Nine Iowa dairies get digester permits since new law, seven plan expansion

Gov. Kim Reynolds in June signed a bill that allows Iowa animal feeding operations to exceed confinement capacity if they install an anaerobic digester to treat all manure.

Anaerobic digesters, which have been used at wastewater treatment plants for decades, use bacteria and microorganisms in closed tanks to convert manure and food waste into methane, which can then be changed into electricity and heat. The leftover digestate, which doesn’t smell like manure, can be applied to farm fields.

Digesters can be finicky, an operator told The Gazette last spring.

“They have to have the kind of ‘food’ they like,” said Bryan Sievers, principal owner of the AgriReNew digesters on Sievers’ family cattle farm near Stockton. “If you get too much nitrogen, you can cause an upset stomach for the bacteria.”

Sievers supplies his two digesters, which cost $7.5 million to install in 2013, with a combination of manure from his cattle, culled potatoes, distillers grains and other food waste.

Earlier this year, Sievers was exploring further processing of his methane to create a liquid transportation fuel called renewable natural gas that could be transported through a pipeline. Some Western states provide a tax credit for renewable natural gas.

Several Iowa environmental groups say claims about the benefits of digesters and biogas are inflated. The potential biogas from digesters at swine and dairy operations in the United States is less than 1 percent of the total natural gas used nationwide in 2019, according to a report from the U.S. Energy Administration.

Opponents think promotion of the biogas industry is a backdoor way to encourage more large-scale animal confinements in Iowa.

What’s happened since

Nine Iowa dairies have applied for and received permits this year to build anaerobic digesters, said Paul Petitti, senior environmental engineer at the Iowa Department of Natural Resources.

The companies that have built or plan to build digesters are: Black Soil Dairy, in Granville; Kirkman Farms, in Kirkman; Legacy Dairy, in Sanborn; Marshall Ridge Farms, in State Center; Meadowvale Dairy North, in Rock Valley; Rock River Jerseys-Inwood Dairy, in Doon; Roorda Dairy, in Paullina; Van Ess Dairy, in Sanborn; and Winding Meadows Dairy, in Rock Valley.

All of the new permits went to existing dairies.

Five will increase the size of their operations with the new digesters, but did not need HF 522 to add cows because they are not exceeding capacity limits of 8,500 animal units, or 6,071 milking cows, Petitti said. Two other dairies, Meadowvale and Kirkman, needed the new law to expand their operations beyond 6,071 milking cows.

The new law allows expansion beyond 8,500 animal units if all manure is treated by digesters. The law does not specify an upper limit, but Petitti said the amount of available land for cows and application of digestate, as well as separation distance requirements, “would likely prevent sites from expanding limitlessly.”

Petitti is aware of three more potential digester applications from Iowa dairies, he said.

“I can’t speculate if they will formally apply, however these digesters appear to need a larger dairy to be worth pursuing,” he said. “There are but a small number of dairies that likely meet their criteria.”

The Iowa House considered another bill, House File 789, earlier this year that would have let state revolving fund money be used for biogas facilities. Although that bill stalled in committee, it could come back in the 2022 session.

There are about 317 farm-based anaerobic digesters in the United States, according to the AgStar database maintained by the U.S. Environmental Protection Agency. This number is up from 270 reported in the database in late April, but still small compared to thousands of on-farm digesters in Europe.

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