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By Natalie Willis, Reporter, Valley Ag Voice

Dairy digesters are most prominent in California, hosting 227 projects that capture methane from 255 dairy farms and create renewable electricity, renewable natural gas, or hydrogen fuel. According to Dairy Cares, the state’s digester program achieves 22% of greenhouse gas reduction from all climate programs in the state, but it operates with 1.7% of the state’s funding.  

Dairy operations with manure management facilities have the ability to earn carbon credits, allowing the credit owner to emit carbon dioxide or other greenhouse gases into the atmosphere with one credit allotting to one ton of GHG. This approach has been contested by environmental advocates who believe the methane-reducing projects could lead to larger dairies and increased emissions. 

Some groups, such as the Center for Food Safety, refer to methane digesters as a Band-Aid fix to reducing agricultural emissions. Now, the California Air Resources Board is considering phasing out climate credits for dairy digesters in its effort to meet the Biden Administration’s goal of cutting methane emissions by 30% compared with 2020 levels by 2030. 

CARB’s Low Carbon Fuel Standard 2023 Amendments report from Sept. expanded on this proposal to phase out methane crediting for dairy and swine manure and landfill-diversion pathways by 2040. According to an email from Dave Clergen, public information officer for CARB, the staff has not formally proposed any updates to the LCFS regulation. 

“CARB will be posting a formal proposal for amendments to the LCFS in the coming weeks,” Clergen wrote.  

Current information on staff proposals to phase out climate crediting for dairy manure is limited to preliminary workshops and other materials requesting public input in developing a formal regulatory proposal.  

The preliminary amendments report explained that avoided methane emissions have low carbon intensity due to the amount of captured methane turned into biogas. With California planning to phase out gas-powered cars, the proposal to gradually eliminate biofuel made from cow manure is indicative of a more regulated future. 


Dairy digesters prevent GHG, such as methane formed in lagoons — holding ponds of manure in dairy facilities — from infiltrating the atmosphere. According to Alice Rocha, Ph.D. student at the University of California, Davis, studying manure management systems, digesters can exist in different forms. Still, the most popular is a covered lagoon containing manure and urine from dairy cattle. Most systems utilize water to clean out barns, which also pull into the lagoons, so covering the lagoon constructs a dairy digester as it creates an environment completely without oxygen. 

“The concept of using a digester is actually very old technology. Just the concept of allowing organic matter to break down in the absence of oxygen and that generation of gases is a pretty refined system,” Rocha said. “However, there has been a lot of research recently going into not necessarily putting more animal waste into a digester, but improving the yield of biogas coming from that digester so that farmers have an additional form of income.” 

Captured gases may be injected into natural gas pipelines to power renewable natural gas vehicles. Compared to more carbon-intensive fuels, vehicles fueled by biogas require between 49% and 359% less carbon, according to a prior study by CARB. 

Rocha explained that dairy digesters do not prevent emissions from occurring, but they do prevent them from reaching the atmosphere, offsetting roughly 2.3 million megatons of GHG emissions. However, high initial costs have limited the number of operations able to support a digester project. 

“However, the CDFA also has the dairy digester research and development project, which offers loans and financial assistance to farmers to help overcome that,” Rocha said. “If you can overcome the financial barrier, there are also the barriers and challenges of maintenance and management of an anaerobic digester because you’re essentially managing a tiny nuclear reactor.” 

As America’s dairy capital, California produced almost 23 million tons of carbon dioxide in 2020, a CARB report stated. Repurposing this into a sustainable approach, the state produced the equivalent of 21 million gallons of diesel fuel at the start of 2023 in renewable biofuel.  


Tulare County, the national leader in dairy commodities, is also leading the state in cutting GHG emissions, reaching 56% of its 2030 pollution reduction goal with a new reduction of 592,131 metric tons in 2021.  

In response to CARB’s proposal to phase out funding for dairy digesters, Tulare County Supervisor and dairy farmer Pete Vander Poel traveled to Sacramento to lobby for continued funding.  

“We have seen the number of dairy digesters in partnership through the LCFS grow. We currently have 40 operational digesters, methane digesters, in Tulare County, and we have 12 that are permitted and being constructed. So, they are approved and ready to get connected,” Vander Poel said at the CARB meeting in September. 

Vander Poel further explained that the program has positively impacted the quality of life for families on the dairy farm and surrounding residents. The CDFA has awarded Tulare County with $78 million in funding for digesters at 50 dairies.  

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