Pesticide and Environmental Update
Fueling
the Farm
Waste for Energy and Independence
Imagine turning a noxious agricultural waste into a
value-added bioenergy product for on-farm heating and power—or even into
transportation fuels.
Agricultural engineer Keri Cantrell, environmental
engineer Kyoung Ro, and research leader Patrick Hunt work at the ARS
Coastal Plains Soil, Water, and Plant Research Center in Florence, South
Carolina. They have teamed up to explore how thermochemical conversion
technologies could be used to generate bioenergy from manure—a resource
that the United States, with its intensive livestock production, has in
abundance.
“Our goal is to develop new waste-treatment
methods and strategies that small farms and concentrated animal-production
facilities could use to meet their energy needs,” Cantrell says.
One approach—wet gasification—converts wet
manure slurry into energy-rich gases and relatively clean water. The
catalytic version of this technology is under development at the U.S.
Department of Energy (DOE) Pacific Northwest National Laboratory. This
process is expected to destroy pathogens and has been found to destroy
odor-generating volatile organic compounds at the processing conditions of
350°C.
At this high temperature, wet gasification can
destroy pharmaceutically active components like hormones. This process
could theoretically convert the manure in as little as 15 minutes, far
exceeding the days and months required by existing anaerobic and
composting methods.
The Florence researchers developed a cost-benefit
model of wet gasification to calculate estimated returns and concluded
that liquid swine waste can have a net energy potential comparable to that
of brown coal.
In addition, the ARS team is investigating pyrolysis
technology, which uses heat and an atmosphere devoid of oxygen to convert
the manure into a char, or “green coal.”
“Green coal can serve as an energy source for
on-farm use, or it can be transported to coal power plants for feedstock,”
Ro says. “It can also be transformed into activated charcoal. This
charcoal can be applied to soil to improve soil quality, and it also
reduces greenhouse gases by permanently sequestering carbon.”
The group is also working in collaboration with the
Advanced Fuels Group at the DOE Brookhaven National Laboratory in New
York. They are evaluating different catalysts needed to facilitate
conversion of “syngas”—the gas produced when animal wastes and other
biomass are gasified—to liquid fuels.
“Computers used to take up the basement of the
math building,” Hunt says. “We’d like to be able to shrink down a
process to run the farm engine in the same way.” With this kind of
system, farmers would be able to produce their own energy sources and
eliminate the need to transport manure offsite. The trick is to make the
system productive and affordable.
The Florence researchers know that the benefits of
any biofuel must be weighed against its economic and environmental
production costs. “The truly exciting reality is that numerous needs in
energy, nutrient recycling, climate change, and biosecurity will foster
synergistic development of technology for future agriculture,” Hunt
says. “Our research is only one part of the answer as we look for new
energy supplies.”—By Ann Perry, Agricultural Research Service
Information Staff.
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