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Coping With Swine Manure
State-of-the-art technology cleans up wastewater from large-scale animal
production.
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Soil scientists Patrick Hunt
(left) and Matias Vanotti examine
a sample of nitrifying pellets.
(K9508-1)
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Scientists at the
ARS Coastal Plains Soil, Water, and
Plant Research Center in Florence, South Carolina, are tackling one of the
nation's greatest environmental problems: the cleanup and disposal of manure
from swine-production wastewater.
"Large-scale swine production is increasing in the United States at a very
rapid rate," says ARS soil scientist Patrick G. Hunt, who leads the
Florence lab. "In North Carolina alone, hog production increased from 2.6
million in 1990 to over 9 million in 1997."
Pork production is a major enterprise that has monumental waste-treatment
challenges. "These problems are related to flushing waste from
high-density confinement facilities into anaerobic lagoons and then applying
the wastewater to cropland," says Hunt. "Besides nitrogen, swine
manure contains phosphorus and other chemicals that can fertilize plants. But
it becomes an environmental concern when more nitrogen is applied than crops or
forage can assimilate," he says. |
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Nitrifying bacteria inside these
polymer gel pellets remove ammonia
from swine wastewater.
(K9509-1)
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According to ARS soil scientist
Matias B. Vanotti at the Florence lab, "As the practice of confined-animal
production grows, we desperately need effective and affordable alternatives for
managing the nutrient byproducts of these large-scale operations."
Vanotti, working with Hunt and a team of ARS colleagues, has devised a quick,
effective, and relatively inexpensive new technology for removing the ammonia
form of nitrogen from large-scale swine-production facilities.
"We adapted Japanese state-of-the-art technology for treating municipal
wastewater," he says. "It uses large populations of bacteria
entrapped in polymer gel pellets to break the ammonia down into nitrite, then
nitrate." This process is known as nitrification. Then, in a process
called denitrification, the nitrate is converted to nitrogen, an odorless gas
that is the main component of air. |
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Swine wastewater before (left)
and after treatment in the
pilot reactor.
(K9508-15)
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Vanotti's team is first to apply the
Japanese pellet technology to disposal of high-ammonia wastewater from
large-scale U.S. animal production facilities.
"Our preliminary research indicated that nitrifying bacteria protected in
pellets could nitrify animal lagoon wastewater at rates comparable to those
used in Japan to clean up municipal wastewater systems," says Vanotti.
The pellets—an eighth- to a quarter-inch wide—are typically made of
polyethylene glycol and polyvinyl alcohol. These polymers are liquefied and
mixed with Nitrosomonas and Nitrobacter bacterial sludge and then
solidified by cold or chemical treatment. The pellets allow ammonia, oxygen,
and carbon dioxide to pass through and nourish the bacteria.
"The pellets provide an ideal environment, because the organisms are
immobilized inside, yet able to perform optimally," says Vanotti.
Nitrification/denitrification of animal wastewater is difficult because it
contains high amounts of ammonia that hinder the nitrifying bacteria, says
Vanotti. The key to success is to let the bacteria adjust, or acclimate, to the
high-ammonia environment. The scientists found that the nitrifying
microorganisms can perform optimally after 2 months of acclimation.
"Acclimation requires exposing the pellets to 10 to 20 times the ammonia
found in municipal wastewater," says Vanotti. "Once acclimated, they
should be able to treat high-strength wastewater effectively for 10 years or
more."
How the Pellet System Works
First, swine manure wastewater is stored in a lagoon to settle the solids. Then
the liquid is pumped into a tank, or reactor, equipped with an aeration system,
which provides the oxygen-rich environment necessary for nitrification to
occur. A wire screen retains the pellets, which take up 7 to 15 percent of the
tank's volume. The subsequent conversion of nitrate into nitrogen
gas—denitrification—occurs under reduced-oxygen conditions.
In small-scale tests, the ARS researchers found that the pellets removed 97 to
100 percent of the ammonia in wastewater.
"The nitrification rates are three times those achieved in the United
States using conventional activated-sludge treatment systems," says
Vanotti. "The new technology is quicker and cheaper, too."
After the small-scale tests, the researchers spent 2 years developing and
perfecting a field-scale pilot test in Kenansville, North Carolina.
"For our first pilot-site reactor, we used wastewater from a 2,600-pig
nursery, which uses a flushing system to recycle liquid from a single-stage
lagoon. The average liquid volume of the lagoon was 144,730 cubic feet. The
lagoon liquid typically contained 365 parts per million nitrogen—mostly as
ammonia," Hunt says.
The team evaluated the pilot unit throughout 1998 and 1999. During the second
year, nitrification rates were greater than 90 percent, with treatment lasting
a total of 12 hours. The ammonia was converted entirely into nitrate-nitrogen
forms without any being lost to volatilization. That ammonia reduction also cut
down foul odors considerably.
The team developed a second pilot reactor in an innovative system where the
lagoon is omitted. The solids and liquid are separated with polyacrylamide
(PAM) treatment, followed by nitrification/denitrification with the pellet
technology. PAM is a water-soluble polymer that clumps the fine, suspended
particles typical of swine manure into larger particles, or flocs. This
enhances the separation efficiency of screens and filters.
During 2000, the team evaluated the second pilot system in cooperation with
North Carolina State University at its Waste Management Center at Lake Wheeler
Farm in Raleigh.
"Solids separation with PAM reduces 98 percent of the oxygen demand, which
allows economical aeration treatment of the liquid-flushed manure," says
Vanotti. "By capturing the suspended particles, we also remove most of the
volatile and oxygen-demanding organic compounds from the liquid stream.
"Instead of breaking down organic compounds, the oxygen in the aeration
treatment is used efficiently to convert ammonia. Combined with the pellet
technology, this system lowers nitrogen concentration from 675 parts per
million to fewer than 25. The purified and deodorized effluent can be recycled
to clean the hog houses or used for crop irrigation."
A full-scale demonstration of such a system has been planned at a 4,360-pig
farm in North Carolina's Duplin County, says Vanotti. The system will separate
solids and liquids, make a soil-free growth medium from the solids, remove the
nitrogen and phosphorus from the wastewater, and recycle and reuse the cleaned
water.—By Hank
Becker, formerly of ARS.
This research is part of Manure and Byproduct Utilization, an ARS National
Program (#206) described on the World Wide Web at
http://www.nps.ars.usda.gov.
Patrick G. Hunt and
Matias B. Vanotti are at the
USDA-ARS Coastal Plains Soil,
Water, and Plant Research Center, 2611 W. Lucas St., Florence, SC
29501-1241; phone (843) 669-5203, ext. 101/108, fax (843) 669-6970. |
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"Coping With Swine Manure" was published
in the July
2001 issue of Agricultural Research magazine.
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