Science / Medicine : A NATURAL RESPONSE TO TOXIC WASTE : When you bury an apple, it decomposes as soil organisms gobble it up. Such organisms also keep busy digesting sewage waste. Recently, scientists have begun to use microbes to destroy the worst hazardous substances that we throw out.
When the warehouse of Westchem Agricultural Chemicals Inc. in Minot, N.D., caught on fire in April, 1987, fire crews rushed in and hosed down the flames. Unfortunately, their quick response only led to more problems.
As it turned out, barrels of pesticides had been stored inside the warehouse, and the water that squelched the fire also washed the toxic chemicals into the soil, posing a threat to the local drinking water supply.
At first, it seemed that the only solution was to haul the contaminated soil to a landfill.
But upon reflection, Westchem’s general manager, Harold Schultz, realized that that course of action only would have moved the toxic chemicals from his back yard to someone else’s. Schultz had grown up in a farming community and felt strong ties to the land.
“Sooner or later,” he said, “five or 10 centuries down the road, when we’re all dead and gone, it’s (dumping toxic materials) going to cause some problems on this earth.”
As the excavation was still going on, a business associate told Schultz about a company that could clean up the contamination by stimulating microorganisms already present in the soil to munch away at the chemicals. The soil-dwelling organisms would do the job thoroughly and For a much lower price.
By June, a team from Ecova Corp., based in Redmond, Wash., was in place, ready to clean up the mess, using this biological method.
Within three months, the bacteria had destroyed 96% of the hazardous chemicals in the soil. Pesticide levels of substances such as 2,4,D and MCPA plummeted from 800 to 10 parts per million.
Using microbes to break down wastes isn’t a novel idea. Knowingly or not, people have been doing it for centuries. When you bury an apple in the back yard, it decomposes as soil organisms gobble it up. Such creatures also keep busy at sewage plants, digesting the endless streams of waste.
Only in the last few decades, however, have scientists begun to tap the greater potential of microbes: using them to destroy hazardous substances.
In the ‘60s, scientists discovered that microbes living in the soil could be used to clean up petroleum waste products, although it wasn’t until the early ‘70s that the new technology was put to work.
One of the first cleanups took place in Ambler, Pa., where a pipeline broke and contaminated the community drinking water supply with 130,000 gallons of high-octane gasoline from the spill. By adding nutrients and oxygen, the microbes in just over a year reduced the level of contamination to under 100 parts per billion--the level considered safe at the time. Without intervention, it might have taken 50 to 100 years, or more, to reach that level.
This technique, called bioremediation, has been used for many years on simple carbon-based petroleum compounds. But only in the last three or four years has the field entered a new arena.
Companies today are using microbes to degrade more complex chemicals, such as pesticides and solvents, although heavy metals and complex petroleum byproducts continue to present a challenge.
While many such firms have used microbes on a commercial basis, most of the work on biodegradation is still at the research stage. Scientists are searching for those “perfect bugs,” as they are called, that have a yen for some rather unappetizing chemicals.
One such chemical group is polychlorinated biphenyls. Once used extensively in the electrical industry as a heat retardant, the manufacture of PCBs was banned in 1979 because of health hazards associated it.
But large quantities of the oily fluid still exist, sealed inside transformers and capacitors. The chemical repeatedly has made its way into the environment, including the food supply, through illegal dumping and accidents.
Chemists who synthesized PCBs in the late 1920s did such a good job that the chemical has proven nearly indestructible.
For the last six years, biochemist Ron Unterman, an expert on PCB bioremediation, and his colleagues at General Electric Co. have found several microbes that could begin to break down PCBs.
The group tested the bacteria last summer at a contaminated New York auto-racing site, where PCBs had been used for dust control. The microbes destroyed 25% of the hazardous chemicals at the site, bringing the contamination levels down from 500 parts per million to under 400.
Although 25% destruction is quite low, Unterman was pleased to see any activity at all. It showed that “you can degrade PCBs, even in the real world.” Unterman said. “The rates are much slower (under real-life conditions), (but) that’s not unreasonable considering the realities of temperature and . . . factors such as that.”
However, the bacteria will have to achieve close to 100% destruction before they are put to work in the commercial arena.
About 20 companies in the United States now offer bioremediation on a commercial basis, according to John Glaser, a chemist in the Environmental Protection Agency’s hazardous waste engineering research laboratory. He said he is “very optimistic” about bioremediation, despite its limits.
Dick Raymond, the man who patented bioremediation for gasoline-contaminated ground water, conceded that “there are going to be a lot of people trying to sell the process for things that won’t work.”
About 20 years ago, Raymond’s methods were first used to clean up oil spills. Now scientists have identified microorganisms that can destroy more complicated chemicals. Some companies now are even beginning to tackle Superfund sites that typically contain a long list of chemical contaminants. Such sites have been designated by the federal government as priority cleanup areas because of their threat to human health.
Karen Arnstein, marketing communications manager for the environmental engineering company ERT, said her firm has just received EPA approval to clean up one such Superfund site, the French Ltd. site in Crosby, Tex. The site looks like a scenic pond on the surface, but beneath the water is an array of hazardous materials, including benzene, chloroform, toluene and vinyl chloride.
Initially, the EPA had planned to incinerate the wastes, at an estimated cost of nearly $150 million. ERT proposed bioremediation as a less expensive alternative, saying it could do the job for under $50 million by using microbes that were already living in the pond to destroy the hazardous chemicals.
The firm has completed a demonstration project on a third-acre plot at the French lagoon, and the EPA has given it the go-ahead to clean up the rest of the site.
Though cleaning up combinations of chemicals offers promise for dealing with Superfund sites, Gaylen Brubaker of International Technology, one of the country’s largest environmental management companies, said these projects move very slowly.
Both the regulatory agencies and the responsible companies have had limited experience with bioremediation, Brubaker said. The approval process can easily be stalled at any stage in the game.
As an example, Brubaker pointed out that ARS, the bioremediation group within International Technology, did a feasibility study for a project 2 1/2 years ago. “But (because of) the permitting, the bureaucracy and the litigious nature of this kind of a business, very little has progressed beyond the feasibility phase,” he said.
The regulatory agencies admittedly are slow to embrace bioremediation. “We don’t see it as a panacea,” Roger Meacham of the EPA said. “It has potential for being a scientifically sound, safe remedy for Superfund sites. But you have to look at each site separately and see which contaminants are involved.”
Brubaker believes the hesitancy of the EPA stems mostly from lack of familiarity. He said, “Up until three years ago, everyone assumed landfill was the answer and so there hasn’t been that much motivation to look at innovative methods.” Bioremediation has not been done on a wide scale, however, and few people are willing to take a risk with an unproven method.
Westchem was willing to take that risk. The Ecova team came to the North Dakota warehouse knowing that the job would entail more than simply sprinkling microbes onto the “hot spots.”
Before taking any action, they had to assess the damage and determine which microorganisms would clean the area most effectively. The scientists found that bacteria already living in the soil would prove most useful.
Once they began, workers constructed a 5-acre treatment bed on the site. The bed, which resembled a large pond, was lined with a thick layer of clay to prevent the contaminants from leaching through.
When the bed was completed, the workers dug up the contaminated soil and transferred it to the treatment bed. There they mixed in the microbes that had been chosen for the task--bacteria indigenous to the soil.
Those single-celled, primitive organisms didn’t do the job unassisted, however.
Like a garden compost pile, the microbes needed nutrients, oxygen and water to stimulate them to devour hazardous chemicals.
Even with the added stimulants, the bacteria did not work quickly enough on all of the soil. Thus with a small, highly contaminated sample, Ecova had to use a more rigorous treatment that sped up the degradation process.
Eventually the highly contaminated soil was moved into a container where rocks and debris were sifted out and water was added to form a slurry. Workers then fed the slurry into bioreactors--large tanks that churn the mixture and microbes together while adding air and extra nutrients.
At each step of the process, workers were required to track the breakdown process of each hazardous compound in order to ascertain that the microbes completed the job, according to Al W. Bourquin, vice president of research and development at Ecova.
Using special labeling techniques, he said, they were able to ensure that the compounds were converted to harmless carbon dioxide and not into another dangerous compound.
The low cost of using microbes to break down hazardous waste is another appealing aspect of bioremediation. Since contaminated soil can be treated on-site, there are no transportation expenses or disposal fees.
And if the microbes can work effectively right in the ground--without the need to excavate soil--there is an additional savings.
But the notion that nature can do the job for free is misguided. “It’s just less expensive than (other methods),” Bourquin said. “It’s not inexpensive to do a really good cleanup job.”
Scientists say that waste-eating microbes offer great promise for the future, although they will not replace present methods. “Everybody wants biodegradation to work,” Unterman said. “There’s nothing better than letting Mother Nature recycle all of the world’s effluent. It’s natural (and) it’s the process that we’ve been doing for thousands of years.”
HOW MICROBES ATTACK WASTE
The Ecova Corp. of Redmond, Wash. used a biological strategy to clean the remains of a 1987 pesticide warehouse fire in Minot, N.D. The local water supply was threatened. Within three months, the bacteria had destroyed 96% of the hazardous chemicals in the soil. Here is a look at the process.
1. Scientists determined which microorganisms would clean the area most effectively, and decide that bacteria already in the soil would prove most useful.
2. On the site, workers built a 5-acre treatment bed that resembled a pond lined with a thick layer of clay. This would prevent contaminants from leaching through.
3. Workers dug up contaminated soil and placed it in the treatment bed. There they mixed in bacteria indigenous to the soil. To accelerate the work of the single-celled, primitive organisms, nutrients, oxygen and water were added to stimulate the bacteria to eat away at hazardous chemicals.
4. Even with the added stimulants, the bacteria did not work quickly enough on all the soil. The firm used a more rigorous treatment on a small, highly contaminated sample to speed the degradation process.
5. The most highly contaminated soil was moved into a long, tube-shaped container, right, where rocks and debris were removed and water added. The resulting mix was placed into bioreactors--large tanks that churn the soupy mixture and microbes together while adding air and extra nutrients.
6. Workers used special labeling to ensure that the compounds have been converted to harmless carbon dioxide and not into another dangerous compound.
Advantages of the Biological Approach
Relative low cost. Since contaminated soil can be treated on-site, there are no transportation expenses nor disposal fees.
No need to excavate soil.
Disadvantages of the Biological Approach
Microbes will have to achieve close to 100% destruction before they bioremediation is considered to have wide acceptance. It remains essentially unproved.
The regulatory agencies are slow to embrace bioremediation. “We don’t see it as a panacea,” said Roger Meacham of the EPA. “you have to look at each site separately and see which contaminants are involved.”
Alternatives to Hazardous Waste Disposal
Each year, about 264 metric tons of liquid and solid hazardous waste are generated in the United States. Just how to get rid of it has become an expensive and complex public problem. Among the methods:
Dumps: Rising costs, lack of protection for land and for underground water facilities, the public attention on the environmental inadvisability of dumping hazardous substances in landfills are all increasingly making this a bad alternative, even at the few approved sites. Incineration: Burning waste at high temperatures has been criticized for producing toxic by-products, including dioxins. Still, only about half of the nation’s incineration capacity is being used to destroy liquid hazardous wastes. Ocean Incineration: Waste placed about ocean-going incineration ships can be burned at much higher temperatures than on land, eliminating most hazardous by-products. The procedure is used in Europe, but has not yet become widespread in the United States, in part because it has not been believed economical. There are some environmental concerns and fear of shoreline spills. Waste Reduction: The Environmenal Protection Agency’s preferred solution is to reduce waste at the source. The agency seems to support installation of clean-up procedures and equipment at industrial and commercial sites.
