Anaerobic Digestion and Alternative Manure Management Technologies for Methane Emissions Mitigation on Californian Dairies

Hamed M. El Mashad, Tyler J. Barzee, Roberta Brancher Franco, Ruihong Zhang, Stephen Kaffka, Frank Mitloehner

Research output: Contribution to journalReview articlepeer-review

1 Scopus citations


California is the leading dairy state in the United States. The total sale of milk and its products represents about $6.3 billion annually out of the $50 billion generated from all agricultural production in the state. However, methane emissions from dairy manure and enteric fermentation represented nearly half of all annual methane emissions in California, with dairy manure accounting for 25%, and enteric fermentation for 20%. Methane emissions originating from manure are produced primarily from anaerobic settling basins and lagoons, which are the most common manure storage systems in the state. To achieve sustainability on dairy farms and to comply with state regulations for air and climate pollutants, dairy farms have implemented technologies such as anaerobic digestion and alternative manure management technologies. In addition, governmental incentive programs have been deployed to partially fund these technologies for eligible dairies in the state. The present article reviews the design and operations, effectiveness, and economics of the most common technologies employed in Californian dairies in reducing methane emissions. The technologies studied include anaerobic digesters, mechanical separators, compost-bedded pack barns, manure vacuuming followed by drying, and weeping walls. The current status and estimated effectiveness of government incentive programs are reviewed and recommendations for improvements presented. Finally, future trends and research needs for mitigating the emissions in Californian dairies are identified.

Original languageEnglish
Article number120
Issue number1
StatePublished - Jan 2023

Bibliographical note

Funding Information:
The Dairy Digester Research and Development Program (DDRDP) was established in 2015. The program awards competitive grants that partially fund anaerobic digesters in Californian dairies to minimize the emissions of CH from manure management and reduce its negative environmental impacts []. shows the number of digester projects and the funding from 2015–2020. From 2105 through 2022, 131 dairy digesters were funded with a total of $213.7 million and are expected to reduce 22,955,633 MTCO over 10 years, or 2,295,563 MTCO per year for at least 10 years, which is the expected minimum life of a DDRDP project. According to CDFA [], by the end of 2022, the application of DDRDP and AMMP accounted for 2.55 MMTCO that represents approximately 28% of the 9.0 MMTCO that needs to be reduced by 2030. Aggregating the emissions reductions expected from all 233 state-funded projects yields an estimated 25,557,283 MTCO for at least 5 years, or 2,555,728 MTCO per year for at least 5 years, which is the expected minimum life of an AMMP project. 4 2e 2e 2e 2e 2e 2e

Publisher Copyright:
© 2023 by the authors.


  • animal farms
  • carbon footprint
  • environmental impacts
  • sustainability

ASJC Scopus subject areas

  • Environmental Science (miscellaneous)


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