Anaerobic Digestion on Dairy Farms


	
Anaerobic Digestion on Dairy Farms	EPA 430-f-21-012
Anaerobic digestion (AD) of dairy 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. Dairy manure is the nation's
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 221 AD systems processing
dairy cow manure in the U.S., and these systems reduce
approximately 4.29 MMTC02e each year.1 In addition, more
than 50 dairy AD systems are currently under construction
with significant opportunity to scale AD capacity over the
coming years. 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 2,700
additional dairy farms, with the potential to reduce 29.9
MMTC02e each year2. That's equivalent to planting nearly
500 million trees!5
Where Dairy Farms Are Located
U.S. dairy populations are concentrated in several states
throughout the country, with the majority, over two-thirds,)
of dairy cows located in the states of: California, Wisconsin,
New York, Idaho, Pennsylvania, Texas, Minnesota, and
Michigan (see Figure 2).
Figure 2. U.S. Dairy Population, 2018
V
300	1,770,000
Source data: USDA Quick Stats: U.S. EPA GHG Inventory of Greenhouse
Gas Emissions and Sinks: 1990-2018
Current Manure Management Practices
Each farm has unique manure handling needs based on size
and location. Some dairy manure is handled as a solid,
stored in piles or stacks, spread daily, or left to lie in
pastures or ranges where animals graze. These
management practices generate minimal methane and are
common for smaller operations.
Large operations, however, tend to manage manure using
systems that have a higher potential for methane
emissions. Flush collection systems use large volumes of
water to collect and remove manure from barns and milking
parlors, while scrape collection systems remove manure
from barns and alleyways. These systems move the manure
into long-term storage in anaerobic lagoons, tanks, or
earthen ponds under anaerobic conditions where the
manure releases methane. Depending on location and
cropping system, some dairies store the manure for up to a
year or longer before field application.
Although national dairy populations have decreased since
1990, the industry has become more concentrated in
1,400,000
1,200,000
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1,292,000
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5 400,000
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Dairy Cattle
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Poultry
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141,000
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Source data: U.S. EPA GHG Inventory of Greenhouse Gas
Emissions and Sinks: 1990-2018.
1 "STAR 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 EPA Greenhouse Gas Equivalencies Calculator.

------- certain areas of the country, leading to a larger average number of animals per dairy farm. As facility sizes increase, these operations are adopting more long-term manure storage systems, which have potential to emit methane. Figure 3 presents the most common types of manure management on dairy farms in the U.S. For more information about manure management system types, see Chapter 9 of the USDA Agricultural Waste Management Field Flandbook or visit the Livestock and Poultry Environmental Learning Center's Manure Collection and Flandling Systems site. Figure 3. Manure Management Practices on Dairy Farms in the U.S., 2018 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 Plug flow digesters, are the most popular type of AD system for dairy operations, currently processing manure from more than 260,000 dairy cattle at about 91 AD sites.4 Complete mix digesters and covered lagoons, which are more suited for manure with low total solids content, are also popular for dairy manure. There are about 70 complete mix systems and 50 covered lagoon systems operating in the U.S., accepting manure from around 110,000 and 210,000 dairy cattle, respectively.5 Project Development Trends Dairy farms are predominantly family owned and managed, and most are members of producer cooperatives, which are jointly owned and controlled equally by member farms. While many dairy AD systems today are operated on site, it is becoming increasingly common for a third-party company to develop and operate AD systems that process manure from multiple farms. These include centralized AD systems, or hub-and-spoke systems, that share the project risk and reward between multiple farmers and developers and reduce interconnection costs, allowing for more efficient project development. The Dane County Digester in Vienna, Wisconsin, for instance, accepts manure piped in from three nearby dairy farms and was the first centralized digester in Wisconsin to process waste from multiple farms. For many centralized systems, such as the Cayuga Regional PiRester in New York, the manure must be trucked in rather than piped. Another business model gaining popularity is when multiple farms that are relatively close to one another each have their own AD system, but the biogas they produce is sent to a centralized location for processing. This type of hub-and- spoke model is particularly common in California, but it is emerging in other states as well. Calgren Dairy Fuels, for instance, collects biogas from 12 dairies in Tulare County, California and upgrades it to pipeline-quality renewable natural gas (RNG), which is injected into a SoCalGas pipeline and transported to existing compressed natural gas (CNG) fueling stations. 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 dairy industry mainly due to economic challenges. In addition to the significant capital cost of the digester, hiring additional staff to operate and maintain the AD system and meeting regulatory or permitting requirements may also be costly. 100% ¦ ¦ ¦ ¦ ¦ ¦ Solid Storage 9« ¦ ¦ ¦ ¦ ¦ I I I I I 70% ¦ ¦ ¦ ¦ ¦ ¦ Liquid/Slurry 60% I I I I ¦ Dry Lot :: 11111: ¦ 30% ¦ _ ¦ ¦ ¦ ¦ Daily Spread 20% ¦ Anaerobic Lagoon 10% l l l l l 0% ¦ ¦ ¦ ¦ ¦ ¦ Anaerobic Digeste & J1 S° r

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Dairy farmers typically have narrow profit margins, which
means they have less capital 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 renewable 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. Furthermore, low electricity rates have made
it increasingly difficult for power generation projects to
remain profitable.
Solutions
The most effective way to address economic barriers is to
develop dependable markets that increase project revenue
and reduce project costs. 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, a large portion of dairy projects
currently in development have plans to produce RNG.
Strategic partnerships. Many companies and utilities are
willingto 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.
Brightmark, for instance, an RNG developer with clusters
of digester projects across the county, has partnered
with Chevron in a joint venture to produce and market
dairy-based RNG. Brightmark owns the projects, and
Chevron purchases and markets RNG produced from the
AD systems for use in vehicles that run on CNG.
Third party build/own/operate models. These models can
relieve the farmer of financial risk, as well as operational
and maintenance responsibilities, while still providing
the farmer benefits like odor reduction and improved
public image. Hub-and-spoke business models like those
noted above take advantage of economies of scale by
using one large, centralized facility for multiple farms.
Codigestion. Depending on the AD system, food waste or
other organics may be codigested with dairy 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. Barstow's Longview Farm, in Massachusetts,
codigests approximately 22,000 tons of organic
byproducts annually from a nearby creamery, in addition
to the 9,000 tons of manure their dairy generates every
year. Biogas from the digester is used to generate over
6,000 kilowatt hours peryear, a portion of which powers
the creamery.
Nutrient concentration. Where technically feasible,
creating other products such as concentrated nutrient
fertilizers can add to revenues or directly reduces costs
of nutrient management. The Audet family, of Blue
Spruce Farm in Vermont, installed a phosphorus
recovery system at their dairy to further dewater
separated digestate solids from their plug flow digester.
The system, which uses dissolved air flotation, can
capture 75 to 85 percent of the fine solids and
phosphorus in the manure stream, yielding low-solids
irrigation water and a stackable nutrient-rich solid
product that can be marketed and sold off site as a soil
amendment or fertilizer.
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.
Anaerobic digestion systems are
great opportunities to achieve
GHG reductions and provide
economic benefits.
AgSTAR is here to help!
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