Agriculture and Harvest Public Media
5:00 am
Mon September 16, 2013

Foaming manure pits pose fire threat, vex researchers

Howard Hill pulls his red Chevy pick-up truck up to a barn near Union, Iowa, that houses 1,000 of his hogs. In the truck’s bed is a 55-pound bag of Rumensin 90, a common antibacterial ingredient in cattle feed that helps reduce bloating. Pigs don’t eat it. Hill brought it here to dump into the manure pit under the hogs.

Hill is among the many Midwestern pork producers who use deep pits under their barns to accumulate manure throughout the year. In the fall, after fields are harvested, the nutrient-rich slurry gets pumped out of the pits and injected into the cropland.

At this time of year, the manure is nearing its deepest levels and many farmers are weary of an ongoing pit problem: a mysterious foam that sometimes forms on the manure. No one quite understands why methane gas gets trapped in the pits, but the foam it creates presents the threat of explosion.  

Outside of the barn, Hill, who owns the hogs, and Kent Reinert, the site manager who owns the barn, remove a fan to gain access to the eight-foot-deep pit. It extends under the barn’s slatted floor, capturing a lot of pig poop. The men peer down at a gurgling brown mass.

“That gas bubbling in there turns the whole thing into…it’s been described as a milkshake,” Hill said. It’s certainly not appetizing. “Typically in a pit you will have the heavy material down at the bottom and that’s why we agitate. And in some cases, we haven’t even had to agitate these pits because it’s homogenous already just from the bubbling process.”

Hill brought the bag of powder to calm the gas. This is his first time dealing with foam--a vexing problem that has become a persistent issue in the upper Midwest since 2008. Several flash fires have killed hogs and injured workers--in one barn 1,500 hogs perished. And still scientists haven’t found the cause. Iowa State University professor Steven Hoff is leading a million dollar, three-state research project funded by the Pork Checkoff.

“What we’re finding is that roughly 25 percent of the producers that we’re surveying are experiencing some sort of foaming,” Hoff said.

Gene Gilman is among them. He’s a hog farmer in Garden City, Minn., who confronted pit foam last year. Like Hill, he turned to the cattle feed ingredient.

“And three weeks later, after Rumensin, there was no foam,” he said.

Gilman has been carefully monitoring this year and has not had the problem. He doesn’t know why. He thinks weather may be a factor—last summer was much hotter than this year. And Hoff, the researcher, says that’s one of the variables scientists are investigating. Another is the bacterial community in pits with and without foam.

“We’re looking very extensively at the chemistry of manure,” Hoff said, “as well as the microbial population shifts that we might have in a foaming manure pit.”

Foaming incidents seemed to take off around the time an ethanol by-product called dried distiller’s grains became a common ingredient in swine feed.

“It’s a very high fiber feed and, in some cases, combined with a higher fat content,” Hoff said. “So those two components are issues, or at least avenues, that we’re pursuing in the research business.”

But Hoff says they haven’t been able to make a conclusive connection between the distiller’s grains and foam. Among swine fed the same feed on the same farm, some pits will have foam and others will have none.

Until a cause is isolated, farmers are at a loss for preventing the problem. So they’re stuck with the Band-Aid of applying a product once the foam is present in order to reduce it and prevent explosions.

Hill pours some of the additive onto the bubbling brown “milkshake” and uses a long stick to gently mix it in. Reinert watches with anticipation.

“Will you be able to see it do something?” Reinert asked, hoping perhaps for the foam’s sudden, dramatic disappearance. But alas, there is no immediate impact.

After two weeks, though, Hill reported improvement. The foam was not completely gone, but it had become consistently lower.

Hill has quieted the milkshake this time. But he and others remain eager for a more permanent fix. And Iowa State’s Hoff promises one will come.

“We’re nine months into a three-year study,” he said in July, “And one way or the other we’re going to solve this issue.”