SURFACE GAS EMISSIONS, CONSUMPTION, AND BUBBLE-TRANSPORT IN SWINE LAGOONS

Authors: DE VISSCHER, A - UNIVERSITY OF GENT; Harper, Lowry; VAN CLEEMPUT, O - UNIVERSITY OF GENT

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2005
Publication Date: N/A
Citation: N/A

Interpretive Summary: It has been thought that most of the nitrogen from animal waste disposed into swine lagoons was lost as volatile ammonia. Ammonia may combine with gases from fossil fuel combustion to form particles that may be suspended in the atmosphere. However, recent studies have shown significant amounts waste nitrogen in these lagoons is converted to harmless nitrogen gas emitted from the lagoon bottom rather than emitted as ammonia. Contamination of these bubbles by atmospheric nitrogen gas diffused into the lagoon water from the atmosphere cannot be excluded. Therefore, a model was developed by the University of Ghent, Belgium, and the USDA-ARS J.P. Campbell Sr. Natural Resource Conservation Center, Watkinville, GA, to quantify this possible contamination. The model describes gas exchange between the bubbles and the lagoon liquid, as well as gas exchange at the lagoon surface. Contamination from the atmosphere was found to be 5-10% of the nitrogen gas found in the bubbles. In contrast, most of the carbon dioxide produced at the lagoon bottom diffused from the bubbles into the lagoon water and was emitted by diffusion at the lagoon surface. We concluded that conversion of nitrogen in lagoons to harmless nitrogen gas is the most important nitrogen loss from swine farms in the Coastal Plains of Southeast USA. These findings indicate animal waste lagoons produce less harmful emissions than originally thought allowing production and regulatory organizations to revise national emissions inventories.

Technical Abstract: Recent studies have shown the production of significant amounts of benign nitrogen gas (N2) in anaerobic swine lagoons. The gas is found in bubbles collected below the lagoon surface. Contamination of these bubbles by N2 from the atmosphere cannot be excluded. Therefore, a model was developed with the aim of quantifying this contamination, and to deduce the production of N2 and other gases at the lagoon bottom from measurements of gas collected below the lagoon surface. The model describes gas exchange between the bubbles and the lagoon liquid, as well as gas exchange at the lagoon surface. On average, contamination was found to be 5-10% of the N2 found in the bubbles. In contrast, most of the CO2 produced diffused from the bubbles into the lagoon water and was emitted by diffusion at the lagoon surface. It is concluded that denitrification to N2 in lagoons is the most important sink of N brought into swine farms in the Coastal Plains of Southeast USA.