
a. The surficial material soils, underlying the refuse to
a depth of at least 5 feet shall be well graded granular
material containing from 15-40% fines, and being relatively
free of cobbles in excess of 6 inches in diameter.
b. All refuse shall be placed at least 5 feet above
groundwater.
c. The site should be moderately sloped, i.e., less than
15 percent.
d. The site boundary shall not lie closer to a classified
body of water than 300 feet.
e. The site boundary shall not lie closer to the nearest
residence or potable water supply than 1,000 feet.
Oregon (Oregon Administrative Rules, Chapter 340, Division 6,
Subdivision 1).
4. Sewage Sludge Lagoon and Sludge Spreading Area Design,
Construction, and Operation.
a. Location.
Sludge lagoons shall be located a minimum of 1/4 mile
from the nearest residence other than that of the
lagoon operator or attendant.
e. Type of Sludge Lagoon.
Lagoons shall be designed and constructed to be non-
overflow and water tight.
h. Sludge Removal from Lagoon.
Water or sludge shall not be pumped or otherwise
removed from a lagoon, except in accordance with a
plan approved in writing by the Department.
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1 . Morn tori ng Wei 1s.
Lagoon sites . . . having . . . potential for contami-
nating usable groundwater resources may be required to
provide groundwater monitoring wells . . . Said
monitoring wells shall be sufficient to detect the
movement of groundwater and easily capable of being
pumped to obtain water samples.
Texas (Solid Waste Regulations, Section E, E-1.4 - Water
Pollution).
b. Solid waste shall not be placed in unconfined waters
which are subject to free movement on the surface, in the
ground, or within a larger body of water.
c. Solid waste shall be deposited in such a manner that
the possibility of leachate percolating into the ground-
water is minimized. An impervious barrier may be either
naturally occurring or artificially placed. The following
procedures are acceptable:
1. Placement of three feet of clay.
2. Placement and compaction of one foot of selected
clayey material under optimum moisture conditions.
3. Placement of an impervious membrane of asphaltic,
plastic, or other approved material.
f. If deemed necessary by the Department, monitor wells
will be drilled . . . to observe changes in the quality of
groundwa ter.
New Jersey (N.J.A.C. Rules 7:26-1 et seq. 7:26-2.6.4.3.).
Any solid waste facility accepting . . . chemical wastes
. . . shall install monitoring wells which are constructed
and located in accordance with instructions available from
the Department. Samples shall be taken from each well and
analyzed by a laboratory acceptable to the Department at
least once every three months . . . (also,) An acceptable
system of interception, collection, and treatment shall be
implemented . . . (as of) September 15, 1975.
Oklahoma (Disposal of Solid Waste, Regulation 5).
5.3 An impervious lining or membrane may be required by
the Department for a site or facility for any given waste
deposited therein. Plans and specifications for such a
lining or membrane must be approved by the Department before
installation or use.
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a. The use of natural or specific clays to develop any
necessary lining is permitted providing: That the
lining is at least 5 feet thick and that the permea-
bility index is no greater than 10"° cm/sec . . .
5.4.1 Soil Characteristics. The soil characteristics of
the subject disposal site used for land disposal of hazard-
ous wastes shall meet the following criteria:
a. The soil shall meet the classification of a clay
consisting of no more than seventy percent (70%) of
particles larger than 0.002 millimeters. The soils
shall be of inorganic nature and origin.
b. The permeability of the clay soil shall be no
greater than 10~° cm/sec . . . Soil testing shall be
performed ... to a depth of at least ten (10) feet
from the farthest reach of the disposal area in all
di rections.
Delaware (Chapter 1 - Disposal Regulation, Section 7, Industrial
Landfill Standards).
7.01 . . . The chemical and physical properties of the
industrial waste and its Teachability characteristics in a
neutral, acidic, and basic environment shall be documented.
The design shall include plans for a leachate collection,
treatment and disposal system.
7.03(g). All leachate shall be collected and treated so as
to provide a degree of removal of pollutants reflecting
the application of a practicable level of technology. The
extent of the design of this collection and treatment
system shall depend on the chemical and physical properties
of the industrial waste and in particular its Teachability
characteristics. When deemed necessary by the Department,
disposal areas and leachate collection ditches and ponds
shall be lined with an impermeable liner. A synthetic
impermeable liner shall be installed unless the applicant
can prove to the satisfaction of the Department that a
natural soil liner is impermeable . . . Wells or other
monitoring devices shall be installed.
Nevada (Solid Waste Management Regulations, Article 2).
2.6.1.b. Hazardous liquid wastes shall be processed in
such a manner so that the waste will be neutralized or
solidified.
c. A completed hazardous waste burial area shall be
covered with a layer of suitable cover material com-
pacted to a minimum uniform depth of thirty-six (36)
i nches.
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It should be noted that most states which require ground-
water monitoring during operation of the fill also require the
monitoring to continue for a specified period after closure.
Flooding and Drainage Considerations--
Most of the state solid waste disposal regulations address
the problem of flooding, and all regulations mention or specify
the fill slope necessary to divert runoff water.
Flood consideration varies with each regulation, from
simple mention of the potential danger to specifications regard-
ing site location based on flood probability. The following are
typical examples:
Montana (Administrative Code, Title 16).
6(c)(iii) . . . sites shall not be subject to flooding by
surface water or have a high groundwater table and shall
not be located within a 100-year floodplain.
Kentucky (401 KAR 2:010).
Section 9. (1) No landfill shall be exposed to a once in
five (5) year flood. Landfills exposed to a once in 100
year flood shall be protected. Where applicable, empirical
data shall be used to determine the frequency of flood
exposure. Where published data is not available, the
frequency of flood exposure shall be established by the
unit hydrograph technique.
Iowa (SW Title IV).
27.1(5)g. (5) Outside a floodplain or shoreland, unless
proper engineering and sealing of the site will render it
acceptable and prior approval of the Iowa Natural Resources
Council and where necessary the U.S. Corps of Engineers is
obtained.
Provisions to eliminate standing water from landfills would
obviously apply only to fixated or dried sludge lagoons. Most
landfills are designed to include a surface grade; several state
requirements are examples:
Oklahoma (Disposal of Solid Waste, Regulation 5).
4.1.23 Drainage of Surface Water. The entire site,
including the fill surface, shall be graded and/or provided
with drainage facilities to minimize runoff into and onto
the fill, prevent erosion of washing of the fill, drain off
rainwater falling on the fill and prevent the collection of
standing water. The final surface of the fill shall be
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graded to a slope of at least one percent, but no surface
slope shall be so steep as to cause erosion of the cover.
New Jersey (N.J.A.C. Rules 7:26-1 et seq.).
All lifts shall be graded so as to facilitate drainage
therefrom. Side slopes and working face shall not exceed
a vertical rise of one (1) foot for each horizontal distance
of two (2) feet.
Delaware (Chapter 1 - Disposal Regulations).
6.03(g) . . . Operations shall be planned and conducted so
rainwater is drained off the fill or disposal area at all
times. Standing water shall not be allowed on the fill at
any time. The completed fill shall have a minimum slope of
2% to facilitate surface drainage and a maximum slope that
precludes erosion.
Missouri (Board of Health Regulations).
2.52 A7. Provisions for surface water runoff control to
minimize infiltration and erosion of cover material. 0 n -
site drainage structures and channels should be designed
for at least a 20-year rainfall frequency.
Provisions for Site Reclamation--
The extent to which a landfill site is reclaimed is up to
the owner. Many states do, however, require a certain amount of
landscaping and planting to prevent devaluation of nearby proper-
ties, excessive erosion, or standing water accumulation.
Reclaimed site uses vary, but most landfills are developed into
recreation areas. The erection of structures over the fill is
generally not recommended due to structural instability and
subsidence. Site reclamation requirements set forth by several
states are enumerated below.
Oklahoma (Disposal of Solid Waste, Regulation 5).
4.1.24 Final Grading. The completed fill shall be graded
to serve the purpose for which the fill is ultimately
planned. The surface drainage shall be consistent with the
surrounding area. The finished construction shall not in
any way cause interference with proper drainage of adjacent
land nor shall the finished fill concentrate runoff waters
into adjacent areas. Seeding of finished portions of the
fill with appropriate vegetation to promote stabilization
of the cover shall be performed.
Hawaii (Environmental Laws and Regulations, Vol. II, Chapter 46).
Section 3B
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9. A completed landfill or a major portion thereof shall
be covered with at least two (2) feet of compacted earth
material, compacted, graded with proper drainage to minimize
soil erosion and sodded or planted immediately after the
grading work has been completed.
10. Provisions shall be made to maintain the landfill site
for at least one year after termination of operation to
prevent health hazards or nuisances from occurring. Main-
tenance shall include, but not be limited to, repair of
cracks or fissures, repair of areas where settling occurs
and control of problems which result from leachate or odors.
Compliance with these requirements shall be a basis for
future recommendations by the Department on land use.
Colorado (Regulations, Solid Waste Disposal Sites and Facili-
ties).
Section 4 j. Final Closure. Prior to closing a solid
waste disposal site except for cause as set forth in Section
36-23-13 CRS as amended, the final cover of the deposited
solid wastes shall be graded to the elevations which shall
be shown in the initial design. The cover shall be of such
thickness and material as will prevent the entrance or
emergence of insects, rodents, or odors. Such closure
elevations shall be such as will provide for the diversion
of rainfall and runoff away from the fill area.
Illinois (IPCB Rules and Regulations, Chapter 7).
Rule 318: Completion or Closure Requirements.
a. The owner or operator of a sanitary landfill site shall
monitor gas, water and settling at the completed site for
a period of three years after the site is completed or
closed.
b. The owner or operator shall take whatever remedial
action is necessary to abate any gas, water or settling
problems which appear during the three year period.
Summary of Solid Waste Disposal Regulations--
As groundwater contamination, flood control, and site
reclamation are all problems associated with FGD sludge disposal,
it is apparent from the preceding excerpts that many states
account for these same problems in their solid waste disposal
regulations. In order to demonstrate the applicability of these
regulations to sludge disposal operations, Table 42 summarizes
the groundwater, flood protection, and site reclamation regula-
tions for each state in which an FGD-equipped utility is
presently located. These regulations do not necessarily repre-
sent the requirements that were applied to the FGD systems
themselves, but serve only as an interpretation of the written
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TABLE 42. STATE SOLID WASTE REGULATIONS PERTAINING TO
SELECTED FGD SYSTEMS
ro
o
State
AZ
CO
FL
IL
KS
KY
MO
MT
NV
PA
Groundwater
General protection
General protection
Monitoring, possible
leachate collection
Monitoring, soil
analysi s
General protection,
soil analysis
General protection,
sol 1 analysi s
Moni toring , soil
analysis, possible
leachate collection
General protection,
soil analysi s
Stabilize or
neutrali ze
Monitoring, soi-1
analysis , possible
leachate collection
Fl oods
None
General rainfall
protecti on
Away from flood
plain
General rainfall
protecti on
None
100 yr flood
100 yr flood
100 yr flood
None
50 yr away from
f 1 ood plain
Rainfall
None
General rainfall
protecti on
General diversion
General rainfall
protection
None
General diversion
20 yr rai nf al 1
20 yr rai nfal 1
None
General diversion
Reel amati on
2 ft minimum cover
2 ft minimum cover,
33% slope (sides)
2 ft minimum cover,
50% slope (sides)
State approval
2 ft minimum cover,
revegetati on
2 ft minimum cover,
33% slope (sides)
revegetati on
2 ft minimum cover,
2 ft minimum cover,
2-4 slope
2 ft minimum cover,
1-15% slope
-------
regulations. Those state regulations that do not specifically
refer to the given problem are indicated by the word "none."
HAZARDOUS WASTE DISPOSAL
Federal regulations controlling the disposal of certain
industrial wastes could be applied to some extent to the disposal
of FGD sludges. Similarities between these industrial wastes and
FGD sludges are based on one or more common potentially hazardous
constituents and/or a similarity in disposal methods.
The industrial wastes covered in this subsection are:
Slimes from phosphate mining,
Acid mine drainage,
Gypsum from phosphoric acid manufacture,
Coal mi ne taili ngs , and
Coal ash disposal.
Although the emphasis here is on the various waste disposal
regulations, a brief description of each individual waste is
also presented.*
Phosphate Slimes
The mining and beneficiation of phosphate rock in the U.S.
produces an estimated 38 million tons of waste slimes annually.
About 75 percent of the country's phosphate mining is done in
Florida and the remainder in North Carolina, Tennessee, and
several western states.
Phosphate ore is mined primarily by the open pit method,
although some underground mining is done in the West. Ore
beneficiation involves a series of size reduction, washing,
desliming, and flotation operations.
While raw phosphate slimes account for approximately one-
third of the mined matrix, the various slurrying operations may
produce waste slimes that occupy more than 150 percent of the
original volume of mined material. Table 43 presents a range of
chemical compositions for typical phosphate slimes solids.
Slime Disposal--
Phosphate slimes have traditionally been disposed of in
decommissioned pit areas. Because of the volume increase from
beneficiation, the pit capacity is necessarily increased by
construction of earthen dams to form large settling ponds. The
slime slurry is usually 4 to 6 percent solids when discharged to
*Unless otherwise noted, the supplementary information is
excerpted from Ref. 135.
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TABLE 43.* CHEMICAL COMPOSITION OF
PHOSPHATE SLIMES SOLIDS
Chemical
P2°5
Si02
Fe203
A1203
CaO
MgO
co2
F
LOI (1 ,000°C) f
BPL#
Typi cal Analyses ,
Percent
9.06
45.68
3.98
8.51
14.00
1.13
0.80
0.87
10.60
19.88
Range
Perce
9 -
31 -
3 -
6 -
14 -
1 -
0 -
0 -
9 -
19 -
nt
17
46
7
18
23
2
1
1
16
37
* Ref. J35
f LOI - Loss on Ignition
# BPL - Bone Phosphate of Lime
209
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the settling pond. The colloidal nature of the solids makes
dewatering difficult, and the maximum attainable solids content
is 25 to 35 percent by gravity settling.
Research is under way to improve the dewatering potential of
phosphate slimes for increasing supernatant recycle, to reduce
settling pond area required, and to investigate possible slime
beneficiation. Investigation of mechanical dewatering techniques
has proved fruitless, due to high cost and limited effectiveness
(50 percent solids maximum) of the techniques. Current emphasis
is on improving the settling operation through the use of sand
tailings, either as a drainage base or by controlled mixing with
slimes in the settling basin. Preliminary indications are that
improved dewatering, up to 80 percent solids content, is attain-
able. Details of the various methods under study can be found in
the 1975 Annual Report for the Florida Phosphatic Clays Research
Project.
Regulation of Slime Disposal--
A limited amount of research has been done to determine the
extent of the various potential environmental hazards associated
with phosphate slime disposal. Areas of interest thus far have
been supernatant discharge, catastrophic dike failure, and pond
seepage.
There appears to be no evidence of harmful effects upon
aquatic life from slime pond supernatant release to nearby water-
ways, except for possible eutrophication due to the high
phosphorus content of the liquor. In studies performed before
pond liquor discharge was outlawed in Florida, no effect was
noted on aquatic life except for an increase in algae growth in
certain estuaries. No change in BOD was noted, although tur-
bidity increased slightly.
Seepage resulting in groundwater contamination has not
received attention as a problem area. Most phosphate mining
companies monitor the streams below their plants on a daily
basis, measuring water flow, suspended solids, phosphate, and
fluorine; however, information on groundwater monitoring was not
found in the literature.
The most critical potential slime disposal problem is
catastrophic failure of the impoundment dams. Several instances
of dam failure have occurred in Florida in the last 30 years;
the most recent in 1971 released 2 billion gal of phosphate
slime into the Peace River. All forms of marine life were
killed for 60 miles of the river and in Charlotte Harbor (Ref.
117).
There are currently no federal regulations governing the
disposal of slimes from phosphate mining operations. The state
of Florida, however, has enacted "Minimum Requirements for
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Earthen Dams, Phosphate, Mining and Processing Operations," for
the purpose of preventing failures of earthen dams. Although
existing requirements are specific to phosphate slime pond con-
struction and maintenance, they could also apply to the ponding
of FGD sludges due to the similar high COD concentration and
volumes. Table 44 lists several relevant excerpts from the
Florida requirements.
Acid Mine Drainage Sludge
The mining of coal and certain other ores exposes the pyrite
(FeS2) fraction to air and water, resulting in the formation of
dilute sulfuric acid (pH 2-3) and suspended and dissolved iron
su 1 fates.
Acid mine drainage (AMD) is normally treated to precipitate
the iron and adjust the pH. It is subsequently ponded to allow
for sedimentation, and the pond supernatant is drawn off and
discharged to surface waters.
An estimated 8.2 million tons of AMD sludge (1-5 percent
solids) are generated annually; Table 45 presents an analysis of
a typical treated sludge.
Disposal of AMD Sludge--
AMD treatment takes place in four stages: pH adjustment,
aeration, sedimentation, and disposal. The use of lagoons often
consolidates the last two stages.
Neutralization reagents commonly used are lime, hydrated
lime, and limestone; also used in some cases are sodium hydroxide
and sodium carbonate. The reagent used influences the settling
characteristics of the sludge. The carbonates yield a more
granular, dense sludge with better dewatering characteristics
than do hydroxides.
The purpose of aeration is to convert iron from the ferrous
state to the ferric oxidation state, which precipitates more
readily at low pH. Minimum solubilities for ferrous and ferric
iron are achieved at pH 8.5-9.5 and 6-7, respectively. As the
desired supernatant pH is 6-9, predominance of the ferric form
reduces the quantity of reagent necessary.
As noted above, sedimentation characteristics of a sludge
are primarily a function of the neutralizing reagent used.
Research aimed at improving the normal settling rate and
dewaterability of AMD sludge has considered both physical and
chemical means. Table 46 summarizes reported research results.
The most common method of final AMD sludge disposal is ponding.
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TABLE 44. EXCERPTS FROM CHAPTER 17-9 OF THE FLORIDA
RULES OF THE DEPARTMENT OF POLLUTION CONTROL
Section
17-9.01
17-9.03(1)(b)
ro
ro
17-9.03(l)(e)
17-9.03(3)
17-9.03(5)(bi)
17-9.04(2)
17-9.05(3)(c)
. . . There shal1 be
phate slime] dams
state of Florida.
Text
no discharge from [phos-
into the waters of the
A program of soil sampling and testing...
shall be performed...including, but not
limited to, the determination of in-place
densities, shear strength, and permeabilities
of the foundation and embankment soils...
Minimum construction safety factors: 1.75
for horizontal shear at the base of fill,
1.5 for horizontal shear within the fill
due to seepage within the outer face...
Material...for dams shall be free of..<
extraneous matter which could affect the
...permeability or shear strength of the
finished dam
If dewatered to not less than 50% solids,
the tailings may be deposited continuously
(if impounded above natural ground level)
The vegetative cover on retired dams shall
be maintained sufficiently low to permit
visual inspection of the soil surfaces...
..oInspection shall include...Determination
of seepage characteristics through analysis
of infrared aerial photographs or thermal
i m a g e ry
Relation to
FGD Sludge Disposal
Supernatant liquor
di s charge
Site characteristics
Pond construction
Pond construction
Pond operation
Pond reelamati on
Pond monitoring
-------
TABLE 45. * AMD TREATMENT PROCESS AERATOR
SLURRY ANALYSES
Concentration
Slurry water 99.83
Filterable solids (percent) .17
Solids analysis (percent):
Fe 10.9
Ca 43.5
Mg .4
Al -6
Si 1.6
so; 14.4
* Ref. 135
f The weight of aerator slurry retained on laboratory
filter paper as a percent of the total slurry
213
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TABLE 46 * RESULTS OF AMD SLUDGE DE-
WATERING RESEARCH
Technique Percent Solids Achieved
Vacuum Filtration
Lime treated 29.8
Limestone treated 45
Lime treated1" 22
Limestone plus lime1" 45
Limestone treated1" 63
Pressure FiItrati on
Batchwise 20-30
Semi continuous 25
Freezing 7.5
Thickener/Clarifying
Hydrated lime .9-4.98
Limestone 12
* Ref. 135
f Using diatomaceous earth as a filter precoat
214
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Disposal Regulations--
Regulations pertaining to the disposal of AMD sludges have
been enacted on both the state and federal level. These regula-
tions deal with the chemical character of the sludge and the
design and maintenance of the impoundment structures. Potential
applicability to FGD sludge disposal is found in the total
suspended solids (TSS) and pH effluent limitations, and pond
design guidelines.
A summary of existing effluent limitations for AMD liquors
is presented in Table 47. Effluent limitations for TSS, iron,
and pH have been implemented in Pennsylvania and West Virginia
due to the predominance of deep mining. Federal regulations
have also been applied to a variety of mining industries, coal
mining is presently subject only to pH limitations.
Guidelines have also been established by the Mine Enforce-
ment Safety Administration (MESA), Department of the Interior,
for the design, construction, and maintenance of impounding
structures for mining wastes. These guidelines can be applied
to AMD sludge. The federal regulations derived from the MESA
guidelines are similar to the phosphate slime storage guidelines
presented in Table 44. The regulations emphasize the control of
surface runoff, and maintenance and reclamation of the impounding
structure.
No information on groundwater contamination from the lagoon-
ing of AMD sludges was found in the literature.
Gypsum from Phosphoric Acid Manufacture
The production of phosphoric acid - an intermediary in
phosphate fertilizer manufacture - generates large volumes of
gypsum as a by-product. Although gypsum is a valuable commodity
in many countries, the abundance of higher quality gypsum in the
U.S. generally precludes the marketing of the phosphogypsum, and
most manufacturers dispose of it in diked ponds.
Phosphogypsum produced in the U.S. consists primarily of
calcium sulfate dihydrate. The exact composition is dependent
both on the particular rock source of phosphorus and the manu-
facturing process itself. Table 48 presents a chemical analysis
of five gypsums from different ores.
Approximately 25 million tons of phosphogypsum were pro-
duced in 1969. The manufacturing process involves a reaction of
the calcium phosphate mineral (usually f 1 uoropati te, Ca^ (P0/i)2"
CaF2) with sulfuric acid, precipitating hydrated calcium sulfate
and forming phosphoric acid. The precipitate forms in needle-
like rhombic crystals, whose character is determined by such
variables as sulfate concentration, acid concentration, impuri-
ties in the rock, and slurry concentrations (Ref. 135).
215
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ro
—i
CTl
TABLE 47. EFFLUENT LIMITATIONS FOR TREATED ACID MINE DRAINAGE
Jurisdiction Effluent Limitations (One-Day Maximum, mg/£)
(waste source)
Total Suspended Iron
pH Solids Total Dissolved Suspended
Federal f 6.0-9.0 30* 4.0*
(coal mining)
Federal* 6.0-9.0 30 -- -- 2.0
(i ron ore mini ng)
Pennsylvania** 6.0-9.0 200 -- 7.0
(coal mining)
West Virginia1"1" 5.0-5.9 -- 10
(coal mining)
*Proposed, Ref. 135
%PA Effluent Guidelines and Standards for Ore Mining and Dressing, 40 CFR 440.12(a)(l)
#EPA Effluent Guidelines and Standards for Coal Mining, 40 CFR 434.32(a)
**Environmental Reporter, p 891:0743, 97.32 (1-5)
tfRef. 135
-------
TABLE 48.* COMPOSITION OF TYPICAL BY-PRODUCT CALCIUM SULFATES
FROM DIFFERENT ROCK SOURCESt
Rock Source
Fl
Te
Mo
ori da
nnessee
rocco
Morocco
Ko
la Peninsula
S
16.
20.
22.
17.
18.
CaO Si02
9
6
4
1
0
40
39
40
30
30
.2 11.8
.4 7.5
.9
.2 1 .2
.9 0.7
A1203 Fe203 P205 F
0.4# -- 0.9
0.6 0.4 1.9 0.4
1.51.3
1.7 0.7
0.5 0.3
* Ref. 135
i" Chemical analysis by weight percent
# Total A1203 and Fe203
-------
Phosphogypsum Disposal--
Phosphogypsum is usually disposed of in diked ponds. The
precipitate is filtered to a cake containing 18 to 35 percent
water, and then either reslurried for piping or conveyed dry to
the disposal area.
Pond design is presently governed by guidelines set forth
by the Florida Phosphate Council. Most ponds are divided into
sections, each operated individually. The drained gypsum is then
either left to dry further or else is piled. The latter prac-
tice, designed to conserve space, has resulted in gypsum piles
as large as 30 m high and 1.6 km long.
Phosphogypsum utilization has been limited by its impuri-
ties, particularly phosphates. However, possible uses are in the
production of gypsum wallboard, gypsum plaster, plaster of Paris,
cement, building blocks, and ammonium sulfate fertilizer.
Regulation of Phosphogypsum Disposal--
The environmental problems associated with gypsum disposal
relate to (1) the ultimate disposition of the drainage water and
supernatant liquor, and (2) the construction of the impoundment
structures. The wastewater is either treated for discharge or
is recycled to the plant. Dike construction, as noted earlier,
follows guidelines established by the Florida Phosphate Council.
Federal regulations pertaining to phosphoric acid manufac-
ture (40 CFR 422.22(a)) state that:
"There shall be no discharge of process wastewater
pollutants to navigable waters from the manufacture
of phosphoric acid. . ."
However, it is assumed that the lime-clarification treatment
process reduces pollutants to an effluent whose quality exceeds
that of the receiving stream; the effluent can therefore be
discharged.
Average annual treated pond discharges total between 2000
and 4000 a/t of phosphate. Periods of heavy rainfall may cause
discharges of up to 300 £/sec for short intervals. While acid
manufacturing regulations do not provide for rainfall compensa-
tion, federal gypsum processing regulations (40 CFR 436) do
allow discharge of
"that volume of water resulting from precipitation
that exceeds the maximum safe surge capacity of a
process wastewater impoundment . . . after application
of the best practicable control technology currently
available. . ."
218
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This would appear to be applicable to both phosphogypsum
and those FGD throwaway sludges that are high in calcium sulfate
Gypsum pile runoff is generally captured in a series of
drainage sluices and treated in a manner similar to pond dis-
charge. Many acid manufacturers monitor waterways downstream of
the ponds.
Data concerning groundwater contamination from pond or
runoff leachate are unavailable.
Coal Mi ne Taili ngs
Coal mining and preparation operations generate large
volumes of by-products, including uncovered coal, ash, slate,
shales, and clay associated with the coal seam. Strip mining,
in addition, generates huge amounts of waste cover material in
the form of ugly spoil banks.
Coal preparation is accomplished in a series of steps,
including crushing, sizing, impurities removal, and washing.
Coarse coal is generally recovered using dense media separation,
while fine coal is cleaned using a flotation process and a
special floating agent. Coarse coal wastes are accumulated in
so-called culm piles (also referred to as gab piles, coal refuse
banks, or breaker refuse). The fine wastes (>1 mm) are usually
discharged to a settling pond.
The composition of the coal wastes is dependent on the
source of the coal and the cleaning efficiency. A selected coal
waste characterization is shown in Table 49. The composition
largely results from the engineering properties of the waste
piles and from the extent of associated environmental hazards.
Extensive sampling of both chemical composition and physical
properties have been undertaken in recent years by the U.S.
Bureau of Mines; their results are available in the literature
(Ref. 157).
Disposal of Coal Mine Tailings--
The choice of a disposal method is site specific and
includes consideration of site characteristics, transportation
distance, disposal method alternatives, and site reclamation.
Since the enactment of reclamation regulations, site
selection has depended primarily on ease of reclamation. Valley
filling is one disposal method, as terracing is simplified.
Backfilling of strip mines is also practiced, using the spoil
banks as cover material in place of compacting and terracing.
The use of flat disposal sites presents difficulty in both
reclamation and environmental control. Most coal companies,
however, continue to use existing waste piles, landscaping only
the edges of the piles.
219
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TABLE 49 .* CHEMICAL AND PHYSICAL CHARACTERIZATION
OF SELECTED COAL PREPARATION PLANT WASTES
Sample Description
Moisture (percent)
Ash (percent)
Sulfur (percent)
Carbon (percent)
Volatile matter (percent)
Loss on ignition
Btu
Culm Bank
(Gob) Material Coal Fines'^
0.6
62.6
3.17
23.32
15.5
37.2
4,710
0.9
15.4
1.56
78.31
25.2
83.8
12,320
Water solubility (percent)
Water absorption (percent)
Bulk density (lb/ft3)
Compacted bulk density (lb/ft3)
Physical Properties
1.4 .88
2.7 28.4
69.0 46.5
78.0 53.0
* Ref. 135
t High carbon containing fines resulting from coal-cleaning
operations, often impounded in slurry form behind the bank
220
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Transportation of coarse wastes is accomplished primarily
by truck, often supplemented with conveyors, trains, or aerial
tramways. Slurried fines can be transported either by truck or
pipeline to the disposal pond.
Waste spreading and compacting operations are typically
accomplished using bulldozers. Compaction serves both to reduce
pollutant migration and improve the base for soil cover.
Site reclamation entails the spreading and compacting of a
soil cover, followed by planting. The soil is cultivated and
seeded with a combination of grasses and legumes. Much research
has been devoted to determining the plant species with the best
survival rates.
Other disposal methods under investigation include hydraulic
backfilling of mine voids, coal reclamation from culm piles, and
waste utilization as a construction material. Of these methods,
only coal reclamation is presently practiced on a large scale.
Wastes generated years ago by inefficient techniques can contain
up to 30 percent coal. Coal wastes can be used as asphalt
concrete aggregate, admixture in cement for mine stoppings, and
landfill material for purposes other than strip mine backfill.
Implementation has been slow due to long distances between
sources and potential markets. The use of coal wastes for mine
subsidence control is being studied by the Bureau of Mines;
preliminary cost estimates are higher than for other disposal
methods, but may be justified where control is required.
Regulation of Coal Refuse Disposal--
Several environmental problems are associated with coal
waste disposal, including ponds, fires, and groundwater contami-
nation from leaching of acid pile runoff or pond water.
Acid runoff from the culm piles is collected in drainage
sluices and neutralized prior to discharge. Regulations usually
apply to effluent pH, suspended solids and iron concentrations.
Both dike construction and coal waste pile configurations
are standardized in federal and state regulations and Bureau of
Mines guidelines. Particular attention has been given to dike
construction, as several catastrophic failures have occurred as
a result of haphazard specification of dike materials. The
Bureau of Mines has published research for specifying construc-
tion materials and trouble-shooting existing impoundments (Ref.
15, 86). Dike construction guidelines are identical to those
for acid mine drainage ponds covered in the previous subsection
of this report entitled "Acid Mine Drainage."
Federal regulations regarding safety standards for coal
waste piles were developed and proposed by MESA. These regula-
tions stipulate that:
221
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• Compacted layers should not exceed 2 ft in thickness
nor have a slope exceeding 2 horizontal to 1 vertical;
• The foundation is to be free of material that may con-
tribute to structural instability-
Also included are general reclamation guidelines (Federal
Register 40(175)).
States that have implemented regulations governing the
disposal of coal wastes include Alabama, Georgia, Kentucky,
Maryland, Pennsylvania, Ohio, Oregon, Tennessee, Iowa, and West
Vi rgi nia.
The contamination of groundwater from tailings pond seepage
or percolation has been studied, particularly with regard to
certain heavy metals and pH (Ref. 86). Few of the above-
mentioned states require groundwater monitoring at pond sites.
Nonetheless, research is under way to reduce the permeability of
mine tailings and thereby reduce the degree of pollutant
mobi1i ty.
Coal Ash
Two types of ash are generated from the combustion of coal:
fly ash, which is suspended in the flue gas; and bottom ash,
which accumulates in the bottom of the furnace. The ratio of
fly ash to bottom ash is determined primarily by the type of
combustion equipment used; the total quantity of ash is a func-
tion of the fuel used.
The character of coal ash was discussed in detail in Section
III and will only be summarized here. Variations in ash compo-
sition are normally attributed to coal composition, degree of
pulverization, types of furnace, and certain boiler operating
parameters such as temperature. Table 50 illustrates the range
of ash composition commonly encountered.
Whether the various elements are entrained in the fly ash
or bottom ash is specific to each element and to the combustion
equipment employed. Coal ash is composed primarily of silica,
alumina, and iron oxide, none of which is volatilized under
normal combustion temperatures; their presence in the fly ash is
due primarily to the force of the underfire air. Volatile
trace metals and their oxides condense on fly ash and are
collected from the exhaust gases, while other less volatile
trace metals are accumulated in the molten slag and bottom ash.
Fly ash generated by utilities is collected by mechanical
collectors, electrostatic precipitators (ESP), and scrubbers.
The mechanical collectors, such as cyclones, generally precede
the ESP and serve to collect the larger particulates (>10y) at
222
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TABLE 50.* POWER PLANT COAL ASH COMPOSITIONS
Percent
Cpnsti tuent by Weight
Silica (Si02) 30-50
Alumina (AloOo) 20-30
L- O
Ferric Oxide (Fe203) 10-30
Lime (CaO) 1.5-4.7
Potassium Oxide (K20) 1.0^3.0
Magnesia (MgO) 0.5-1.1
Sodium Oxide (Na20) 0.4-1.5
Titanium Dioxide (Ti02) 0.4-1.3
Sulfur Trioxide (S03) 0.2-3.2
Carbon (C) and volatiles 0.1-4.0
Boron (B) 0.1-0.6
Phosphorus (P) 0.01-0.3
Uranium (U) and Thorium (Th) 0.0-0.1
*Ref. 135
223
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efficiencies in excess of 90 percent. ESP's collect the remain-
ing fly ash in many instances at 99+ percent efficiency.
Depending on the relative collection efficiencies, the mechanical
collector may retain a higher percentage of the fly ash yet less
of the condensed trace elements than retained by the ESP. This
occurs because the trace metals are often more concentrated in
the smaller fly ash which has a greater specific surface area.
An estimated 2 to 5 percent of fly ash is normally water-
soluble, depending on the presence of alkaline constituents such
as lime. The physical properties of fly ash are somewhat unpre-
dictable; compacted permeability is normally on the order of 10~°
cm/sec, while compressive strength and settleability are similar
to that of soil. Fly ash is also pozzolanic, producing a
cementitious reaction with lime and water.
Bottom ash is composed primarily of silica, alumina, and
iron oxide. "True" bottom ash accounts for about 10 percent of
all utility coal ash and is produced in dry bottom boilers.
Boiler slag, as differentiated from bottom ash, possesses much
the same chemical composition. The differences are due to wet
bottom collection, which gives boiler slag a lower porosity and
higher specific gravity than bottom ash.
Coal Ash Disposal--
The disposal of fly ash, bottom ash, and slag can be
accomplished through ponding, landfill, or utilization. In ash
ponding, the ash slurry enters one end of a pond basin and flows
to the other end while allowing the ash particles to settle out.
Assuming the quantity of soluble elements is low, the supernatant
can be discharged to surface waters. Staged settling ponds are
sometimes used to improve ash particle removal efficiencies.
The choice of ponding over other disposal methods is often
contingent upon land availability. For a 1000-MW plant, the
pond area required is about 100 ha at a 3-m depth (Ref. 92).
The pond must also be near enough to the plant to permit piping,
since truck transport of slurried ash is generally not cost
competitive with landfilling dry ash. Pond liners, although not
required at the present time, may eventually become an added
cost consideration.
The use of a landfill to dispose of coal ash is common
practice for both utility and industrial boilers. Proximity
requirements are not as important, since the ash is generally
transported in the dry state by truck. The potential for
leachate formation in ash landfilling is unknown. Although no
evidence of groundwater contamination could be found in the
literature, laboratory studies have demonstrated the potential
mobility of certain trace contaminants such as sulfate, chloride,
boron, phosphorus, and zinc.
224
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A variety of utilization schemes have been proposed and/or
implemented for coal ash. Fly ash is presently used as a
concrete additive for various construction purposes. Most of
the skyscrapers constructed in Chicago during the last decade
utilized concrete containing fly ash. Boiler slag and bottom
ash have found use primarily as fill materials for applications
such as road beds and structural fill. However, it was estimated
that only 9 percent of all combustion by-products generated in
the U.S. during 1969 were used for any beneficial purpose. By
comparison, Britain and France reused over 40 percent of their
combustion by-products (Ref. 116).
Regulation of Coal Ash Disposal--
Discharge of the clarified coal ash pond effluent is
commonly practiced at power plants. Those that operate under an
NPDES permit are required to monitor the effluent for TSS, heavy
metals (As, Cr, Cu, Fe, Pb, Hg, Ni, Se, Zn), pH, and oil and
grease.
Coal ash is considered in many states to fall into the
category of solid waste and, therefore, is subject to groundwater
monitoring requirements exercised in those states. Details on
these requirements were presented in an earlier subsection
entitled Solid Waste Disposal.
WASTEWATER DISPOSAL
All states currently operate a water quality standards
program for surface waters, which is used as a basis for issuance
of discharge permits. These standards would only be applicable
to FGD sludge liquors if they were discharged to a surface water.
The liquor constituents and their respective maximum concentra-
tions according to these standards are discussed below.
Dissolved Oxygen (DO)
Recommended EPA standards for dissolved oxygen are based on
the type of aquatic biota existing in the waters. State stan-
dards recommend a minimal 5 mg/a DO concentration for freshwater
biota for warm water species, and a minimal 5 to 6 mg/£ DO
concentration (7 mg/a at spawning times) for cold water biota.
A minimum of 6 mg/a is recommended for small inland lakes or for
large lakes that have insufficient mixing of constituent layers.
For saltwater organisms, minimal DO levels of 5 mg/s. are recom-
mended in the open coastal waters and 4 mg/5. in the estuarine
and tidal tributaries.
The dissolved oxygen criteria for all states fall between
2.0 mg/£ and 8 mg/a, although some states limit dissolved oxygen
by saturation, with limits ranging from 50 to 90 percent.
225
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pH and Acidity/Alkalinity
All state pH limits fall between 5.0 and 10.0, with the
majority falling between 6.0 and 9.0. Some states limit pH by
deviation from the naturally occurring pH of the water. Only
Delaware has limits for alkalinity (20 to 80 mg/£) and acidity
(5 mg/£) both as CaC03-
Suspended and Other Particulate Solids
EPA published an "Example Water Quality Standard" that is
followed closely by the states. General criteria recommended
by EPA are as fol1ows:
All surface waters shall meet the generally accepted
aesthetic qualifications and shall be capable of supporting
desirable diversified aquatic life, and these waters shall
be --
1. Free from substances attributable to municipal,
industrial, or other discharges or agricultural
practices that will settle to form objectionable
sludge deposits.
2. Free from floating debris, scum, and other floating
materials attributable to municipal, industrial, or
other discharges or agricultural practices in amounts
sufficient to be unsightly or deleterious.
3. Free from materials attributable to municipal,
industrial, or other discharges or agricultural prac-
tices producing color, odor, or other conditions in
such degree as to create a nuisance.
4. Free from substances attributable to municipal,
industrial, or other discharges or agricultural prac-
tices in concentrations or combinations which are
toxic or harmful to human, animal, plant, or aquatic
life.
This, or similar wording is found in all state regulations.
The Alaska Wastewater Disposal Regulations (Adm. Code,
Title 18, Chapter 72) require written permission for subsurface
disposal:
No person may discharge sewage or industrial liquid
waste into the ground by well, crevice, sinkhole,
gravel pit or depression, or any other opening,
whether natural or manmade, without written approval
from the department.
226
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The West Virginia regulations, Section 17, Water Purifica-
tion Wastewater Control Measure, stipulate certain pond design
standards that might be applied to FGD sludge ponds:
1. Lagoon design must provide the following:
a. Location free from flooding.
b. Dikes, deflecting gutters or other means of
diverting surface water when necessary.
c. A minimum depth of 4 to 5 feet.
d. Multiple cell.
e. Adjustable decanting devices.
f. Convenient cleaning.
Heavy Metals
Many states restrict toxic substances by narrative state-
ment. A few restrict toxic substances by median tolerance limit,
e.g., not to exceed 1 mg/i of the 48-hr TLm. Many states limit
heavy metals by elements for some or all of the water-use
classes. Typical limits follow:
Concentration
mg/£
Arseni c .05
Bari urn 1.0
Cadmium .01
Chromium (total hexavalent) .05
Copper (range: .01-1 )
Iron .3
Lead .05
Selenium .01
Silver .05
For surface waters used as public drinking water supply,
the following constituent limits are often also limited.
Cyanide .02-.2
Fluoride 1.0
The following typical narrative statement is excerpted from
the Nevada Water Quality Standards, Article 4(4.If):
f. No wastes from municipal or industrial or other
controllable sources containing arsenic, barium, boron,
cadmium, chromium, cyanide, fluoride, lead, selenium,
227
-------
silver, copper and zinc that are reasonably amenable to
treatment or control will be discharged untreated or uncon-
trolled into the waters of Nevada. In addition, the limits
for concentrations of the chemical constituents will provide
water quality consistent with the mandatory requirements of
the 1962 Public Health Service Drinking Water Standards.
WATER QUALITY CRITERIA FOR VARIOUS BENEFICIAL USES
Federal Water Quality Control Laws: Surface Waters
The Federal Water Pollution Control Act Amendments of 1972
(Public Law 92-500) established the framework for water quality
control laws and regulations used by the various states. Under
this law, the states retain the primary responsibility for water
quality protection. However, the U.S. EPA is authorized to
intervene if the states do not enforce the law. The relevant
elements of Public Law 92-500 are the water quality standards
program, the NPDES program, treatment requirements, and the
effluent guidelines.
Water Quality Standards Program--
All states administer a water quality standards program
wherein the surface waters of the state are categorized by
beneficial uses, e.g., drinking water supply, recreation, fish
and wildlife, agricultural, industrial, etc. For each class of
water use, narrative and/or numerical limits are established for
various parameters, such as dissolved oxygen, pH, temperature,
and turbidity. The parameter limits are to be maintained in the
receiving water to protect its beneficial uses. The important
distinction here is that the limits are upon the receiving
water - not upon the discharges to it.
NPDES Program--
All discharges to navigable waters require an NPDES permit.
These permits are issued by the EPA and by states that are
delegated the authority by EPA. An NPDES permit can stipulate
any of the following: effluent limitations, maximum flow,
monitoring requirements, schedule of compliance, operation and
maintenance requirements, etc. In the case of FGD sludges, if
overflow from a scrubber sludge pond is discharged into a surface
water, an NPDES permit is required.
Treatment Requirements--
Regarding required treatment for control of water pollution,
Public Law 92-500 states:
• Industries must use the "best practicable" technology to
control water pollution by July 1, 1977, and the "best
available" technology by July 1, 1983.
228
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t Publicly owned waste treatment plants must provide a
minimum of "secondary treatment" by July 1, 1977, and
must apply the "best practicable" technology by July 1,
1983.
Effluent Guidelines--
EPA has established national effluent limitations and
performance standards for many industrial waste sources.
However, no standards have been promulgated as yet for the
scrubber sludges from power plants.
Federal Drinking Water Standards
EPA is authorized by the Safe Drinking Water Act of 1974 to
establish interim primary drinking water standards. Table 51
shows the maximum contaminant levels for various inorganic
chemicals as specified by the interim standards promulgated in
December 1975.
Federal Irrigation Water Standards
The regulation of irrigation water quality must take into
consideration the short-term effects on crop quality, long-term
effects on soil characteristics and surrounding groundwaters,
and the intended utility of the crop. Water classified as
irrigation water is generally applied to (1) agricultural crops,
(2) pasture land, (3) turf and landscape, and (4) stock watering.
Absolute limits on irrigation water are difficult to establish
due to a number of site-specific factors, e.g., soil type,
climate, irrigation practices, etc.
Table 52 presents general limits for irrigation water con-
stituents as suggested by the U.S. EPA for both short-term and
extended (over 20 years) use. Many of the allowable contaminant
concentrations are several times higher than those allowed by
the drinking water standards (examples: arsenic, chromium, lead,
and selenium; constituents such as mercury are not listed in the
irrigation standards).
State Groundwater Protection Regulations
In nearly all cases, the state regulatory agencies are
authorized to protect both surface and subsurface waters, e.g.,
to prevent degradation of groundwater. However, only a few
states have specific criteria for groundwater protection. The
Maryland Groundwater Quality Standards (Reg. 08.05.04.04), for
example, identify three types of underground aquifers - types I,
II, and III - based on transmissivity, permeability, and total
dissolved solids concentration of the natural water. The
following limitations are established for each type:
229
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TABLE 51.
NATIONAL INTERIM PRIMARY DRINKING WATER
REGULATIONS — MAXIMUM CONTAMINANT LEVELS
FOR INORGANIC CHEMICALS
Contaminant
Arsenic
Bariurn
Cadmium
Chromium
Fluoride
Lead 0.05
Mercury 0.002
Nitrate (as N) 10.
Selenium 0.01
Silver 0.05
Level (mg/£)
- 0.05
- 1.
- 0.010
- 0.05
t
Federal Register, p 59570, December 24, 1975
Fluoride is regulated as a function of average
daily maximum air temperature:
Ai r Temperature
Fluoride Level
(mg/£)
12
12.
14.
17.
21 .
26.
1
7
7
5
3
0
_
-
-
_
-
14
17
21
26
32
.6
.6
.4
.2
.5
2
2
2
1
1
1
.4
.2
.0
.8
.6
.4
230
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TABLE 52.*
LIMITS OF POLLUTANTS FOR IRRIGATIOI
WATER RECOMMENDED BY EPA
Constituents
Heavy Metals
Alumi num
Arseni c
B e ry11i u m
Boron
Cadmi urn
Chromi urn
Cobalt
Copper
Fl uori de
Iron
Lead
Lithium
Manganese
Molybdenum
Nickel
Selenium
Bacteri al
Coliform density
Chemi cal
PH
TDS
Herbi ci des
For Water Used
Conti nuously
on all Soi 1 s
For Short-Term Usef
on Fine Textured,
Neutral, and
Alkaline Soils
Dalapon
TCA
2,4-D
5.0
2.0
0.1
0.75
0.01
0.1
0.05
0.2
2.0
5.0
5.0
2.5
0.2
0.01
0.2
0.02
,000/100m£
4.5-9.0
5,000
0.2
0.2
0.1
20.0
10.0
0.5
2.0
0.05
1 .0
5.0
5.0
15.0
20.0
10.0
10.0
0.05
2.0
* Ref. 134
t Short-term used here means a period of time as long as
20 years
231
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1. Type 1 Aquifers
The characteristics of constituents of waters or wastewaters
discharged into Type 1 Aquifers may not exceed, or cause the
natural groundwater quality to exceed, mandatory or recom-
mended standards for drinking water as established by the
Federal Government.
2. Type II Aquifers
The characteristics or constituents of waters or wastewaters
discharged into Type II Aquifers may not exceed or cause the
natural groundwater quality to exceed receiving (surface)
water quality standards as established for Class I Waters
by the State. In addition, the person responsible for the
discharge shall provide the Water Resources Administration
with evidence that the discharge will not result in pollu-
tion of Type I Aquifers.
3. Type III Aquifers
The characteristics or constituents of waters or wastewaters
discharged into Type III Aquifers shall be identified to the
Water Resources Administration, and evidence shall be
provided to assure the Water Resources Administration that
there will not be pollution of either Type I or Type II
Aquifers or surface waters, and that the public health and
welfare will not be endangered as a consequence of such
dis posal.
According to the New York Groundwater Classification and
Standards (Part 703):
a. The ground waters of the State are classified according
to best use, and all fresh ground waters are best used as
sources of potable water supply. Such fresh waters, when
subjected to approved disinfection treatment and/or addi-
tional treatment to reduce naturally present impurities to
meet New York State Health Department drinking water
standards, are deemed satisfactory for potable purposes.
Contaminant limits established in New York for groundwaters
to be used as potable water supply are shown in Table 53.
Missouri has Regulations for Ground Water Recharge and
Irrigation Return Water, shown below:
This section shall apply to percolating water from all areas
of land on which wastes or wastewater is applied or allowed
to accumulate whether or not additional treatment is to be
obtained by application to the land. Such percolating
water shall be considered an effluent to the subsurface
232
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TABLE 53.*
STATE OF NEW YORK GROUNDWATER
TAMINANT LIMITS
CON-
Substance
Concentration in mg/£
Schedule I Schedule II
(ABS)
Alkyl benzene sulfonate
Arsenic (As)
Barium (Ba)
Cadmi um (Cd)
Carbon chloroform extract residue
Chloride (Cl)
Chromium (hexavalent) (Cr+6)
Copper (Cu)
Cyanide (CM)
Fluoride (F)
Iron (Fe)
Lead (Pb)
Manganese (Mn)
Nitrate (N)
Phenols
Selenium (Se)
Silver (Ag)
Sulfate (SO*)
Total dissolved solids
Zinc
(CCE)
1 .5
0.1
2.0
0.02
0.4
500
0.10
0.4
0.4
3.0
0.6
0.10
0.6
20.0
0.002
0.02
0.10
500
1000
0.6
6.5-8.5
1.0
0.05
1.0
0.01
0.2
250
0.05
0.2
0.2
1 .50
0.3
0.05
0.3
10.0
0.001
0.01
0.05
250
500
0.3
6.5-8.5
New York State
(Part 703)
Groundwater Classifications and Standards
t When natural groundwaters have a pH outside of range indicated
above, the natural pH may be one extreme of the allowable range
233
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"Waters of the State" when it reaches a depth of more than
4 feet or is within 12 inches of bedrock if such bedrock
occurs at depths of less than 5 feet, and shall be subject
to the following requirements. Percolating water which is
intercepted by either natural or artificial means and
reappears on the surface shall be considered indirect
release to surface "Waters of the States. . ."
The specific requirements for Missouri state groundwater
contaminant limits are shown in Table 54.
Kansas has Underground Storage Regulations that require a
permit for all surface ponds. The regulations apply as follows:
This article regulates the construction and use of under-
ground storage reservoirs and the construction and use of
disposal wells and surface ponds for the confinement,
storage and disposal of industrial fluids including but not
limited to brines, but does not include regulations per-
taining to oil field activities described in L 1965, Ch.
506, Sec. l(4)p.
The Kansas Regulations also state the following regarding
operation and maintenance:
Operators of underground reservoirs shall maintain a
permanent record of the type and quantity of all products
stored there, and a continuous record of the injection
pressures, and shall report immediately to the chief
engineer for the state board of health any failures or
defects in the underground reservoir.
The Idaho regulations have a section on Land Treatment
and/or Disposal of Wastewater(s), shown below:
Land treatment and/or disposal of liquid waste material(s)
requires that
. . . Provision shall be made for monitoring the quality
of the ground water in proximity of the disposal area. All
data and reports resulting from the ground water monitoring
program will be submitted to the Department upon request.
The minimum frequency of monitoring and data submittal will
be dependent upon the nature and volume of wastewater
material, the frequency and duration of disposal, and the
characteristic of the soil mantle on the disposal site.
3. Land treatment and/or disposal shall not create a
ground water mound or result in a salt build-up on another
person's property.
234
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TABLE 54.* STATE OF MISSOURI GROUNDWATER CON-
TAMINANT LIMITS
Maximum Value
Contaminant Allowed
Arsenic 50
Bari urn 1 ,000 )ug/l
Cadmi urn 30 JUg/£
Chromium (total) 500 JUg/£
Copper 20 JLig/£
Cyanide 10 Jug/£
Fl uoride 1 ,200 JLig/£
Lead 50 jug/£
Nickel 800 Jjg/£
Phenols 5 Jug/£
Selenium 10 jug/£
Si Iver 50 jLig/£
Zinc 100 Jug /I
COD 10 mg/l
Threshold Odor Number (TON) 3
Linear Alkylate Sulfonates 1.0 mg/l
Chlorides 250 mg/l
Sulfates 250 mg/l
Total dissolved solids 500 mg/l
Nitrate as (N03) 10 mg/l
Heavy metal ratio shall not
exceed 1.00+
+ Cu . Zn Pb Cr Cd Nj_ _ ,
20" TOO 50" 500" 30 800 ~ ' 'UU
Where the abbreviation for the metal in the
fraction is the measured concentration in the
effluent in micrograms per liter (|ig/£)
* Missouri: Groundwater Recharge and Irrigation
Return Water (Appendix II)
235
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4. Land treatment and/or disposal shall not create a public
health hazard, a nuisance condition, or an air pollution
problem.
The Michigan Liquid Industrial Waste Disposal Act governs
the methods of disposal of liquid industrial wastes, including
licensing of persons and vehicles. It states the following
regard ing disposal:
. . . The licensee shall not dispose of wastes onto or
into the ground except at locations specifically approved
by the commission ... No waste shall be placed in a
location where it could enter any public or private drain,
pond, stream or other body of surface or ground water.
AIR POLLUTION REGULATIONS
With the promulgation of the New Source Performance
Standards (NSPS) for Fossil Fuel-Fired Steam Generators (40 CFR,
Part 466, 8/17/71), wet lime/limestone scrubbers became the
anticipated "best method" of removing S02 from the flue gas of
a power plant. NSPS confessed to the problem of sludge disposal,
yet placed it on a hazard level similar to that of fly ash.
The NSPS were remanded to EPA by a U.S. Court of Appeals
in 1973, with one of the allegations involving insufficient EPA
consideration of the sludge disposal problem. The court decision
stated that the record be remanded for further "consideration and
explanation ... of the adverse environmental effects of requir-
ing a 1.2 Ibs/million BTU standard for those . . . plants which
must use a lime slurry scrubbing system . . ."
In its Draft Response to Remand (40FR 42045), EPA concluded
that the standards should not be revised to account for sludge
disposal. It was noted, however, that "EPA considers permanent
land disposal of raw sludge to be environmentally unsound,
because it definitely degrades on large quantities of land"
(Section C.I.(c)). As an acceptable solution, both fixation and
alternate control systems that do not generate sludge are con-
sidered acceptable. The response states that "fixation of the
sludge will greatly reduce its environmental impact," as it has
a "much lower 1eachabi1ity" than untreated sludge, "and the
leachates . . . are potentially less of a disposal problem than
(those) from fly ash."
It was also suggested in the Draft Response to Remand that
some plants that must postpone fixation utilize lined holding
ponds for temporary storage. Permanent disposal of raw sludge
in any type of pond, however, is not considered acceptable due
to the indefinite degradation of large quantities of land.
236
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Although the Draft Response to Remand is not to be con-
strued as regulation, it was nonetheless apparent that EPA views
sludge fixation as the best available technology for FGD sludge
disposal.
While many of the state SC>2 emission regulations are at
least as stringent as the federal regulations, it could not be
determined from the literature which states have included sludge
disposal recommendations as part of the standard.
WASTE DISPOSAL TO OCEANS
The Marine Protection, Research and Sanctuaries Act of 1972
(Public Law 92-532) has been the basis for domestic control of
ocean dumping. The act removes ocean dumping regulation from
state, interstate, or regional authorities and consolidates
control under the administrator of the federal EPA (Sec. 104
(d)). The administrator may issue permits for ocean disposal
after:
1. Determining "that such dumping will not unreasonably
degrade or endanger human health, welfare, or amenities,
or the marine environment, ecological systems, or
economic potentialities," or,
2. Applying criteria established expressly for reviewing
and evaluating such permit applications. These criteria
shall include but not be limited to the following:
a. The need for the proposed dumping.
b. The effect of such dumping on human health and
welfare, including economic, aesthetic, and
recreational values.
c. The effect of such dumping on fisheries resources,
plankton, fish, shellfish, wildlife, shore lines
and beaches.
d. The effect of such dumping on marine ecosystems,
particularly with respect to -
i. the transfer, concentration and dispersion of
such material and its by-products through
biological, physical, and chemical processes,
ii. potential changes in marine ecosystem
diversity, productivity, and stability, and
iii. species and community population dynamics.
237
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e. The persistence and permanence of the effects of
the dumping.
f. The effect of dumping particular volumes and con-
centrations of such materials.
g. Appropriate locations and methods of disposal or
recycling, including land-based alternatives and
the probable impact of requiring use of such
alternate locations or methods upon considerations
affecting the public interest.
h. The effect on alternate uses of oceans, such as
scientific study, fishing, and other living resource
exploitation, and nonliving resource exploitation.
i. In designating recommended sites, the Administrator
shall utilize wherever feasible locations beyond
the edge of the Continental Shelf.
3. Determining that no applicable water quality standards
will be violated (Sec. 102 (a));
4. Consulting with federal, state, and local officials,
and interested members of the general public, as may
appear appropriate to the Administrator when establish-
ing or revising such criteria.
The act specifies that any feasible disposal alternatives
should be considered in lieu of ocean disposal. Consequently,
the regulatory environment is not presently conducive to ocean
disposal of FGD sludges.
The Key West Utility Board Stock Island Plant occasionally
discharges sludge pond supernatant directly into the Gulf of
Mexico. This practice is currently regulated by an NPDES permit
and Florida State Industrial Waste guidelines. The Marine
Protection, Research and Sanctuaries Act has not been adapted
to regulate this effluent.
WASTE DISPOSAL TO MINES
There are currently no state or federal regulations that
relate specifically to the disposal of FGD wastes to mines.
Regulations that apply indirectly to mine disposal include:
t Waste disposal
• Water quality
• Health and safety
The specific applicability of these regulations to FGD
sludge disposal to mines is currently under study by Arthur D.
238
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Little, Inc. under contract to EPA. A discussion of waste
disposal regulations and water quality criteria as they relate
to FGD sludge disposal was presented earlier in this report.
For mine disposal operations where use of some type of
impoundment structure is indicated, the Dam Safety Act (Public
Law 92-367) regulates impoundment construction and monitoring.
However, where no dam is necessary, no statutes require consider-
ation of catastrophic release of desulfurization wastes or any
wastes from mine disposal.
The law states that the Secretary of the Army shall deter-
mine "whether a dam constitutes a danger to human life or
property." Furthermore, he "shall take into consideration the
possibility that the dam might be endangered by overtopping,
seepage, settlement, erosion, sediment, cracking, earth movement,
earthquakes, failure of bulkheads, flashboard, gates on conduits,
or other conditions which exist or which might occur in any area
in the vicinity of the dam" (Sec. 4). This could be interpreted
to regulate FGD sludge mine disposal.
To be regulated by this law, the impoundment must either be
greater than 6 ft in height, or have a storage capacity greater
than 15 ac-ft (Sec. 1). Certain mine disposal operations may
not be regulated by the Dam Safety Act because of this require-
ment.
Transportation of various materials similar to desulfuriza-
tion sludge is effectively regulated. By interpretation, the
Hazardous Materials Transportation Act of 1970 could adequately
regulate FGD sludge transportation to mine disposal sites. The
act defines hazardous materials as: "substances or materials in
a quantity and form which may pose an unreasonable risk to
health and safety or property when transported in commerce"
(Public Law 91-458).
Protection of health and safety appear to be subject to
adequate regulation by various Mining Enforcement and Safety
Administration (MESA), and Occupational Safety and Health
Administration (OSHA) standards and guidelines. Protection can
be accomplished by adaptations of the existing statutes. These
are:
a. Materials shall be stored and stacked in a manner which
minimizes stumbling or fal1-of-material hazards.
b. Materials that can create hazards if accidently
liberated from their containers shall be stored in a
manner that minimizes the dangers.
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c. Hazardous materials shall be stored in containers of a
type approved for such use by recognized agencies; such
containers shall be labeled appropriately. (MESA,
Guideline 77.208)
No person shall be permitted to walk or stand immedi-
ately above a reclaiming area or in any other area at
or near a surge or storage pile where the reclaiming
operation may expose him to a hazard. (MESA, Guideline
77.209)
CASE STUDY: THE COMMONWEALTH OF PENNSYLVANIA*
In Pennsylvania, the Commonwealth's Solid Waste Management
Program (hereafter referred to as "the Program") has primary
responsibility for regulating the disposal of FGD sludges; this
responsibility is based upon the Pennsylvania Solid Waste
Management Act 241. Because permits must be obtained in other
regulatory jurisdictions, the Program coordinates its activities
with the Water Quality Management Program within the Pennsylvania
Department of Environmental Resources.
Since 1972, the Program has permitted sludge disposal
operations at three power plants in the Commonwealth: the
Duquesne Light Company Phillips and Elrama stations, and the
CAPCO Bruce Mansfield Station. Initially, the Program took a
passive role. Lacking FGD sludge data and experience, their
role was to monitor the experimental work being performed at
the Phillips station and to keep abreast of related research
nationwide. However, the design and construction of the Bruce
Mansfield Power Station obligated the Program to review the
various proposals for FGD sludge management and formalize the
evaluation criteria required of applicants.
Evaluation Criteria
Disposal system evaluation criteria were developed by the
Solid Waste Management and Water Quality Management Programs
jointly. The approach taken was to evaluate each proposed
treatment process and site design individually for its potential
environmental impact. It was decided that the most important
evaluation criteria were:
• Potential for ground and surface water pollution
• Nuisance prevention
• Proper dam construction, and
• Site reclamation
*Personal communication with Gary Merritt, Pennsylvania Depart-
ment of Environmental Resources, February 22, 1977.
240
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In order to best employ these criteria when evaluating a
potential disposal operation, three basic areas of analysis were
proposed :
• Product (or waste) characteristics;
• Storage (or disposal) site characteristics; and
• Operating requirements.
Product (Waste) Character!'sti cs--
Of major concern is the potential contamination of ground
and surface waters in the vicinity of storage and disposal areas.
A secondary concern is the physical characteristics of the
material which will control its engineering use. The information
required for an evaluation of these concerns is:
• Chemical and physical analyses of the materials;
t Potential for generating leachates; and
• Character of the leachate with respect to total dissolved
solids and heavy metals.
Physical characteristics such as triaxial strengths,
permeability, moisture content compaction, and particle size
distribution are needed to determine the stability and design
of any site.
Storage (or Disposal) Site Characteristics--
Site characteristics of interest from an environmental
standpoint include local hydrology, geology, topography, and
meteorology. Evaluation criteria must take into account the
interaction of these factors and their effect on the environment.
Since the criteria are site-specific, only general considerations
can be addressed. The single most critical element of the site
is its hydrogeologic characteristics. These will dictate the
design and possible limitations on the use of the site due to
potential ground and surface water pollution.
Operating Requirements--
Operating plans will be assessed for possible environmental
impact. Activities of interest include truck routes and
frequency of travel, pipeline right-of-way, placement of sludge
at the landfill, and operation of the pond. Also, possible
fugitive dust emissions must be accounted for. Completed site
characteristics and projected land use must be assessed.
Regulation of the Bruce Mansfield Disposal Operation
The CAPCO Bruce Mansfield Power Station, located in
Shippingsport, Pennsylvania, is a 2,700 MW, three-unit, coal-
fired plant. Unit 1 began operation in December, 1975; units
2 and 3 are expected to begin commercial operation in October
241
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1977 and October 1979 respectively (Ref. 34, 40). During the
design of the Bruce Mansfield FGD sludge disposal operation, two
methods of commercial stabilization were proposed: those
offered by I U Conversion Systems and the Dravo Corporation (see
Section VII). The disposal of raw sludge and non-commercially
stabilized sludge was not considered.
Permit Procedures--
The permitting procedure for land disposal of FGD wastes
is governed by three pieces of Pennsylvania legislation: the
Solid Waste Management Act, the Water Obstructions Law, and the
Clean Streams Law. Because of the variety of environmental
considerations involved in selecting and operating a disposal
site, the legislation mandates coordination of water quality and
solid waste activities between the associated programs.
The Solid Waste Management Act provides for the issuance
of solid waste disposal permits. These permits are required for
the disposal of any solid waste on land. The first phase of the
two-phase procedure involves (1) the submittal of chemical and
physical data on the sludge characteristics, and (2) a detailed
hydrogeo1ogic study of site conditions. Phase II consists of
a detailed review of the system engineering, including specifics
of design, operation, and end use.
The Clean Streams Law provides for the issuance of three
permits in the water quality area:
t Industrial Wastes Discharge Permit;
• Sedimentation and Erosion Control Permit; and
• Pollution Incident Prevention Plan (PIPP).
The Industrial Wastes Discharge Permit applies to liquid dis-
charges to surface waters of the state. Standards include (1)
state effluent discharge limitations, and (2) standards of
quality established for each stream. The discharge from an FGD
sludge disposal site must conform to the most stringent of these
standards, although some flexibility is allowed for certain
streams. The Sedimentation and Erosion Control Permit requires
that a formal plan for sedimentation and erosion control around
the disposal area be developed. This plan is submitted to the
Soil Conservation Service for final approval. A PIPP involves
the identification of potential pollution problems and the
submittal of a plan to deal with them should they arise. The
identification of problem areas is the responsibility of the
owner or operator.
The Water Obstructions Act applies to any activities which
alter the existing surface waters or provide for new waterways.
The permits provided for under this act include:
242
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• Encroachment permits; and
• Dam construction permits.
An encroachment permit is required when (1) a waterway is dammed
up and allowed to encroach upon adjacent land, or (2) the path
of a waterway is altered. A detailed hydrologic study of the
surrounding area is required. The dam construction permit is
an engineering evaluation of a proposed dam, evaluating test
borings and construction monitoring, as well as the specification
of safety factors.
It must again be emphasized that the successful implementa-
tion of these permitting procedures require coordination between
the various environmental programs.
Discuss ions between Program officials and I U Conversion
Systems concerning their process and conceptual approach to
managing the flue gas desu1furization sludges were held in late
1972. The IUCS process produces a product that is both stable
for disposal and useful in a variety of structural applications.
The proposed disposal methods were backfilling of abandoned
surface mines and use as embankment fill. It was decided that
either method would require permitting.
The permits required for the disposal of the sludge proces-
sed using the IUCS process would be dependent upon which disposal
concept was selected. If the backfilling of abandoned surface
mines were chosen, then two permits (and a PIPP) would be
required: a Solid Waste Disposal Permit and a Sedimentation and
Erosion Control Permit. If the sludge were to be used as an
embankment fill, four permits (and a PIPP) would be required:
a Solid Waste Disposal Permit for any discharge from the pond;
a Sedimentation and Erosion Control Permit; and depending upon
the size of the drainage basin, perhaps an Encroachment Permit.
Discussions with Dravo concerning their proprietary process
and conceptual approaches to disposal of the Bruce Mansfield FGD
sludges were held in late 1972. Their conceptual approach
involved treatment with a proprietary process, followed by
pipeline transport of the wet slurry to the final disposal site.
The disposal area was to consist of a dam located near the base
of a valley. There, scrubber sludge would be discharged to
settle and harden (under water) in place behind the dam.
Collected wastewater would be returned to the scrubber cycle as
make-up water.
Under Dravo's proposal, four permits and an approved PIPP
program would be required. The permits would include a Solid
Waste Disposal Permit, a permit for the construction of a dam,
an Industrial Waste Permit for any discharges to surface waters,
and a Sedimentation and Erosion Control Permit. The Dravo
concept, as stated above, was eventually selected. The Little
243
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Blue Run impoundment area will eventually occupy 1,300 ac behind
a 420 ft impoundment structure. As the impoundment area will
eventually straddle the Pennsylvania-West Virginia border,
permits were required from both states.
Evaluation of Potential Water Quality Impacts--
In the process of evaluating the above permit applications,
the Solid Waste Management Program conducted leaching tests on
samples of materials processed by Dravo and IUCS. The leaching
methodology used for the sludge samples consisted of the follow-
ing tests:
9 Mix 500 gr of solid processed sludge with 2,000 ml of
deionized distilled water;
• Agitate the mixture continuously for a minimum of 48
hours;
• Pass the supernatant through a filter (#42); and
• Analyze the filtrate.
The tests were performed on both raw sludges and sludges
stabilized by the Dravo and IUCS processes. In addition, as a
basis for comparison, tests were performed on fly ash, bottom
ash, and Basic Oxygen Furnace (BOF) slag.
Based upon the results of those tests, Program officials
concluded that leaching from neither raw nor stabilized sludge
would present a hazard to the environment. The leaching tests
presented an extreme leaching environment, but few of the metals
analyzed in the leachate exceeded drinking water standards.
Furthermore, the elutriates were superior in quality to most of
the fly ash leachate samples.
Conclusions
The Solid Waste Management Program, based upon their find-
ings during the Bruce Mansfield investigation, compared FGD
sludge disposal to the disposal of other solid and liquid wastes.
In particular, they compared the leaching results to various
leachates from other waste products (coal ash, fly ash, and
basic oxygen furnace slag) and to existing water quality
standards.
Their conclusions were as follows:
"A. The environmental problems which may result from the
disposal of sludge generated by the slaked lime-wet scrubber
operations will be mainly those of logistics:
244
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(1)
(2)
(3)
(4)
Tremendous volumes of sludge will be generated in
relatively concentrated point sources. Large
quantities of land will be required for the
disposal of this waste.
There may be some materials-handling problems
(proper equipment, spillage, etc.) which seem to
be solved by pre-processing of the sludge before
disposal.
Supernatant to be used as
be viable (comparatively
process.
make-up water appears
ow TDS) from this
to
There is a possibility of a very high chemical
oxygen demand from the untreated sludge if the
calcium sulfite is released into the water environ'
ment."
"B. Heavy metals appear to be highly insoluble in the
sludge samples tested. The pH is fairly high in every case,
Ninety-eight (98) percent of the measurements of heavy
metal ions are below detection limits or effluent standards
"C. Dissolved solids and sulfates decrease considerably
with the aging of the sludge" (as leaching becomes diffu-
sion-limited)
"D. The methodology used in preparing the sample has no
significant effect on the test results for heavy metal ions,
However, the total dissolved solids and sulfates do show
significant differences. Actual physical conditions to
which the deposited wastes will be subjected will not be
as turbulent (less surface area will be exposed) as that
experienced in the shaking tests.
"E. The results of this study are only relevant
lime-wet scrubber operation.
to slaked
"F. The sample preparation methods ensured that the
leachate was produced under aerobic conditions only.
"G. Heavy metals ions will not be a problem in the disposal
of the sludge treated or untreated."
245
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SECTION XII
ACKNOWLEDGEMENTS
This document is the result of an extensive data base eval-
uation, which included research and development findings from
industry, universities, EPA, and other state and federal agen-
cies. The guidance and assistance of Mr. Donald Sanning, Pro-
ject Officer, Municipal Environmental Research Laboratory (MERL)
of U.S. EPA, Cincinnati, Ohio, is gratefully acknowledged.
Also, Mssrs. Julian Jones, IERL/RTP, and Norbert Schomaker and
Robert Landreth, MERL, Solid and Hazardous Waste Research Divi-
sion (SHWRD), Cincinnati, contributed to the project.
The individuals in the R & D community who contributed time
and effort to the project are too numerous to mention. Major
contributors to the project are listed below:
• Mr. Wayne Barrier, Tennessee Valley Authority, Muscle
Shoals , Alabama.
• Mr. James Crowe, Tennessee Valley Authority,
Chattanooga, Tennessee.
• Mr. Paul Leo, Aerospace Corporation, El Segundo,
Cali fornia .
• Mr. Richard Lunt, Arthur D. Little, Inc., Cambridge,
Massachusetts .
• Mr. Jerome Mahloch, Waterways Experiment Station,
Vicksburg, Mississippi.
• Mr. Gary Merritt, Pennsylvania Department of Environ-
mental Resources, Harrisburg, Pennsylvania.
• Mr. Jerome Rossoff, Aerospace Corporation, El Segundo,
Cal i form'a .
SCS project participants were Curtis J. Schmidt, Project
Director; Dr. Dallas E. Weaver, Project Manager; and John P.
Woodyard, Technical support was provided by Mark Montgomery,
Howard Rischel (Economics), and Pamela Horton (Legal). Dr.
Donald Shilesky reviewed much of the technical information.
246
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SECTION XIII
REFERENCES
1. Aerospace Corporation. Disposal of By-Products from Nonre-
generable Flue Gas Desulfurization Systems. EPA Contract
No. 68-02-1010. Los Angeles, 1976.
2. Air Quality Criteria for Sulfur Oxides. National Air Pollu-
tion Control Administration Publication AP-50, April 1970.
3. Andrew, A. W., Y. Talmi, and D. H. Klein. Selenium in Coal-
Fired Steam Plant Emissions. Environmental Science and
Technology, 9(9):856-858 , September 1975.
4. Arthur D. Little, Inc. An Evaluation of Alternatives for
the Disposal of FGD Sludges. Progress Report No. 4. EPA
Contract No. 68-03-2334. U.S. Environmental Protection
Agency, December 17, 1975.
5. Babu, S. P- Trace Elements in Fuel. American Chemical
Society, Washington, D.C., 1975.
6. Barrick, S. M. and G. F. Moore. Empirical Correlation of
Coal Ash Viscosity with Ash Chemical Composition. American
Society of Mechanical Engineers, New York, 1977.
7. Battelle, Columbus Laboratories. Fuels Technology: A State
of the Art Review. EPA Contract No. 68-02-1323 Task 14,
NTIS/PB-242 535, April 1975.
*
8. Berst, A. H. and J. Reisinger. Startup of American Air
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-------
156. Sprute, R. H. and D. J. Kelsh. Laboratory Experiments in
Electrokinetic Den sificat ion of Mill Tailings. Part 1.
Bureau of Mines Report #7892. Dept. of the Interior,
Washington, D.C., 1974.
157. Sprute, R. H. and D. J. Kelsh. Laboratory Experiments
in Electrokinetic Densification of Mill Tailings. Part 2.
Bureau of Mines Report #7900. Dept. of the Interior,
Washington, D.C., 1974.
158. Stabilizing Waste Materials for Landfills. Environmental
Science and Technology, 11(5):436-437, May 1977.
159. Stern, A. C. et al. Fundamentals of Air Pollution.
Academic Press, New York, 1973.
160. Stober, W. G. Operational Status and Performance of the
Commonwealth Edison Company Will County Limestone Scrubber,
Paper presented at the EPA Symposium on Flue Gas Desulfuri-
zation, New Orleans, March 8-11, 1976.
161. Stukel, J. et al. Flue Gas Desulfurization and Low BTU
Gasification: A Comparison: Appendix G. NSF Grant No.
GI-35821(A), NTIS/PB-248 064, May 1975.
162. Study Committee to Assess the Feasibility of Returning
Underground Coal Mine Wastes to the Mined-Out Area.
Underground Disposal of Coal Mine Wastes. National
Academy of Sciences, Washington, D.C., 1975.
163. Sulfur Dioxide Processing. Reprints, Chemical Engineering
Progress, American Institute of Chemical Engineers, New
York, 1975.
164. Symposium Proceedings: Environmental Aspects of Fuel
Conversion Technology, II (December 1975, Hollywood,
Florida). EPA-600/2-76-149, U.S. Environmental Protection
Agency, June 1976.
165. Taub, S, I. Treatment of Concentrated Waste Water to
Produce Landfill Material. Presented at the International
Pollution Engineering Exposition and Congress, Anaheim,
California, November 10, 1976.
166. Vasan, S. The Citrex Process for SOp Removal. Chemical
Engineering Progress. 75(5):61-65, Flay 1975.
167. Vitez, B. Trace Elements in Flue Gases and Air Quality
Criteria. Power Engineering, 80(1):56-60, January 1976.
260
-------
168. W. A. Wahler and Associates. Evaluation of Mill Tailings
Disposal Practices and Potential Dam Stability Programs
in Southern United States. NTIS/PB-243 074. December
1974.
169. W. A. Wahler and Associates. Evaluation of Mill Tailings
Disposal Practices and Potential Dam Stability Problems
in Southwestern United States. Bureau of Mines, Spokane,
1974.
170. Walter, W. R. A Systematic Procedure for Taxing Agricul-
tural Pollution Sources. Colorado State University.
NTIS/PB-246 656, October 1975.
171. Water Quality and Treatment. McGraw-Hill Book Company.
New York, 1971.
172. Weaver, D. E. The Diffusivity and Solubility of Nitrogen
in Molybdenum and the Trapping of Nitrogen by Carbon in
Molybdenum. University of California, Lawrence Livermore
Laboratory, Berkeley, 1968.
173. Weinstein, N. J. and R. F. Toro. Control Systems on
Municipal Incinerators. Environmental Science and
Technology, 10(6):545-547 , June 1976.
174. Weir, A. Jr. Results of the 170 MW Test Modules Program,
Mohave Generating Station, Southern California Edison
Company. Paper presented at the EPA Symposium on Flue
Gas Desulfurization, New Orleans, March 8-11, 1976.
175. Weir, A. Jr., et al. Factors Influencing Plume Opacity.
Environmental Science and Technology, 19(6):539-544,
June 1976.
176. Wen, C. Y., et al. Scale Control in Limestone Wet Scrub-
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179. Yan, C. J. Evaluating Environmental Impacts of Stack Gas
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261
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SECTION XIV
GLOSSARY
ABBREVIATIONS
ac acre
ac ft acre feet
AMD Acid Mine Drainage
Btu British thermal unit
cm centimeter
cm/sec centimeter per second
m3 cubic meter
ft3/sec cubic feet per second
COD Chemical Oxygen Demand
oc degrees centigrade (Celsius)
OF degrees fahrenheit
EPA Environmental Protection Agency
EPRI Electric Power Research Institute
ft feet
ft/s feet per second
FDS Flooded Disc Scrubber
FGC Flue Gas Cleaning
FGD Flue Gas Desulfurization
ft foot
gal gal 1 on
gpm gallons per minute
g gram
ha hectare
hr hour
IERL-RTP Industrial Environmental Research
Laboratory - Research Triangle
Park
in inches
in/s inches per second
262
-------
ABBREVIATIONS (continued)
J
J/s
kg
kcal /kg
km
kw
L/G
£
M
MW
MWh
MESA
mgd
No.
NPDES
OSHA
ppm
Ib
psi
sec
SCE
TCA
IDS
TOS
TPD
TSS
TVA
USDA
W
WES
Joul e
Joule per second
ki logram
kilocalorie per kilogram
ki1ometer
ki1owatt
Liquid to Gas ratio
1 i ter
liters per minute
Mega
Megawatt
Megawatt hour
Mine Enforcement and Safety
Admi nistration
million gallons per day
newton
number
National Pollutant Discharge
Elimination System
Occupational Safety and Health
Admi nistrati on
parts per mi 11 ion
pound
pounds per square inch
second
Southern California Edison
square meter
Turbulent Contact Adsorber
Total Dissolved Solids
Total Oxidizable Sulfur
metric Tons Per Day
Total Suspended Solids
Tennessee Valley Authority
United States Department of
Agriculture
Watt
Waterways Experiment Station
(U.S. Army, Vicksburg,
Mississippi)
263
-------
METRIC - ENGLISH UNIT CONVERSION TABLE
Length
1 meter = 39.37 inches - 3.28 feet = 1.09 yards
1 kilometer = 0.62 miles
1 millimeter = 0.03937 inches
1 centimeter = 0.3937 inches
1 micrometer = 3.937 x 10-5 inches
Area
1 square meter = 10.744 square feet = 1.196 square yards
1 square kilometer = .384 square miles = 247 acres
1 square centimeter = 0.155 square inches
1 square millimeter = 0.00155 square inches
1 hectare = 2.471 acres
Volume
1 cubic meter = 35.314 cubic feet = 1.3079 cubic yards
1 cubic centimeter = 0.061 cubic inches
liter = 1.057 quarts = .0264 gallons = 0.81 x 1Q-6 acre-feet
Mass
1 kilogram = 2.205 pounds
1 gram = 0.035 ounces = 15.43 grains
1 milligram = 0.01543 grains
Velocity, linear
1 meter per second = 3.28 feet per second
1 millimeter per second = 0.00328 feet per second
1 kilometer per second = 2,230 miles per hour
1 meter per second = 2.24 miles per hour
Flow (volumetric)
1 cubic meter per second = 15,850 gallons per minute =
2,120 cubic feet per minute
1 liter per second = 15.85 gallons per minute
V i s c o s i ty
poise = 1.45 x 10~5 pounds (weight) seconds/square inch
Density
1 gram per cubic centimeter = 62.428 pounds per cubic foot
264
-------
METRIC - ENGLISH UNIT CONVERSION TABLE (Continued)
Pressure
1 newton per square meter = 0.00014 pounds per square inch
1 newton per square centimeter = 1.4 x 10~10 pounds per square
inch
1 kilogram (force) per square centimeter = 14.223 pounds per
square inch
1 dyne per square centimer = 1.450 x 10-5 pounds per square
inch
Temperature
1 degree Kelvin or 1 degree Celsius = - 17.77
9
Work, energy, quantity of heat
1 Joule = 2.778 x 10~7 kilowatt hours = 3.725 x 10"7 horsepower
hours = 0.73756 foot-
pounds = 9.48 x 10-4
British thermal units
1 kilojoule = 2.778 kilowatt-hours
265
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APPENDIX A
AVAILABLE TECHNOLOGY AND REGULATORY OPTIONS
GENERAL
This section suggests an approach to the formulation of
guidelines and limitations for FGC sludge management based upon
best practical control technology currently available. The
mechanisms for attenuation or dilution of FGD sludge contaminants
under real world conditions have been evaluated both in theory
and practice. The physical properties of FGD sludge have also
been studied in detail. These physical and chemical properties
set need for regulation.
The suggested regulatory approach is analogous to the pro-
cedures being followed by state regulatory agencies in establish-
ing guidelines and limitations for treated wastewater point
sources. Regulatory agencies in their review of proposed new
wastewater treatment facilities for point source discharges go
through the following steps:
1. The beneficial use of the receiving water is
established, e.g., use as a trout stream, a
drinking water supply, recreational body
contact, etc .
2 . Based upon the beneficial use established,
maximum concentrations for various contaminants
in the treated effluent are set, e.g., 10 mg/£
BOD, 3 mg/£ nitrogen, etc.
3. Given the effluent limitations (maximum contami-
nant concentrations) which must be met, the
applicant responds with a treatment technology
which will theoretically supply sufficient
treatment to meet the effluent limitations on
a sustained basis, e.g., activated sludge fol-
lowed by chemical coagulation and filtration,
etc. The regulatory agency reviews the pro-
proposed technology.
4. Upon approval of the technology, the regulatory
agency will provide the applicant with specific
design criteria for use in preparing detailed
266
-------
design plans and specifications, e.g., clarifier
overflow rates, distance to nearest residence,
etc .
5. Finally, the regulatory agency establishes moni-
toring, control, and reporting procedures which
the applicant must implement to ensure that the
effluent limitations established in No. 2 above
are being met.
The above approach is site-specific, as opposed to a uni-
versally applied "one number" approach and recognizes that local
site conditions are important in establishing best practical
control technology. In addition, the above approach allows the
applicant to make cost-effective decisions within established
technical boundaries. Finally, the approach provides continuous
interaction between applicant and regulatory agency to ensure
that environmental protection objectives are met.
The wastewater effluent limitations approach outlined above
can be adopted to FGD sludge treatment/disposal guidelines and
limitations. Figure 22 shows in a simplified flow diagram the
major steps involved. If each of the steps shown can be care-
fully defined in a procedural manner, it will provide a uniform,
organized approach to decision-making based upon site/waste
specific data. Each step is individually discussed in the
following subsections. The reader is cautioned that the discus-
sion is conceptual. It is recognized that substantial additional
site-specific analysis is required before a comprehensive cook-
book procedure can be developed that is universally applicable
to all FGD disposal operations.
DEFINE BENEFICIAL USES
In this step, the regulatory agency, with the cooperation
of the applicant, performs an evaluation of the proposed disposal
site to determine what beneficial environmental resources
require protection. The environmental factors which warrant
protection during FGD sludge disposal are the following:
1. Groundwater resources underlying the site;
2. Surface water resources at elevations lower
than the site; and
3. Future land uses at the site location.
Groundwater Resources
Considering first groundwater resources underlying the
site, a comprehensive hydrological report is required which
includes the following information:
267
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Establish Environmental Benefits
to be Protected at
the Treatment/Disposal Site
Determine Degree of Protection
Necessary to Protect
Environmental Benefits
Categorize Treatment/Disposa1 System
Capability to Provide Necessary Environmental
Benefit Protection
Establish Monitoring,
Control, and Reporting Procedures
Figure 22.
Stepwise Approach to the Proposed
Regulatory System
268
-------
1. Identification of the groundwater aquifers in
the area which could be affected by migration
of leachate from the disposal site. Each
aquifer should be defined to the extent feasi-
ble in terms of depth, size, storage capacity,
replenishment rate, and maximum withdrawal rate.
It is recognized that hydrogeology is an in-
exact science; however, a qualified profes-
sional can utilize background information and
field tests (test wells, seismic readings,
etc.) to make his estimates.
2. Determination of the quality of the existing
groundwater in each aquifer potentially af-
fected by leachate from the proposed disposal
site. Quality analyses should include normal
chemical, physical, and bacteriological tests
for potable water supplies.
3. Best estimate of the existing and/or potential
beneficial uses of the groundwater in each
aquifer potentially affected by leachate from
the proposed disposal site. Existing and/or
future probable usage could include the follow-
ing categories :
Community water supply
Individual home/ranch/farm water supply
Agricultural irrigation supply
Industrial process water supply
Surface Water Resources
As previously stated in this report, FGD disposal sites
constitute a major hazard to surface waters if there is a
failure of the retention structure and the stored sludge escapes.
Whether the proposed site poses such a danger can be evaluated on
the basis of the following criteria:
• Distance from site to surface water(s)
• Elevation difference between site and surface water(s)
• Type of surface water(s), e.g., lake, river, etc.
§ Present or projected beneficial uses of surface water(s)
• Volume and/or flow rate(s) of the surface water.
It is anticipated that this evaluation will not always be
clear-cut, i.e., that there is a serious danger to valuable
269
-------
surface water resources in case of impoundment failure, or that
no danger exists because of favorable topography and location.
Future Land Uses at the Site Location
As discussed elsewhere in this report, the load bearing
capability of ponded unstabilized sludge is generally poor. With
proper cover material, light recreational use is possible, but
in essence the pond area is eliminated for higher use purposes.
In many disposal site areas this situation may be acceptable,
because the land has little projected value.
CATEGORIZE SITES ACCORDING TO DEGREE OF PROTECTION NECESSARY
General
At this point in the procedure, an estimate is made of the
acceptability of the site for FGC sludge disposal based on
natural site characteristics and the characteristics of the FGC
waste. It is desirable to formulate a series of site categories
based on possible beneficial uses. A simplistic site categori-
zation system has been developed based only upon protection of
groundwater resources, surface water resources, and future land
use. Table 55 summarizes the seven categories of sites selected.
They range from site category 1, where there is essentially no
environmental benefit to protect, up to site category 7, which
is unacceptable for FGC sludge disposal because no practical
technique will adequately protect a valuable groundwater re-
source. Figure 23 shows a decision tree approach to disposal
site categorization into one of the seven categories. The
remainder of this subsection will discuss the use of Figure 23-
Decision Tree Approach
As shown in Figure 23, each of the decision points is based
upon a site variable. These variables, discussed in Section IV,
are listed below along with decision levels used in the decision
tree:
1. Possible future land use
a. Possible urban or industrial development in the
surrounding area in the reasonable future
(excluding power plant use).
b. Little or no probability of development beyond
range land or agricultural land in the surround-
ing land.
270
-------
TABLE 55. PROPOSED CATEGORIZATION OF FGC DISPOSAL SITES
Site
Category
No.
1
2
3
4
5
6
7
Environmental Benefi
Requiring Protection
Land Surface
Value Water
Low No
Low Yes
High No
High No
Low No
Low Yes
Site unacceptable regard!
of adequately protecting
t
Ground-
water
No
No
No
Yes<3>
Yes
Yes
Protection Method site Mod1fl-cation .
Sludge
Pretreatment
No
No
Stabilize^
Stabil ize
No
No
ess of protection methods used
groundwater
resource
Retention
Dikes
Standard
(2)
Extraordinary^ '
Standard
Standard
Standard
Extraordinary
due to impossibili
Reduce Mass
Transport
No
No
No
Yes
Yes
Yes
ty
(1) It is assumed that stabilized sludge will not flow and poses no threat to surface water
regardless of retention dike integrity.
(2) Dual dikes, supplementary interceptor pond, or other failsafe method of preventing
escape of sludge if primary dikes fail.
(3) See narrative for discussion of pollutant mass transfer potential through soil.
-------
ro
~-j
ro
SLUDGE
CHARACTERISTICS
START
SITE
CHARACTERISTICS
CATEGORY 1
UNSTABLE
CATEGORY 2
UNSTABLE , HIGH
RELIABILITY DIKE
«N<
1 IS
EN
t
1
SURFA
fER
3ANGER
CE
ED7
YES
i
NO
i
YES
IS EVAP/
PREC1P >
NO
IT
YES
4 —
YES
NO
IS GROUNDWATER
USEFUL?
4-1
IYES
MASS
TRANSPORT
MODEL
1
IS FLOW
< 1M/YR7
JNO
IS FLOW
<10 M/YR7
JNO
WILL
GROUNDWATER
4 TDS >10X7
NO
NO
YES
IS SLUDGE
STABLE7
JNO
ESTIMATE
FUTURE
LAND USE
I
HIGH
LAND
STABILIZE
SLUDGE
YES
STABILIZE
SLUDGE
t
YES
*>
IS GROUNDWATER
USEFUL7
IYES
MASS
TRANSPORT
MODEL
1
IS FLOW
<0.3 M/YR7
I NO
IS FLOW
<3 M/YR7
NO
CATEGORY 3
STABLE
YES
YES
*"
WILL
4 TDS >10X7
IS EVAP/
PRECIP
l- 17
NO
1
— »
YES
NO
MODIFY SITE TO
LOWER MASS
TRANSPORT
CATEGORY 6
LOW FLOW, HIGH
RELIABILITY DIKE
CATEGORY 5
LOW FLOW
YES
NO
I YES
MODIFY SITE TO
LOWER MASS
TRANSPORT
WILL
GROUNDWATER
4 TDS > 10X7
I NO
IS SURFACE
WATER
ENDANGERED?
YES
WILL
GROUNDWATER
A TDS > 10X?
1
YES
NO
CATEGORY «
STABLE, LOW FLOW
CATEGORY 7
UNACCEPTABLE
Figure 23. Decision tree approach to disposal site categorization.
-------
Groundwater resources
a. The near-surface aquifers under the site contain
potentially useful water.
b. Existing near-surface aquifers do not meet
useful standards and are not interconnected
with potentially useful aquifers, or, even
if the water quality is satisfactory, the
quantity and potential pumping rates per
well exclude economic use of the water (e.g.,
near-surface aquifers have a low permeability --
silty clay or clay with little sand and
gravel) .
Evaluation of natural protection to groundwater
resources afforded by site .geology and hydrology,
if the groundwater is considered valuable
a. Time constants -- Calculate the time neces-
sary for migration of leachate over a 100 m
distance.
a-| . Time greater than 30 years (flow velocity
less than 10~5 cm/sec)
a2- Time less than 30 years (flow velocity
higher than 10~5 cm/sec)
a3. Time greater than 300 years (flow velocity
less than 10~6 cm/sec)
b. Rate constants -- Calculate the equilibrium
mass transport of TDS out of the disposal
site (see Section VIII and Appendix B for
calculation approach). Estimate the probable
rate of groundwater movement through the
aquifer(s) affected (hydrology study).
Determine increase over background TDS in
the groundwater resulting from mixing with
1eachate.
b-j . Rate and quality of leachate, at
equilibrium flow rates, are low
enough relative to ambient ground-
water quality and flow rates such that
the groundwater (assumed mixed)
leaving the site shows a less than
10 percent (arbitrary number) increase
in TDS. Calculations should neglect
soil adsorption.
273
-------
b0. Rates will cause an increase in ground-
2 '
water IDS of greater than 10 percent.
4. Surface water protection from catastrophic events
a. Sulfite-bearing sludges can reach a water
course should impoundment or pipe failure
occur.
b. Sulfite-bearing sludges cannot reach a water
course following catastrophic release.
5. Site meteorology
a. Evaporation rate from wet sludge exceeds
precipitation rate minus runoff from
specific site design
b. Precipitation exceeds evaporation from
wet sludge
The rationale for selecting the number shown in 1 through
5, above, is partially subjective. This subjective quality
becomes necessary when one considers the following:
1. Zero impurity transport from the disposal site for
infinite time is a physical impossibility;
2. The relevant time scale for pollutant movement has not
been defined in either a legal sense or in terms of
consensus in the scientific community;
3. Since zero degradation of groundwater over infinite
time periods is impossible, what is acceptable degra-
dation? (Ne have used a 10 percent change in TDS.)
4. The value to be placed on future land use versus
current costs has not been defined either legally or
socially.
Recognizing the subjective nature of these numbers, the
following rationale can be given for each value shown:
• Potential land uses - If there is no prospect of the
land being used for some purpose with a higher value
than range or agricultural land in the next 100 years,
the load bearing strength and associated physical
properties of the completed disposal site are of lesser
importance.
• Groundwater protection - If the groundwater is of low
quality or inaccessible because of low extraction rates
274
-------
it cannot be classified as a resource needing
protection.
• Mass transport rate - 0.3 m/yr. If the rate of pollu-
tant movement is this slow, it can be considered in-
significant (10~6 cm/sec flow rate).
• Mass transport rate - 3 meters/year. If the impuri-
ties have only moved 90 meters in 30 years and the
meteorology is such that the site will dry out after
closure (power plant life is 30 years or less),
little movement will occur after closure and can be
neglected .
• Mass transport rate - 10 percent contamination of
mixed groundwater: Considering the variations in
groundwater quality over short distances, it is
believed that the 10 percent increase would be accep-
table at virtually any site. The percentage is
obviously an arbitrary number and at many sites a
larger percentage increase would be acceptable.
• Surface water protection - It is not necessary to pro-
vide extra protection for surface waters if the sludge
cannot reach the water upon accidental release. A
release of this type would only create an unpleasant
situation and not an ecological disaster.
The combination of these variables to categorize disposal
sites was shown in Figure 23. This figure interrelates the
site variables in such a way that environmental protection can
be achieved without placing extensive and expensive restrictions
on sites which naturally protect the environment.
ESTABLISH MONITORING, CONTROL, AND REPORTING PROCEDURES
General
Once the disposal site has been subjected to the above cri-
teria, it becomes operational under the appropriate category
and its restrictions. Monitoring, control, and reporting proce-
dures should be specified for all FGD sludge disposal sites.
During the categorization procedure, the potential for
environmental impact from several parameters was evaluated.
These parameters included:
• Groundwater contamination
• Sludge in-place stability
e Catastrophic sludge release to surface waters
275
-------
Groundwater Monitoring
The potential for groundwater contamination from sludge
leaching is determined as part of the site evaluation. Input
parameters include sludge leachate characteristics, soil and
sludge permeability, hydraulic gradients, groundwater hydrology
and quality, and attenuation and ion exchange capacity of the
soil. These parameters together comprise the simplified mass
transport model described in Section VIII. Therefore, the
purpose of the monitoring program should be to confirm or con-
tradict these projections based upon field sampling data.
As discussed in Section IX, the best chemical regulating
parameter is total dissolved solids. The TDS "front" should
precede all other trace metal detection in the groundwater due
to limited attenuation of the common monovalent cations and
anions. Limited theoretical knowledge of attenuation procedures
makes TDS the simplest parameter to model and perform field
comparisons with.
Present techniques for monitoring groundwater contamination
are often inadequate. Regulations usually require the instal-
lation of sampling wells around the site perimeter and periodic
analysis of samples from the wells to detect increases in back-
ground levels of various contaminants. The drawback to this
technique is that the sampling wells are drilled to a depth
below the groundwater table in order to reach saturated soil.
There is no evidence of contamination until the leachate has
reached the groundwater. At this point in time the leachate has
already passed through the soil between the bottom of the pond
and the groundwater aquifer and the situation is irreversible.
Sampling techniques should be developed which measure the rate
at which the leachate is leaving the disposal pond and passing
through the soil between the pond bottom and the groundwater
aquifer. Such techniques will provide early warning if theo-
retical calculations were incorrect at a time when preventative
measures can still be implemented. It is beyond the scope of
this report to define alternate sampling techniques; however, it
is a universal problem which deserves research and development.
Accidental Spill Monitoring and Prevention
Procedures for monitoring spill potential are available
for other specialized waste disposal/hand!ing systems. These
procedures can be readily adopted to FGD sludge disposal.
Maintenance of impoundments for phosphate slimes is governed
by the Rules of the State of Florida Department of Pollution
Control (See Section XI). These rules govern inspection of dams
and dikes during disposal and periodically following closure.
Documentation of operations is also required. The control of
sludge spillage from pipe failure is analogous to the monitoring
requirements for oil handling and storage facilities. Under EPA
276
-------
Regulations on Oil Spill Prevention (38 FR 34164, December 11,
1973), all aboveground pipelines and valves require regular
examination to avoid spill events (Section 112.7, Spill Preven-
tion Control and Countermeasure (SPCC) Plan). While not
directly applicable to sludge due to the variety of storage,
handling, and transportation alternatives, substantial techno-
logy transfer appears feasible.
In-Place Sludge Stability Monitoring
Several states currently use stability as one evaluation
criterion but have not as yet developed a comprehensive defini-
tion for regulating purposes. Stability as it is used in cur-
rent research refers to the sludge load bearing strength as a
function of time and nature of the applied force (static vs.
dynamic). For sites requiring stabilization for load bearing
purposes, stability should be similar to that of the surrounding
soil (nondegradation).
277
-------
APPENDIX B
THE EQUATIONS OF MASS TRANSPORT
In Section VIII, it was shown that disposal site character-
istics influence the rate at which FGD sludge contaminants are
released to the environment. Adsorption, precipitation, and
desorption effects on concentration terms in relation to overall
mass transport have been under investigation by scientists. Soil
scientists have applied mass transport theory to the migration
of various ions through soils.
The present state of knowledge with respect to mass trans-
port of contaminants through soils is not totally satisfactory,
but this knowledge is advancing rapidly.
There are several approaches to describing mass transport
of contaminants through soils and groundwater. The equations
used to describe this phenomenon usually include a convection
term and dispersion term. The convection term describes the
movement of contaminants relative to the liquid flow velocity.
The dispersion term accounts for the spread of contaminants with
time due to the concentration gradient. The convection and
dispersion terms have been combined into an overall mass trans-
port equation in the EPRI study by Radian Corp. (Ref. 133). A
discussion of this theoretical approach is appropriate here.
OVERALL MASS TRANSPORT THEORY
In the approach used by EPRI, the concentration terms are
similar to those used in chromatography theory. The overall mass
transport equation can be described as follows:
. . ^v C + D V2 C (1)
where, C = fluid-phase solution concentration
Q = solid-phase concentration per unit volume of solid
u = interstitial fluid velocity
t = time
278
-------
e = void fraction
D = dispersion coefficient
v = gradient operator
2
v = Laplacian operator
The implicit assumptions in the formulation of the above
mass transport equation are (1) that the dispersion terms are
not a function of concentration, and (2) that any uniformities
in the interstitial velocity term are accounted for in the
dispersion term.
If the solid phase concentration is equal to a constant
times a liquid phase concentration, the following relationship
hoids true:
Q = KC (2)
where:
K = distribution coefficient (which may be a non-linear
function of C)
This is only valid for concentrations well below the solubility
limit or site adsorption capacity.
Utilizing equation (2) and assuming local equilibrium
exists, it is possible to define a retardation parameter R as
fol1ows:
R = y (1 + K (!=£)) * (3)
This retardation parameter has been adopted from chroma-
tography theory. It is the same parameter utilized in the
theory associated with trap diffusion in solids. This retarda-
tion parameter provides an effective method of dealing with the
*The definition of this retardation parameter from random walk
theory is derived in several fashions in the literature
(Ref. 21 , 165). It has also been defined as
1 + (i^-) K
rather than the inverse used in this narrative (Ref. 123).
This difference in terminology definitions is important when
works are reviewed in this subject.
279
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fact that a moving contaminant spends part of its time in the
liquid and part of its time on the immobile solid phase. The
partitioning coefficient provides an idea of the relative time
spent in either of the two phases, with the solid phase being
stationary. It is assumed that the contaminant does not make
forward progress while it is spending time on the solid.
There are also implicit assumptions of no precipitation in
this formation of the transport equation. They mean that this
equation will predict faster migration than would be observed
in field situations where precipitation occurs. In the proper
formulation of this equation, the constant K is a function of
C-j, T, and the soil (where C-j is all the ions in solution,
expressed in terms of activities).
Using Equation (3), Equation (1) can now be rewritten in
the fol1owi ng form:
|£ = -FU7vC + RDv C (4)
o "C
The above overall mass_transport equation contains two terms.
The first of these, -RuvC; is the convection term, which depends
upon the velocity of the liquid flowing through the interstitial
voids in the material. The second, RDv2C, is a dispersion term
that is related to molecular diffusion, multipath dispersion,
fluid-phase mass transfer, interparticle diffusion, adsorption
phenomena, and other factors that tend to disperse the concen-
tration profile.
The velocity term u in Equation (4) is related to the
permeability of the material through which the fluid is passing
according to Darcy's Law. It should be noted that the velocity
in Equation (4) is velocity through the interstitial space and
not the overall average velocity (superficial velocity) as
generally computed from Darcy's equation. Therefore, Darcy's
equation must be modified as follows to include the void fraction
term:
u" = - - v-$ (5)
where:
$ = the hydraulic potential = (P + pgh)
k = hydraulic permeability (includes viscosity term)
As shown earlier in this document, k is not necessarily constant,
and may depend on v-$ or the degree of saturation of the
material.
280
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Equations (1), (3), and (4) can be written in a more
general form, in which the effective dispersion coefficient (D)
and the retardation coefficient (R) are both a function of con-
centration. In this form, the dispersion term entering into
Equation (4) would be nonlinear (v-RD-vC rather than RDv C).
As shown in Section VIII, the dispersion term is insignificant
to overall mass transport for the times and distances relevant
to stabilized sludge disposal. Therefore, these nonlinear
effects and subtleties in the equations are of no significance.
In attempting to show the relative magnitudes of the con-
vection and dispersion terms in Equation (4), it is useful to
look at each term individually- In the dispersion term, the
value for R will range from virtually 0 to a maximum of 1. The
maximum case of 1 is obtained for zero adsorption; consequently,
there is no retardation. Values of R less than 1 are achieved
when this impurity is significantly adsorbed by the soils
through which the liquid passes. The value of R for an ions is
typically on the order of 1, with a corresponding partitioning
coefficient near 0. However, the high cation exchange capacity
of many soils (in particular, clays or high organic soils)
causes the cations to have much smaller values of R and corres-
pondingly higher values for the partitioning coefficient.
Typical R values for multivalent cations are on the order of
10-3.
The dispersion term D in Equation (4) is comprised of two
classes of terms. The first class includes terms that are
independent of velocity. These terms correspond to the diffu-
sion through the liquid phase that would be experienced for the
ions in question, unaffected by velocity, adsorption, or
desorption. This conventional diffusion term is the same as
the diffusion coefficient in liquid for the ion in question.
However, the term is corrected for the void fraction effects
resulting from the occupation by solids of much of the volume.
The term is also corrected for a corresponding increase in
effective path length. This increase is due to the fact that
the ions must circumvent the particles. These correction
factors may decrease the effective diffusion coefficient by, at
most, a factor of 10 over that measured in a static all-liquid
system.
The second class of terms entering into the dispersion
term is produced by the velocities of flowing interstitial
liquids. This class of terms includes, among others, multipath
dispersion, fluid phase, mass-transfer kinetics, interparticle
diffusion, and adsorption and desorption kinetics. The multi-
path dispersion contribution can be visualized by observing that
some pores in the soil are larger than others and would have a
higher interstitial velocity. Therefore, some parts of the
stream will flow at different velocities than other parts. As
a result, any concentration front would tend to be dispersed.
281
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At this point, it should be noted that the basic theory asso-
ciated with chromatography has derived functional forms for
plate heights and has derived other related phenomena for the
velocity-dependent terms. These velocity-dependent terms are
the primary determinants of the dispersion characteristics for
chromatography theory. For the flow of fluids from the disposal
pond operation through soils, very low velocities are encoun-
tered.
At such low velocities, the diffusive component of the
dispersion coefficient may be the dominant term. This will
depend upon the actual velocities and specific geological condi-
tions in question. As a result, the correction factors that
must be applied to the known liquid-phase diffusion coefficients
for the ions in question become more important for soil migration
than for chromatographic theory. This correction factor will be
different in soils than in a chromatograph, which has a fairly
open and well-defined packing. As previously mentioned, this
correction factor would have an expected value range of 0.1 to
0.3, rather than the .6 characteristic of chromatography-
These velocity-dependent terms in the dispersion depend
strongly upon the uniformity of the geological conditions.
Where the flows are highly nonuniform, such as in the case of
cracked rock, these terms may be thousands of times larger than
they are in uniform conditions, such as in sand.
LABORATORY ANALYSIS OF MASS TRANSPORT
The interplay between diffusion and convection terms is
important when evaluating the environmental impact of FGD sludge
disposal, as discussed in Section VIII under site characteris-
tics. Convection is the dominant term in untreated sludge
leaching, provided the underlying soil is fairly permeable.
Diffusion can limit leaching of highly soluble salts and certain
trace metals from stabilized sludges.
While modeling the convective cases is fairly straight-
forward, research efforts are continuing to evaluate diffusion-
limited leaching from stabilized sludges. Four different
approaches to leaching stabilized sludge have been employed thus
far, each one of which combines both diffusion and convection
but with one or the other possibly dominating the mass transport.
These methods are:
1. Pressurized flow of small volumes of water or leaching
solution through stabilized sludges, with results
giving some indication of soluble salts depletion as
a function of pore volumes leached (Ref. 96);
2. Surface washing of stabilized sludge in a packed
column, representing rainwater and groundwater washing
282
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of the sides of a sludge monolith, sich as a stable
landfill (Ref. 162);
3. Agitated washing of a sludge plug, representing
surface runoff from a stable landfill*;
4. Elutriation of crushed, stabilized sludge, representing
the solubility limits of the various sludge contaminants
(Ref. 96).
Approaches 1 and 4 are representative of convective leaching of
stabilized sludge, while 2 and 3 represent primarily diffusion-
limited leaching. The latter approaches most closely represent
the mechanics of leaching within a stabilized mass.
In interpreting diffusion-limited experiments using
approaches 2 and 3, it is useful to construct a conceptual
model of what is happening. Assume that the solid material is
made up of an insoluble, interconnected matrix that surrounds an
interconnected group of semisoluble materials, highly soluble
materials, and voids filled with either air or liquid. After
initial removal of loose material from the surface, the inter-
connected matrix material is chemically and physically stable.
The group of semisoluble materials would include components
such as CaSOA-2H20, CaS03-l/2 H20, CaF^- and other components,
whose solubility limits and concentrations in the solid phase
indicate that a solid phase will exist when the sample is water
saturated. The group of soluble components would include
materials such as Na2S04, Nad , CaC^, etc., whose solubility
limits and concentrations in the sample would allow them to be
in solution in the liquid-filled interstitial volume under
saturation conditions.
The limited solubility components will behave differently
than the highly soluble components under different experimental
conditions. Hence, one cannot discuss the problem from the
standpoint of TDS alone. The individual components making up
the TDS must be looked at separately-
The limited solubility components have a very large reserve
of solid phase near the surface, with relatively short diffusion
distances. If the rates of achieving local equilibrium between
the interstitial liquids and the solid phases are fast, there
would be a denuded zone near the surface where no soluble phase
of the component exists. Clearly this assumes that: (1) the
matrix does not fall apart when the soluble phase is removed;
(2) there are no driving forces for liquid movement through the
matrix; and (3) diffusion in the liquid phase is rate control-
1i ng.
*Personal communication with Steven I. Taub, I U Conversion
Systems, December 28, 1976.
283
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The highly soluble salts will behave differently than the
limited solubility salts. The highly soluble salts, such as
NaSO^, will be diffusing from further inside the specimen and
will not have the effective reserve of a large-volume solid
phase. Once the sample is fully saturated, one can assume that
all these salts are in the interstitial liquid phase. If there
is 2 percent Na2S04 in the sample and the sample contains 10
percent water-filled voids, one would expect this interstitial
water to contain 200,000 ppm of Na
These solubility differences manifest themselves in the
results of approaches 2 and 3. Approach 2 is a long-term
experiment, so the system would be expected to be near equili-
brium for all major components within the specimen (but not for
some heavy metals which may be absorbed). Since these experi-
ments are near equilibrium, they will provide information with
respect to contaminants that may be tied up chemically or
physically in a manner that prevents them from achieving
equilibrium with the interstitial liquids (i.e., co-precipita-
tion, incorporation as substi tutional impurities in insoluble
solid phases, etc.). The system in approach 3 would be near
equilibrium for limited solubility salts with large reserves in
the solid phase, but would be near nonequi 1 i bri urn for highly
soluble salts. If the data from approaches 2 and 3 on the
components making up the TDS were compared, one would expect
to find similar results between 2 and 3 for the CaS04 and
different results for NaSO^ NaCl , etc., and possibly for heavy
metal s .
There are several factors encountered in practice that can
effect the analysis. The percentage saturation as a function of
position within the sample would cause the effective diffusion
coefficient to be a function of position. Adsorption/desorption
phenomenon on surfaces with the matrix would reduce the effec-
tive diffusion coefficient (this may be very significant for
heavy metals). Details of the experimental procedures will
affect the boundary conditions used in the derivations of
Equation (4) and may dictate that a different solution be
utilized. The various species that are contained within the
sample do interact; there will be effective solubility constants
in the various components, which are functions of position and
composition within the sample. Another complicating factor may
be slow dissolution kinetics associated with some solid phases,
which may control the overall rates.
Therefore, it can be concluded that both approaches 2 and
3 have some value in gaining an understanding of leaching from
stabilized sludge. The mathematics can only estimate what will
occur in the field. Laboratory studies and site monitoring are
essential to confirming the estimates.
284
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-77-118
3. RECIPIENT'S ACCESSI ON- NO.
4. TITLE AND SUBTITLE
Data Base for Standards/Regulations Development for
Land Disposal of Flue Gas Cleaning Sludges
5. REPORT DATE
December 1977 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Dallas E. Weaver,
John P. Woodyard
8. PERFORMING ORGANIZATION REPORT NO.
Curtis J. Schmidt, and
9. PERFORMING ORGANIZATION NAME AND ADDRESS
SCS Engineers
4014 Long Beach Boulevard
Long Beach, California 90807
10. PROGRAM ELEMENT NO.
EHE 624 (RQAP 77 ABA, TaskOOS)
11. CONTRACT/GRANT NO.
68-03-2352
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory--Cin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Fina 1
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer - Donald E. Sanning 513/684-7871
16. ABSTRACT
This study addresses the problem of flue gas cleaning {FGuJ sludge disposal
to the land. It considers the problem from a potential regulatory approach, looking
at the various aspects which could play a part in determining the best practical con-
trol technology currently available. Factors that were taken into consideration
include: (1) the origin of the FGC sludge problem (character of the fuel, combustion
process, gas cleaning and sludge management); (2) criteria for the evaluation of
sludge disposal options (sludge characteristics, health, ecological, safety, and
aesthetic considerations; (3) applicable, existing or proposed standards/regulations
(solid waste, hazardous waste, drinking water, and air pollution regulations); and
(4) impacts of applying existing standards/regulations to the disposal of flue gas
cleaning sludges (cost aspects). The report presents 14 conclusions supporting the
need for FGC sludge disposal regulations and suggests a decision tree approach to
the formulation of guidelines and limitations for FGC sludge management which takes
into account site specific geographical and hydrological considerations. The report
contains 179 references and an Appendix on The Equations of Mass Transport.
The report was submitted in fulfillment of Contract No. 68-03-2352 by SCS Engineers
of Long Beach, California. The work was completed July 22, 1977.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/GlOUp
Sludge Disposal
Regulations
Waste Disposal
Byproducts
Disposal
Air Pollution
Desulfurization
Air Pollution Control
Stationary Sources
Non-Regenerable Process
3B
8. DISTRIBUTION STATEMENT
PUBLIC DISTRIBUTION
19. SECURITY CLASS (This Report/
UNCLASSIFIED
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
21. NO. OF PAGES
299
22. PRICE
EPA Form 2220-1 (9-73)
285
OUS GOVERNMENT PSINT1NC OFFICE 1978— 757-1-10/6680
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