Hurricane Florence was an important reminder that North Carolina’s livestock and poultry producers—and the people and ecosystems residing downstream of those producers—are vulnerable to the potentially toxic impacts of flooding. The risk of swine production wastewater entering streams and rivers during flooding has also renewed a broader interest in identifying environmentally superior technologies for manure management to mitigate air and water emissions, both as part of routine farm operations and during extreme weather events.
Air emissions of ammonia (a nitrogen-based compound) from swine farms can deposit in local watersheds and over-enrich waters causing algal blooms and other adverse impacts. Airborne ammonia can also bind with nitrogen oxides and sulfur oxides that cars and power plants emit, forming fine particles that when inhaled are harmful to people’s respiratory health. Recently published research documents the ongoing health and environmental impacts discussion.
Back in 2000, the most extensive swine manure treatment technology research study conducted in North Carolina was funded through an agreement between the North Carolina Attorney General’s office and Smithfield Foods and its North Carolina subsidiaries. The terms of that Smithfield Agreement included funding a North Carolina State University-directed program in which multiple researchers evaluated alternatives to conventional anaerobic lagoon and sprayfield swine manure management systems.
The number, location, and manure management technologies of North Carolina’s swine farms have not changed significantly since 2000, and environmentally superior technologies have not been adopted due in large part to economic feasibility. Therefore, many of the assessment’s findings remain relevant today.
We and others at RTI International were tasked with assessing the environmental impacts and benefits of conventional vs. new technologies developed to reduce nitrogen pollution by 10 percent to 50 percent, and the findings of our evaluation continue to be pertinent. Our research focused on understanding the impacts of ammonia air emissions and stormwater runoff from 2,295 swine farms’ housing, lagoon, and sprayfield systems located across five river basins (Tar-Pamlico, Neuse, Cape Fear, White Oak, and New River).
Our research findings included the following:
- We predicted that 37,000 tons per year of ammonia air emissions were deposited in the five-river basin study area. Furthermore, this prediction only represented the ammonia that would deposit into watersheds within 50 km of each swine farm.
- The airborne ammonia that did not deposit was available to form fine particles. While methods for predicting particle formation were limited at that time, we estimated that the five-river basin ambient average air concentration of these ammonium particles was 0.6 µg/m3. (Today, our State’s ambient air quality health standard for fine particles is 12.0 µg/m3.)
- We estimated that Duplin County, NC, would have the highest level of ammonium fine particles generated by swine farm ammonia air emissions. The estimated level of 3.5 µg/m3 was about 25 percent of the North Carolina Department of Environment and Natural Resources’ (now NC DEQ) ambient air concentration estimate of fine particles in Duplin County from all emission sources.
- While we estimated that a 10 percent to 50 percent reduction in swine farm nitrogen loadings to surface waters would benefit public recreation such as boating, fishing, and swimming up to $10 million per year, we predicted that new technologies that could reduce ammonia air emissions 10 percent to 50 percent could achieve a 7-to-8-figure cost savings by preventing premature respiratory-related deaths. (We used a U.S. Environmental Protection Agency benefits estimation model for this estimate.)
Our findings reported in 2003 remain relevant today and indicate that when environmentally superior technologies are developed and adopted, the State of North Carolina can benefit. When swine producers operate more resilient and environmentally sustainable farms, whether through alternative land use or improved practices and technologies, they can address risks associated with flooding and routine air emissions and runoff. However, it is important to recognize that some practices and technologies may only target certain air pollutants. For example, anaerobic digesters can capture the potent greenhouse gas methane as a potential renewable fuel, but digesters are not designed to decrease ammonia emissions. To achieve the greatest benefit to our State residents’ health and the environment, better livestock and poultry manure management technologies and practices should also aim to decrease ammonia emissions and subsequent ammonium air particle formation.
Given that 15 years have passed since completing the last major research study of swine manure treatment alternatives in North Carolina, and with the destruction caused by hurricanes this year raising questions similar to those in 2000, it is important to assess our current situation and plan for a safer, healthier future.