Resource Magazine — September/October 2013
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“Pig Bang” Theory
Sara Specht

Regional partners work to solve the mystery of exploding hog barns

It began like any other phone call for an Extension engineer. A farmer with a problem, albeit an odd one: Some kind of foam was suddenly bubbling up through the slats in the floor of his hog barn. How should he deal with it?

There were more calls in the following weeks—more foam, from a few inches deep to four feet deep, even threatening to suffocate livestock. Then came reports of flash fires, and explosions, all related to this mystery foam rising from manure pits. ASABE members Larry Jacobson and Chuck Clanton, both professors in the Department of Bioproducts and Biosystems Engineering (BBE) at the University of Minnesota, visited the afflicted farms and began surveying other Minnesota pork producers. It seemed like a straightforward problem that they would be able to resolve quickly.

That was in the summer of 2009. Three years later, Jacobson, Clanton, and colleagues from several Midwest universities joined forces to try to answer the question that once seemed so simple: What is causing hazardous foam in manure pits in the region’s hog barns?

An explosive situation

“This foaming is something that we’d only heard about very sporadically in the past,” said Jacobson, an Extension engineer. “Then in the summer of 2009, we started hearing from farmers who were noticing this foam on the floors of their barns. It was pretty alarming for them, and they wanted to try to knock it down.”

Most hog barns in the upper Midwest use deep-pit manure storage throughout the year. The storage system consists of 2.4 m (8 ft) deep pits beneath the slatted floors. The pits preserve nutrients in the manure, which is pumped out in the fall and used as fertilizer on harvested agricultural fields. The pits also have become popular with neighbors, since they keep swine manure out of sight.

Rather than pumping out the pits early and then having to find alternative cropland for the manure, several farmers tried to knock the foam down by agitating the pits or spraying the foam with water. This was when the real trouble started. When they examined the foam, Jacobson and Clanton discovered that it acts like a sponge over the manure, collecting the methane gas produced in the pit. Analysis by a researcher at Iowa State University showed that the foam consisted of nearly 60 percent methane.

“It was a methane tank on top of the manure,” Jacobson said. “When the farmers started to agitate the foam, the bubbles released all this methane in a matter of minutes into the barn. At that point, all it needed was a spark—a pilot light, a motor starting, a welding torch, a light switch, or a cigarette. The lesser problem would be a flash fire, a whoosh of blue flame. But the worst-case scenario is an explosion.”

As recently as September 2011, the foam caused about a half-dozen explosions in the upper Midwest, where this phenomenon is centered. One explosion destroyed a barn on a farm in northern Iowa, killing 1,500 pigs and severely burning the worker involved.

Jacobson and Clanton and their team spent much of that first year in the field using a grant from the Minnesota Agricultural Experiment Station Rapid Response Fund, examining both foaming and non-foaming pits, as well as surveying farmers throughout southern Minnesota. Their results showed a frustrating lack of connection between the problem sites. At that time, about 25 percent of the farmers they contacted had some issue with foaming pits, but nothing appeared to be a common tie among them. Even on a farm with a double-wide barn consisting of two rooms and two pits beside each other, sharing a single wall, it was common to find foaming in one pit and none in the other.

“We heard from one producer with three barns that one is foaming and the other two aren’t,” Clanton said. “We tried to identify the differences, but it was the same pigs, the same feed, the same genetics, management, and building. Everything was the same.”

“We thought, maybe naively, that we would find some obvious commonality,” Jacobson said. “Maybe we would do some simple lab analysis and something would jump out at us, allowing us to trace it back to a cause. But that didn’t happen.”

Burning through theories

By the summer of 2010, instances of pit foaming had begun to spread beyond southern Minnesota and northern Iowa, and without a clear connection between cases, the team needed a closer look at the foam. They brought BBE scientist Bo Hu on board to analyze their field samples at a microbial level.

On a basic level, three things must be present for a liquid to foam: gas, surfactant, and stabilizer. Methane gas is present in all manure pits, and the filamentous bacteria might serve as a stabilizer—something that keeps the bubbles from bursting. Hu decided to look at a possible surfactant—soaplike chemicals that initiate bubbles—in this case, long-chain fatty acids.

The most likely source of an increase in fatty acids in pig manure is the addition of distiller’s dry grains with solubles (DDGS) into the livestock’s diet, which may cause incomplete digestion of oils. DDGS is a byproduct of corn processing for ethanol that is added to most swine feed. DDGS has shown nutritional value for pigs, but Hu thinks that the high levels of unsaturated fatty acids in DDGS may be part of the foaming equation. Identifying how big an issue this is will be a challenge, since the quality and quantity of DDGS varies widely by refinery, season, and farmer.

“From a dietary standpoint, the pig can only metabolize about half of the fatty acids in DDGS, so it all goes back to how much you put into the diet,” said Clanton. “But this is the frustration we’re running into. We’re dealing with a pit where manure’s accumulated over a year, in a building where two groups of pigs have turned over, and with diets changing weekly. In a 2,400-head building, it’s hard to pinpoint which pigs, or which diet.”

A coordinated attack

Something that will help narrow down the likely causes of foaming are the numerous samples that the team will collect and exchange with their new research partners at Iowa State University, the University of Illinois, and the University of Nebraska in a multi-year project funded by the Iowa Pork Producers Association. The group of scientists has established protocols for collecting and sharing field samples to build a foundation for coordinated research.

While each organization focuses on different aspects of the problem, the Minnesota team will continue its outreach with producers and survey analysis. The researchers also plan to continue their work to refine feed and DDGS sources, targeting specific conditions that generate foam. In 2011, Hu hit a landmark in the research by producing foaming manure in the lab, providing a key diagnostic resource.

One of their goals, he said, is to come up with a tool that farmers can use to assess the likelihood of foaming from a formulated diet. However, the long-term solution to preventing foaming is to trace it back to its source. “What started out like a routine Extension phone call has led to a real CSI mystery type of thing,” Jacobson said. “What’s causing this thing, and how can we fix it?”

Sara Specht, writer and graphic designer, College of Food, Agricultural, and Natural Resource Sciences, University of Minnesota, St. Paul, USA,