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ARS Home » Southeast Area » Florence, South Carolina » Coastal Plain Soil, Water and Plant Conservation Research » Research » Publications at this Location » Publication #246849
Title: Denitrification in anaerobic lagoons used to treat swine wastewater.

Author
item Hunt, Patrick
item MATHENY, TERRY - Retired ARS Employee
item Ro, Kyoung
item Vanotti, Matias
item Ducey, Thomas

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2010
Publication Date: 7/12/2010
Citation: Hunt, P.G., Matheny, T.A., Ro, K.S., Vanotti, M.B., Ducey, T.F. 2010. Denitrification in anaerobic lagoons used to treat swine wastewater. Journal of Environmental Quality. 39:1821-1828.

Interpretive Summary: Livestock are important to both food stability and global economics. Much of the livestock production in the developed world including the USA is in confined livestock production. In the case of swine and dairy production, the wastewater is often treated in anaerobic lagoons. Although these lagoons were once thought to be relatively simple; their physical, chemical, and biological processes are actually very complex. In particular, there are differences in both data and theory about the significance of nitrogen lost as harmless di-nitrogen gas. The most well-established pathway for this denitrification to occur is via classical nitrification and denitrification. If this is a dominant process, the enzymes associated with this process should be present in abundance. Fortunately, there is a good procedure to measure the denitrification enzyme activity (DEA). This study of anaerobic lagoons had twofold objectives: 1] quantify DEA; and 2] evaluate the influence of lagoon characteristics upon the DEA. The DEA was measured by a method called “the acetylene inhibition method.” Wastewater samples and physical/chemical measurements were taken from the wastewater column of nine anaerobic-swine lagoons during May 2006 to May 2009. These lagoons were typical for anaerobic swine lagoons in the Carolinas in the USA relative to their size, operation, and chemical/physical characteristics. The mean value was small. In a lagoon with 2-m depth, this rate of DEA would be compatible with a very small amount of di-nitrogen loss, less than 5 lbs. Moreover, the amount of a greenhouse gas, nitrous oxide, from the denitrification process would not have been a significant part of the system nitrogen balance. While alternate pathways of denitrification may exist within or beneath the wastewater column, this paper documents the lack of sufficient denitrification enzyme activity within the wastewater column of these anaerobic lagoons to support large N2 gas losses via classical nitrification and denitrification.

Technical Abstract: Anaerobic lagoons are commonly used for treatment of swine wastewater. Although these lagoons were once thought to be relatively simple; their physical, chemical, and biological processes are actually very complex. This study of anaerobic lagoons had twofold objectives: 1] quantify denitrification enzyme activity (DEA); and 2] evaluate the influence of lagoon characteristics upon the DEA. The DEA was measured by the acetylene inhibition method. Wastewater samples and physical/chemical measurements were taken from the wastewater column of nine swine wastewater lagoons during May 2006 to May 2009. These lagoons were typical for anaerobic swine lagoons in the Carolinas relative to their size, operation, and chemical/physical characteristics. Their mean value for DEA was 87 mg N2O-N m-3/d. In a lagoon with 2-m depth and one ha in surface area, this rate of DEA would be compatible with 1.64 kg N/d loss as N2. When non-limiting nitrate was added, the highest DEA would be compatible with 4.38 kg/ha/d loss as N2. Nitrous oxide from incomplete denitrification would not have been a significant part of the system nitrogen balance. Using stepwise regression for this treatment, the lagoon characteristics (i.e., soluble organic carbon, total nitrogen, temperature, and nitrate-N) provided a final step model R2 of 0.69. While alternate pathways of denitrification may exist within or beneath the water column, this paper documents the lack of sufficient denitrification enzyme activity within the wastewater column of these anaerobic lagoons to support large N2 gas losses via classical nitrification and denitrification.