title: Characterization of methane flux from photosynthetic oxidation ponds in a wastewater treatment plant.
abstract: Photosynthetic oxidation ponds are a low-cost method for secondary treatment of wastewater using natural and more energy-efficient aeration strategies. Methane (CH(4)) is produced during the anaerobic digestion of organic matter, but only some of it is oxidized in the water column, with the remaining CH(4) escaping into the atmosphere. In order to characterize the CH(4) flux in two photosynthetic oxidation ponds in a wastewater treatment plant in northern California, the isotopic compositions and concentrations of CH(4) were measured in the water column, in bubbles and in flux chambers, over a period of 12 to 21 months to account for seasonal trends in CH(4) emissions. Methane flux varied seasonally throughout the year, with an annual average flux of 5.5 g CH(4) m⁻² d⁻¹ Over half of the CH(4) flux, 56.1-74.4% v/v, was attributed to ebullition. The oxidation efficiency of this system was estimated at 69.1%, based on stable carbon isotopes and a calculated fractionation factor of 1.028. This is the first time, to our knowledge, that a fractionation factor for CH(4) oxidation has been empirically determined for oxidation ponds. Quantifying CH(4) emissions from these systems is essential to properly identify their contribution and to mitigate their impact on global warming.
authors.affiliation: NASA Ames Research Center, Exobiology Branch, Mail Stop 239-4, P.O. Box 1, Moffett Field, CA 94035, USA E-mail: angela.m.detweiler@nasa.gov; Bay Area Environmental Research Institute, 625 2nd St., Petaluma, CA 94952, USA.
authors.forename: Angela M
authors.initials: AM
authors.lastname: Detweiler
authors.affiliation: NASA Ames Research Center, Exobiology Branch, Mail Stop 239-4, P.O. Box 1, Moffett Field, CA 94035, USA E-mail: angela.m.detweiler@nasa.gov.
authors.forename: Brad M
authors.initials: BM
authors.lastname: Bebout
authors.affiliation: NASA Ames Research Center, Exobiology Branch, Mail Stop 239-4, P.O. Box 1, Moffett Field, CA 94035, USA E-mail: angela.m.detweiler@nasa.gov; Bay Area Environmental Research Institute, 625 2nd St., Petaluma, CA 94952, USA.
authors.forename: Adrienne E
authors.initials: AE
authors.lastname: Frisbee
authors.affiliation: University of Missouri, Department of Geological Sciences, 101 Geological Sciences Building, Columbia, MO 65211, USA.
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Kelley
authors.affiliation: Florida State University, Department of Earth, Ocean and Atmospheric Science, P.O. Box 3064520, Tallahassee, FL 32306, USA.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Chanton
authors.affiliation: NASA Ames Research Center, Exobiology Branch, Mail Stop 239-4, P.O. Box 1, Moffett Field, CA 94035, USA E-mail: angela.m.detweiler@nasa.gov.
authors.forename: Leslie E
authors.initials: LE
authors.lastname: Prufert-Bebout
mesh_terms: D001272:Atmosphere; D002247:Carbon Isotopes; D008697:Methane / Q000737:chemistry*; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology*; D061005:Ponds / Q000737:chemistry*; D064091:Waste Disposal Facilities; D062065:Wastewater / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D008697:Methane; D062065:Wastewater