Bovine biogas
Dairy co-op sees major potential in methane gas recovery technology
By Steve Thompson
USDA Rural Development
Editor’s note: this article is the first of a series examining
alternative energy technologies being used, or explored, by farm and
utility cooperatives. In an upcoming issue of “Rural Cooperatives,”
the focus will be on a utility co-op pursuing methane recovery from
a landfill operation and other co-ops that use wind and solar power.
he late Buckminster Fuller, the inventor of the
geodesic dome and many other brilliant innovations,
used to say that pollution is merely a
resource that isn’t being used properly. That’s a
concept some co-ops are finding helpful as they
struggle to both improve the bottom line and meet their
environmental obligations.
In Oregon, the Tillamook County Creamery Association,
maker of the famous Tillamook Cheese and other high-quality
dairy products, hopes turning manure into methane will
help its members do their part in preserving water quality in
the beautiful Tillamook Bay estuary.
Manure disposal poses environmental challenge
Tightening environmental regulations regarding the use
and disposal of manure are affecting increasing numbers of
livestock farmers across the country, and the dairy farmers
of Tillamook County want to deal with the issue before it
becomes a problem. Located in a coastal area on a large
estuary, co-op members hope to increase production and
keep down costs while continuing to make sure their
manure management practices are environmentally sound.
For solutions, the co-op and its partners in local government
are looking not at exotic new management practices or
high-tech methods, but at technology similar to one in use
in sewage treatment plants for the past 50 years: methaneproducing
digesters.
A single lactating dairy cow produces up to 119 pounds
of manure a day. In Tillamook County, most farmers use
the traditional method of disposal—storing it and then
spreading the manure on pasture and cropland. Despite
improvements in traditional conservation measures, such as
increases in the width of streamside buffer zones, manure
spreading can result in nutrient and bacterial runoff
(including phosphorus and nitrogen compounds) from the
fields into the streams and rivers that feed into the estuary.
If nutrient levels are too high, the nutrient compounds can
promote growth of unwanted aquatic plants and algae,
which, when they decay and die, can use up dissolved oxygen.
This process can kill fish and other aquatic organisms.
More and wider buffer zones may offer increased protection,
but these buffers also hurt the bottom line for farmers
by shrinking productive land.
Excessive nutrient levels are not a problem in the Tillamook
Bay watershed, although the coastal ecosystem is
already stressed by high levels of sediment runoff from a
large area of forestland denuded by fires. While nutrient
levels in the estuary remain within acceptable limits, contamination
from fecal coliform bacteria is another matter.
Harvesting oysters and other shellfish in Tillamook Bay is
an important source of income in the county, and bacteria
levels in the bay prevent shellfish harvesting between 90 and
120 days every year. Recreational swimming and boating
activities are also affected.
Most of the bacteria come from nonfarm
sources: an Oregon State University
study found that dairy livestock were the
source of only 28 percent of the bacteria,
much of it due to manure spreading during
the rainy season—November through
March. Spreading manure during these
months increases the risk of runoff of
nutrients and bacteria.
Government agencies have responded to
the problem by resorting to stringent regulations.
This year, the Oregon Department of
Environmental Quality established standards
for maximum bacterial “load” caused by
runoff into the estuary watershed.
Seeking cost-effective solutions
Meanwhile, demand for the world-famous
Tillamook cheese is increasing, and the coop
and its members want to ensure that environmental
considerations do not hinder future expansion.
Cost and regulatory considerations put the co-op in a bind
when seeking alternative means of disposal. Trucking manure
any farther than a few miles is not cost-effective, and anywhere
it is taken, there can be no escaping environmental
problems and associated costs caused by the large amount of
waste generated by 160 dairy operations and more than
60,000 cows. Increasing manure storage capacity on the farm
is not ideal, because it requires significant capital expenditures.
What the Tillamook co-op needs is a more lucrative
use for manure—to increase its value, which in turn will make
its disposal less costly.
Jack Crider, manager of the Port of Tillamook Bay, thinks
methane generation can provide the solution. For the past 12
years, the Port has been attempting to find a practical way to
apply methane generation technology, similar to that used in
thousands of municipal sewage treatment plants, to Tillamook’s
manure disposal dilemma.
Methane generation from animal or human waste is not a
complicated process. Manure is loaded into a digester—which is
basically a large tank. There, anaerobic bacteria already present
in the manure ferment the waste, producing heat and gas. The
gas produced is called “biogas,” and consists of 50 to 80 percent
methane—the same gas distributed by utilities as “natural gas.”
The rest is carbon dioxide, water (5 percent) and small amounts
of contaminants including hydrogen sulfide and other corrosive
and odor-causing compounds.
According to the Department of Energy’s National
Renewable Energy Laboratory (NREL), biogas has an energy
value of approximately 600 to 800 Btu per cubic foot. It
can be used to produce heat through direct, external combustion,
or it can run internal combustion engines that power
generators. Electricity produced from dairy manure using
this process costs about 6 to 7 cents a kilowatt-hour—
approximately twice the wholesale price of conventionally
produced power in the Tillamook area.
However, as far as the Tillamook farmers are concerned,
generating electricity from methane isn’t the only benefit of
the digestion process. Molecules containing carbon are
known to chemists as “organic compounds.” Cellulose and
other organic compounds make up the majority of the plant
material cows eat and about 50 percent of the dry mass of
their manure.
According to Ralph Overend, a researcher at NREL,
these carbon compounds are undesirable bulk when manure
is used as fertilizer. Moreover, the high proportion of organic
substances in cow manure ordinarily inhibit the action of
beneficial microbes, which, if given the chance, can transform
ammonia and other smelly, volatile and problematic
nitrogen-bearing substances in the manure. “By turning 70
to 90 percent of the carbon present in manure into methane
and carbon dioxide,” says Overend, “the digestion process
reduces what we call ‘organic loading’ and allows the beneficial
microbes to work.”
The result is nitrogen compounds that are far less obnoxious
and far more useful as fertilizers. Nearly odorless, they are
much more readily utilized by plants, and, if applied properly,
much less likely to run off and contaminate ponds, lakes and
waterways. The remaining bulky organic substances can be
separated out, greatly reducing storage needs. And the problem
of bacterial contamination is solved, too. The heat produced
by biogas generation kills fecal coliform and other
harmful bacteria.
The final products are a solid, fibrous material and a liquid
with the consistency of milk—both nearly odorless. The
fiber can be used as animal bedding or as a high-quality potting
soil. The liquid can be stored and applied to fields as
high-quality fertilizer.
AgSTAR promotes technology
The Environmental Protection Agency EPA administers a
program called AgSTAR to promote methane generation
technology for livestock facilities. EPA estimates that over
2,000 such facilities could install and operate cost-effective
biogas systems.
When the program was first instituted in the 1970s,
approximately 100 on-farm digester systems were built using
AgSTAR technical assistance and subsidies. However, most
were failures, for a number of reasons. The materials used
for construction, it later turned out, were not appropriate for
digesters: tanks and pipes were made of mild steel, which
quickly rusted when exposed to the highly corrosive compounds
produced by biologic action on manure. According
to Overend, the units were also too small to be practical—
capable of handling 1,000 to 3,000 tons
of manure per year. Maintenance and
operation of the digesters imposed
unacceptable time burdens and skill
requirements on farmers already
required to be welders, mechanics,
plumbers, electricians and general jacksof-
all-trades.
Finally, the digester systems did not
have provisions for dealing with hydrogen
sulfide—the substance that gives rotten
eggs their offensive smell—and other
potential pollutants. When burned,
hydrogen sulfide combines with oxygen
to produce sulfur dioxide, which reacts
with moisture to produce sulfuric acid.
This not only has a deleterious effect on
equipment, but contributes to the acid
rain problem as well.
Agricultural digester technology has
come a long way since those first
attempts. Much of the progress has
been achieved in Denmark and other
been achieved in Denmark and other
European countries, with changes forced by rigorous environmental
regulations and public opinion. Where necessary,
steel has been replaced by concrete, fiberglass, PVC and
other non-corrosive materials. Scrubbing technology similar
to that used in coal-fired power plants now removes
harmful sulfur and other compounds, and larger digester
operations have proven to be more efficient.
In the 1990s, some of the units were updated and expanded,
and others were built using more developed technology in
response to increasing environmental regulatory pressures.
Today, about 20 on-farm digesters are in operation, with
mixed success.
Recognizing the possibilities
Tillamook recognized the possibilities
of digester technology more than a
decade ago. In 1989, the Methane Energy
and Agricultural Development
(MEAD) project was founded through
an intergovernmental agreement
between the Tillamook Public Utility
District and the Tillamook County Soil
and Water Conservation District. The
project managed to gain special funding
from Congress, administered through
the AgSTAR program, to develop a plan
for a digester system that would provide electrical power to the
public utility grid.
MEAD issued three requests for proposals (RFPs) in the
1990s, calling for the design and construction of a centralized
facility that would handle all the dairy cow manure produced
in the county. Unfortunately, none of the proposals received
proved to be feasible. Though a large
digester-generator facility did offer efficiencies
of scale on its own, the transport
of manure from throughout the
county by trucks drove up costs. Participating
farmers would be required to
pay tipping fees that were too high to
be cost effective. In any case, the project
was just too big and expensive for
the county to obtain financing for.
Meanwhile, Craven Farms, a large
dairy farm in the county, went ahead
with its own anaerobic digester-generator
project. This project used a plugflow
digester (see sidebar) designed by
Resource Conservation Management
Digesters Inc., a consultant firm located
in Berkeley, Calif. Generating 120
kilowatts of power, the set-up helped
alleviate the dairy’s manure problem,
while at the same time providing
income both from electricity sold to
the utility district and from fiber solids
sold as animal bedding. It also provided heat for the milking
parlor and the farm’s hot water supply.
While the project was successful for a short time, the farm
was later sold. The new owners shut down the digester last
year. However, it had demonstrated the potential of available
technology. After further research and consultation with the
Department of Energy (DOE), the National Renewable
Energy Laboratory and the firm that built the Craven facility,
MEAD decided to try a new approach.
Instead of building a huge, centralized facility, the plan is to
build one to handle the manure of a few dairies. It will be
located close enough to the farms to keep transportation costs
acceptable. If it proves successful, the revenues from the pilot
project could be used to service financing for a second system,
and so on. The ultimate goal is to have a network of digestergenerators,
each facility handling the manure from four to six
nearby dairies, each large enough to take advantage of
economies of scale.
The contractor, RCM Digesters, is the largest firm in the
United States building agricultural digester systems, and has built
a number of successful projects. Together, MEAD and RCM
developed a plan to build and operate a project that would
process the manure from 2,000 dairy cows, using two digesters
operating side by side. A site is readily available: a former U.S.
Navy base, now an industrial park owned by the Port of Tillamook,
with a large concrete pad—the remnant of a World War II
blimp hangar.
Power generated by the project will be sold to the utility
district. The processed liquid will be returned to the farm for
storage until application on crop and pastureland. Oregon
State University researchers have developed a marketable
potting soil from dairy digester solids, and Crider is working
on a deal for its sale, adding to the revenue stream. He is
confident of the substance’s market appeal: a Chinese dairy
digester project exports its digested solids to the Netherlands
for use in growing tulips.
One potential problem is the spread of contaminants
through the mixing of manures from different farms.
“That’s why the facility will have two digesters instead of
one,” says Crider. Only manure from two farms will be
processed in the same digester, and care will be taken to
reduce mixing to a minimum. The microbial profiles of
the farms will be carefully matched to minimize cross-contamination.
The final hurdle
Financing the project is the final hurdle. Neither the Port
of Tillamook, the county, nor the Tillamook co-op has the
funds for the initial capital investment, and private sources
are not willing to shoulder the risk. Crider and his colleagues
believe that if the pilot project proves economically successful,
financing the others won’t be a problem. “The digesters
already operating will give us a reliable revenue stream to
cover debt service,” he says.
In August, MEAD applied for funding from the DOE’s
Energy Efficiency and Renewable Energy (EERE) program.
DOE policy is to offer assistance in the building of methane
recovery systems, including financing for electrical generation
projects through its Biopower program. Biopower funding
is available for both demonstration projects and proven
commercial applications of alternative biomass energy
sources. Biomass refers to organically produced energy
sources, including manure; plant byproducts such as wood
chips, bagasse (sugarcane residue), and others; and also crops
grown specifically as fuel.
Jack Crider is confident the project can work. If it does, it
may provide a model for other dairy co-ops across the nation
as conflicts occur over the need to produce food and to protect
water supplies.
