Scientists Sift Through Trash In Search Of Perfect Landfill

February 16, 1998

MADISON - Robert Ham believes well-designed landfills can be tools for recycling, rather than tombs that harbor trash for generations.

As one of the country's leading landfill experts, the UW-Madison emeritus professor of civil engineering has spent his career studying the things we put on the curb and forget. Ham's latest study might be the clearest indication yet of what happens to landfilled materials.

Knowing how and what materials degrade is the first step toward making landfills better garbage-eating machines - and providing an energy source from methane, Ham says.

At the start of a six-year study, Ham's research team loaded up mesh sacks full of fresh all-American garbage, from soiled diapers to lima beans, and lowered them 10 feet into three landfills across the country. Then they dug them up again - after one year, after 2.5 years and after six years - and sorted through the mass, dried it, weighed it and ran chemical tests.

What Ham and former graduate students Timothy Baldwin and Jeffrey Stinson found might surprise people: Much of our garbage, under the right conditions, moves quite nicely toward oblivion.

This study was a reversal of most landfill surveys, which take core samples from material already buried. Ham says this study gave them controlled information at landfills in Florida, Pennsylvania and Madison on 11 representative types of trash.

"By tracking what happens to the very items we put down, we know exactly what the weight and composition was at day zero," Ham says. It showed conclusively that landfills need not be "tombs" holding waste unchanged for decades.

The study found that food decomposes relatively quickly. After six years in the Madison site, pasta, lima beans, peanuts and sunflower seeds all lost at least half of their dry weight, and pasta almost completely vanished. In Florida, the food samples were all more than 75 percent decomposed after only two years.

Newspaper was the only material that showed little change: Only 17.4 percent decomposed in Florida after two years, and 8.5 percent in Madison after six years.

Diapers, seen by many as a symbol of landfill problems, produced mixed results in the study. Nearly all diapers on the market contain additives, such as absorbent gels or waterproof plastics, that slow decomposition rates. The buried diapers were between 12 and 56 percent decomposed after six years in the Madison site. In Florida, however, the same types of diapers degraded between 65 and 75 percent in two years.

Why the difference? The Florida did not have a clay cap during the study, which would have sealed it from the elements. Caps are federally mandated to reduce pollution from water flowing into landfills. In the process, however, they reduce moisture content in the waste, the "master variable" in helping garbage decompose.

Capping landfills does reduce production of contaminated water or leachate, but the practice virtually guarantees that the material stays around indefinitely. Ham believes there's an environmentally better alternative, that would control water contamination and accelerate decomposition.

Charles Pettigrew, senior scientist with Procter and Gamble, which co-funded Ham's six-year study, says the information it revealed about decomposition rates confirms many of their laboratory findings about landfilled materials. Procter and Gamble has been funding solid-waste alternatives for years, including studies of large-scale composting alternatives, Pettigrew says. But so far, municipalities have been reluctant to try other methods because landfills remain the cheapest alternative.

Using information from this study, Ham has started a new project to design "landfills of the future." In partnership with a Wisconsin waste-management company and Montgomery Wattson, an engineering consulting firm with a Madison office, Ham is creating a full-scale demonstration that will promote degradation of waste in landfills, forming methane gas for use as an energy source. "There are some landfills in the country putting out enough energy to provide electricity for 10,000 homes," Ham says.

The approach could allow the majority of waste that decomposes quickly to disappear while safely sealing away the rest in a capped landfill, he says.

Ham says the country should be doing more to eliminate long-term problems with garbage. "We've shown that we can accelerate decomposition over a shorter period of time, rather than leaving it for our grandchildren to deal with," he says.

- Brian Mattmiller, (608) 262-9772

University of Wisconsin-Madison

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