Environmentally Safe Hog Waste Disposal Methods

By North Carolina State University - Researchers at NC State University are taking the lead role in developing new technologies that will enable hog farms to protect environmental quality while providing jobs and agricultural income for North Carolina and other hog-producing states. Research has focused on five promising technologies that may be up and running on hog farms in less than five years. This article looks at these technologies.
calendar icon 15 November 2000
clock icon 6 minute read
The hog industry is an important economic engine in North Carolina and several other states -- but one that has generated concern about the impact of livestock waste disposal on water, soil and air quality.

Researchers at North Carolina State University are taking the lead role in developing new technologies that will enable hog farms to protect environmental quality while providing jobs and agricultural income for North Carolina and other hog-producing states.

This summer, NC State received a $15 million grant to coordinate the development and identification of environmentally friendly technologies for the treatment of hog waste. The funding, from Smithfield Foods, Inc., was the result of a landmark agreement between Smithfield Foods and N.C. Attorney General Mike Easley to phase out open-air hog lagoons and sprayfields in North Carolina over five years. Smithfield is the largest pork producer in the United States.

NC State received a second, $2.5 million grant from a similar agreement signed in October between Easley and Premium Standard Farms, the nation's second-largest pork producer.

Research has focused on five promising technologies that may be up and running on hog farms in less than five years, said Dr. Mike Williams, director of NC State's Animal and Poultry Waste Management Center, which is leading the research effort.

"Animal waste treatment is not an issue only in North Carolina," Williams says. "We feel that some of these technologies may have national as well as worldwide applications."

Currently, most swine waste is treated as a liquid in earthen containment structures called lagoons, in which bacteria break down the waste aerobically. The treated effluent from the lagoons is then sprayed onto field crops that use the nutrients contained in the effluent. The N.C. Department of Environment and Natural Resources estimates that the state's 2,400 hog farms use 4,000 active lagoons.

Treatment of livestock waste is a controversial subject in North Carolina and several other states. Waste from large hog and poultry farms has been blamed for polluting surface waters, contaminating wells, creating noxious odors, and discharging ammonia into the air. Treatment and disposal of the waste costs farmers tens of millions of dollars each year.

Research indicates that the lagoon and sprayfield approach to treating hog waste is reliable, when properly designed, sited, constructed and managed, Williams says. But, he adds, evidence suggests that there's reason to study the impact of that approach on water, air and soil quality.

Easley negotiated the Smithfield and Premium Standard agreements following the torrential rains and flooding of Hurricane Floyd, which caused many North Carolina hog waste lagoons to overflow. Smithfield, with its subsidiaries, is the largest hog producing and hog processing company in the world. Smithfield's farms represent 70 percent of North Carolina's hog industry.

The NC State Animal and Poultry Waste Management Center is leading the two-year process of evaluating and developing new technologies for treating waste and determining the feasibility of those technologies for the North Carolina hog industry. Once a technology is developed and identified by the university as technically and environmentally sound, Smithfield and its subsidiaries will be required to implement it within three years.

Five technologies are in the advanced stages of development and testing, while others are in the works. Those nearly ready for implementation, following pilot projects at commercial and research farms throughout eastern North Carolina, are:
  • A covered in-ground lagoon system. In this sealed system, bacteria digest the animal waste anaerobically, creating biogas that is used to power an electricity generator. Heat from the generator is then utilized to heat a hog farrowing house. Treated water from the digester unit is transported to a second earthen unit, from which it is used to flush waste out of livestock buildings and into the digester system. The effluent is irrigated seasonally onto Bermuda grass to remove excess nutrients. Plans are to use the effluent in the future for aquaculture and/or greenhouse plant production.
  • Aerobic upflow fixed-media biofiltration/solids separation/solids coating. This system flushes pre-screened liquid manure through two biofilters containing plastic media, on which a film of bacteria is cultivated. The bacteria convert almost all the harmful ammonia in the wastewater into nitrates and nitrites, and reduce the concentration of odor-causing compounds. The system results in liquid effluent and solids that can be used as fertilizer.
  • Sequencing batch reactor. This technology -- which has been used to treat wastewater from small communities for many years -- treats swine manure in a three-step sequence. The waste is transported to a containment vessel and subjected to an aeration cycle before solids are allowed to settle out for disposal. The process reduces organic carbon and phosphorus in the treated effluent. It also converts ammonia to nitrate and then turns the nitrate into nitrogen gas that can be released safely into the atmosphere.
  • Constructed wetlands system. This system uses natural wetland plants to remove nitrogen from treated swine wastewater, therefore preventing the overloading of nutrients on agricultural land to which the effluent is applied. The plants are arranged in a series of free-surface-flow constructed wetland cells. The waste water is pre-treated by a solids-separation and aeration process before the wetland treatment, removing excess nutrients, odor-causing compounds, and converting ammonia into nitrate. As a result, harmless nitrogen gas rather than ammonia is released into the wetlands system.
  • High temperature anaerobic digestion and solids composting. In this system, the manure is anaerobically digested in an enclosed and heated tank. The resulting biogas is used to produce electricity. Partially digested solids are combined with composted material; the resulting high-nutrient compost can be used for greenhouse crop production.
In addition to addressing environmental concerns, Williams says, all five of the technologies significantly reduce odors usually associated with hog waste treatment systems.
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