March 14, 2012
Hog farmers have a lot to worry about, such as fluctuating pork prices and sick pigs. Now they have a new concern: barn explosions. The culprit appears to be a strange new foam that has begun growing on the pools of liquid manure beneath large pig farms. The foam traps methane, a flammable gas that, when ignited, can cause catastrophic blowups. One explosion last September in Iowa leveled an entire barn, killing some 1,500 pigs and injuring one worker.
On big farms in the Midwest, pigs spend the latter part of their lives in large, low buildings called finishing barns. These barns have slotted floors and sit atop eight-foot-deep concrete pits. When the pigs defecate and urinate, the waste falls between the slats and into the pit, forming an underground manure lagoon. Once a year, the farmers empty these pits and sell the manure as fertilizer. This model has been used in the Midwest for the past 30 or 40 years, says Larry Jacobson, an agricultural engineer at the University of Minnesota.
In 2009, Jacobson and other agriculture experts began to hear reports of a mysterious foam growing on swine manure ponds. “Sometimes it would be enough that it would come up through the slats,” he says. To get rid of the foam, some farmers poured water on it. Others used machines to break it up. That’s when the explosions began.
Why these explosions happen is well understood. As manure ferments, it releases methane gas, which bubbles to the surface of the pit. Normally this methane doesn’t pose a risk. The gas seeps out of the pit, and the barn’s ventilation fans carry it away. But when thick, gelatinous foam covers a manure lagoon, the methane can’t rise. The foam acts like a sponge, Jacobsen says, soaking up the gas. Jacobsen and his colleagues have collected foam samples that are 60 percent methane by volume. When a farmer disturbs the foam by agitating the manure or emptying the pit, the methane gets released all at once. In barns without adequate ventilation, the concentration of methane can quickly reach the explosive range, between 5 percent and 15 percent. A spark from a fan motor or a burning cigarette can ignite the gas. An explosion in southeastern Minnesota raised a barn roof several feet in the air and blew the hog farmer, who was on his way out, 30 or 40 feet from the door.
For the past three years, Jacobson and his colleagues at the University of Minnesota and the University of Iowa have been trying to figure out why the foam forms. The slimy stuff appears to be the byproduct of bacteria. But the researchers don’t yet know which strain or why these foam-producing bacteria suddenly appeared. The researchers are in the midst of conducting DNA analyses to try to identify the microbes, comparing foamy manure with non-foamy samples.
One explanation may be dietary changes. About five years ago, pig farmers began mixing distillers grains, a fermented byproduct of the ethanol production process, into their pig feed. Distillers grains are much cheaper than traditional feed. But that can’t be the only factor, Jacobson says. Today, nearly everyone feeds their pigs distillers grains, but only a quarter of the swine barns grow foam.
Jacobson and his colleagues have identified a few additives that seem to help eliminate the foam. But those fixes are just “band-aids” Jacobson says. What he really wants is a way to prevent the foam from forming.
Want to see what the foam looks like? Check out this YouTube video, and prepare to be disgusted.
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