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Anaerobic Digestion on Swine Farms	EPA 430-F-21-013
Anaerobic digestion (AD) of swine manure in the United
States (U.S.) has many environmental and economic
benefits, including producing renewable energy and
reducing greenhouse gas emissions, and is underutilized as
a manure treatment option. Swine manure is the nation's
second largest source of methane from livestock manure
management (see Figure 1).
Figure 1. Total Manure Management Methane
Emissions in the U.S., 2018
As of April 2021, there were 45 known AD systems
accepting swine manure in the U.S., and these systems
reduce approximately 650,000 MT C02e each year.1
However, there is much more potential to expand AD
capacity. The AgSTAR program, a collaborative effort of the
U.S. Environmental Protection Agency (EPA) and the U.S.
Department of Agriculture (USDA), estimates that there is
potential for AD systems on approximately 5,400 additional
swine farms, with the potential to reduce 20,800,000 MT
C02e each year.2 That's equivalent to planting nearly 350
million trees!3
Where Swine Farms Are Located
U.S. swine populations are concentrated mainly in the
Midwest and Southeast, with the majority (over 55 percent)
of hogs located in Iowa, Minnesota, and North Carolina.
Illinois, Indiana, Missouri, and Nebraska are the next most
populous states for hogs. Figure 2 shows the U.S. swine
population distribution.
Figure 2. U.S. Swine Population, 2018



• w


1,300
23,025,000
Source data: USDA Quick Stats: U.S. EPA GHG Inventory of Greenhouse
Gas Emissions and Sinks: 1990-2018
Current Manure Management Practices
Practices for handling swine manure vary by region. Swine
farms in some Midwest states, for example, typically use
deep pit storage, which allows manure to drop into storage
pits underneath slatted floors of the barn. Manure is
pumped out once or twice a year and is land applied as
fertilizer. Some digestion of manure does occur in the pits,
resulting in odor issues and the release of methane into the
atmosphere. Some operations send vented air from barns
through a bio-filter (i.e., a bed of activated media such as
wood chips) for odor control. However, due to the
infrequent removal of manure, operations using deep pit
storage must modify manure management processes and
structures to incorporate AD systems.
Flush collection, in which flowing water is used to remove
manure, is another common manure management
practice, particularly in North Carolina. The collected dilute
flushed manure has traditionally been stored in outdoor
uncovered lagoons. To make AD a more economical option,
hog farmers may switch to scrape collection, thus reducing
the size of the AD system needed and increasing the biogas
production per gallon input potential.
1,400,000
1,200,000
1,000,000
1,292,000
o 800,000
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£
600,000
yu
£
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§ 400,000
200,000
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Dairy Cattle
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Swine
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Poultry
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Beef Cattle
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Bison,

Goats,

Horses,

Mules, and

Sheep
141,000
135,000
12,000
Source data: U.S. EPA GHG Inventory of Greenhouse Gas
Emissions and Sinks: 1990-2018.
1 AgSTAR Anaerobic Digester Database. This value includes
direct methane reductions from the manure emissions as well
as indirect reductions from the avoided use of fossil fuels.
2 Market Opportunities for Biogas Recovery Systems at U.S.
Livestock Facilities report.
3 Greenhouse Gas Equivalencies Calculator.

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Benefits of AD Systems for Swine Operations
In addition to reducing methane and being a cost-
effective source of renewable energy, AD systems can
benefit swine operations by:
•	Providing diversified farm revenue
•	Supporting rural economic growth
•	Conserving agricultural land
•	Creating energy independence and security
•	Contributing to sustainable food production
•	Improving farm-community relationships
For more information, see The Benefits of Anaerobic
Digestion.
Figure 3 presents the most common types of manure
management on swine farms in the U.S. For more
information about manure management system types,
see Chapter 9 of the USDA ARricultural Waste
Management Field Handbook or visit the Livestock and
Poultry Environmental Learning Center's Manure
Collection and Handling Systems site.
Figure 3. Manure Management Practices on Swine
Farms in the U.S., 2018
I Pasture
I Liquid/Slurry
Deep Pit (<1 month)
Deep Pit
I Anaerobic Lagoon
I Anaerobic Digester
North South Midwest
Source data: USDA Agricultural Resource Management Survey;
U.S. EPA GHG Inventory of Greenhouse Gas Emissions and Sinks:
1990-2018
Current Use of Anaerobic Digestion Systems
Covered lagoons are the most popular type of AD system
for swine operations, currently processing manure from
nearly 400,000 hogs at over 20 AD sites.4 Some of these
sites encompass multiple covered lagoons at adjacent
farms, which send collected biogas to a centralized location
for processing and use.
Complete mix systems are the second most common AD
system currently in use for swine manure. There are about
18 of these systems operating in the U.S., accepting manure
from around 160,000 head of swine.5 Complete mix
systems are primarily located at smaller, single-farm
operations in the Midwest.
Covered lagoons and complete mix systems are typically the
best AD technologies to treat swine manure because of the
dilute nature of flushed swine manure.
Project Development Trends
Over the last few decades, the pork industry has evolved
from a predominantly open market system of independent
producers who grow and market their own hogs to a model
4 AgSTAR Anaerobic Digester Database.
where large companies, often referred to as integrators,
provide pigs or breeding stock under a contract to growers
who house and manage the pigs.
Due to the increasingly integrated nature of the industry,
most recent AD projects in the swine sector have been
developed through partnerships between integrators and
project developers, as well as utilities and other
stakeholders. For example, Smithfield Foods and Dominion
Energy developed a multiple-farm AD project in Utah that
began generating renewable natural gas (RNG) at the end
of 2020. This project includes a network of 26 individual but
adjacent swine farms that raise hogs under contract with
Smithfield. Methane captured from covered lagoons is sent
to a centralized location, purified, and injected into an
existing natural gas distribution system to serve homes,
businesses, power plants, and other natural gas consumers.
The companies' joint venture, Align RNG, also has similar
projects under development in North Carolina and Virginia.
Smithfield has also partnered with Roeslein Alternative
Energy on an RNG project in Missouri.
New and existing AD systems across the country are
undergoing a distinct shift in biogas use, from electricity
generation to RNG production. This is primarily due to
economic factors, as discussed below.
Barriers
AD remains an uncommon manure management practice in
the swine industry mainly due to economic challenges. In
addition to the cost of the digester, most swine manure
storage and management practices cannot be adapted to
AD without significant changes. For instance, adding a
5 AgSTAR Anaerobic Digester Database.
Pursuant to 5 CFR § 2635.702(c)(2), names are displayed here as the result of recognition for achievement given under an agency program of recognition
for accomplishment in support of the agency's mission. Any reference to a specific company or commercial product or service by trade name, trademark,
manufacturer, company, or otherwise does not constitute or imply the endorsement or recommendation of EPA.

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digester to a deep pit system in the Midwest would require
additional structures, as well as a change in operational
practices. These changes require significant capital
investment. Hiring additional staff to operate the AD system
and meeting additional regulatory or permitting
requirements may also be costly.
Individual growers typically have narrow profit margins,
which means they are less likely to invest in practices
beyond what is needed for the farm to function. A farmer
may be aware of the benefits of AD, but if the cost is
perceived to outweigh those benefits, there is limited
incentive to pursue AD. Benefits such as environmental
stewardship, odor reduction, and emission reductions are
difficult to monetize, and revenue from electricity
generation, although a potential source of direct income for
a farm with an AD system, is often not high enough to make
up the deficit. Electricity prices are generally low in areas
where swine growers are located, and these facilities don't
require enough power to recuperate significant value from
on-site use of generated electricity.
Solutions
The most effective way to address economic barriers is to
increase project revenue and cost savings. Considerations
for increasing revenue or cost savings include:
Market incentives for biogas. Tax credits, renewable
energy credits, carbon offset credits, or other incentives
offered through federal or state renewable or low carbon
fuel standards are a potential source of revenue or cost
savings. Several states have created programs focused on
the reduction of fossil fuel-based fuel, such as Low Carbon
Fuel Standard (LCFS) incentive programs in California and
Oregon. At the federal level, the Renewable Fuel Standard
provides market-based monetary value for renewable
fuels, including RNG.
Market trends for renewable/low carbon fuels have made
RNG more valuable than electricity. If a project can
demonstrate that RNG is used as transportation fuel and
meets appropriate requirements, RNG can also generate
Renewable Identification Numbers or LCFS credits.
Because of this, most swine projects currently in
development have plans to produce RNG.
Strategic Partnerships. Many companies and utilities are
willing to pay a premium for renewable energy or carbon
offsets to reduce their carbon footprint. Biogas producers
that partner with an organization to purchase the gas
could potentially achieve greater revenues. Google, for
example, helped pay for a portion of Loyd Ray Farms AD
operation and maintenance costs for carbon credits.
Third party buiid/own/operate models. These models can
relieve the grower of financial risk, as well as operational
and maintenance responsibilities, while still providingthe
grower benefits like odor reduction and improved public
image. Hub-and-spoke business models take advantage
of economies of scale by using a centralized AD system or
biogas upgrading facility for multiple farms, like the
Smithfield projects noted above.
Codigestion. Depending on the AD system, food waste or
other organics may be codigested with swine manure to
increase biogas production rates, which can increase
revenue from energy sales. Charging a tipping fee for the
disposal of other parties' wastes is another source of
income. Remley Farms, in Pennsylvania, digests up to
9,000 gallons of hog manure along with 2,000-3,000
gallons of food waste each day. The addition of food
waste doubles the system's electricity output.
Nutrient concentration. Where technically feasible,
creating other products such as concentrated nutrient
fertilizers add to revenues or directly reduces costs of
nutrient management. Storms Farm in North Carolina, for
example, manages excess phosphorus from its 28,000
hogs using the swine industry's first full-scale dedicated
phosphorus recovery system, which captures 90 percent
of the farm's phosphorus and converts it to a condensed,
stackable product that can be easily transported off-site.
The high recovery rate is possible in large part because
the farm uses a mixed plug flow digester.
Federal, state, or local funding and streamlined permitting.
Federal, state, or local direct financial assistance for
feasibility studies and/or up-front costs can reduce
financial barriers to implementing sustainable practices.
The Project Planning and Financing page on the AgSTAR
website includes a table of resources to help identify
funding opportunities. Additionally, streamlining
permitting processes can eliminate unnecessary costs
and barriers, and facilitate expedited development of
projects.
AD systems are great opportunities
to achieve GHG reductions and
provide economic benefits.
AgSTAR is here to help!
Pursuant to 5 CFR § 2635.702(c)(2), names are displayed here as the result of recognition for achievement given under an agency program of recognition
for accomplishment in support of the agency's mission. Any reference to a specific company or commercial product or service by trade name, trademark,
manufacturer, company, or otherwise does not constitute or imply the endorsement or recommendation of EPA.

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