One out of every five dairy cows in the United States lives in California—that’s 1.79 million milk cows. The California Air Resources Board (ARB) identifies dairies as the source of 60 percent of agricultural contributions of methane (CH4) and nitrous oxide (N20), which are greenhouse gases.

ARB ranks livestock manure second on the methane-emitting scale with 10.228 million tons CO2 equivalent. This is 2.25 percent of the state’s total greenhouse gas emissions. Dairy cattle count for 9.89 million tons CO2 equivalent in the state and are distantly followed by poultry at 0.095 million tons CO2 equivalent. Methane is released into the atmosphere as microbial organisms decompose the manure.

In 2015, the ARB set a 40 percent reduction, from 2013 levels, in methane and fluorinated gases by 2030 (this is 11 years from now). The ARB cannot regulate methane from dairies and cattle farms until 2024. Until then, reductions are voluntary. Farmers and researchers aren’t waiting another five years to develop ways to reduce methane emissions though.

Manure methane

At Maas Energy Works, based in Redding, Daryl Maas invents new technology to benefit traditional farming. His company builds and operates anaerobic digesters for livestock manure, mainly dairy. Maas Energy has built digesters since 2007. They currently have 17 covered-lagoon digesters on line in California and 38 in development.

Digesters had a rough start. “A lot of the original digesters were built with grant money,” explains Maas, Chief Executive Officer of Maas Energy Works. “Because the revenue from the sale of generated electricity was so low, it often wasn’t worth maintaining the digesters. The earlier generations didn’t have an incentive to operate long after startup, and therefore didn’t.”

New markets for renewable energy, both electricity and gas, make digesters financially sustainable and capture methane emissions. Mechanical design of digesters also improved. “The early digesters were complicated and expensive affairs,” Maas explains. “Their designs were patented and licensed to specific companies. We’ve moved away from that to standard, basic designs without proprietary engineering.”

Digester operating models

Maas Energy not only builds digesters, they also offer operating and maintenance services. Farmers select which combination works for them: purchase equipment for Maas Energy to install, operate and maintain the digesters themselves, and/or contract Maas Energy to own and manage the digester.

“Farmers have the option to choose,” Maas says, “but we tend to operate nearly all the digesters ourselves now. Because of our knowledge, we can improve quality and consistency.”

If a farmer chooses to own the digester facility and receive all the revenues, Maas Energy operates the facility for a fee. When Maas invests in the equipment, the company pays the farmer to supply manure on a per cow basis. The dairy gas captured by a digester can power a generator to sell electricity or be converted to compressed natural gas and sold into the pipeline.

Dairy energy

Electricity in California costs 19.65 cents per kilowatt hour, which ranks the state fifth in the U.S. by power cost. Most digesters in California are built to generate electricity to net meter. This means the power from a farm’s digester is used on-site, and if there’s any extra it will be sent to the main power grid for other users.

Manure from multiple farms is required for the scale necessary to convert dairy gas to natural gas for the main pipeline. Maas Energy developed a dairy cluster to serve Calgren Dairy Fuels, LLC in Pixely, Calif. As the lead developer of the Calgren project, Maas built digesters on 12 dairy farms in Tulare County.

A low-pressure pipeline moves dairy gas from each farm to the Calgren facility where it is cleaned to rate as R-CNG (renewable compressed natural gas). In February 2019, this gas began to inject into Southern California Gas Company’s (SoCalGas) pipeline for customer use.

“The utilities, like PG&E [Pacific Gas and Electric Company] and SoCalGas, are very happy to have renewable gas,” Maas says. “It provides more options to customers. We’re excited to see if we can make renewable natural gas more quickly and cheaper, and scale it for smaller dairy farms.

“A cow's milk is still worth much more than a cow's manure, but manure is valuable enough that a farmer can add to their profits by substantial margins. Through this technology, farmers can decrease methane emissions and earn more revenue.”

Methane burps

The amount of methane emitted from manure is outranked by enteric fermentation: the methane produced during digestion and released by cattle burps. The ARB measures enteric at 8.08 million tons CO2 equivalent from California’s dairy cattle (1.84 percent of state greenhouse gas emissions) and 2.97 million tons CO2 equivalent from beef cattle. In 2015, the ARB calculated bovine burps as almost 30 percent of state methane emissions from the agriculture.

“Ruminants have a four chamber stomach,” explains Ermias Kebreab, University of California, Davis animal science professor. “When they digest high fiber materials, such as grass and hay, the fermentation process yields hydrogen and then enteric methane. Our team researches how to reduce the amount of methane that ruminants belch out.”

Australian researchers discovered that seaweed reduces enteric methane release in lab animals. Kebreab’s team built on those findings by feeding seaweed to dairy cattle in California. “We found that feeding a milk cow seaweed for one percent of its daily diet,” Kebreab explains, “reduces enteric methane emissions by 60 percent.”

This reduction is from seaweed’s active ingredient bromoform, which is brominated organic solvent, colorless liquid. Currently, Kebreab ships seaweed in from Australia. He hopes to locate a large-scale source for seaweed to feed cattle.

“Our next step, which we already started,” Kebreab says, “is to track the effect of a seaweed supplement over an extended time period. Now we are feeding seaweed to beef cattle for six months to monitor effects on cattle health and meat quality. Seaweed could help California’s dairy farmers meet new methane-emission standards and sustainably produce dairy products.”

Learn more

"Can Seaweed Cut Methane Emissions on Dairy Farms?" video from the University of California-Davis: https://youtu.be/gvqhFEouzGQ .