Nitrous oxide and methane production from denitrifying woodchip bioreactors at three hydraulic residence times

Davis, Morgan
Martin, Emily
Moorman, Thomas
Isenhart, Thomas
Soupir, Michelle
Soupir, Michelle
Isenhart, Thomas
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Iowa Nutrient Research Center
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The Iowa Nutrient Research Center was established to pursue science-based approaches to evaluating the performance of current and emerging nutrient management practices and providing recommendations on practice implementation and development. Publications in this digital repository are products of INRC-funded research. The INRC is headquartered at Iowa State University and operates in collaboration with the University of Iowa and the University of Northern Iowa. Additional project information is available at:
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Natural Resource Ecology and ManagementAgronomyAgricultural and Biosystems EngineeringIowa Nutrient Research Center

Denitrifying bioreactors remove nitrate (NO3−) from agricultural drainage and are slated to be an integral part of nitrogen reduction strategies in the Mississippi River Basin. However, incomplete denitrification can result in nitrous oxide (N2O) production and anaerobic conditions within bioreactors may be conducive to methane (CH4) production via methanogenesis. Greenhouse gas production has the potential to trade excess NO3− in surface water with excess greenhouses gases in the atmosphere. Our study examined N2O and CH4 production from pilot scale (6.38 m3) bioreactors across three hydraulic residence times (HRTs), 2, 8, and 16 h. Production was measured from both the surface of the bioreactors and dissolved in the bioreactor effluent. Nitrous oxide and CH4 was produced across all HRTs, with the majority dissolved in the effluent. Nitrous oxide production was significantly greater (P < 0.05) from 2 h HRTs (478.43 mg N2O m−3 day−1) than from 8 (29.95 mg N2O m−3 day−1) and 16 (36.61 mg N2O m−3 day−1) hour HRTs. Methane production was significantly less (P < 0.05) from 2 h HRTs (0.51 g C m3 day−1) compared to 8 (1.50 g C m3 day−1) and 16 (1.69 g C m3 day−1) hour HRTs. The 2 h HRTs had significantly greater (P = 0.05) impacts to climate change compared to 8 and 16 h HRTs. Results from this study suggest managing HRTs between 6 and 8 h in field bioreactors could minimize total greenhouse gas production and maximize NO3− removal.


This article is published as Davis, Morgan P., Emily A. Martin, Thomas B. Moorman, Thomas M. Isenhart, and Michelle L. Soupir. "Nitrous oxide and methane production from denitrifying woodchip bioreactors at three hydraulic residence times." Journal of environmental management 242 (2019): 290-297.