Biogas Collection: Covered Manure Storage and Flare
alternative practice names:
Cap and Flare; Cover and Flare; Capped Manure Storage and Flare
Covered manure storage and flare ("cap and flare") can be an option for farms with liquid/slurry storage that do not have an anaerobic digester. For this practice, manure storage facilities and/or anaerobic lagoons are covered with a geomembrane to capture biogas generated from the anaerobic environment. As the biogas is generated, the membrane inflates, serving as a storage area for the biogas. This biogas, consisting largely of methane (a potent greenhouse gas), is transferred to a flare either by a vacuum/pump system or by the pressure generated under the geomembrane. Once the biogas reaches the flare, it is combusted and the methane in the biogas is converted to carbon dioxide and discharged into the atmosphere. Burning methane releases carbon dioxide, which has a much lower impact on global warming than methane.
When used, in what regions in the U.S. is the practice found:
Northwest, Upper Midwest, Northeast, Southeast
FARM SIZE
When used, typically found on farms of the following sizes:
100 to 2500 cows

Practice Benefits
Reduces dairy odors: Anaerobic conditions in covered lagoons or liquid manure storage systems help minimize nuisance odors. Manure treated anaerobically also emits fewer odors during land application, making it easier to apply manure near property boundaries without causing disturbances.
Prevents dilution: The cover prevents rainwater from entering manure storage, avoiding dilution and allowing for maximum storage capacity. This maintains a smaller manure volume with a higher nutrient concentration, ultimately reducing transport costs.
Increases storage capacity: For existing facilities, increased capacity extends the storage period and supports dairy expansion without significant changes to the storage system. For new facilities, excluding precipitation allows for smaller storage designs.
Retains nitrogen: Anaerobic storage with a cover preserves higher nitrogen levels in the manure by reducing nitrogen loss through volatilization, reducing the need for commercial nitrogen inputs.
Generates diversified income: Flaring biogas from covered manure storage converts methane into carbon dioxide, significantly lowering greenhouse gas emissions. This process can create opportunities for carbon credits and additional revenue streams.

Implementation Insights
Site-specific or Farm-specific requirements

No anaerobic digesters: Cover and flare systems are commonly implemented in dairies where anaerobic digesters are not economically viable.
Liquid manure storage: Cover and flare systems are appropriate on farms with liquid or slurry manure storage.
Required Capital Expenditures (CapEx)

Engineering and site work: Manure storage facilities, whether earthen or tank-based, must be engineered to withstand cover loads and external forces such as snow, wind, and vacuum. Earthen storages typically secure covers or liners with a below-grade concrete anchor around the perimeter. For tanks, engineers must design an appropriate anchoring system for the liner.
Fencing: Fencing is essential for safety and security, preventing wildlife or unauthorized access that could damage the cover.
Electrical infrastructure: Power is needed to operate pumps, ignite the flare, and support control and communication systems. Since biogas production is continuous (under optimal conditions), backup power may also be necessary to ensure uninterrupted system control.
Impermeable covers: Geosynthetic or HDPE covers are commonly used due to their durability, odor control, and emissions reduction. They typically last 10–20 years, depending on environmental factors.
Liners: Liners are often recommended for earthen manure storage systems. Welding the cover to the liner can significantly reduce the risk of leaks.
Pressure relief systems: A pressure relief system is recommended to prevent overpressure and protect the geomembrane cover in the event the flare is temporarily non-operational.
Gas flow meter: Installing a gas flow meter is important for tracking the volume of biogas flared, especially for carbon credit documentation. Carbon credit providers should be consulted to ensure compliance with gas meter requirements.
Water removal system: A water removal system, such as a pump, is needed to eliminate rainwater that pools on the cover. Rainwater should be safely discharged to avoid erosion or environmental harm.
Biogas collection and combustion: Biogas is captured under the cover using perforated drainage tiles, either passively or with a blower. A buried biogas line with a condensation trap transports the gas to a flare skid, which includes a flame arrestor and monitoring equipment. Pressure relief systems, like manually controlled valves, prevent damage from over-pressurization.
Manure removal system: A system for adding and removing manure from the sealed storage is necessary. Proper agitation during manure removal must also be considered, and additional access pipes for agitation may need to be installed when the cover is put in place.
Other potential related expenses include:
Lagoon construction: Constructing a covered storage facility is expensive for new operations. However, since precipitation is excluded from the storage volume, the facility can be built smaller than uncovered storage systems while still providing the same storage capacity for the required period.
Solid-liquid separation (and sand separation, if applicable): Solid-liquid separation (and sand separation, where relevant) can play a crucial role in preventing solid accumulation in the system. In cap and flare systems, managing solids can be more challenging due to the complexity of agitating and removing manure from beneath the cover.
Required Operational Expenditures (OpEx)

Performance monitoring: Monitoring the liquid levels in a covered storage facility plays a significant role in preventing overfilling and unplanned overflows. Effluent levels set at specific points can help to optimize biogas production and facilitate its transfer. Furthermore, tracking biogas production and flare performance contributes to the system's overall efficiency, ensuring that methane is effectively converted to carbon dioxide, which has a lower environmental impact.
Leak monitoring: Checking for leaks in the cover and biogas transfer piping is an important aspect of maintaining system performance. Minimizing leaks allows for more effective destruction of biogas through the flare, increasing the potential to earn carbon credits. Since biogas is a flammable substance, addressing leaks is also a key factor in maintaining safety for workers, livestock, and the surrounding environment.
Implementation Considerations

Solids accumulation: In a covered facility, managing solids can be complex. Waste separation or the use of a settling basin may be necessary before manure enters the storage facility to prevent solids buildup. Alternatively, agitation ports can be installed in the geomembrane cover, which adds complexity but may enhance gas production due to higher organic content. Another option is periodic cover removal, typically after several years, to agitate the storage and remove accumulated solids. This method requires extra storage volume to account for the solids during removal.
Nutrient management/nitrogen retention: Anaerobic storage with a cover preserves higher nitrogen levels in the manure by reducing nitrogen loss through volatilization. This increased nitrogen availability can reduce the need for synthetic fertilizers, but farmers need to adjust their nutrient management plans to avoid environmental risks.
Regulatory compliance: Dairies may need to navigate complex environmental regulations, such as air quality standards for greenhouse gas emissions and wastewater discharge. Securing permits for installing and operating cap and flare systems can add complexity to the project, particularly in regions with stringent environmental policies.
Flare Performance: any flares rely on a sufficient methane flow rate to maintain combustion. During cooler months (fall, winter, and spring), when manure degradation and methane production slow down due to lower temperatures, the gas flow might drop below the threshold needed to support continuous combustion. When this happens, the methane may be vented rather than combusted, which reduces the effectiveness of the system in capturing and destroying methane emissions during these periods.
Financial Considerations and Revenue Streams
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: Roofs and Covers (367).
Notes:
Check with the local NRCS office on payment rates and crop rotations relevant to your location.
To quality for EQIP funds, the dairy is required to obtain a Comprehensive Nutrient Management Plan (CNMP) to guide practice implementation.
FINANCIAL RESOURCES, TOOLS, AND CASE STUDIES
Additional Resources
Presentation: Dairy Manure Storage: GHG Mitigation & Adaptation to Build Farm Resiliency (Cornell University)
Video: Dairy Farm Manure Cover & Flare Off Systems Reduce Odors and Methane (Cornell Cooperative Extension)
Website: AgSTAR: Biogas Recovery in the Agricultural Sector (EPA)
White Paper: Covering and Flaring Manure Storage Units as a Potential Small to Mid-Size Dairy Methane Reduction Strategy (DMI)

Environmental Impacts
REDUCES FARM GREENHOUSE GAS FOOTPRINT
A cap and flare system captures biogas from manure and combusts it, converting methane into carbon dioxide, which has a lower global warming potential. This process significantly reduces a farm's greenhouse gas footprint compared to not capturing the methane. Additionally, the manure is stored under the cap until applied to fields, minimizing the potential for methane release throughout the year.
Manure cap and flare systems reduce nitrous oxide emissions by covering manure to limit exposure to air, thereby decreasing conditions that promote nitrification and denitrification, which produce nitrous oxide. The collected biogas, mainly methane and carbon dioxide, is burned in a flare. This combustion process stabilizes the manure and reduces the potential for nitrous oxide formation. Thus, the system helps mitigate nitrous oxide emissions by controlling manure decomposition and preventing conditions that lead to nitrous oxide production.
REFerences

Alignment with FARM Program
FARM Environmental Stewardship (ES) V2-V3 Alignment
The manure section of FARM ES Version 3 includes cap and flare as an option.
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.
Covered manure storage and flare ("cap and flare") can be an option for farms with liquid/slurry storage that do not have an anaerobic digester. For this practice, manure storage facilities and/or anaerobic lagoons are covered with a geomembrane to capture biogas generated from the anaerobic environment. As the biogas is generated, the membrane inflates, serving as a storage area for the biogas. This biogas, consisting largely of methane (a potent greenhouse gas), is transferred to a flare either by a vacuum/pump system or by the pressure generated under the geomembrane. Once the biogas reaches the flare, it is combusted and the methane in the biogas is converted to carbon dioxide and discharged into the atmosphere. Burning methane releases carbon dioxide, which has a much lower impact on global warming than methane.
Practices and technologies
Biogas Collection: Covered Manure Storage and Flare
alternative practice name:
Cap and Flare; Cover and Flare; Capped Manure Storage and Flare