Before polychlorinated biphenyls (PCBs) were banned in 1977, they were used as insulating fluids for transformers and other electrical equipment. When the discarded devices deteriorated, PCBs leaked into nearby soil and water. Millions of pounds of PCBs from leaking electrical equipment and industrial discharges still remain in soil, sediments, and groundwater.
Because of their stability and lack of reactive properties, PCBs were good insulators. However, these same properties cause PCBs to persist in the environment and to resist removal. From water and soil, they enter the food chain and build up in the tissues of plants and animals. Eventually, people eating these tissues accumulate PCBs, which have been linked to birth defects, cancer, and other illnesses.
Recently, ORNL researchers have harnessed two types of bacteria to break PCBs' hold on the environment. Here's the story.
In the early 1990s, Terry Donaldson and Mark Reeves sought to remove PCBs from soil using naturally occurring bacteria. Then Reeves became the ORNL principal investigator for a cooperative research and development agreement (CRADA) involving General Electric Company. The goal of the CRADA was to find the most effective way to use bacteria from river sediments to remove toxic PCBs from the contaminated sediments of the Hudson River in New York.
Thomas Klasson and Betty Evans examine a gas chromatogram showing PCB removal by anaerobic and aerobic bacteria.
When Reeves became head of the Laboratory Directed Research and Development Program, K. Thomas Klasson became the ORNL principal investigator for the project. Klasson is leader of the Remediation Technology Group in ORNL's Chemical Technology Division. Klasson, Reeves, chemical engineer John Barton, and technician Betty Evans came up with an effective but inexpensive remediation system using two types of bacteriaanaerobic bacteria, which do not require oxygen, and aerobic bacteria, which do.
|We successfully transferred the anaerobic bacteria to PCB-contaminated soil and achieved PCB degradation without adding any sediment.|
"This is an important advance," Klasson says of the results of his research. "Previously, researchers had to mix PCB-contaminated soil with river sediment to cause PCB degradation. Sediment is the only environment in which anaerobic PCB-degrading bacteria were known to thrive. We successfully transferred the anaerobic bacteria to PCB-contaminated soil and achieved PCB degradation without adding any sediment. We also developed and used our two-stage anaerobic-aerobic biodegradation method to enhance the removal of PCBs from the soil."
The toxicity and persistence of PCB compounds in the environment depend upon the number and location of their chlorine atoms. During anaerobic dechlorination, the first stage of treatment, the bacteria convert PCB compounds into less hazardous products.
When an anaerobic microbe metabolizes a PCB, it removes a chlorine atom from a PCB ring and replaces it with a hydrogen atom. As a result, the PCB is easier for an aerobic microbe to attack. The aerobic bacterium then replaces another chlorine atom with carboxylic acid (COOH), transforming the less hazardous product from the first stage into harmless carbon dioxide and water.
"The two-stage treatment degrades 70% of the PCBs in our soil samples to harmless substances," Klasson says. "Our preliminary studies show that chemical reactions between the remaining PCBs and a solution of special suspended solids to which the toxic compounds are attached eliminate the rest of the PCBs. That's encouraging because our goal is complete destruction of PCBs."
GE supplied the ORNL researchers with both anaerobic bacteria in river sediment and a strain of the aerobic bacterium Pseudomonas. Klasson's group separated out the anaerobic bacteria from the river sediment and successfully transferred them to soil samples from a Tennessee Valley Authority (TVA) site and ORNL. The TVA soil contained PCBs from transformers and capacitors at power substations. The ORNL soil came from White Wing Scrap Yard, which is contaminated with PCBs from electrical equipment. The work on the TVA site is being funded by the Electric Power Research Institute.
"Although we separated out anaerobic bacteria from the river sediment," Klasson says, "we could not isolate the strain to identify or name it."
In the ORNL study, flasks about the size of 10-oz. drinking glasses were filled with PCB-containing soil, bacteria, water, mineral salts, and an organic carbon source such as acetone. To promote mixing, many flasks were shaken in an orbital shaker. Every 3 or 4 weeks each flask was sampled to assess its PCB content. The anaerobic process takes 15 weeks to a year to reach completion.
The anaerobic process was developed for the CRADA with GE. ORNL researchers developed the aerobic process outside the CRADA. In 1997, after the Environmental Protection Agency issues a permit for field application of genetically engineered organisms, a demonstration of the anaerobic-aerobic process will be held in Chattanooga, Tennessee, by ORNL, TVA, and the University of Tennessee. The goal is to show that this approach to PCB bioremediation can be scaled up.
GE has already run two demonstrations using anaerobic bacteria at a New York site on the Hudson River and at Woods Pond, Massachusetts. "GE found that large-scale processes mimic lab experiments," Klasson says, adding that scaled-up processes will consist of large tanks in which the solution of soil and bacteria is mechanically agitated or of artificial ponds in which automated rakes do the mixing.
The work was funded by DOE's Mixed Waste Integrated Program and Buried Waste Integrated Program, both of which are part of its Office of Technology Development.
|The ORNL process shows potential for complete PCB degradation.|
Today, Klasson says, small environmental companies are
aerobic bacterial processes to demonstrate partial PCB degradation
at electrical utility sites. The ORNL process currently being
developed, however, shows potential for complete PCB degradation. Someday,
some version of the ORNL process may be used widely to undo
electrical transformers' environmental damage by transforming
PCB-contaminated soils into clean ones.Carolyn Krause
To keep the dream alive, DOE's Hydrogen Program sponsored a hydrogen-powered bus during the 1996 Summer Olympic Games in Atlanta, Georgia. At one time, it was believed that hydrogen could be produced inexpensively from water by electrolysis using nuclear power, once envisioned to be a source of cheap electricity. Now, DOE is looking at other ways to produce hydrogen, including use of microorganisms.
In a dream world, where rags become riches, trash would be turned into fuel. Energy would be extracted from old newspapers, grass clippings, and cheese wheywaste products of renewable resourcesto heat and light buildings and propel cars and planes. How? Use the fungal enzyme cellulase to convert cellulose, starch, and lactosecomplex sugar molecules that make up these wastesinto the simple sugar glucose. Then use bacterial enzymes to convert glucose (C6H12O6) into hydrogen.
In ORNL's Chemical Technology Division, Jonathan Woodward and colleagues from the University of Georgia and the University of Bath in England have demonstrated a new biological method for converting glucose into hydrogen. The process also produces gluconic acid, a metal-binding chemical widely used in the manufacture of foods and drugs and the treatment of metal.
The new process has also generated considerable excitement. Following publication of a paper by Woodward and colleagues on the method in the journal Nature Biotechnology, Woodward received considerable media attention from organizations such as Reuters, BBC, Voice of America, the Washington Post, Washington Times, New Scientist, and Chemical and Engineering News.
|The 16 billion pounds of cellulose in a year's worth of U.S. newspapers could generate enough hydrogen to replace all the natural gas consumed by 37 cities the size of Oak Ridge.|
Not surprisingly, the media seemed particularly fascinated by what the Woodward paper said about newspapers. It stated that the 16 billion pounds of cellulose in a year's worth of U.S. newspapers could generate enough hydrogen to replace all the natural gas consumed by 37 cities the size of Oak Ridge (pop. 27,000).
This bacterial enzyme process converts glucose from renewable resources into hydrogen.
The development of the process was supported by DOE's Office of Energy Efficiency and Renewable Resources, Hydrogen Program, Office of Utility Concepts. "Our biological process produces hydrogen at the same rates as other biological methods," Woodward says. "Right now we produce one atom of hydrogen for every molecule of gluconic acid. Under ideal conditions, we should produce 12 times as much hydrogen. We must find the best conditions to make current enzymes more efficient and experiment with other enzymes to extract more hydrogen from glucose and convert gluconic acid to hydrogen."
At the same time, Woodward's group is trying to tackle the more difficult first step of the two-step process of making hydrogen from cellulose and other complex sugar compounds that are abundant, inexpensive, and renewable. "The bottleneck in the cellulose-to-glucose process is the cellulase enzyme," says Woodward, who has long been experimenting with the fungal enzyme cellulase to increase its efficiency in breaking down cellulose into glucose. "We need a stable enzyme that works faster to catalyze production of glucose from cellulose. Right now it takes two days to produce glucose from cellulose. Our goal is to make cellulase ten times faster to get glucose in 30 minutes to an hour."
In the new process, glucose is combined with glucose dehydrogenase, a bacterial enzyme. In the presence of a compound called NADP, this enzyme converts a glucose molecule into gluconic acid and attaches a freed hydrogen atom to NADP, forming NADPH. Another enzyme, a hydrogenase isolated from bacteria found in a deep-sea hydrothermal vent, then releases the hydrogen from NADPH, generating hydrogen gas and enabling NADP to repeat the cycle. The process requires a temperature of 50°C (122°F).
The hydrogenase used is an expensive enzyme that Woodward obtained from Mike Adams of the University of Georgia. Woodward learned about it from his former section head, Chuck Scott, who bought the enzyme from Adams for his experiments in using bacteria to liquefy coal. "Hydrogenase," says Woodward, "is one of two enzymes that I know about that will accept electrons from NAPDH to evolve hydrogen."
Once the enzyme process for producing hydrogen from complex sugars is optimized, the next step will be to find ways to make inexpensive enzymes so that the process will be practical for industry. "Through genetic engineering," Woodward says, "scientists should come up with cheaper enzymes. They will isolate and clone microbial genes responsible for the desired enzymes. To churn out the enzymes in great quantities, the cloned genes could be inserted into rapidly reproducing E. coli bacteria."
The enzymes would likely be placed in a bioreactor column, where they would convert cellulose into glucose, and glucose into hydrogen. It's the stuff of dreams now, but someday it may be reality.Carolyn Krause
Infrared night-vision imaging systems typically installed in military vehicles and aircraft cost about $100,000, making them impractical for most civilian applications. Researchers at ORNL, however, have developed a revolutionary uncooled micro-cantilever infrared camera using microcantilevers, which are similar to miniature phonographic needles. The new technology could improve resolution and reduce the cost to less than $1,000 per unit if mass production can be achieved.
In automobiles, night-vision cameras could allow drivers to see past oncoming headlight glare and beyond what they can see with headlights. These cameras would most likely be used in much the same way drivers use rear-view mirrors, for occasional but vital monitoring of traffic. Aboard airplanes, infrared cameras could aid pilots when weather conditions reduce visibility.
While conventional infrared night-vision systems require cryogenic coolers, sophisticated optics, and costly sensor materials, ORNL's uncooled microcantilever infrared camera uses inexpensive, mass-produced silicon microcantilevers and a mirror.
"The heart of this novel camera consists of a mirror and a cantilever placed at the focus of the mirror," says Thomas Thundat, principal researcher and a member of ORNL's Molecular Imaging Group, a part of the Life Sciences Division. "The mirror forms an infrared image of the object to be photographed. Brighter areas of the image formed at the focal plane have a higher number of photons and are, therefore, hotter compared to darker areas. The infrared photograph is taken by scanning the cantilever sensor over the image at the focal plane."
As the cantilever scans the focal plane, the amount of cantilever bending changes with brightness of the image because of heat absorption by the cantilever. This bending is monitored as electrical resistance changes in the cantilever and is displayed as a two-dimensional photograph of the object.
Instead of scanning using a single cantilever, ORNL's team is developing a device that can generate instantaneous photographs by using a two-dimensional array of microcantilevers closely packed on a support structure.
Research for the uncooled microcantilever infrared camera was funded in part by DOE's Environmental and Biological Sensor Development Program and by the National Science Foundation. Thundat and colleagues Bruce Warmack, Rick Oden, and Panos Datskos envision possible use of the camera in hundreds of industry process control systems, military operations, automobiles, airplanes, and security systems. It could also be adapted for use by firefighters and for energy conservation.
According to the researchers, the main advantages of the uncooled microcantilever infrared camera are its lower cost, reduced size, and ability to operate without liquid nitrogen coolingthus, the use of "uncooled" in its name.Ron Walli
Researchers in ORNL's Instrumentation and Controls (I&C) Division have adapted a commercial video camera to make it easier for law enforcement personnel to use. The researchers reduced the size of the lens and equipped it with a transmitter that sends the picture to a site up to 30 meters (100 feet) away, such as a police car.
Preston Leingang, president of Turtle Mountain Communications in Maryville, says the camera should be able to transmit pictures to a remote location, such as a police station, after further development. Turtle Mountain Communications specializes in communications suites for command, control, communication, computer, and intelligence systems.
|The hidden lens makes the camera unobtrusive, and thats important to law enforcement personnel.|
A special diffractive optical element is the key to ORNL's patented lens, which is about the size of a button. David Sitter (left), an inventor of the lens, says that ORNL overcame a technological barrier by shrinking the size and number of lenses in the optical system. The ORNL unit uses just two lenses. Photograph by Tom Cerniglio.
Another key feature of the camera is its disguised lens. The aperture, which admits light into the optical system, has been moved from the middle of the lens mechanism to the front, leaving only a pinhole size opening. "The hidden lens makes the camera unobtrusive," says co-inventor David Sitter, "and that's important to law enforcement personnel."
The researchers have submitted a proposal to the National Institute of Justice to commercialize the camera in a joint venture with Turtle Mountain Communications. Their goal, says Richard Crutcher of the I&C Division, is to cost-efficiently enhance a commercial camera containing single-chip electronics with new lens developments.
The researchers expect the camera to be a little larger than a microcassette case, making it possible to place it in a police or security badge or other small object.
"This technology has been looked at by a number of customers," says Scott McKenney of ORNL's Special Projects office. "Potential user agencies have overwhelmingly been impressed with the technology and consider it to be state of the art."
Leingang is enthusiastic about his company's involvement in this project. "Many people are not aware that the U.S. government can assist businesses with new technologies," he says. "A lot of companies just don't have the money to do the research necessary to make technological advancements. National laboratories are essential to the future of high-technology ventures."
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