United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-025 July 1984
SERA Project Summary
Research Planning Task Group
Study—Thermal Destruction
Final Report
Michael J. Binder and Roger A. Strehlow
The objectives of this study were to
determine the state-of-the-art for
thermal destruction of industrial toxic
waste, and to identify and prioritize
research needs in this area. The study
consisted of a literature search, discus-
sions with EPA personnel and other
authorities in the area of thermal
destruction, and attendance at a national
meeting on the subject. The state-of-
the-art of thermal destruction of indus-
trial toxic waste was determined, and
research needs identified.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory. Cincinnati. OH.
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The modern technological society
produces large quantities of industrial
wastes Some typical industrial classifi-
cations and types of wastes generated
are listed in Table 1. Typical industrial
waste production rates are listed in Table
2 A sizable fraction of this waste is
considered hazardous, i.e , an estimated
57 million metric tons in 1980.
Toxic chemical wastes in the environ-
ment represent one of today's most
serious environmental problems. The
ever increasing quantities of these toxic
residues have overburdened the receiving
environment (air, water, and land) Lack
of adequate process waste disposal
facilities is aggravating environmental
problems, forcing some industries to
close or restrict certain operations.
Although the need for proper disposal
and control of toxic wastes is widely
recognized, in many instances effective
control techniques available have not
been adequately applied. Land disposal
and ocean dumping of toxic substances
have contaminated and interfered with
the biological systems of streams, rivers,
lakes, and oceans.
Alternative methods for disposal of
industrial toxic wastes include a number
of thermal destruction techniques in
which the pollutant is oxidized or pyrolized
at a high temperature to produce benign
products. As a hazardous waste disposal
technology, thermal destruction tech-
niques offer several advantages:
• Toxic components of hazardous
wastes can be converted to harmless
compounds or, at least, to less
harmful compounds.
• Ultimate disposal of hazardous
wastes eliminates the possibility of
problems resurfacing in the future.
• The volume of hazardous waste is
greatly reduced.
• Heat recovery makes it possible to
recover some of the energy produced
by the combustion process.
The Congress of the United States via
Section 3004 of Subtitle C of the
Resource Conservation and Recovery Act
(RCRA) of 1976 (PL94-580) mandated
that the Administrator of the U.S.
Environmental Protection Agency pro-
mulgate regulations establishing per-
formance standards applicable to owners
and operators of hazardous waste treat-
ment, storage, and disposal facilities
necessary to protect human health and
the environment. These standards are to
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Table 1. Combustible Wastes Generated by Various Industries
Industry Wastes
Ordnance and accessories
Food and kindred products
Textile mill products
Lumber and wood products
Apparel and finished products
Furniture (wood)
Furniture (metal)
Paper and allied products
Printing and Publishing
Chemicals
Petroleum
Rubber and miscellaneous
plastics
Leather
Fabricated metal products
Machinery (except electrical)
Electrical
Transportation
Professional, scientific
controlling instruments
Miscellaneous manufacturing
Plastics, rubber, paper, wood, cloth, and chemical residues
Meats, fats, oils, offal, vegetables, fruits, nuts and shells,
and cereals
Cloth and fiber residues
Scrap wood, shavings, sawdust, plastics, fibers, glues, sealers.
paints, and solvents
Cloth, fibers, plastics, and rubber
Same as lumber plus cloth and padding residues
Plastics, resins, rubber, adhesives, cloth, and paper
Paper, fiber residues, chemicals, coatings, filler, inks, and glues
Paper, newsprint, cardboard, chemicals, cloth, inks, and glues
Organic chemicals, plastics, rubber, oils, paints, solvents, and
pigments
Asphalt, tars, felts, paper, cloth, and fiber
Scrap rubber and plastics, curing compounds
and dyes
Scrap leather, thread, dyes, oils, and processing and curring
compounds
Coatings, solvents, lubricants, and pickling liquors
Wood, plastics, rubber, cloth, paints, solvents, and petroleum
products
Rubber, plastics, resins, fibers, and cloth residues
Fiber, wood, rubber, plastics, cloth, paints, solvents, and
petroleum products
Plastics, resins, wood, rubber, and fibers
Plastics, resins, leather, rubber, cloth, straw, adhesives, paints,
and solvents
Table2. Industrial Solid-Waste Production Rates
Industry
Waste Production Rate
(tons/employee/year}
Meat processing
Cannery
Frozen foods
Preserved foods
Food processing
Textile-mill products
Apparel
Sawmills and planning mills
Wood products
Furniture
Paper and a/lied products
Printing and publishing
Basic chemicals
Chemical and allied products
Petroleum.
Rubber and plastic
Leather
Stone, clay
Primary metals
Fabricated metals
Nonelectrical machinery
Electrical machinery
Transportation equipment
Professional and scientific
instruments
Miscellaneous manufacturing
6.2
55.6
18.3
12.9
5.8
0.26
0.31
162.0
10.3
0.52
2.00
0.49
10.00
0.63
14.8
2.6
0.17
2.4
24.
1.7
2.6
7.7
1.3
0.12
0.14
include, but need not be limited to,
requirements concerned with (1) operat-
ing methods, techniques, and practices;
(2) location, design, and construction; and
(3) contingency plans for effective action
to minimize unanticipated damage that
might occur at these facilities. As applied
to the incineration of toxic industrial
wastes, present regulations require
incinerators to achieve a destruction and
removal efficiency (ORE) of 99.99 percent
for each designated principal organic
hazardous constituent (POHC) in the
waste feed. Destruction and removal
efficiency for an incinerator/air pollution
control system is defined by the following
formula:
ORE =W,n- Wo
t(inn)
W,n
where
ORE = destruction and removal efficien-
cy, percent;
W,n=mass feed rate of the principal
organic hazardous constituent(s)
to the incinerator;
Woui= mass emission rate of the principal
organic hazardous constituent(s)
to the atmosphere (as measured in
the stack prior to discharge).
Thus, DRE calculations are based on
the combined efficiences of destruction
in the incinerator and removal from the
gas stream in the air pollution control
system. Specification of the principal
organic hazardous constituents in a
waste is subject to best engineering
judgment, considering the toxicity,
thermal stability, and quantity of each
organic waste constituent. POHC's are
identified on the incinerator permit
application. To allow for the formation of
any hazardous combustion byproducts,
the EPA has proposed an amendment
that the amount of the byproducts must
not exceed 0.01 percent of the total mass
feedrate.
For fundamental studies of thermal
oxidation processes, a thermal oxidation
destruction efficiency (DE) is of more use
than the DRE. The DE is defined in a
fashion similar to the DRE with the
exception that Wout is defined to be the
mass emission rate of the POHC's out of
the incinerator combustion stack. Thus,
the DE is a thermal oxidation destruction
efficiency only and does not include
removal by any air pollution control
system as does the DRE used in the EPA
incinerator regulations.
A great deal of effort is currently being
focused on the subject of thermal
destruction of toxic industrial wastes. A
number of studies, reviews, conferences,
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and courses dedicated to this topic have
appeared recently. A listing of these
recent efforts is given in the Appendix to
the final report. The specific objectives of
this task group study were to examine the
literature on thermal destruction pro-
cesses in depth in order to determine how
well the fundamentals of the processes
are understood and to prioritize research
needs in the areas of thermal destruction
of industrial toxic wastes.
Classification and
Characterization of Hazardous
Wastes Potentially Treatable by
Thermal Destruction
The term "hazardous wastes" covers a
wide range of chemicals. Heavy metals,
pesticide residues, organic solvents,
acids, inorganic salts, explosives—all of
these may fall under the heading of
"hazardous." Each has its own chemical
characteristics; each must be handled
differently. Analysis and characterization
of wastes is vitally important both from
the standpoint of determining the best
treatment or disposal strategy and of
preventing dangerous reactions which
could result from mixing incompatible
materials. The most basic chemical waste
classification is based on elemental
composition. For those wastes potentially
treatable by any of the various thermal
destruction techniques, four classifica-
tions are used. These are listed in Table 3.
Difficulty in treating the waste by thermal
destruction techniques increases as one
T»ble3. Chemical Waste Classifications
Waste Elemental
Class Composition
progresses from Waste Class 1 to Waste
Class 4.
There are two basic types of hazardous
wastes which are organic, or partially
organic, in nature and which can be
incinerated:
(1) Combustible wastes, which will
sustain combustion without the
use of auxiliary fuel; and
(2) Noncombustible wastes, which will
not sustain combustion without
auxiliary fuel.
Noncombustible types usually contain
significant amounts of water or other
inert compounds. Either of these two
types of wastes may contain small or
large amounts of inorganic salts, halogen
compounds, nitrogen compounds, sulfur
compounds, or phosphorus compounds.
The final report fully describes the
technology for thermal destruction of all
compounds of hazardous wastes.
Thermal Destruction Devices
A survey of commercial incinerator
installations reported in the literature,
showed that the methods of incineration
most commonly used are liquid injection
incineration, fluidized bed incineration,
multiple hearth incineration, rotary kiln
incineration, catalytic combustion, molten
salt combustion, pyrolysis/starved-air
combustion, and wet air oxidation. An
excellent review of the state-of-the-art of
these incineration processes may be
found in a recent publication produced by
the Noyes Data Corporation (1). A
Example
1
2
3
4
C.H and/or
C.H.O
C.H.N and/or
C,H,N,0
C.H.Ct and/or
C.H.CI.O
C.H.N.Cl and/or
C.H.CI.N.O
C.H.S and/or
C.H.S.O
C.H.F and/or
C.H.F.O
C.H.Br and/or
C.H.Br.O
C.H.P and/or
C.H.P.O
C.H.Si and/or
C.H.Si.O
C.H.Na and/or
C.H.Na.O
Tars from production of styrene
Off-specification phenol
Solid residue from manufacture
of aromatic amines
TDI manufacture reactor tar bottoms
Vinyl chloride monomer manufacturing wastes
Phenolic tar from 2, 4-D manufacture
Nitrochlorobenzene manufacturing wastes
Petroleum refining sour waste
Fluorinated herbicide wastes
Ethylene bromide manufacturing wastes
Malathion
Tetraethyl orthosilicate wastes
Refinery spent caustic
technical resource document entitled
Engineering Handbook for Hazardous
Waste Incineration, was prepared for the
U.S. Environmental Protection Agency by
Monsanto Research Corporation (2). The
latter document provides technical
information for use in the design and
performance evaluation of hazardous
waste incineration facilities. Topics
covered include a state-of-the-art survey
of incineration and air pollution control
design evaluations, overall incineration
facility considerations, capital and op-
erating costs, and trial burn summary data.
Because rotary kiln and liquid injection
are at present the most highly developed
and most commonly used incinerators for
hazardous waste incineration, primary
emphasis has been given in the handbook
to these two incineration processes. The
final report of the current study presents
a brief description of the various com-
monly used hazardous waste incineration
devices. The interested reader is urged to
consult the above two references for
more detailed information.
Commercial Scale Hazardous
Waste Thermal Destruction
Tests
In order to provide a broad assessment
of the capabilities of commercially
available thermal destruction units, the
U.S. Environmental Protection Agency
awarded a two-phase contract to the
team of TRW Defense and Space Systems
Group and Arthur D. Little, Inc. (3). The
first phase was the development of an
operational plan for selecting chemical
wastes and thermal destruction units that
could be tested for their capabilities to
destroy chemical wastes containing
hazardous components. This encom-
passed the following tasks:
(1) Classification, identification, priori-
tization and selection of wastes
which provided a reasonable cross-
section of currently generated
industrial wastes with particular
attention to quantities and hazard-
ous properties of the waste.
(2) Selection of units chosen to be
representative of the most advanced
engineering methods of thermal
destruction.
(3) Assignment of top priority wastes
to specific units on the basis that
the wastes could be expected to be
destroyed effectively, the transport-
ation and handling of the wastes
would be feasible, and all units
would be tested with at least one
priority waste.
The second phase of the project used the
results from the first phase and encom-
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passed the following tasks:
(1) Development of a testing and
analytical protocol and outfitting a
mobile laboratory for field testing.
(2) Obtaining wastes from generating
sources and arrangingforshipment
to the thermal destruction units.
(3) Contracting with the operators of
thermal destruction facilities for
the tests.
(4) Preparing a detailed test and
analytical program for each facility
and carrying out the program at the
thermal destruction facility.
(5) Analyzing samples in the mobile
laboratory and interpreting data.
(6) Preparing a report on each unit
tested
Two criteria were developed with
which to prioritize candidate waste
materials These were:
(1) Hazard Rating (rmax) - A given
compound or waste may have a
number of properties for which it is
considered hazardous (f lammabihty,
oral toxicity, inhalation toxicity,
carcmogenicity, etc) For each
hazardous property, four ratings
were established with assigned
values of 1, 10, 100, 1,000—the
higher the rating, the more hazard-
ous the waste. In assigning a
hazard rating to an individual waste
with several hazardous properties,
the highest hazard rating was used
irrespective of which hazardous
property the rating represented
(2) Quantity Rating (Q) - Four ranges of
waste generation volume were
chosen The ranges selected were
over 45,400 metric tons per year,
4,540 to 45,400 metric tons per
year, 454 to 4,540 metric tons per
year and less than 454 metric tons
per year These volume ranges
were assigned ratings of 1,000,
100, 10, and 1, respectively
After hazard and quantity ratings were
assigned to a waste, the priority category
was determined by multiplying the two
ratings together A total of 50 wastes
were selected and ranked as prime
candidates for consideration for the
thermal destruction tests The distribution
among priority categories for these 50
wastes and brief description of the
wastes finally chosen for the actual
thermal destruction tests are presented
in the final report
Laboratory Scale Thermal
Destruction Tests
When individual toxic organic sub-
stances or multicomponent industrial
organic wastes are subjected to thermal
destruction, the technique used may be
quite successful in bringing about the
destruction of the parent molecule;
however, other secondary or intermediate
reaction products may be produced that
are more toxic or more thermally stable
than the parent substance. Thus, in order
to determine the thermal requirements1
necessary for environmentally acceptable
disposal of hazardous materials, it is
essential that fundamental thermal
decomposition data for these toxic
substances be obtained.
There are several advantages to
generating fundamental thermal decorri:
position data in the laboratory. First;
thermal decomposition experiments carj
be conducted much more safely in a
properly equipped laboratory than in
larger throughput units. Second, data
generated in the laboratory can be much
more precise and comprehensive than
thermal decomposition data can be
obtained economically and in a shorter
period of time.
Once the thermal decomposition
properties of a particular material have
been characterized in the laboratory, the
preliminary decision can be made as to
whether high-temperature incineration is
a viable disposal route for that particular
material. If no adverse characteristics are
detected during the laboratory experi-
ments, then the material may be subjected
to larger-scale thermal decomposition
studies. However, if the laboratory data
indicate difficulties or problem areas,
then thermal decomposition is probably
not a viable disposal method for that
particular substance
Laboratory-scale thermal decomposition
studies of various organic materials are
being performed at the University of
Dayton Research Institute These experi-
ments are being performed using recently
developed second generation thermal
decomposition instrumentation, (4,5). The
present instrumentation is referred to as
a thermal decomposition analytical
system (TDAS). This system incorporates
a versatile in-line thermal decomposition
unit with sophisticated analytical instru-
mentation capable of analyzing the
various decomposition products.
The TDAS is designed to evaluate the
thermochemical behavior of volatile
materials under controlled conditions.
The TDAS consists of a modular control
panel (where the operating parameters
for tests are established), several gas
cylinders (that supply reaction atmos-
pheres with known compositions), a
sample insertion and vaporization cham-
ber, a special quartz tube reactor, in a
furnace (for the decomposition of samples),
a product collection trap, a gas chromato-
graph, a mass spectrometer, and a mini-
computer.
In operation, several micrograms of a
solid sample (or several microliters of a
liquid or gaseous sample) are introduced
into a sample injection chamber. The
chamber is then sealed and flushed with
the controlled atmosphere to be used for
the experiment. Solid and liquid samples
are heated, vaporized at temperatures up
to 300°C (over a controlled time interval),
and mixed with a continuous stream of
the reaction atmosphere. Samples may
be flash pyrolyzed or gradually vaporized,
depending on the desired reaction
conditions. The mixture than passes
through a reactor (location M) consisting
of a 98 cm long, 0.097 mm inside diameter,
thin walled, helical quartz tube enclosed
in an electric furnace. The furnace and
tube can be operated at temperatures up
to 1150°C (±2°). The temperature of the
reaction is monitored by a thermocouple
located at a point representing the mean
temperature for the reactor furnace. The
final report presents a fuller, more
detailed discussion of the laboratory
scale thermal destruction tests.
Extension of Laboratory Scale
Test Data to Commercial
Scale Units
Pilot plant scale thermal destruction
efficiency tests have been performed by
the Swedish Water and Air Pollution
Laboratory (6). The pilot plant thermal
oxidation system used for these studies
has primary and secondary combustion
chambers, followed by a sampling duct
and a variable speed fan. The primary
combustion chamber is a cylindrical,
refractory-lined vertical furnace with a
stationary grate at the bottom. The
chamber has the capability to handle
liquid waste and/or solid waste. The
furnace can use either sawmill chips or
liquid petroleum gas (LPG) as auxiliary
fuel or both. The system's secondary
combustion chamber has a cyclonic
separator configuration with a tangentially-
tired LPG burner of the same type and
size as the primary chamber. Destruction
efficiency tests were carried out using
PCB Pyraline 3010, PCB Arochlor 1254,
and hexachlorobenzene. Test conditions,
which are results of the pilot plant studies
for these compounds, are shown in the
final report. Destruction efficiencies of
greater than 99.99 percent were obtained
for seven of the nine PCB Pyralene 3010
samples, six of 13 PCB Arochlor 1254 t
samples, and 11 of 13 hexachloro- "
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benzene samples. Multiple linear regres-
sion analysis was used to investigate the
reaction of this analysis which, indicates
that the data did not follow the Arrhenius
equation and hence could not be described
by using first-order kinetics.
Since the pilot plant data did not fit
first-order kinetics, no direct comparison
of T99.99/2 values can be made between
pilot and bench-scale data (e.g. TDAS
data). However, it appears that the
temperatures required for 99.99 percent
destruction at a 2-second residence
time in the pilot plant studies are 200°C
to 300°C higher than the temperatures
required for the same degree of destruc-
tion in the laboratory bench scale unit.
The final report presents a fuller discus-
sion of all phases of extending laboratory
scale data to commercial scale units.
Theoretical Analysis of
Chemical Reaction
Mechanisms
Equilibrium Considerations
While mixing and kinetic rate processes
determine the overall rate at which
thermal destruction occurs, the ultimate
products of the thermal destruction
processes is controlled by equilibrium
considerations. It is true that virtually all
toxic materials are thermodynamically
unstable at high temperatures. However,
the persistence of carbon monoxide and
hydrogen cyanide, for example, in the
high temperature effluent from a fuel rich
oxidation process is one reason why
virtually all thermal oxidation processes
are carried out in the presence of a large
excess of oxygen. It is also true that the
high temperature stability of sulfur
dioxide, sulfur trioxide, hydrochloric acid
gas and hydrobromic acid gas require that
some type of alkaline scrubbing be used
when the elements sulfur, chlorine, or
bromine are present in the toxic waste
that is being destroyed using a thermal
method.
The above mentioned equilibrium
considerations, while important to the
subject of thermal destruction, are very
well understood at the present time, and
there appears to be no need for new
research in the area of high temperature
equilibrium chemistry.
Studies of Detailed Chemical
Reaction Kinetic Mechanisms
At the present time, the detailed
reaction processes that lead to the
oxidation of simple molecules are reason-
ably well understood and developed. The
literature reports several studies of the
oxidation of hydrogen, carbon monoxide,
methane, and methanol. The reaction
sequences developed for these simple
compounds are relatively complex and
are fully described in the final report.
Overall Kinetic Studies
The detailed kinetics of the pyrolysis
and oxidation of more complex hydrocar-
bons than methane (a Ci hydrocarbon)
are considerably more difficult to model
using elementary reaction kinetic steps
(particularly on the fuel rich side).
Nevertheless, these studies do show the
complexity of higher molecular weight
hydrocarbon oxidation processes and
lead one to the general conclusion that
detailed chemical mechanisms for the
oxidation of higher molecular weight
hydrocarbons (and substituted higher
hydrocarbons which may be toxic) will not
be forthcoming in the near future.
Mathematical Modeling of
Combustion Processes
Problems with Mathematical
Modeling
Efficient thermal destruction requires
that the toxic fuel and the oxidizer air be
rapidly mixed to the molecular level at
high temperature so that the oxidation
chemistry required for destruction can
occur rapidly. This problem is exemplified
by the discussion in the final report which
indicated that reactor contact times for
the TOAS experiments were much less
than those required in larger, full-scale
devices where turbulent mixing must be
used to obtain the intimate contact which
is necessary for chemical destruction
to occur. The key to this problem is the
attainment of high levels of turbulence in
the reactor without paying the penalty of
excessive pressure drop, which requires
higher power levels for the operation of
the device. A general solution to this
problem is not available at the present
time and the current understanding of
the turbulent mixing problem, particularly
when the system is chemically reactive,
is really not well developed at all. The
final report presents a full description of
current research efforts in the area of
turbulent reactive mixing as applied to
combustion problems, particularly in jet
engines or diesel combustion. Very little
systematic work has been done on the
improvement of Incinerator design. At the
present, the approach is to search for the
solution by continually adjusting the
configuration of an incinerator until
optimum incineration is obtained.
Conclusions and
Recommendations
The objectives of this study were to
determine the state-of-the-art of thermal
destruction of industrial toxic waste and
to identify and prioritize research needs
in this area. The study consisted of a lit-
erature search, discussions with Envi-
ronmental Protection Agency (EPA)
personnel, discussions with other author-
ities in the area of thermal destruction,
and attendance at a national meeting on
the subject. The state-of-the-art of
thermal destruction of industrial toxic
waste was determined, and the following
research needs were identified:
1. Continue and expand the thermal
decomposition analytical system
(TDAS) studies to determine values
of the temperature required to obtain
a 99.99 percent destruction effici-
ency at a residence time of two
seconds and general temperature/
residence time thermal decomposition
data for a variety of hazardous
compounds representing different
molecular structures.
2. Generate auto ignition temperature
(AIT) values for the substances
studied in (1) and determine the
degree of correlation between AIT
and T99.99/2.
3. Generate ionization energy data for
the substances studies in (1) and
determine the degree of correlation
between ionization energy and
T99.99/2.
4. Determine the effects of molecular
structure of T99.99/2 values.
5. As a part of the TDAS study, examine
the concentration of carbon monoxide
(CO) as a function of temperature and
residence time to determine if
regulations governing the thermal
destruction of CO will successfully
govern the thermal destruction of all
products of incomplete combustion
(PICs).
6. Investigate the possibility of monitor-
ing only CO to certify an incinerator
for burning toxic wastes.
7. Continue development and imple-
ment the EPA rotary kiln pilot plant in
Arkansas and use the generated data
to develop scale-up laws for rotary
kiln incinerators.
8. Develop a pilot plant as in step (6) of
the generation of scale-up laws for
liquid injection incineration.
9. Pursue the newer approaches to
reactive turbulent flow modeling in
the presence of large density gradi-
ents. Virtually all of the extant
turbulent modeling is not predictive
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when applied to a turbulent diffusion
flame.
10. Fundamental kinetic studies, in
which individual reaction steps are
identified and each of their rates
measured, would not be useful at
this time, because in practical
incineration, turbulence so restricts
the rate of the chemistry that it
controls the conversion rate. Also,
the combustion chemistry of large
organic molecules is a very complex
subject and detailed mechanisms
have not been identified as yet. Thus
it appears that the simple first-order
kinetic approach that has been used
jn the IDAS studies will be adequate
for a considerable period of time.
References
1. Sittig, M., Incineration of Industrial
Hazardous Wastes and Sludges,
Pollution Technology Review No. 63,
Noves Data Corporation, 1979.
2. Bonner, T.,
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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