Perspectives Online

Two waste management technologies may be alternatives for swine industry

These large tanks are part of the Super Soil system that treats both liquid and solid swine waste and that has been shown to be environmentally superior to currently used waste treatment methods.
These large tanks (seen from top view) are part of the Super Soil system that treats both liquid and solid swine waste and that has been shown to be environmentally superior to currently used waste treatment methods.
(Photos by Dave Caldwell)
Two alternative methods of treating the waste from swine farms have cleared a major hurdle toward being declared “environmentally superior” to the method now used by most North Carolina hog farms to treat waste.

he two alternatives, or technologies, have met what Dr. Mike Williams, director of the Animal and Poultry Waste Management Center at N.C. State University, called “environmental performance criteria” necessary for the technologies to be considered environmentally superior.

Williams directs a 4-year-old $17.3 million effort to identify and evaluate alternative swine waste management technologies. The effort is funded by pork producers Smithfield Foods and Premium Standard Farms under agreements the two companies reached with the North Carolina Attorney General in 2000.

The agreements, which are commonly known as the Smithfield agreement, designate Williams to direct an effort to identify, then evaluate, technologies that could become alternatives to the lagoon and spray field system now used on most North Carolina swine farms. Under the agreements, experts from N.C. State University and elsewhere have been evaluating 15 alternative technologies.

On July 26, Williams announced what he called phase I technology determinations covering eight of the 15 technologies.

While the Smithfield agreement spells out environmental criteria the technologies must meet, it also stipulates the technologies must be economically feasible. Williams stressed Monday that an economic feasibility analysis is not complete, and that until the economic work is finished, the determinations should be considered conditional.

Indeed, Williams said that while six of the technologies being evaluated do not currently meet the environmental criteria, it may be possible to make changes in some of the technologies that will satisfy the environmental conditions.

One of the two technologies given conditional approval treats the entire waste stream from a swine farm, while the second is designed to treat only the solid portion of the waste stream.

The technology that treats the entire waste stream is an “on-farm separation/nitrification-denitrification/soluble phosphorus removal system.” It was developed by a company called Super Soil Systems USA and is often called Super Soil.

The Super Soil system treats swine waste in a series of large metal tanks that look somewhat like oil tanks. Waste is flushed from pig houses with water, and the first step in the Super Soil system is removal of the solid waste that remains in the liquid. The solid portion of the waste stream is removed using chemicals called flocculating agents.

The remaining liquid then flows through the tanks, where bacteria remove much of the nitrogen. The liquid then flows to a settling tank, where chemicals and a “dewatering bag system” are used to remove phosphorus. Nitrogen and phosphorus are both nutrients and essential for plant growth but in excess can cause environmental damage.

The phosphorus removal process produces calcium phosphate, which has value as a fertilizer, while the solid manure that is removed also has value as a fertilizer or soil amendment.
The Super Soil system first separates solid from liquid waste portions, with the solid conveyed out for potential use as a fertilizer or soil amendment and the liquid portion treated in a series of tanks.

From top: The Super Soil system first separates solid from liquid waste portions, with the solid conveyed out for potential use as a fertilizer or soil amendment and the liquid portion treated in a series of tanks.
(Photos by Dave Caldwell)
Roughly 80 percent of the liquid that remains after treatment is recycled to pig houses to again flush waste from the houses, while 20 percent is used to irrigate crop fields. The system does not require a conventional earthen lagoon.

The system was evaluated at a farm near Warsaw.

The second technology to receive conditional approval is an off-farm high solids anaerobic digester. The technology was developed by a company called Organic Biotechnologies LLC of Clinton and Arlington, Va., and is sometimes called ORBIT. This system employs an anaerobic digester to treat solid waste.

A digester is a vessel in which microbes degrade waste. In this case, two digesters are being used. One looks much a truck trailer, while the other looks like a truck tank. Raising the temperature of a digester speeds up degradation, thus reducing the amount of space needed.

Treatment in the digesters produces sludge, which is processed using a screw press to separate the liquid and solid portions. The liquid portion is to be used to make liquid fertilizer, while the solid portion may be used as a value-added fertilizer or soil amendment.

Among the other technologies considered in this phase of the study are two designs for belts that are positioned below the pens in which pigs are raised and are designed to separate solid manure and urine. Solids separation is seen as a way to decrease odor, as it is easier to move solid manure than a liquid waste stream. Being able to move waste could make producing value-added products from the waste more feasible.

Also considered were an earthen digester that produces biogas used to run a generator and produce electric power used on the farm and a system in which waste is treated in closed tanks. In addition, phase I included two other solid separation systems combined with combustion of the solids to produce ash that could be used as fertilizer and a system that treats waste in gravel-filled basins. The gravel acts as a surface on which waste-degrading microbes reside.

Williams said that while none of these technologies now meet the environmental performance criteria, several could, with relatively minor changes. He said it may also be possible to combine elements, or processes, from the technologies being evaluated to produce systems that will meet the environmentally superior standard.

According to the agreements, technologies must be technically, operationally and economically feasible and eliminate the discharge of animal waste to surface or groundwater in order to be designated environmentally superior. Environmentally superior technologies must also substantially eliminate the release from swine farms of ammonia, air borne pathogens and odor and disease-transmitting vectors, and they must eliminate contamination of soil or groundwater with nutrients or heavy metals.

Smithfield Foods is providing $15 million to evaluate technologies, while the attorney general allocated $2.3 million from the Premium Standard Farms agreement, for a total of $17.3 million.

In 2002 the attorney general entered a third agreement with Frontline Farmers, an organization made up of independent swine farmers. While Frontline Farmers is not providing funding, the organization’s membership agreed to work with the attorney general and N.C. State University to develop and implement environmentally superior technologies.

The technologies that are being evaluated were selected by Williams working with panels made up of representatives from government, the swine industry and environmental groups as well as economists and waste management experts.

Eighteen technologies were originally selected for evaluation. For various reasons, three of the original 18 dropped out of the evaluation process. The remaining 15 technologies are in various stages of evaluation. The phase I report concerns eight of these.

In many cases, technologies have been evaluated on hog farms at full scale. And in most cases, evaluations have taken at least a year. Once a technology was up and running, it was necessary to take cold-season and warm-season samples to determine how the technology operates year round.

—Dave Caldwell