SCIENCE / MEDICINE : The Truth About Trash : Landfills: Although biodegradable garbage supposedly breaks down over time, the type of disposal now used may simply mummify it for future generations.
Dear Sir: We are in Mrs. Miller’s fourth-grade class, and we tried that plastic bag that says, “Here Today, Gone Tomorrow.” But how long is tomorrow? We did 92 tomorrows and it still didn’t dissolve. And it had the same strength as it did when we put it in the dirt.
--A letter from Stephen Swagerty to the makers of biodegradable plastic bags.
Stephen Swagerty and his fourth-grade classmates at Sunset Lane School in Fullerton conducted a scientific experiment with the newly marketed plastic bags labeled biodegradable. The children buried the bags for three months in a simulated landfill--a coffee can filled with corn chips, coffee grounds and pieces of paper. They were trying to find out exactly what the company meant by “biodegradable.” When the children retrieved the bags, Stephen said, they hadn’t dissolved and they still had their strength.
With the new “garbage consciousness,” citizens have tried to ease the crunch by buying products labeled biodegradable. The term has become equated with environmental virtue. If it’s biodegradable, it will break down in the landfill, making room for additional trash. That’s how some interpret the word. Others believe biodegradability must be a positive attribute, though they have a more vague concept of the term. If it’s biodegradable, they say, it will dissolve and return to nature--a notion that somehow makes the production of vast quantities of trash less repugnant.
Americans produce approximately 157.7 million tons of waste per year--about three pounds of trash per person each day. Landfills accumulate the majority of this waste, and they are filling up and closing down at an alarming rate, forcing cities to find new ways of dealing with their waste.
In Los Angeles, it is projected the 10 principal landfills will begin shutting down as early as 1991 and could all be closed by 2009. And it has become increasingly difficult to open new sites as neighborhoods resist them.
There are proposals to transport waste by train to the desert. But these too are met with opposition from those who wish to protect open lands from the rejected refuse of the crowded cities.
Can biodegradable products make a dent in the crisis? If we continue to rely on landfills as they are currently built, the answer is no, experts say. Almost nothing breaks down in these huge garbage receptacles--be it plastic or paper, synthetic or organic. With today’s sophisticated landfill design, trash is essentially mummified in a large tomb.
With the passage of the federal clean air act in 1970, incinerators were slowly phased out and the sanitary landfill became the primary method of trash disposal. Intending to limit odors and disease, landfill engineers developed a sophisticated new model of the old-fashioned dump. Today they line each trash depository with plastic to create a barrier between its contents and the environment. When the landfills reach capacity, they seal the structures with a clay cap, intended to be impermeable to the elements.
Engineers designed garbage receptacles in this fashion to protect the environment from hazardous materials in the trash. Without such precautions, scientists feared that fluids, known as leachate, would seep through the earth and ultimately contaminate ground water. By sealing the landfill so completely, both moisture and oxygen remain at a minimum.
Consequently, and to the surprise of those who designed the structures, biodegradation also remains at a minimum; the contents break down at a very sluggish pace.
“It’s very important for people to realize what biodegradability means,” said William Rathje, professor of anthropology at the University of Arizona and head of the university’s “Garbage Project,” “because I think--next to Santa Claus--it’s the most treasured myth in America today.”
Rathje began excavating landfills 15 years ago. From deep in the bowels of these garbage mountains, he and his team retrieved perfectly legible newspapers with articles covering the Korean War, headlines featuring President Harry S. Truman and photos picturing Dwight D. Eisenhower in uniform. The scientists have also pulled out 20-year-old carrots, hot dogs, corn-on-the-cob--all completely intact--from the innards of the garbage mountains.
Rathje has found that about one-fourth of the organic waste--food and yard debris--does degrade in the first 15 years. After that, he says, the material stabilizes and only half a percent or less continues to break down. Scientists know some degree of degradation must be taking place, because landfills produce a steady stream of methane, the gaseous byproduct of biological activity. But the degradation comes only from food and yard waste. Paper and cardboard, which readily degrade in a compost pile, remain intact.
Since Rathje’s discoveries, waste management experts have been trying to explain why the compost theory doesn’t apply to landfills. They suspect that low levels of both oxygen and water, combined with minimal circulation of microorganisms, all contribute to the end result: garbage preservation.
By understanding why degradation is not taking place, scientists hope to flip the coin and use that knowledge to develop methods for speeding the breakdown process. They call it enhanced degradation.
“Our goal,” said James Noble, senior engineering research associate at the Center for Environmental Management at Tufts University, “is to try and come up with a process or some technology to force the degradation to occur.” He said he hopes they can speed the degradation process, so half the contents of a landfill will be gone in five years rather than the current estimate of 50 years.
Both Noble and Riley Kinman, professor of civil and environmental engineering at the University of Cincinnati, are refining one technique for enhancing degradation called leachate recycle.
As Noble explains it, engineers collect leachate through pipes placed in the bottom of the landfill. They then remove undesirable material and pump remaining leachate back in, allowing the fluid to redistribute throughout the trash pile. Such a system allows the microorganisms--those responsible for degrading the garbage--to be mixed evenly through the trash. Without this boost, these microbes travel at an exceedingly slow rate.
But Noble quickly admits to the drawbacks of this method, particularly in areas like Southern California. “Your landfills in Los Angeles,” he said, “don’t produce leachate because they’re so dry. So if you were to do something like this in the field, you would actually have to purposefully admit moisture in the landfill to make the leachate.” And that’s directly contrary to the idea of keeping moisture out to protect ground water.
Scientists in Germany investigated another approach to enhancing degradation, They experimented with composting as an intermediate step in landfill management, taking advantage of the oxygen-using microbes that are present in a compost pile and unavailable in the oxygen-depleted landfills.
Under anaerobic conditions (without oxygen), decomposition requires three different kinds of bacteria. The first type chops the long cellulose chains into simple sugars. The second converts sugar molecules into acids. And the third breaks acids into gases that then dissipate into the atmosphere or, in a landfill, are captured in the gas-collection system.
Those microbes responsible for the first step of degradation proceed at a painstakingly slow rate. To hasten the pace, the German scientists pretreated garbage in an open-air compost pile. Fungi found in these oxygen-rich conditions can sever the cellulose chains considerably faster than the anaerobic bacteria performing the same function. The researchers then buried the pretreated material, allowing the other microbes to take over underground. With the bulk of the garbage in the sugar state, it decomposed completely in just five years. This method holds promise, but the scientists did experience problems with odors in their open compost piles.
Kinman mentions several other approaches to enhancing degradation that have not been fully developed. These include injecting the landfill with nitrogen and fertilizer, adding organic waste to provide nutrients for the microbes and pumping fluid into the garbage directly. He has done studies adding sewage sludge to the landfill as a source of both moisture and microorganisms.
While methods are being developed to speed the breakdown process in landfills, scientists and policy-makers are wondering if enhanced degradation is indeed a desirable goal. When weighing the risks and benefits, Rathje argues, “The issue is, do you biodegrade things into gray slime and concentrate the hazardous materials that will then leak out? Or do you mummify the garbage in a form from which it will not change, thereby in effect trapping the hazardous material in the product . . . as it is sitting in a landfill, so even if the landfill does leak, the hazardous material isn’t going to be generated into leachate?”
Noble contests Rathje’s position, arguing that simply postponing the degradation process just preserves the garbage for future generations to deal with. Under current regulations, landfills must be maintained for 20 to 30 years. During this period, landfill managers must ensure that the integrity of the cap is maintained, that the structure remains well-sealed. After that guardian stage ends, however, landfills can be abandoned and left to nature.
The once tightly sealed enclosures then become vulnerable to a variety of natural forces. If a tree sprouts on a landfill, the cap may crack and leave the pit open to rain and moisture. Other events, such as earthquakes, could cause fissures or splits in the cap.
Once this occurs, no one can predict what will happen in the landfill and how it will affect the area around it. By speeding up decomposition, landfill managers will be forced to deal with these questions today while averting liability in the future.
In addition, Noble says, hazardous materials make up a very small quantity of total garbage in landfills, and landfills are not ticking time bombs of toxic waste.
While enhancing degradation, the toxic materials can be removed or degraded themselves, Noble says. Methods already exist for using microorganisms to break down hazardous chemicals such as oils and solvents. The remaining substances include heavy metals. Though no techniques are now in use for extracting these contaminants, Noble expressed optimism that such technologies would be developed.
Aside from the hazards of leachate, landfills present a structural challenge to builders. “We did a study on 40 different applications for landfill,” Noble said. “They included things like shopping centers and highways. Every one of them had problems with settlement over the long period of time.”
He says that when buildings are constructed on top of landfills, one of two things must be done. Either the garbage must be dug out, or a complicated piling system must be used.
But Kinman doesn’t see landfill construction as an insurmountable challenge. “There’s no question that when we as engineers design some structure on a landfill, we have to take into account the subbase material. And we have to design the footings and the subbases and the gas collection systems to keep the gas from migrating into the building. But we can build on these landfills. For example, our veterans hospital here in Cincinnati is built on an old landfill, and there are no problems at all.”
In general, Kinman sees the landfill as an acceptable means of trash disposal. He judges the enhanced degradation debate in terms of economics rather than risk. It depends on your objectives, he says. If the purpose of collecting gas is to harness energy, “you might well want to enhance (degradation), to pull the gas off in a shorter period of time.” Otherwise, he sees no reason to speed up Mother Nature. “The other part of the equation,” Kinman adds, “is that it costs money to enhance.”
Until techniques are perfected for degrading landfill trash, garbage will continue to remain intact for decades. As civilizations have been preserved underground for hundreds of years, we will continue to mummify our refuse as relics that future generations may one day unearth.
WHAT’S IN OUR TRASH? Materials discarded into the municipal waste stream in 1986, in percent of total. Paper and paperboard: 35.6% Yard wastes: 20.1% Rubber and leather, textiles, wood, other: 9% Food wastes: 8.9% Metals: 8.9% Glass: 8.4% Plastics: 7.3% Misc. Inorganic wastes: 1.8%
