Researchers study why waste in bioreactor landfills degrades in haste
 art of Professor Craig
Benson’s laboratory looks—and smells—like a landfill.
It’s not that Benson is excessively messy. Rather, he’s
studying bioreactor landfills, a relatively recent technology in solid-waste
management that may help landfill owners make better use of their land—and
of the waste itself.
Traditional landfills incorporate systems to collect
leachate and limit waste exposure to liquids like rain. However, bioreactor
landfills, which have emerged over the past decade, are designed to
recirculate liquids such as rainwater or leachate through the waste
to break it down more efficiently. “Rather than sending the leachate—the
contaminated liquid—off site to be treated at a plant, we just
pipe it back up and send it through the waste to help the degradation
process,” says Benson.
He and Morton Barlaz (MSCEE ’85, PhDCEE ’88),
a professor of civil and environmental engineering at North Carolina
State University, are developing computer-based tools that will help
predict bioreactor landfill behavior. Their comprehensive research project
combines their expertise in solid-waste containment, hydrology and decomposition.
Thanks to advances like improved liners and barrier
systems for traditional landfills, bioreactor landfill managers can
operate their sites without worrying that the liquid will leak and contaminate
groundwater. “Things that go in a landfill stay in there,”
says Benson. “So we can put liquids in confidently.”
Because liquids enhance microbial processes key to
waste degradation—meaning that waste breaks down and compacts
more quickly than in traditional dry landfills—one benefit to
bioreactor landfill owners is increased “airspace,” or volume,
in the landfill. Since landfills close when the land and airspace are
full, bioreactor landfill owners are able to squeeze more years of life
out of their land.
Owners of traditional landfills pay to send their
leachate to a water-treatment plant, while bioreactor landfill owners
recirculate leachate. “It has an in situ
treatment system—so you just loop it through, and as the system
goes through its biochemical changes, it tends to lock up most of the
contaminants, which is a real advantage,” says Benson. “So
you have a more sustainable management system. It’s cleaning itself.”
A number of demonstration bioreactor landfills exist,
including those in Canada and the United States. “There’s
a lot of interest in this nationwide in the solid-waste community because
of the practical and economic advantages,” he says. “This
is something that a lot of people are trying.”
Bioreactor landfills are relatively simple in concept;
yet, it’s difficult to predict their behavior—in part, because
there are so many variables, says Benson. For example, the waste material
itself is comprised of many materials. The biological processes that
break down waste can vary. Thermal conditions within the landfill, as
well as the amount, temperature and type of recirculated liquid, can
change.
For their research, Benson and Barlaz each have established
bioreactor landfills in their own laboratories. With their industrial
partners, they have installed sensors in several operating bioreactor
landfills around the country and are monitoring their processes and
conditions. Eventually, they will construct computer models to simulate
those processes and conditions.
Their data and resulting predictive tools could help
state and federal agencies regulate and evaluate bioreactor landfills.
They also may help waste management companies make decisions about siting
and operating new landfills.
A three-year, $750,000 National Science Foundation
Partnerships for Innovation grant is funding the project.
| |
