California converting more livestock emissions to Renewable Natural Gas (RNG)

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There’s no getting around the fact that livestock farming adds greenhouse gasses (GHG) to mankind’s burgeoning output. Estimates put the livestock attributable number at between 14% and 16% of all GHG emissions. Methane is a particular problem, the gas has a warming effect 25-28 times higher than carbon dioxide. With around 10% of the world’s cattle, the USA has a key role to play in limiting cattle produced emissions.

California’s manure methane digesters

In California it is estimated that their 1.4 million dairy cows are the largest source of methane in the entire state. Typically manure methane digesters are the primary means used to combat dairy emissions. Digesters offer the added benefit of capturing and recycling methane as renewable natural gas for energy. Scale is a key component affecting digester costs. A minimum of 2,000 cows is the threshold in California, where the typical digester is a covered lagoon digester producing gas for pipeline injection. Generally, each additional 1,000 cows reduces the cost per cow of digester projects by 15-20%.

A Dairy Digester Research and Development Program (DDRDP) is part of 2020 California Department of Food and Agriculture (CDFA)’s combined strategy to achieve their legislated goal of a 40% reduction in dairy manure methane emissions by 2030. The DDRDP provides financial assistance for the installation of dairy digesters across California, which will result in reduced greenhouse gas emissions through the production of renewable natural gas (RNG) for transportation fuel.

Another grant for Aemetis Biogas LLC

On Friday 20th Nov, Aemetis Biogas LLC (a subsidiary of Aemetis, Inc.) was awarded $7.8 million in matching DDRDP grants. The company was previously awarded $3.1 million through the 2018 DDRDP grant cycle, and successfully completed two digesters and four miles of private pipeline as phase one of its 18 dairy digester cluster.

We’re grateful to the CDFA for their strong demonstration of confidence in our 18 dairy RNG dairy digester project,” said Eric McAfee, Chairman and CEO of Aemetis. “After completing phase one of our project in just over one year, we’re poised to quickly accelerate the construction and operation of 16 additional digesters and 25 miles of private pipeline by mid-2022.  The combined project will annually displace approximately 6.9 million gallons of petroleum-based diesel fuel, eliminate approximately 2.6 million metric tons of CO2 equivalents, and create over 100 project related jobs in California’s Central Valley,” added McAfee.

To date, California’s dairy digester development program has awarded more than $183 million in grants for 108 digester projects to a number of companies. Aemetis is building this biogas anaerobic digester network and pipeline to convert dairy animal waste gas to Renewable Natural Gas (RNG) AND is developing a plant to convert waste orchard wood into cellulosic ethanol.

In December 2020, Aemetis will begin construction of its biogas upgrading facility that will allow the company to inject RNG into PG&E’s natural gas pipeline by the end of the first quarter of 2021.  The company expects to offer truck fleet fuelling of R-CNG at the Aemetis Advanced Fuels Keyes ethanol biorefinery in the second quarter of 2021.

A related US industry report “Interest in California Dairy Manure Methane Digesters Follows the Money,” is available to download at

UK farmers are also cutting energy costs on farms with anaerobic digesters and biogas.

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About Author


Matt has worked in digital publishing for twenty years, holding management positions at Nature ( and William Reed Business Media ( etc.). He has also worked with BBC Worldwide, Centaur Media, UKi Media and Mark Allen Group. Since 2010 Matt has been a digital consultant working with B2B media companies in the agricultural, automotive, aviation, robotics and technology sectors. As Chairman of his local allotment association Matt grows his own food whilst chasing the dream of a one tonne giant pumpkin. He is a member of the British Garden Media Guild and was a finalist in the Garden Media Guild Awards 'blog of the year' category in 2018 and 2019.

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