EPA-230/2-86-004
Office of Policy, March 1985
Planning and Evaluation
Agency Washington, DC 20460
Policy Planning and Evaluation
Assessment of Incineration
As A Treatment Method for
Liquid Organic Hazardous
Wastes
Background Report II: ..
Assessment of Emerging
Alternative Technologies
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ASSESSMENT OF ALTERNATIVE TECHNOLOGIES
March 1985
A background report for the study by EPA's
Office of Policy, Planning and Evaluation:
"Assessment of Incineration As A Treatment
Method for Liquid Organic Hazardous Waste."
Prepared by:
James Basilico, Harry Freeman,
Tim Oppelt, Glen Shira
U.S. Environmental Protection Agency
Office of Research and Development
Hazardous Waste Engineering Research Laboratory
26 West St. Clair Street
Cincinnati, Ohio 45268
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TABLE OF CONTENTS
Page
EXECUTIVE SUMMARY 1
INTRODUCTION 7
EXISTING ALTERNATIVE THERMAL PROCESSES 9
Hazardous Waste as Fuel in Industrial Processes 9
Incineration of Hazardous Waste in Power Boilers 10
EMERGING ALTERNATIVE TECHNOLOGIES 13
High Temperature Electric Reactor 16
Molten Salt 17
Plasma Arc 18
Wet Air Oxidation 20
Molten Glass Incineration 23
Supercritical Water 24
BIOLOGICAL TREATMENT 26
CHEMICAL TREATMENT 27
Appendix 29
References 32
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EXECUTIVE SUMMARY
Assessment of incineration as a treatment method for
liquid combustible and other liquid organic waste streams must
take into account the availability of technologies that offer
suitable treatment and destruction alternatives to conventional
incinerators. This report reviews existing and emerging thermal,
chemical, and biological hazardous waste destruction processes
that can be used to treat or destroy the same types of liquid
organic wastes that are presently destroyed in incinerators.
The processes reviewed are those that currently exist, or
may exist in the next five years. Existing alternative technologies
are defined as those processes other than conventional incineration
that are in existence today, are suitable for treating or destroying
liquid organic waste streams, and are available for commercial
use. Emerging alternative technologies are innovative processes
that are suitable for treating or destroying liquid organic
waste streams, but have not yet been adopted for commercial use.
This report addresses the following questions:
1. What technologies other than incineration are now
available, or may be available in the near future, to
treat, destroy, or recycle combustible liquid hazardous
wastes?
2. What is the likely commercialization rate of each of
these technologies?
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3. How do these technologies compare to incineration in
terms of cost, capability, benefits, and environmental
and human health impacts?
Each alternative technology is described in terms of the
types of waste the system is capable of accepting, throughput/
capacity of the process, operational costs, anticipated environmental
impact, and anticipated date for commercialization (for emerging
technologies).
Although liquid organic waste streams can theoretically be
treated in various thermal, chemical, and biological processes,
only thermal processes were determined to be significant alternatives
to conventional incineration. This is because biological and
chemical processes are only in the initial stages of development,
have environmental impacts that are numerous and hard to predict,
are expensive, and are frequently incapable of handling combustible
liquid organic hazardous wastes. Biological and chemical processes
were found to be either inappropriate or suitable for only small
amounts of the waste streams in question.
EXISTING ALTERNATIVE TECHNOLOGIES
The existing thermal alternative technologies believed to be
most suitable are industrial processes (cement kilns, lime kilns,
and aggregate kilns), and co-combustion in industrial boilers.
At the present time, susbstantially more hazardous waste is burned
in industrial boilers than in incinerators.
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EMERGING ALTERNATIVE TECHNOLOGIES
Twenty-five emerging technologies were initially considered
for inclusion in the report using the following criteria:
1. Is the process designed for a liguid organic waste stream?
2. Is the process at a development stage to be commercially
available within five years?
3. Is the process innovative, or is the process just a
modification of conventional incineration technology?
Only a few of the processes reviewed meet all three criteria
and thus were determined to be relevant to this study. Those
emerging processes selected for further consideration in the
study are:
1. High Temperature Electric Reactor
2. Wet Air Oxidation
3. Plasma Arc
4. Supercritical Water
5. Molten Salt Reactor
6. Molten Glass Incineration
It should be noted that not all of these alternatives are
able to destroy the full range of wastes handled by conventional
incinerators. However, for the purpose of this study, candidate
waste streams for treatment by emerging alternative technologies
were identified, based on EPA data that they represent the highest
volumes of waste incinerated in the United States in 1981.
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COMPARISON OF ALTERNATIVE TECHNOLOGIES WITH CONVENTIONAL
INCINERATION
Cost
Cost figures for all of the technologies, especially some of
the emerging technologies, are not available. Although it varies
by waste, there is a considerable reclamation of energy value in
the existing alternative processes (cement kilns and boilers).
Therefore, their overall costs are less than those for incineration,
Another major advantage is that the use of existing facilities
requires little capital investment. Among emerging processes,
costs for supercritical water, plasma arc, and molten glass will
exceed conventional incineration, while costs for wet oxidation,
the high temperature electric reactor, and molten salt appear
comparable to conventional incineration.
It should be pointed out that each of these systems offers
advantages over conventional incineration for specific waste
streams that may more than offset the increased costs. Some
advantages are: the ability to handle small or large quantities
of highly toxic wastes; smaller units to make on-site treatment
economically feasible and eliminate safety factors of handling
and transportation; portable units; and less production of air
emissions. Thus, decisions about the probability of these
technologies replacing incinerators cannot be made on the basis
of cost alone.
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Throughput/Capacity
Capabilities and capacities of the various processes evaluated
vary widely. Existing alternative technologies are capable of
consuming significant amounts of liquid wastes, especially under
existing regulations which exempt these processes from RCRA
incineration standards. However, the Agency is now developing
standards for these processes similar to those for hazardous
waste incinerators. As a result, the capability of these processes
to dispose of waste may be lessened considerably. (The potential
impact of these standards on the market for incineration is not
addressed in this report.)
Commercial Status
Emerging alternative technologies will have minimal impact on
the quantity of liquid hazardous waste currently destroyed in
conventional processes. Although all of the emerging processes
evaluated offer some technical advantages, their commercial
adoption will not significantly affect the market for conventional
incineration, since it is expected that these new processes will
only be used on the most toxic wastes, representing only 2-3% of
liquid combustible waste streams.
Environmental Impact
More testing will be needed to determine the environmental
effects of both existing and emerging alternative technologies.
Environmental effects of the existing alternative technologies
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are currently being assessed. RCRA regulations are now being
proposed for industrial boilers to assure that their operating
performance is protective of human health and the environment.
For most emerging alternative technologies, the environmental
impacts have not been tested. In many cases, their effects are
expected to be roughly comparable to those of conventional
incineration.
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INTRODUCTION
The purpose of this task is to assemble available information on
technologies, both existing and new, that offer alternatives to either
land based or ocean incineration of liquid hazardous wastes.
The processes of interest in this task are those that currently
exist, or that may exist in the next five years. They are not incineration
processes, but can be used to treat or destroy the same types of liquid
organic waste streams that are presently destroyed in incinerators.
Existing alternative technologies are defined as those processes other
than conventional incineration that are in existence today, are suitable
for treating or destroying liquid hazardous waste streams, and are
available for commercial use. For example, the process of burning
hazardous waste as a fuel in cement kilns is an existing alternative
technology because it is an alternative to conventional incineration
that is practiced commercially.
Emerging alternative technologies are innovative processes that are
suitable for treating or destroying liquid hazardous waste streams, but
have not yet been adopted for commercial use. The process of using high
temperature plasma to destroy wastes is an emerging technology, because
it is still under development and has yet to be widely used for the
treatment of hazardous wastes.
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Another point to emphasize is that this report addresses only those
processes that are intended to treat or destroy liquid organic waste
streams. Many emerging technologies for hazardous waste treatment are
designed to treat other types of waste streams, i.e. solids, or inorganic
waste streams. Finally, for the purpose of this report, improved
incineration processes such as fluidized bed incinerators or mobile
incinerators are treated as conventional incineration rather than
alternative technologies, and are not discussed.
The task is directed towards answering the following three questions:
1) What technologies besides incineration are available (or may be
in the near future) to treat, destroy or recycle combustible
liquid hazardous wastes?
2) What is the likely commercialization rate of each of these
technologies?
3) How do these technologies compare to incineration in terms of cost,
capability, benefits, and environmental and human health impacts?
In the subsections that follow are brief discussions of the alternative
processes included in the study. Each discussion is structured as follows:
1. Brief discussion of technology involved.
2. What type of wastes is the system capable of accepting.
3. Throughput/capacity of process.
4. Operational costs.
b. Anticipated date of commercialization (for emerging technologies).
6. Environmental considerations.
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EXISTING ALTERNATIVE THERMAL PROCESSES
The following existing technologies were identified as alternative
technologies that are practiced commercially and should be included in
this study:
0 Disposal in industrial processes (cement kilns, lime kilns,
aggregate kilns)
0 Co-combustion in industrial boilers
HAZARDOUS WASTE AS FUEL IN INDUSTRIAL PROCESSES
An integral part of the production of products such as cement,
limestone, and aggregate is the roasting of the feed material in large
rotary kilns. The purpose of this roasting is to produce a temperature
high enough for the chemical reactions necessary to produce the product
to occur. Because of the high process temperatures (2000 - 2600°F), and
because of the long residence times for combustion, kilns are potential
thermal treatment devices for destroying many organic wastes. These
wastes can be used as supplemental fuels, replacing some of the primary
fossil fuels such as fuel oil or coal normally used to fire the kilns.
Suitable Wastes
The types of waste suitable for co-combustion in kilns is very
dependent upon the individual process. However, generally kilns can
accept waste solvents, bottoms from solvent reclamation operations, and
paint residues.
Throughput/Capacity
1,000 - 25,000 gallons/day of liquid organic wastes can be processed
in a kiln depending upon the size of the kiln and the percentages of the
primary fuel replaced by the waste fuel.
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COST PER UNIT OF WASTE PROCESSED
Costs can vary from zero, reflecting a company's accepting a very
high energy waste solely for its fuel value, to some 20 to 25 cents per
gallon.
ENVIRONMENTAL DATA
Assessments conducted by EPA and others have produced mixed results
on the environmental and health effects of combusting waste chemicals in
cement kilns. However, they indicate that when a kiln is operated
properly, its emissions are comparable to those of a well operated
incinerator, and meet emissions standards for incineration.
Anticipated Date of Commercialization
Technology is currently being utilized on a commercial basis. An
estimated 3.5 million tons of waste went to industrial processes in
1981 (1).
INCINERATION OF HAZARDOUS WASTES IN POWER BOILERS
Under RCRA, the regulations and specific process performance standards for
hazardous waste incineration do not apply to the use of combustible hazardous
waste as fuels in energy recovery operations such as power boilers. In part
because of this regulatory situation and because of the obvious attractiveness
of reclaiming energy from waste, significant quantities of liquid hazardous
waste are disposed of in industrial boilers. EPA studies have estimated that
3.5 million tons of hazardous wastes were disposed of in this manner in 1981,
more than twice the amount disposed of in incinerators that year (1).
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1,800
300
8,100
14,200
400
15,900
9,200
1,800
46,000
37,300
2,000
57,700
5,200
1,500
11,500
2,200
11,300
11,300
There are currently about 400,000 boilers of all types in the U.S.
including industrial, commercial, residential and off-site power. Of
these boilers, about 240,000 can be classified as industrial installations.
This figure includes boilers of all types and all sizes. Table 1 breaks
down the industrial boiler population by fuel type and size.
Table 1
Capacity (BTU/HR) of Industrial Boilers by Fuel Type (1975)
Fuel Type < 106 106 and < 107 > 10?
Stoker Coal
Pulverized Coal
Residual Oil
Distillate Oil
By-Product Gas
Natural Gas
Most of these boilers are very small natural gas or oil-fired firetube
or cast iron units used for space heating. Such installations are generally
package units and do not easily lend themselves to either waste firing or
to the fuel blending required in waste co-firing. However, examination
of Table 1 shows that there are about 43,000 industrial boilers in the
U.S. with capacities larger than 10 million BTU's per hour. These larger
boilers have the greatest potential for use in hazardous waste destruction
processes.
It is more the rule than the exception that large organic chemicals
producers operate one or more boilers on the plant premises. Some of
these plants use boilers for on-site destruction of organic chemical
wastes; the number of boilers used is not known.
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Suitable Wastes
Boilers are generally capable of accepting any lowly halogenated
liquid organic waste stream. It is possible to burn up to 3% halogenated
wastes, but usually because of corrosive waste streams only approximately
1% halogens are burned.
Process Throughput
Depends on the size of the boiler. A large boiler using organic
wastes to replace 25% of the feed would consume 500 gallons per day of
waste. However, studies have indicated that 10% of the feed is more
typical.
Cost Per Unit of Waste Processed
No specific cost figures were located. However, given that most
waste that is burned in boilers is burned on-site and replaces conventional
incineration, the additional cost is minimal compared to providing for a
separate facility for incineration of the waste.
Anticipated Date of Commercialization
Burning waste in boilers is widely practiced. The EPA has estimated
that 13UU boilers utilized hazardous waste as fuel in 1981 (1).
Environmental Data
The Agency is presently supporting a large research program to obtain
environmental effects information on burning wastes in boilers. Field test
data have shown that boilers can achieve waste destruction efficiencies
comparable to those of incinerators. Current evaluations are underway to
determine emissions from boilers operating at less than optimum conditions.
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EMERGING ALTERNATIVE TECHNOLOGIES
Currently there are many new processes in various stages of
development for treating and destroying all types of hazardous waste,.
Some of these processes are essentially improvements on conventional
treatment and destruction methods. Examples of such are fluidized bed
incineration, which is considered by many to be an improvement over
conventional incineration. Other processes represent entirely new approaches
to waste treatment. The former group are included with conventional
methods and not addressed, and the latter considered emerging technologies.
The processes discussed in this section were compiled from responses
to two national solicitations for new hazardous waste treatment ideas,
from several literature reviews, and from contact with experts in the
field. This procedure identified many processes that represented new
approaches to hazardous waste treatment and destruction. However, only a
few of the processes identified were determined to be relevant to this
study, i.e. designed for liquid organic wastes and sufficiently close to
commercialization to significantly affect within the next five years the
waste management practices of the Country as a whole. A list of the
processes reviewed for this study is attached as Appendix A. Those
processes determined to be emerging processes relevant to this study are:
0 High Temperature Electric Reactor
0 Molten Salt Reactor
0 Plasma Arc
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0 Wet Oxidation
0 Supercritical Water
0 Molten Glass Incineration
It should be noted that none of these alternatives are able to destroy the
full range of wastes now handled by conventional incinerators.
Candidate Waste Streams
The following waste streams were identified as candidate streams for
treatment by alternative technologies. This selection was based on EPA data
indicating that these waste streams represented the highest volumes incinerated
in the U.S. in 1981.
EPA Waste # Description
DUU1 Hazardous waste that exhibits characteristic of ignitability
D002 Hazardous waste that exhibits characteristic of corrosivity
D003 Hazardous waste that exhibits characteristic of reactivity
F001-F002 Spent halogenated solvents
FU03-F005 Spent non halogenated solvents
K049 Slop oil emulsion solids from the petroleum refining industry
KUbl API separate sludge
PCB's
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TABLE 3
ALTERNATE TECHNOLOGY VS WASTE STREAMS
Incineration
Industrial
Processes
Boiler
Co-combustion
High Temp. Electric
Reactor
Molten Salt
Plasma Arc
Wet Oxidation
Molten Glass
Supercritical H20
D001 D002 D003
XXX
X
X
X
X
X
X
X
X
F001-002
X
X
X
X
X
X*
X
X*
F003-005 K049 K051 PCB
X XXX
XX X
X
X X
X
X X
X X
* In Aqueous Solutions
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HIGH TEMPERATURE ELECTRIC REACTOR
This process utilizes a vertical reactor heated by electrodes implanted
in the walls to pyrolize organic wastes. The process is offered by two
companies, Thagard Research, which developed the process, and Huber
Corporation, which acquired rights to the process and introduced several
modifications.
The process utilizes a reactor with a core enclosed by porous refractory
material. Carbon electrodes implanted in the wall of the reactor heat
the reactor core to radiant temperatures. Heat transfer is accomplished
by radiation coupling from the core by means of a gaseous blanket formed
by flowing nitrogen through the walls of the core. In the process organic
compounds are rapidly heated to temperatures in the range of 3800° -
440UQF and destroyed.
In the Huber process product gas and waste products pass through
two port reactor treatment zones which provide for additional exposure
to high temperatures and for product gas cool down.
Suitable Wastes
The process is primarily designed to pyrolize organics attached to
particulates such as carbon black or soil. However, the developer claims
that recent tests have shown the process is also effective for liquid
refractory waste streams such as carbon tetrachloride.
Throughput/Capacity
The Huber unit will process from 75 to 125 pounds of contaminated
solids per minute. Hard numbers are not available for pure liquids.
However, capacity would be less.
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Costs
Costs information is not available. However, the Huber Corporation
claims the cost of operating a unit is comparable to conventional incineration,
Anticipated Date of Commercialization
Mid summer 1985.
Environmental Data
Huber recently completed a test of the process which showed that DRE's
far in excess of the 99.99% RCRA requirements can be obtained.
MOLTEN SALT
Process Description
Molten-salt destruction is a method of burning organic material while,
at the same time scrubbing in situ any objectionable byproducts of that
burning and thus preventing their emission in the effluent gas stream.
This process of stimulating combustion and scrubbing is accomplished by
injecting the material to be burned with air or oxygen-enriched air,
under the surface of a pool of molten sodium carbonate. The melt is
maintained at temperatures on the order of 90QOC, causing the hydrocarbons
of the organic matter to be immediately oxidized to carbon dioxide and
water. The combustion byproducts, containing such elements as phosphorous,
sulfur, arsenic and the halogens, react with the sodium carbonate. These
byproducts are retained in the melt as inorganic salts rather than being
released to the atmosphere as volatile gases. In time, inorganic products
resulting from the reaction of organic halogens, phosphorous, sulfur,
etc., build up and must be removed from the molten bed to retain its
ability to absorb acidic gases. Ash introduced by the waste must be
removed to preserve the fluidity of the melt. An ash concentration in
the melt of about 2U% by weight provides an ample margin of safety to
maintain melt fluidity.
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Suitable Wastes
The Molten Salt process is designed for solid and liquid waste streams.
It is especially applicable to highly toxic wastes and to highly halogenated
waste streams. Waste streams with high percentages of ash and non-combustibles
are not very good for the system since such waste makes it necessary to replace
the molten bed more often.
Process Throughput
A new pilot scale facility capable of processing 80 to 200 pounds of
waste per hour has recently been constructed. No commercial scale units have
been built to date.
Costs Per Unit Processed
No cost data available.
Anticipated Date of Commercialization
This process has been demonstrated successfully with many different
liquids and slurries, and is currently available for commercial use. No
commercial units are currently operational.
Environmental Impacts
A variety of chemical wastes have been successfully incinerated in
bench-scale molten salt combustors. Destruction efficiencies for organic
chemicals, pesticides and chemical warfare agents ranged from 99.99% to
99.999999%. Tests were performed by Rockwell International for the State
of California (2).
PLASMA ARC TECHNOLOGY
One of the emerging technologies receiving much attention is plasma
arc technology, which is a process using the extremely high temperatures
of plasmas to destroy hazardous waste.
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A plasma is a substance consisting of charged and neutral particles
with an overall charge near zero. A plasma arc is generated by electricity
and can reach temperatures up to 50,0000p. When applied to waste disposal,
the plasma arc can be considered as an energy conversion and energy
transfer device. The electrical energy is transformed into a plasma. As
the activated components of the plasma decay, their energy is transferred
to the waste materials exposed to the plasma. The wastes are ultimately
decayed and destroyed as they interact with the decaying plasma.
In a mobile prototype of a patented process, a five hundred kilowatt
plasma device is fitted to one end of a stainless steel reaction chamber
and mated to a hollow graphite core to form an atomization zone. Residence
time in this atomization zone is approximately five hundred micro-seconds.
The reaction chamber serves as the equilibration zone where the atomized
species recombine to form new simple non-hazardous products. This zone
is equilibrated at a temperature range of 1200-1800 Kelvin and the residence
time in this zone is approximately one second. All hardware is designed
to be located within a forty five foot long moving van type trailer.
Suitable Waste Streams
Plasma arc technology is designed for highly toxic liquid waste streams,
The operation of the process is not significantly impacted by the degree of
halogenation of a waste stream.
Process Throughout
A unit currently being demonstrated through partial support of the
Agency will process 600 Ibs. of waste per hour. This unit is sized to be
operated commercially.
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Cost Per Unit of Waste Processes
Cost figures not available.
Analytical Date of Commercialization
A commercialization scale unit is to be operating within 1-3 years.
Environmental Data
No environmental data from a commercial scale unit is currently
available. A current demonstration in the State of New York is to produce
information on destruction efficiency, and characterization of emissions.
WET AIR OXIDATION
Process Description
Wet air oxidation is a process for oxidizing organic contaminants in
water. Wet air oxidation refers to the aqueous phase oxidation of dissolved
or suspended organic substances at elevated temperatures and pressures.
Water, which makes up the bulk of the aqueous phase, serves to modify
oxidation reactions so that they proceed at relatively low temperature
(35U°F to 650°F) and at the same time serves to moderate the oxidation
rates removing excess heat by evaporation. Water also provides an excellent
heat transfer medium which enables the wet oxidation process to be thermally
self-sustaining with relatively low organic feed concentrations.
An oxygen-containing gas, usually air, is bubbled through the liquid
phase in a reactor used to contain the process, thus the commonly used
term "wet air oxidation" (WAD). The process pressure is maintained at a
level hiyh enough to prevent excessive evaporation of the liquid phase,
generally between 300 and 3000 psi.
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A wastewater stream containing oxidizable contaminants is pumped to
the system by means of a positive displacement-type pump. The wastewater
passes through a heat exchanger which preheats the waste by indirect heat
exchange with the hot oxidized effluent. The temperature of the incoming
feed is increased to a level necessary to support the oxidation reaction
in the reactor vessel. Air and the incoming liquid are injected into the
reactor where the oxidation begins to take place. As oxidation progresses
up through the reactor, the heat of combustion is liberated, increasing
the temperature of the reaction mixture. This heat of oxidation is
recovered by a heat exchange that utilizes the incoming feed. Thus it is
thermally a self-sustaining operation. After energy removal, the oxidized
effluent, comprised mainly of water, carbon dioxide, and nitrogen is
reduced in pressure through a specially designed automatic control valve.
Of all variables affecting wet air oxidation, temperature has the
greatest effect on reaction rates. In most cases, about 300°F is the
lower limit for appreciable reaction, about 482°F is needed for reaction
to the 80 percent reduction of Chemical Oxygen Demand (COD) range, and at
least 572°F is needed for 95 percent reduction of COD or better reaction
within practical reaction time.
The use of catalysts have been evaluated for improving the destruction
efficiency of WAO. However, there are no commercial application of WAO
utilizing a catalyst at the present time.
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Suitable Wastes
The process is designed primarily for very dilute aqueous wastes
which are too dilute to incinerate economically yet too toxic to treat
biologically. WAO also has application for inorganic compounds combined
with organics. It is not very effective in oxidizing highly refractory
chlorinated organics.
Process Throughput
An existing unit is being demonstrated on various waste streams in
California. This unit can process up to 10 gallons per minute.
Cost Per Unit of Waste Processed
A cost range of b cents to 1U cents/gallon of waste processed is cited
by one of the developers of a wet oxidation process. These costs are for
the 10 gallon per minute system. Costs for larger systems are not available.
Anticipated Date of Commercialization
Technology is available now. Wider adoption could occur within the
next two years, however, application would be limited to aqueous wastes
that cannot be economically incinerated. Adoption will also depend on
the destruction efficiency and whether post treatment is required.
Environmental Effects
Limited environmental data from bench-scale tests is available.
However, the USEPA-ORD, under a cooperative agreement with the State of
California, is currently evaluating a full-scale (10 GPM) unit (3). All
of the full scale tests have not been completed; wastes being tested
include: cyanide wastes, phenolic wastes, sulfide wastes, non-halogenated
pesticides and solvent still bottoms.
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MOLTEN GLASS INCINERATION
Process Description
The integral part of this process is an electric furnace approximately
22' long and 3' wide that has a pool of molten glass covering the bottom.
This type of furnace is used extensively in the glass manufacturing industry
to produce glass. When used as a waste incinerator the extremely high
temperatures in the combustion chamber destroy organic waste streams.
Waste materials, both combustible and non-combustible, are charged
directly into the combustion chamber above the pool of molten glass. The
waste can either be contained in fiberboard boxes, or uncontained in loose
form. Electrodes immersed in the pool maintain the temperature of the
pool of molten glass above 2300° (1260°C). Combustible waste are oxidized
above the pool, and inorganics and ash fall onto the pool where they are
melted into the glass. Combustion off gases pass through ceramic filters
which are themselves charged into the molten glass when they are no
longer effective.
Suitable Wastes
Any combustible waste is acceptable. Degree of halogenation is not a
consideration. However scrubbers will be required for HC1 emissions.
Process Throughput
Since this technology is used in the glass manufacturing industry,
existing units are capable of processing from 10U pounds per hour to 21,000
pounds of raw materials per hour. However these have not been demonstrated
as devices for destroying hazardous wastes.
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Cost Per Unit of Waste Processed
No cost figures were available.
Environmental Effects
Although no actual data on hazardous waste is available, the fact
that the unit uses ceramic filters for air emissions and encapsulates the
inorganic residues in a glass slag seems to indicate that environmental
emissions would be minimal and at least comparable to incineration.
However, this remains to be tested.
SUPERCRITICAL WATER
Process Description
In the supercritical water process an aqueous waste stream is subjected
to temperatures and pressures above the critical point of water, i.e. that
point at which the densities of the liquid and vapor phase are identical.
(For water the critical point is 379°C and 218 atmospheres). In this super-
critical region water exhibits unusual properties that enhance its capability
as a waste destruction medium. Because oxygen is completely miscible with
supercritical water, the oxidation rate for organics is greatly enhanced.
Also inorganics are practically insoluble in supercritical water. This
factor allows the inorganics to be easily removed from the waste streams.
The result is that organics are oxidized extremely rapidly and the resultant
stream is virtually free of inorganics.
A patented process has been developed that incorporates the properties
of supercritical fluids to oxidize organic contaminants in aqueous streams.
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The following Is a brief summary of the process.
a. Waste is slurried with make-up water to provide a mixture of 5
percent organics. The mixture is heated using previously processed
supercritical water and then pressurized,
b. Air or oxygen is pressurized and mixed with the feed. Organics are
oxidized in a rapid reaction. (Reaction time is less than 1 minute.)
For a feed rate of 5 percent by weight of organics, the heat of
combustion is sufficient to raise the oxidizer effluent to 500°C.
c. The effluent from the oxidizer is fed to a salt separator where
inorganics are removed by precipitation.
d. Waste heat from the process can be reclaimed to provide sufficient
energy for power generation and high pressure steam.
Suitable Waste Streams
Supercritical water processes are designed for aqueous waste streams
with high levels of inorganics and toxic organics. The system's capability
for treating aqueous waste streams with high percentages of halogenated
material has not yet been demonstrated.
Process Throughput
A unit is currently being demonstrated to treat from 1,000 to 23000
gallons per day of aqueous wastes.
Cost Per Unit of Waste Processed
No cost figures are available.
Anticipated Date of Commercialization
The developer of the system claims that commercial scale units will
be available in 1-3 years.
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Environmental Impact
Bench scale tests on a variety of hazardous materials have indicated
OHE's of 98.5 to 99.8. A demonstration unit is currently being evaluated
by industry, and will generate environmental data for a larger unit.
BIOLOGICAL TREATMENT
Biological treatment encompasses the use of living organisms or their
by-products, such as enzymes, to effect destruction or detoxification of
hazardous waste. Procedures ranging from acclimation to genetic engineering
are used to develop appropriate organisms to accomplish the degradation
process. In most cases a "reactor" of some type is constructed to provide
a suitable environment for the required biochemical reactions. The
reactor may be as simple as a storage lagoon or as complex as a fermentation
tanks, with ability to control temperature, pH, moisture, nutrients,
oxzygen, off-gases, mixing with the waste and/or separation from the
treated material. Land treatment and composting are low tech applications
of biological treatment. Most biological treatment systems are suitable
only for treatment of very dilute aqueous wastes (organic content <1% by
weight) or for detoxification of contaminated soils or sediments, especially
when the detoxification can be accomplished while leaving the soil or
sediment essentially in place. No significant use of biological treatment
for combustible liquid hazardous wastes is anticipated in the foreseeable
future.
The potential environmental impacts of biological treatment are numerous
and sometimes difficult to predict. Biological processes tend to be slow,
thus contaminants with even low to moderate volatility can be transferred
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to the atmosphere from lagoons, composting facilities, land treatment or
spray irrigation. Pollutant transfer by air stripping is an important
concern in any aerated biological treatment process. Even very low
levels of some toxic compounds may remain in biological treatment residuals
could warrant regulation. The pollutants are too dilute to be effectively
used as a food source by suitable organisms in activated sludge, composting,
anaerobic digestion or land treatment systems. The eventual use or
disposal of the biological residuals thus becomes a hazardous waste
concern. The complexities of biological processes result in frequent
upset or out of control conditions and corresponding reductions in pollutant
removal efficiencies. Such excursions could not be tolerated when treating
hazardous wastes. Finally, estimating the environmental impacts of
introducing genetically engineering organisms into the open environment
is a difficult and controversial problem. It is unlikely that biological
treatment based upon genetically engineered organisms will rapidly develop
for commercial use.
Chemical Treatment
Major chemical treatment processes applied to hazardous waste include
chemical oxidation or reduction, hydrolysis, neutralization and photolysis.
Precipitation as a separation technique may be accomplished by using one
or more of these treatment processes. Common applications for hazardous
waste treatment are oxidation of phenol or cyanide in aqueous wastes,
neutralization of corrosive wastes such as pickling liquors or caustic
wastes, and detoxification of contaminated soils. Combustible liquid
hazardous wastes are generally not good candidates for chemical treatment,
although dehalogenation may in special cases result in the recycling or
recovery of a waste.
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Cost and environmental impact are important considerations in applying
chemical treatment technology.
The cost of reactants can be significatn if large quantities of the
target pollutant are to be processed. Often, large doses of reactants
are necessary to destroy even low concentrations of hazardous constituents,
because of interference from non-hazardous components or, as is often the
case with ozonation, the difficulty of effectively mixing the reactants
with the waste to achieve stoichiometric amounts of oxidant. For example,
the necessity of using large doses of degalogenating chemicals on dioxin
contaminated soils presents a current researcn problem of how the
dehaloyenation reaction can be enhanced to effectively use near stoichiometric
amounts of reactants.
Operational and capital costs are also a factor. Energy requirements
and thus costs increase as additional temperature and pressure are
required. As a result, capital costs also increase because high temperature,
pressure and corrosivity mandate the use of exotic construction materials.
Chemical treatment poses several problems with regard to environmental
impact. The safety of reactions which produce heat or emit gases can be
a significant problem. Also, the reaction by-product may be hazardous.
The process may also cause disposal problems, because adding chemicals to
waste often increases the amount of material ultimately requiring disposal.
Eventhouyh these detoxified residuals are non-hazardous, their disposal
would be costly and could present a public relations problem.
Therefore, in terms of cost and environmental impact, incineration
of combustible hazardous waste will continue to have advantages over
chemical processes currently being used or under development.
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APPENDIX A
EMERGING PROCESSES CONSIDERED
PROCESS
PROCESS IS DESIGNED TO:
INCLUSION/EXCLUSION CRITERIA
DESIGNED FOR AVAILABLE INNOVATIVE
LIQUID WASTE WITHIN 5 TECHNOLOGY
STREAM YEARS
*1. High Temp. Electric
Reactor
*2. Molten Salt
Reactor
3. Rotary Pyrolyzer
4. Low Temp. Fluid Bed
5. Multi Solid Fluid
Bed
*6. Molten Glass
7. Catalytic
Dehalogenation
8. High Temp. Pyrolysis
with Q
pyrolize organics off surface of
particles using high temp, radiant
heat
destroy organics using a molten bed
of sodium carbonate
detoxify organic sludges in a quiescent
environment
utilize limestone and a catalyst with
high velocity fluidizing air in fluid
bed processes
destroy solids and liquids in a dense
bed of large particles
destroy organics using glass manufac-
turing furnace
to replace halogen atoms with hydrogen
atoms in presence of a catalyst
destroy organics in a saturated oxygen
furnace
X
X
X
X
X
* Process Selected
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PROCESS
PROCESS IS DESIGNED TO:
INCLUSION/EXCLUSION CRITERIA
DESIGNED FOR
LIQUID WASTE
STREAM
AVAILABLE
WITHIN 5
YEARS
INNOVATIVE
TECHNOLOGY
to
O
9. Corona Glow Processing
10. Fluid Phase Oxidation
11. Circulating Bed Waste
12. Aqueous Phase Alkaline
Destruction
13. Fluid Bed Incinerator
14. Microwave Plasma
Detoxification
15. Plasma Temp.
Incinerator
16. Mobile Incinerator
17. O'Connor Combustor
*18. Plasma Arc
utilize a plasma with a high volumetric
flow rate of process gas
destroy toxic organics in aqueous waste
streams in the presence of oxygen
utilize a hot cyclone chamber in
conjunction with a traditional packed
bed incinerator
convert organic solids to oil in a thermo-
chemical process
destroy homogenous waste in a traditional
fluidized bed reactor
utilize microwaves within a plasma to
oxidize toxics
burn PCB waste in a pressurized stream
of preheated oxygen
rotary kilns or liquid injection units
on wheels
advanced traditional incinerator technology
using a hollow water-cooled steam cylinder
extremely high temperatures produced
by plasma generators
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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PROCESS
PROCESS IS DESIGNED TO:
INCLUSION/EXCLUSION CRITERIA
DESIGNED FOR
LIQUID WASTE
STREAM
AVAILABLE
WITHIN 5
YEARS
INNOVATIVE
TECHNOLOGY
*19. Wet Oxidation
*20. Supercritical Fluid
Oxidation
21. "Cyclin" Cyclone
Incinerator
22. Consertherm Rotary
Kiln Oxidizer
23. Joule-Heated Glass
Me Her
24. Fast Rotary Reactor
25. Burlesan/Kennedy
Submerged Reactor
use high temperatures and pressures to
oxidize organic contaminants in aqueous
streams
utilize a high temp, high pressure wet
oxidizer
include a potential-like flow at pre-
mixed fuel, waste, and air within a
combustion chamber
modify a conventional rotary kiln
approach thermal destruction
utilize the material being heated as
the resistance element in an electrical
circuit
increase contact between solids and gases
by modification of rotary kiln design
utilize underground wells to achieve
conditions for supercritical water reactor
X
X
X
X
X
X
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REFERENCES
EPA 530/SW-84-005, April 1984; "National Survey of Hazardous Waste
Generators and Treatment, Storage and Disposal Facilities Regulated
under RCRA in 1981".
EPA/California Cooperative Agreement R808908, August 1981; "Molten
Salt Destruction Process: An Evaluation for Application in California",
EPA/California Cooperative Agreement Project, "Demonstration of
Wet Air Oxidation of Hazardous Waste", Proceedings of Tenth Annual
EPA Hazardous Waste Research Symposium, April 1984.
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GPO 914-025
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