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Denitrification Enzyme Activity in Swine Wastewater Lagoons

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2007 ASAE Annual Meeting  074055.(doi:10.13031/2013.23093)
Authors:   P G Hunt, T A Matheny, K S Ro, M B Vanotti, G B Reddy
Keywords:   Denitrification, Denitrification enzyme activity, DEA, Oxygen transfer, Nitrate, Nitrous oxide

Recent publications of high levels of di-nitrogen emissions and high levels of potential surficial oxygen transfer indicated that large amounts of nitrogen may be removed via denitrification in anaerobic lagoons. If this denitrification is occurring via classical denitrification, the denitrification enzyme levels should be correspondingly high. We measured denitrification enzyme activity (DEA) in five lagoons with varying loads of swine wastewater. The lagoons varied from lightly loaded with oxidative reductive potentials (ORP) that favored aerobic processes to heavier loaded with ORPs that favored anaerobic processes. The Acetylene inhibition method was used to access DEA in the untreated control conditions. Acetylene was added to block nitrous oxide conversion to di-nitrogen gas and allow total denitrification to be accessed via nitrous oxide measurements. Samples were taken in four quadrants of the lagoons at the surface, midway to the bottom, and just above the bottom of the lagoon. Initial results indicate that the quadrants were reasonably similar, but the depths were somewhat variable. Two commercial lagoons with COD values >1800 had surprisingly low DEA. These results suggest that di-nitrogen may be produced at different levels and by different means in different lagoons.

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