Documents, Tools and Resources
Methane Recovery from Manure: Control Odor and Produce Energy
by Paul Miller, USDA-Natural Resources Conservation Service,
Des Moines
It might surprise a lot of people, but manure can be nearly
odor free. And it could make you money! New advances in methane
digestion technology are finding success in Iowa. Several different
types of anaerobic digesters have recently been installed in
Iowa with assistance from the USDA-Natural Resources Conservation
Service (NRCS) and AgSTAR. AgSTAR is a voluntary program of
the U.S. Environmental Protection Agency that is designed to
encourage the widespread use of livestock manure as an energy
source.
Methane Process. According to Shihwu Sung, assistant professor
in environmental engineering, and director of Anaerobic Systems
Engineering at Iowa State University, anaerobic digestion occurs
when bacteria produce biogas by decomposing organic matter,
such as manure, in an environment without air. The process
involves the following three steps:
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Hydrolytic bacteria convert complex particulate matter
into dissolved compounds with low molecular weight.
-
Acidongenic/acetogenic bacteria convert the dissolved
compounds into organic acids and hydrogen.
-
Methanogenic bacteria finally consume these acids or hydrogen
to generate methane and carbon dioxide.
Anaerobic digesters are sealed with covers that trap the
biogas produced in the digester. The biogas is then pulled
from the digester by providing a slight vacuum on a pipe with
a gas pump or blower. Biogas, which contains 60-80 percent
methane and has a heating value of approximately 600-800 Btu/ft3,
is then used to produce energy. Methane can power an engine
generator to produce electricity and can be used to operate
a boiler or space heater, as well as chilling and refrigeration
equipment. Gas that is not used for energy production is ignited
and flared to reduce methane emissions and odor.
Success Stories. Gary Boland of Williamsburg, Iowa, wanted
to reduce the odor coming from his earthen manure basin that
served his pig nurseries. A floating cover, placed over the
basin and kept afloat on top of the manure with 10-foot-long
foam board logs, captures the biogas (approximately 60 percent
methane). Methane produced by the stored manure is burned in
a solar-operated flare, reducing or eliminating odor. The manure
can still be used as fertilizer because none of the nutrients
are lost or destroyed. Gary's extra cost for the cover was
about $7.50 per head for his 2,700 head nursery (about $1.00
per square foot of basin surface).
Steve Crawford, a Story County hog producer, is testing new
anaerobic digestion technology. The anaerobic sequencing batch
reactor (ASBR), developed at Iowa State University, has been
highly successful at converting swine manure to biogas. The
ASBR is currently producing biogas with more than 70 percent
methane and is using the biogas to operate a boiler to produce
heat. This on-farm system treats the manure from 2,800 hogs
and is being used for a demonstration site. The per-head cost
was approximately $65 based on 5,000 head the unit was designed
to handle.
SWIneUSA, located in Union County, is currently operating
a complete mix anaerobic digester on a 5,000-head farrow-to-wean
swine operation. The biogas from the $100-per-sow digester
is operating an engine generator that currently produces 60
kilowatts of electricity for use at the operation. The unit
provides most of the energy needed by the farm. Waste heat
from the engine generator is captured and used to heat the
digester.
Pollution Concerns. Growth of the livestock industry has generated
the need for improved methods of manure management that are
cost-effective and reliable. Pollutants from decomposing livestock
manure can cause major problems, including surface and groundwater
contamination as well as surface air pollution caused by odors,
dust, and ammonia. Then there is the additional concern over
the contribution of methane emissions to global climate change.
In response, researchers have developed advances in biogas
technology. The technology promotes the recovery and use of
biogas to generate electricity or for heating and cooling needs.
The First Farm-Based Digester. In 1972, a farm near the town
of Mt. Pleasant, Iowa, became the site of the first farm-based
methane digester in the United States. The McCabe farm, a hog
production facility, was near a town that was expanding to
the farm's border and the McCabe's had to find an odor-free
system of managing swine manure. It took several years of development,
but a successful digester was created by adapting technology
from a municipal wastewater treatment facility. The system
has experienced very few problems and is used solely for odor
control.
Major Improvements. The recovery of methane from animal manure
is not new technology. More than 2 decades of research has
gone into biogas systems that were developed in the 1970s when
oil prices began to escalate. These early systems often failed.
Biogas systems such as anaerobic digesters have a much greater
success level now because of the improved technical support
and increased profitability through the sale of manure by-products.
Some dairy facilities report that they generate more revenue
from the sale of electricity and other by-products than from
the sale of milk. Aside from the moneymaking factors, digesters
do help reduce odors. And that is a major concern for many
livestock producers in Iowa.
For More Information. The USDA-NRCS can help landowners decide
if a biogas system is appropriate for their operation. AgSTAR
estimates that more than 2,000 livestock facilities across
the United States could benefit from biogas recovery systems.
For more information, please contact me at 515-284-4370. For Internet resources
on manure management and the AgSTAR program, visit http://extension.agron.iastate.edu/immag  under
the Publications link.
Reprinted with permission from the Fall 1999 issue of the
Iowa State Extension Bulletin.
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