Dairy digesters use cow power to make clean energy

By Ching Lee

With more than 100 methane digesters operating in California—and more than 100 others in various stages of development—the Golden State has become a leader in harnessing so-called “cow power” to produce renewable fuels and other clean energy.

In doing so, California dairies are reducing methane emissions from their farms and well on their way to becoming climate neutral—that is, getting to a point where they no longer cause additional warming, said Frank Mitloehner, an air quality specialist at the University of California, Davis.

“The whole world views us right now as a role model,” he said.

Mitloehner made his remarks to a group of mainly legislative and state government staffers on their way to look at two Central Valley dairies with digester technology and a company that makes biofuels from dairy manure and other agricultural waste. The tours were arranged by the California Farm Bureau, California Bountiful Foundation and California Cattle Council.

Even though dairy manure digesters have been around for decades, their numbers have exploded in recent years thanks to state funding aimed at helping dairy farmers reduce greenhouse gas emissions. The building of digesters is a key part of the state’s strategy to cut methane emissions produced by dairies and other livestock. As required by Senate Bill 1383, the sectors must produce 40% less methane than they did in 2013.

To date, state digester projects have reduced emissions coming from some 200 dairy manure lagoons. They do this by placing covers over the lagoons to trap biogas that previously went into the air. This biogas is then turned into usable biofuel.

In covering the lagoons, the state’s dairy sector has cut 2.2 million metric tons of its total contribution of 7.1 million metric tons of carbon dioxide-equivalent greenhouse gas, Mitloehner said.

Researchers also continue to study ways to reduce the main source of methane from dairies—enteric emissions from cow belching. Mitloehner noted a handful of feed additives have been shown to be “quite effective in reducing dairy methane without affecting performance of milk quality” when added to the cow’s diet.

“If we continue on the current trajectory, we have calculated that we will achieve climate neutrality in this decade in our dairy sector,” he said.

Fiscalini Farmstead in Modesto, which also operates a cheesemaking facility, was one of the state’s first adopters of digester technology. It installed its first digester in 2008 and is now building a new one. Dairy farmer Brian Fiscalini described the old and current generations of digesters as analogous to the BlackBerry and the latest iPhones.

Before 2002, fewer than five dairies operated digesters, according to the California Environmental Protection Agency. In those days, the biogas produced by the older digesters ran engines that powered generators to produce electricity for use on the farm.

Today, Fiscalini’s manure management and methane digestion remain about the same: The farm uses a flush system to collect the manure in a covered lagoon. The manure is then piped to the digester to produce methane gas. But rather than creating electricity, the biogas is now converted to low-carbon fuel. Eventually, the fuel can be injected into a natural gas pipeline.

Fiscalini said renewable fuels production tax credits available for this type of system are “far better” than for converting methane gas to electricity. Back when the farm built its first digester, there were no such credits or programs available.

“Producing electricity was kind of the only option that we had,” he said.

Back then, the technology to convert methane gas to natural gas wasn’t proven or readily available, Fiscalini said. Also, the nearest natural gas pipeline was more than 2 miles away from the farm, and putting one in the ground would have cost $1 million a mile, plus an additional $2 million one-time fee to connect to Pacific Gas & Electric Co., he pointed out. While those costs haven’t changed much, the tax credits have changed to make such an investment feasible today, he added.

By shifting to making low-carbon fuel, he said, the dairy could potentially power a fleet of trucks and “work directly with somebody versus working with the utility grid system.”

“California’s already pretty good at producing electricity,” he said. “For a dairy farm to try to become a utility doesn’t really make a whole lot of sense.”

The tour group then visited Aemetis’ ethanol biorefinery in Keyes, where biogas produced by Central Valley dairies is transported via its 40-mile underground pipeline. The biogas is then upgraded to renewable natural gas and goes to PG&E via another pipeline. The biogas can also be used as a replacement fuel for diesel or converted to electricity to fuel electric vehicles, said Aemetis President Andy Foster.

The company’s goal, Foster said, is to build 66 dairy digesters. About 30 dairies have signed up. Digesters on two dairies—with 1,800 cows and 3,700 cows—have been online since 2020. Five more are expected to come online by the end of the year, with five new ones starting construction next year, he said.

One of the company’s most recent operational digesters is located at AC Machado Dairy in Crows Landing, the final stop on the tour. The 1,800-cow dairy completed construction on its digester in March.

That Aemetis was able to get permitting for its 40-mile biogas pipeline in about a year “was a pretty remarkable feat,” Foster said. Working with Stanislaus and Merced counties, the company was able to put the pipeline in the public right of way alongside of the road with other utilities, which “saved us a lot of hassle of having to try to get easements from individual landowners,” he added.

“By being in the public right of way, we have to be safer. We have to follow the same standards that the utilities have to follow,” Foster said.

The first four miles of the pipeline cost $1 million a mile, with the last 40 miles costing $465,000 a mile, according to CEO Eric McAfee.

Biogas pipelines are currently not regulated, said Robbie Macias, Aemetis’ vice president of biogas. But he said the company has “taken all the steps” through third-party engineering inspections and testing to have a utility-grade pipeline “in the name of public safety.”

(Ching Lee is an assistant editor of Ag Alert. She may be contacted at clee@cfbf.com.)