Q CP/V United States Environmental
                            Protection Agency
Managing Manure with
Biogas Recovery Systems
Improved Performance at Competitive Costs

           The AgSTAR Program

Office of Air and Radiation (6202J)
Winter 2002

Managing  Manure  with   Biogas
Recovery  Systems                           *
 Improved  Performance  at  Competitive Costs
       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
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

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
"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
         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
         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,

         • 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.
           Manure Source
         and Collection System
                                                                              Flare or
                                                                              Heat Source
    Managing Manure with Biogas Recovery Systems

                                              Total Solids (%)
                                          10        15       20
                              Water Added
                                                               Bedding Added
                                                As Excreted
          Classification |   Liquid   |  Slurry  |       Semi-Solid     |
      Handling Options
     Biogas Production |_
	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

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
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

The  Environmental
Benefits of
Anaerobic Digestion
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

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
  • FarmWare, an expert decision-support software package that
    you can use to conduct biogas recovery system prefeasibility
  • 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

 Environmental Effectiveness of Manure Management Options
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
Cost Range+t
(per 1,000 Ibs/
live weight)
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

  "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
      Greg Booth, Power Manager,
   Tillamook People's Utility District,

  "/ 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)
                                ENERGY AND POLLUTION PREVENTION
Managing Manure with Biogas Recovery Systems