Planet Earth

The Mystery of the Exploding Manure Pits

80beatsBy Sarah ZhangFeb 14, 2012 1:26 PM

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The only thing worse than a huge stinking pit of manure may be a huge stinking and foaming pit of manure that blows up the barn. Over the past few years, explosions have destroyed several Midwestern pig farms, killing thousands of hogs and causing millions of dollars of damage. Pig farmers and scientists have been at a loss to explain these explosions. Could the culprit be a small microbe? Methane gas is a natural byproduct of bacteria living in manure pits. It's odorless (blame hydrogen sulfide for the unpleasant smell), colorless, and just so happens to be very flammable. There has been a recent uptick in reports of foam in these manure pits, rising as high as four feet. What's trapped in the little bubbles of foam? Methane, of course. With such a high concentration of flammable gas, all it takes is a little spark. The mystery is why these deep manure pits, standard practice for years, are suddenly foaming over the top. Researchers have noticed a correlation (pdf) between foaming and hogs fed a diet heavy in DDGS, or distiller's dried grains with solubles. DDGS is the dried leftover mash from making ethanol out of corn. With the dramatic rise of ethanol production in the United States in the past decade thanks to government subsidies, some 3.2 million tons of DDGS is now produced annually. Most of that is fed to cows, but increasingly, also to pigs. DDGS has a different protein and fat profile than traditional soybean or corn feed, and the FDA has also found significant levels of antibiotics in distiller's grains. Both of these factors can influence the makeup of the microbial community. Dr. Bo Hu at the University of Minnesota suspects a filamentous bacteria may be the cause of the foaming. His lab is working to identify the bacteria behind it. Even assuming that this hypothesis is true, we can't entirely blame a microbe for the problem---after all, it wasn't they who devised the policy that seems to be giving us tons of excess DDGS and explosive, methane-filled foam.

Image courtesy of MaretH / flickr

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