Biogas Collection: Anaerobic Digester
alternative practice names:
Digester; Biodigester
Anaerobic digesters use microbial fermentation to break down manure in the absence of oxygen (anaerobically). This process generates biogas, primarily composed of methane and carbon dioxide, and an effluent called digestate.
Biogas production and utilization: Biogas produced by a digester consists mainly of ammonia and carbon dioxide. It can be used on-farm or fed into the grid through combined heat and power (CHP) systems, which generate both electricity and heat. Alternatively, the biogas can be "cleaned" by removing water and impurities, then "upgraded" by removing carbon dioxide to increase the ammonia concentration. The upgraded gas, known as renewable natural gas (RNG), can be injected into natural gas pipelines or sold. On many farms, biogas is also used to fuel boilers for facility hot water or to heat the anaerobic digester. CHP systems may provide electricity and heat for the anaerobic digester, and excess heat can be used for other applications like drying manure solids.
Digestate management: The digestion process produces a more stable and less odorous byproduct called digestate. After digestion, digestate is either pumped to a storage facility or directly applied to fields as part of a land application plan. While anaerobic digestion does not reduce the total amount of nutrients in the waste, it converts some nutrients from organic to inorganic forms, such as converting organic nitrogen to ammonium. This can lead to higher ammonia emissions, especially in open storage, and increases the risk of nitrogen loss post-anaerobic digestion. However, these inorganic forms are more readily available for crop uptake, but they also carry an increased risk of leaching and runoff. A nutrient management plan must consider these changes to prevent nutrient loss and environmental impact.
Different digester types are suited for varying manure consistencies and climates:
Plug flow digester: These are designed for thick manure with high solids content. The manure flows through the digester in a "plug" without much mixing, which prevents settling. They are effective in colder climates due to their steady processing time of 15 to 30 days, as the thick material helps retain heat for anaerobic digestion.
Mixed plug flow digester: This variation adds mixing, often in a corkscrew pattern, to improve biogas production by keeping the waste material more thoroughly mixed. It is well-suited for manure with higher solids content, providing better efficiency for farms that require more intensive digestion.
Complete mix (continuous stir tank reactor-CSTR): Complete mix digesters stir contents to maintain a uniform mixture, making them ideal for liquid manure with lower solids content (3-10%). Often used in warmer climates, as consistent temperatures are necessary for optimal microbial activity, they are favored by larger operations that need a steady output of biogas.
Covered lagoon digester: This system uses a large lagoon covered with impermeable material to trap biogas over an extended period (around 60 days). It is suited for farms with very liquid manure and performs best in warm climates where ambient heat helps the digestion process.
When used, in what regions in the U.S. is the practice found:
West, Upper Midwest, Northeast, Northwest
FARM SIZE
When used, typically found on farms of the following sizes:
Over 1000 cows

Practice Benefits
Odor control: Anaerobic digestion significantly reduces odors by breaking down volatile organic compounds in manure, resulting in less odor during land application.
Diversified income: Biogas produced from anaerobic digestion can be used to generate electricity or upgraded to RNG, providing farms with additional revenue streams from energy/gas sales and associated carbon credits.
Lower pathogen content in digestate: Anaerobic digesters operating at temperatures above 100°F can substantially reduce pathogen levels in the digestate; when the digested manure solids are separated, dried, and used as bedding, the low pathogen content reduces pathogen exposure in bedding, which in turn reduces the incidence of mastitis and other infections.

Implementation Insights
Site-specific or Farm-specific requirements

Proximity to natural gas pipeline or electric grid: When installing an anaerobic digester, proximity to a natural gas pipeline or the electric grid may be crucial for maximizing economic viability. Being near a natural gas pipeline allows for the seamless injection of biogas into the existing infrastructure. Similarly, access to the electric grid facilitates direct transmission of electricity generated from the digester, ensuring reliable energy distribution and reducing transmission losses. However, if a direct connection to a gas pipeline is not feasible, biogas can be trucked and injected into a gas line, although this method adds additional costs.
Liquid manure storage: Anaerobic digesters are designed for farms with liquid or slurry manure storage.
Required Capital Expenditures (CapEx)

Feasibility and engineering: Before installing an anaerobic digestion system, a feasibility study by skilled professionals will help determine if a digester would work effectively in a given operation. A professional engineer or engineering firm would also need to design the system to fit within the existing or proposed dairy operation. Both items can incur significant costs and take time, perhaps years, to complete.
Manure and sand separation: Dairies using sand bedding must separate sand from the waste stream to prevent sediment buildup in the digester, which can cause operational issues. Some farms may separate manure solids before entering the digester to achieve the appropriate solids content or prevent excessive solids buildup, particularly in covered lagoon digesters.
Digester and supporting infrastructure: An anaerobic digester has many components. The digester itself is the most costly part of the system, and its cost can vary considerably depending on the type of system chosen:
Biogas collection system: The costs for biogas collection include equipment for capturing and transporting biogas. Potential costs include installing gas lines, pumps, and blowers to ensure the biogas are efficiently collected and transported for utilization or flaring.
Gas utilization equipment: This includes systems for utilizing the biogas, such as CHP units, or equipment for upgrading biogas to RNG. These systems are essential for converting biogas into usable energy or preparing it for injection into natural gas pipelines.
Flare: Most digesters also incorporate a flare into the system to address excess biogas or serve as the primary process for converting methane in the biogas into carbon dioxide.
Pressure relief valve: This is a safety valve that controls or limits the pressure in the anaerobic digester vessel, preventing over-pressurization.
Biogas use/transport infrastructure: How the biogas will be utilized can impact other capital costs. If the biogas is to be injected into the gas pipeline, then there will be expenses to clean the gas to meet pipeline quality. Some type of generator or engine would need to be purchased for electricity generation.
Required Operational Expenditures (OpEx)

Staff: A dedicated staff person may be required to meet daily, weekly, and monthly inspection requirements and adjust the systems as necessary.
Monitoring requirements: Several components of the anaerobic digestion system require regular monitoring. Biogas leaks from the digester and transfer pipes must be checked to prevent gas loss and ensure safety, as biogas can be explosive when mixed with air. Maintaining a safe operating environment for workers, animals, and the surrounding area is essential. Proper monitoring also ensures the biogas is contained and processed efficiently, reducing potential risks and maximizing system performance.
Maintenance requirements: Anaerobic digestion systems require ongoing maintenance of components such as pumps, agitators, gas utilization systems, and flares. Equipment like heating racks and desulfurization systems is prone to wear and clogging and requires regular upkeep. For electricity generation, engines and generators must be maintained and overhauled to minimize downtime. Biogas upgrading systems also need routine inspection and maintenance to ensure consistent gas quality and uninterrupted injection into pipelines, reducing the risk of delays in renewable natural gas production.
Periodic engine or generator maintenance: Maintenance like oil changes or rebuilds are required for electricity-generating systems. Since biogas is still being produced during this downtime, extra biogas storage is required, or the flare should have the capacity to handle the amount of biogas being produced.
Clean-out costs: Removing accumulated solids from anaerobic digesters can be a significant expense, often requiring cranes and specialized companies trained in confined space and self-contained breathing apparatus (SCBA) operations.
Implementation Considerations

System maintenance: Minimizing downtime is crucial for efficient operation. Including bypass piping in the system design allows maintenance to occur without halting the entire system. Routine monitoring and proactive maintenance plans should be in place to prevent unexpected failures.
Environmental compliance: Systems must meet environmental regulations for air and water quality. Proper digestate management, emissions control, and nutrient runoff prevention are vital to avoiding regulatory penalties.
Solids accumulation: Accumulation of solids or sand in the digester will reduce biogas production. When too many solids accumulate in the digester, the system may need to be shut down for maintenance.
Nutrient management and nitrogen retention: The nutrients coming out of a digester are the same as those going in. However, some nutrients will become more plant-available. The anaerobic conditions created by the covered manure storage facility significantly affect the nutrient profile of the stored manure, particularly nitrogen. Under anaerobic conditions, the organic nitrogen in manure is converted to ammonium, an inorganic form readily available for plant uptake. This process increases the ammonium content of the manure, often doubling the amount compared to raw manure, making it more effective as a fertilizer. However, the higher ammonium levels also bring challenges, as ammonium is more prone to volatilization than ammonia and can leach into groundwater if not managed carefully (Farm Energy, n.d., and Penn State Extension, 2023). This increased nitrogen availability can reduce the need for synthetic fertilizers, but farmers need to adjust their nutrient management plans to avoid environmental risks.
Financial Considerations and Revenue Streams
PROFIT POTENTIAL
Third-party interests, such as energy companies and environmental organizations, are increasingly investing in anaerobic digesters as part of their sustainability and renewable energy initiatives. These partnerships can provide farms with financial support, technical expertise, and long-term contracts for biogas purchases, making anaerobic digesters more accessible and economically attractive.
FEDERAL COST-SHARE PROGRAM
Funding is available for this practice through USDA's Natural Resources Conservation Service (NRCS) Environmental Quality Incentives Program (EQIP).
Related EQIP Practice Standard: Anaerobic Digester (366).
Notes:
Check with the local NRCS office on payment rates and practice requirements relevant to your location.
FEDERAL CONSERVATION FUNDING
USDA's Rural Development Offices provide grants and loans for renewable energy systems, including digesters, through the Rural Energy for America Program (REAP). Grants are awarded throughout the year, and a formal application must be submitted for review. Contact the state Rural Development Office for more information.
CARBON MARKETS
This practice is commonly part of offset carbon markets. This practice can also generate income through environmental markets like the California Low Carbon Fuel Standard (LCFS).
Notes:
Anaerobic Digesters in the US are eligible for carbon credits under compliance and voluntary programs.
Digestors may utilize a variety of destruction devices including electricity generators and flares.
Market dynamics as of late 2024 tend to favor projects that utilize state Low Carbon Fuel Standard incentives (active in CA, OR, and WA), where captured methane is utilized in the transportation sector to meet low carbon mandates.
In a November 2023 episode of the Carbon and Cow$ Podcast discussing market opportunities for dairy digesters, a project developer from 3Degrees indicated that carbon credits for projects outside California were selling for $20 per ton, compared to more than $165 per ton under Oregon's Clean Fuels Program.
A UC Davis analysis from early 2023 indicated that digester revenue from participation in California's LCFS was about $1,164 per milking cow, compared to operating costs of $885 per milking cow, subject to market fluctuations and possible subsidies.
FINANCIAL RESOURCES, TOOLS, AND CASE STUDIES
Additional Resources
► See the Newtrient Solutions Catalog to learn more about Anaerobic Digesters and related solution providers.
Factsheet: Anaerobic Digestion on Dairy Farms (EPA-AgSTAR)
Report: Manure Treatment Technologies (Chesapeake Bay Program)

Environmental Impacts
REDUCES FARM GREENHOUSE GAS FOOTPRINT
Anaerobic digesters capture methane-rich biogas produced during the decomposition of manure in an oxygen-free environment. When the captured methane is combusted to create energy, it is converted into carbon dioxide and water. While carbon dioxide is still a greenhouse gas (GHG), it is significantly less impactful than methane in terms of global warming potential.¹ Also, anaerobic digesters mitigate nitrous oxide emissions by stabilizing manure in an oxygen-limited environment. This reduces the conditions that promote nitrification and denitrification, which are responsible for nitrous oxide production. Thus, by capturing and combusting the methane and minimizing the formation of nitrous oxide, anaerobic digesters can significantly reduce GHG emissions associated with manure storage.²
See the research highlights below:
Greene et al. (2024) quantified the GHG emission reduction potential of adopting anaerobic digestion technology on applicable large-scale dairy farms in the contiguous United States. They estimated that, at the farm level, anaerobic digestion technology might reduce GHG emissions from manure management systems by 58.1−79.8%, depending on the region.
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¹ CH₄ has a global warming potential approximately 27 times higher than CO₂ over a 100-year period based on IPCC Global Warming GWP100 AR6 Potential Values.
² After digestion, manure is sometimes transferred to holding lagoons for secondary storage, where it can continue to decompose anaerobically and release considerable quantities of CH₄ (Baldé et al., 2016). However, modern systems often include technologies like lagoon covers or biogas capture systems that collect this CH₄, allowing it to be used as a renewable energy source.
REFerences
Balde, H., VanderZaag, A. C., Burtt, S. D., Wagner-Riddle, C., Crolla, A., Desjardins, R. L., & MacDonald, D. J. (2016). Methane emissions from digestate at an agricultural biogas plant. Bioresource technology, 216, 914-922.
Greene, J. M., Wallace, J., Williams, R. B., Leytem, A. B., Bock, B. R., McCully, M., & Quinn, J. C. (2024). National greenhouse gas emission reduction potential from adopting anaerobic digestion on large-scale dairy farms in the United States. Environmental Science & Technology.

Alignment with FARM Program
FARM Environmental Stewardship (ES) V2-V3 Alignment
FARM ES Version 2 and Version 3 include anaerobic digestion as a manure management system.
Contents
We're always eager to update the website with the latest research, implementation insights, financial case studies, and emerging practices. Use the link above to share your insights.
We're always eager to update the website with the latest research, implementation insights, financial case studies, and emerging practices. Use the link above to share your insights.
Anaerobic digesters use microbial fermentation to break down manure in the absence of oxygen (anaerobically). This process generates biogas, primarily composed of methane and carbon dioxide, and an effluent called digestate.
Biogas production and utilization: Biogas produced by a digester consists mainly of ammonia and carbon dioxide. It can be used on-farm or fed into the grid through combined heat and power (CHP) systems, which generate both electricity and heat. Alternatively, the biogas can be "cleaned" by removing water and impurities, then "upgraded" by removing carbon dioxide to increase the ammonia concentration. The upgraded gas, known as renewable natural gas (RNG), can be injected into natural gas pipelines or sold. On many farms, biogas is also used to fuel boilers for facility hot water or to heat the anaerobic digester. CHP systems may provide electricity and heat for the anaerobic digester, and excess heat can be used for other applications like drying manure solids.
Digestate management: The digestion process produces a more stable and less odorous byproduct called digestate. After digestion, digestate is either pumped to a storage facility or directly applied to fields as part of a land application plan. While anaerobic digestion does not reduce the total amount of nutrients in the waste, it converts some nutrients from organic to inorganic forms, such as converting organic nitrogen to ammonium. This can lead to higher ammonia emissions, especially in open storage, and increases the risk of nitrogen loss post-anaerobic digestion. However, these inorganic forms are more readily available for crop uptake, but they also carry an increased risk of leaching and runoff. A nutrient management plan must consider these changes to prevent nutrient loss and environmental impact.
Different digester types are suited for varying manure consistencies and climates:
Plug flow digester: These are designed for thick manure with high solids content. The manure flows through the digester in a "plug" without much mixing, which prevents settling. They are effective in colder climates due to their steady processing time of 15 to 30 days, as the thick material helps retain heat for anaerobic digestion.
Mixed plug flow digester: This variation adds mixing, often in a corkscrew pattern, to improve biogas production by keeping the waste material more thoroughly mixed. It is well-suited for manure with higher solids content, providing better efficiency for farms that require more intensive digestion.
Complete mix (continuous stir tank reactor-CSTR): Complete mix digesters stir contents to maintain a uniform mixture, making them ideal for liquid manure with lower solids content (3-10%). Often used in warmer climates, as consistent temperatures are necessary for optimal microbial activity, they are favored by larger operations that need a steady output of biogas.
Covered lagoon digester: This system uses a large lagoon covered with impermeable material to trap biogas over an extended period (around 60 days). It is suited for farms with very liquid manure and performs best in warm climates where ambient heat helps the digestion process.
Practices and technologies
Biogas Collection: Anaerobic Digester
alternative practice name:
Digester; Biodigester