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Greenhouse Gases
Published in Lisamarie Windham-Myers, Stephen Crooks, Tiffany G. Troxler, A Blue Carbon Primer, 2018
Inorganic nitrogen availability is a key control of N2O fluxes. In aerobic environments, increased NH4+ leads to increased nitrification and associated “leaked” N2O. Under anaerobic conditions, increased NO3− availability provides the necessary terminal electron acceptor for denitrification and increases N2O flux through this process (Murray et al. 2015 and references cited therein). In most ecosystems, nitrification serves as the primary source of NO3− for denitrification. Given that these two processes have different oxygen requirements (i.e., nitrification is aerobic, denitrification is anaerobic), denitrification is often highest at anaerobic/aerobic interfaces, including at the water level, in the oxidized rooting zone or adjacent to burrows of bioturbating organisms (Chapin et al. 2011; Murray et al. 2015). As noted above, increased NO3− availability relative to organic matter availability also generally increases the N2O:N2 ratio produced during denitrification. Increases in either NH4+ or NO3− associated with eutrophication of coastal water bodies will thus likely increase N2O fluxes from blue carbon ecosystems. Indeed, nitrogen fertilization frequently increases N2O flux from blue carbon ecosystems, often causing them to shift from N2O sinks to N2O sources (Kreuzwieser et al. 2003; Moseman-Valtierra et al. 2011; Chmura et al. 2016), and nitrogen-rich waste water can also increase N2O emissions (Chen et al. 2011).
Evaluation of denitrification performance and bacterial community of a sequencing batch reactor under intermittent aeration
Published in Journal of Environmental Science and Health, Part A, 2020
Ji Hyeon Kwon, Hyung-Joo Park, Yun-Yeong Lee, Kyung-Suk Cho
Most denitrifying bacteria are identified as facultative microorganisms, thus denitrification can occur under both anoxic and aerobic conditions.[2,9] These aerobic denitrifying bacteria can utilize oxygen and nitrate (or nitrite) simultaneously as electron acceptors and nitrate (or nitrite) is sequentially reduced to N2 gas.[2,3] In wastewater treatment, denitrification is primarily performed under anoxic conditions while aerobic denitrification is less significant.[9] However, aerobic denitrification in wastewater treatment has garnered increasing attention owing to its advantages.[10–12] Aerobic denitrification can reduce the cost of space and operation because nitrification and denitrification can be conducted simultaneously in a conventional system.[13] Additionally, it is economical because it requires fewer chemicals to adjust the pH value of the system.[2] Therefore, aerobic denitrification is recognized as a promising process for nitrogen removal in a single system such as a sequencing batch reactor (SBR) or continuous stirred reactor.[3]
Characterization of nitrous oxide reduction by Azospira sp. HJ23 isolated from advanced wastewater treatment sludge
Published in Journal of Environmental Science and Health, Part A, 2020
Hyung-Joo Park, Ji Hyeon Kwon, Jeonghee Yun, Kyung-Suk Cho
Aerobic denitrification by denitrifying bacteria, such as Paracoccus denitrificans, Bacillus, and Acinetobacter, is of growing interest for simultaneous nitrification and denitrification applications using one process under aerobic conditions.[3,14,23] The influence of oxygen on N2O reduction remains unclear, although N2O reduction by various denitrifying species has been studied.[14,18] Suenaga et al.[18] reported that among four bacterial strains, only one Azospira strain exhibited low N2O reduction activity under microaerobic conditions (DO: 3.52 mg/l). The other strains included Pseudomonas stutzeri and Paracoccus denitrificans, the activities of which were strongly inhibited by O2 exposure. They also observed that another Azospira strain had the highest N2O reduction activity in the absence of oxygen. Nam et al.[38] introduced Azospira sp. PMJ as a facultatively anaerobic denitrifier along with a novel perchlorate-reducing bacterium, which removed nitrate and perchlorate simultaneously. In this study, after replacing the headspace of the serum bottle containing the medium with nitrogen, the N2O-reducing activity of Azospira sp. HJ23 was evaluated. Considering the experimental condition, Azospira sp. HJ23 displayed N2O reduction activity in anaerobic and/or microaerobic conditions. Further study on the oxygen effect on the N2O reduction activity of strain HJ23 is required.