Research
from North Carolina State Univ. shows that so-called biodegradable products are
likely doing more harm than good in landfills, because they are releasing a
powerful greenhouse gas as they break down.
“Biodegradable
materials, such as disposable cups and utensils, are broken down in landfills
by microorganisms that then produce methane,” says Dr. Morton Barlaz, co-author
of a paper describing the research and professor and head of NC State’s
Department of Civil, Construction, and Environmental Engineering. “Methane can
be a valuable energy source when captured, but is a potent greenhouse gas when
released into the atmosphere.”
And
the U.S. Environmental Protection Agency (EPA) estimates that only about 35% of
municipal solid waste goes to landfills that capture methane for energy use.
EPA estimates that another 34% of landfills capture methane and burn it off
on-site, while 31% allow the methane to escape.
“In
other words,” Barlaz says, “biodegradable products are not necessarily more
environmentally friendly when disposed in landfills.”
This
problem may be exacerbated by the rate at which these man-made biodegradable
materials break down. Federal Trade Commission (FTC) guidelines call for
products marked as “biodegradable” to decompose within “a reasonably short
period of time” after disposal. But such rapid degradation may actually be
environmentally harmful, because federal regulations do not require landfills
that collect methane to install gas collection systems for at least two years
after the waste is buried. If materials break down and release methane quickly,
much of that methane will likely be emitted before the collection technology is
installed. This means less potential fuel for energy use, and more greenhouse
gas emissions.
As
a result, the researchers find that a slower rate of biodegradation is actually
more environmentally friendly, because the bulk of the methane production will
occur after the methane collection system is in place. Some specific
biodegradable products such as bags that hold yard waste and are always sent to
composting or anaerobic digestion facilities were not included in the study.
“If
we want to maximize the environmental benefit of biodegradable products in
landfills,” Barlaz says, “we need to both expand methane collection at
landfills and design these products to degrade more slowly—in contrast to FTC
guidance.”
The
paper, “Is Biodegradability a Desirable Attribute for Discarded
Solid Waste? Perspectives from a National Landfill Greenhouse Gas Inventory
Model,” was co-authored by Barlaz and NC State PhD student James Levis, and
was published online in Environmental Science & Technology.
