NEW WASTE TECHNOLOGIES
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A growing national concern over contamination of the soil, the
water supply, and even the air we breathe is one of the driving
forces behind current efforts by government and industry to more
aggressively address the problems associated with hazardous waste
management.
Several factors have contributed to this increased concern over
environmental contamination. Recent studies have shown that many
commonly used compounds, previously thought to be harmless, are
powerful pathogens, mutagens, and carcinogens. Also, as more is
learned about the effects of chemical pollutants on the
environment, researchers are finding that levels of contamination
previously considered insignificant can have serious environmental
consequences.
These findings both reveal a threat and present a challenge. The
threat is obvious. We are inexorably tied to the environment--we
cannot afford to kill it. The challenge is to stem the tide of
waste and to develop ways of cleansing and reclaiming areas that
have already been fouled.
To meet this challenge, ORNL researchers in a range of disciplines
are developing the tools needed to determine the type and extent of
environmental contamination, to remove those contaminants from the
environment, and to monitor potential waste sources to prevent
further releases. A number of these projects are described below.
PUTTING PCBS ON THE MICROBIAL MENU
For years, polychlorinated biphenyls (PCBs) were considered ideal
insulating fluids for transformers and other electrical equipment
because they are nonconductive, inert, and chemically stable.
After years of widespread use, these chemicals were determined to
be potential carcinogens, and their production was banned in 1977.
By that time, PCB contamination of soil and water from the
deterioration of discarded equipment and discharges from
manufacturing processes had become an environmental concern.
Further evidence of the serious nature of the problem is DOE's
$350-million phased plan to clean up PCB contamination at the K-25
Site in Oak Ridge and uranium enrichment plants in Paducah,
Kentucky, and Portsmouth, Ohio.
Ironically, the properties that make PCBs good insulators--their
stability and lack of reactivity--are also the properties that make
them so long-lasting in the environment. Until recently,
conventional wisdom was that PCBs were impossible to degrade
biologically. However, in the last decade, research has shown that
certain microbes can break down PCBs into harmless substances, but
only slowly and selectively.
PCBs are a large class of chlorinated (chlorine-containing)
biphenyl chemicals, known as congeners, that differ primarily in
the number of chlorine atoms they contain. As a result, PCB
contamination may involve several different congeners, each of
which is treated differently by different microbes.
HOW MICROBES DEGRADE PCBS
There are two pathways for microbial PCB degradation. In an
aerobic, or oxygen-containing, environment, congeners containing
fewer than five or six chlorine atoms can be degraded by aerobic
microbes that use enzymes to add oxygen atoms to the congeners.
Oxidation of these congeners breaks them down into carbon dioxide
and water.
"The more chlorine atoms a molecule has, the more difficult it is
to oxidize," says Terry Donaldson of the Chemical Technology
Division (CTD). "Molecules with more than four or five chlorine
atoms are very difficult to oxidize." The inability of aerobic
organisms to degrade these highly chlorinated molecules may be
partly the result of "steric hindrance"--the presence of so many
chlorine atoms prevents the microbial enzymes from getting close
enough to the biphenyl backbone of the molecule to oxidize it.
Fortunately, researchers have found that certain anaerobic
microbes--organisms that exist in an oxygen-free environment--can
remove chlorine atoms from highly chlorinated molecules.
Once the molecules have been stripped down to fewer than four or
five chlorine atoms, they can be oxidized by aerobic organisms.
For the past several years, Mark Reeves and Betty Evans, also of
CTD, have been working in the laboratory to isolate microorganisms
that can degrade a broader range of congeners more efficiently and
to find ways of enhancing their performance. They have searched
PCB-contaminated soil on the Oak Ridge Reservation (ORR) for
microorganisms with a particular talent for degrading PCBs and have
found several likely candidates.
"Looking for these organisms in PCB-contaminated areas is a good
strategy," says Donaldson. "The microorganisms at contaminated
sites have had time to adapt to the presence of PCBs and are more
likely to have the biological qualities we're looking for."
The microbial cultures found on the ORR consist of several types of
organisms, but no attempt has yet been made to culture a pure
strain of microbe. "The advantage of using a mixed culture,"
Donaldson says, "is that a mixed population of microbes can
probably degrade a wider range of PCB compounds."
To obtain optimum performance from these microorganisms, Reeves and
Evans studied the effects of various nutrients on microbial
metabolism by varying their diet. As in humans, the type and amount
of nutrients microbes receive affect their metabolic behavior. Most
microbes require nitrogen, potassium, phosphorus, and trace levels
of minerals, metals, vitamins, and other nutrients. "Figuring out
how to manipulate metabolism is an art," says Donaldson. "The
relationships between microbe metabolism and diet are not very well
understood."
WORKING TOWARD FIELD TESTS
Before field testing begins at ORNL, small-scale bioreactor tests
of remediation techniques are being used to investigate the
dechlorinating effect of anaerobic microbes. The bioreactors are
1-L glass containers filled with a soil slurry--a mixture of soil,
water, and microbes. These containers are generally spiked with a
particular PCB congener, and samples are taken and analyzed every two
to four weeks to measure the amount of dechlorination that has taken
place. "The degradation process is slow," Donaldson says. "An experiment
may take six to nine months." However, results from recent tests indicate
it may be possible to accelerate the degradation rate.
The goal of this research is to accelerate the development and
testing of new technologies for the biodegradation of PCBs to meet
Martin Marietta Energy Systems cleanup standards, which are as low
as 2 parts per million in solid materials.
"When we get this technology into the field, remediation techniques
are likely to be site-specific," says Donaldson. "One approach to
treatment would be to place the contaminated soil in a tank along
with water, nutrients, and the microbial culture. This approach
would let us control conditions closely, but it's cost-intensive.
As we gain experience with the process, we want to be able to treat
the soil in place."
BATTLING PBBS IN THE SOUTH PACIFIC
In 1944, the U.S. Army drove the Japanese from Kwajalein Atoll in
the South Pacific. Nearly fifty years later, the Army is fighting
a different kind of battle on Kwajalein--against potential
environmental contamination resulting from its decades-long
presence on the island.
One of several environmental concerns is a collection of 100
electrical transformers at the U.S. Army Kwajalein Atoll. This
equipment is filled with about 15,000 gal of askarel, an insulating
oil containing high levels of polychlorinated biphenyls (PCBs).
The Army is considering several options for destroying the
contaminated oil, including shipping it back to the mainland for
destruction in a specially designed incinerator, bringing a
portable incinerator to Kwajalein, or using a noncombustion
chemical technology, such as the base-catalyzed decomposition (BCD)
process.
The BCD process is currently being developed under a set of
agreements among ORNL; S. D. Myers, Inc.; DOE's Hazardous Waste
Remedial Actions Program (HAZWRAP); and the Environmental
Protection Agency (EPA).
Cliff Brown and Lloyd Youngblood, both of ORNL's Chemical
Technology Division, are working under a cooperative research and
development agreement (CRADA) between Martin Marietta Energy
Systems, Inc., and S. D. Myers to refine the process so it can be
scaled up and moved out of the laboratory. "Our goal," says Brown,
"is to get this technology in the field and demonstrate it on
Kwajalein."
S. D. Myers' staff have a wealth of experience in building and
operating transformer oil decontamination systems, and they
specialize in decontaminating and recycling old transformers. The
CRADA combines this experience with ORNL's chemical engineering
expertise and ability to select and conduct the development
activities necessary to design a BCD system. After the technology
has been successfully demonstrated on Kwajalein, S. D. Myers will
be able to market it in the private sector. Several organizations
have already expressed interest in a system capable of treating
oils containing high levels of PCBs.
DOE also has a vested interest in seeing BCD technology through to
its fruition because of its potential for treating the large
quantities of PCB-contaminated mixed waste (containing both
radioactive and hazardous chemical wastes) sludges, soils, and oils
stored at Oak Ridge and other DOE sites.
The BCD process was originally developed by the EPA at its Risk
Reduction Engineering Laboratory in Cincinnati, Ohio. In this
process the PCB-contaminated oil; an uncontaminated "donor" oil,
used as a source of hydrogen atoms; sodium hydroxide; and a carbon
catalyst are reacted together at high temperature. "As a result,"
says Youngblood, "hydrogen atoms from the donor oil take the place
of the chlorine atoms on the PCB molecules, leaving environmentally
manageable biphenyl molecules. The sodium then reacts with the
displaced chlorine atoms to form salt." Plans are for waste oil
from the process to be recycled and burned to provide the heat
(approximately 300øC) required to sustain the reaction.
BCD processing potentially extends the range of noncombustive PCB
decontamination technologies by several orders of magnitude.
Conventional technologies can decontaminate oils with PCB
concentrations of a few thousand parts per million or less. The BCD
process, on the other hand, can potentially handle oils containing
concentrations of 100,000 parts per million or greater.
The most obvious advantage to using the BCD process is that the
destruction of the PCBs can be accomplished on-site, avoiding the
risk involved in shipping thousands of gallons of hazardous
material 6900 kilometers (4300 miles) to the mainland. Other
factors to be considered by the Army before choosing a solution to
its PCB problem are the efficiency of the process and its cost of
implementation.
Current research at ORNL involves bench-scale studies of the
effects of changes in temperature, reaction time, mixing, and other
process variables. "Once these variables are understood," says
Youngblood, "the next step will be to optimize the chemistry of the
process and work out the details of transferring the process from
the laboratory to the field."
BIOREMEDIATION OF TCE THROUGH CO-METABOLISM
Trichloroethylene (TCE), a potential carcinogen, was widely used as
an industrial degreaser for cleaning metals and as a dry-cleaning
agent until it was classified as a hazardous waste by the Resource
Conservation and Recovery Act (RCRA) of 1976.
Because RCRA regulations greatly increased the costs of disposing
of TCE, most uses of the chemical were discontinued in the United
States by the early 1980s.
Up to that point, most TCE was disposed of in a fairly haphazard
manner. "For years," says Steve Herbes of the Environmental
Sciences Division, "practically every metal machining shop,
automotive repair shop, and dry cleaner in the country used TCE,
and many of them disposed of it improperly when they were done with
it." As a result, TCE is now one of the most commonly found
groundwater contaminants in the United States. It is also found at
most DOE sites, including the Oak Ridge K-25 Site.
Researchers in ORNL's Environmental Sciences and Chemical
Technology divisions are testing two innovative biological
techniques for removing TCE from groundwater. In a process known as
co-metabolism, digestive enzymes produced by certain microorganisms
are applied to the task of degrading contaminants, such as TCE.
"Under natural anaerobic (oxygen-free) conditions, such as those
found in groundwater, TCE degrades to vinyl chloride, an even more
toxic compound," says Herbes. "Our goal for co-metabolic
remediation is to encourage degradation of TCE along pathways that
result in less harmful products."
Two basic groups of microorganisms are involved in co-metabolism of
groundwater contaminants. The first is methano-trophs--bacteria
that live on methane. The enzymes these bacteria produce to digest
methane can also metabolize TCE. When methane and TCE-contaminated
water are added to a bioreactor containing methanotrophic bacteria,
their digestive enzymes break down both the methane and the TCE.
The TCE is first broken down into TCE epoxide and then into other
products that can be further degraded by normal biological
processes.
To prove the usefulness of this technology, the project team is
demonstrating the co-metabolism process at the K-25 Site with the
support of DOE's Environmental Restoration and Waste Management
Program's Office of Technology Development. The heart of the
project is a specially modified bioreactor, on loan from the U. S.
Air Force Civil Engineering Support Agency, that houses
methanotrophic bacteria cultures. The bioreactor consists of two
reactor columns that are 2.13 m (7 ft) tall and 40 cm (16 in.) in
diameter and are filled with polypropylene support material for the
cultures to grow on. A control system is mounted with the columns
on a portable platform, which is housed in a trailer at the K-25
Site. The goal of the project is to treat seepage from a series of
pits used in the 1980s for the disposal of a variety of organic
compounds, including TCE.
The drainage from these pits amounts to several liters per minute,
a fraction of which is diverted for use in the demonstration
project. Before the water can be pumped into the bioreactor,
however, it must pass through an air oxidation system to decrease
its iron content because the high level of iron in the seepage
would eventually foul the bioreactor system. As the seepage passes
through and out of the bioreactor, it is collected in a storage
tank that is periodically emptied at K-25's Central Neutralization
Facility.
Bench-scale bioreactors, developed by Terry Donaldson and Jerry
Strandberg of ORNL's Chemical Technology Division, were first used
to demonstrate the feasibility of this technology and to evaluate
various methanotrophs. The cultures selected for use in the K-25
demonstration project were evaluated on the basis of their
stability and level of activity over time. Of the three cultures
finally selected, one was from groundwater at the K-25 Site and two
were from DOE's Kansas City Plant.
The second group of microorganisms involved in co-metabolic
research is bacteria that consume toluene or phenol. Herbes and his
project team have been working closely with a private biotechnology
firm to develop a culturing and bioreactor system for determining
the feasibility of employing these bacteria in a bioremediation
system. Like their methanotrophic cousins, these bacteria produce
enzymes that metabolize TCE as a side-effect of their normal
metabolic processes.
In initial bench-scale tests, this process removed up to 80% of the
TCE from simulated groundwater containing a mixture of organic
contaminants similar to that at the K-25 Site.
A field test of this technology is planned for the K-25 Site for
the summer of 1992. "At the end of this test," says Herbes, "we
will have data that provide a head-to-head comparison of the two
most promising techniques for the bioremediation of TCE in
groundwater. There are many possible applications within the DOE
system for this technology. It could be scaled up and used as the
treatment of choice at K-25 or other DOE sites."
BIOLUMINESCENT BACTERIA: ANOTHER BRIGHT IDEA
Since petroleum-eating microbes were used to help scour the beaches
of Alaska's Prince William Sound in the aftermath of the Exxon
Valdez oil spill, the world has gotten used to the idea of using
microscopic "bugs" to clean up environmental contamination.
But do you ever wonder if there's a way to tell if these critters
are eating or not? Or if they're undernourished? Or too hot to
work? These are some of the questions that researchers at ORNL and
the University of Tennessee are addressing as they develop a new
technology to monitor the efficiency of micro-organisms in cleaning
up soil and groundwater.
In a project originally sponsored by the Laboratory Director's
Research and Development Fund, ORNL researchers have been
developing bioluminescent sensor technology to monitor bacteria as
they digest soil and groundwater contaminants, converting them to
relatively harmless substances, such as water and carbon dioxide.
Bioluminescent sensor technology is a method for detecting the
light emitted in the visible range by genetically engineered
bacteria that luminesce during metabolism of certain types of
chemicals.
Robert Burlage of the Environmental Sciences Division (ESD) started
experimenting with the bioluminescent, or "lux," genes while
working with Gary Sayler in the University of Tennessee's
Microbiology Department, where most of the initial work on the gene
was done. Burlage and his collaborator Tony Palumbo, also of ESD,
continue to collaborate with the university group with whom they
share "constructs"--combinations of the lux genes.
The lux genes were originally taken from bioluminescent bacteria
that live symbiotically with several species of deep-sea fish. It
is theorized that, because the bacteria are also a food source for
smaller fish, they are used by the larger fish as a sort of "bait"
to lure the small fish into attack range. This type of
bioluminescence is similar to that found in lightning bugs and
other insects.
Once the lux gene was isolated, researchers incorporated it into
genes from common soil and water bacteria that are activated in the
presence of toluene, a component of gasoline and other solvents,
and use it to indicate degradation of trichloroethylene (TCE), a
common industrial degreaser. This combination of genes causes the
genetically altered bacteria to light up when they metabolize
toluene or TCE. As a result, researchers can monitor the rate at
which the bacteria are metabolizing the TCE by measuring the amount
of light they give off.
"It also gives us a way to control their activity," says Palumbo.
"Depending on the light level, we add or withhold nutrients as
necessary." To respond to the bacterial culture's specific
nutritional needs, researchers are also developing strains of
bacteria that light up when the culture is lacking a particular
nutrient, such as nitrogen or phosphorus.
Almost all DOE sites have problems with toluene, TCE, or other
types of contamination resulting from disposal or spills of
gasoline and various chemicals used in research labs. A variety of
bacteria will be needed to metabolize the potpourri of chemical
wastes at some sites because each strain of bacteria eats only
certain types of waste. Because these bacteria light up
selectively, they can also be used to identify the types of
contamination present at the site.
"When we look at a site we ask two questions," Burlage says. "Does
it have bacteria that can handle bioremediation? The answer is
usually yes. Once the lux gene is added to these bacteria, the next
question is, `Are the genes that control the digestion of
contaminants turned on?'" If the genes are not turned on, causing
them to turn on may be as simple as adding nutrients or as
difficult as identifying other environmental factors that adversely
affect the bacteria. For example, one of the current challenges
facing Palumbo and Burlage is developing a construct that remains
active above 37øC, the temperature at which the current construct
turns off.
"To determine the optimum conditions for a bacterial culture," says
Palumbo, "you can either take all the nutrients away and add them
back one at a time until you see an improvement or you can look at
the soil chemistry and add things that you think are missing." The
culture's response is determined by its light level--the more
light, the more the bacteria are metabolizing. This luminescence,
too dim to be seen in normal room light, is measured by precision
light-sensing equipment.
Palumbo and Burlage's latest refinement of the system is a
cooperative effort with Tuan Vo-Dinh of the Health and Safety
Research Division to develop a fiber-optic containment system that
will enable researchers to lower a bioluminescent bacteria culture
into a well to monitor groundwater. To prevent release of
genetically engineered bacteria into the environment, the system
will include a container that admits groundwater without letting
the bacteria escape.
This type of apparatus would be used primarily as a continuous
monitor for waterborne contaminants; however, some of the same
technology also could be used for soil sampling. They expect to
have a prototype system working by the end of the summer of 1992.
"The applications of this technology are widespread," says Burlage.
"The only things that limit us are our imagination and knowledge."
SCREENING METHOD SPEEDS SEARCH FOR WASTE EATERS
So many bacteria and so little time. That was the problem faced by
researchers in ORNL's Environmental Sciences Division (ESD) when
asked to evaluate the ability of thousands of bacteria samples to
metabolize environmental contaminants common to many DOE sites.
At the time, standard diagnostic tests involved culturing each
strain of bacteria in a separate container, adding a contaminant,
and measuring the breakdown of the contaminant with a gas
chromatograph. This process was time-consuming and produced a
fairly large amount of waste requiring special handling and
disposal.
"The volume of testing requested by DOE's Subsurface Science
Program was more than we could handle using standard methods," says
ESD researcher Tony Palumbo. So--necessity being the mother of
invention--Palumbo and his colleagues spent about three months
developing and testing a new procedure for rapidly identifying
waste-eating bacteria.
The procedure uses palm-size plates containing 96 cm-deep cells
that are filled with bacteria, water, and a dye that is sensitive
to the bacteria's metabolic processes. The plates, along with a
beaker of a contaminant--usually toluene, xylene, or carbon
tetrachloride--are place in a dessicator and allowed to incubate
for 24 to 48 hours. The contaminant evaporates into the air inside
the dessicator and is eventually absorbed by the water in the
cells.
As the contaminant is absorbed, those bacteria that are able to
metabolize it remove carbon from its atomic structure. This action
frees hydrogen atoms, which react with the dye, changing its color
from clear to purple. Because not all bacteria metabolize the
contaminant equally well, many shades of purple may result--the
more contaminant that is metabolized, the deeper the color. A
"control" group of plates is incubated in ordinary air to ensure
that any changes in the experimental plates are caused solely by
the contaminants.
When the incubation is complete, the plates are placed in a
spectro-photometer that shines a light through each cell, measuring
its depth of color, or optical absorbance. These readings are then
translated into computer data. Only the bacterial strains in those
cell showing high levels of metabolic activity are required to
undergo more definitive gas chromatography (GC) testing. "With the
old method, every strain would undergo GC testing," says Palumbo.
"Using the screening procedure, only one in 50 is tested." This
increase in efficiency has enabled ESD researchers to evaluate 10
times as many samples as would have been possible using standard
methods. Also, the amount of waste generated by the screening
process is 10 to 50 times less than that produced by standard
methods.
Palumbo and his group are using this technique to study bacteria
gathered through DOE's Subsurface Science Program from contaminated
areas at the Savannah River Site, Idaho National Engineering
Laboratory (INEL), and Pacific Northwest National Laboratory, as
well as bacteria gathered at ORNL by ESD researchers. The bacteria
received from the Subsurface Science Program are cultured on the
surface of a substance known as agar, which provides the general
types of nutrients needed to keep bacterial colonies alive. To
increase the chances of isolating useful organisms, the ORNL
bacteria are cultured in a contaminant-enriched environment,
enabling contaminant-degrading organisms to thrive. "We're getting
very good results using this process," Palumbo says.
Palumbo indicates that the Subsurface Science Program may be
sampling bacteria sometime this year from ORNL's Melton Branch area
as part of its ongoing study of diversity in bacterial communities.
ESD researchers are also working with INEL on a related project
using many of the same techniques. This work, funded by DOE's
Office of Technology Development, involves finding bacteria that
metabolize chelators--compounds that attach themselves to
radionuclides, preventing them from reacting with other elements in
the environment and allowing them to move more freely through soil
and groundwater. Because chelators are used to clean
radionuclide-contaminated equipment, they have often been disposed
of along with radionuclides. Chelator-metabolizing bacteria would
be useful in slowing or stopping the migration of radioactive
contaminants.
WASTE-FIGHTING CONSORTIUM OF BACTERIA FOUND IN AMOEBAS
Researchers in ORNL's Health and Safety Research Division (HASRD)
spend a fair amount of time studying the effect of amoebas living
in ORNL's cooling towers and other warm water systems around the
Lab.
The reason for all this attention is simple--in their travels,
amoebas pick up a lot of bacterial hitchhikers, which can cause
illnesses in humans ranging from minor infections to tuberculosis
and Legionnaires disease. These bacteria are particularly hard to
eliminate because they live inside the amoebas, an arrangement
known as a consortium, giving the bacteria an extra layer of
defense against environmental stresses, such as toxic compounds and
changes in water temperature or pH.
While studying amoebas found in a well on the Oak Ridge
Reservation, researchers have found consortia made up of
microorganisms with a knack for bioremediation of hazardous wastes.
"The well was primarily contaminated with the industrial solvent
trichloroethylene (TCE)" says Arpad Vass of HASRD, "so we looked
for organisms in the well that could metabolize TCE. Because we
knew that some methanotrophic bacteria--those that live on
methane--degrade TCE, we took amoebas from the well and put them in
a methane atmosphere. In this environment, 20 different bacteria
were isolated from within the amoebas, one of which was able to
degrade TCE. This is one of the most, if not the most, complex
microbial consortium known in the world."
Vass says no one is sure why these consortia occur, but a high
degree of interdependence apparently exists among the organisms.
"The theory is," says Vass, "that one of the organisms metabolizes
methane making methanol. In turn, another metabolizes the methanol,
making formic acid, and so on. Most significantly, the consortia
can be maintained on mineral salts in a methane and carbon dioxide
atmosphere--an environment that will not support most of the
bacteria individually."
In addition to the TCE-degrading bacteria, researchers have also
identified bacteria that produce biodispersants (compounds that
break up oil and other organic contaminants) as well as others that
metabolize creosote and trinitrotoluene (TNT).
A number of applications have been proposed for members of this
unusually versatile group of microorganisms. The first field test
for the biodispersants will come this summer at DOE's Savannah
River Site (SRS) where a large amount of creosote-contaminated
lumber has been stockpiled over the years. Because creosote, a wood
preservative used on railroad ties, telephone poles, etc., is both
a toxin and a mutagen, SRS personnel have been searching for an
environmentally acceptable way to dispose of it. The ability of
biodispersants to remove contaminants from substrates like wood,
rock, or soil prior to biode-gradation makes them ideal candidates
for this job.
When mixed in relatively low concentrations (1-2%) with compounds
such as creosote, oil, or solvents, the biodispersant breaks these
substances into tiny droplets, known as a microemulsion,
dramatically increasing their surface area. Once a compound is
separated from its substrate in this manner, it can be more
efficiently degraded by other microorganisms. Also, using
microemulsions of solvents for various industrial processes could
potentially decrease the amount of solvent needed, reducing the
amount of waste produced.
Biodispersant-producing bacteria will be field tested in
conjunction with creosote-eating bacteria from both ORNL and SRS.
It is hoped that the results of these experiments will confirm
laboratory results supporting the effectiveness of bioremediation
of creosote contamination.
Other applications for biodispersant/bacteria combinations include
secondary oil recovery. When an oil well has been pumped "dry"
using conventional methods, it is often abandoned because of the
high cost of retrieving the residual oil. It is hypothesized that
pumping biodispersant-laden water into these wells could loosen the
oil from its rock substrate and allow it to be economically
recovered.
Another combination of biodispersant and bacteria has developed a
taste for TNT, first removing the explosive from its soil or water
substrate and then breaking it down into harmless components. This
process has shown a potential for removing soil and water
contamination around munitions plants and storage facilities--so
much potential, in fact, that it has been licensed to Oak
Ridge-based EODT Services, a company specializing in cleaning up
sites contaminated with explosives-related waste.
"Historically, our interest in amoebas has been pathogenic--related
to its ability to transmit disease," says Vass, "but since we found
this consortium, we've been broadening our interests and, at the
same time, helping the environment."
WASTE IDENTIFICATION: BUILDING A BETTER ION TRAP
Normally, when soil, water, or air sampling is done in the field,
samples are taken back to the lab, processed, and analyzed. Hours
or even days later, toxins contained in the samples are identified.
If other work depends on these test results, it waits, too.
Obviously, this is a problem begging for a cost-effective
solution--a system that can be used in the field to provide rapid
identification of specific toxins.
Enter ORNL's Analytical Chemistry Division (ACD). ACD researchers
have developed a portable mass spectrometry system for identifying
organic toxins in air, water, and soil samples in the field. It
consistently outperforms conventional analytical methods,
quantifying toxins in as little as two minutes down to the
parts-per-billion level.
The system was originally developed to detect volatile organic
solvents in soil and water, but its versatility has resulted in its
use for several other purposes, including "sniffing" air samples to
detect organic contaminants; detecting semivolatile pollutants,
such as pesticides; and directly analyzing body fluids for commonly
used drugs, such as cocaine, codeine, and nicotine.
"This technique is not expected to replace existing Environmental
Protection Agency methods," says ACD's Mike Guerin. "Its immediate
uses are screening for the presence or absence of certain chemicals
in the environment--this avoids having to send samples off to be
analyzed at $500 a shot--and repetitive monitoring of specific
pollutants, as is done in remedial action programs."
Starting with a commercially available ion trap mass spectrometer,
Guerin and his group have developed a system to introduce samples
directly into the ion-trap and standardized procedures for
analyzing samples. (For more information on this technique, see
Review, No. 4, 1991, p. 54.)
"People are primarily interested in the speed of the system and the
ability to do the analysis in the field," says Guerin. With this
system, checking a soil sample for carcinogenic solvents such as
benzene is as simple as mixing the soil with distilled water,
bubbling helium through the mixture to remove the solvent, and
routing the solvent-containing off-gases into the ion trap for
analysis. All of this is accomplished in a matter of a few minutes.
Work on the system was originally funded by the Department of
Defense as a method of quantifying organic compounds used as nerve
gases. "During the course of this work, we observed that this
technology might be applicable to environmental studies," says
Guerin. Further research proved the system's environmental
applications, and the cost of its continued development is now
underwritten by both DOE's Office of Technology Development and the
U.S. Army's Toxic and Hazardous Materials Agency.
In September 1991, the first field trial for the system was held at
DOE's Volatile Organic Compounds in Non-arid Soils Integrated
Demonstration test site at the Savannah River Site, a proving
ground that has horizontal well setups to demonstrate gas
extraction and bioremediation technologies. The trial was highly
successful and led to a second trial in March. During the March
trial, Marc Wise and Cyril Thompson, both of ACD, used a more
portable version of the system to monitor volatile organic
chemicals in the headspace of a groundwater well and in the waste
stream of a soil remediation process known as steam stripping.
Also, groundwater samples were analyzed in the field at a rate of
20 samples per hour.
As a result of their success at the test site, Guerin's group has
received funding from DOE's Office of Technology Development to
build another system for the Savannah River Site and train their
people to use it. "We want to know whether people who have not been
involved in the development of this technology can be trained to
use it," says Guerin. "We also want to see what kind of problems
the system will encounter if it is used intensively."
Guerin and his group are in the process of testing and calibrating
the system using pure compounds to determine its sensitivity and
durability. The current system is about the size of a two-drawer
filing cabinet and is mounted on a shock-absorbing base, so up to
two of the units can be transported into the field in a van. Also,
an even smaller version of the system is in the works.
Guerin is encouraged by the success of a recent unplanned test of
the system. In March 1992, an environmental remediation group was
pulling a tank out of a waste burial ground at ORNL when their
field monitor indicated a high level of organic contaminants. They
also noticed a strong odor and a hole in the bottom of the tank.
"They brought us some air and soil samples to analyze," Guerin
recalls, "and we had preliminary results for them within
minutes--even before they were back in their office. They were
pleased with that kind of response. Typically emergency response in
this business takes from several hours to as much as a day."
FIBER-OPTIC PROBE SHEDS NEW LIGHT ON GROUNDWATER CONTAMINANTS
One of the problems facing researchers interested in measuring
groundwater contamination is a lack of accessibility.
Groundwater is usually sampled by either lowering a collection
device down a well, taking a sample, and pulling it back up for
analysis or by using equipment that "sniffs" the air in the well to
identify the substances dissolved in the water.
The new and improved Derivative Ultraviolet Absorption Spectrometer
(DUVAS ) system, developed by John Haas of the Health and Safety
Research Division, solves the accessibility problem and a few more
problems besides. "To my knowledge," says Haas, "this is the first
fiber-optic spectroscopic device designed to identify and measure
volatile aromatic compounds directly in the groundwater."
Why direct sampling? By detecting and measuring the concentration
of groundwater contaminants directly, rather than by "sniffing" the
air above the water, the DUVAS system is able to more accurately
characterize groundwater contamination and avoid problems posed by
air sampling. "For example," says Haas, "because some chlorinated
hydrocarbons are heavier than water, they could go undetected by
air sampling above deep aquifers."
Direct sampling also enables researchers to use a technique known
as depth profiling--analyzing groundwater samples from various
depths. Depth profiling provides a more accurate assessment of
contamination by considering the possibility of varying
concentrations at different depths, rather than relying on a single
measurement.
Other advantages of using the DUVAS system for groundwater analysis
are that it offers
- Rapid analysis of groundwater contaminants in the field.
The system conducts a complete spectral analysis in less
than a minute.
- Increased safety. Because groundwater samples are not
removed from the well, workers are not exposed to chemical
and radioactive contamination.
- No chain of custody for samples and no storage concerns.
- Direct measurement of groundwater contamination, making
possible continuous monitoring.
NEW APPLICATIONS
DUVAS was originally developed in the early 1980s in response to
the push in the United States to replace fuels refined from
imported oil with coal- and shale-based alternatives. DUVAS was
designed to "sniff" air samples at synthetic fuel production plants
to detect carcinogenic vapors. The technology is now being applied
to the detection of aromatic hydrocarbons in groundwater.
Aromatic compounds are a particularly important class of chemicals
because of their presence in fuels (benzene and toluene) and their
use in the manufacture of paper (phenol) and insulators
(polychlorinated biphenyls, or PCBs). They are also widely used as
solvents, dyes, and explosives. Topping the list of organic
chemicals most commonly found at DOE sites, including ORNL, are
volatile aromatics, such as benzene and toluene, which are among
the most migratory components of fuels contaminating groundwater.
As a result, they are usually found farthest from the source of
contamination. DUVAS' sensitivity to these chemicals makes it
especially adept at detecting the first signs of groundwater
contamination.
The system is well suited for several applications, including
monitoring groundwater around underground fuel storage tanks or
disposal areas where solvents, such as benzene, are buried;
monitoring manufacturing discharges or chemical spills in surface
water; and monitoring reagent concentrations in chemical process
streams.
Over the past three years, Haas has received funding to update the
DUVAS system and to develop a new fiber-optic sampling probe. The
updated system is computer controlled, battery powered, and, at
about 9 kg (20 lb), it is completely portable.
Now that this phase of his research is complete, Haas is field
testing the system at Lawrence Livermore National Laboratory's
technology demonstration site where about 68,000 L (17,000 gal) of
gasoline have been spilled. There DUVAS will be used to monitor the
effectiveness of a remediation process known as dynamic underground
stripping. This technique uses a combination of steam injection and
electrodes to heat contaminated soil, turning water in the soil to
steam that drives out volatile contaminants. The ability of the
DUVAS system to provide continuous monitoring of the process in
underground wells at the site will help researchers determine the
effectiveness of the process and optimum conditions for "steam
cleaning" gasoline contamination out of the soil.
HOW IT WORKS
DUVAS is a spectroscopic technique based on the principle that
virtually all molecules absorb light. When light is shone on a
groundwater sample, the difference between the amount of light that
enters the sample and the light that passes through can be
measured. That difference is attributed to absorbed light.
Measuring the amount of absorbed light at many different
wavelengths produces an absorption spectrum. Because individual
compounds absorb light at characteristic wavelengths, the presence
of each chemical is indicated by its absorption spectrum.
The system operates by generating ultraviolet light in the range
from 230 nm to 350 nm and transmitting that light through an
optical fiber to a submerged probe. Ultraviolet light is used
because it is absorbed well by aromatic compounds.
When the light reaches the probe, it is focused through the
groundwater sample onto the detector. The probe is fitted with a
pump and a filter to ensure that water samples are free of dirt and
other particulate matter. Because ultraviolet light is not
conducted well by optical fiber, Haas incorporated a detector into
the probe and added an electronic feedback loop, rather than using
an optical fiber to transmit light from the probe back to a
detector on the surface. As a result, the required length of the
optic fiber is reduced by half, allowing the probe to be used in
wells as deep as 50 m. The information gathered by the detector is
then transmitted back to the surface where it is analyzed by a
laptop computer.
Concentrations of chemicals that absorb ultraviolet light weakly,
such as benzene, can be measured to as low as 100 parts per
billion. Strong absorbers, such as polynuclear aromatics, some of
which are potent carcinogens, can be detected at parts-per-trillion
levels. The system's analysis of contaminant concentrations is
typically accurate to within 1%.
Future enhancements of the DUVAS system include coupling the probe
with a camera to examine phenomena such as high-velocity
contaminant jets entering a well through small cracks in the well
casing. Modifying the system to accommodate analysis of contaminant
vapors in subsurface soil gas is also being considered.
LASER SYSTEM SIZES UP FERNALD WASTE PROBLEM
DOE's Fernald Feed Materials Production Center had a problem. In
1951, four domed storage silos were built, and two of them were
filled with radium-rich uranium ore residue, a by-product of
uranium processing at the site.
The ore was originally stored in the four-story-tall silos for use
in commercial processes, such as producing luminous paint for watch
and instrument dials. However, before the radium could be
recovered, its health hazards were discovered, and the ore was
reclassified as waste.
Four decades later, this material is still sitting in aging silos
20 m (60 ft) above the largest aquifer in the Midwest, and the
decaying radium continued to generate large amounts of radioactive
radon gas.
Under terms of a 1990 agreement between DOE and the Environmental
Protection Agency (EPA), the ore residue is scheduled to be removed
from the silos beginning in 1995 as part of the Fernald
Environmental Management Project. Until then DOE and EPA agreed to
suppress radon emissions by putting foot-thick bentonite clay caps
over the waste in the two silos. These caps contain the radioactive
gas until it decays into non-gaseous elements that are trapped in
the bentonite. The deadline for putting the cap in place was
December 1991.
In December 1990, Barry Burks of ORNL's Robotics and Process
Systems Division attended a meeting at Fernald on how robotic
technology could be used to help meet remediation needs at the
site. During a coffee break, Burks talked with a representative
from Parsons Engineering, one of the contractors remediating the
site. Parsons was looking for a way to ensure that the clay cap
they were preparing to install was at least a foot thick over the
entire surface of the waste.
ORNL engineers who had previously used laser range cameras to map
three-dimensional robot environments saw that this technology could
be used to build a three-dimensional surface map of the waste
before and after the bentonite was applied. A comparison of these
measurements would verify that the bentonite seal was at least a
foot thick. Having accurate information about the surface of the
waste would also keep the amount of bentonite used to a minimum.
This was especially desirable given that the contents of the silos,
both the ore residue and the bentonite, would be removed and
treated prior to permanent storage, beginning in 1995.
Burks suggested the surface-mapping technique to the group, and in
January 1991, this approach was officially adopted. Only 9 months
were left for the system to be developed, tested, and used to map
the surface of the wasteforms before the clay seal was scheduled to
be applied in October. "By the time we figured out what equipment
we needed and began detailed design, it was May," says Burks, "and
we had to have the system working by the end of July, so we could
test it at Fernald in August."
Several ORNL groups helped Burks' group meet the deadline. "The
Plant and Equipment Division helped us when we urgently needed
fabrication work done," says Burks, "and the Finance and Materials
Division gave us a warehouse where we roped off an area 24 m (80
ft) in diameter to use as a mock storage silo. Then we set our
equipment up on stands to simulate conditions at Fernald."
Despite all the simulations, conditions at Fernald were not what
Burks and his group were used to. Protective clothing was required,
even in the control area, and when repairs had to be made, the task
fell to the ORNL researchers. "One of our guys had to dress out
completely, including wearing respiratory equipment and three pairs
of gloves, before entering the restricted area around the silo.
This kind of field work was a new experience for many of us who
were used to laboratory conditions," says Burks. Other trying
conditions included evacuations of the area several times a day
because of high radon concentrations, poor weather, and high winds
that prevented workers from reaching the access doors, called
"manways," located on top of the silos.
In August 1991, Burks and colleagues John Rowe, Fred DePiero, and
Marion Dinkins conducted a cold test (a test in a nonradioactive
environment) of the system's performance in an empty silo at
Fernald. It performed beyond requirements, measuring the height of
a 0.3-m(1-ft) tall calibration target to within 0.64 cm (0.25 in.)
of its actual height with a variation of less than 0.25 cm (0.10
in.) between repeated measurements. Also during the cold test, an
alignment and calibration scheme was developed that was a major
factor in the success of the measurements. "The tests demonstrated
the superior accuracy and reliability of the measurement system,"
says Burks. "Practicing installing the system in an empty silo also
helped us determine the tools we needed to do the job. When you're
working in a contaminated environment, you don't want to stop
halfway through the installation and go get a tool."
Before the cold test, the project team had focused on system
function and accuracy. The test successfully demonstrated the
system's performance, but it also highlighted the need to increase
its rate of gathering and processing data. In response, the group
developed a piece of menu-driven software which enabled the user to
calculate, set, and change system parameters as often as necessary.
"This cut down on the time it took to gather data," says Burks. "It
also allowed us to specify a series of lines for the system to scan
and then leave the computer to run the system at night or when high
radon levels forced evacuation of the control area."
To map the large, irregular waste surfaces inside the silos, Burks
and his group used three camera-laser units (one was a backup) and
rotated them among the silo's manways to obtain a complete surface
map. Maps were built up a section at a time using an infrared laser
equipped with a cylindrical lens to project a line on the surface
of the waste. A high-resolution, black-and-white video camera was
used to record an image of the line.
"In one image, you can get up to 50 to 60 data points on the
surface being scanned, each several inches apart," says Burks.
"Thousands of images were acquired and analyzed to map each silo."
an image-processing system digitized each image and fed it into a
computer that performed high-speed geometric transformations on the
processed image to determine the location of the line in space. The
results of these calculations were then fed to a workstation where
they were displayed for the operator. From the workstation, the
operator could control system parameters, such as the starting and
ending points of regions to be scanned and various image analysis
parameters.
Mapping the entire surface of the waste required that it be
surveyed from several different perspectives. Each silo has five
manways, one in the center of the dome and four around the
perimeter; data were gathered using the measurement unit in the
center manway in conjunction with units located in each of the
perimeter manways. A frame of reference was established by placing
lights in sounding ports along the edges of the domes, several feet
above the waste. As a result, maps of surface features before and
after the application of the bentonite could be compared, verifying
that the entire waste surface had been covered to the required
depth.
The cold-test silo took two weeks to scan. Using the new software
and techniques developed over the course of their work at Fernald,
Burks' group scanned the final silo in only 47 hours, enabling them
to finish taking data on October 11--one day ahead of schedule. The
bentonite caps were applied by Thanksgiving, and mapping of those
surfaces was finished in late December.
"The people at Fernald were happy to get the results," Burks says.
"The surface features of the waste were different from what they
expected, and that made a big difference in the amount of bentonite
they applied and how they applied it. Various scenarios called for
the application of up to 3000 m3 (80,000 ft3) of the clay sealant.
Using our data on surface features, they met DOE-EPA requirements
using only about 900 m3 (24,000 ft3)."
The highly accurate data on the waste's surface features resulted
in considerable cost savings because it eliminated the need to buy
and apply thousands of extra cubic feet of bentonite. It also made
it unnecessary to retrieve and treat the excess radon-contaminated
clay that would have been applied if Burks' surface data had not
been available. "It cost about $700,000 to develop the system and
about $300,000 to put it in place," says Burks,
"The savings have been estimated at 15 to 25 million dollars.
That's a good return on an investment by any measure."
MICROWAVES CHIP AWAY AT CONTAMINATED CONCRETE PROBLEM
Why, you might ask, would anyone want to develop new ways to clean
concrete?
Well, for starters, there are over 200 acres of radiation- and
hazardous waste-contaminated concrete under roof at the Oak Ridge
K-25 Site, and concrete tainted with contaminants, such as uranium
or polychlorinated biphenyls, is a common problem at nearly every
DOE laboratory or production plant. Before these areas can be used
for other purposes or demolished, the contamination in the concrete
must be reduced to safe levels.
Using a microwave generator originally developed for fusion energy
research, Terry White of the Fusion Energy Division has developed
a method of decontamination that uses microwaves to rapidly heat
concrete surfaces. The heat causes water present in the concrete to
turn into steam, generating internal pressure. This pressure
combines with the thermal stresses produced by rapid microwave
heating to break the surface layer of concrete into small chips.
Because the vast majority of contamination is confined to the top
several millimeters of the concrete, removing the concrete's
surface is an effective form of decontamination.
Several methods are currently used to remove contamination from
concrete surfaces, but they all have shortcomings. Pneumatic
chisels are used to chip away contaminated surfaces, but this
approach generates a lot of dust, creating an airborne
contamination hazard. The dust can be minimized by working on a wet
surface, but the water causes soluble forms of contamination, such
as uranyl nitrate, to soak into the concrete. Also, the impact of
the chisel can drive contamination farther into the concrete.
High-pressure water can be used to blast contamination free, but
the waste water must be treated afterward to remove contaminants.
High-pressure water cleaning also causes soluble contaminants to
penetrate farther into the concrete.
A third approach has been steel shot blasting, a surface-finishing
technology that creates a uniform finish by removing and compacting
surface material. Its shortcomings as a decontamination method are
that it creates a lot of dust, it is relatively slow, and it also
tends to pound contaminants back into the concrete.
Microwave heating, on the other hand, solves the dust problem by
creating chips small enough to be removed by a vacuum system, but
generally too large to create an airborne contamination hazard. As
a result, the surface can be kept dry, eliminating problems with
soluble contaminants. This approach also avoids the problem of
driving contamination farther into the concrete because no external
impacts are required to remove the surface.
In his initial research, White simulated a mobile microwave heating
system by sliding a concrete slab under a stationary applicator.
The applicator is designed to minimize reflected power so as not to
damage the system. During the course of the experiments, detectors
measure forward power, the amount of microwave power applied to the
concrete; transmitted power, the power passing through the
concrete; and scattered power, power that escapes around the
applicator.
White's experimental setup consists of a stationary microwave
generator, a waveguide system and applicator to channel the
microwaves from the generator to the concrete, a concrete slab
mounted on a roller system used to slide it along beneath the
waveguide applicator, and a vacuum system to remove debris
generated by the heating process.
Two different microwave generators have been used in White's
research--a 6-kW, 2.45-GHz generator and a 10-kW, 10.6-GHz
generator--allowing him to control the depth of concrete removal by
varying the frequency of the microwave source. Higher frequencies
concentrate more of their energy near the surface of the concrete
and remove a thinner layer of material. Lower frequencies are
absorbed deeper in the concrete and, therefore, remove a thicker
layer. "A lot of microwave design is based on intuition,
experience, and trial and error," White says. "There aren't many
standards in this kind of work."
The next step will be to construct a 15-kW, 18-GHz system designed
to remove thinner layers of concrete more efficiently. The
increases in frequency and power, combined with improvements in the
applicator design to spread the microwaves over a larger area, are
expected to result in considerably higher removal rates.
"We expect the process to be faster than conventional technologies
when it is fully developed," says White. A mobile microwave heating
prototype is expected to be completed by the end of this year, and
testing will begin in 1993.
Jim Pearce
(keywords: waste management, hazardous waste, bioremediation)
------------------------------------------------------------------------
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Date Posted: 2/7/94 (ktb)