Q CP/V United States Environmental
Protection Agency
Managing Manure with
Biogas Recovery Systems
Improved Performance at Competitive Costs
The AgSTAR Program
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Office of Air and Radiation (6202J)
EPA-430-F-02-004
www.epa.gov
Winter 2002
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Managing Manure with Biogas
Recovery Systems *
Improved Performance at Competitive Costs
mi.
One of the biggest challenges
that livestock producers face
is managing manure and
process water in a way that
controls odors and protects environ-
mental quality. Biogas recovery systems
can help producers meet this challenge.
The environmental benefits provided
by these systems far exceed those sup-
plied by "conventional" liquid and
slurry manure management systems
(e.g., storage tanks, storage ponds,
lagoons). These benefits include odor
control, improved air and water quality,
improved nutrient management flexi-
bility, and the opportunity to reduce
greenhouse gas emissions and capture
biogas—a useful source of energy.
About Anaerobic
Digestion
Biogas recovery systems are sometimes
known as anaerobic digesters, because
they use a process called anaerobic
digestion. (Conventional lagoons oper-
ate on the same biological principle.)
During anaerobic digestion, bacteria
break down manure in an oxygen-free
environment. One of the natural prod-
ucts of anaerobic digestion is biogas,
which typically contains between 60 to
70 percent methane, 30 to 40 percent
carbon dioxide, and trace amounts of
other gases.
Biogas and energy. When biogas is cap-
tured, it can be used to generate heat,
hot water, or electricity—significantly
reducing the cost of electricity and
other farm fuels such as natural gas,
propane, and fuel oil. Biogas can also
be flared to control odor if energ
recovery is not feasible. Both the flar-
ing and use of biogas reduce
greenhouse gas emissions. Biogas is a
renewable source of energy with much
lower environmental impacts than
conventional fossil fuel. The methane
generated from anaerobic digestion
provides rural electric cooperatives and
utilities with a source of "green power"
to sell to customers who wish to pur-
chase power from renewable sources.
Biogas recovery also provides rural
energy benefits such as distributed
generation and voltage support.
High-quality fertilizer and soil
amendment. Because anaerobic diges-
tion reduces ammonia losses, digested
manure can contain more valuable
nitrogen for crop production. Also, the
fiber in digested dairy manure can be
used on the farm as bedding or recov-
ered for sale as a high-quality potting
soil ingredient or mulch.
Floating gas collection cover on a
8,600-hog finishing farm lagoon.
Managing Manure with Biogas Recovery Systems
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Creating Energy on the Farm and for the
Community - The Haubenschild Experience
In September 1999, Dennis Haubenschild and sons Tom and Bryan,
owners and operators of Haubenschild Farms in Princeton, Minnesota,
completed the installation of a heated plug flow digester at their
500-cow freestall dairy. The methane-rich biogas generated by the
system fuels an engine attached to a 150 kWh generator set.
The Haubenschilds sell the excess electricity produced to their local
electric cooperative, East Central Energy (ECE). Heat, recovered as
hot water from the engine and exhaust, is stored in an insulated
tank and is used to maintain the digester's temperature and heat the
milking parlor floor.
In its first two years of operation, the system produced 1.9 million kWh
of power from 46 million cubic feet of biogas. The methane recovery
system has produced revenues from the sale of electricity and reduced
farm expenditures by virtually eliminating propane purchases, while
contributing to the farm's environmentally sound manure management
strategy. "Its great!" reports Dennis Haubenschild. "My digester system
is working, meeting and exceeding my expectations—particularly my
environmental expectations."
Under a power purchase agreement, ECE purchases all excess
energy from the Haubenschild farm and resells the energy to other
customers who participate in the cooperative's renewable energy
program.
"We're very pleased to assist the Haubenschilds in the development
of this exciting new renewable energy project, and the results are
particularly noteworthy," said Henry Fischer, ECE's Manager of
Business and Community Development. "This project exemplifies
ECE's mission, which is to enhance the quality of life and provide
premier service to our customers," Fischer added.
Fischer said, "The Haubenschild Farm project is an excellent example
of how agriculture, utilities, environmental organizations, community
groups, and others can effectively pool their resources to develop
renewable energy, promote sustainable agriculture, and ensure envi-
ronmental stewardship."
Status of Anaerobic
Digestion
Biogas recovery systems are a proven
technology. Currently, more than
30 digester systems are in operation at
commercial U.S. livestock farms,
and an additional 30 are expected to be
in operation by 2003.
How Are Biogas
Recovery Systems
Designed?
Biogas recovery systems have four basic
components: a digester, a gas-handling
system, a gas-use device, and a manure
storage tank or pond to hold the treat-
ed effluent prior to land application
(see Figure 1). Biogas recovery systems
separate the treatment and storage
functions. This design provides several
financial benefits to producers,
including:
• Lower total volume requirements,
which reduce excavation costs and
the land area required for the waste
management system.
• Lower cover costs because of smaller
lagoon surface areas.
This multiple-cell process also improves
environmental performance. These
environmental benefits are described
later in this document.
Figure 1. Schematic showing the
components and products of a biogas
recovery system.
Effluent
Electric
Generation
System
Manure Source
and Collection System
Gas
Handling
System
Flare or
Heat Source
Managing Manure with Biogas Recovery Systems
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Total Solids (%)
10 15 20
25
30
Manure
Water Added
Bedding Added
As Excreted
Classification | Liquid | Slurry | Semi-Solid |
Solid
Handling Options
Pump
Scrape
Biogas Production |_
Recommended
Scrape and Stack J>
Not Recommended j>
Digester Type Covered Compiete Plug
Lagoon Mix Flow
Figure 2. Appropriate
manure characteristics and
handling systems for
specific types of biogas
digester systems.
Is a Biogas Recovery
System Right for
My Farm?
To determine if a biogas recovery system
is right for your facility, you will need
to consider the following factors: how
manure is handled at your facility, the
frequency of manure collection, and
the options available for using the
recovered biogas.
• Manure handling. Biogas digester
systems can accommodate manure
handled as a liquid, slurry, or semi-
solid (with little or no bedding
added). The total solids content of
the manure—a measure of manure
thickness—determines these classifi-
cations. Figure 2 shows the manure
characteristics and handling systems
that are appropriate for specific types
of biogas digester systems.
• Frequency of manure collection.
Facilities best suited for biogas
digester systems typically have stable
year-round manure production, and
collect at least 50 percent of the
manure daily.
• Gas use. Several gas-use options are
available, including engines, chillers,
and boilers, or gas can simply be
flared. When choosing among these
options, you will need to take into
account how the option affects a sys-
tem's financial performance, the
labor requirements associated with
the option, and the skills needed to
maintain and repair energy produc-
ing equipment.
What Kind of
Digester Will Work
on My Farm?
Three different types of biogas recovery
systems have been commercialized for
managing manures, and several other
types of biogas recovery systems are
currently being developed. The most
suitable type of system for your opera-
tion depends on how you collect
manure and on the total solids content
of the collected manure.
• A covered lagoon digester is an earth-
en lagoon fitted with a cover that
collects biogas as it is produced from
the manure. These digesters are best
A compact, clean, low-maintenance
waste management system.
Managing Manure with Biogas Recovery Systems
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Complete mix digester.
Plug flow digester.
suited for flush or pit recharge
manure collection systems with a
total solids content of 0.5 to
3 percent.
A complete mix digester is a heated
tank, constructed of either rein-
forced concrete or steel, with a
gas-tight cover. The digester contents
are mixed periodically, either by a
motor-driven impeller or a pump.
This digester type works best with
slurry manure and with a total solids
content of 3 to 10 percent.
A plug flow digester is a long, rela-
tively narrow, heated tank, often
built below ground level, with a gas-
tight cover. Plug flow digesters are
used only for dairy manure. This
type of digester requires thick
manure ranging between 11 and 13
percent total solids. Plug flow
digesters can tolerate some bedding,
but the amount should be mini-
mized, and sand bedding must be
avoided.
Plug flow and complete mix digesters
are heated systems that operate at a
constant temperature year-round, pro-
ducing stable gas flows that support
gas-to-energy applications in all cli-
mates. Covered lagoon digesters are not
heated, and this can affect gas flow. In
warmer climates, gas flows are relatively
stable during all seasons, and the sys-
tems produce enough biogas to
financially justify energy gas uses.
However, in northern climates, gas
flows are lower during winter months,
so gas use is likely to be limited to
flares, with odor control and green-
house gas reductions as the
management objective.
AgSTAR provides several project sup-
port products about each of these
digester systems. They are available free
of charge from the AgSTAR program
at l-800-96AgSTAR (1-800-952-4782)
or on the AgSTAR Web site at
www.epa.gov/agstar.
The Environmental
Benefits of
Anaerobic Digestion
Systems
Livestock confinement facilities gener-
ate large amounts of animal waste that
can create serious environmental con-
cerns. The concentrated waste product
from decomposing livestock manure
can be environmentally detrimental if
it enters rivers, streams, or groundwater
supplies. Decomposing manure also
causes air quality concerns associated
with odor, ammonia emissions, and the
contribution of methane emissions to
global climate change. Anaerobic diges-
tion offers a number of air and water
quality benefits, including:
• Odor control. The effluent odor
from anaerobic digesters is signifi-
cantly less than odors from
conventional manure management
systems. Odor reduction using
anaerobic digestion can be very
cost-effective when compared to
other alternatives such as aeration.
Managing Manure with Biogas Recovery Systems
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Greenhouse gas reduction.
Conventional liquid and slurry
manure management practices emit
large amounts of methane, a green-
house gas that contributes to global
warming. Biogas recovery systems
capture and combust methane, thus
reducing greenhouse gas emissions.
In addition, by off-setting energy
that would otherwise be derived
from fossil fuels, biogas recovery and
use can help reduce overall quanti-
ties of carbon dioxide, another
critical greenhouse gas.
Ammonia control. Ammonia emis-
sions from livestock manures—
especially emissions from anaerobic
lagoons used in the treatment and
storage of these manures—are a
growing environmental concern. To
control ammonia emissions, produc-
ers can cover manure storage tanks.
Because gas handling is not required,
the storage structures of anaerobic
digester systems, which separate
treatment and storage, are smaller
and easier to cover than the larger
structures of traditional systems.
Water quality protection. Anaerobic
digestion provides several water
quality benefits. When an anaerobic
digester system, especially a covered
lagoon, is properly managed, phos-
phorous and metals, such as copper
and zinc, will settle out in the
process cells, thus reducing phospho-
rous and metals loadings to surface
waters when manure is land-applied.
Digester systems, especially heated
digesters, isolate and destroy disease-
causing organisms that might
otherwise enter surface waters and
pose a risk to human and animal
health. Anaerobic digestion also
helps protect ground water.
Synthetic liners provide a high level
of groundwater protection for
manure management systems. These
protective liners are a more afford-
able option with anaerobic digester
systems than with conventional
lagoons, because the multiple-cell
design of anaerobic digesters requires
less volume and, therefore, less lin-
ing material is needed. The concrete
or steel tanks used in plug flow and
complete mix digesters also effective-
ly prevent untreated manure from
reaching ground water.
How Much Do These
Benefits Cost?
Livestock producers can choose from a
wide range of waste management
options provided by a variety of agri-
cultural engineers, vendors, and
equipment suppliers. The costs of these
options can vary greatly, in terms of
both initial investment and annual
operation and maintenance. For exam-
ple, the cost of a typical manure storage
facility can range between $60 per
Animal Unit (AU) for a typical pond
to $300 per AU for an above-ground
prefabricated tank. (An AU equals
1,000 pounds live animal weight, or
approximately the weight of one beef
What AgSTAR Provides
To find out more about the opportunities that digester technology
can offer the livestock industry, AgSTAR provides information and
tools to help swine and dairy producers make informed decisions
about these technologies:
• The AgSTAR Handbook, a comprehensive manual developed to
provide guidance on developing biogas technology at commercial
farms.
• FarmWare, an expert decision-support software package that
you can use to conduct biogas recovery system prefeasibility
assessments.
• The AgSTAR Industry Directory, which you can use to identify
consultants, project developers, energy services, equipment
manufacturers and distributors, and commodity organizations.
• The AgSTAR Web site (www.epa.gov/agstar), which contains a
library where you can download the resources listed above. In
addition, the Web site includes information on farm-scale
digesters currently operating at commercial livestock farms in
the U.S., as well as articles and case studies.
Contact an AgSTAR representative at 1-800-952-4782 or visit the
AgSTAR Web site at www.epa.gov/agstar.
Managing Manure with Biogas Recovery Systems
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Environmental Effectiveness of Manure Management Options
Greenhouse
Options Odor Gas
Control Reduction
Covered lagoon digesters with open storage ponds
Heated digesters (i.e., complete mix and plug flow) with
open storage tanks
Aerated lagoons with open storage pondst
Separate treatment lagoons and storage ponds
(2-cell systems)
Combined treatment lagoons and storage ponds
Storage ponds and tanks
E
E
G-E
F-G
P-G
P-F
H
H
H
L
L
M-H
Water
Quality
Protection
G
G
F-G
G
F-G
P-F
Cost Range+t
(per 1,000 Ibs/
live weight)
$150-400
$200-400
$200-450
$200-400
$200-400
$50-500
Key: P=poor, F=fair, G=good, E=excellent, L=low, M=medium, H=high
t Aerated lagoon energy requirements add an additional $35-50 per 1,000 Ibs/year.
ranges do not include annual operation and maintenance (O&M) costs.
cow.) Similarly, an open-air conven-
tional lined lagoon that combines both
treatment and storage functions can
range between $200 to $400 or more
per AU, depending on annual rainfall
and process water use at the facility.
Anaerobic digestion is cost-competitive
when compared to conventional waste
management practices. For example,
the installed cost of both a covered
lagoon and heated digester (including
an attached storage pond) ranges
between $200 and $450 per AU. These
systems can also have financially attrac-
tive payback periods of 3 to 7 years
when energy gas uses are employed.
Here's what some digester
owners have to say about
their biogas recovery
systems:
"Community and consumer-
owned electric systems can
realize benefits from
distributed generation, while
supporting biogas projects
that conserve energy and
provide economic and
environmental solutions for
farmers and rural
communities."
Greg Booth, Power Manager,
Tillamook People's Utility District,
Oregon
"/ want my operation to
produce and exist without
my neighbors even knowing
I'm there. And I want to
leave the environment in
better shape than I found it."
Julian Barham, speaking about
the environmental benefits of the
covered lagoon digester at his
4,000-sow farrow-to-wean
operation in North Carolina
Conventional waste systems, in con-
trast, do not provide this payback
opportunity and become sunk costs to
the farm enterprise.
The Environmental Effectiveness Table
above compares conventional waste
management options to their environ-
mental benefits. The table is intended
to provide livestock producers with an
easy-to-use tool to understand the envi-
ronmental performance that they can
achieve with their investment dollar.
This type of comparison can help pro-
ducers make informed business
decisions related to the environment
and the neighboring community.
For more information about methane
recovery technologies, contact an
AgSTAR representative at:
1 -800-95AgSTAR (1-800-952-4782)
(Hours of Operation: 9:00am to
5:00pm EST)
www.epa.gov/agstar
ENERGY AND POLLUTION PREVENTION
8
Managing Manure with Biogas Recovery Systems
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