We all want to leave a lighter mark on the planet, so when we see products advertised as "biodegradable," it's natural to assume they're a greener choice. After all, who wouldn't want a product to degrade back into the planet from which it came? But thanks to the garbage collection system in the U.S., in which 55 percent of all our garbage winds up in landfills, "biodegradable" could actually be a bad thing, according to a study in the journal Environmental Science & Technology.
THE DETAILS: As things like food waste, yard clippings, paper, and other purportedly biodegradable goods break down in oxygen-deprived landfills, they release two potent greenhouse gases, methane and carbon dioxide. While the carbon dioxide doesn’t escape (it usually stays underground and is stored in the landfill), methane escapes into the atmosphere, exacerbating global warming. In fact, landfills are the third-largest source of man-made methane emissions in the U.S. A third of the garbage we toss goes to landfills that collect that methane and convert it to energy, and the authors wanted to know whether the garbage in those landfills was degrading slowly enough for the gas to be converted to energy, mitigating its global warming effects, says James W. Levis, a PhD candidate in the department of civil, construction, and environmental engineering at North Carolina State University. "And what our study shows is, no," he says.
Using computer modeling, the researchers studied how various materials would decompose under different landfill conditions. Specifically, they looked at food waste, standard solid waste, newsprint, office paper, and a new biodegradable plastic polymer called PHBO that's usually created from plant sugars or starches (this type of plastic is different from corn-based plastics and is made by Proctor & Gamble, which provided funding for the study) to see how much methane gas each generated as it decomposed. In the average landfill, biodegradable plastic generated the most methane, followed by office paper, food waste, newspaper, and other forms of solid waste. Collection efficiencies for all the methane produced (the amount of methane collected that was converted into usable energy) didn't exceed 57 percent. Because the items decomposed at different rates—food waste degrades faster than biodegradable plastics, which degrade faster than office paper and newsprint—they released methane at different rates and times making it difficult to capture all the methane.
Published on: August 11, 2011