Bugs At Work

Bioremediation uses microscopic organisms to clean up soil and water pollution—but how well do these hungry bacteria swallow the scrap industry’s contaminants?

By Robert L. Reid

They work tirelessly, day and night, cleaning up the contaminants that spill onto soil or leach into groundwater, and once their job is done they’re simply left to starve.
   It all sounds too cruel—like some nightmare exposé on exploited migrant workers or Third World sweatshops—except that the “workers” we’re talking about are simply microscopic organisms. These microbes, or “bugs” as they’re popularly known, are the key elements in a pollution cleanup approach called bioremediation. It’s a technique that U.S. EPA still considers “new or innovative” but one that scrap recyclers have been using for more than a decade and a half. 
   Bioremediation—which is used primarily for organic compounds such as petroleum-based contamination—was even a 1995 cover story in Scrap, with at least one expert at that time predicting a “bright future” for the technique in the scrap industry.
   Today, however, experts disagree over just how widely used or widely applicable bioremediation is for the recycling industry. Some remain enthusiastic supporters, noting that innovations in bioremediation research and techniques mean that these hungry little bugs can clean up more and more organic compounds. There have even been efforts to bioremediate inorganic contaminants such as metals and PCBs.
   Others see only limited use for bioremediation at scrap facilities due to factors ranging from the complexity of multiple contaminants to the physical size of the facilities themselves to the often-lengthy duration of bioremediation projects, which can take years to complete.
   It’s enough to drive a microbe mad.

A-OK With Oil
On one point, at least, almost everyone agrees: Bioremediation does work well on hydrocarbon contaminants such as gasoline, diesel fuel, motor oil, and hydraulic fluid.
   “Microscopic ‘bugs’ or microbes that live in soil and groundwater like to eat certain harmful chemicals, such as those found in gasoline and oil spills,” explains EPA in its April 2001 Citizen’s Guide to Bioremediation. “When microbes completely digest these chemicals, they change them into water and harmless gases such as carbon dioxide.”
   That’s good news for the scrap industry, notes Rich Schowengerdt, principal hydrologist in the Salmon, Idaho, office of Envirogen Inc., an environmental consulting firm. “Virtually every scrap yard I’ve been involved with—and that’s about a hundred—has had some type of oily waste that entered the ground sometime during the life of its operation,” he says, adding that “most oily waste-type conditions can be bioremediated.”
   Such cleanups are often performed in situ, or right at the site of the contamination, either in the ground, in groundwater, or in an oil/water separation pond. Others are performed ex situ, which involves digging up the soil, for instance, and either moving it to another part of the yard where it can be treated biologically or taking it completely off-site for treatment.
   The bacterium used in such treatments is often a naturally occurring, petroleum-consuming microbe and frequently one that was already in the soil or water (albeit probably not in a large enough concentration to effectively consume the amount of contamination present). Or there might be various inhibiting factors that keep the bugs from doing their job—the soil could be too dry, for instance, or there might not be enough nutrients present, or there could be too much (or too little) oxygen for the microbes to work at their best.
   “We try to overcome these limiting factors,” explains Jay Diebold, principal engineer in Envirogen’s Pewaukee, Wis., office. “We manipulate the environment to optimize the growth conditions for the cells that are already present in the soil and groundwater and try to increase the amount of these cells and improve their metabolism rate to make them more efficient.”
   This is done either right on the surface of the contaminated area or below the ground by adding nutrients (including regular garden-variety fertilizer) and water, and either injecting oxygen when aerobic conditions are needed or removing oxygen when anaerobic treatment is preferred. 
   Often, these measures to enhance the growth of the already-present microbes are enough to get the bioremediation ball rolling. One consultant says that anywhere from 50 to 60 percent of his bioremediation work involves such indigenous bacteria, while another puts the number as high as 90 percent.
   There are times, though, when the problem requires “inoculating” the site with a larger concentration of that microbe or with a microbe that wasn’t previously present but that has been carefully selected—and sometimes even genetically modified—to clean up that particular contaminant.
   “Even when you add bacteria,” Schowengerdt points out, “they’re bacteria that already do this work. It’s not something where someone pulled a DNA strand out of a laboratory and made some kind of hybrid.”
   Instead, the environmental firm can simply order the right bugs from a supplier that grows them on “microbe farms” for this specific purpose, explains Michael Place, president of Continental Placer Inc./CPI Environmental Services Inc. (Glen Ellyn, Ill.). Based on soil or water tests, the supplier then provides the bioremediation firm with the right quantity of microbes for the type, volume, and concentration of contamination being treated. 
   Other firms will collect their own bugs from other sites where the natural bacteria are already at work on a particular contaminant—such as the La Brea tar pits in Los Angeles, where microbes have been consuming petroleum products for thousands of years, says Schowengerdt. “Then we separate out the naturally occurring bacteria species that do really well on lube oil or diesel fuel, and that’s what we apply,” he notes. 
   If these completely natural microbes don’t get the job done, however, bioremediation firms can also use genetically engineered microbes, called GEMs. Envirogen, for instance, took one bacteria that previously would live only about a week in groundwater—hardly long enough to bioremediate anything—and engineered it to store a sack of food within its body. As a result, that GEM can now live for 40 days. “This is a naturally occurring bacteria that is known to consume the contaminant we want consumed,” Schowengerdt stresses. “We just want to make them live longer.”
   While at least one environmental firm reports using GEMs in as many as a third of its bioremediation projects, Envirogen’s Jay Diebold believes the genetically altered bugs aren’t widely used and certainly not for the most likely contaminants in the scrap industry. Besides, he says, people are “concerned about introducing these things into the environment because of how they may mutate and result in other unforeseen problems.”
   “Developing engineered microbes is a costly process,” adds Ken Quinn, principal hydrologist in the Madison, Wis., office of Montgomery Watson Harza. So it’s a question of using the most appropriate level of technology—which most often means the existing bugs because “nature seems to be doing a pretty good job of engineering its own bacteria for taking care of these contaminants,” Quinn says. 
   Nature also takes care of all those microbes once the contaminant is cleaned up. The bugs simply die off after their petroleum-based food supply is depleted.

Weighing the factors
   Though bioremediation is often less expensive than other cleanup solutions—one environmental engineer recalls a scrap yard where the cost of hauling away contaminated soil was at least four times higher than biologically treating it in situ—it is far from cost-free. 
   For one thing, the bioremediation process itself can involve much more than just spraying some microbes over the ground. Diebold recalls a large project at a former scrap facility’s turnings storage area that required a network of 30 air sparging lines, each 300 feet long, to add oxygen to the subsurface, as well as a huge sprinkler system for treating approximately 6 acres of contaminated soil. Plus, bioremediation sites often must be monitored for nutrients and moisture levels over a period of years, with the soil repeatedly turned over for aeration, other engineers note.
   So for scrap processors, the question of whether or not to use bioremediation depends on many factors, including the size of the contaminated area, where it’s located on their property, what environmental regulations they face, and even what the local weather is like.
   If the contamination is confined to a relatively small area, for instance, it can be quicker and cheaper to simply dig it up and haul it away to a special landfill, notes Bill Baumgartner, president of W.Z. Baumgartner & Associates Inc. (Franklin, Tenn.). Or if the contamination covers a large area in a vital, heavily trafficked part of the facility that can’t be taken out of service—and there’s time pressure from state regulators to clean it up—the best solution again could be to just get the soil off the property, he says.
   Geography is key here, given that landfill costs vary widely. For instance, landfilling petroleum-contaminated soil can be a cost-effective solution in the Midwest—where tipping fees are as low as $10 a ton—but bioremediation is far more attractive in the Northeast, where fees can exceed $90 a ton, notes Continental Placer’s Michael Place.
   Bioremediation also works well if the contamination is in an isolated part of a facility that can easily be idled for a while or if it’s located under the foundation of a building where excavating the soil might make the whole structure unstable, Baumgartner says. 
   That’s assuming, again, that your geographic location helps out. Some state regulators require faster cleanups than others, Baumgartner explains, which can work against the time-consuming bioremediation process. Likewise, the bugs themselves work better in warmer climates, meaning that a scrap yard in Arizona will have a longer bioremediation “season” than one in Maine.
   On the regulatory front, consultants are divided over how much time pressure scrap plants can face. Some, like Envirogen’s Schowengerdt, say that “the whole regulatory scheme of remediation has really changed” since the mid-1990s when bioremediation was first gaining popularity. They note that regulators now often accept a risk-based approach to cleanups that means “you don’t have to dig out every spoonful of contaminated dirt anymore” so long as what’s left doesn’t pose an exposure hazard, Schowengerdt says.
   “This makes bioremediation a more viable part of regulatory closure,” he explains, “because even though you aren’t actively doing things per se, bioremediation keeps cooking and continues to reduce the contamination in place,” which is acceptable to regulators so long as you’ve reduced the risks.
   That mainly applies to soil that’s contaminated with lighter-weight hydrocarbons (lighter in a molecular sense) such as diesel fuel and gasoline. If the contamination includes heavier molecular hydrocarbons such as polynuclear aromatics (PNAs)—a potential carcinogen found in waste oil that isn’t readily degraded biologically—the regulations get tougher, sources note.
   In part that’s because regulators used to lump all hydrocarbons together to measure total petroleum hydrocarbons (or TPH) in contaminated soil, says Dennis Caputo, president of Quest Consulting Inc. (Bellaire, Texas), an environmental, health, and safety consulting firm. But now they increasingly require measurements of individual contaminants such as PNAs, which must be cleaned up to far lower levels—less than 1 ppm of a PNA, for instance, compared with 500 ppm for diesel fuel, notes Caputo (who ran bioremediation programs for Proler International Corp. in the 1990s).
   As a result, bioremediation—especially when conducted in situ—“does not work on many of the types of hydrocarbons that we’re finding in soils in scrap operations,” says Caputo. “So one thing we’ve found is that the dig-and-haul approach appears to be getting preference from our scrap clients.”
   This is especially true at smaller yards, he adds, where there just isn’t room to set aside a contaminated area for lengthy bioremediation treatment—which can take twice as long with PNAs as with other hydrocarbons, Caputo says.
   The presence of hazardous metals such as lead and cadmium as well as other contaminants such as PCBs can also complicate a nice, clean bioremediation. For one thing, it isn’t possible—yet—to bioremediate them, though there are various biological treatments being considered and tested for such hazards. More importantly, though, these materials can inhibit or even kill the microbes that you’re using to remediate hydrocarbon-based contamination. Thus, bioremediation can be just one part of a larger cleanup effort—and not always the major part.
   It’s a familiar problem at scrap plants where Michael Place has handled cleanups. “The biodegradation may not do what we need it to because of those other contaminants,” he explains. “So we end up hauling away the contaminated soil anyway.”

A Growing List
On the positive side, the list of contaminants that bioremediation can handle is growing and includes certain compounds or materials that were once thought to be untreatable.
   Take trichlorethylene, for instance. This chlorinated solvent, called TCE, posed special problems for bioremediation because, if it wasn’t degraded completely, it could turn into vinyl chloride, “which is actually more toxic than TCE,” notes Montgomery Watson’s Ken Quinn. But as environmental engineers learned more about the degradation process, they were able to determine that a two-step process—in which TCE is initially bioremediated under anaerobic conditions while the vinyl chloride stage is remediated aerobically—would reduce the compound all the way down to carbon dioxide and water, Quinn explains.
   Likewise, the compound MTBE—commonly found in gasoline—is more readily biodegraded these days thanks to discoveries both of certain microbes that consume MTBE and of the right conditions to assist those microbes in breaking down the compound, Quinn says.
   It’s all part of a growing knowledge-base about bioremediation and a greater ability to match the right bug to the right problem, environmental engineers note.
   One company—Sarva Bio Remed L.L.C. (Trenton, N.J.)—offers microbe-based products that work strictly on water-based contaminants. Developed from the company’s patented “biodispersion” technology, these products have been successfully tested on oily waste in scrap applications, notes Satya Ganti, president and CEO. They have also been used in a nonscrap application to treat radioactively contaminated waste oil.
   Likewise, the U.S. Department of Energy reported in 1999 that bioremediation’s success with hydrocarbons has “led scientists and engineers to be optimistic about applying this technology to mixtures of metals and radio-nuclides that are found at some of the most contaminated DOE sites.”
   Efforts are also under way to biologically reduce the harmful effects of lead and chromium. The microbes won’t actually break down such metals, of course. To do that requires either nuclear physics or alchemy, jokes Envirogen’s Schowengerdt. But certain bugs can “change the speciation of lead from a hazardous, highly mobile version to a nonhazardous and immobile version,” he explains. “So you can ‘fix’ the lead in place instead of either having to pump-and-treat or dig it up.”
   Another hazardous metal—hexavalent chromium, commonly found in electronic scrap—will readily migrate through soils to contaminate groundwater, notes Ken Quinn. But certain microbes will create a “reducing” condition to convert hexavalent chromium to trivalent chromium, which is quite immobile and can easily be precipitated out of groundwater, he explains.
   Despite such advances, though, bioremediation remains a slow, sometimes painstaking process. Even with new knowledge and techniques, a bioremediation project that would previously have taken three years to complete might still take at least two and a half years, says Jay Diebold.
   “I don’t think the promise of bioremediation has been as dramatic as people anticipated in the 1990s,” he concludes. “The myth and the reality were a little bit different. Still, it can be a cost-effective, major component in most remediation projects.” •

Robert L. Reid is managing editor of Scrap.