EPA-450/3-74-016
November 1973
EVALUATION
OF LIME/LIMESTONE
SLUDGE DISPOSAL OPTIONS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-74-016
EVALUATION OF LIME/LIMESTONE
SLUDGE DISPOSAL OPTIONS
by
Radian Corporation
8500 Shoal Creek Boulevard
P.O. Box 9948
Austin, Texas 78766
Contract Number 68-02-0046
EPA Project Officer: Robert T . Walsh
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, N. C. 27711
November 1973
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This report is issued by the Environmental Protection Agency to report technical
data of interest to a limited number of readers. Copies are available free of charge
to Federal employees, current contractors and grantees, and nonprofit organizations
as supplies permit - from the Air Pollution Technical Information Center, Environ-
mental Protection Agency, Research Triangle Park, North Carolina 27711, or from
the National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22151.
This report was furnished to the Environmental Protection Agency by
the Radian Corporation, Austin, Texas, in fulfillment of Contract No. 68-02-0046.
The contents of this report are reproduced herein as received from the Radian
Corporation. The opinions, findings, and conclusions expressed are those of
the author and not necessarily those of the Environmental Protection Agency.
Mention of company or product names is not to be considered as an endorsement
by the Environmental Protection Agency.
Publication No. EPA-450/3-74-016
11
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ABSTRACT
The report presents results of a study of technology
for disposal of sludge created by lime and limestone flue gas
desulfurization systems at steam-electric power plants. Effects
of operating variables on the volume of sludge produced are ex-
plained with emphasis on plant situations in the State of Ohio.
Properties of sludges are reviewed, including settling character-
istics, rewatering tendency, strength, particle size, bulk den-
sity and chemical composition. The report considers potential
environmental hazards of sludge disposal, namely contamination
of water and ground water supplies. Methods of avoiding these
hazards are presented and evaluated. Technologies for solidify-
ing (fixating) sludge are discussed and evaluated along with the
current status of full-scale projects. The report concludes that
any large degree of commercial utilization is unlikely. Based on
available data, there are no insurmountable technological prob-
lems in disposing of sludge in an environmentally acceptable
manner. While economics of disposal are not well-defined,
studies a-re underway that should provide better cost information
and other valuable information.
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TABLE OF CONTENTS
Pas
1.0 INTRODUCTION 1
2.0 NATURE OF THE MATERIAL 8
2.1 Chemical Properties of Sludge and
Related Materials 8
2.2 Physical Properties and Settling
Characteristics of Scrubber Sludges. . 14
3.0 DISPOSAL OF SCRUBBER SLUDGE 19
3.1 Methods of Disposal 20
3.1.1 Disposal by Ponding 21
3.1.1.1 Pond Management. ... 22
3.1.1.2 Water Pollution
Potential and Control
for Ponding 23
3.1.2 Disposal by Landfill 31
3.1.2.1 Dewatering Techniques. 32
3.1.2.2 Sludge Fixation. ... 38
3.1.2.3 Water Pollution
Potential and Control
For Landfill Disposal. 49
3.1.3 Other Disposal Methods 56
3.2 Sludge Handling and Transport 58
3.3 Land Reclamation Aspects of Disposal
Sites 64
3.3.1 Rewatering Characteristics. . . 64
3.3.2 Strength of Disposed Material . 65
3.3.3 Support of Vegetation 69
3.3.4 Related Experience in Land
Reclamation 70
3.4 Commercial Utilization of Sludge ... 74
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TABLE OF CONTENTS (Cont.)
4.0 PRESENT AND PLANNED UTILITY INDUSTRY
DISPOSAL PROGRAMS 82
5.0 CONCLUSIONS 92
6.0 BIBLIOGRAPHY 97
APPENDIX A
APPENDIX B
APPENDIX C
APPENDIX D
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SUMMARY
One of the major problems inherent in any flue gas
desulfurization system is the necessity to dispose of or utilize
large quantities of sulfur removed from the flue gas. The
sulfur compounds produced by flue gas desulfurization systems
fall into two general categories: throwaway or saleable products
Lime/limestone scrubbing systems generate a throwaway sludge
with little commercial value at the present time.
The environmental effects of sludge disposal will be
dictated by the chemical and physical properties of the material,
and these properties may vary widely for different operations.
One potential environmental effect of considerable concern is
water pollution, both surface water and groundwater, and it is
the chemical properties of the sludge which are relevant to
this area. Another environmental concern is land reclamation
of disposal sites, and it is the physical properties of the
sludge which are most relevant to this area. With proper site
selection and design, including a permanent impermeable liner,
and sound operating practices, surface and groundwater pollution
can be avoided. Comparison of available ash pond and SOP scrub-
ber liquors indicates that the dissolved solids and trace metals
concentrations in both types of liquors fluctuate greatly
depending on pH, fuel composition, SOS reactant composition
and concentration, and operating conditions. Since many of the
sludge samples examined thus far have contained varying amounts
of ash, it is possible that pollution potential would have
existed from ash ponds even if no SOP control were employed.
Ash is typically disposed of by ponding by the utility industry.
The construction, lining, and operation of ash ponds are
established technologies. Additional technology required for
scrubber sludge disposal includes dewatering and stabilization
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processes. Although these have been developed, the economics
are uncertain at this point. Further technical refinements
may be necessary once additional full-scale data become available.
The results of numerous studies now underway at pilot plants
and full-scale systems around the country will soon provide
additional information in this area, as well as providing
improved data on the chemical and physical properties of untreated
and treated (fixed) sludge and its permeability and leachability.
It should be noted that if necessary sludge can be stabilized
now, but in most cases final disposal can wait until more experi-
ence has been gained.
The following report contains a discussion of technology
available for the disposal, treatment, and handling of lime/lime-
stone sludges. Necessary chemical and physical data describing
the waste material are presented. The potential water pollution
and land reclamation problems are quantified to the extent
possible with available data. In conclusion, based on presently
available data, there are no insurmountable technological prob-
lems in disposing of sludge in an environmentally acceptable
manner.
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1.0 INTRODUCTION
One of the major problems inherent in any flue gas
desulfurization system is the necessity to dispose of or utilize
large quantities of sulfur removed from the flue gas. The
sulfur compounds produced by flue gas desulfurization systems
fall into two general categories: throwaway or saleable products
Lime/limestone scrubbing systems generate a throwaway sludge
with little commercial value at the present time. Lime scrub-
bing processes ordinarily produce sludges containing CaS03-^HsO,
Ca(OH)s, CaS04-2HsO and CaC03 ; limestone sludges generally
contain CaS03-^HaO, CaS04-2HP0, and CaC03 . For coal-fired
installations where efficient particulate removal is not
installed upstream of the wet lime/limestone absorber, such
sludges can contain large quantities of coal ash.
The amount of sludge generated by a given plant is a
function of the sulfur and ash content of the coal, the coal
usage, the on-stream hours per year (load factor), the mole
ratio of additive to SOj, , the S0a removal efficiency of the
scrubbing system, the ratio of sulfite to sulfate in the
sludge, and the percent moisture in the sludge. Table 1 lists
values of these various sludge parameters for a typical Ohio
plant and a hypothetical plant representing the National average
expected between 1973 and 1980.
The sulfur and ash content of coal will vary from
plant to plant. According to FPC data the average coal burned
in Ohio in 1971 contained 3.3370 sulfur and 12% ash.
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TABLE 1
TYPICAL SLUDGE PRODUCTION PARAMETERS
Typical Ohio National
Sludge Production Parameters Plant Average*
Coal :
Sulfur Content 3.33% 3.070
Ash Content 12% 12%
Plant:
Load Factor 65-80% 73%
Coal Usage .4 kg/kw-hr .4 kg/kw-hr
Scrubbing System:
S08 Removal Efficiency 80-90% 85%
Moisture in Sludge 20-60% 50%
CaO/SOa(inlet) Mole Ratio 1.0 1.0
CaCOa/SOa (inlet) Mole Ratio 1.2 1.2
Sulfite/Sulfate Mole Ratio 9:1 9:1
The values listed as the National average represent a mix of
Western and Eastern plants expected in 1980 based on the
trends shown by present flue gas desulfurization system orders
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The SOS removal efficiency will vary from one flue
gas desulfurization system to the next as a function of local
requirements. Air pollution control regulations adopted by the
State of Ohio call for reduction of SOS emissions in certain
high priority areas of the state to 1.8 mg/Kcal (1 lb/106 BTU)
by July 1, 1975. An S0a removal efficiency of about 85% will
be required to meet the standard for plants burning 3.33%
sulfur coal.
Since unreacted additive is disposed of with the
sludge, the stoichiometry of lime or limestone addition, that
is, the CaO/SOs or CaC03/SOS mole ratios, greatly influences
the amount of sludge to be handled. The CaO/SOs and CaC03/S02
mole ratios vary from system to system at present but the general
trend is toward lower values as operating experience is gained.
It is expected that reasonable values for this ratio will be
1.0 and 1.2, respectively.
Other factors influencing the amount of sludge to be
handled are the load factor of the plant, the coal use rate,
and the mole ratio of sulfite to sulfate in the sludge. The
amount of sludge produced by a plant is directly proportional
to the number of hours per year that the plant operates and the
coal usage of the plant. The 6400 hr/year and .4 kg/kw-hr
(0.88 Ib coal/kw-hr) values used for those calculations are
typical of large modern generating stations (DU-044, SU-031).
Obviously if the plant is on line a larger fraction of the
year or more coal is required per kw-hr, the amount of sludge
produced will increase. The sulfite to sulfate ratio in the
sludge affects the weight of the sludge produced as CaS04-2HsO
is heavier than CaS03-%H30. The ratio assumed in this paper
(9:1) is taken from the SOCTAP report (SU-031). However, some
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system designers are considering trying to completely oxidize
the sludge to improve settling characteristics and decrease
chemical oxygen demand. If this were done on a widespread
basis the weight of dry sludge produced per plant would increase
but improved settling characteristics would tend to lower the
proportion of water in the sludge. This would enhance solid/
liquid separation of the waste and possibly reduce land reclama-
tion problems associated with sludge disposal.
Table 2 shows the quantities of ash and sludge
produced per year by a 1000 MW coal-fired Ohio generating
station controlled by lime/limestone flue gas desulfurization
systems. The National average sludge and ash production sta-
tistics are shown for comparison.
Using the forecast demand for flue gas desulfurization
given in the SOCTAP report (SU-031) and the National average
annual sludge production rates per 1000 MW of controlled generat-
ing capacity, the amount of wet ash containing sludge (5070
moisture) that will have to be disposed of annually by 1980 is
predicted to be 113 million metric tons (125 million tons).
This value is based on the assumption that there will be 116,000
MW of generating capacity controlled by 1980 and that 75% of
the control will be by lime/limestone scrubbing systems.
In a related report it was predicted that 70% (12,400
MW) of the existing 1971 Ohio generating capacity could be
retrofitted (RA-089). Assuming a growth rate of 7% in installed
generating capacity the total Ohio generating capacity that
would need to be controlled would be 16,400 MW by 1975 and
21,250 MW by 1978. Using these estimates, the amount of wet
ash containing sludge (50% moisture) that would be produced
annually in Ohio would be 30 million metric tons (33 million
tons) by 1978.
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i
Ui
TABLE 2
TYPICAL QUANTITIES OF ASH AND SLUDGE PRODUCED PER YEAR BY A 1000 MW COAL-FIRED GENERATING
STATION CONTROLLED WITH LIME/LIMESTONE FLUE GAS DESULFURIZATION SYSTEMS
Coal Ash, dry
Coal Ash, wet (807. solids)
Limestone Sludge, dry*
CaS03-%H90
CaS04-2H90
CaC03 Unreacted
TOTAL
Limestone Sludge, wet
(507. solids)
Limestone Sludge, wet (with
ash)
Lime Sludge, dry*
CaS04-2HB0
CaO Unreacted
TOTAL
Lime Sludge, wet (50% solids)
Lime Sludge, wet (with ash)
Ohio
307,000 metric tons/year
384,000 metric tons/year
234,000 metric tons/year
27,000
84.000
345,000 metric tons/year
690,000 metric tons/year
1,304,000 metric tons/year
234,000 metric tons/year
27,000
20.000
281,000 metric tons/year
562,000 metric tons/year
1,176,000 metric tons/year
National Average
307,000 metric tons/year"
384,000 metric tons/year
264,000 metric tons/year
39,000
99.000
402,000 metric tons/year
804,000 metric tons/year
1,418,000 metric tons/year
264,000 metric tons/year
39,000
43.000
346,000 metric tons/year
692,000 metric tons/year
1,306,000 metric tons/year
ASSUMPTIONS:
Coal:
Plant:
Scrubber:
3.337. S; 127. Ash
6400 hr/yr; .4 Kg Coal/kw-hr
857. S08 Removal
1.0 CaO/SOa(inlet) Mole Ratio
1.2 CaC03/SOa(inlet) Mole Ratio
3.07. S; 127. Ash
6400 hr/yr; .4 Kg Coal/kw-hr
857. S0a Removal
1.0 CaO/SO,(inlet) Mole Ratio
1.2 CaC03/SO,(inlet) Mole Ratio
* S'.il f i tc/sul fate ratio based on performance of Chcmico scrubbing unit at Mitsui Aluminum Co., Japan.
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The solid waste disposal problem presented by
lime/limestone scrubber sludges can be put in perspective
by comparison to other industries and activities. Table 3
presents the quantities of waste, typical compositions, disposal
methods, and potential environmental problems for some of the
major solid waste producing activities in Ohio and other states.
It can be seen that in terms of quantity, estimated Ohio scrubber
sludge production in 1978 will present a disposal problem similar
to that provided by the present disposal of municipal refuse
in Ohio. Because of its lower density, however, the volume
required for refuse disposal is eight to ten times greater
than would be required for scrubber sludge. In terms of weight
the present disposal of phosphate rock slime and gypsum from
fertilizer manufacturers in Florida alone presents a problem
two to three times that of scrubber sludge in Ohio. The infor-
mation presented in this table shows that solid waste from
other industries presents problems of greater magnitude and
of no less serious natures than that posed by scrubber sludge.
Ponding and landfilling provide the major mechanisms
of disposal for most solid waste products. In terms of land
use and reclamation, these disposal mechanisms have many points
of similarity for various industries. Land use for waste
disposal may be esthetically objectionable. The wastes could
provide varying degrees of surface and groundwater pollution
depending on chemical composition, solubilities, and the location,
design and operation of the disposal site. For land reclamation,
most of the stable wastes will require only a cover material
to support vegetation and prevent eventual erosion. However,
some wastes are very resistant to dewatering and could reslurry
in the pond or landfill. If this is shown to be true, it is
likely that fixation will become a necessary practice.
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Waste Material
Quantity Disposed
of Annually
(dry basis)
Phosphate Rock Slime 36,000,000 (1967)
from Fertilizer Manu-
facturer1
TABLE 3
COMPARISON OF MAJOR SOLID WASTE DISPOSAL PROBLEMS
Composition
4-6% Solids
Solids Composition:
P,0, 9-177. Al,03 6-97.
SiOs 31-467. CaO 14-237.
Fe,0j 3-77i MgO 1-27.
F 0-17. Trace Elements
Method of Disposal
Ponding
Land Use or
Reclamation Problems
Environmental
Considerations
Water Pollution
Potential -
Possible Bogs
(Settles to only 30%
solldp after years. ,
Not established wheth- Ll ornl .
er dried solids will groundwater
support vegetative 2. Runoff to surface
growth.) water
Gypsum from Fertlll- 25,000,000 (1973)
zer Manufacturer3
85-907. Solids
Solids Composition:
CaS04'2HB0 1007.
Ponding and Sur-
face Piles
Cover material re-
quired for plant
growth.
Potential ground and
surface water pollu-
tion.
Ohio Municipal
Refuse1
18,000,000 (1973)9
Garbage, Paper, Wood, Metals,
etc.
Landfill and
Incineration
Cover material
needed to support
vegetation.
Potential ground and
surface water pollu-
tion; potential air
pollution.
Fly Ash from Ohio 10,000,000 (1978)T
Power Plants
807. Solids
Solids Composition:
SiO. 30-507.
Al,0j 10-20%
Fe.Oa 10-25%
CaO 2-20%
T10, 0.2-27.
MgO 1-107.
K,0 1-57.
C 1-37.
Trace Elements
Ponding and Land-
fill
Needs cover material.
Potential ground
and surface water
pollution
Scrubber Sludge
from Ohio Power
Plants'
17,000,000 (1978)*
507. Solids
Solids Composition:
Ponding and Land-
fill
367.
CaSOซ-2H,0 47.
CaC03 127.
Fly Ash 48%
Trace Elements
Possible Bogs
(difficult to de-
water if untreated);
needs cover ma-
terial.
Potential ground and
surface water pollu-
tion.
1. Water Pollution Control Research Report #12020 FTD 09/71
2. 807. disposed of in Florida.
3. Personal Communication, Mr. Stowalzer, Bureau of Mines, Phosphate Commodity Office, August, 1973.
4. 807. disposed of in Florida.
5. Personal Communication, Norbert Schomaker, OSWMP-EPA, August, 1973.
6. Excludes agricultural and mining wastes.
7. 24,550 MW of .installed coal-fired generating capacity in 1978; 73% load factor; 0.4 Kg Coal/kw-hr; 127. ash.
8. Without ash.
9. Assuming that 21,250 MW out of an anticipated total coal-fired Installed generating capacity of
24,550 MW Is controlled by limestone scrubbing systems; 737. load factor; 0.4 Kg Coal/kw-hr;
3% sulfur; 85% S08 removal; 1.2 CaC03/SO, (inlet) mole ratio; 10% oxidation.
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2.0 NATURE OF THE MATERIAL
The environmental effects of sludge disposal will be
dictated by the chemical and physical properties of the material,
and these properties may vary widely for different operations.
Important variables include the sulfur and ash content of the
coal, the type of scrubber operation (lime or limestone) and amount
of excess material added, the amount of ash in the sludge, the
type of limestone (limestone or dolomite), type of recycle (closed
loop, open loop, or partially closed loop), the degree of dewater-
ing of the sludge, and the degree of oxidation of the sulfite.
Several studies are currently underway to quantify the influence
of these variables. Those data which are available are presented
in this section. It should be noted that only recently has a sig-
nieicant effort been extended to characterize sludge materials.
The information presented in this section should be considered
preliminary until additional test data are available. EPA.'s pro-
gram with Aerospace Corporation (Contract 68-02-1010) should be
particularly important in providing further understanding of
these materials.
One potential environmental effect of considerable
concern is water pollution, both surface water and groundwater;
and it is the chemical properties of the sludge which are rele-
vant to this area. Another environmental concern is land re-
clamation of disposal sites, and it is the physical properties
of the sludge which are most relevant to this area. Chemical
and physical characteristics of the sludge will be discussed
separately.
2.1 Chemical Properties of Sludge and Related Materials
The potential water pollution problems derived from
the chemical properties of the sludge can be broken down into
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the following categories:
1. Soluble toxic species (toxic meaning
elements which can cause health pro-
blems even at low concentrations),
2. Chemical oxygen demand,
3. Excessive total dissolved solids,
4. Excessive levels of specific species,
e.g., sulfate and chloride, not
generally thought of as toxic,
5. Excessive suspended solids (some
of which might dissolve later).
Some data have already been generated which help to
put these potential problems in perspective. It should be noted,
however, that the great majority of these data have been generated
in laboratory studies, pilot plants, or large units which do not
have a lengthy record of continuous operation. It is, therefore,
not clear how closely the results parallel those that would be
obtained by a large system in continuous operation. In addition,
since almost every system is unique in terms of the coal, lime-
stone, and scrubber system parameters, the results should best
be interpreted as trends rather than as established facts.
Data describing the chemical compositions of coal and coal
ash are given in Tables Al and A2 (all tables prefaced by the
letter A are in Appendix A). These analyses are important for
several reasons. First, in many cases the ash will be disposed
of together with the sludge. Therefore, ash composition will
affect composition of liquors associated with potential leachate
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and runoff. Secondly, ash ponds alone may possibly be no less
potentially harmful than sludge ponds with respect to the total
dissolved solids as well as heavy metal concentrations. The
fuel is one of the chief origins, along with the lime or limestone
and even makeup water, of these species. Data sets 1 and 2 in
Table Al compare the trace element compositions found in an
Eastern versus a Western composite coal sample. Relative to
the Western coal, the Eastern coal is very high in boron, lead,
zinc, manganese, barium, chromium, and vanadium. The Western
coal, on the other hand, contains greater amounts of arsenic,
antimony, selenium, and nickel. The chlorine content may prove
to be of special concern because of its effect on trace metal
solubility. The chloride ion, which is extremely soluble and is
capable of forming soluble metal complexes with a number of ele-
ments, could promote solution of toxic metals in pond liquors.
Analyses of fuel ashes, including Western and Eastern
coal bottom ashes and several fly ash samples, are also given in
Table Al. Although it is not possible to trace an element's ulti-
mate disposition to bottom or fly ash because of the inconsis-
tency of available data, some trends may be noted. Examination
of data sets 3 and 7 reveals that except for manganese and cad-
mium, fly ash contains considerably greater concentrations of
all trace elements measured for that Western coal. Sets 5 and
6 illustrate that all elements measured except bromine, chromium,
and yttrium became more concentrated in the fly ash by passage
through TVA's turbulent contact absorber (TCA) scrubber at Shawnee.
Typical concentration ranges for major and minor con-
stituents of U. S. fly ashes are included in Table A2. Also
shown are comparative values for fly ash from a lignite versus
a bituminous coal. These data serve to indicate the wide varia-
tion found in typical fly ashes.
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The purpose of Table A3 is two-fold. The data show the
variation in composition of particulate in a fly ash pond with
respect to location of sampling point. This variation corresponds
to the change with respect to retention time in the pond. These
particles which do not settle out are represented by Samples B and
C which are buoyant fly ash microspheres. In this sample set,
aluminum, barium, lead, and iron particulate concentrations tended
to decrease as the particles travel through the pond. In many in-
stances, however, the concentrations in the solid phase either
remain constant or increase. Liquid phase analyses of fly ash
ponds are limited. The pH values reported range from slightly
acidic to alkaline. Some ash liquors, however, are known to be
so highly acidic that neutralization prior to ponding is neces-
sary (private communication).
Another possible origin of pollutants in air pollution
control system sludge besides the fuel is the lime or limestone
employed as the S0a reactant. Table A4 presents available analyses
of several limestones.
Table A5 gives some analyses of major and minor species
found in sludge samples collected from eight units around the
country. This table demonstrates the variability which may occur
between different sludge samples. The trace elements present in
the sludge may originate from either the coal, the lime or lime-
stone (or other S0a reactant), or the makeup water. Table A6 gives
the content of metals and other trace species for the solids col-
lected at various points in a TCA limestone scrubber.
Their final distribution in the solid and liquid phases
can be used to predict whether or not a water pollution problem
exists, either from the pond effluent or from landfill leachate.
In Table A7 it is interesting to compare the relative amounts of
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metals in the clarifier solids with those in the liquid associated
with the solids from a prototype limestone TCA scrubber operating
in partially closed loop. As might be expected, sodium, potassium,
magnesium, and calcium are soluble. However, such species as
boron, molybdenum, manganese, silicon, and copper also occur at
significantly higher levels in the liquid. Other trace metal
species are concentrated in the solids. It should be noted that
equilibrium may or may not have been reached, i.e. , given time
additional solids might dissolve.
The concentrations of various species in the solid and
liquid effluents from a centrifuge can be compared in Table A8.
These data are from a limestone turbulent contact absorber (TCA)
scrubber pilot plant; the fuel was a Western coal. It can be
seen that many metals are concentrated in the liquid phase, in-
cluding iron, aluminum, magnesium, sodium, boron, titanium, man-
ganese, chromium, copper, and nickel. The pH of this liquid is
not known, but a low pH might account for the high metal solubil-
ity. In Table A9 the relative content of metals in the scrubber
output solids versus the centrifuged solids can be compared for
this same pilot plant. These data were obtained employing a
different analytical technique.
A few chemical analyses of scrubber liquors at various
points throughout the system are available. Table A10 gives in-
teresting results for a pilot plant scrubber which uses fly ash
as the absorbent material. Analyses for dissolved species are
presented, and compared to Public Health Service Standards. The
low pH (3.3) of the scrubber recycle liquor is noteworthy, and
probably accounts for the relatively high levels of some metals.
The lime treatment of the recycle water raises the pH to 9, and
considerably reduces the solubility of the metals; however, boron,
cadmium, lead, and manganese are still present at levels high
enough to be of some concern.
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Scrubber liquor compositions are expected to vary under
open versus closed loop operation. Several sets of data are
available to illustrate this. Tables All and A12 present concen-
trations of major species in clarifier effluent samples from TVA
pilot plant limestone systems. The open loop concentrations are
surprisingly high, especially chloride and total dissolved solids.
Table A13 compares some metal concentrations for open and closed
loop operation of a pilot plant to Alabama effluent guidelines.
Zinc, nickel, iron, copper, and cadmium are higher for open loop
operation than for closed loop. pH values are not given. All
metal effluents are below the guidelines.
Information presented in Tables A1-A13 indicates that
careless disposal of untreated scrubber sludge may pose some
environmental problems in terms of surface or groundwater con-
tamination. The data on chemical compositions of scrubber liquors
are of particular significance in this regard. Using standards
for permissible limits in drinking water as a reference, some
scrubber liquors have excessive amounts of one or more of the
following: manganese, lead, copper, cadmium, selenium, boron,
nickel, magnesium, chloride, sulfate, and total dissolved solids.
In many cases the drinking water standards are not greatly ex-
ceeded but sulfate and total dissolved solids ar"e generally far
in excess of the limits. In regard to the metals it appears that
pH is an important factor, a high pH reducing the metal content.
Limestone sludge liquors typically have a pH in the range of 5 to
7, while lime system liquors are more alkaline, possibly having
a pH as high as 10. These numbers can vary widely, however,
depending to a large extent on the amount of ash present. It
appears that sludge liquors are generally of much higher dissolved
solids content than ash liquor and both liquors contain scattered
levels of trace metals although the scarcity and variation of
available data makes interpretation difficult. For some sludges
containing large amounts of ash, radioactivity might present an
occasional problem.
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The fact that the sludge does contain significant
quantities of soluble material indicates that considerable care
will be required in the design and operation of sludge disposal
projects. The particular cases of ponding and landfill disposal
are treated at length in later sections.
2.2 Physical Properties and Settling Characteristics
of Scrubber Sludges
As for the chemical properties, physical properties of
sludge may vary widely, and may be influenced by many factors in
a manner that is not yet well understood.
The physical properties are important in terms of
initial sludge disposal since they have an influence on the
difficulty of handling, transporting, and treating the material.
Physical properties also are important in regard to land re-
clamation of abandoned disposal sites. The areas of potential
concern here are:
1. Settling characteristics, i.e., ease
of dewatering,
2. Rewatering of the dried, aged material,
3. Strength, i.e., load-bearing capability,
4. Ability to support vegetation growth
(chemical properties also are important
here).
This section presents those data that are presently available on
physical properties of sludge. As for the chemical properties,
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it is important to note that those materials tested so far may
not be typical of the material which will be obtained from a
large scale continuous operation.
Particle size measurements have been reported by Dravo
for a number of sludge compositions (SE-066). Both wet screen
and sub-sieve analytical techniques were utilized. The results
are presented in Tables A14 and A15. Identification of the samples
analyzed is given in Table A16.
A related parameter, Elaine Index, which is a measure
of total surface area of dry solids, was also determined. ASTM
method C204-55, which measures the permeability of a packed bed
of material, was used in this study. Since two entities, per-
meability and Elaine Index, are inversely related relative de-
grees of permeability may be ascertained from the results pre-
sented in Table A17 (SE-066).
The bulk density of various scrubber sludges varies
similarly as a function of water content. As the percent of
water increases from zero, the bulk density increases as the pore
volume becomes filled. When completely filled, a maximum bulk
density is reached. With greater percentages of water, a dilution
effect is observed as the bulk density decreases. For Shawnee
clarifier underflow samples from a limestone scrubbing system with
simultaneous fly ash removal, the peak bulk density was reported
n
to be 1.7 g/cm at 3070 water content. The bulk density of a
3
packed and dried Shawnee sample was 1.20 g/cm . These data are
compared to the true density of Shawnee solids equal to 2.48 g/cm"
(AE-008). The peak bulk density for an individual sludge will
depend on the nature of the scrubber system from which it was
obtained. For example, the sludge from a western power plant
employing a limestone system was shown to have a maximum bulk
3
density of 1.87 g/cm at 22% water content.
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Viscosity measurements for Shawnee limestone scrubber
sludges and sludge from a western coal-burning plant with lime-
stone scrubbing have also been reported (AE-007, AE-008, AE-009).
The Shawnee samples, 50-60% solids, exhibited a viscosity which
decreased with stirring time. The other sludge tested displayed
markedly different properties. In fact, the sludge settled so
rapidly and was so viscous that measurements were limited to those
less than 50 poise. Some of the especially stiff mixtures dis-
played sporadic rheopectic behavior, i.e., the viscosity in-
creased with stirring time. This behavior is the opposite of
that observed with Shawnee sludges.
Based on preliminary results of experiments designed to
study settling properties of scrubber wastes produced by lime/
limestone systems, this phenomenon is not expected to result in
extensive separations. From a bench-scale experiment conducted
by TVA, a settling rate of 5 cm/hour was observed for the first
and second phases of settling, which were defined as the induc-
tion period during which floe formation occurs and the second
stage, free settling (SL-034). The third phase is compression
settling, i.e., when the floes begin to touch each other and gel
formation occurs. The settling rate during this stage was
greatly reduced. After 48 hours the settling rate decreased
to practically zero and no further settling was observed, even
over a period of several months.
It has been reported that limestone sludges with high
sulfate content settle to 4570 solids with no drainage provided.
This is compared to final settled solids content of 50?0 with
underdrainage. Sludges having high sulfite content settle only
to 35% solids regardless of whether drainage is provided (RO-084).
Dravo Corporation compared solid contents of various power plant
wastes after one day of settling. The data are presented in
Table A18 (SE-066).
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Settling characteristics of lime/limestone scrubbing
sludges are directly related to the degree of compaction. The
factors affecting this parameter include the following, all of
which are currently under investigation by TVA (SL-034).
Hydraulic head
Ash content
Degree of oxidation
Stirring
Agglomeration
Lime vs. limestone
Results of bench-scale studies indicate that increas-
ing the height of the slurry column increases the degree of com-
paction. When the height of an experimental column was increased
from 13 cm to 100 cm, compaction was increased by 157o. It is
predicted that a high ash content in the sludge would also produce
favorable effect on settling although no data are available to
support this point.
Degree of oxidation is under intensive study. It is
known that calcium sulfate crystals, because of their large
blocky nature, settle better than the thin plate-like calcium
sulfite hemihydrate crystals. Thus, oxidation to sulfate should
improve the degree of compaction. It has been reported that a
high degree of oxidation is required, however, to produce a
noticeable effect. Methods under study to promote oxidation of
limestone scrubber slurries include:
Air introduction into the scrubber,
Oxidation in separate unit,
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Spinning cup oxidizer,
Use of catalysts.
Identification of scrubber conditions which promote
agglomeration of sulfite crystals has not been made yet. Some
sulfite crystal agglomeration has been noted. Flocculating
agents are being investigated to determine their effectiveness
in promoting appreciable agglomeration.
The data presented above describes the physical pro-
perties of scrubber sludge from various pilot operations. It
should be pointed out that there are several large-scale pro-
jects underway or planned that should supply data on the long-
term physical properties of sludge. These projects are discussed
in Section 4.0.
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3.0 DISPOSAL OF SCRUBBER SLUDGE
Several methods are being considered for disposal of
waste material generated by lime/limestone scrubbers. The most
common approaches are ponding of untreated sludge and landfill-
ing of treated and untreated material. Other possibilities
which have not received much attention thus far are deep well
injection and mine subsidence.
The first two mentioned are the chief methods used by
the utility industry to dispose of ash from fuel combustion.
Most technology available to date is based on experiences with
that material. Technology associated specifically with sludge
is just now under development, thus posing a shortage of avail,-
able information in that respect. The following sections describe
the various features of each disposal operation and, on the basis
of available data, present the potential impact on water pollu-
tion. Land reclamation aspects for both ponding and landfill
are dealt with in a single discussion because of the similarity
of an abandoned, dried-up pond and an exhausted landfill.
A major factor in the selection of a disposal method
is the geology of the proposed site. There are several basic
types of geologic features in the State of Ohio. It is difficult
to generalize, however, due to the great extent of variation
within each type. Basically, approximately two-thirds of the
state is covered with glacial deposits. These glaciated areas
fall into two general categories, the glacial tills and glacial
moraines. The tills are characterized by soil of high clay
content, thus resulting in a region highly impermeable to water
flow. The moraines, on the other hand, are generally permeable
because of the large sand, rock, and gravel composition. The
eastern and southeastern sections are non-glaciated areas having
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distinctly different features. This region is densely populated
with mining sites. The bedrock remains exposed since no glacier
movements were experienced here. The permeability associated
with this region is dependent on the type of bedrock in each lo-
cation. Limestone bedrock is selectively permeable; sandstone
is generally permeable; and shale bedrock is relatively im-
permeable .
The river valleys located throughout the state are the
regions of greatest concern for surface waste disposal. These
are composed of alluvial fill, which is a very coarse combination
of sand, gravel, and rocks. The high degree of resulting per-
meability makes Ohio's river system, in general, a prolific
aquifer experiencing continuous recharge along the watercourse.
Thus, the State of Ohio contains a wide range of
geologic and hydrogeologic features. This necessitates an in-
vestigation of each proposed disposal site prior to its design
to ensure a minimum of environmental hazard potentially posed
by sludge leachate.
An alternative to disposing of the scrubber sludge is
commercial utilization. Development in this area is currently in
progress under both government sponsorship and private industry.
3.1 Methods of Disposal
In this section of the report the technical and poten-
tial pollution aspects of ponding, landfill, and other less
promising disposal schemes are described.
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3.1.1 Disposal by Ponding
Disposal of wastes by ponding has historically been a
favored technique in a number of industries, e.g., gypsum sludge
from fertilizer plants, phosphate slime from phosphate mining,
and fly ash from coal burning facilities. The mechanics of
pond construction and pond operation are well known; however,
much of this technology was developed with less regard for
environmental effects than is now required. This is particularly
true in regard to (1) loss of pond liquor by percolation into
underlying aquifers, and (2) allowing overflow into surface
waters. In the past, there was often little attention paid to
pond site selection or to pond lining. The general attitude
seemed to be that fine particles from the pond liquor would
eventually plug the soil and minimize percolation. Nowadays,
careful study of pond sites will be necessary and when there is
a danger of groundwater pollution suitable pond linings must be
provided. Changes in regard to pond overflow may be especially
significant. In the past dilution by the receiving stream was
considered to provide acceptable treatment. Regulations are
moving toward a "no degradation" basis which means pond overflow
must be eliminated in almost all cases. This will require total
recycle of pond liquor.
One attraction of ponds is that the volume can be in-
creased as needed by building up the sides of the pond. In some
cases (e.g., gypsum sludges from the fertilizer industry) the
pond walls can be built up using settled solids from within the
pond. In the case of scrubber sludges this may require special
treatment of the sludge. Ponded scrubber wastes are typically
not stabilized; however, stabilization of that sludge used for
building up the walls via certain commercial processes (to be
discussed later) might provide a suitable approach.
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3.1.1.1 Pond Management
The start-up and day-to-day operation of a disposal
pond involves answers to the following questions pointed out
by Slack and Potts (SL-034).
Will the pond be operated as a single
unit or divided into sections?
Will the original depth be the limit or
can walls be built up using the settled
material?
Will the pond be partially filled with
water before operation begins?
Can the pond be filled to the top of the
dike or must some freeboard be allowed?
The first question is related to the settling character-
istics of the material as previously discussed (Section 2.2).
Ash ponds are typically operated such that the slurry enters
one end of the single pond. As it flows to the opposite side,
the well-settling ash drops out and a pool of supernatant forms
at the far end. The effluent is removed via weirs or stand-
pipes, thus allowing continuous operation of the pond until
full. In contrast, waste gypsum from phosphoric acid manufacture
is usually ponded in several units. Since the settling charac-
teristics of the waste are poor, one pond is allowed to dry and
be emptied while another pond is being filled.
The second question deals with the dimensional sta-
bility of the settled material. In ash pond management, the
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settled ash is seldom used to extend the height of the walls be-
cause its spherical form results in a low angle of repose. Waste
gypsum, on the other hand, lends itself readily to this applica-
tion. Excavating equipment is employed to pile up the dried
material as high as 30 meters. Preliminary data for untreated
scrubber sludges presented in Section 2.2 are not yet sufficient
to predict whether this type of operation could be successfully
applied.
If the scrubber is operated under closed-loop, smooth
start-up may necessitate partial filling of the disposal pond
before hand. This would provide a source of recycle water at
the onset of operation and eliminate the need for additional
start-up pumping arrangements. This would produce overall in-
creasing concentrations with respect to composition of liquor
associated with solids until steady state is achieved.
The amount of freeboard required for any particular
pond is chiefly a function of climate. If the area receives
large amounts of precipitation during periods when evaporation
rate is low, then more freeboard would be necessary than for
ponding operations in hot, dry climates. Ponds which lack
drainage provisions would also tend to require greater free-
board.
3.1.1.2 Water Pollution Potential and Control for Ponding
Potential hazards associated with contamination of
surface and/or groundwaters by sulfur oxide sludges exist in
the following areas:
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soluble toxic species (toxic meaning ele-
ments which can cause health problems even
at very low concentrations),
chemical oxygen demand due to sulfite,
excessive total dissolved solids,
excessive levels of specific species,
e.g., sulfate and chloride, not generally
thought of as toxic,
excessive suspended solids.
These could promote problems via leachate and/or runoff routes.
Although similar in nature, these routes will be considered
separately in this presentation.
Leachate from Sludge Disposal Ponds
The composition of the leachate formed is a function
of several factors including chemical composition of the sludge,
pH, solubility of the individual species present, and age of
the disposal site. The nature of the leachate expected from un-
treated sludge can be judged by analysis of liquors associated
with scrubber samples, especially clarifier supernatant or
scrubber recycle water in closed-loop operation. Since fly ash
will be collected and/or disposed of together with the scrubber
sludge in many cases, it is likely that many of the potentially
leachable elements originate with the ash. Although ash ponds
have been in operation for years, there has been little concern
with environmental contamination either by high dissolved solids
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content or by trace element constituents of the pond waters.
Both have recently been shown to be present in varying amounts
in several ash pond samples.
A disposal pond provides maximum opportunity for
contamination of groundwater. Unlike a landfill, the sludge is
always saturated with water, and the '"head" of liquor in the
pond assures a continuous driving force for percolation. Under-
lying strata will also become saturated, and if an unconfined
aquifer exists beneath the pond, the pond site will act as a "re-
charge" zone for that aquifer. If no unconfined aquifer exists,
the pond liquor will continue to seep into the existing strata
beneath the pond. It is not clear whether this would be con-
strued as a detrimental environmental impact.
Given that an aquifer does exist, the important factors
are the rate at which pond liquor permeates into the groundwater
and the chemical composition of that liquor as it enters the
aquifer (any suspended material will probably be filtered out by
the soil).
It should be noted that vertical and especially lateral
movement of groundwater can be very slow, e.g., about a meter per
year. It also is important to note that groundwater movement may
occur in a "plug flow" fashion. Given that a pollution source
exists above an aquifer, vertical flow of polluted water into the
aquifer may be greater than the natural lateral movement of the
groundwater. This, plus the "plug flow" nature of groundwater
means that there may be little opportunity for dilution of the
polluted water even over a period of years. This situation is
very different from the case of allowing pond overflow to enter
a stream, where even high pond liquor concentrations may be diluted
in a matter of minutes. It can be seen that it might be many years
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before a groundwater contamination problem would be discovered
by some groundwater user down-gradient from the site. It should
also be noted that unless carefully designed even a disposal
pond monitoring program might take years to produce useful
results.
With regard to groundwater contamination by con-
stituents of pond liquor, there are some possible mechanisms
to reduce the impact of the pond liquor. These involve a group
of reactions commonly referred to as "soil attenuation" mech-
anisms. Reactions between solution species and soil particles
can occur via adsorption, ion exchange, or precipitation. Since
ion exchange and precipitation are essentially displacement of
one ion by another, only simple adsorption provides a true
removal mechanism. For ion exchange and precipitation, it is to
be hoped that a toxic species might be lost from solution and a
less toxic species gained, however, there is no assurance of
this. It is unlikely that a large change in total dissolved
solids would occur via soil attenuation mechanisms. The dis-
solved species might, however, move through the soil slower than
the liquid in which they entered. Unfortunately, no data are yet
available on this important topic for scrubber sludge liquors
although the soil type is clearly important. A large study of
soil attenuation mechanisms is being done for municipal wastes
under the sponsorship of the Office of Solid Waste. Their
experimental program is just getting underway, however, and no
results are yet available.
STEAG, a government organization in West Germany,
has instrumented a sludge disposal pond for lime scrubber sludge
to determine effects on groundwater. This group has been visited
and a description of their system obtained. Their system is
described in detail in Appendix B. So far their monitoring
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system has not detected any contamination of the aquifer which
is located only about a meter below their unlined pond. How-
ever, their observation wells are far enough away from the pond
that sufficient time probably has not elapsed for any contamina-
tion to reach the wells. Combustion Engineering and Kansas Power
and Light are also doing a study of this type, but no results
have been released.
There is one piece of information which, although
not well documented, seems to be of significance in regard to
pollution of groundwater by leachate. That is that no pollu-
tion problems have been documented due to ash pond leachate,
even though ash ponds have been widely used for decades, mostly
without liners, and in all types of soils. It seems reasonable
that if pollution problems resulted from this practice they
would have been discovered by now, especially if toxic species
were involved. High total dissolved solids, sulfates, and
chlorides might be passed unnoticed since they occur naturally
in many aquifers. However, toxic species should have been
noticed. The effect of pH on trace metal solubility is great;
therefore liquors having a relatively low pH, such as ash ponds
for high sulfur coal or limestone sludge ponds, may pose a
greater threat in this respect than liquors associated with
lime scrubbing systems or alkaline ash, for example. Neverthe-
less, the fact that no problems have been traced to ash ponds
is encouraging.
Even though no problems have been attributed to ash
ponds the information on the chemical properties of sludge indi-
cates a need for proper site selection and possibly lining of
ponds. In some situations a continuing monitoring program may
be necessary, for example, when a disposal pond is to be located
over an unconfined aquifer.
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Overflow of Pond Liquor
Disposal ponds have typically been operated with
less than total recycle of pond liquor. The excess liquid has
often been permitted to flow into receiving streams with little
treatment beyond neutralization, settling, or skimming. Acci-
dental spills have occurred frequently.
Newer and more stringent regulations on waste water
disposal will likely reduce the practice of overflowing excess
liquor into lakes and streams. This will necessitate the use
of closed loop (total recycle) operation for scrubber sludge
disposal by ponding, with treatment of any blowdown streams.
Alternatively, blowdown streams might be disposed of via evapora-
tion or disposal in the ocean. This sort of operation, combined
with proper site selection, design, and lining of ponds could
eliminate contamination of surface or groundwater by ponded
scrubber sludge, thus making ponding a viable method for sludge
disposal. A problem which might remain, however, would be the
eventual land reclamation of the pond site due to the resistance
to dewatering exhibited by many unstabilized sludges.
Control of Pollution Potential from Ponding
Pond linings have been finding greater favor in
recent years. In some cases the intent has been to decrease
pollution, in other cases the intent has been to avoid loss of
water which could be recycled. In many areas, clay, concrete,
wood, or metal has been used as a liner. Recently synthetic
linings are finding increasing usage. These include the follow-
ing materials (KU-061):
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Polyvinyl Chloride
Natural Rubber
Synthetic Rubbers
Polyethylene
Polypropylene
Nylons
With so many varieties of membranes on the market,
it is sometimes difficult to select the material suitable for
the desired purpose. The following criteria may be helpful.
The liner should have high tensile
strength and flexibility and should be
able to elongate sufficiently without
failure. It should resist abrasion,
puncture, and the fluid to be stored
and should conform to other desired
physical properties.
Should have good weatherability and a
guaranteed long life.
Should be immune to bacterial and fungus
attack.
It should be able to stand the desired
temperature variations and other ambient
conditions.
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It should be capable of being repaired
easily at any time during its life.
A leak detection system may be built into the pond
system. Two types of leak detection systems are:
(1) Underbed Drainage System. This con-
sists of a network of gravel packed
drainage canals or perforated drainage
pipes. All seepage is channeled to
the outer perimeter of the pond and
collected in a sump outside the pond,
where inspections can be made. A
variation is to monitor the fluid in
standpipes (piezometers) placed within
the pond. The tops of the pipes extend
above surface level; the bottoms pene-
trate the liner into the underlying
soil. Wells in the proximity of the
ponds may also be utilized.
(2) Ground-Resistivity Measurement System.
Several metallic pins may be buried
beneath the pond. Using a resistivity
meter, ground resistivity between these
pins may be measured. A marked decrease
in ground resistivity may indicate pond
leakage.
Some approximate cost figures have been estimated
for lined ponds (RO-084). Factors influencing the price include
size and type of lining required. For a 0.02-0.04 square kilo-
meter (5-10 acre) pond with no provision for drainage, $1,200,000
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to $5,000,000 per square kilometer ($5,000-20,000/acre) is
estimated for clay or stabilized pozzolan base lining. The
cost of a drained pond fitted with a soil covered plastic liner
can be as much as $6,200,000 to $7,500,000 per square kilometer
($25,000>30,000/acre).
3.1.2 Disposal by Landfill
A second approach to the problem of disposal of
waste solids generated by lime or limestone scrubbing systems is
landfill. Currently less than 40% of existing or planned in-
stallations have adopted this alternative, while approximately
60% have included ponding facilities. Eventually, however,
ponding sites may have to be reclaimed. This possibility would
necessitate future conversion to a landfill type of operation.
Characterization of lime/limestone scrubber sludge
thus far has revealed a nature not readily applicable to un-
treated landfill disposal. The sludge does not settle or de-
water readily, and the results of some experiments have indi-
cated that once dried, the untreated material will reabsorb
moisture to its original water content (see Section 3.3). This
creates the unattractive possibility of the disposal site be-
coming a bog. A second aspect of untreated sludge is its
leachate characteristics, discussed in the preceding section.
For these reasons, chemical and physical fixation processes
have been proposed and are now under investigation. The market-
ing agents for these fixation techniques claim that conversion
to a physically and chemically stable landfill material is pos-
sible. In some cases, a saleable by-product can be made.
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In the following discussion, the term landfill will
mean the disposal of a scrubber sludge treated via dewatering
and/or stabilization techniques.
The technology associated with disposal of waste
scrubber sludges by landfill operations is currently in the
development stage. There are three basic features requiring
discussion to accurately describe the current state of know-
ledge regarding this disposal method: dewatering, fixation,
and handling of sludge.
3.1.2.1 Dewatering Techniques
The object of any sludge dewatering process is to
recover the solid content of the sludge in a concentrated form
suitable for disposal or further processing. The liquid con-
tent is recovered from suspended solids for recirculation within
the process or for safe discharge as a processed effluent. Pre-
sented in this section of the report is a discussion of methods
available for dewatering of air pollution control system sludges.
Many of these techniques have been experimentally and industrially
applied to sludges generated by lime or limestone wet scrubbing
systems.
Interim Ponding
An interim pond has three purposes. It is a clarifi-
cation basin, a sludge dewatering area, and a sludge storage
area. A single pond cannot perform all of these functions ef-
fectively. The effectiveness of ponding as a dewatering tech-
nique is a function of the settling characteristics of the
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sludge. This aspect has been dealt with in a previous section
of this report (2.2).
Clarification
Thickeners are currently employed in some sulfur
oxide removal systems as a primary dewatering device in cases
where the solids content is low. Thickeners are sized in terms
of the surface area per rate of throughput; i.e., if a particu-
lar slurry settles slowly, a longer time and consequently a
greater surface area is required to effectively provide separa-
tion of solids and liquor. The thickener surface area can vary
from 1.0 to 10 ms/metric ton/day (10-100 ft2/ton/day) from
sludge to sludge (SE-066) depending on the settling characteris-
tics of the sludge. Limestone scrubber sludges containing
unreacted additive are reported to thicken well compared to
lime sludges because of the coarse limestone present, but re-
sult in a turbid supernatant. Therefore the design should be
based on clarification considerations. On the other hand, zone
settling rates should be the basis for design of thickeners for
sludges consisting of more uniformly fine particles.
Bed Drying
The use of a porous bed for sewage sludge dewatering
is common. Dewatering occurs by two mechanisms: drainage and
evaporation.
In general, drainage is affected by solids content,
depth of sludge application, depth of supporting media, sand
grain size, degree of paving, the presence or absence of
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coagulants, and the chemical composition and physical charac-
teristics of the sludge (JE-013, JE-014). Climatic and atmo-
spheric conditions are also important variables. These include
temperature, humidity, rainfall, air velocities, barometric
pressure, and solar radiation.
Aerospace Corporation is investigating the effects
of underdrainage on the drainage rate employing bench-scale
column studies (AE-007, AE-009). The steady state drainage
rate for wet limestone scrubber sludge from Shawnee was re-
ported to be 0.046 cm3/min. When sludge was allowed to air
dry in the columns, several days were required for initiation
of drainage; the drainage rate was then much less than that ob-
served for wet sludge. Eventually, enough water was retained
by the sludge column to return it to its original water content
(51.7%).
The mechanism suggested for drainability of scrubber
sludges involves a wicking action. If the sludge is saturated
to begin with, no delay is observed for start of drainage.
The second mechanism involved in dewatering by bed
drying is evaporation. In general, dewatering by evaporation
occurs in two phases. Phase I is a constant drying period dur-
ing which the surface moisture is exhausted until it can no
longer be replenished by the interval transport of water to the
sludge surface. Phase II is a falling rate drying period. This
depends on the nature of the dewatering material (JE-013).
Presently, an experimental program at Hollywood,
Pennsylvania, is studying the feasibility of a coal mine sludge
drying basin. Three methods of drying, open sun, loose-fitting
cover, close-fitting cover (solar shell effect) are being ex-
amined. Results so far are inconclusive.
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Centrifugation
Centrifuges are well-suited for the separation of
waste solids from a liquid suspension. This technique produces
well concentrated cakes and offers a high degree of effluent
clarification. Space requirements for equipment are minimal.
However, they have the disadvantage of significant power con-
sumption.
Centrifugation has been investigated by Dravo, EPA,
and TVA as a possible dewatering method for sulfor oxide sludges.
Results of centrifugation of various scrubber sludges have been
reported by Dravo Corporation (SE-066). Most of the tests were
performed with a standard laboratory centrifuge. A limited
series of tests on lime scrubber sludges from Duquesne Light
Company's Phillips Station was conducted using a Bird 6-inch
continuous centrifuge. These results are given in Table A19.
A 75% solids content was achieved for various TVA
pilot plant samples employing a centrifugal force of 1000 x
gravity (SL-034). Short-term centrifuge tests conducted by EPA
at Shawnee produced promising results. Limestone scrubber
sludges from the clarifier bottoms were used. The results are
shown in Table A20 (EL-030). Long-term tests are planned.
Because of the physical, blocky nature of sulfate
crystals as opposed to sulfite, dewatering is improved by a
higher sulfate/sulfite ratio. Thus, good results (85-90%
solids) have been reported for a sample obtained from the Chiyoda
process, which results in a sludge with an extremely high sul-
fate to sulfite ratio. This process is based on aqueous scrub-
bing of S02 to produce sulfurous acid followed by oxidation to
sulfuric acid. Reaction with limestone at this stage produces
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calcium sulfate; thus the sludge contains only negligible
amounts of sulfite.
Aerospace Corporation has reported the results of
a comparative study of dewatering techniques utilizing clari-
fier samples from Shawnee's limestone scrubber. The water
content of the original clarifier sample was ~80%; centrifuga-
tion reduced the water content to 44%. Associated bulk densi-
ties were also determined, and the results are tabulated in
Table A21 (AE-006). A similar study was conducted with clari-
fier samples from a Western power plant's limestone scrubber.
These results are also shown (AE-007, AE-010). Although both
clarifier samples contained approximately equal amounts of water,
centrifugation resulted in greater reduction in water content
with the Western plant sample. The reason suggested for this
was the physical nature of the sludge; i.e., maximum density
of Western sludge (1.87 g/cm3) is achieved at a slightly lower
water content (22% H20) than for the Shawnee sludge (1.7 g/cm3
at 30% HgO). Further details of these physical properties were
given in Section 2.2 of this report.
Vacuum Filtration
The most commonly used type of vacuum filter is the
revolving drum. Some of the variables affecting the ability to
dewater a sludge are:
Sludge Variables
Concentration of Solids
Age
Temperature
Operating Variables
Vacuum
Amount of Drum Submergence
Drum Speed
-36-
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Sludge Variables
Viscosity
Compressibility
Chemical Composition
Nature of Solids
Operating Variables
Degree of Agitation
Filter Media
Prior Conditioning of Sludge
One of the first attempts to dewater a lime treated acid mine
drainage sludge by vacuum filtration was by Rummel (WE-078).
Using the conditions of 3.2 square meters filter area of special
nylon, 20 sec. drying time, and 0.6 atm vacuum, a cake was
obtained with 23% solids; the original solids content was 0.6%.
Sometimes, a dense impermeable cake is found that blocks the
filter so that liquid flow is impeded. Filter aids can be
added to the sludge slurry or as a precoating to the filter sur-
face .
When vacuum filtration .was applied to various pilot
plant limestone sludge samples in TVA laboratories, 55-70%
solids contents were achieved (SL-034). Original solids content
and sulfate/sulfite ratio were not reported. Typical filtration
rates employed were 2000-2200 lit/hr/m2 (50-55 gal/hr/ft2).
These results compared favorably with 38% solids obtained on
settling alone. Considerable problems were encountered, however,
because of the thixotropic nature of the sludge (EL-030). When
the vacuum was released, the filter cake rewatered. Also,
cracks formed in the filter cake in early stages of filtration
which prohibited further dewatering. A third problem of diffi-
cult removal of the cake from the filter cloth may possibly be
eliminated by air blast discharge.
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Thermal Drying
Thermal drying of sludges is accomplished by the
introduction of hot gases to remove the moisture from the
solid. The four types of dryers used are flash, multiple
hearth, rotary drums, and atomizing spray dryers. All of
these units are capable of drying wastewater sludges to less
than 10% moisture. However, due to the high fuel requirement
thermal drying is economically unattractive compared to other
methods. A range quoted for the capital and operating costs
for a heat drying sewage sludge treatment is $28-44/dry metric
ton ($25-40/dry ton) (WE-078).
Koch Engineering Company currently markets an S0a/
fly ash control process involving a unique sludge dehydration
operation (EB-003) in conjunction with a wet limestone or other
alkali scrubbing system. The clarifier underflow having a
typical solids concentration of 30% is pumped to the dehydrator
where atomization occurs via a unique apparatus. The atomized
slurry passes downward concurrently with the hot flue gases
(~149ฐC) through the unit. The water content of the waste is
reduced by 90-95%. The dry powdered solids are removed from the
bottom. Fly ash is also removed along with the scrubber solids
in this process. Figure 1 is a process diagram for-a Koch
limestone scrubbing system.
3.1.2.2 Sludge Fixation
Sludge fixation is the chemical and physical sta-
bilization of sludge or sludge/fly ash mixtures. The intent of
the processes is to convert the waste to a non-toxic, load-
bearing material via chemical reaction and, in some cases,
-38-
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MIST BAFFLES
MIST
ELIMINATOR
SECTION
MASS TRANSFER
SCRUBBER TRAY
SYSTEM
FRESH WATER
MAKE-UP
ADJUSTABLE
1 FLEXI VENTURI
DRY POWDER
V5-1 OH MOISTURE
ID FAN
MVFT-MULTIVENTURI
FLEXI TRAY
FIGURE 1 - FLY ASH - S0a EMISSION CONTROL SYSTEM
(from EB-003)
-------
aggregate addition. Chemical fixation of scrubber sludge and
related materials is currently under development by several
commercial groups including Dravo Corporation, I. U. Conversion
Systems, Inc., Chicago Fly Ash, and Chemfix Corporation. Infor-
mation available regarding the chemical and physical nature of
lime/limestone scrubber sludge indicates a need to investigate
potential stabilization techniques. Quantitative data describ-
ing various properties of scrubber wastes are presented in other
sections of this report. Basically, these data seem to indicate
a tendency for untreated, dewatered sludge to rewater upon con-
tact with an aqueous environment. In addition, leaching and
permeability features of dried sludges pose potential environ-
mental hazards. The ability of proposed fixation techniques
to prevent rewatering and leaching from treated sludges is
under investigation. The current status of the fixation tech-
niques now being marketed is described here.
I. U. Conversion Systems, Inc., offers several fixa-
tion processes based on the pozzolanic reaction between fly ash
and lime (MI-084). Poz-0-Pacฎ, the original process on which
sulfur oxide sludge fixation technology was based, has been
industrially applied to the stabilization of fly ash for pro-
duction of structural materials. Three basic chemical reactions
are involved: (1) the reaction between the fly ash silica and
hydrated lime to form cementitious hydrated calcium silicates,
tobermorite; (2) the reactions between soluble salts present
in fly ash with lime and the alumina content of fly ash glass;
and (3) aggregate addition resulting in mechanical support.
*
Poz-0-Tec is a commercial process for the stabili-
zation of fly ash using sulfur oxide sludges in addition to
*
A service mark owned by I. U. Conversion Systems, Inc.
-40-
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lime. The chemistry is comparable to that describing portland
cement technology. Calcium sulfate reacts preferentially with
calcium aluminates or calcium ferrites resulting in hydrated
calcium sulfoaluminates (ettringite) or sulfoferrites, respec-
tively. The cementitious reactions which take place in the
Poz-0-Pacฎ process also are an important feature of the Poz-0-
Tec* process. Sulfite ion, introduced in large quantities as
magnesium sulfite or calcium sulfite in the sludge, acts as a
catalyst in the cementitious reactions. Addition of aggregate
may or may not be required, depending on the characteristics of
the starting materials and the desired strength of the product,
referred to as Sulf-0-Pozฎ. This product is primarily a dis-
posal material, but in some instances could be used as a struc-
tural material in land reclamation projects, structural embank-
ments, etc. after a couple of weeks of curing (FO-018). Further
processing of Sulf-0-Pozฎ is another alternative; utilization
of the treated sludge as synthetic aggregate or road base
material is then possible.
The tail end process itself can be retrofitted to
existing power plant facilities. Application to oil-fired
systems is 'not feasible, however, since availability of fly ash
is essential to the process. Conditions of relatively higher
pH, as in lime systems compared to limestone, favor the reac-
tions, although both types of scrubber sludges can be treated
by the IUCS process (AE-007). The presence of soluble magnesium
compounds introduced as dolomitic limestones is claimed to
result in faster, stronger reactions because of the higher sul-
fate solubilities.
*
A service mark owned by I. U. Conversion Systems, Inc.
-41-
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The initial step in the process involves dewatering
of the sludge by one or more of the techniques discussed in
the preceding section. If fly ash is collected dry, addition
to the sludge at this stage aids in the dewatering. If col-
lection is by a wet method, the fly ash slurry may be introduced
into the primary dewatering device. The sludge/fly ash mixture
is then conditioned with make-up additives which may include
additional lime, limestone, fly ash, bottom ash, other sulfur
oxide salts, and optional aggregate or other waste products.
The output from the mixing and conditioning device is suitable
for utilization as a stabilized fill material. The flow dia-
gram for this process is shown in Figure 2. To date, this
process has not been applied to a flue gas desulfurization
system, but extensive bench-scale testing of that application
and the fixed product is currently being performed in the IUCS
laboratories.
The economics of the fixation process offered by
IUCS have been recently presented (MI-084). Because of the
many factors influencing the actual costs that would be incurred
by a power plant utilizing this system, the estimated cost can-
not be considered typical. In addition, IUCS is not presently
disposing of scrubber sludge on an industrial level; therefore,
actual cost figures are not available.
Those factors affecting the cost of this or any fix-
ation process are given below:
annual tonnages to be handled by the
conversion process,
new boiler installation versus existing
facilities,
-42-
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!
1
FLY ASH
| t 1 1 ซ 1 I I
M
1
U>
I
SULFUR
OXIDES
UNDERFLOW
PRIMARY DEWATER ING
uiiiiiitMii
MAKE-UP PROCESS
ADDITIVES
iniiiiiiiy
** ปป*
'***
ฃiiiiigiiiiiiiiiiiiiiiiiiiiiiifiiiiiiiiiiiiiiiiiiiiiiii>niiiiiiiiiiiiiiiiiiiiii
s* :
SECONDARY
DEWATER ING
il'rlil"n'' [i"-* m J " ^*nY~'ni"frLr_Ui*;r
MIXING &
CONDITIONING
JT^IL-.-JJfJgB>.:
Damt
Reservoirs
Impermeable Liners
Road Base
Structural Fill
I Structural Products
.-:.^, .^.u,...,,.* I Aggregate
-i.iMi f.irtrtrr? 9 Concrete
* Structural Sh*pซ
FIGURE 2 - SCHEMATIC DIAGRAM OF POZ-0-TEC PROCESS
(From MI-084)
-------
the type of equipment selected for fly
ash removal for example, electrostatic
precipitators versus wet scrubbers,
the chemical analysis of coal sulfur,
CaO, and ash contents,
location of plant on-site versus off-
site,
transportation costs to and from con-
version plant,
redundancy factor duplication of equip-
ment versus emergency holding basins, etc.
type of scrubber limestone versus lime,
acquisition and cost of land, and
type of end-product selected.
Based on estimates for newly installed plants in the range
1000 - 2000 MW, burning coal with 3-4% sulfur and 10-15% ash
content, and incorporating a lime scrubbing system, the cost
of sludge disposal is estimated to be $1.65 - 2.76 per dry
metric ton ($1.50-$2.50/dry ton) to convert the sludge to a
disposable Sulf-0-Po2ฎ material. This is equivalent to 7.9-
13.9<:/lOekg-cal (2-3.3<:/10eBTU) . This includes the cost of
chemicals and process services, but not a hauling charge which
is a major factor.
The Chicago Fly Ash Company also markets a sulfur
oxides sludge fixation process based on quicklime/fly ash
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addition (OB-005). They are currently working with Commonwealth
Edison and the University of Illinois to dispose of the sludge
generated by a limestone wet scrubbing system installed on a 163
megawatt unit at Will County Station (GI-017, GI-030, ST-117,
JO-083). The spent scrubber slurry presently receives dewatering
treatment by clarification. Possible secondary treatment, vacuum
filtration or thermal disc drying, is being considered to reduce
the volume of sludge requiring fixation. Clarifier underflow is
pumped to a pond, then to a loading station where the additives
and sludge are blended to produce a stable landfill material.
For every 1000 pounds of settled sludge, 100 pounds of fly ash
and 50 pounds of lime are added. If higher water content is
present, the proportion of additives required goes up rapidly
(GI-033) . The treated sludge (5070 solids) is transported by cement
truck to an on-site sealed basin about one-half mile away. An
off-site location is planned for the future. At the present time,
this fixation process results in physical but not chemical
stabilization of the sludge (GI-033). The leachate does not meet
Illinois water standards which state that any water entering an
aquifer cannot be of lower quality than water removed from it.
A Chicago Fly Ash spokesman quoted a cost of $16.5/
metric ton ($15/ton) on a dry solid basis for their process
(OB-005). Additional economic information associated with
this disposal method can be derived from estimated operating and
capital investment costs reported by Will County. A utility
spokesman has recently estimated the annual costs for the disposal
system as 1.1 million dollars in addition to the initial capital
investment of 1.7 million dollars (GI-017). The annual cost
included a sludge disposal figure of $823,000 which is equivalent
to $7.70/metric ton ($7/ton) of sludge (dry basis), $1.68/metric
ton ($1.52/ton) of coal, or 30.2c/kg-cal (7.6c/10sBTU). Entailed
in the sludge disposal figure are costs for operating the sludge
disposal plant, maintenance, hauling, and landfill. Actual costs
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incurred on this project, however, are reported to be as high
as $17.10/ton of dry sludge (GI-033). Costs possibly may be
reduced in the future to -$12/dry ton. This figure appears
relatively high compared to the price quoted by I.U. Conversion.
This situation is typical, however, in that the Chicago Fly Ash
operation depends on a labor intensive trucking scheme in a con-
gested area. This accounts for the relatively high cost in this
specific application.
Dravo Corporation also offers a chemical fixation
process for lime/limestone scrubbing waste products (SE-066).
Much of their technology has been developed using sludge samples
obtained at a pilot-scale lime scrubber operating at Duquesne
Light Company's Phillips Station; sludge from additional sources
has also been examined. The testing of their process has involved
basic chemical and engineering evaluations of the sludge and
treated product on a bench-scale level; they are currently under
contract to Duquesne to dispose of their lime sludge. The
chemistry of the process has not been revealed because of current
patent applications on the additive. The amount of additive
required, however, is approximately 3-570 by weight of sludge
solids. It is reported that following chemical addition to the
settler underflow, the sludge can be pumped for 6 to 60 miles
to a disposal site, preferably an area which can be dammed up,
where the setting up takes place underwater. The supernatant
can be drained off. Dravo has observed wide variations in sludge
behavior even under controlled operating conditions (AE-006). These
variances have not been explained by either total chemistry or
sulfite/sulfate ratio. Polyelectrolyte addition is being
investigated to control these phenomena. The economics associated
with this process includes an additive cost of less than $19.8/
metric ton ($18/ton). Dravo offers a complete package for sludge
disposal. If a pumping operation is selected, the cost of the
environmental impact statement preparation is estimated to be
-46-
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$500,000. Design of the system would be $1-1.5 million, while
the cost of the process itself would run $12-13/dry metric ton
($ll-12/ton) according to Duquesne figures. Dravo, however,
claims that the process cost would be considerably lower,
depending on the pH of the sludge (LO-070). If the sludge is
to be treated and stored at the plant site (i.e., no pumping
operations) three settling ponds are required. The cost of
sludge disposal in this case is $l-3/ton of wet solids (35-40%
solids) for a 1000-2000 MW facility. This figure does not include
pond construction or equipment costs.
Chemfix Corporation markets a proprietary fixation
process for conversion of various industrial sludges to stable
landfill using at least two inorganic chemicals, one liquid
and one powder. Little information is available on the chemistry
of the system, although one source reports that "lime and
silicates apparently are not used" (TR-026). Polyvalent metal
ions react with Chemfix process chemicals resulting in a stable
insoluble, inorganic compound within three days, although
gelation time can vary with the system being treated. Certain
species, including chlorides, monovalent cations, colloidal
material and some organics, cannot be fixed by this treatment.
This aspect, however, will be dealt with in a later section of
this report (Section 3.1.2.3). At present, Chemfix is not
working on an industrial scale with any utilities on scrubber
sludge disposal although it has been applied to other types of
problems. In one commercial operation, up to 380,000 i (100,000
gal) of sludge per day were treated (SO-048) at the Jones and
Laughlin Hennepin Works. This involved treating the contents
of a 19,000,000 9. (5 x 106 gal) lagoon. Completion of the job
was accomplished in 21 days, ten-hour shifts. At Ford's Lorain
assembly plant, 208,000 H (55,000 gal) per day of an industrial
sludge containing toxins associated with painting operations has
been periodically converted to a solid disposable landfill
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material at an annual cost of $100,000 (TR-026). On the order
of four million liters per year are treated.
The price range quoted by Chemfix for their services
is 0.51-2.6c/je (2-10
-------
I. U. Conversion Systems whose results are discussed in Section
3.1.2.3. Chemfix Corporation has furnished leachate analyses
to Radian for specific treated sludges. These results are
also presented in Section 3.1.2.3. No data from Dravo Corpora-
tion or Chicago Fly Ash was available for release at this time.
3.1.2.3 Water Pollution Potential and Control for Landfill
Disposal
Disposal of sludge generated by lime/limestone scrub-
bing systems in landfill sites creates two potential areas of
water pollution, leachate to groundwater and runoff to surface
water. Careful evaluation of available research results
associated with both runoff and leachate must be made in order
to assess any potential environmental hazards which may exist.
In this section, information pertaining to factors of water
pollution and effect of chemical and physical properties of
stabilized scrubber sludge/fly ash mixtures are discussed.
Also presented here are possible control measures which have
had application in disposal of sludge or other solid waste
materials.
Leaching Aspects of Landfills
In order to predict leachate characteristics of a
landfill, it is first necessary to describe the general features
of water movement and geological considerations for this dis-
posal method. Due to the recent surge of ecological interest
in sanitary landfills utilized for solid waste disposal, there
is an abundance of information available. Emrich's review of
research in this field presents an overall view of progress in
the following areas (EM-003):
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leachate generation
chemical characteristics of leachate
movement of water in a landfill
effects of topography, geology, soil,
and groundwater on leachate
leachate or landfill management.
This section will present a discussion of landfill leachate in
general with specific reference to formation, nature, and
movement of leachate generated by lime/limestone scrubber
wastes.
The first consideration when looking at the potential
impact of landfill leachate is the volume of leachate which will
be produced. This is a direct function of the amount of water
reaching the landfill. There are two possible sources of this
water: rainfall and naturally occurring subsurface flow through
the landfill site. This second situation occurs when the land-
fill extends below the existing water table. Climate obviously
will determine the rainfall. In humid areas leachate will be
generated in a relatively short period of time; leachate forma-
tion may be delayed for years until field capacity is reached,
however, in semi-arid and arid regions (EM-003). In general,
the field capacity of a landfill is the water that can be
retained indefinitely against gravitational force.
Subsurface flow is a natural phenomenon which can
seriously interfere with safe operation of landfills in two
ways. First, it is a source of additional volume of potentially
harmful leachate. The second consideration is that it can
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serve as a direct means of groundwater contamination. Pre-
vention can be effected by thorough geologic study of the site
beforehand and, if needed, installation of rerouting devices
for the groundwater flow.
In a similar vein, coverage of the landfill area
when complete will greatly reduce, if not eliminate, the
amount of leachate produced. This aspect will be discussed in
a later section dealing with potential pollution control
measures.
Infiltration and permeability characteristics .of
the landfill material determine the relative amounts of runoff
versus leachate as well as the leaching rate. Minnick has looked
at the effect of aging on permeability of fly ash stabilized
with lime (Poz-0-Pacฉ) and fly ash stabilized with sulfur oxide
sludges in addition to lime (Poz-0-Tec*) (MI-084). As shown
in Figure 3, a great reduction in permeability of fly ash
mixtures can be achieved by inclusion of sulfur oxide sludges.
In terms of the subject of this report, these results indicate
not only the low permeability values of the fixed scrubber
sludges (~10~7 cm/sec after 7 days of curing at 100ฐF or 38ฐC),
but also the relatively great reduction in permeability compared
to freshly prepared sludge/fly ash mixtures. This reduction
is on the order of two orders of magnitude. More specific data
obtained with samples of sludge stabilized by I. U. Conversion
System's process is presented in Table A22. These data were
measured using standard falling head permeability procedures.
Dravo Corporation reportedly has obtained permeabil-
_5
ity values of 2 x .10 cm/sec for sludge conditioned in their
laboratories with 370 additive (AE-006). This is compared to
_7 _8
high quality clays having permeation values of 10 to 10
- ฃ?
cm/sec versus fly ash for which a representative range is 10
3
to 10~ cm/sec.
-51-
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100
10--
X
o
I
o
CO
<
01
S
cc
UJ
Q.
Standard Fly Ash Mix
1.0-
0.1
Sludge Fly Ash Mix
2 4 6.8
AGE-DAYS OF CURING AT 100CF
FIGURE 3 - Comparison of Poz-0-Pacฎ and Poz-O-Tec*
permenhility values. (MI -084)
10
-52-
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Minnick has presented analytical results obtained by
atomic absorption analysis of leachable ions on selected
materials subjected to the Poz-0-Tec* or Poz-0-Pac ฉ process
(MI-084). The tests were conducted by shaking 500-gram test
specimens for 48 hours in two liters of distilled water. The
results of those studies are shown in Table A23- When leachate
from materials treated by Poz-0-Tec* process were compared to
Federal specifications for drinking water standards, only man-
ganese greatly exceeded the limits. It was noted that materials
not treated by either stabilization process experienced much
greater leaching phenomena, thus indicating the effectiveness
of this type of chemical fixation. In Table A23 the decrease in
total dissolved solids with aging for the Dulles cylinder is
noteworthy.
The Chemfix process, although not applied to sulfur
oxide sludges, has been shown to lack ability for some sludges
to retain several elements, including chloride, cyanide, and
hexavalent chromium species (TR-026). One source reports that
a test of leachate from a Chemfix solid contained 1,000 ppm
chloride, four times the permitted level in drinking water
(FO-018). Chlorides are of special concern in lime/limestone
scrubbing wastes because of their high solubility and unavoid-
able build-up during closed-loop operation. The presence of
very high concentrations of this anion could have an appreciable
effect on trace metal ion concentration in scrubber liquors and
sludge leachate. This potential pollution aspect requires
further investigation.
A sludge sample from an Eastern coal-burning power
plant controlled by a limestone scrubbing system was Chemfix
treated (CO-123). Analyses of the raw untreated sludge and
leachate from the fixed sample were performed. The results
-53-
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as shown in Table A24 indicate that the concentrations of re-
ported toxic elements and ions were reduced in most cases to
less than 0.10 ppm. Copper and lead concentrations also de-
creased to this value after the first leachate portion.
Runoff Considerations for Landfill
I. U. Conversion has performed tests to determine the
extent of dissolution of species associated with fly ash-
stabilized sulfur oxide sludges (MI-084). The experiments were
conducted by allowing two liters of deionized water to flow
over the fixed samples and then subsequently collected.. Re-
sults of atomic absorption analyses of this runoff were reported
as shown in Table A25. They were interpreted as providing a
preliminary basis for the effectiveness of the fixation process's
ability to tie up soluble species within the lattice complexes.
Preventive Measures for Potential Pollution from
Landfills
Methods available to prevent contamination of surface
and groundwaters include landfill sealing, coverage, and pro-
vision of drainage to divert naturally occurring surface or
groundwater flows around the landfill.
Landfill sealing is very similar to the practice of
pond lining discussed in Section 3.1.1.2. The sealant can be
any impermeable material such as an asphalt-membrane recently
tested at a site near Tullytown, Pennsylvania (RE-071, LA-079).
Many other potential lining materials have been tested in bench-
scale and experimental plot arrangements. A few of the more
promising of those tested included:
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1070 bentonite (Wyoming clay used for
mud drilling)/90% soil
10% bentonite/90% sand
10% red mud slurry (a bauxite residue)/
90% soil
10% latex/90% soil
307, asphalt emulsion/70% soil.
In an arrangement where a landfill liner is used, the leachate
is trapped at the bottom. It can then be collected and sub-
jected to water treatment, if necessary, before release to the
surrounding area.
Interception of subsurface flow is achieved by
placement of drains upstream of the entire area of the land-
fill. These cut-off drains should be placed at a depth a few
feet below the bottom of the landfill to keep the groundwater
level low as well as to provide hydraulic gradient for drainage
(SA-103).
To prevent infiltration from surface flow, two
measures can be taken. One involves providing vertical gravel
or stone paths extending below the level of the bottom of the
landfill through which surface and/or groundwater can quickly
drain. The second approach involves using a cover material.
This may be a natural material such as clay or clay loam, or an
artificial membrane. If an impermeable cover is employed, pre-
caution must be taken to allow release of gases to the atmos-
-55-
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phere. In some instances, carbon dioxide produced in a land-
fill has been observed to contaminate groundwater with addi-
tional hardness.
3.1.3 Other Disposal Methods
Several other possible options are available for
disposal of air pollution control system sludges although they
are not under investigation to the same extent as landfill and
ponding. These alternatives involve direct deposit of the
waste below the surface, either in deep injection wells or in
subsurface mines.
Deep mine filling has been used for the disposal of
power plant ash (HA-158). The ash is sluiced into the mine
through boreholes. Normally, gravity is sufficient to create
a flow into the mine. Pumps and additional boreholes were
provided in case of hole plugging or increased friction losses.
A dewatering sump and a settling basin were formed by con-
structing dams across the mine flow. Overflow from the settl-
ing basin flows to the sump from which it is pumped to an
above-ground basin. This type of approach is not directly
applicable to disposal of lime/limestone scrubber sludges for
several reasons. First, the viscosity of this waste is such
that it is probable that it would not spread laterally through-
out the mine disposal area. Secondly, the settling characteris'
tics have been shown to be poor; ready solid/liquid separation
is not expected (Section 2.2). This would eliminate the
attractive features of a mine subsidence operation in that
very little geological support would be provided by the water
pollution aspects. Possibly the last two foreseeable problems
could be avoided or reduced by a fixation treatment. Investi-
gation of this approach may be worthwhile to those utilities
-56-
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to which abandoned deep mines are available as a possible dis-
posal site.
Reclamation of strip mine areas with waste sludge is
another possibility. This could be viewed as a specialized
]aidfill operation; as was discussed in the preceding section,
it is not yet certain whether or not pretreatment of the sludge
will t>e required for strength development and to prevent en-
vironmental contamination. The benefits of this type of dis-
posal are obvious, however, if shown to be a feasible approach.
In addition, land availability would not be a problem in many
areas of the nation, including the State of Ohio where strip
mining is a large industry, especially along the eastern and
southeastern borders. Strip mine reclamation with fly ash has
been in practice for many years now, much of it under the de-
velopment of the Bureau of Mines. Additional development is
needed for utilization (disposal) of scrubber sludges in this
capacity.
Another alternative to ponding and landfill is deep
well injection. This method has been utilized by a number of
industries seeking permanent disposal of hazardous waste
materials. There is no. information, however, concerning its
potential use as a scrubber sludge disposal technique. The
high solids content of the sludge probably would cause rapid
plugging of the subsurface strata, resulting.in decreased per-
meability and continually diminishing injection rates. Possibly
some very permeable formations exist where this would not occur.
Although this method offers another alternative to the sludge
disposal problem, it is not regarded as a highly feasible
solution.
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3.2 Sludge Handling and Transport
The handling operations involved in disposing of
scrubber sludge may include one or more of the following: wet
sluicing of sludge and/or fly ash; trucking of ash and other
fixation additives; trucking of sludge to landfill site; use
of conveyor belts for sludge transport between dewatering,
treating, landfilling, and/or trucking facilities; barging;
and rail transport. Each of these is briefly described below
with emphasis placed on any aspects possibly associated with air
pollution control system sludge.
Transport of waste scrubber sludge to the ponding
site can be carried out by sluicing operations, i.e., piping
the slurried solids. This method is also being considered
for transport of sludge to the fixation site. Individual
sludge properties such as viscosity, velocity, temperature,
composition, particle size, and solids concentration affect the
pumping characteristics of the material. Also of major concern
is the distance to be covered. Special problems specifically
related to sulfur oxide sludges such as corrosion or erosion
potential also require investigation. Dravo Corporation is
investigating the transport of fixed sludges to the disposal
site by pipeline.
In general, the transport of solids in pipes depends
on the use of a carrier fluid to transmit pressure from the
pump or compressor to the solid being moved. The viscosity of
the material greatly influences the transport characteristics.
Viscosity is a physical property defined as the cohesive
force between particles of a fluid that cause the fluid to
offer resistance to the relative sliding motion between
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particles. It is a measure of the resistance to flow. This
physical property has been determined for a number of individual
scrubber sludges; the data were presented in a previous section
of this report (Section 2.2). Specific characteristics such as
thixotropic or rheopectic behavior unique to some scrubber
sludges are related to viscosity and therefore will influence
sluicing operation parameters. For instance, sludges with
high sulfite composition exhibit thixotropic behavior as des-
cribed in Section 2.2. This observed loss of viscosity with
stirring would result in lower head loss at constant velocity
of the fluid. A different sludge, however, has been shown to
exhibit rheopectic behavior. This would tend to have an adverse
effect on pumping operations. Therefore, the physical nature
of the sludge being transported must be known.
The critical velocity for a particular sludge must
be determined since it is the flow velocity at which solids
are most economically moved for a given pipe size and sludge.
This velocity will occur somewhere in the turbulent flow
region; i.e., the region in which particles may move in any
direction with respect to each other.
Other technical aspects of pipelining of sludge re-
quiring consideration prior to design of a system are materials
of construction and possible use of pumping aids. Transport
can be accompanied by erosion problems due to the physical nature
of the solids. In many installed lime/limestone systems, much
of the piping, blades, and pumping equipment used to transport
slurries are rubber lined to protect against the abrasive pro-
perties of the slurry, especially in pipes carrying sludges of
higher solids content.
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The use of long-distance piping systems is increas-
ing rapidly since the demonstration of technical and economic
feasibility. Table 4 summarizes the commercial applications
which have been installed in recent years.
Truck transport of dry materials such as fly ash,
lime, and aggregate is an established practice in various in-
dustries. Major considerations in employing this handling
method are proper equipment for loading and unloading, and
control of fugitive dust. Dry materials (lime, e.g.) are most
often handled by pneumatic sluicing systems which can be de-
signed to load the material directly to the truck or hopper.
Pneumatic unloading systems which blow the material from the
trucks are employed to handle materials which do not flow
freely. Pneumatic systems are not necessary, on the other
hand, for relatively free-flowing materials. In this case,
the unloading equipment requirements depend on other physical
characteristics of the material.
The second consideration involved in truck transport
of dry materials is control of fugitive dust, i.e., wind-blown
dust. Proper precautions must be taken in order to avoid air
pollution problems associated with this feature. Again, the
extent of the potential problem depends on the physical charac-
teristics of the material being handled. Usually properties
associated with materials posing this hazard are small particle
size and low density. Although this is unlikely to be a problem
with scrubber sludge due to its high water content, condition-
ing of fixation process additives such as fly ash or lime would
be necessary.
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TABLE 4
Consolidation Coal
American Gilsonite
Rugby Cement
Columbia Cement
South African Companies
Savage River Mines
Black Mesa Pipeline, Inc.
Hyperion Wastewater Treatment
Plant
Mogden Wastewater Treatment
Plant
Easterly Pollution Control
Center
SUMMARY OF COMMERCIAL SLURRY
PIPELINES
(TH-041)
Location
Ohio
Utah
England
Columbia
South Africa
Tasmania
Arizona
Los Angeles
England
Cleveland
Material
Coal
Gilsonite
Limestone
Limestone
Gold Tailings
Iron Concentrate
Coal
Digested Sewage
Sludge and Effluent
Digested Sewage
Sludge
Raw Sludge
Length
(miles)
108.0
72.0
57.0
9.2
21.5
54.0
273.0
7.5
7.0
13.0
Diameter
(inches)
10
6
10
5
6 & 9
9
18
22
12
12
Throughput
(million tons
per year)
1.30
0.38
0.70
0.35
1.05
2.25
5.70
Solids
Specific
Gravity
1.40
1.05
2.70
2.70
2.70
4.90
1.40
1.80
1.80
1.80
Weight
(% Solids)
52.0
46.0
61.0
55.0
50.0
60.0
50.0
1.0
4.0
2.5
Years in
Operation
or Status
6*
11
5
25
14
2
In Start -Up
Phase
11
33
32
* Commercial operation ceased in 1963 for non-technical reasons. Now maintained in standby condition.
-------
Transport of sludge to a landfill site via truck is
one of the most feasible approaches being considered by utilit-
ies if off-site disposal is used. The results of one study are
available at this time. (TA-040). Combustion Engineering trans-
ported 68 metric tons (75 tons) of waste (50% sludge, 50% ash)
from the limestone scrubber at Kansas Power and Light's Lawrence
facility to Dulles Airport in Washington, B.C., a distance of
approximately 2100 km (1300 miles). Two types of vehicles, flat-
and round-bottomed trucks, were employed in order to compare the
effect of various features on handling characteristics. Prior
to loading, the untreated sludge had been stored in a settling
pond at the utility site for six months. It was dredged up and
allowed to drain for 24 hours before loading. At various inter-
vals during the non-stop trip measurements and samples were
taken. No leakage of sludge was observed although excess water
drained from the tailgate while on the road. Unloading problems
were encountered with the flat-bottomed trucks; complete re-
moval of the sludge necessitated manipulation with a backhoe.
The sludge slid out readily, however, from the round-bottomed
trailers.
Conveyor belts and related bucket elevators are
potential modes of transport for dewatered sludge over short
distances. Potential areas of use include conveying of de-
watered solids to a fixation facility, lifting of wastes to
hoppers or mixing devices, and transport of fixed sludge to
landfill sites. The water content of the sludge is the major
factor determining feasibility of this application. If the
nature of the sludge is such that water drains in large amounts,
precautions such as installation of troughs below the conveyors
must be taken to avoid potential water pollution problems.
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Other Handling aspects which would be mentioned in
this discussion are alternate methods of transporting the waste
from the scrubber site to the ultimate disposal site. Encom-
passed in this category would be barge and rail. Both would
be feasible only in unique situations where geography and sur-
rounding environment would permit such application.
The economics of solids handling by sluicing or pip-
ing operations depends mainly on two factors: amount to be
handled and distance to be covered. One source, in comparing
the economics of piping versus truck transport, stated that
80 km (50 miles) should be considered the cut-off distance.
For distances greater than 80 kilometers piping appears more
economically attractive (BO-075). Thompson reported total
pipeline transport costs (including power, labor, supplies,
and capital charges) to range from $1.76 per dry metric ton
of sewage sludges (3.570 solids) for a 40 kilometer, 820 metric
tons/day system ($1.60/ton for a 25-mile, 900 tons/day system)
to a maximum cost of $22 per dry metric ton for a 160 kilo-
meter, 91 metric tons/day system ($20/ton for a 100-mile,
100 tons/day system) (TH-041).
The results of another survey in which off-site
disposal costs were reported gave figures in the range of
$0.01 - 0.10/m3-km ($0.05 - 0.50/1000 gal-miles) for pipeline
conveyance of brines and sludges (BU-087). These costs did
not include fees charged by the receiving agency. The authors
of the report concluded that pipeline conveyance is the most
economical mode for quantities in excess of 100 cubic meters
(26,000 gallons) per day irrespective of distance. Over long
distances it seems reasonable to expect that piping would be
more economical than trucking for smaller quantities. For
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smaller volumes and short distances, trucking or rail becomes
more economically attractive. In this case distance should be
the basis of selection; trucking for distances shorter than 35
miles (50 km) and rail haul for longer distances.
3.3 Land Reclamation Aspects of Disposal Sites
Certain aspects of land reclamation following aban-
donment of a landfill site or dried up.pond used for scrubber
sludges may lead to potential problems. These aspects may be
assessed by examining the engineering, physical, and chemical
natures of treated and untreated sludge.
At the present time no attempts have been made to
reclaim land committed to scrubber sludge disposal. However,
Florida's phosphate mining industry has successfully accom-
plished several full-scale reclamation projects. These in-
volved conversion of the ponding, mining and disposal areas
to recreational areas and residential subdivisions. The work
done in this area is described in Section 3.3.4.
3.3.1 Rewatering Characteristics
One consideration is the tendency of dried scrubber
sludge to absorb water with which it; comes in contact. As
discussed in previous sections of this report, sulfur oxide
sludges are relatively difficult to dewater. One sludge
sample was observed over a period of several months during which
time little or no settling took place after the first 48 hours.
Preliminary results of one TVA study indicated that dry solids
from a limestone scrubber sludge do not expand when submerged
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in water or exposed to rainfall (SL-034). Drainability studies
conducted by Aerospace, on the other hand, resulted in retention
of enough water by dried Shawnee limestone sludge to return to
its original water content. The calculated water retention
for sludge with underdrainage was 51.7% (AE-007). Behavior of.
chemically stabilized sludge samples is expected to be greatly
improved although specific tests for rewatering potential have
not been reported. A practical consideration in regard to re-
watering is that for a thick layer of dried sludge, an accumula-
tion of a few meters of rain might be required for rewatering.
With proper design of the site plus some low permeability cover
material (clay, plastic, or treated sludge) even untreated
sludge might never rewater since the small amount of water
collected during a rain should be lost by evaporation before
the next rain.
3.3.2 Strength of Disposed Material
A second consideration in land reclamation of sludge
disposal areas is the weight which can be supported by the site,
This factor can be determined by measuring the pozzolanic
strength, compaction strength, and penetration resistance of
the throwaway product. The strength associated with any land-
fill or construction material is a function of composition,
moisture content, and compacted density.
Untreated scrubber sludge has been shown to lack any
appreciable degree of compressive strength based on studies
performed by Aerospace on Shawnee and Mohave samples (AE-009).
Compaction strength is measured by the resistance of wet
sludge to penetration of a flat bottom ram, 1 cm in diameter.
This parameter is used to evaluate the amount of weight which
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could be supported by ponded sludge. Shawnee limestone sludge
3
at 447o water content was found to support 320 kg/m' (0.45 psi).
Sludge dried to 40% water possessed a higher compaction strength
9 *
of 1500 kg/m (2.2 psi). When compared to the stress required
g
to support a normal person, 2100 kg/m or 3 psi, both dried and
wet sludge were judged to lack any appreciable degree of com-
paction strength (AE-008). More recent test results of Shawnee
sludge dried to 307o water content, however, showed a substantial
increase in strength (24,000 kg/m9 or 34 psi) (AE-009).
Pozzolanic strength determinations were made by apply-
ing compression strength at a constant strain rate to samples
which had been cast in cylindrical molds and cured for a given
time in a humid environment. This property was reported to
vary as a function of water content. Testing was carried out
with an Instron test machine using a cross-head speed of 0.05
cm/min (0.02 in/min). Results are shown in Table A26 (AE-009).
Water content of the samples, however, was not stated.
Samples subjected to the I. U. Conversion Systems'
fixation process have been tested for various strength charac-
teristics (MI-084). The penetration resistance is a measure
of the pressure that must be applied in kilograms per square
meter to cause a penetration of 2.54 cm (1 inch) of a needle
with cross sectional area of 1.6 x 10~ square meters (1/40
square inch). The effect of aging on the strength of a
Sulf-0-Poz ฎ composition was presented in graphical form
(Figure 4). The results indicate that completion of curing
occurs approximately 16 weeks after mixing. When 5x5x5-
centimeter cubes of similar composition were tested for uncon-
fined compressive strength, curing was completed much sooner
(~6 weeks). Graphical display of results is shown in Figure 5.
Individual data points obtained during bench-scale compressive
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6000
*
V)
O
u
c
CO
VI
W
CC
,0
"^
2
*-
O)
I
4000
2000
'One psi is equivalent to 703 kg/
Age (Weeks)
FIGURE 4 - Penetration resistance for a typical fly
ash-calcium sulfate-lime mixture. (Fixed Sludge-
(from MI-084) Sulf-0-Po20
m-'
-------
2000
oo
i
00
0.
O)
4-1
CO
CD
0.
O
O
o
cp
1000
0
8
Ag\s (Weeks)
One psi is equivalent to 703 kg/m2
FIGURE 5 - Compressive strength for a composition similar
to that given in Figure 4 Moisture
content of composition is 35%. (Fixed Sludge)
(from MI-084)
-------
strength determinations of Sulf-0-Poz ฎ materials with moisture
contents of ~2070 are shown in Table A27. Also presented are the
results of compressive strength determinations for field tested
road base materials (Table A-28).
In addition to strength, another consideration in an
engineering evaluation is structural integrity. Experimental
data which can be used to describe this characteristic are
dimensional stability measurements and field testing.
Untreated sludges reportedly have very poor dimen-
sional stability. On exposure to drying conditions, shrinkage
and cracking was observed (AE-006). 3.7% linear shrinkage was
measured for Shawnee sludge. This was found to be a function
of water content. This phenomenon can be prevented by addition
of a pozzolanic material such as is involved in most of the
stabilization processes now offered. I. U. Conversion has
reported the results of behavior of Sul-0-Poz ฎ material
molded into 2.5 x 2.5 x 25-cm bars and cured at 23ฐC (73ฐF)
(MI-084). In each case, an initial slight expansion was ob-
served; the degree of expansion leveled off within 3-4 weeks
for low lime content samples and within 5-6 weeks for high
lime samples, with respective overall increases in length of
~0.003 and 0.008 cm/cm. Field tests to date have produced
good results with regard to structural integrity.
3.3.3 Sypport of Vegetation
An additional factor to be considered in reclamation
of abandoned sludge disposal sites is whether growth of vegeta-
tion can be supported on the area. At the present time no studies
are available directly concerning this aspect.
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3.3.4 Related Experience in Land Reclamation
Florida's phosphate mining industry is effectively
dealing with reclamation of mined-out areas and slime pits.
Several types of solid wastes are generated from the mining
practices. Phosphate rock slimes resulting from the initial
washing process are generally handled as a 7% solids slurry of
extremely fine-grained clays. This waste is typically dis-
posed of by ponding, but settles only to 25% solids even after
two years. Figure 6 illustrates a typical slime pond in
operation. Mine tailings consist of non-phosphate sands which
are separated from the phosphate minerals by a double flotation
process. These tailings have proven very valuable in several
capacities: mine fill, construction material for pond dams,
and pond reclamation fill. In the first capacity great success
has been achieved. Several abandoned mining areas in Florida
have been converted to residential areas which support abundant
vegetation. An additional benefit is the change in land contour
resulting from the mining/reclamation activities; what was once
extremely flat uninhabited land, is now esthetically contoured
residential area.
A primary use of mine tailings is in the construction
of dikes and dams for slime dewatering ponds. This practice
has been employed for many years in the industry. The con-
tents of the ponds are capable of supporting abundant water
life. When filled some ponds have been successfully reclaimed
as recreational areas such as parks and golf courses as shown
in Figure 8 although they do not possess the engineering strength
required for support of buildings. The reclamation is achieved
by covering the slimes with a three to four foot layer of
tailings. In Figure 7 the reclamation of a pond is shown in
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FIGURE 6 - PHOSPHATE SLIME POND IN OPERATION
FIGURE 7 - A SLIME POND RECLAMATION OPERATION
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FIGURE 8 - SLIME POND CONVERTED INTO RECREATIONAL AREA
FIGURE 9 - TYPICAL BY-PRODUCT GYPSUM DISPOSAL
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progress. Although this has been demonstrated to be technically
feasible, it is not always practiced because of the short supply
of tailings which are more needed in dam construction applications
In a related industry, the wet process phosphate
manufacture, one of the main waste products is a fairly pure
grade gypsum. Figure 9 shows how this waste is disposed of in
huge gypsum piles, rising to sometimes a hundred feet and
extending for miles. This material has been stockpiled for
years with little effort to reclaim the disposal areas. Some
effort has been expended to develop new commercial uses, although
there is currently little outlet for the gypsum in this direction
in Florida. Limited information is available on possible
environmental hazards associated with this disposal technique.
This information is relevant to lime/limestone scrub-
ber sludge disposal in several ways. First of all, the re-
clamation of slime ponds has proven the technical feasibility
of converting a disposal site for a low solids, poor settling
material such as scrubber sludge to a beneficial, life-support-
ing area. Secondly, the vast stockpiles of relatively pure
waste gypsum indicate that potential marketing of scrubber
sludge as gypsum in some geographic areas is highly unfeasible,
particularly since the scrubber sludge in many cases will
contain large quantities of fly ash. The fact that no environ-
mental episodes have been reported from either properly con-
structed slime ponds or gypsum piles does not necessarily
indicate that no hazards exist, but it does seem to indicate
that no major problems are associated with either type of
disposal.
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3.4 Commercial Utilization of Sludge
The alternative to disposal of scrubber sludges is
development of commercially applicable utilization processes.
Numerous programs in this area have been conducted through
government sponsorship and by industry alone. These are sum-
marized in Table 5. In this section of the report different
areas of utilization of lime/limestone scrubber sludge are dis-
cussed. First, those efforts are described for which technology
has been demonstrated on a relatively large scale. Then an over-
view of other potential uses for which limited technology exists
is given.
Combustion Engineering, in cooperation with the Re-
search and Development Division of the Federal Highway Administra-
tion, studied the potential of several industrial sulfate sludges
as highway construction materials (TA-040, BR-112). The major
portion of a parking lot of the Dulles Airport in Washington,
D.C., was paved with a mixture of fly ash, lime, and sulfate
sludge from a hydrofluoric acid plant.
In another section a mixture of lime (3%, dry basis),
S0g scrubber sludge (8%), fly ash (59%), and aggregate (30%)
was tested as a road course material. The sludge was a 50% solids
slurry obtained from Combustion Engineering's limestone scrubbing
system at Kansas Power and Light's Lawrence facility. The paving
mixture was placed in a seven-inch layer over a compacted subgrade,
compacted to five inches, and sealed with a bituminous material
to prevent water infiltration. During the construction period,
weather conditions were especially wet. Consequently, neither
the subgrade nor the paving mixture hardened sufficiently, and
compacting operations were hindered. The sealant, which consisted
of a material not usually used in this application, also failed
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TABLE 5
SLUDGE UTILIZATION SCHEMES
I. FILLER MATERIAL
A. Structural Fill
B. Mine Void Fill
C. Filler in Bituminous Concrete
D. Waste Disposal/Sanitary Structural Land Fill
II. Pozzolanic Products
A. Road Base Course
III. Autoclave Products
* Concrete Admixture (Structure and Products)
* Fired Brick
* Lightweight Aggregate
IV. Pressure Sintered Products
A. Metal Coatings
B. Pipes
V. Gypsum Products
A. Plaster
B. Wallboard
VI. Soil Amendment
VII. Mineral Wool
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TABLE 5
(Cont.)
VIII. Mineral Recovery
A. Lime
B. Aluminum
C. Iron
D. Pozzolan (glass particles)
E. Titanium
F. Silicon
G. Rare Elements
IX. Sulfur Extraction
A. Sulfur
B. Sulfuric Acid
X. Polluted Water Treatment
A. Recovery of polluted streams, ponds, lakes
B. Neutralization of Acid
Polluted Waters
C. Sewage Plant Treatment
B. Neutralization of Acid Mine Drainage and
Polluted Waters
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to prevent seepage of moisture to underlying layers. As a result,
the parking lot surface broke up in many spots and generally did
not stand up to traffic as well as results of bench-scale tests
had predicted. Despite these problems, however, the demonstra-
tion project served to firmly establish the feasibility of this
utility scheme.
IUCS offers a process called Poz-0-Tec* to convert
power plant scrubber sludge to stabilized structural fill material
or to usable manufactured by-products. As described in Section
3.1.2.2, the process is based on technology of the Poz-0-Pacฎ
process which is also a fly ash stabilization technique.
The product of the Poz-0-Tec* process, Sulf-0-Pozฎ,
can be used as a stabilized fill material. It possesses certain
structural qualities permitting its use in some cases as struc-
tural embankments, land reclamation projects, and liners for
ponds and reservoirs. Sulf-0-Pozฎ can be further processed to
produce cementitious material of other compositions such as
synthetic aggregate suitable for production of structural shapes,
portland cement or asphaltic concrete. Sulf-0-Pozฎ may also be
supplied directly for use as stabilized road base required in
primary highways, airport runways, trucking terminals, and
similar applications.
The engineering properties of Sulf-0-Po2ฎ material have
been described previously in this report. The characteristics are
functions of the fly ash/sludge ratio and the lime and water con-
tents. Poz-0-Tec* mixtures that have been placed in dams and
reservoirs are expected to show little deterioration for many
years. In the same fashion, these mixtures, when used for road
base work, have proven to be superior to the Poz-0-Pacฎ composi-
tions .
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Gypsum is one of the solid by-products of the wet
lime/limestone gas desulfurization process. This material can
be recovered although the feasibility of doing so is limited by
the amount of foreign material in the sludge, i.e., fly ash,
unreacted lime or limestone, and calcium sulfite. Elimination
of fly ash can be achieved by burning oil rather than coal or
by installing efficient electrostatic precipitators upstream of
the scrubber unit. Oxidation of sulfi'te to sulfate is currently
practiced in Japan and is under investigation in this country
as well. The fly ash elimination and oxidation processes result
in a clean grade gypsum, CaS04*2H20, which is used in making
wallboard, wall plaster, or as a cement additive for construc-
tion use. This approach has already been taken in Japan. In
one plant sulfite is oxidized to sulfate in special equipment.
Similarly, sulfite oxidation equipment is being installed at the
Mitsui Aluminum Plant in Japan. It was recently predicted, how-
ever, that the Japanese supply of gypsum will soon exceed the
demand (AN-059). The economics of this utilization process may
not be acceptable in the United States where there exist large
natural sources of relatively pure, dry gypsum. Moreover, if an
efficient precipitator is not employed, the dark color of gypsum
due to fly ash and other impurities could be a significant prob-
lem for a potential gypsum market. The economics of the utiliza-
tion are more favorable in the Chiyoda and Hitachi processes
where the gypsum is manufactured from sulfuric acid and hence
the oxidation step is circumvented.
The potential utilization technologies described up to
this point are fairly well established in that they are either
commercially practiced or have at least been successfully demon-
strated on a large test scale. A list of less promising schemes
which have been suggested are included in Table 5 . Those
marked with an asterisk were judged to be economically unfeasible
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in a study conducted by Aerospace Corporation for EPA (Contract
F04701-70-C-0059). The following were the chief factors making
a particular scheme unattractive:
need to dewater the sludge prior to
utilization
release of sulfur d.uring a heating step
involved in manufacture of product
relatively low pozzolanic properties com-
pared to ash alone
inability to compete with less costly
products.
Progress in several of the more developed technologies are
described briefly below.
Autoclaved Products
The technology for autoclaved products was developed
at the Coal Research Bureau, West Virginia University, under
contract to EPA (CO-118). Three classes of autoclaved products
employing lime/limestone scrubber sludge as the principal raw
material have shown potential: (a) calcium silicate brick,
(b) aerated concrete, and (c) poured concrete. In general,
production of autoclaved products from scrubber sludges is tech-
nically sound, but lacks economic sureness. The calcium-silicate
bricks have the advantage of binding the sulfur components with-
in a calcium-silicate matrix. They are immediately marketable.
In addition, the compressive breaking strengths of these bricks
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are 3,500,000 kg/m2 (5,000 psi) as compared to the minimum ASTM
specification of 3,200,000 kg/m2 (4,500 psi). The envisioned
utilization areas for these brick are low-cost construction
materials, decorative and interior walls, and acoustic insulating
walls.
Aerated concrete is used commonly as a structural
material in Europe. The product has a density of 0.8-0.9 g/m3
(50-56 lb/ft3) and a controllable compressive strength between
280,000 - 600,000 kg/m2 (400-850 psi). Envisioned areas of
utilization are in non-load bearing walls, interior surfacing
for exterior walls and sandwich construction with brick or con-
crete for insulating purposes.
The feasibility of using scrubber sludge as the cement-
ing agent for the production of concrete block was also studied
(CO-118). The product has a bulk density of 1.4 g/cm3 (90 Ibs/
ft3) and a compressive strength of ca. 630,000 kg/m2 (900 psi)
as compared to 2.4 g/cm3 (150 lbs/ft3) and 700,000 kg/m2 (1000
psi) for conventional block.
Mineral Wool
The technology for producing mineral wool from fly ash
has been developed by the Coal Research Bureau at West Virginia.
The physical characteristics of wool fibers produced from scrub-
ber sludge are reported to equal or excel commercially available
mineral wool (CO-118). It is expected that mineral wool will
find use as insulation material in electrical testing. Although
technically feasible, this approach is not considered economically
attractive because of its inability to compete with conventional
mineral wool (AE-003).
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Soil Amendment and Soil Stabilization
Several Virginia and West Virginia research groups
have cooperated to study the properties of scrubber sludge with
respect to soil amendment and soil stabilization (WE-074). The
concensus is that as a result of the low cost of modified ash
and its forecast abundance, the neutralizing powers and soil
stabilization abilities of this desulfurization sludge can be
put to use in reclamation of strip mines, spoil banks and other
highly acidic areas which texturally cannot sustain or support
plant growth. Modified fly ash can be employed in agriculture
to regulate the pH of the soil as well as the boron supplying
power of certain soils. An additional advantage is that de-
watering may not be necessary for direct application of the
ash, although this is not certain at this time. Possible ad-
verse effects due to excessive buildup of elements such as boron
and molybdenum require further investigation.
To summarize the potential for sludge utilization, it
appears that several possible markets for scrubber sludge could
develop. It is likely, however, that the growth of these markets
will lag far behind the growth of sludge production, resulting
in the great majority of sludge being disposed of as a throw-
away product. The circumstances at some plants might be such
that most or all of their sludge could be marketed, however.
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4.0 PRESENT AND PLANNED UTILITY INDUSTRY DISPOSAL PROGRAMS
Those utilities currently operating lime or limestone
scrubbing systems are faced with the immediate problem of disposal
of waste sludges. Other utilities committed to a sludge generat-
ing system for future installation are in a. similar position.
There is little experience in dealing with this waste material
on a large scale, and what data and results have been obtained
are not always released. The purpose of this section of the
report is to review current and planned practices regarding dis-
posal of scrubber sludges on an industrial level. The results
of an EPA survey of utilities regarding sludge treatment tech-
niques are summarized in Table 6.
Ponding is currently being employed by a number of
utilities including the following:
TVA- Shawnee
NSP - Black Dog
SCE - Mohave
KP&L - Lawrence
KCP&L - Hawthorne
KCP&L - LaCygne
TVA's Widow Creek installation will include ponding facilities
for both sludge and ash disposal. In addition, Lousiville Gas
and Electric (Paddy's Run) and City of Key West (Stock Island)
are presently disposing of their scrubber sludges by unfixed
landfill; Montana Power Company is considering dumping their
untreated sulfur oxide sludges in an abandoned strip mine area.
In essence, these are also ponding operations. A solar evapora-
tion pond is planned for Arizona Public Service's Cholla facility.
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oo
TABLE 6
POTENTIAL SLUDGE TREATMENT/DISPOSAL PROGRAM
Facility
(Availability
Status)
TVA-Shawnee
(Current)
City of Key
West-Stock
Island
(Current)
Commonwealth
Edison Co. -Will
County
(Current)
Southern
California
Edison-Mohave
Kansas City
Power ง Light-
Hawthorn
CCurrent)
Kansas Power 5
Light-
Lawrence
(Current)
Louisville Gas
5 Electric-
Paddy's Run
(Current)
UTILITY PARTICIPANTS (JO-083)
(X = Current; P = Possible Additions)
Sorbent
Fuel
Limestone now, ^s^
lime later ^s^
^^^^ Eastern
^^^^ coal
Limestone ^^
(coral marl) ^^'^
^^""^ Residual
^^ oil
Limestone ^^^^
^^^^ Eastern
.s^'^ coal
Limestone .^
6 lime ^^^"^
^^"^ Western
^^""'^ coal
Boiler s'
injected s^
limestone ^^
.S Coal
s' (possible EfiW
^^ blend)
Boiler ^^^
injected ^^^
limestone^^^^^^
^s^ Eastern
^s^ coal
Carbide ^^^
sludge ^
(Ca(OHK)^--^
^^"^ Eastern
^^^^ coal
Scale
Proto-
type
Full
Full
Pilot
Full
Full
Full
Dewatering Technique
Clari-
fier
X
X
X
X
X
Filter
X
P
X
X
Centri-
fuge
X
X
Dryer
P
Pond
X
X
(Well
points)
X
(Well
points)
X
Final Disposition
Ponding
X
(un lined)
X
X
(un lined)
X
(unlined)
Landfill
X
(Unfixed)
X
(Sealed)
(Fixed)
X
Other
-------
TABLE 6 (Cont.)
POTENTIAL SLUDGE TREATMENT /DISPOSAL PROGRAM
UTILITY PARTICIPANTS (JO- 083)
(X = Current; P = Possible Additions)
Facility
(Availability
Status)
Northern
States Power-
Black Dog
(Current)
Kansas City
Power 5
Light-
LaCygne
(Current)
Arizona
, Public
oo Service-
f- Cholla
(Approx
mid-1973)
Duquesne
Light-
Phillips
(Approx
mid-1973)
Detroit
Edison-
St. Clair
(Late 1973)
TVA-
Widows Creek
(1975)
Sorbent ^ """
_^-~ """" Fuel
Limestone ^^^^
^^- Western
^^^"^ coal
Limestone ^s^
^^
^s Eastern
^^ coal
^^
.^
Limestone .s'
^^
.s^
.^^ Western
^^ coal
^^^^ Eastern
^^^ coal
Limestone ^^^^
^
^^^"^ Eastern
^ coal
Limestone ^^-"'^^
^^---^Eas tern
^^^^^ coal
Scale
Pilot
Full
Full
Full
Full
Full
Dewatering Technique
Clari-
fier
X
x
Filter
,
Centri-
fuge
Dryer
Pond
X
(Curing)
X
X
Final Disposition
Ponding
X
(unlined)
X
(unlined)
X
(Solar
evap)
(unlined)
X
(unlined)
Landfill
X
(Fixed)
X
(Unfixed)
Other
-------
The only utility presently employing a fixation process
to produce a stabilized landfill material is Commonwealth Edison
at Will County. Several utilities including Duquesne Light are
now testing one or more fixation techniques for future use in
landfill operations.
EPA's prototype scrubbing facility at Shawnee is cur-
rently testing both lime and limestone. The facility is
being used to test .several modes of sludge treatment, all
entailing oonding as an ultimate disposal approach. The three
configurations are:
clarifier/pond
clarifier/solid bowl centrifuge/pond
clarifier/rotary vacuum filter/pond
Bench scale studies of the various dewatering techniques (described
in Section 3.1.2.1) were used as the basis for selection of sludge
treatment options. Another aspect being investigated in TVA's
labs is the ability of settled sludge to seal clay linings.
Sludge from this facility has been sampled and analyzed by
Aerospace Corporation under contract to EPA in an attempt to
characterize scrubber sludges and define any potential problems
which may be incurred in its disposal. Results of this investi-
gation have been presented throughout this report.
The pond itself is divided into three sections. The
dikes are made from fly ash and covered with a local clay. A
monitoring program was installed around the pond to observe seep-
age, which was reported to be fairly heavy during initial operation
of the pond before any solids had settled. Under closed loop
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operation, sludge is discharged to a large settling area from
the scrubber circuit, thickener underflow, and/or filter or
centrifuge. The supernatant is returned via a small "polishing"
pond .
Two clarifiers were evaluated, one 6.1 meter in
diameter and a larger one 9.1 meter in diameter. The smaller
of the, two proved to have been underdesigned. This was a direct
result of the poor settling characteristics observed. The con-
centration of the underflow approached 40% solids which was the
final expected settled composition. The following recommendations
were made concerning optimum sludge handling:
maintain steady feed flow to clarifier
optimize sulfite oxidation
investigate effect of limestone particle
size on settling characteristics
control density of clarifier underflow -
let level of sludge vary
operate clarifier in series with filter
or centrifuge
use flocculants
At Widows Creek a new pond for disposal of sludge
generated by the limestone scrubber is under construction which
will have an initial seven year capacity of 3.4 MM m3 (4.5 MM
yd3) (MC-068, TE-1L3, SL-034). This can be increased by 1.0 MM m3
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(1.3 MM yd3) by raising the dikes. An estimated additional
2.7 MM m3 (3.5 MM yd3) of capacity for which no provision has
yet been made may be needed before 1995. A total of 0.93 krrf
(230 acres) of land is taken up by the new pond which is section-
ed for separate disposal of ash and sludge. The pond is unlined;
the perimeter and divider dikes are 9.1 meters (30 feet) tall
with 1.2 meters (4 feet) of freeboard and constructed of com-
pacted earth.
Under closed loop operation, the scrubber wastes will
be pumped to the sludge disposal section of the pond as a 15-16%
solids slurry. The ash pond effluent will be released to the
Guntersville Reservoir. A thickener will not be employed. A
final settled density of 4070 solids is expected, based on pilot
plant data showing 57-66% water content after 240 days of set-
tling. The overall disposal rate is calculated to be 115 m3/hr
(150 yd3/hr).
Northern States Power is currently employing ponding
operations to dispose of the sludge and ash from the pilot scale
limestone scrubber at Black Dog Station (JO-083). Clarification
is used for primary sludge dewatering. A future limestone
scrubber installation is planned for NSP's Sherburne County site.
There sealed basins will receive the clarified solids, with
clarifier liquor being recycled (SW-011). The precipitated
solids and unreacted limestone will be carried to the pond by
wash water where they will be disposed of together with fly ash.
Supernatant from the pond will also be recycled (JO-090).
The pilot scrubber at Southern California Edison's
Mohave Station will be tested under both limestone and lime
scrubbing conditions. Three modes of sludge separation arc
under investigation: centrifugation, rotary filtration, and
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clarification (WE-068); the effect of degree of oxidation of
sulfite is also being studied. No results of these tests were
presented. Ponding is being utilized as the final disposal
method.
The full scale boiler injected limestone scrubbers,
Units 4 and 5 at Kansas Power and Light's Lawrence Station,
operate under closed loop. Ponding is used both as a dewatering
technique and an ultimate disposal approach. An experimental
sludge pond has been constructed; fourteen well points have
been placed outside the perimeter (TA-040). A monitoring study
is being carried out in conjunction with Combustion Engineering
to determine possible adverse effects on the groundwater. Samples
of groundwater will be taken weekly for two months prior to
introduction of sludge to the pond and will continue for one
year thereafter. Preliminary results are not available for
release at this time.
Kansas City Power and Light is currently running two
full scale limestone systems at LaCygne and Hawthorn Stations.
At the Hawthorn site clarification and ponding are employed
to dewater the sludge. Ultimate disposal is by ponding at both
locations (JO-083).
The current and future sludge disposal practices for
Paddy's Run, Louisville Gas and Electric, involve landfill
operations. The scrubber itself is a full scale carbide sludge
rCa(OH)P] system. Clarification and vacuum filtration result
in a 50% solids sludge which is temporarily placed in an interim
pond. At the present time, the sludge is being trucked to an
off-site disposal area, a trench excavated by the Kentucky
Highway Department. The sludge receives no stabilization treat-
ment. Future plans, however, may include such treatment; the
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utility is currently looking at those offered by Dravo and IUCS.
Research in this area is also being conducted by the University
of Kentucky and the State Highway Department. Another aspect
of sludge disposal being considered by the utility is pipelining
the solid waste s-lurry to the fixation site (VA-068) .
Experience in untreated sludge disposal has also been
obtained at the City of Key West's Stock Island facility where
a prototype (37 MW) limestone process has been operating.
Residual oil is burned, thus resulting in a solid waste of low
ash content. The scrubber solids are placed in one of two set-
tling ponds where drying takes place (PA-049). While one pond
is being filled, the other is emptied. The dried sludge is then
dumped in an adjacent 81,000 nf (20 acre) city owned site which
is bay bottom land. The material has been placed above sea
level in compliance with a Florida state law which prohibits
filling of submerged land productive to marine life.
The approach under consideration by the Montana Power
Company entails disposal of their desulfurization sludges in
abandoned strip mine areas. Coal ash high in CaO and MgO is
to be used as an absorbent material.
Because of the climatic conditions at Arizona Public
Service's Cholla facility, a solar evaporation pond will be used
as a sludge disposal technique. The clarifier underflow from
the 115 MW limestone system will be transported to the existing
ash pond (MU-022). Clarifier effluent will be recycled under
the closed loop operation.
Commonwealth Edison has the greatest amount of in-
dustrial experience with disposal of stabilized sulfur oxide
sludges. The full scale limestone scrubber is installed on Will
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County's Unit 1 boiler (163 MW) . Initially, a 22,000 iri5 (5.5
acre) pond 1.8 meters (6 feet) deep was used for sludge dis-
posal, but since it has a limited (6 months) capacity, another
approach was sought. Presently, the spent slurry from the
scrubber is pumped to a clarifier 20 meters (65 feet) in diameter
The underflow is temporarily held in a pond where further de-
watering occurs. The pond supernatant and the clarifier liquor
are returned to the scrubber cycle via a second pond. The de-
watered sludge is pumped to a loading station where it is mixed
in a cement truck with fly ash and other dry ingredients to
produce a stable landfill material. Chicago Fly Ash is under
contract to carry out the stabilization and disposal operations
(ST-117). The fixed material is presently being placed in an
on-site clay lined basin approximately half a mile away. This
practice will continue until the environmental soundness of the
material has been demonstrated (GI-017). In the future, they
plan to utilize additional dewatering procedures such as vacuum
filtration and possibly thermal disc dryers to reduce the volume
of sludge requiring stabilization treatment.
Pilot scale sludge samples generated by the lime scrub-
bing system at Duquesne Light's Phillips Station have been tested
and characterized by Dravo Corporation. When the full scale
system starts up, the sludge disposal method will entail a fixed
landfill operation in conjunction with clarification and curing
pond as dewatering methods. Dravo Corporation, which has been
working on dewatering and stabilizing Duquesne's sludges on a
bench scale up to now, is being considered to provide the indus-
trial scale disposal process.
For a detailed description of the project underway
at STEAG, see Appendix B. There an experimental sludge pond
is being monitored to determine extent of potential groundw'ater
contamination.
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Two dual stage venturi scrubbing systems utilizing
carbide sludge as an absorbent have been retrofitted to the
156 MW power plant of the Mitsui Aluminum Company. The unit
has operated under continuous closed loop mode since March, 1972,
with no significant scaling or plugging problems. A bleed stream
from the system containing mostly calcium sulfite (80%) and
calcium sulfate is disposed of in a preexisting 90,000 square
meters ash pond (SA-099). Pond liquor which is saturated with
respect to calcium sulfate is recycled via rubber lined piping
to the scrubber circuit for reuse. Now that this SO? control
system has begun operation, production of high quality gypsum
from waste sludge is planned. There is a definite market for
by-product gypsum in Japan for the very near future. However,
the Japanese supply of this by-product is soon expected to
exceed the demand (AN-059).
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5.0 CONCLUSIONS
Lime and limestone scrubbing systems will have wide
application for SOP removal in the next decade. Since removal
of one pound of sulfur will generate approximately ten pounds
of wet sludge, a tremendous amount of solid wastes will be gen-
erated. Because of the large quantities involved, the environ-
mental effects of disposal of this material is a matter of con-
siderable concern. A quantification of these effects and the
identification of environmentally acceptable disposal techniques
are, therefore, of great importance.
A limited amount of data is available on the chemical
nature of various sludge materials, and this data can be used to
help quantify potential environmental effects of sludge disposal.
Sludges from different units exhibit a wide variation in chemical
properties. Since there are no large scale units with a lengthy
history of continuous operation, it is not clear how applicable
existing data are to such a system. Nevertheless, those data
have been used to put the problem into perspective (see Section
2.1). The main problem area related to sludge disposal appears
to be the presence of soluble materials in the sludge, resulting
in potential water pollution problems for both surface and ground-
water. The soluble species can be classified as follows:
(1) Soluble toxic species, e.g., trace
metals
(2) Excessive total dissolved solids
(3) Excessive levels of specific species
not generally thought of as toxic,
e.g., sulfate and chloride
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A consequence of the presence of soluble species is that care-
ful attention must be paid to the design and operation of sludge
disposal sites. It appears that many variables (coal, limestone,
and operating parameters) can influence the amount of the soluble
species. More work is needed to quantify the extent of influence
of these variables on sludge composition and behavior, and to
better define the chemical characteristics of sludge from large
continuously operating systems. Several studies are under way
at power generating stations around the country which may provide
some of this type of information. EPA is also funding efforts
in this area.
A limited amount of data are also available regarding
the physical properties of sludge (Section 2.2). Again, there
is a wide variation in properties for sludges from different
units. These properties are influenced by many system variables
in a manner that is not well understood. The physical properties
strongly influence the ease with which the material may be handled
and transported, and magnitude of the land reclamation problems
for abandoned sludge disposal sites. The main problems with
regard to the physical properties of sludge are difficulty in
dewatering and a tendency to rewater to its original water
content and permeability. A lack of strength by dried unfixed
sludge material is another potential problem. In terms of
handling problems, special dewatering techniques (besides set-
tling) may be required. In terms of land reclamation, the
effects of rewatering and lack of load bearing strength have
not been quantified. Another land reclamation problem which
has not been addressed is the ability of the sludge to support
growth of vegetation.
Electric utilities who now operate or plan to install
lime/limestone scrubbing systems in the State of Ohio are faced
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with selecting at least an interim sludge disposal scheme.
On the basis of the information contained in this report, the
following should be taken into consideration determining the
method to be employed:
Ponding and landfill are the most viable
alternatives.
Stabilized landfill offers a more permanent
solution.
Geography will determine disposal site and
technique in many situations.
Utilization may be feasible in special cases
although the probability is extremely low,
especially in the near future.
The major disposal options for sludge are ponding and
landfilling. Even though the presently available data on
chemical and physical properties indicate some potential problem
areas, it appears that both of these disposal options are viable
methods if proper engineering and operation are practiced.
Ponding of sludges, which probably will account for
60% of sludge disposal based on existing and planned installations,
will require particular attention to proper practice because of
the increased potential for groundwater pollution (see Section
3.1.1.2). This type of pollution is particularly bad because,
unlike surface water pollution, there is little opportunity for
dilution of the contaminants, and the pollution may go undetected.
With proper site selection and pond lining, however, leaching
of contaminants to an aquifer from a pond can be avoided. It
-94-
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appears that overflow of pond liquor into surface water should and
can be avoided. This will require proper pond design and partial
or total recycle of pond liquor, with treatment of any blowdown
streams. The construction and lining of ponds is established
technology.
Landfilling (Section 3.1.2) probably will account for
some 40% of the sludge disposal, based on existing and planned pro-
jects (this percentage may increase as the state of the art of fix-
ation advances and costs decrease). Whereas ponding is largely
planned with untreated sludge, the physical properties of sludge
may necessitate treatment (fixation) by one of several commercially
available processes to convert the sludge to a more easily handled
material. The feasibility of landfilling without fixation requires
further investigation at this point. Even if the sludge is not
treated, some type of dewatering will likely be required. An ad-
ditional advantage claimed for sludge fixation is a great decrease
in the permeability and amount of soluble species in the sludge.
Since landfilling basically presents the same type of potential
water pollution problems as ponding, fixation might eliminate
the need for such procedures as linings and cover material for
disposal sites. Both dewatering and fixation processes are cur-
rently being tested and compared by several independent groups
in order to determine the technical feasibility of each. Results
available to date seem to indicate that stabilized landfill may
provide the most permanent solution to the disposal of throw-
away products from S08 removal systems. Reliable economic data
associated with this disposal scheme, however, are not available
at this time because of the lack of long term, full scale ap-
plications in this area.
Another consideration in the selection of a disposal
site is the geography and hydrogeology of the area. This will
be unique to each Ohio utility. These factors will influence
-95-
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the economic and the environmental aspects of the disposal
method in the event that contamination of groundwaters by sludge
is shown to be a problem. Precautionary measures such as liners,
covers, fixation or drainage facilities will be selected, if
needed, on the basis of the geology. For instance, if the water
table is in close proximity to the bottom of the disposal site
(pond or landfill), or if the soil is extremely permeable to
potential leachate, then preventive measures will be required.
Commercial utilization of scrubber sludges at this
stage of development appears unfeasible to any great extent.
The variability in the sludge composition and properties (amount
of ash, water content, calcium sulfite and sulfate concentrations,
water retention, etc.) is one hinderance to extensive utilization.
A second obstacle is the sheer volumes forecast on a nationwide
basis (see Section 1.0). It has been shown that several of the
utilization schemes may be technically promising. However, it
is unlikely that any great percentage of sludge generated could
be utilized in any one commercial market.
In conclusion, based on presently available data,
there are no insurmountable technological problems in disposing
of sludge in an environmentally acceptable manner. The economics
of such disposal have not been well defined, but the results of
numerous studies now under way at pilot plants and full scale
systems around the country will soon provide additional infor-
mation in this area, as well as providing improved data on the
chemical and physical properties of untreated and treated (fixed)
sludge and its permeability and leachability.
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>v
AE-003 Aerospace Corp., Office of Corporate Planning,
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v\
AE-006 Aerospace Corp., Urban Programs Div., Limestone-Coal
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>v
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>v
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/v
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Many Cost Problems Yet", Commerce Today J3(23) ,
4 (1973).
RO-084 Rossoff, J., R. C. Rossi, and J. Meltzer, "Study of
Disposal & Utilization of By-Products from Throw-
away Desulfurization Processes", Presented at
the Flue Gas Desulfurization Symp., New Orleans,
La., 14-17 May 1973.
-102-
-------
RO-093 Rohrman, F. A., "Analyzing the Effect of Fly Ash on
Water Pollution", Power 115 (8), 76-7 (1971).
SA-099 Sakanishi, Jun, and Robert H. Quig, "One Years
Performance and Operability of the Chemico/
Mitsui Carbide Sludge (Lime) Additive S0a
Scrubbing System", Presented at Flue Gas
Desulfurization Symposium, New Orleans, La.,
14-17 May 1973.
SA-103 Salvato, Joseph A., William G. Wilkie, and Berton
E. Mead, "Sanitary Landfill-Leaching Prevention
and Control", J. WPCF 43(10), 2084-2100 (1971).
SC-122 Schmitt, C. R. , Survey .of the Fly-Ash Disposal System
_at the Oak Ridge Y-12 Plant, Y-1713, Oak Ridge,
Tenn., 1970.
'SE-066 Selmeczi, Joseph G. and R. Gordon Knight, "Properties
of Power Plant Waste Sludges", Paper #B-7,
Presented at 3rd International Ash Utilization
Symposium, Pittsburgh, Pa., March 13-14, 1973.
SH-110 Shannon, E. S., "Underground Disposal of Activated
Sludge", J. WPCF 1968(12), 2059.
SL-034 Slack, A. V. and J. M. Potts, "Disposal and Use of By-
Products from Flue Gas Desulfurization Processes
Introduction and Overview," Presented at the Flue
Gas Desulfurization Symposium, New Orleans, La.,
May 14-17, 1973
-103-
-------
SO-048 "Solid Waste: From Dirty Sludge to Clean Dirt", Iron
SP-029 Sparr, Anton E., "Pumping Sludge Long Distances",
2- WPCF 43(8), 1702-11 (1971).
ST-117 Stewart, J. F., "A Review of Babcock and Wilcox Air
Pollution Control Systems for Utility Boilers"
Presented at the Flue Gas Desulfurization Symp.,
New Orleans, La., 14-17 May 1973.
SU-031 Sulfur Oxide Control Technology Assessment Panel
(SOCTAP) , Projected Utilization o_f Stack Gas
Cleaning Systems _by_ Steam-Electric Plants ,
Final Report, April 1973.
SW-011 Swanson, A. E., Testimony, Northern States Power Co.,
Sherburne County Hearings (NO.-028) , Minneapolis,
Minn., April 1972.
TA-040 Taylor, W. C., "Experience in the Disposal and Utiliza-
tion of Sludge from Lime-Limestone Scrubbing
Processes", Presented at the Flue Gas Desulfuriza-
tion Symp., New Orleans, La., 14-17 May 1973.
TE-112. Tennessee Valley Authority, Review of Wastewater
Control Systems, Widows Creek Steam Plant,
Muscle Shoals, Ala., 1971.
-104-
-------
TE-113 Tennessee Valley Authority, Environmental Statement.
Experimental S02 Removal System and Waste
Disposal Pond. Widows Creek Steam Plant.
Final Environment Statement TVA-EP-EIS-73-1,
Chattanooga, Tenn., 1973.
TH-040 Thomas, C. M., "The Use of Filter Presses for the
Dewatering of Sludges", J. WPCF 43(1), 93 (1971)
TH-041 Thompson, T. L., P. E. Snoek, and E. J. Wasp, "Eco-
nomics of Regional Waste Transport and Disposal
Systems", Water-1970. CEP Symposium Series 107
(67), 413-22 (1971).
TR-026 "Truckloads of Land Fill from Waste Sludge", Chem.
Week 110(4), 41 (1972).
VA-068 Van Ness, R. P., Louisville Gas and Electric, Private
Communication, 13 August 1973.
WA-083 Walker, William R. and R. C. Stewart, "Deep-Well
Disposal of Wastes", Proc. ASCE J_. Sanitary Eng.
Div. 1968 (SA 5), 945.
WE-068 Weir, Alexander,Jr. and Lawrence T. Papay, "Scrubbing
Experiments at the Mohave Generating Station",
Presented at the Flue Gas Desulfurization Symp.,
New Orleans, La., 14-17 May 1973.
-105-
-------
WE-074 West Virginia Univ., Coal Research Bureau, Pilot
Scale Up of Processes to Demonstrate Utiliza-
tion of Pulverized Coal Fly Ash Modified by
the Addition of Limestone-Dolomite Sulfur
Dioxide Removal Additives, PB 213 639, Morgan-
town, West Virginia, 1971.
WE-078 West Virginia Univ., Coal Research Bureau, Dewatering
of Mine Drainage Sludge, Water Pollution Control
Research Series 14010, Morgantown, W. Va., 1971.
YE-005 Yeh, Show-Jong and Charles R. Jenkins, "Disposal
of Sludge from Acid Mine Water Neutralization",
J. WPCF 43, 679 (1971).
-106-
-------
APPENDIX A
-------
TABLE Al
Analytical
Method
Ref.
Li
Na
K
Rb
Cs
Be
Mg
Sr
Ba
B
Al
C
Pb
N
P
As
Sb
S
Se
F
Cl
Br
1 2
Eastern Coal' Western Coal
(Shawnee) (Composite)
Spark Source
Mass Spectro- Not Reported
graphic Analysis
AE-008,
RO-084 RO-084
3.3
1700
3000
24
N.D.
<0.01 N.D,
1700
1100
1800 400
46 15
7500
(>U)
30 4
30
40
N.D. 3
<0.05 0.17
(>1%)
N.D. 1.6
7.9
280 38
N.D.
ELEMENTAL COMPOSITIONS OF COAL AND ASH (IN ppm)
345
Bottom Ash Bottom Ash Fly Ash
(Western Coal) (Eastern Coal (Eastern Coal
Shawnee) Shawnee)
S[ ark Source
Not Reported Mass Spectro-
graphic Analysis
RO-084 AE-008
42
350
1300
63
6.0
<2
9700
170
1500 (<17.)
70 220
(
-------
TABLE Al Continued
ELEMENTAL COMPOSITIONS OF COAL AND
1
Eastern Coal
(Shawnee)
11
V
Cr
Mn
Fe
Ni
Cu
Zn
Y
Cd
Hg
5900
180
310
350
4500
N.D.
N.D.
180
95
N.D.
<0.01
ASH (IN ppm)
2
Western Coal
(Composite)
9
5
15
25
0.56
<0.5
0.05
3
Bottom Ash
(Western Coal)
-.
70
70
150
15
25
<0.5
<0.01
4
Bottom Ash
(Eastern Coal
Shawnee)
(>1%)
290
700
530
(>1%)
220
640
340
5
Fly Ash
(Eastern Coal
Shawnee)
6000
65
440
180
25
290
73
~
~
6
Fly Ash
(Eastern Coal
Shawnee)
(>1%)
820
230
290
--
--
140
1600
47
--
7
Fly Ash
(Western Coal)
--
150
150
150
--
70
--
70
--
<0.5
0.03
I
NJ
-------
TABLE A2
CHEMICAL COMPOSITION OF FLY ASH - MAJOR AND MINOR CONSTITUENTS
NaaO
KaO
MgO
CaO
B
A1303
C
SiOfl
P
S03
TiOw
Fe 0.
National
for Typical
0.4 -
--
0.5 -
1.5 -
0.1 -
20 -
0.1 -
30 -
0.01
0.02
0.4 -
10 -
Range
Samples
1.5
-
1.1
4.7
0.6
30
4.0
50
- 0.03
- 3.2
1.3
30
Bituminous
0.05
1.42
1.00
4.48
--
16.25
2.21
49.10
--
0.73
1.09
22.31
Lignite
0.87
0.68
7.31
18.00
--
10.70
0.11
32.60
--
2.60
0.56
10.00
Ref. RO-093 CO-119 CO-119
A-3
-------
TABLE A3
>
-P-
Analytical
Method
Ref.
pH
Li
Na
K
Bo
Mg
Ca
Ba
B
Al
C
Si
Pb
As
Sb
A1
Solids (wt %)
Oak Ridge Y-12 Steam
Ba
Spectrographic Spectrographic
SC-122
--
0.04
0.6
--
__
0.6
0.6
0.12
0.03
>20
12.08
20
0.01
SC-122
--
0.08
0.7
3
-
1.0
0.6
0.12
0.05
20
11.94
35
<0.01
CHEMICAL
Plant
c3
Spec trographic
SC-122
...
0.08
0.6
2.5
__
0.9
0.6
0.10
0.05
18
12.51
30
<0.01
COMPOSITION OF ASH PONDS
Unidentified
Ash Pond
(EPA Data)
RO-084
--
--
0.002
..
--
0.07
0.5
--
0.01
Liquors (ppm)
Range for Ten TVA's Widow Creek
Ohio Plants Ash Pond 1971
Quarterly Samples
1/4 4/5 7/6 10/4
RO-093 TE-112 TE-112 TE-112 TE-112
6.2-11.5 7.3 9.0 9.8 9.1
--
--
--
--
4.6 3.4 3.7 4.3
20 34 47 45
-_
<100-1600
--
as SiOa / 5.4 4.4 6.1 5.6
0.1 - 1.9 (as NH3)
[-0.1 (as NO,)
0.1 - 0.6
0.01
0.015
-------
TABLE A3 Continued
I
Ln
CHEMICAL COMPOSITION OF ASH PONDS
Solids (wt %)
S(as S04)
Se
Cl
Ti
V
Cr
Mn
Fe
Ni
Cu
Zn
Cd
Hg
Oak Ridee
A1
--
--
0.3
0.03
0.03
0.04
10
0.02
0.02
--
--
Y-12 Steam Plant
B'
--
--
--
1.0
0.04
0.03
0.04
10
0.03
0.03
--
--
Unidentified
, Ash Pond
C (EPA Data)
--
0.035
0.8
0.08
0.03
0.08 0.075
7
0.03 0.015
0.03
0.03
0.01
<0.001
Total Dissolved
Solids
Liquors (ppm)
Range for Ten TVA's Widow Creek
Ohio Plants Ash Pond 1971
Quarterly Samples
1/4 4/5 7/6
100 95 70
--
21 11 19
--
..
0.44 0.02 <0.01
0.29 0.42 0.27
--
--
--
.-
240 190 210
10/4
60
--
17
..
--
--
0.02
0.69
--
--
--
--
--
210
1 Sample A was collected at the overflow from the primary retention basin to
a water-filled quarry which acts as a settling pond.
2 Sample B was collected at the outfall of the quarry.
3 Sample C was
collected where
the overflow enters a lagoon of a lake.
-------
TABLE A4
Sample
Analytical
Method
Ref.
Li
Na
K
Rb
Cs
Mg
Ca
Sr
Ba
B
Al
Ga
C
Si
Sn
Pb
N
P
As
S
Shawnee
Limestone
Emission
Spectrographic
Analysis
AE-007
..
0.036
ND
--
--
2.9
35.
0.078
--
ND
0.012
ND
..
0.65
--
ND
..
--
--
~ "
CHEMICAL ANALYSES
Shawnee '
Limestone
Spark Source
Mass Spectro-
graphic Analysis
AE-008
0.00018
0.0360
0.0580
0.00017
ND
>1
--
0.15
0.0010
0.00015
0.42
--
0.4900
--
--
ND
0.00045
0.0085
ND
0.0220
OF LIMESTONE (WT. %)
Western
Limestone
Emission
Spectrographic
Analysis
AE-009
--
TR<0.06
KTX0.40
0.30
39.
0.039
NIX0.20
NIX0.005
0.0099
ND<0.006
..
0.24
ND<0.008
NTK0.01
__
NIX0.50
~
Western
Limestone
Spark Source
Mass Spectro-
graphic Analysis
AE-009
0.000031
0.17
0.033
0.00007
ND
0.40
--
0.0220
ND
0.000080
0.33
--
__
--
0.00022
0.0050
0.0011
0.0030
Balance is sulfate, sulfite, oxides, and carbonates
-------
TABLE A4 Continued
Chemical Analyses of Limestone CWt. "7.)
Sample
Analytical
Method
F
Cl
Br
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Y
Mo
Shawnee
Limestone1
Emission
Spec trographic
Analysis
._
--
ND
0.00084
0.011
0.10
ND
ND
0.00011
Nil
Shawnee
Limestone'-
Spark Source
Mass Spectro-
graphic Analysis
0.0012
.0038
ND
0.0440
0.0015
0.00076
0.0140
0.25
--
--
ND
0.0059
ND
Western
Limestone1
Emission
Spectrographic
Analysis
--
--
--
ND<0.004
ND<0.008
0.0014
0.025
0.070
ND<0.002
NTX0.002
0.00022
ND<0.06
..
Western
Limestone1
Spark Source
Mass Spectro-
graphic Analysis
0.00043
--
--
0.0160
0.00053
0.0019
0.0150
0.0900
--
--
ND
--
0.006
Balance is sulfate, sulfite, oxides and carbonates
-------
TABLE A5
i
00
S10a
Ala03
Fe,0a
CaO
MgO
NasO
K90
TiOa
PaOs
C0a
S0a
S03
CaCOa
STD II
1.5
0.32
0.27
49.6
0.54
0.04
0.17
<0.02
0.05
29.2
11.7
3.5
65.7
STD III
30.7
6.6
8.6
22.7
1.5
0.50
1.1
0.26
0.11
5.3
5.8
6.5
12.0
From TA-040
STD II
STD III
STD IV
STD V
STD VI
STD VIA
STD VII
STD VIII -
MIC/vL ANALYSIS OF SLUDGE S^
STD IV
0.79
0.05
0.18
42.5
0.10
0.03
0.05
<0.02
0.06
3.7
38.8
3.3
8.4
STD V
19.4
6.8
5.4
27.6
3.2
0.08
0.24
0.32
0.08
7.2
2.2
12.3
16.3
IDENTIFICATION OF SLUDGE
STD VI
1.1
0.01
0.09
52.5
0.52
0.02
0.14
<0.02
0.13
36.6
6.3
0.5
80.6
STANDARDS
STD VIA
27.7
14.7
8.3
24.2
0.70
0.16
1.2
0.79
0.19
15.3
3.4
<0.1
34.7
STD VII
4.6
2.3
1.6
40.1
0.20
0.05
0.29
0.11
0.08
13.6
5.4
24.9
30.9
STD VIII
1.2
0.48
0.72
42.5
0.90
0.05
0.07
<0.02
0.06
11.5
24.1
8.4
26.1
STD IX
2.0
0.45
0.72
46.2
0.40
0.04
0.21
<0.02
0.07
24.4
13.7
4.4
55.4
C-E sludge - CaC03, 150% stoichiometry, 2000 ppm S0a
Kansas Power and Light sludge
C-E sludge - Ca(OH)a, 38% to 50% stoichiometry, 50 to 60% S0a removal, slurry feed 220 gpm,
recycle 165 gptn with 55 gpm blowdown
Union Electric sludge
C-E sludge - CaC03, 150% stoichiometry, 45 to 55% removal, no recycle
STD VI plus 50% STD I (fly ash)
C-E sludge - 300 to 325% stoichiometry, 64% SQS removal, 300 Ib/hr fly ash, 550 Ib/hr CaC03
C-E sludge - 120 to 130% stoichiometry Ca(OH)r, 90.8% removal, 120 gpm (Ca(OH);, slurry underbed,
inlet SOP 860 to 840 ppm, outlet S02 80 ppm, 145 Ib/hr Ca(OH)a, no fly ash addition
STD IX - C-E sludge - 220 gpm H.,0 spray, 275 Ib/hr lime feed, 300 F reaction temperature
-------
TABLE A6
SPARK
Element
Li
B
C
N
F
Na
Mg
Al
P
S
Cl
K
Ti
V
Cr
Mn
Fe
Cu
Zn
As
Rb
Sr
Y
Cs
Ba
Pb
Br
SOURCE MASS SPECTROGRAPHIC ANALYSIS OF SCRUBBER SOLIDS'
(In Parts
1
TCA Effluent
Separated
Solids
5.1
28
1,700
1
30
2,800
(>!*)
(>1X)
170
<>!%)
47
3,700
4,500
94
240
180
(>1%)
33
330
24
13
750
63
1
1,600
20
N.D.
Per Million By Weight)
2
TCA Effluent
Slurry Solids
7.9
42
170
3
16
290
<>!*)
(>1%)
150
2,100
79
760
5,300
150
250
230
(>1%)
49
450
53
30
1,500
45
1.2
870
64
N.D.
3
Clarifier
Solids
1.2
7.6
140
3
5.9
270
<>ซ)
(>1%)
110
330
42
860
4,200
150
66
190
<>!*>
N.D.
90
16
9.0
1,100
27
N.D.
520
N.D.
N.D.
Notes;
1. Sample for columns 1, 2, and 3 were centrifuged and dried at Aerospace.
2. Samples for colums 1 and 2 were obtained upstream of the clarifier.
Column 1 sample was filtered at the scrubber site.
* From AE-008
A-9
-------
TABLE A7
EMISSION SPECTROGRAPHIC ANALYSES OF LIMESTONE
Ca
Mg
Si
B
Mn
Fe
Al
Mo
Cu
Na
Ni
Sr
K
Co
Cr
Ti
Pb
Ca
Other
Cations
AND CLARIFIER
Distilled
Water
ppm
TR < 0.004
0.0040
0.085
0.018
**ND < 0.01
0.055
ND < 0.04
< 0.02
0 . 0064
ND < 1.0
0.058
ND < 0.01
ND < 2.0
Nil
Nil
Nil
Nil
Nil
Nil
LIQUOR AND SOLID*
Clarifier
Liquor
ppm
1100.
67.
14.
11.
1.6
0.17
0.34
0.56
0.0017
***TR < 7.5
0.05
2.1
19.
Nil
Nil
Nil
Nil
Nil
Nil
Clarifier
Solids
Wt. %
27.
1.4
8.9
0.0092
0.013
0.25
2.6
Nil
0.00053
0.23
0.0017
0.099
0.88
TR < 0.001
0.0025
0.53
0.015
0.0027
Nil
Balance is sulfate, sulfite, oxides and carbonates
*From AE-007
**ND - Not detected
***TR - Trace
A-10
-------
Element
Si
Ca
Fe
AL
Mg
Na
Ba
B
P
Ti
Mn
K
Pb
Ga
Cr
Ms
Sn
V
Cu
Zn
Ni
Co
Sr
Other
Scrubber Input
From Holding Tank
ND <
TR <
ND <
TR <
TR <
ND <
ND <
ND <
ND <
ND <
ND <
10.%
25.
1.2
3.4
0.53
2.4
0.20
0.005
0.50
0.10
0.017
0.40
0.02
0.006
0.0071
0.004
0.008
0.008
0.0041
0.06
0.0024
0.002
0.030
Nil
Scrubber Output
To Holding Tank
1.6%
35.
0.29
0.90
0.18
1.6
0.0063
0.056
0.0076
TR < 0.40
0.016
0.0070
0.0025
0.0041
0.11
V V
Centrifuged
Solids
1.4%
37.
0.18
0.79
0.20
0.69
TR < 0.005
0.044
0.0055
TR < 0.01
0.0042
0.00089
0.0029
0.14
V
Centrate
18.%
4.2
3.6
15.
1.3
5.2
0.19
0.016
TR < 0.50
0.94
0.046
0.94
0.064
0.024
0.072
0.0088
0.030
0.036
0.014
0.0043
0.095
ป
Make-Up
Water
22.%
9.6
4.2
6.2
1.4
TR < 0.20
TR < 0.20
0.017
2.6
0.12
0.13
ND < 0.40
0.034
TR > 0.006
0.038
ND > 0.004
TR > 0.008
ND > 0.008
0.38
0.86
0.0028
TR < 0.002
0.16
From AE-009
-------
TABLE A9
SPARK SOURCE MASS SPECTROMETRY ANALYSIS OF SOLIDS
FROM A WESTERN STATION*
Element
Li
B
C
N
P
Na
Mg
Al
P
S
Cl
K
Ti
V
Cr
Mn
Fe
Cu
Zn
As
Rb
Sr
Cs
Ba
Detection
Limit, ppm
0.07
0.1
0.1
1
0.1
0.07
0.7
0.5
0.2
2
0.5
0.1
1
0.5
0.7
0.5
1
1
1
1
0.7
3
3
5
Scrubber
Output to
Holding
Tank, ppm
7.9
28
920
72
190
(c)
7,400
(c)
1,100
(c)
1,600
1,100
1,100
42
250
90
(c)
1
71
58
22
1,700
53
1,400
Centrifugad
Solids, ppm
5.5
35
5,500
41
3,500
(c)
5,600
(c)
390
(c)
1,400
2,100
3,700
59
290
180
(c)
1
210
46
7.3
1,600
N.D.
2,000
'From AE-009
A-12
-------
TABLE A10
LO
(Private Communication)
Element or
Constituent
B
Cd
Cu
Pb
Mg
Mn
Hg
Ni
K
Na
Zn
Ag
As
Ca
pH
Sulfates
TDS
Hardness as
CaCOa
II
Make-up
Water
_
.01
.01
<.05
44
.01
<.0002
<.05
5.5
780
.01
-
<.02
-
9.6
310
2,500
328
III
Scrubber
Recycle
Water
64
.07
1.6
.4
236
2.2
.0002
2.2
28
2,080
2.3
.04
<.02
590
3.3
9,000
15,400
2,450
IV
Scrubber Recycle
Water After Lime
Treatment*
33
.07
.02
.14
-
.16
-
.11
-
,
.03
.02
-
930
9
3,700
-
V
PHS Drinking
Water
Standards
.01
1.
.05
.05
5.
.05
250
500
Ca(OH)g treatment test to precipitate metallic elements; added Ca(OH)3 at or near
stoichiometric; flocculated, settled, and filtered.
These data are from a pilot scrubber in which fly ash is used as an absorbent.
The coal contains less than 170 sulfur, and a 4070 reduction in S03 is achieved.
-------
TABLE All
(MO-028)
CONCENTRATIONS IN OPEN-AND CLOSED-SCRUBBER SYSTEMS
Closed-Loop Open-Loop
Mode Mode
Milligrams per Liter Milligrams per Liter
Calcium
Magnesium
Hardness (as CaC03)
Sulfite
Sulfate
Nitrate
Total Dissolved Solids
pH
1,600
1,150
7,100
5,400
6,500
1
13,000
5.0
1,100
*
**2,700
1,700
2,600
6
**7,000
5.3
Not determined, MgO content of limestone less than 1%.
*
Not determined, estimated minimum values.
These data are from a TVA pilot plant scrubber. The coal was
37o sulfur, the limestone had 1% MgO and was added at 150% of
s toichiometric.
A-14
-------
TABLE A12
(TE-113)
Parameter Concentration Parameter Concentration
(Closed Loop Operation) (Open Loop Operation)
(mg/1) (mg/1)
Calcium 1058 815
Magnesium 788 85
Hardness (as CaC03) 5890 2425
Sulfite 145
Sulfate 3461 1450
Chlorides 1720 675
Sodium and Potassium
Composite 105 59
Total Dissolved Solids 7277 4500
These data are from TVA's pilot plant at the Colbert Steam Plant.
The sampling point was the effluent from the clarifier.
A-15
-------
Iron (Total)
Cyanide
Zinc
Nickel
Copper
Chromium (Total)
Chromium (Hexavalent)
Cadmium
Phosphates (Total)
TABLE A13
(TE-113)
Material Concentrations, mg/A
Scrubber Wastes
Open-Loop
0.17
< 0.01
0.04
0.22
0.035
0.07
0.004
0.1
Closed-Loop
0.07
< 0.01
0.02
< 0.05
0.03
0.11
< 0.001
0.01
Mist
Eliminator
Wash Water
0.11
< 0.01
0.06
0.25
0.04
0.08
0.0052
0.05
Alabama
Guidelines
3.0
< 0.1
0.8
0.5
0.5
0.5
0.1
< 0.1
1.0
NOTE: These data are from TVA's pilot plant at the Colbert Steam Plant. The sampling
point was the effluent from the clarifier.
-------
TABLE A14
WET SIEVE ANALYSIS OF SCRUBBER SLUDGES
(SE-066)
Cumulative Wt.% Retained
Fly Ash.
Eastern Coal Lime Sludge
Western Coal Lime Sludge
Dry/Wet Process Sludge
Limestone Sludge
Smelter Sludge
+40M
0.2
+100M +200M
1.7
7.1
+325M
(44u)
15.1
7.5
+400M
(37u)
13.5
1.0
29.2
18.4
2.4
TABLE A15
SUB-SIEVE ANALYSIS OF FLY ASH AND AN
EASTERN COAL LIME SCRUBBER SLUDGE
(SE-066)
Cumulative
+50 Micron
+40 Micron
+30 Micron
+20 Micron
+17 Micron
+15 Micron
+10 Micron
+ 7 Micron
+ 5 Micron
+ 2 Micron
+ 1 Micron
Fly Ash
15
27
32
47
62
92
97
A-17
Eastern Coal Sludge
1
2
5
12
21
39
51
68
88
-------
TABLE A16
Dravo Sample Identification
Eastern Coal Lime scrubbing sludge from a
power plant burning Eastern
coal; ash present.
Western Coal Lime scrubbing sludge from a
power plant burning Western
coal; no ash present.
Dry Injected with Wet Sludge produced by limestone
Scrubbing injected into the boiler
followed by wet scrubbing;
ash present.
Limestone Scrubbing Limestone scrubbing sludge
from a pilot plant burning
oil; no ash.
Smelter Gas Lime scrubbing sludge from
molybdenum sulfide smelter;
no ash present.
A-18
-------
TABLE AI7
Elaine Indices for Untreated Scrubber Sludges
a
Sample (refer to Table AI6 Elaine Index (cm /g)
Fly Ash 2,640
Eastern coal sludge 12,500
Western coal sludge 27,500
Dry injected/wet scrubber sludge 14,100
Limestone scrubbed sludge 11,100
Smelter sludge 3,670
A-19
-------
TABLE A18
Settling Characteristics of Sludge
Sludge Source* Wt % Solids
Eastern Coal <30-45
Western Coal 21.5
Dry Injected with Wet Scrubbing 24
Limestone Scrubbing 39
Smelter Gas 37-40
Fly Ash 64
Vc
See Table Aib for sample identification.
A-20
-------
Run
No.
2
3
4
5
6
7
8A
8B
Feed
Drum 8
Drum 8
Drum 8
Drum 8
(Diluted)
Drum 8
(Diluted)
Drum 8
(Diluted)
Drum 13
Drum 13/14
(50% Each)
8A Discharge
TABLE A19
(from SE-066)
Centrifuge Tests - Pilot Plant Sludge
Bird 6" Continuous Centrifuge
4130 RPM - 1400 G Force
Feed
Z Solids
33.6%
33.6%
33.8%
29.8%
20.0%
19.5%
44.3%
42.3
Pool
Depth
Intermediate
Minimum
Maximum
Maximum
Maximum
Minimum
Minimum
Minimum
Feed
Rate
GPM*
3.4
3.4
3.4
3.3
1.1
3.3
3.3
3.3
%
Solids
47.8
48.1
47.3
50.1
50.2
50.2
58.8
55.0
Effluent
Solids
m/
/
4.6%
0.9%
3.4%
0.8%
0.2%
0.6%
9.3%
13.2%
57.4%
Minimum
59.5
9.2%
Drum 8: Si02 4%, CaO 437,, S 19.9%, S03 26%, S03 17.2%, C03 5.8%
Drum 13: Si03 31.8%, CaO 18.2%, total S 7.5%, S02 8.8%, S03 8.0%, C03 2.8%
* One gallon is equivalent to 3.785 liters.
-------
TABLE A20
(EL-030)
SUMMARY OF TVA SHORT-TERM CENTRIFUGE TESTS
Machine
Test Speed,
Series rpm
I 2000
HB 2000
> III 2000
i
N>
N>
IV 2500
V 2500
Centrifuge
Feed
Source
HF clarifier
bottoms
HF clarifier
bottoms
HF clarifier
bottoms
HF clarifier
bottoms
Scrubber bleed
(clarifier
bypassed)
Feed
Rates,
11-22
10-22
10-22
9-33
11-35
Wt. %
Solids
in Feed
15-22A
16-24A
19-29A
19-27A
10-14
Wi- 7
W U . /o
Moisture
in Cake
43-47
44-46
39-42
36-40
37-41
Wt. 7o
Solids in
Centrate
0.2-0
0.3-0
0.1-0
0.1-1
0.1-0
.6
.5
.5
.1
.6
^Increase the values by about 3 for pump seal water correction.
BTest Series II was a replicate of Test Series I.
C0ne gallon is equivalent to 3.785 liters.
-------
TABLE A21
COMPARISON OF DEWATERING TECHNIQUES FOR LIMESTONE SCRUBBER SLUDGES
Shawnee Samples
Western Power
1
UJ
Technique
Clarification
Settling
Centrifugation
Vacuum Filtration .
Bulk Density
(g/cm3)*
1
1
1
1
.14
.3
.4
.6
ฑ ฐ
ฑ ฐ
ฑ ฐ
+ 0
.02
.04
.04
.05
Plant Samples
% Solids
20
40
56
64
ฑ ฐ
ฑ ฐ
ฑ ฐ
H- 0
.5
.5
.5
.5
% Solids
~ 20
50
> 65
> 65
(freely
* The true density of Shawnee solids is reported to be 2.48 g/cm3.
-------
TABLE A22
(MI-084)
RESULTS OF TESTS OF SELECTED STABILIZED ROAD BASE MIXTURES
PREPARED AT DULLES AIRPORT TRANSPO 72 PROJECT
Falling Head
Permeabilities
Moisture Dry (cm/sec)
Content Density
(%) (pcf) 7 Days
19.5 98.8 2.4 x 10~6
19.4 98.1 N.D.*
20.0 98.3 2.9 x 10"6.
19.8 98.2 6.5 x 10"6
19.7 100.6 5.7 x 10"s
20.0 98.8 1.0 x 10"6
19.1 100.4 N.D.
VN'.D. - Not Determined
aOne pcf is equivalent to 16,028 g per cubic meters.
A-24
-------
TABLE A23
ATOMIC ABSORPTION TESTS FOR LEACHABLE IONS ON SELECTED
SPECIMENS SUBJECTED TO 48 HOUR SHAKING TEST
(from MI-084)
Total
I Dissolved
pH Solids
FEDERAL SPECIFICATIONS-MAX.3
Individual Solid Specimen
Dulles Cylinder (13 Days)
Dulles Cylinder (22 Days)
Poz-0-Tec* Test Road Core
Poz-0-Tec* Test Road
Cylinder
Poz-0-Pacฎ Cylinder
Fly Ash Concrete
Cinder Block
Clay Brick
Asphalt Roofing Shingle
Aggregate
Argillite
Dolomitic Limestone
Calcitic Limestone
Steel Slag Aggregate
Pumice
Fly Ash-Sludge Aggregate
Cement Mortar Balls
Mine Tailings
Loose Powdered Materials
Fly Ash
Portland Cement
Water Samples
Tap Water
Snow Sample from Pittsburgh
Water Supply (Peggs Creek)
10.6
9.5
9.5
6.7
9.2
9.3
10.7
8.2
7.3
7. 1
6.9
9.75
8.4
10.8
7.1
11.7
9.0
3.95
9.8
12.0
7.5
6.45
7.25
500
840
620
90
250
150
440
410
110
150
120
96
180
840
120
700
530
130
2900
3700
180
40
316
Sulfate
250
100
120
16
136
44
170
60
28
46
28
8
8
16
< 1
< 1
27
6
1500
200
36
< 1
Cl
250
8
12
14
16
26
46
6
12
22
22
18
-
28
10
16
8
2
8
20
76
6
"
Al
None
.38
.37
.03
.05
. 10
.22
.01
.03
.01
.07
.02
.02
.05
.06
.03
.04
.05
. 11
.05
.02
.06
Total
Iron
.3
.08
.08
.06
. 10
.25
.01
.04
. 10
. 12
.06
.36
1.8
. 15
2.2
.26
.17
. 15
.26
.44
< .01
.46
2.9
Mn
.05
. 18
.16
<.05
.10
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
<.05
Cu
1.0
.08
.08
< .01
.08
.08
.04
< .01
.01
< .01
.08
< .01
< .01
< .01
< .01
< .01
< .01
. 16
< .01
< .01
.08
< .01
.05
Zn Cd
5.0 .01
.02 <.01
< .01 <.01
< .01 <.01
< .01 <.01
< .01 <.01
< .01 <.01
< .01 <.01
< .01 <.01
< .01 <.01
< .01 <.01
.02 <.01
.04 <.01
.02 .01
.03 <.01
.02 <.01
.01 <.01
.02 <.01
.01 <.01
< .01 <.01
.05 <.01
< .01 <.01
.02 <.01
Cr"*" As Hg
.05 .01 .001
.02 .02 <.001
<.01 .02 <.001
<.01 <.01 <.001
<.01 .01 <.001
<.01 .01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
c.Ol <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
<.01 <.01 <.001
Pb
.05
.08
.09
<. 01
.01
.02
<.01
.02
<.01
<.01
<.01
.07
.03
.01
.06
.06
.03
.07
.06
.04
.04
.02
.02
Sn
None
. 10
.10
<. 01
<.01
<.01
<. 0 1
<. 01
<.01
<. 01
<.01
<. 5
<. 5
<.05
<.05
.5
<. 01
<.05
<.5
<.5
^.01
^. 0 1
<.01
With the exception of pH, all values are reported in parts per million.
Public Health Service Drinking Water Standards.
-------
TABLE A24
PRELIMINARY LEACHING STUDY
OF LIMESTONE SCRUBBING SLUDGE-
LAB LEACHATE OF 2/28/73 FIELD CHEMFIX PRODUCT^
Inches of Leachate Water'
Constituent
Aluminum (Al)
Cadmium (Cd)
Tot. Chromium (Cr)
Iron (Fe)
Nickel (Ni)
Phenol
Cyanide (CN~)
Zinc (Zn)
Copper (Cu)
Lead (Pb)
Raw Sludge
1.2
1.1
0.8
760
11
<0.25
<0.10
29
9.0
3.7
0-25"
<0.10
<0.10
<0.10
<0.10
<0.10
<0.10
<0.10
<0.10
<0.25
<0.25
25-50"
<0.10
<0.10
<0.10
<0.10
<0.10
<0. 10
<0.10
<0.10
<0.10
<0.10
50-75"
<0.10
<0.10
<0.10
O.10
<0.10
<0.10
<0.10
<0.10
<0.10
<0.10
75-100"
<0.10
<0.10
<0.10
O.10
<0.10
<0.10
<0. 10
<0.10
<0.10
<0.10
+
o
All Results in ppm
Composite Material From Three (3) Disposal Cells
Each 25" of Leachate Water Represents Approximately 800cc
of Water
< = Less Than
A-26
-------
TABLE A25
I
r-o
Dulles Cylinder (13 Days)
Dulles Cylinder (23 Days)
Sulfite Beam
ATOMIC
Total
Dissolved
pH* Solids
7.0 100
6.9 96
7.2 85
ABSORPTION TESTS MADE ON SURFACE RUNOFF OF A
STABILIZED FLY ASH-SLUDGE MIXTURE
(from MI-084)
Total ,
Sulfate Cl Al Iron Mn Cu Zn Cd Cr As Hg Pb Sn
26 12 .10 .22 <.05 <.01 <.01 <.01 <.01 <.01 <.001 <.01 <.01
32 18 .15 .06 <.05 <.01 <.01 <.01 <.01 <.01 <.001 <.01 <.01
8 18 .13 .06 .60 .12 <.01 <.01 <.01 <.01 <.001 .03 <.01
*With the exception of pH, all values are reported in parts per million.
-------
TABLE A26
Pozzolanic Strength Determinations (kg/ms)
Molding Time
5 days
1 month
Shawnee Sample
18,000 (26 psi)
18,000 (26 psi)
Western Power Plant
Sample
119,000 (freshly
demolded damp) (170 psi)
70,000 (dried over-
night) (100 psi)
A-28
-------
TABLE A27
RESULTS OF TESTS OF SELECTED STABILIZED ROAD
BASE MIXTURES PREPARED AT DULLES
AIRPORT TRANSPO '72 PROJECT
(from MI-084)
Moisture Dry* Hon'?
Content Density at 100 F
(pcf) 2 Days 14 Days 28 Days
19.5 98.8 301 732 881
19.4 98.1 267 586 662
20.0 98.3 369 630 889
19.8 98.2 196 458 490
19.7 100.6 333 772 861
20.0 98.8 290 761 789
19.1 100.4 200 868 1091
10ne pcf is equivalent to 16,028 g/m3
P0ne psi is equivalent to 703 kg/m3
A-29
-------
TABLE A28
u>
o
RESULTS OF FIELD TESTS SHOWING COMPARISON
OF POZ-0-PAC" AND POZ-0-TEC" FORMULATIONS
(from MI-084)
4 n 5Compressive Strength 5 Strength of Cores
Densit at LOOฐF (Psi) from Roadl (Psi)
Description (pcf)
Standard
Fly Ash-S
Fly Ash-S
Fly Ash Mix
ludge Blend
ludge Blend
(Poz-0-PacR) 121.2
A (Poz-0-Tec*)3 121.4
B (Poz-0-Tec*)3 120.8
2 Days 7 Days
66 770
348 729
318 746
4 Weeks 6 Weeks
NCPS NCP
NCP 1034
756 1089
1 Average temperature during curing period was 10ฐC.
SNCP - No core possible due to insufficient strength.
3Blends A and B not identified.
40ne pcf is equivalent to 16,028 g/m3
8 One psi is equivalent to 703 kg/ms.
-------
APPENDIX B
LEACHING TESTS FROM SLUDGE DEPOSITS
PERFORMED BY STEAG-BISCHOFF
AT LUNEN, GERMANY
August, 1973
-------
1.0 INTRODUCTION
This paper describes the leaching tests from sludge
deposits performed by Steag and Bischoff at Lllnen, Germany.
Steag-Bischoff are operating a lime based wet scrubber which
treats a slip stream of the Kellermann steam plant at Lunen.
The information presented herein was obtained from
Dr. Klaus Goldschmidt (Steag) and Dr. Kramer (Bischoff) during
a visit at Steag in Essen. The report presents pilot tests per-
formed during 1969 and field tests that started in 1972. No
trace element analyses were performed. Of main interest was the
build-up of sulfate, sulfite, total solids, the change of the
pH and BOD and COD of the groundwater.
2.0 DESCRIPTION OF TESTS
The leaching experiments were done during the end of
April, 1969, through August, 1969, on a pilot scale and from
1972 through the present in unlined pits close to the Kellermann
steam plant at Lunen. Trace elements were of no concern during
the two test series. The components of interest were sulfate,
sulfite, cyanide, BOD, COD, pH, total solids and weight after
ignition.
2.1 Pilot Experiments
The results of these experiments were presented by
Dr. Klaus Goldschmidt at the Lime/Limestone Wet Scrubbing Symposium,
March 16-20, 1970 in Pensacola, Florida. The goal of the tests
was to find the effect of a permeable and impermeable ground soil
and the effect of different thicknesses of the deposited slurry.
-------
2.1.1 Description of the Pilot Setup
The setup for the pilot experiments (April through
August, 1969) consisted of three tanks (see diagram in Appendix
C). All tanks were of cylindrical shape. The diameter was 1 m
and the height 0.5 m for tanks #1 and #2 and 1 m for tank #3.
The sludge was filled upon gravel which rested on a sieve.
Tanks #1 and #3 were continuously drained. Tank #2 was normally
closed. Samples from tank #2 were taken once a week.
2.1.2 Results
The analysis of the sludge showed 14% CaO, 11%
and 2% S03 on a dry basis. Total water content of the wet
sludge was 50%. (Consider the high degree of oxidation!) The
total rainfall per mฐ during the test period was about 240 liters
The leachate was analyzed for calcium, sulfate, sulfite and pH
(see Tables 1, 2, and 3 in Appendix C on pages 3 and 4 of the
analytical results). The main conclusions drawn from these
experiments were the following.
1. 20% of the rainwater passed through
the deposit. 80% was lost due to
evaporation during dry periods.
2. The amount of the total dissolved
solids decreased continuously.
3. The total amount of leachate was
greater at tank #1 then at tank #3.
Therefore, it may be better to deposit
the sludge in thick layers.
B-2
-------
4. The total amount of the dissolved solids
from tank #2 was highest and nearly con-
stant over the test period. The sulfate
content evidently did not reach the
saturation point.
2.2 Field Tests
Bischoff is presently treating a'slip stream at the
Kellermann unit which corresponds to a 35 MW boiler. The sludge
of the lime based scrubber is stored in ponds. The change in
the groundwater composition is monitored by analysis of water
samples taken from wells drilled around the storage site.
2.2.1 Description of the Pond Area
Figure I shows the location of the individual sludge
ponds at the test site at Lunen. The scale is given on the
diagram. The individual ponds show a dimension of about 40 x 40
mp. The ponds were filled with sludge starting with pond #1 at
the right of Figure I. The figures in the drawing show the
elevation of the corresponding points in meters above sea level.
The cross-section indicated for pond #2 is schematically shown
in Figure II.
The depth of the ponds is approximately 3.5 meters.
The sludge is filled into the ponds up to 40-60 cm below the
top of the dam. The ponds are unlined. The top soil consists
of sand and gravel, then follows a silt layer. The groundwater
table stands approximately 1 to 1.5 meters below the bottom of
the ponds. It reaches either the silt formation or the sand-
B-3
-------
(Well I)
-------
40 meters
Gravel
Silt
Ui
Sludge Level
40 to 60 cm below /
top of dam / ' c "
=Top of Dam
c ~ 51.6 m Above Sea Level
c" Bottom of Pond
~ 48.2 m Above Sea Level
c v -, A - - r 0 ..,
< <- *- c c. - r /N r , c o t . r - (_ . c
.^ uo f Pf0 f| t c^c ^ t. c c' gravel c c c^i.-'
V C o 0 6 c> ^ r i ซ c o ฐ ' '" e. -i. c. _. '^
-' ;.-1-1.5 meters.'.-.;:....-'.. -."*:."
*':'"ป '.' ''-"I-.-':':-':: -:- silt:.:. '.'--':.:- Ground Water Level
FIGURE II - SCHEMATIC CROSS SECTION OF POND NO. II
-------
gravel formation. Thus, the pond is surrounded by very permeable
material.
2.2.2 Slurry Composition
Appendix D shows the sludge analysis from August, 1972
Three interesting points are:
1. The sludge was wet chemically analyzed
for manganese. Manganese (oxidation
catalyst) could not be found.
2. The degree of sulfite oxidation was
only about 16%.
3. The high pH value of 9.8 (1 g sludge
. dissolved in 100 ml water) indicates
free CaO in the sludge.
The low degree of sulfite oxidation is in contrast to the sludge
found during the pilot experiments (11% SO^ and 2% SO^).
2.2.3 Description of Wells
The locations of the wells are shown in Figure I.
Until recently only wells No. I, II and III were monitored for
groundwater pollution. The Water Quality Board insisted on the
installation of two new wells, No. IV and No. V, which were
drilled in March, 1973. The profile of the soil is shown in
Figure III. The main difference between these two wells in
comparison to wells No. I, II and III is the elevation of the
B-6
-------
Formation Characterizatiov
i?.CO
57.00
SO. CO
43. CO
4S.C3
4? 13
45.00
4S.CO
43. CO
17 fin
ฅ
o
-------
groundwater table. Here it reaches sand formation and is about
one to two meters higher than that of wells No. I, II and III.
The exact height is shown in Table I.
2.2.4 Analytical Results
The analytical results from October, 1972 through
April, 1973 are shown in Table II for wells No. I, II and III.
The values reported in Table II are fairly constant and show
no anomalies in comparison to the groundwater from other locations
around Lunen. Results from wells No. IV and No. V are presently
not yet available.
2.2.5 Conclusions
No conclusions can be drawn so far from the data col-
lected; the main reason being that the groundwater movement was
not considered at all. The average rainfall needs to be put in
correlation to the groundwater movement from wells No. IV and
No. V to wells No. I, II and III. If the groundwater movement
is much greater than the average rainfall, one would not expect
much of a solids build-up at all in wells No. I, II and III.
B-8
-------
TABLE I
HEIGHT OF GROUNDWATER TABLE FOR WELLS NO. I - V
STEAG
Well 1
Well 2
Well 3
Well 4
Well 5
Measurement of Groundwater Level
Date; 30-6-73
Measured by:
Elevation of upper well casing
Distance to groundwater
Groundwater level
Elevation of upper well casing
Distance to groundwater
Sroundwater level
Elevation of upper well casing
Distance to groundwater
Groundwater level
Elevation of upper well casing
Distance to groundwater
Groundwater level
Elevation of upper well casing
Distance to groundwater
Groundwater level
5/076.54
48,90 m
2,94 m
45,96 m
48,38 m
1,40 m.
46,98 m
48,68 m
1,36 m
47,32 m
52,30 m
"3,40 m
48,90 m
'
52,52 m
3,68 m
48,84 m
B-9
-------
TABLE II
WATER ANALYSES FOR WELLS NO. I. II. AND III
pH
Dissolved
Matter:
Total (mg/1)
Loss on
ignition
(mg/1)
Potassium
Permanganate
Consumption
(mg/1)
BOD (mg/1)
Sulfate (SO,")
(mg/1) U
Sulfite (GO")
(mg/1) J
Cyanide (CN1)
(mg/1)
Well 1
October 72
7,3
759
U2U
18
7
209
^ 1
<-0,1
December 72
7,U
695
UUU
18
5
2U1
^ 1
<:o,i
Well 2
October 72
7,1
609
275
17
2
217
<^ 1
<:0,1
December 72
7,2
686
322
18
3
278
^ 1
^0,1
Well 3
October 72
7,3
1273
530
15
2
2^6
^i 1
-------
TABLE II (Cont.)
pH
Dissolved
Matter:
Total j[mg/l)
Loss on
ignition
(me/ll
Potassium
Permanganate
Consumption
(mg/1)
BOD (mg/1)
Sulfate (SO,")
(mg/1) U
Sulfite (SO'-J)
(mg/1)
Cyanide (CN1)
(mg/1)
Well 1
Jan. 73
7,2
752
526
11*
1*
21*1
<. 1
^0,1
Febr. 73
7,9
928
25
6.
28k
<1
^0,1
Well 2
Jan. 73
7,3
731
1+69
16
3
197
^1
^0,1
Febr. 73
7,8
778
13
3
223
*C1
1
9^0
568
12
3
211*
^ 1
^0,1
Febr. 73
7,3
-
11*
3
221
<1
-------
TABLE II (Cont.)
PH
Dissolved
Matter:
Total (tng/1)
Loss on
ignition
(mg/1)
Potassium
Permanganate
Consumption
(mg/1)
BOD (mg/1)
Sulfate (SO?)
mg/1
Sulfite (SO")
IMC/1 3
Cyanide (CN1)
mg/1
Well 1
March 73
7,3x
1230
990
5U
17
259
< 1
-------
APPENDIX C
DEPOSIT-TESTS WITH LIME-FLY ASH-SLURRY OF THE
WET SCRUBBER PILOT PLANT SYSTEM "BISCHOFF"
Prepared by:
Dr.-Ing. K. Goldschmidt
Steag
-------
\) 0 V C' VI
S T E A G Essen, den 11. 3. 1970
5/076.54
5/129
Deposit-tests with lime-fly ash-slurry of the wet scrubber
pilot plant system "Bischoff"
by Dr.-Ing. K. Goldschmidt
presented at the lime/limestone scrubber symposium,
March 16 - 20, 1970, Pensacola (Florida)
The strict regulations in West Germany, specially in the Ruhr-
district, against water pollution forbid the deposition of flyash
or other wellknown materials without the licence of the district
water board.
It is therefore quite more difficult to receive the allowance
depositing a new product like the slurry of a wet scrubber plant
for desulphurizing and dust off waste gases of a power plant.
If you want to order such a prototype or fullscale plant the
question of the possibility to deposit the slurry must be settled.
Therefore a main point of our tests with the prototype scrubber
plant, which is under construction, will be to control the influence
of the deposited lime-flyash-slurry on the ground-water.
Our considered deposit area is a ground dip in a distance of about
500 m from the boiler- and scrubber-plant, surrounded by a street
and a dam. Between the earth bank and the creek we intend to install
three ground-water wells to control the quality of the ground-water.
The layout of these wells is directed by the district water board
and this authority will analyse the ground-water by itself once
per month.
-------
If the concentration of foreign substances in the ground-water
surpasses the limit, we have the order to stop the deposit and
eventually to remove the deposited slurry.
The start with ground-water analysis will be in May to find the
zero conditions; the beginning of slurry deposit we assume during
November this year.
To overlook what may happen, tentatively we set up three tanks,
shown in picture 1. each with a cross-section area of 1 sqm.
The bottoms of the tanks are conical with a drain tube in the middle
Inside the tank, above the drain tube, are located a sieve, a fill
of gravel and grit and the slurry.
The filling height of the slurry is 0.5 m in the tanks no. 1 and 2
and 1.0 m in the tank no. 3.
The drain tubes of the tanks no. 1 and 3 are permanently opened, so
the slurry is always drained. The drain-water is sampled in a bottle
separate for each tank. The drain tube of the tank no. 2 is normally
closed and only opened during the water-sampling one time per week.
Thereby the tanks no. 1 and 3 represent the situation of slurry
deposited with different bulk height on a region with water permeable
ground, whilst the tank no. 2 demonstrates the condition of slurry
deposit on a region with an impermeable ground to water.
The tanks were filled with slurry of the wet scrubber pilot plant
system "Bischoff" at the end of April, 1969. The slurry had a water
contents of about 50 % per weight. In relation to the dry substance
C-2
-------
of the slurry we found about
14 % of CaO
11 % of S04" and
2 % of S03ป
After opening the valves in the drain tubes of the tanks no. 1
and 3, 10 % of the water contents of the slurry drained immediately
(30 litres respectively 60 litres).
At the end of August, 1969, the total amount of rain per sqm ran
up to 240 litre's. 20 % of this amount of precipitate passed through
the slurry and arrived at the bottles at the lower end of the tanks
no. 1 und 3. 80 % of the rainwater was storaged in the slurry and
recycled to the atmosphere by surface evaporation during dry weather
periods.
During these four months the concentrations of the soluted sub-
stances in the drain water decreased continuously. The max.
amounts at the beginning and the minimum at the end of August are
shown in the following table:
Table 1; Analysis of drain water from tank no. 1
(concentrations in mg/1)
CaO
S04"
so3ป
PH
max.
1390
185
27
12
min.
104
5,3
1,8
7,6
The analysis of the drain water from tank no. 3 produced the same
concentrations.
C-3
-------
The total amount of the substances washed out during this period
shows table 20 In relation to the basic concentration of these
components in the slurry the washing out amounts to
2 o/oo of the total contents of CaO) ,. , . . .
or tank no* 1 and
0,3 o/oo of the total contents of S )
1 o/oo of the total contents of CaO) _ . . ซ
of tank noe 3
0,1 o/oo of the total contents of S >
In regard to these results it may be better to deposit the slurry
in a thick layer than in a thin one.
Table 2; Total quantity of washing out by rain (April - August 1969)
tank 1 tank 3
CaO
so4ป
SO ป
77 g
8 g
1,9 g
97 g
9,5 g
1,6 g
Last not least the concentrations of the soluted substances in the
water samples of tank no. 2 show more a constant than a decreasing
tendency, see tableT 3e The amount of these concentrations
gave no occasion to be concerned.
Table 3: Analysis of drain water from tank no. 2
(concentrations in mg/1)
CaO
so4ป
so 3"
PH
max.
583
372
26
10,7
mln.
448
180
11,6
8,3
C-4
-------
Schlamm
(Sludge)
Kl'eS (Gravel)
Sieb (Sieve)
^^\^^v^^^/^/^/^/^^^
SET-UP FOR LEACHING EXPERIMENTS PERFORMED DURING
APRIL THROUGH AUGUST 1969
STEAG
1969
Behdlter fur Schlammuntersuchungen
von der Bischoff-Versuchsanlage
V
10-2780
-------
APPENDIX D
-------
TE< HNICAL LtTERAiURE FilJE
PR , ii NT ~L i 'i:l * 'tiJ'-o ' NAPCA
fia ,nto
9 30 ฃ 8 ._ Ruhrkchle
t ^L__ ปซ.ป- ซ* *ซป*ป<ฃ-
------ 1 ...... -,
Aktiengesellschaft
Ruhrkohle Aktiengesellschaft -4300 Essen - P. 0. Box 5
S T E A G
Aktiengesellschaft
Development and New Facilities Department
ATTN: Dr. Goldschmidt
Your File No.: Your Letter Dated: Department/ leisphone (Direct Date:
Our File No. : Dial) :
5/076.54 8/15/72 UP2/Dr.DuA^ 177-3969 9/25/72
Gs/Schu
Subject: BISCHOFF-PLANT IN 'LJhEN; SLUDGE ANALYSIS
Dear Dr. Goldschmidt:
You sent us a sample of the dried residue of the washing liquid used to
desulfurize a flue gas component current in Lllnen.
Due to the lime employed in the Llinen plant, the aqueous extract of your
sample material shows an alkaline reaction. One gram of sample in 100 ml
water shows a pH value of 9.8.
At 500 ฐC, the loss on ignition is 1.9%. At 800 ฐC it is 3.5%, while it
equals 11.4% at 1100 ฐC. During the burning of the sample, we determined 2. OK
organic carbon. In addition, we noted the development of 2.6.5% water of com-
bustion, which is undoubtedly silicate-bonded water present i.i the hydroxide
form.
A majority of the sulfur is present in the form of sulfit.e. Surprisin0ly,
no carbonates were determined. Wet chemical analyses also did not detect an"
manganese.
Translated for Air Pollution Technical Information Center from the German
-------
sample showed the following composition:
41.3% SiO
22.0% A10
0.9%
7.4% Fe203
9.5% CaO
2.0% MgO
0.8% Na20
4.2% K20
5.5% S02
0.8% SO
0.02% P205
0.07% F
0.15% Cl
2.65% EJO (water of combustion)
2.0% C
Very Sincerely,
RUHRKOHLE AKTIENGESELLSCHAFT
(2 signatures illegible)
D-2
-------
NUMERICAL TABLE 5
u>
Sample
1/1
1/2
1/3
1/4
1/5
1/6
1/6
RESULTS
pH Value
7,4
2,8
7,5
7,7
7,4
9,1
vr 2+
Mg
22 mg/1
OF THE CHEMICAL
LIQUIDS AND
Ca2+
zLL.
1,64
1,72
1,95
0,19
1,65
mg/1
98
Na+
0,58 g/1
ANALYSES OF THE
THE FRESH WATER
Cl"
3,30
3,23
3,30
0,67
2,32
0,76
K+
18 mg/1
SUPERNATANT
S042"
g/1
1,35
1,46
1,26
mg/1
254
798
174
Total Solids
1,7 g/1
so2
mg/1
10
14
16
17
17
21
-------
Rohacs
Reing.as O (W)
ซ... tx. ?_ it
I
Tropfen-
absch eider
Waschturm (c
Eincffcher KalkmHchansetzbehalter
STEAG
Bischoff-Anlage Lunen
mit Kalkmilch-Dosierstation
V10-293,
STEAG Bischoff-Plant in LUnen With Lime Milk Dosing Station V10-2985
LEGEND: 1 = drop separator 2 = raw gas 3 = lime silo 4 = lime
milk application container 5 = thickener 6 = washing tower
7 * deposit 8 ป pure gas to hearth
D-4
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-74-016
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Evaluation of Lime/Limestone Sludge Disposal
Options
5. REPORT DATE
19 November 1973
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
NA
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
8500 Shoal Creek Boulevard
P. 0. Box 9948
Austin, Texas 78766
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
No. 68-02-0046
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
27711
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The report presents results of a study of technology for disposal of
sludge created by lime and limestone flue gas desulfurization systems at
steam-electric power plants. Effects of operating variables on the volume
of sludge produced are explained with emphasis on plant situations in the
State of Ohio. Properties of sludges are reviewed, including settling
characteristics, rewatering tendency, strength, particle size, bulk density,
and chemical composition. The report considers potential environmental
hazards of sludge disposal, namely contamination of water and ground water
supplies. Methods of avoiding these hazards are presented and evaluated.
Technologies for solidifying (fixating) sludge are discussed and evaluated
along with the current status of full-scale projects. The report concludes
that any large degree of commercial utilization is unlikely. Based on
available data, there are no insurmountable problems in disposing of sludge
in an environmentally acceptable manner. While economics of disposal are
not well defined, studies are underway that should provide better cost
information and other valuable information.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Chemical Reaction
Desulfurization
Sulfur Dioxide
Limestone
Coal
Sulfur
Sludge Disposal
Calcium Oxides
Combustion Products
Flue Gases
Air Pollution Control
Boilers
Electric Power Plants
13B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS {ThisReport)'
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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