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Water quality systems
Published in A. W. Jayawardena, Environmental and Hydrological Systems Modelling, 2013
Denitrification is the process by which nitrates are converted into molecular nitrogen in the presence of denitrifying bacteria (Paracoccus denitrificans). It is an anaerobic process with the intermediate stages of converting nitrates (NO3) to nitrites (NO2), nitric oxide (NO), and nitrous oxide (N2O). NO3−→NO2−→NO→N2O→N2
Transcriptomics uncover the response of an aerobic denitrifying bacteria to zinc oxide nanoparticles exposure
Published in Environmental Technology, 2022
Kongyan Luo, Long Chen, Yuanyi Zhao, Guyu Peng, Zhaobo Chen, Qian Chen
Denitrification plays an important role in the process of nitrogen returning from the terrestrial and aquatic environment to the atmosphere, and is an important part of the nitrogen cycle[1]. It is mainly driven by microbes which continuously reduce nitrate (NO3−-N) to nitrite (NO2−-N), nitric oxide (NO), nitrous oxide (N2O) and dinitrogen gas (N2)[2]. Conventional denitrification occurs at anoxic or anaerobic conditions. Recently, the concept of aerobic denitrification is formally proposed with the discovery of aerobic nitrate removal in stain Paracoccus denitrificans (Thiosphaera pantotropha)[3, 4]. Aerobic denitrification not only challenges the traditional theory that denitrification can only occur under anaerobic conditions, but also shows unique advantages over conventional anoxic denitrification[5], such as allowing simultaneous nitrification and denitrification in an aeration reactor[6, 7]. It has been proven that anaerobic and aerobic denitrification jointly regulates the removal of bioavailable nitrogen from natural and human-altered systems, and directly affect the generation of greenhouse gas N2O[8].
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
Several factors affect the performance of aerobic denitrification such as dissolved oxygen (DO) concentration, C/N ratio, temperature, and pH.[3,14–17] Lukow and Diekmann[14] investigated denitrification rate using Paracoccus denitrificans strain DSM 2944, a representative aerobic denitrifying bacteria, and found that the denitrification rate ranged from 16.2 to 23.0 nmol·min−1·mg−1 when air saturation was 30–70%. Genera of Pseudomonas, Achromobacter, and Acinetobacter were isolated from river sediment and soil, and aerobic denitrification occurred when the DO was maintained at 3–10 mg·L−1.[15]Citrobacter diverse was isolated from the denitrification sludge, and the optimum denitrification rate was obtained at the C/N ratio of 4–5.[16] In a study using Pseudomonas putida strain AD-21 that was isolated from soil,[17] the optimum C/N ratio was 8 with a maximum denitrification rate of 255 mg·L−1·h−1. Additionally, the optimum temperature and pH range for aerobic denitrification was found to be 25–37 °C and 7–8, respectively.[3] Most previous studies evaluated the major factors affecting aerobic denitrification using a single bacterial strain. However, denitrification performance primarily depends on the composition and structure of the bacterial community in a system. Therefore, it is necessary to evaluate the system performance and community comprehensively.
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.