Feb. 29, 2008 -- Like flatulence that never dissipates, gaseous ammonia and other odorous gases resulting from animal manure can attach to dust particles, leaving behind matter that is both unpleasant and unhealthy for humans, according to new research that evaluated the levels of dust stink.
The study, which will be published in next month's Biosystems Engineering journal, is among the first to quantify dust gas emissions. Dust from structures housing cattle, laying hens and pigs was studied, with the dust particles produced mainly from feed, manure, bedding, soil and the animals' dry skin.
Co-author Jongmin Lee explained that an attraction-producing force, known in physics as the Van der Waals force, causes gas molecules to bond with those of the dust. The resulting bond is weaker than most chemical bonds, but it's enough keep the gas stuck to the dust.
"The reverse of adsorption, desorption, is the transfer of gas from dust particles to the surrounding air, and the principles are the same as for adsorption," Lee, a graduate student in the Department of Agricultural and Biological Engineering at the University of Illinois at Urbana-Champaign, explained to Discovery News.
He added that heat can permit the gases to volatize and separate from the dust.
Lee and his advisorYuanhui Zhang therefore created a closed cylinder device that both introduced heat and then allowed for the measurement of the released gas from dust that was scraped off of barns, pipelines and exhaust fans from animal structures located in Illinois. They focused on ammonia, one of the smelliest gases produced by animals.
Based on their findings, laying hens and pigs produced far more ammonia dust than cattle did. The researchers attribute this to the way in which the animals were housed.
The cattle were in a roomier building with open areas and plenty of natural ventilation. The pigs and chickens, on the other hand, were in more cramped quarters with mechanical ventilation.
Aside from the stink problem, the gassy particles may pose human health risks.
"Particles smaller than 10 micrometers can penetrate into the large upper branches just below the throat where they are caught and removed by coughing and spitting or by swallowing," said Lee. "Also, particles smaller than 2.5 micrometers can get down into the deepest portions of human lungs and can cause respiratory disease."
As if that wasn't enough, there is a minor threat that contained buildings could actually explode due to gassy dust buildup.
Zhang said that while there is no official report of an animal building exploding, "methane digesters on animal facilities have the potential to explode." Similar explosions have occurred in grain elevators.
To resolve the problem, the scientists suggest that animal keepers improve ventilation, frequently clean their structures, properly treat manure and add oil or fat to feed.
Gary Riskowski, a professor and head biological and agricultural engineer at Texas A&M University, told Discovery News that "the key to this paper is that they are trying to develop a method to measure how much odor actually attaches to particles," which may lead to ways of diluting the gas and its malodorous properties.
Pigs are particularly stinky, Riskowski indicated, even though their ammonia emissions are slightly lower than those found in poultry structures.
"Pig facilities have a more complex mix of odorants and the characteristic swine odor comes primarily from gases other than ammonia so many people will find swine odor more objectionable," he explained.
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How Stuff Works: What Causes Flatulence?
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