• Journal of Microbiology and Biotechnology
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• v.23 no.5
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• pp.719-723
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• 2013

Nitrification in wastewater treatment emits a significant amount of nitrous oxide ($N_2O$), which is one of the major greenhouse gases. However, the actual mechanism or metabolic pathway is still largely unknown. Selective nitrification inhibitors were used to determine the nitrification steps responsible for $N_2O$ emission with activated sludge and enriched nitrifiers. Allylthiourea (86 ${\mu}M$) completely inhibited ammonia oxidation and $N_2O$ emission both in activated sludge and enriched nitrifiers. Sodium azide (24 ${\mu}M$) selectively inhibited nitrite oxidation and it led to more $N_2O$ emission than the control experiment both in activated sludge and enriched nitrifiers. The inhibition tests showed that $N_2O$ emission was mainly related to the activity of ammonia oxidizers in aerobic condition, and the inhibition of ammonia monooxygenase completely blocked $N_2O$ emission. On the other hand, $N_2O$ emission increased significantly as the nitrogen flux from nitrite to nitrate was blocked by the selective inhibition of nitrite oxidation.

• Journal of Microbiology and Biotechnology
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• v.21 no.9
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• pp.988-994
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• 2011

A significant amount of nitrous oxide ($N_2O$), which is one of the serious greenhouse gases, is emitted from nitrification and denitrification of wastewater. Batch wastewater nitrifications with enriched nitrifiers were carried out under oxygen-limited condition with synthetic (without organic carbon) and real wastewater (with organic carbon) in order to find out the effect of ammonium concentration on $N_2O$ emission. Cumulated $N_2O$-N emission reached 3.0, 5.7, 6.2, and 13.5 mg from 0.4 l of the synthetic wastewater with 50, 100, 200, and 500 mg/l ${NH_4}^+$-N, respectively, and 1.0 mg from the real wastewater with 125 mg/l ${NH_4}^+$-N. The results indicate that $N_2O$ emission increased with ammonium concentration and the load. The ammonium removal rate and nitrite concentration also increased $N_2O$ emission. Comparative analysis of $N_2O$ emission from synthetic and real wastewaters revealed that wastewater nitrification under oxygen-limited condition emitted more $N_2O$ than that of heterotrophic denitrification. Summarizing the results, it can be concluded that denitrification by autotrophic nitrifiers contributes significantly to the $N_2O$ emission from wastewater nitrification.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.37 no.1
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• pp.13-17
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• 2004

The effects of temperature on nitrification of enriched nitrifiers were investigated by using kinetics and thermodynamics method through the batch test. Aquaculture recirculating water, which was sampled at Chung Cheong Buk-Do Inland Fisheries Research Institute, was analized to observe the characteristics of nitrification. Temporal variation of ammonium, nitrite and nitrate concentration was measured at batch experiments. Activation energy was calculated using Arrhenius equation with the oxidation rates of specific ammonium or nitrite ion. These oxidation rates were measured at temperature range of $6-35^{\circ}C$ and ammonium concentration range of 0.2-1.8 mg/L. Two distinct activation energy of Nitrosomonas sp. at temperature $6-15^{\circ}C\;and\;15-35^{\circ}C$ was 93.1 and 25.0 KJ/mol, respectively. Nitrate accumulation was observed at temperature over $15^{\circ}C.$

• Journal of Ecology and Environment
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• v.31 no.3
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• pp.167-176
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• 2008

Atmospheric N deposition has far-reaching impacts on forest ecosystems, including on-site impacts such as soil acidification, fertilization, and nutrient imbalances, and off-site environmental impacts such as nitrate leaching and nitrous oxide emission. Although chronic N deposition has been believed to lead to forest N saturation, recent evidence suggests that N retention capacity, particularly in the forest floor, can be surprisingly high even under high N deposition. This review aims to provide an overview of N retention processes in the forest floor and the implications of changing C-N interactions for C sequestration. The fate of available N in forest soils has been explained by the competitive balance between tree roots, soil heterotrophs, and nitrifiers. However, high rates of N retention have been observed in numerous N addition experiments without noticeable increases in tree growth and soil respiration. Alternative hypotheses have been proposed to explain the gap between the input and loss of N in N-enriched, C-limited systems, including abiotic immobilization and mycorrhizal assimilation, both of which do not require additional C sources to incorporate N in soil N pools. Different fates of N in the forest floor have different implications for C sequestration. N-induced tree growth can enhance C accumulation in tree biomass as observed across temperate regions. C loss from forests can amount to or outweigh C gain in N-saturated, declining forests, while another type of 'C-N decoupling' can have positive or neutral effects on soil C sequestration through hampered organic matter decomposition or abiotic N immobilization, respectively.

• Journal of Microbiology and Biotechnology
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• v.19 no.12
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• pp.1656-1664
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• 2009

Bioaugmentation of bioreactors focuses on the removal of numerous organics, with little attention typically paid to the maintenance of high and stable nitrite accumulation in partial nitrification. In this study, a bioaugmented membrane bioreactor (MBR) inoculated with enriched ammonia-oxidizing bacteria (AOB) was developed, and the effects of dissolved oxygen (DO) and temperature on the stability of partial nitrification and microbial community structure, in particular on the nitrifying community, were evaluated. The results showed that DO and temperature played the most important roles in the stability of partial nitrification in the bioaugmented MBR. The optimal operation conditions were found at 2-3 mgDO/l and $30^{\circ}C$, achieving 95% ammonia oxidization efficiency and nitrite ratio ($NO_2^-/{NO_x}^-$) of 0.95. High DO (5-6 mg/l) and low temperature ($20^{\circ}C$) had negative impacts on nitrite accumulation, leading to nitrite ratio drop to 0.6. However, the nitrite ratio achieved in the bioaugmented MBR was higher than that in most previous literatures. Denaturing gradient gel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH) were used to provide an insight into the microbial community. It showed that Nitrosomonas-like species as the only detected AOB remained predominant in the bioaugmented MBR all the time, and coexisted with numerous heterotrophic bacteria. The heterotrophic bacteria responsible for mineralizing soluble microbial products (SMP) produced by nitrifiers belonged to the Cytophaga-Flavobacterium-Bacteroides (CFB) group, and $\alpha$-, $\beta$-, and $\gamma$- Proteobacteria. The fraction of AOB ranging from 77% to 54% was much higher than that of nitrite-oxidizing bacteria (0.4-0.9%), which might be the primary cause for the high and stable nitrite accumulation in the bioaugmented MBR.