California’s dairy industry, a major contributor to the state’s economy and a significant source of methane emissions, is making strides in sustainability through the adoption of innovative technologies. Dairy digesters, also known as anaerobic digesters, are emerging as a game-changer, slashing methane emissions by as much as 80% on participating farms. This technological advancement marks a significant step towards California’s ambitious climate goals and sets an example for dairy regions worldwide.
The Methane Challenge in Dairy Farming
Dairy farms, particularly those with large herds, face the challenge of managing vast quantities of manure. Traditional manure management practices, such as storing liquid manure in open lagoons, can lead to substantial methane emissions. Methane is a potent greenhouse gas, with a significantly higher warming potential than carbon dioxide over a shorter period. In California, dairy and livestock operations contribute to over half of the state’s methane emissions, highlighting the urgency for effective mitigation strategies.
Agricultural operations accounted for roughly half of California’s methane emissions in 2022. Enteric fermentation contributed 10.98 million metric tons, while manure management accounted for 8.47 million metric tons.
How Dairy Digesters Work
Dairy digesters offer a sustainable solution to manure management while simultaneously reducing methane emissions. These systems work by:
- Collecting Manure: Manure is collected from dairy barns and directed into an airtight digester.
- Anaerobic Digestion: Inside the digester, microorganisms break down the organic matter in the manure in the absence of oxygen (anaerobically). This process produces biogas, a mixture primarily composed of methane and carbon dioxide.
- Methane Capture: The digester captures the biogas, preventing methane from escaping into the atmosphere.
- Biogas Utilization: The captured biogas can be used in several ways:
- Renewable Natural Gas (RNG): The biogas can be upgraded to RNG and injected into natural gas pipelines for use as a transportation fuel or for heating and electricity generation.
- Electricity Generation: The biogas can be burned in a generator to produce electricity.
- Hydrogen Fuel: Biogas can be used to produce hydrogen fuel.
- Digestate Management: The remaining material after digestion, called digestate, can be used as a fertilizer, with improved nutrient availability and reduced odor compared to raw manure.
Benefits Beyond Emission Reduction
Dairy digesters offer a multitude of benefits beyond methane emission reduction, including:
- Renewable Energy Production: Dairy digesters generate renewable energy in the form of biogas, reducing reliance on fossil fuels.
- Improved Air Quality: By capturing methane, digesters reduce air pollution and odors associated with manure storage.
- Water Quality Protection: Digesters can reduce the risk of water contamination from manure runoff.
- Soil Health Improvement: Digestate, a byproduct of the digestion process, can be used as a fertilizer, improving soil health and reducing the need for synthetic fertilizers.
- Economic Opportunities: Digesters can create new revenue streams for dairy farmers through the sale of renewable energy or carbon credits.
- Job Creation: The construction, operation, and maintenance of digesters create jobs in rural communities.
California’s Leadership in Dairy Digester Technology
California has emerged as a leader in the adoption of dairy digester technology, driven by state policies, financial incentives, and the commitment of dairy farmers to environmental stewardship.
State Support and Incentives
The California Department of Food and Agriculture (CDFA) plays a crucial role in supporting the implementation of dairy digesters through programs like the Dairy Digester Research and Development Program (DDRDP) and the Alternative Manure Management Program (AMMP). These programs provide financial assistance to dairy farms for the installation of digesters and the implementation of alternative manure management practices.
Between 2015 and 2022, CDFA supported approximately 133 dairy digester projects in California, with grants of more than $200 million to various dairy farms. Since 2015, $356 million in grants has been awarded to help fund these initiatives
California’s Methane Reduction Targets
California has set ambitious goals for reducing methane emissions from the dairy sector. Senate Bill 1383 (SB 1383) mandates a 40% reduction in livestock methane emissions below 2013 levels by 2030. California is the only jurisdiction with such a target set in statute.
The state is well on its way to achieving this goal, with dairy farms already reducing methane emissions by 5 million metric tons of CO₂-equivalent (MMTCO₂e) annually. This progress brings the state more than two-thirds of the way toward its legislated goal.
Number of Operating and Planned Digesters
As of May 2025, California has 168 dairy digesters in operation and approximately 75 more in development. In total, California has 243 dairy digester projects, capturing methane from 271 dairy farms, and creating either renewable electricity, renewable natural gas, or hydrogen fuel.
Dairy Cares
Dairy Cares, a non-profit organization, plays a vital role in ensuring the long-term sustainability of California’s dairy farming families. According to Dairy Cares, more than 300 methane-reduction projects have been installed on California dairy farms thanks to support from programs like the DDRDP.
Challenges and Criticisms
Despite the numerous benefits, the adoption of dairy digesters also faces challenges and criticisms:
- High Costs: The initial investment for installing a dairy digester can be substantial, ranging from $5 million to $10 million.
- Technical Expertise: Operating and maintaining a digester requires technical expertise, which may not be readily available to all farmers.
- Carbon Credit Concerns: Some environmental groups have expressed concerns that the incentives for dairy digesters might shift investment towards dairy farms rather than other important sources of methane. There are also concerns about the program becoming unwieldy and the potential for oversupply in the Low Carbon Fuel Standard (LCFS) credit market.
- Phasing Out Climate Credits: The California Air Resources Board (CARB) is considering phasing out climate credits for dairy digesters, which has sparked debate about the long-term financial viability of these projects.
- Potential for Increased Emissions: Some environmental advocates argue that methane-reducing projects could lead to larger dairies and increased emissions, referring to methane digesters as a “Band-Aid fix” to reducing agricultural emissions.
Success Stories
Several dairy farms in California have successfully implemented dairy digesters and are reaping the benefits:
- Vander Eyk Dairy: Located in Merced County, Vander Eyk Dairy operates an anaerobic digester that converts methane to renewable natural gas.
- Fiscalini Farms: In Modesto, Fiscalini Farms utilizes a first-of-its-kind fuel cell project that generates electricity from dairy waste.
- Central Valley Dairy Representative Sampler Project: This project involves a collective biogas operation that reduces emissions from multiple Central Valley dairies.
The Future of Dairy Digesters
Dairy digesters are poised to play an increasingly important role in the future of sustainable dairy farming. As technology advances and costs decrease, digesters are likely to become more accessible to smaller farms.
California’s Climate Neutrality Goal
A recent analysis by UC Davis researchers indicates that the California dairy sector could reach climate neutrality—contributing no additional warming to the atmosphere—as soon as 2027.
Global Implications
California’s success in reducing methane emissions from dairy farms serves as a model for other regions around the world. By sharing its experiences and technologies, California can help other countries achieve their climate goals while ensuring a sustainable future for dairy farming.
Conclusion
Dairy digesters represent a significant advancement in sustainable agriculture, offering a win-win solution for dairy farmers and the environment. By capturing methane emissions and generating renewable energy, these systems are helping to reduce greenhouse gas emissions, improve air and water quality, and create new economic opportunities. As California continues to lead the way in dairy digester technology, the future of dairy farming looks brighter and more sustainable than ever before.
