Currently there are about 75,000,000 pigs in the United States. They generate a lot of poop, for which disposal is an ongoing problem in need of good solutions. North Carolina is home to about 12% of the nation’s hogs, and a lot of solid and liquid waste (urine) is collected in open ponds or lagoons, in which the urea is converted to nitrate that can be sprayed on nearby farm fields as fertilizer. Some of the nitrate in lagoons is also converted to nitrogen gas by microbes and returned to the atmosphere.
Depending on their condition, lagoons are also a source of ammonia, hydrogen sulfide, and methane gases that leak to the atmosphere. These gases account for the odor of hog lagoons, which are currently under lawsuits for their impact on human health and property values. Methane is of particular concern, because methane is an important “greenhouse gas” in Earth’s atmosphere, leading to global warming of our planet. The methane from hog lagoons, known as biogas, is an identical molecule to the methane that we remove from the Earth’s crust, where it is known as natural gas and used for heat, electricity, and other demands for fossil fuels. Methane from hog lagoons is identical to methane captured from landfills.
Currently, nearly all the methane from hog lagoons is vented to the atmosphere. If we could capture the methane from hog lagoons, we could see the dual benefits of reducing the potential for climate change and increasing the revenue derived from raising pigs. Some of the structures needed to capture the methane could simultaneously capture ammonia and hydrogen sulfide, reducing this public nuisance.
Let’s put some numbers on what might be possible. A few studies have estimated that about 2000 cubic feet of methane per year are generated when the waste of a single animal that is confined in a lagoon. North Carolina hosts about 10,000,000 hogs, so they would produce 20 x 109 ft3/year. For North Carolina, recent consumption of natural gas each year amounts to about 500 x 109 ft3/yr, so, roughly 4% of the demand for natural gas in North Carolina could be met by biogas. North Carolina has a lot of hogs; a rough calculation for the entire United States indicates that hog waste could supply about 0.5% of our natural gas consumption.
It would be more difficult to capture methane produced from the cattle manure, since so much of it is deposited in pastures and rangelands. Still, the manure from dairy operations and local feedlots might be managed to capture methane. Overall, the disposal of animal wastes contributes about 7.5% of the human contributions of methane to the atmosphere, worldwide. Cattle, of course, are responsible for another 30% that stems from their digestional belches.
The methane from hog and cattle wastes is currently allowed to leak into the atmosphere. As a way to reduce these emissions and provide supplemental income to meat producers, methane capture as biogas can help contribute to our solutions to climate change.
Energy Information Agency. 2016. North Carolina State Profile and Energy Estimates https://www.eia.gov/state/data.php?sid=NC
Lory, J.A., R.E. Massey, and J.M. Zulovich. 2010. An evaluation of the USEPA calculations of greenhouse gas emissions from anaerobic lagoons. Journal of Environmental Quality 39: 776-783.
Mangino, J., D. Bartram, and A. Brazy. 2001. Development of a methane conversion factor to estimate emissions from animal waste lagoons. https://www3.epa.gov/ttnchie1/conference/ei11/ammonia/mangino.pdf
Schlesinger, W.H. and E.S. Bernhardt. 2013. Biogeochemistry: An analysis of global change. Academic Press/Elsevier. San Diego.
Translational Ecology. 2017. Ammonia. https://blogs.nicholas.duke.edu/citizenscientist/ammonia/
2 thoughts on “Pig Poop”
There may also be more pressing present day health issues. Recent studies of Kravchenko, et al (1) have pointed out the health risks of CAFOs. Indeed, this was discussed as part of the Duke Environmental Health Scholars Form in November(2). Their work becomes all the more significant in light Hurricane Florence and perhaps Hurricane Mathew. The spread of antibiotic resistance bacteria by the flood waters may be worthy of long term study.
The CDC Has pointed out in Antibiotic Resistance Threats in the United States, 2013 (AR Threats Report that each year in the U.S., 23,000 people are lost in 2 million infections. Indeed the State of North Carolina has sounded the alarm about antibiotic resistance disease (4)
Three troubling observations come to mind. Fist, antibiotic treatment in CAFOs produces considerable Antibiotic resistant bacteria (5) Secondly in a study out of Rice University, Pingfeng Yu et al (6) found elevated levels of antibiotic resistant genes following Hurricane Harvey’s flooding of Houston. Finally, sulfonamide resistance genes were noted in fields in the United Kingdom in manured agriculture soils (7).
I does not seem to be much of a stretch to suggest that a continued and increasing risk to the population of the Carolinas resides in the production and dissemination of Antibiotic Resistant genes. It has been reported that MRSA has been popping up in North Carolina. and that North Carolina does not require reporting of MRSA infections. (7).
(1)Kravchenko, J. and 4 others. 2018. Mortality and health outcomes in North Carolina communities located in close proximity to hog concentrated animal feeding operations. N.C. Medical Journal 79:
(5) Pingfeng Yu† , Avery Zaleski†, Qilin Li† , Ya He†, Kris Mapili‡, Amy Pruden‡, Pedro J. J. Alvarez† , and Lauren B. Stadler*† Elevated Levels of Pathogenic Indicator Bacteria and Antibiotic Resistance Genes after Hurricane Harvey’s Flooding in
Houston Environenatla Science Techologoy LettersEnviron. Sci. Technol. Lett., 2018, 5 (8), pp 481–486
(6) Byrne-Bailey KG1, Gaze WH, Kay P, Boxall AB, Hawkey PM, Wellington EM.,Prevalence of sulfonamide resistance genes in bacterial isolates from manured agricultural soils and pig slurry
in the United Kingdom. Antimicrob Agents Chemother. 2009 Feb;53(2):696-702. doi: 10.1128/AAC.00652-07. Epub 2008 Dec
My blog touches only the tip of the iceberg–gaseous emissions. There are many other bad impacts associated with CAFOs and the sewage lagoons they use for animal wastes. In addition, to the gases and health issues you describe, the impacts on water quality, especially during overflows, are extreme.
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