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
Contact: Robert Ham
University of Wisconsin-Madison