What is a Dairy Digester and How Does it Affect Methane Emissions?

Dairy Digester
Dairy digester in California. Image courtesy of Dairy Cares.

Dairies typically use lagoons to help manage manure from cattle. These lagoons produce methane, a greenhouse gas that affects our climate. In recent years, California dairies have been working with state agencies to implement new ways to manage manure and reduce the amount of methane being released into the atmosphere. One way is by using dairy digesters. 

A dairy digester is a technology that can generate biogas from dairy manure. The dairy digester breaks down solid waste in the absence of oxygen – hence why the process is known as anaerobic digestion – and turns it into natural gas.  

Dairy Digester in California
Dairy Digester on a California dairy. Image courtesy of Dairy Cares.

The biogas generated by a dairy digester can run an on-farm generator, be sold to a local utility for profit, be sold as renewable energy credits and can also be injected into natural gas pipelines as renewable natural gas (RNG), and be used with RNG vehicles.  

According to the California Department of Food and Agriculture, methane emissions from current manure management account for about 2.7 percent of the total statewide GHG emissions. CDFA estimates dairy digesters reducing greenhouse gases by 12.8 million metric tons (MMT) CO2-equivalent over ten years, or about 1.3 MMT CO2e annually. 

And the efforts to reduce methane are working. California currently has more than 120 digester projects in the works, with 30 digesters already in use. A 2019 CDFA report stated that the use of dairy digesters, along with other methods, helped cut down about 25 percent of total 2013 dairy and livestock manure methane emissions, as part of the state efforts to reduce methane by 40 percent

The CDFA noted that 213 dairy families in California contributed significant methane reductions through the Dairy Digester Research and Development Program (DDRDP), as well as through the Alternative Manure Management Program (AMMP) – which are manure management projects not using digesters. Since 2015, DDRDP and AMMP reduced an estimated 2.2 million metric tons of greenhouse gases (2.2 MMTCO2e) per year, which is equivalent to removing more 460,000 cars from the road.  

California Dairy with digester
A California dairy with a dairy digester and solar panels. Image courtesy of Dairy Cares.

Methane is a potent greenhouse gas, but the renewable capabilities of methane give the greenhouse gas potential to help offset other greenhouse gases, such as carbon dioxide. Through dairy digesters, and other manure management practices, the methane produced by livestock can help dairies operate climate neutral and not add additional warming to the atmosphere.  

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