• Journal of Aquaculture
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• v.12 no.1
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• pp.47-56
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• 1999

Denitrification by anaerobic bacteria is one of the most common processes of removing nitrate from recirculating aquaculture systems. This process is affected by many factors such as external carbon sources, hydraulic retention time (HRT), and $COD/NO_3-N$ ratio. Although external organic carbon sources are essential for the denitrification process, these also contribute to increase dissolved organic carbon concentration in recirculating aquaculture systems. So these external organic carbons must be removed from the systems. This study was conducted to find out the optimum operating conditions for the removal of external organic carbons in a submerged denitrification biofilter. Combinations of two external carbon sources (glucose and methanol), two HRT (4- and 8-hour), and four different C:N ratios (3, 4, 5, and 6) were used in this experiment. The removal efficiencies of organic carbon sources at 8-hour HRT were always better than those at 4-hour's (P<0.05). Maximum removal efficiencies were achieved when C:N ratio was 5 in both glucose and methanol. The removal efficiencies of methanol were always better than those of glucose. The maximum removal efficiencies of glucose and methanol were 76.5% and 84.0%, respectively and the removal rates were 223.5 $g/m^2/day$ and 247.1$g/m^2/day$. The maximum removal rates of glucose (290.9 $g/m^2/day$) and methanol (355.6 $g/m^2/day$) were achieved at 4-hour HRT and 5 C:N ratio. But the concentrations of SCOD in the effluent of both glucose ($52.5 mg/\ell$) and methanol ($40.9 mg/\ell$) were too high for rearing fish. Therefore, the optimum operating conditions for the removal of external carbon in a submerged denitrification biofilter were 8-hour HRT and 5 C:N ratio. And methanol showed better efficiency as an external carbon sources.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.10
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• pp.1024-1030
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• 2006

Genus Nitrospira and Nitrobacter species are the key nitrite-oxidizing bacteria(NOB) in nitrifying wastewater treatment plants. It has been hypothesized that genus Nitrospira are K-strategists(low $K_6$ value) that can exploit low amounts of nitrite more efficiently than Nitrobacter. In contrast, Nitrobacter species are r-strategists(high $V_{max}$) that can grow faster than Nitrospira. It has also been known that the availability of organic compounds and dissolved oxygen as well as nitrite affects the distribution of NOB. In this study, we determined the distribution and competition of NOB in wastewater nitrification systems where nitrite, organic compounds, and dissolved oxygen concentrations were compositively varied. For the purpose, several compounds of the laboratory-scale nitrificaiion bioreactor and full-scale $A_2O$ wastewater treatment plant and their distribution of NOB were analyzed and compared. The analysis showed that Nitrobacter was the dominant NOB in nitrification bioreactor where average nitrite was maintained at 5 mg-N/L with very low organic concentration in aerobic condition, whereas Nitrospira was the dominant NOB in full-scale $A_2O$ plant where nitrite was maintained very low and organic compounds were maintained relatively high in alternating aerobic-anoxic condition. The result indicates that nitrite concentration is more critical factor than organics and dissolved oxygen which determines the dominant NOB in nitrification system and it is confirmed that Nitrospira and Nitrobacter showed the characteristics of r-strategist and K-strategist, respectively.

• Proceedings of the Korea Society of Environmental Toocicology Conference
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• 1991.05a
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• pp.8-12
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• 1991

Biodegradation of carbon tetrachloride (CTC) in denitrifying and aerobic columns was investigated under various conditions of electron-acceptor and electron-donor availability. CTC removal increased when the electron-acceptor (nitrate) injection was stopped in the denitrifying column ; however, CTC removal decreased when electron donor (acetate) was deleted in the denitrifying and the aerobic column. Small fractions of the CTC removed appeared as chloroform, indicating that reductive dechlorination of CTC was occurring. The results from the denitrifying column support the hypothesis that CTC behave as an electron acceptor that competes for the pool of available electrons inside the bacterial cells.

• Journal of Wetlands Research
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• v.18 no.4
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• pp.488-498
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• 2016

In order to assess the role of aeration in stormwater wetlands, oxygen supply and consumption in a wetland treating runoff from livestock farms were estimated and analyzed. Furthermore, oxygen mass balance was conducted during day time and night time. Internal production by algal photosynthesis dominated the oxygen production particularly in the shallow marsh due to the large amount of algae. Consequently, algal respiration was also the major oxygen depletion element with nitrification and biodegradation estimated as 5.35% and 6.43% of the total oxygen consumption. This excessive portion of oxygen consumption by algae was associated to the highly turbid water caused by the resuspension of sediment particles in the aeration pond, which also affected the subsequent wetland. Moreover, an abundance of oxygen was estimated during the day indicating that oxygen produced by algal activity is sufficient to meet the oxygen demand in the wetland. Thus, supplemental aeration was deemed not necessary at daytime. In contrast, oxygen was greatly depleted at night when algal photosynthesis stopped which induced denitrification. Therefore, it was suggested that supplemental aeration may be operated continuously instead of intermittently to avoid oxygen deficit in the wetland at night or it may be stopped entirely to further enhance denitrification.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.493-502
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• 2013

This study investigates the design parameters for riverbed filtration (RBF) based on the geochemistry of river water and groundwater. The study area consists of alluvium, and the area is readily affected by non-point sources of chemical contaminants in the surface environment; this is expected to affect the design parameters for RBF. River and groundwater samples were collected at three points along the river flow and at nine points along a transect normal to the river, respectively. The geochemical data indicate that the sources of individual chemical contaminants are industrial facilities and agricultural activity near the study area. In addition, The samples are mainly Ca-Na-$HCO_3$, Ca-Cl, and Ca-$HCO_3$-Cl type waters. The design parameters of RBF in the study area should consider K, $HCO_3$, $NO_3$, and Cl. We divided the study area into three regions based on the concentrations of stable nitrogen isotopes: Region A, the origin of the river and denitrification; Region B, denitrification in the flow direction of tributaries; and Region C, the origin of natural soil, sewage, and anthropogenic pollution.

• Journal of Wetlands Research
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• v.19 no.1
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• pp.90-102
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• 2017

In this study, various types of nutrient models were tested by using two tears's water quality data collected from the stormwater wetland in Korea. Based on results, most important factor influencing nitrogen removal was hydraulic loading rate, which indicates that surface area of wetland is more important than its volumetric capacity, and model proposed by WEF was found to give a least error between measured and calculated values. For the phosphorus, in case assuming a power relationship between rate constant and temperature, the best prediction result were obtained, but temperature was most sensitive parameter affecting phosphorus removal. In addition, denitrification was always a limiting step for the nitrogen removal in this particular wetland mostly due to the lack of carbon source and high dissolved oxygen concentration. In this paper, several alternatives to improve nitrogen removal, including proper arrangement and designation of wetland elements and use of floating plants or synthetic fiber mat to control oxygen level and to capture the algal particles were proposed and discussed.

• Korean Journal of Ecology and Environment
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• v.46 no.3
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• pp.409-418
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• 2013

Global warming due to climate change is a problem facing the entire world. Several factors, such as $CO_2O$ concentration, level of warming, soil temperature, precipitation, water content of soil and denitrification by denitrifying bacteria influence the emission of nitrous oxide ($N_2O$) from soil. In this study, we investigated nitrous oxide emissions from the soil of two wetlands, Jilmoineup in Mt. Odae and Moojechineup in Mt. Jungjok, according to temperature change. Soil collected in Jilmoineup in July showed increasing $N_2O$ emissions as temperature increases, but did not show any significant differences at $10^{\circ}C$ (p<0.05). Soil of $15^{\circ}C$ and $20^{\circ}C$ showed increasing pattern of $N_2O$ emissions until 24 h. After that, however, there was no difference in temperature. Overall, $N_2O$ emissions showed significant differences according to temperature (p<0.05). Soil collected from Moojechineup in July showed increasing $N_2O$ emissions according to temperature increase, but did not show any significant differences at $10^{\circ}C$ (p<0.05) as was the case for Jilmoineup soil. On the other hand, two wetland soils showed a slight increase of $N_2O$ emissions by additional nitrogen supply, but did not show any significant differences in the presence of nitrogen or between nitrogen sources. In conclusion, increasing temperature the wetland soil increased the emission of $N_2O$, which is a known greenhouse gas. In order to more clearly identify $N_2O$ emissions, various subsequent studies such as the influence and correlation of several factors are required.

• Journal of Wetlands Research
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• v.6 no.4
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• pp.59-69
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• 2004

Constructed wetlands are regarded as an important water treatment system for agricultural water quality improvement and management. The purpose of this study is to evaluate the application of subsurface flow wetland(SFW), using the Pharagmites australis as macrophytes, and to clarify the basic and essential factors to be considered in the construction and management of constructed wetlands. This study was carried out relatively short hydraulic residence time(HRT), 6hr ~ 72hr (3days), using eutrophic reservoir water with relatively low concentrations of influent and large quantity to be treated. The effluent satisfied the criteria of agricultural water quality. Removal efficiencies of Biochemical oxygen demand(BOD), Chemical oxygen demand(COD), Suspended solids(SS) and Chlorophyll a(Chl-a) were high in HRT 24hr, not any more significant increasement of removal efficiencies in HRT 48hr and 72hr. However, removal efficiencies of nitrogen and phosphorus increased as HRT increased, showing the highest efficiency at the 72hr of HRT in nitrogen, and 48hr in phosphorous. The SFW was very effective system for reservoir water quality improvement, and had the advantages of the reduction of purchasing cost to land required, lack of odors, and harmful insects, especially mosquito, the improvement of the scenic beauty and minimal risk of public exposure. Therefore, it was evaluated that the SFW was very available water treatment system for the water quality improvement of agricultural reservoir. However, it was need to consider with application of the SFW in high cost of construction and troublesome of management.

• Korean Journal of Soil Science and Fertilizer
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• v.43 no.1
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• pp.68-74
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• 2010

Since ${NO_3}^-$ is amore favorable electron acceptor than Fe, high ${NO_3}^-$ loads function as a redox buffer limiting the reduction of Fe and following release of ${PO_4}^{3-}$ in flooded paddy soil. The effect ${NO_3}^-$ loaded through irrigation water on Fe reduction and ${PO_4}^{3-}$ release in paddy soil was investigated. Pot experiment was conducted where irrigation water containing 5 or 10 mg N $L^{-1}$ of ${NO_3}^-$ was continuously applied at 1 cm $day^{-1}$, and changes of ${NO_3}^-$, $Fe^{2+}$ and ${PO_4}^{3-}$ concentrations in soil solution at 5 and 10 cm depths beneath the soil surface were monitored as a function of time. Irrigation of rice paddy with water containing 5 mg N $L^{-1}$ of ${NO_3}^-$ led to reduced release of $Fe^{2+}$ and prevented solubilization of P at 5 cm depth beneath the soil surface. And application of irrigation water containing 10 mg N $L^{-1}$ of ${NO_3}^-$ could further suppress Fe reduction and solubilization of P through 10 cm depth soil layer beneath the surface. These results suggest that the introduction of high level ${NO_3}^-$ with irrigation water in rice paddy can strongly limit Fe reduction and P solubilization in root zone soil layer in addition to the excessive supply of N to rice plants.

• Journal of Wetlands Research
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• v.21 no.4
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• pp.334-343
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• 2019

A lab-scale vertical flow subsurface (VFS) wetland composed of three parallel columns with polypropylene synthetic fiber as main substrate was operated. Piggery stormwater diluted from swine excreta was fed to the wetland on the basis of three different hydraulic regimes or hydraulic retention time (HRT) of 2, 4, and 8 days with daily internal recirculation. Then, monitoring of common water quality parameters was carried out. Unexpectedly, an increase of effluent COD concentration accompanying the appearance of foams was observed during a distinct period in the wetland with HRT 2, 4, and 8 days, successively. Subsequently, a series of experiments was conducted to investigate the origin of the foams. Foams and the increase of COD concentration were found to be induced by the release of organic matter from the synthetic polypropylene fiber which was fed with piggery stormwater. Meanwhile, nitrogen removal was found to be enhanced during a period which overlapped the distinct foaming period signifying that foaming played two important functions in biological nitrogen removal. Foams which form rapidly and then burst easily could hold up and then release oxygen for nitrification. Foams which contain organic surfactants could serve as carbon sources for denitrification as well. Hence, nitrogen removal was enhanced during the foaming stage. After that, COD concentration decreased slowly to a level prior to the foaming stage, and nitrogen removal efficiency declined as well.