Scientists at the USDA Agricultural Research Service’s Florence, SC, center are using municipal waste water treatment systems from Japan to treat hog manure in North Carolina.
The system uses large populations of bacteria, inside polymer gel pellets, to break down the ammonia in manure into nitrite and then into nitrate. This process is called nitrification. Subsequently, the nitrate is converted to nitrogen, in a process called denitrification.
ARS scientists Matias Vanotti and Patrick Hunt are the first to apply this treatment to large-scale U.S. production facilities.
In a swine operation, the system works like this:
First, manure is pumped to lagoons to settle the solids. The liquid is pumped into a tank, or reactor, equipped with an aeration system and the bacteria-laden pellets, which occupy 7 to 15% of the tank’s volume, and the ammonia turns to nitrite.
Then, the nitrite is converted to nitrogen gas – denitrification – that occurs under reduced oxygen conditions.
The researchers found that the pellets removed 97 to 100% of ammonia in small-scale tests.
Then, the technology was applied to a 2,600-head nursery at Kenansville, NC, which uses a flushing system to recycle liquid to a single-stage lagoon.
The pilot unit was evaluated in 1998 and 1999, and the nitrification rates were more than 90% in the second year.
Then the researchers developed a second pilot system without a lagoon. The solids and liquid were separated with polyacrylamid (PAM) treatment.
Then the nitrification/denitrification with the pellets. PAM is a water-soluble polymer that clumps the fine particles into larger particles.
During 2000, the team, along with researchers from North Carolina State University, evaluated the second system.
The solids separation reduced the 98% of the oxygen demand, Vanotti says. Combined with the pellet technology, the system reduced nitrogen concentration from 675 ppm to fewer than 25 ppm.
A full-scale demonstration system is planned for a 4,360 head Smithfield Foods farm in Duplin County. The system will separate solids and liquid and make a soil-free growth medium from the solids. It will remove the nitrogen and phosphorus from the wastewater and recycle the cleaned water.
Researchers: Patrick G. Hunt and Matias B. Vanotti. Phone Hunt at (843) 669-5203 or email: hunt@florence.ars.usda.gov.