"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梞ostly 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.
Swine wastewater before (left) and after treatment in the pilot reactor.
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.
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.
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.