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ShareNov. 24, 2000 — GAINESVILLE, Fla. --- With hundreds or thousands of cows eating, drinking and, well, doing what cows do naturally, dairy farms have earned a reputation for bad odors.
Combine that with urban sprawl that brings city dwellers and dairy farms closer together, and you have a recipe for conflict.
But thanks to new technology developed by University of Florida researchers, dairy farms -- and swine and poultry operations as well -- may come out smelling like a rose as far as their neighbors are concerned.
The new system, called a fixed-film anaerobic digester, is up and running at UF's Dairy Research Unit north of Gainesville after about four years of development, said Ann Wilkie, an associate professor of environmental microbiology with UF's Institute of Food and Agricultural Sciences. The project is an interdisciplinary effort between the soil and water science department and the departments of animal sciences and agricultural and biological engineering.
Wilkie, who developed the system, said it is capable of reducing odors by about 90 percent.
"Bacteria in the digester convert organic matter in the animal waste into methane and carbon dioxide," said Wilkie. "At the same time, the microbes convert material that cause odor into nonoffensive compounds, so when the processed wastewater leaves the digester it can be applied to the land without the problem of nuisance odor."
Wilkie said the new anaerobic digester is faster and more efficient than previous designs because dozens of plastic pipes have been added inside the 100,000-gallon tank. That gives the bacteria more surface area on which to degrade smelly or harmful compounds.
"Normally, bacteria just flow into a digester with the animal waste and then back out again," Wilkie said. "We retain the bacteria inside our system on the plastic pipes.
"There are miles of surface area inside the tank covered with the bacteria that are the workforce of this system," she said. "Since there are more bacteria per cubic foot inside the digester, the system has the ability to do more work."
Wilkie said wastewater remains inside the digester only two days, compared with about 25 days for previous anaerobic digester designs or about 60 days when wastewater is treated in anaerobic lagoons.
She said this is the first time this type of technology has been applied to animal waste management. Similar systems have been used by the pharmaceutical and liquor distilling industries, Wilkie said.
UF researchers said the ability to control odors is becoming increasingly important as more and more rural land is converted to urban uses.
"The dairy farmers benefit because they are able to stay in business," Wilkie said. "And their neighbors will be happy because they are not going to be sitting in their backyards smelling cow manure."
But improving the smell of animal enterprises is not the only benefit of the new system. The farms also get a clean and free source of energy in the process.
"This particular system addresses several environmental issues," Wilkie said. "These include the reduced odor, the reduced release of greenhouse gases that can cause global warming and reducing our dependence on fossil fuels."
One byproduct of the digestion process is biogas, a mixture of methane and carbon dioxide. Wilkie said the fixed-film digester produces biogas that is 82 percent methane, where existing units reach only about 65 percent methane. The methane currently is being used to heat water for the Dairy Research Unit, with plans to use it this winter to fuel the space heaters in the milking parlor as well.
Additionally, the system will result in less water use, Wilkie said.
"We also are able to treat the wastewater to the point where it can be recycled back into the barns, allowing increased water conservation," she said.
As regulations on animal enterprises increase, greater pressure will be placed on farms to manage their waste output effectively, said David Armstrong, the farm manager at the Dairy Research Unit. The digester will allow farms to take a waste product and turn it into something useful, he said.
"This system will become more economically feasible as the cost of energy goes up," Armstrong said. "We can use the gas it produces to heat water or we can generate electricity with it that we can either use onsite or sell to the power cooperatives, giving us another income stream."
Wilkie said a digester like the one at the 500-milking cow UF dairy could be built for about $150,000. Once the technology is licensed and put into commercial production, the cost should come down, she said. Also, for larger animal enterprises, economies of scale will come into play, she said.
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