MINIMIZATION OF COMBUSTION BY-PRODUCTS: TOXIC METAL EMISSIONS
by
C.C. Lee and G.L. Huffman
Paper to be presented at
HMCRI's 12th Annual National Conference & Exhibition
"Hazardous Materials Control '91"
Washington, DC, December 3-5, 1991
U.S. Environmental Protection Agency
Office of Research and Development
Office of Environmental Engineering and Technology Demonstration
Risk Reduction Engineering Laboratory
.Waste ^Minimization, Destruction and Disposal Research Division
. : • Thermal Destruction Branch
Thermal Processes Section
Cincinnati, Ohio 45268
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Minimization of Combustion By-Products: Toxic Metal Emissions
C.C. Lee, Ph.D
George L. Huffman
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio
ABSTRACT
It .has been well recognized that, although there are many potential solid
waste treatment technologies, none is as universally applicable as
incineration for the treatment of the many types of waste which are governed
by the many different Federal laws and State regulations. However,
incinerators may release trace amounts of unwanted combustion by-products
(CBPs.), particularly if the incinerators are not well designed or properly
operated.
Control of the emissions of CBPs is one of the major technical and
sociological issues surrounding the implementation of incineration as a waste
treatment alternative. Much of this is due to the lack of detailed knowledge
about CBPs. The Clean Air Act Amendment is emphasizing the control of toxic
air pollutants from all combustion and process sources; some of these
pollutants are CBPs. CBPs include: (1) unburned principal organic hazardous
constituents (POHCs); (2) products of incomplete combustion (PICs); (3) metal
emissions; (4) residuals/ashes; and (5) acid gases.
This Paper is a part of a series of writings on the subject of the CBP
issue from EPA's Risk Reduction Engineering Laboratory in Cincinnati, Ohio and
is one of the first metal emission papers in the series. It specifically
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addresses the aspect of potential toxic metal emissions from combustion/
incineration processes. The main objective of the series is to ultimately
compare combustion by-products from all major combustion activities including
fossil fuel combustion and waste incineration. Hopefully, the series will
serve as an initial step in the eventual minimization of the release of CBPs
to the environment.
INTRODUCTION ,
It has been well documented that incineration is the best available
technology for disposing of various waste streams, when compared to other
treatment technologies (1). A recent study has shown that essentially only
four technologies were active in treating Superfund waste through 1989 and
three out of the four technologies were thermal processes. These three
thermal technologies have more than 80% of the market share in remediating
Superfund sites (2).
Compared with other treatment technologies, incineration has the
following major advantages: (1) volume reduction (the reduction rate depends
on the ash content of the waste incinerated); (2) detoxification (incineration
can achieve nearly 100% destruction of any pathogenic, toxic or hazardous
substance); (3) potential energy recovery (it has been a general practice for
many industries to recover energy from waste incineration processes); (4) no
long-term liability (once a waste is incinerated, the problem will not
resurface again as it often does when landfills are used); and (5)
effectiveness (it only takes seconds to destroy what landfills may take years .
to decompose). However, waste incineration can produce unwanted combustion
by-products (CBPs) such as partially burned ash and toxic air pollutants such
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as particulate (heavy metals) and dioxins and furans (PCDD and PCDF),
particularly if the incinerators are not well designed and operated. The
general issue of CBPs has been one of the major technical and sociological
issues surrounding the implementation of incineration as a waste treatment
alternative. In addition, the public has developed the so-called "NIMBY" (not
in my back yard) attitude which makes siting an incineration facility
extremely difficult.
The authors have been writing a series of papers addressing the issues of
CBPs. The series of already published papers cover:
(1) Regulatory aspects: Papers published in this area are:
• Regulatory Framework for Combustion By-Products from
Incineration Sources (3)
• Environmental Law Relating to Medical Waste in the United
States of America (4)
(2) Theoretical aspects: Papers published in this area are:
• Incineration of Solid Waste (5) •
• Thermodynamic Fundamentals Used in Hazardous Waste
Incineration (6)
• Incinerability Ranking Systems for RCRA Hazardous
Constituents (7)
(3) Waste characteristics: Papers published in this area are:
• Minimization of Combustion By-Products: Characteristics of
Hazardous Waste (8)
(4) Organic combustion by-products: Papers published in this area are:
• PIC Formation - Research Status and Control Implications (9)
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(5) Metals: Papers published in this area are:
• A Model Analysis of Metal Partitioning in a Hazardous Waste
Incineration System (10)
• Metals Behavior During Medical Waste Incineration (11)
EPA defines toxic metals as metallic elements with high atomic weight and
density such as mercury, chromium, cadmium, arsenic, and lead. They are toxic
to living organisms and can damage living things at low concentrations and
tend to accumulate in the food chain (12).
Metals present in the feed to combustion devices are typically emitted in
combustion gases as particles rather than vapors. However, some of the more
volatile elements (e.g., mercury and selenium) or their chemicar compounds may
be released to the atmosphere partially in the vapor state. The processes
involved in the formation of particles are very complex and are only partially
understood at present. Most of the current state of know!edge'on metal
behavior in combustion has come from research on coal combustion (1).
This Paper supplies general information about toxic metals. Specific
subjects covered include: (1) metals regulated under various Federal laws;
and (2) selected properties of regulated metals and their potential
chlorinated species resulting from incineration.
METALS REGULATED UNDER VARIOUS FEDERAL LAWS
Metals Regulated Under the Resource Conservation and Recovery Act (RCRA)
It has been well documented that hazardous waste, contains various metals
such as arsenic, barium, beryllium, chromium, lead, mercury, nickel, zinc,
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etc. Incineration changes the form but not the content of metal fractions in
waste streams. As a result, metals are expected to emerge from the combustion
zone essentially in the same total quantity as they were in the input feed
(i.e., exiting in both the flyash and bottom ash streams).
Because of the public interest in early 1991, EPA promulgated the BIF
. (Boiler and Industrial Furnaces) Rules. The rules contain regulations
(provisions) on the emissions of ten metals. The summary of metal information
contained in the BIF rules is as follows (40CFR-260, 1991):
The rules establish emission limits for 10 toxic metals listed in
Appendix VIII of 40 CFR Part 261 based on projected inhalation health
risks to a hypothetical maximum exposed individual (MEI). The standards'
for the carcinogenic metals (arsenic, beryllium, cadmium, and chromium)
limit the increased lifetime cancer risk to the MEI to a maximum of 1 in
100,000. The risk from the four carcinogens must be summed to ensure
that the combined risk is no greater than 1 in 100,000. The standards
for the non-carcinogenic metals (antimony, barium, lead, mercury, silver,
and thallium) are based on reference doses (RfDs) below which adverse
health effects have not been observed.
The standards are implemented through a three-tiered approach.
Compliance with any tier is acceptable. The tiers are structured to
allow high emission rates (and feed rates) as the owner or operator
elects to conduct more site-specific testing and analyses (e.g.,
emissions testing, dispersion modeling). Thus, the feed rate limits
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under each of the tiers are derived based on different levels of site-
specific information related to facility design and surrounding terrain.
Under Tier I, the Agency has provided very conservative waste feed rate
limits in "reference" tables as a function of effective stack height and
terrain and land use in the vicinity of the stack and assumed reasonable,
worst-case dispersion. The owner or operator demonstrates compliance by
waste analyses, not emissions testing or dispersion modeling.
Consequently, the Tier I feed rate limits are based on an assumed
reasonable, worst-case dispersion scenario, and an assumption that all
metals fed to the device are emitted in the stack gases [i.e., no
partitioning to bottom ash or products, and no removal by an air
pollution control system (ARCS)].
Under Tier II, the owner or operator conducts emissions testing (but not
dispersion modeling) to get credit for partitioning to bottom ash or to
products, and for ARCS removal efficiency. Thus, the Agency has
developed conservative emission rate limits in reference tables, again as
a function of effective stack height and terrain.and land use in the
vicinity of the stack. The Agency also assumed reasonable, worst-case
dispersion under Tier II.
Under Tier III, the owner or operator wo.uld conduct emissions testing and
site-specific dispersion modeling to demonstrate that the actual
(measured) emissions do not exceed acceptable levels considering actual
(predicted) dispersion. %
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The standards are implemented through limits on specified operating
parameters, including hazardous waste feed rate and metals composition,
feed rate of metals from all feed streams, combustion chamber
temperature, and air pollution control parameters.
The rules limit particulate matter (PM) emissions to 0.08 grains/dry
standard cubic foot (dscf) corrected to 7 percent oxygen (02) This is
the same standard that currently applies to hazardous waste incinerators
and is intended to supplement the risk-based metals controls. Compliance
with the standard is demonstrated by emissions testing, and the standard
is implemented by operating limits set in the permit.
All boilers and industrial furnaces must comply with the standard;
however, cement and aggregate kilns need not monitor the ash content of
fall feed streams to demonstrate compliance with the standard given that
particulate matter from these devices is generated primarily from raw
materials. Instead, the rule provides that these devices must comply
with the operating limits on the particulate matter control system to
ensure continued operation at levels achieved during the compliance test
(under "Interim Status") or trial burn (under the Part B permit
application).
Metals Regulated Under the 1990 Clean Air Act (CAA) Amendments
The 1990 Amendments completely overhaul the regulatory approach used for .
air toxics, originally regulated under the 1970 Clean Air Act. Under this new
regulatory strategy, 189 substances were listed as hazardous air pollutants
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(HAPs) by the Act and these will be regulated by EPA. Substances can. be added
to or deleted from the list after rulemaking. The HAPs contain many metal
compounds.
All metals are regulated under the "PM-10" approach. "PM-10" means the
particulate matter with an aerodynamic diameter less than or equal to a
nominal 10 micrometers as measured by an applicable reference method (12).
Under the 1990 CAA Amendments: (1) EPA is directed to promulgate control
technique guidelines for reasonably available control measures and best
available control measures for PM-10 emissions from both major stationary
sources and area sources; and (2) States must implement all reasonably
available control measures and designate periodic milestones until attainment
is achieved.
PM-10 plan revisions are to provide for automatic implementation of
contingency measures if the area fails to attain the PM-10 NAAQS (National
Ambient Air Quality Standards) by the mandated deadline. States are to adopt
these contingency measures as regulations prior to the deadline for attainment
to ensure that these, back-up measures can go into effect without delay if the
target date is missed. .
Metals Regulated under the Clean Water Act (CWA)
In general, sludge waste includes both municipal sludge and industrial
sludge. Incineration of sludge is regulated under Section 405(d) of the CWA.
EPA's Office of Water is currently developing standards for municipal sludge
incineration. The standards for industrial sludge incineration have not been
developed yet.
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Metals Regulated under the Superfund Act (CERCLA)
In general, thermal equipment used at CERCLA sites will not require
formal RCRA incineration permits; however, in most cases, consent orders will
be negotiated which will generally require that the RCRA incineration
performance standards be achieved. The consent order route can reportedly
save up to a year of permitting time for a clean-up project. The RCRA
performance standards are 99.99 percent destruction and removal efficiency for
specific Appendix VIII principal organic hazardous constituents (POHCs),
particulate emissions no greater than 0.08 grains per dscf corrected to 7
percent oxygen, and either 99 percent HC1 removal or a maximum stack emission
of four pounds of HC1 per hour. Metals contained in CERCLA waste are
regulated under the RCRA particulate standards (2).
SELECTED PROPERTIES OF REGULATED METALS AND THEIR CHLORINATED COMPOUNDS
Because metals are increasingly receiving more attention due to their
potential impact on the environment, being aware of the properties of
regulated metals is important in that these properties often influence the
degree of metal partitioning that takes place during combustion. Because many
chlorinated metal compounds have lower volatility temperatures than that of
their corresponding metal elements, the chlorinated metal compounds are easier
to vaporize and to escape from air pollution control devices. Common
chlorinated metal compounds are provided in the metal property information
provided below (most information was excerpted from Merck)(13).
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Antimony (Sb)
• Melting point: 630°C
• Boiling point: 1635°C
• Common chlorinated compounds:
- Antimony chloride oxide (SbOCl): Monoclinic crystals or
crystalline powder;
- Antimony pentachloride (SbCl5): Colorless to yellow, oily
liquid. Fumes in air; and -
- Antimony trichloride (SbCl3): Fumes in air.
• Health effect: Antimony and its compounds have been reported to cause
dermatitis, keratitis, conjunctivitis and nasal septal ulceration by
contact, fumes or dust. Antimony can react with nascent hydrogen to
form stibine (H3Sb) which is extremely toxic. Stibine can cause
vomiting, headache, stomach pain and even death.
Arsenic (As)
• Melting point: 818° at 36 atm. (at atmospheric pressure, it sublimes)
• Boiling point: 615°C (sublimation temperature)
• Common chlorinated compounds:
- Arsenic trichloride (AsCl3): Oily liquid, intensely poisonous,
fumes in air.
• Health effect: Most forms of arsenic are toxic. This substance and
certain other arsenic compounds have been listed as carcinogens by
EPA.
Barium (Ba)
• Melting point: 710°C
• Boiling point: 1600°C
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• Common chlorinated compounds:
- Barium chlorate [Ba(C103)2]: Monohydrate, monoclinic prismatic
crystals, and poisonous;
- Barium chloride (BaCl2): Dihydrate, crystals or granules or
powder; bitter salty taste and poisonous; and
- Barium perchlorate [Ba(C104)2]: Trihydrate, crystals and
poisonous.
• Health effect: All water or acid soluble barium compounds are
poisonous.
Beryllium (Be)
• Melting point: 1287°C
• Boiling point: 2500°C
• Common chlorinated compounds:
- Beryllium chloride (BeCl2): White to faintly yellow, very
deliquescent; and
- Beryllium perchlorate [Be(C104)2]: Trihydrate, very hygroscopic
crystals.
• Health effect: Death may result from exposure to the element and
its compounds.
Cadmium (Cd)
• Melting point: 321°C
• Boiling point: 765°C
• Common chlorinated compounds:
- Cadmium chloride (CdCl2): Hygroscopic, rhombohedral crystal.
• Health effect: This substance and certain cadmium compounds have
been listed as carcinogens by EPA.
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Chromium (Cr)
• Melting point: 1900°C
• Boiling point: 2642°C
• Common chlorinated compounds:
- Chromous chloride (CrCl2): Lustrous needles or fused, fibrous
mass; and
- Chromyl chloride (CrCl202): Deep red liquid; appears black under
reflected light. Fumes in moist air. Burns and blisters skin.
t Health effect: This substance and certain cadmium compounds have
been listed as carcinogens by EPA.
Lead (Pb) .
• Melting point: 327°C
• Boiling point: 1740°C
• Common chlorinated compounds:
- Lead chlorate [Pb(C103)2]: Colorless, deliquescent crystals,
poisonous.
- Lead chloride (PbCl2): White, crystal powder, poisonous.
• Health effect: Acute; most common in children with history of pica;
anorexia, vomiting etc. Chronic: Children show weight loss,
weakness, etc. Lead poisoning in adults is usually occupational due
mainly to inhalation of lead dust or fumes.
Mercury (Hq)
• Melting point: - 38.87°C
• Boiling point: 356.72°C
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t Common chlorinated compounds:
- Mercuric chloride (HgCl2): Crystals or white granules or powder,
highly toxic;
- Mercury amide chloride (HgNH2Cl): Odorless powder, poison, may
produce allergic dermatiti.s;
- Mercurous chlorate [Hg2(C103)2]: White crystals; decomposes at
about 250°C to form oxygen, mercuric oxide and mercuric chloride;
and
- Mercurous chloride (Hg2Cl2): white, odorless, tasteless, heavy
powder; slowly decomposes by sunlight into mercuric chloride and
metallic mercury.
t Health effect: Acute: violent corrosive effects on skin and
mucous membranes, vomiting, abdominal pain, etc. Chronic:
inflammation of mouth and gums, excessive salivation, loosening of
teeth; kidney damage, etc.
Silver (AqV
• Boiling point: 960.5°C
• Boiling point: 2000°C
• Common chlorinated compounds: .
- Silver chlorate (AgC103): White, tetragonal crystals;
- Silver chloride (AgCl): White powder; darkens on exposure to
light; and
- Silver perchlorate (AgC104): Deliquescent crystals, irritating to
skin, mucous membranes.
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• Health effect: Does not cause serious toxic manifestations, but
prolonged absorption of silver compounds can lead to grayish blue
discoloration of skin. Many silver salts are irritating to skin and
mucous membranes.
Thallium (Tl)
• Melting Point: 303°C
• Boiling point: 1457*C
• Common chlorinated compounds:
- Thallium chloride (T1C1): White crystal powder; poisonous.
• Health effect: Acute: vomiting, diarrhea, tingling, pain in
extremities, etc. Chronic: weakness and pain in extremities, loss of-
hair.
CONCLUSION
This Paper has provided some general technical information regarding the
toxic metals often found in incinerator stack emissions. It described the
metals that are regulated under various Federal laws. It also has provided.
selected properties of the ten metals that are regulated under RCRA.
REFERENCES
1. Oppelt, E.T., "Incineration of Hazardous Waste, A Critical Review,"
Journal of Air Pollution Control Association, May 1987.
2. Lee, C.C., Huffman, G.L. and Oberacker, D.A., "Review of Mobile Thermal
Technologies for Solid Waste Destruction." Presented at the 83rd
National Meeting of the Air and Waste Management Association, Pittsburgh,
Pennsylvania, June 24-29, 1990.
3. Lee, C.C. and Huffman, 6.L., "Regulatory Framework for Combustion By-
Products from Incineration Sources." Presented at the 1990 Pacific Basin
Conference on Hazardous Waste held in Honolulu, Hawaii, November 12-16,
1990.
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4. Lee, C.C. and Huffman, G.L., "Environmental Law Relating to Medical Waste
in the United States of America," The Journal of the International Solid
Wastes and Public Cleansing Association (ISWAK Volume 9, Number 2, April
1991.
5. Lee, C.C. and Huffman, G.L., "Incineration of Solid Waste." Presented at
the 1988 AIChE Annual Meeting and 80th Anniversary Commemoration,
Washington, DC, November 27-December 2, 1988 and Published inn J_he
Journal of Environmental Progress. August 1989.
6. Lee, C.C. and Huffman, G.L., "Thermodynamic Fundamentals Used in
Hazardous Waste Incineration." Presented at the 1990 Incineration
Conference, San Diego, California, May 14-18, 1990.
7. Lee, C.C., Huffman, G.L. and Sasseville, S.M., "Incinerability Ranking
Systems for RCRA Hazardous Constituents," Hazardous Waste & Hazardous
Materials. Volume 7, Number 4, April 1990.
8. Lee, C.C. and Huffman, G.L., "Minimization of Combustion By-Products:
Characteristics of Hazardous Waste." Presented at the National Research
and Development Conference on the Control of Hazardous Materials held in -
Anaheim, California on February 20-22, 1991.
9. Dellinger, B., Taylor, P.H. and Lee, C.C., "PIC Formation - Research
Status and Control Implications." Presented at the 16th EPA Annual
Meeting, Cincinnati, Ohio, April 3-5, 1990.
10. Lee, C.C., "A Model Analysis of Metal Partitioning in a Hazardous Waste
Incineration System," JAPCA. July 1988.
11. Lee, C.C. and Huffman, G.L., "Metals Behavior During Medical Waste
Incineration." Presented at the National Meeting of the American
Chemical Society, New York, August 26-30, 1991.
12. Lee, C.C.i Environmental Engineering Dictionary. Published by Government
Institutes, Inc., 966 Hungerford Drive, #24, Rockville, Maryland 20850,
September 1990.
13. The Merck Index: An Encyclopedia of Chemicals. Drugs, and Bioloaicals,
Tenth Edition, Merck & Co., Inc., Rahway, New Jersey, 1983.
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