Dumping Myths About Trash
Some people may think this column is garbage, but chances are it will be around a long, long time--not because of any literary merit, but because it is published on newsprint.
A major study of how various materials decompose in landfills has surprised experts, who expected newsprint to degrade rapidly because one of its principal constituents--cellulose--normally decomposes quickly.
But it turns out cellulose is virtually encapsulated by another organic component of wood products, lignin. And lignin decomposes very slowly, thereby preserving the cellulose and greatly retarding the decomposition process.
“That’s been the biggest surprise,” said Robert Ham, professor emeritus of civil engineering at the University of Wisconsin in Madison, who headed a six-year study of landfills. The subject is of great concern across the country because landfills, the ultimate repositories for the waste we generate in our homes and factories, take up enormous amounts of space.
And space problems can be eased by accelerating decomposition.
“Decomposition translates to a lot less material,” he said.
Decomposition also produces methane gas. Ham, who is one of the nation’s leading authorities on landfills, had expected the rate of decomposition--and thus the production of methane--to be considerably higher than it has turned out to be.
“I wrote some things 15 years ago that I wish I hadn’t written,” Ham said in a telephone interview.
Part of the problem, he said, stems from our success at isolating the hazardous materials in landfills. Keeping them dry has reduced the chances of water leaching out some of the contaminants, retarding decomposition.
Six years ago, Ham’s research team packed garbage into mesh sacks and lowered the sacks 10 feet into landfills in Florida, Pennsylvania and Wisconsin. The sacks included everything from pasta to newsprint.
The sacks were dug up at varying intervals: some at one year, some at 2 1/2 years, and the rest at six years.
By analyzing the contents, the researchers were able to determine the rate of decomposition of various materials. Pasta had disappeared almost completely after six years, and other foods also decomposed fairly quickly.
But the system worked far more efficiently in Florida than in the other sites. It turns out that water, which Ham calls the “master variable” in decomposition, was far more pervasive in the Florida site than in the others.
Florida was the only site not covered by a clay cap, now required by federal law at all landfills. The lack of a cap allowed more water to seep into the garbage.
Diapers, which contain additives such as absorbent gels or waterproof plastics that slow decomposition rates, degraded between 65% and 75% after only two years in the Florida site. But at the Wisconsin site, the diapers had decomposed by only about 56% after six years, and some of the diapers there resisted decomposition almost entirely.
About 17.4% of the newsprint decomposed in Florida after two years, but only 8.5% rotted in Wisconsin after six years.
The difference, Ham said, was in the moisture. He concluded that controlled introduction of water into landfills could accelerate decomposition significantly without endangering the environment.
“I can’t live with releasing any of that stuff into the environment,” Ham said. “We’re trying to promote decomposition within existing guidelines.” In other words, add enough moisture to speed up decomposition, but not enough to compromise the integrity of the landfill.
Faster decomposition also leads to a higher production of methane gas, which is both a curse and a blessing from landfills. But even that has not turned out the way Ham had expected.
Southern California Edison was a pioneer in the effort to capture methane from landfills and use it to generate electricity. The Palos Verdes landfill was the first such facility in the country.
But production of methane has been much lower than expected. A spokesman for the Southern California utility said the company is no longer aggressively pursuing that technology, apparently because of disappointing results.
If landfills can be made more efficient in their rates of decomposition, the production of methane would go up, making the substance a more viable resource.
Despite the disappointing rates of gas production, landfills still create significant amounts of methane, which has been targeted as a global warming gas and under federal law must be controlled. That’s one reason nearly all large landfills--at least 150 across the country--capture the gas and convert it into electricity.
“You have to collect the gas for regulatory purposes, so you might as well get some money out of it,” Ham said.
Ham will soon get a chance to put some of his ideas to the test. He will direct research on a new Wisconsin landfill, which will be designed as sort of a garbage-pile laboratory. He will be able to control moisture in the landfill, for example, to see just how much he can boost decomposition.
He hopes that will break down the lignin, for example, which would allow this column to degrade at a much faster rate.
He also plans to do a number of other things, including mixing the bacteria from degraded materials with fresh garbage to see if that accelerates decomposition.
What the research suggests, he said, is the value of recycling. But nationally, such efforts have been spotty, at best. He said he knows of some demolition projects in which 90% of the waste has been recycled.
Various materials that were once destined for landfills are now being used in consumer products. National Gypsum Co., for example, recently announced the construction of a new plant in St. Louis to use some byproducts from coal-burning generating plants as raw materials for wallboard.
Recycling programs reduce the amount of material going into landfills, Ham said, but they do not eliminate the need.
“You’ve got to have a landfill to back up the system,” he said.
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Lee Dye can be reached via e-mail at leedye@compuserve.com
