• Environmental Engineering Research
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• v.17 no.2
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• pp.95-102
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• 2012

To evaluate the effect of the 4 major rivers restoration project in the Nakdong River to water quality of the river, the Environmental Fluid Dynamics Code (EFDC) and Water Quality Analysis Simulation Program (WASP), are applied in series. Results showed overall decrease in biochemical oxygen demand ($BOD_5$) concentrations and increase in chlorophyll-a concentrations, while total nitrogen and total phosphorous concentrations did not show significant changes, relatively. Decrease in $BOD_5$ concentrations seems to be influenced by an increased hydraulic residence time, which may allow more time for the degradation of organic material. Changes in Chlorophyll-a (Chl-a) concentration, due to the project were more significant for the upper stream areas that show relatively low Chl-a concentration ranges (less than 20 g/L). After the introduction of the Geumho River in the middle part of the Nakdong River, rapid growth of phytoplankton was observed. However, in this middle part of the Nakdong River, the ratio of Chl-a concentration change are less significant, compared to the upper stream areas, due to the project. In the lower stream area, Chl-a concentration decreased after the project. This seems to be resulted from the decreased light availability, due to increased depth, while the nutrient concentrations have been high enough to support phytoplankton growth.

• Journal of Korean Society on Water Environment
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• v.34 no.3
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• pp.270-284
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• 2018

Paldang is a river reservoir located in the Midwest of Korea, with a water volume of $244{\cdot}10^6m^3$ and a water surface area of $36.5km^2$. It has eutrophied since the construction of a dam at the end of 1973, and the phosphorus concentration has decreased since 2001. Average hydraulic residence time of the Paldang reservoir is about 10 days during the spring season and 5.6 days as an annual level. The hydraulics and water quality of the reservoir can differ greatly, both temporally and spatially. For the spring period (March to May) in 2001 ~ 2017, the reservoir mean total phosphorus concentration calculated from the budget model based on a plug-flow system (PF) and a continuous stirred-tank reaction system (CSTR) was 13 % higher and 10 % lower than the observed concentration, respectively. A composite flow system (CF) was devised by assuming that the transition zone was plug flow, and that the lacustrine zone was completely mixed. The mean concentration calculated from the model based on CF was not skewed from the observed concentration, and showed just 6 % error. The retention coefficient of the phosphorus derived from the CF was 0.30, which was less than those of the natural lakes abroad or river reservoirs in Korea. The apparent settling velocity of total phosphorus was estimated to be $93m\;yr^{-1}$, which was 6 ~ 9 times higher than those of foreign natural lakes. Assuming CF, the critical load line for the total phosphorus concentration showed a hyperbolic relation to the hydraulic load in the Paldang reservoir. This is different from the previously known straight critical load line. The trophic state of the Paldang reservoir has recently been estimated to be mesotrophic based on the critical-load curve of the phosphorus budget model developed in this study. Although there is no theoretical error in the newly developed budget model, it is necessary to verify the validity of the portion below the inflection point of the critical-load curve afterwards.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.3
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• pp.328-337
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• 2022

This study investigated the removal performance of a foam fractionator under seawater conditions. The foam fractionator was tested using a 3×3×3 factorial design for operating conditions by combining different solids concentrations (SS; 1, 5, and 10 mg·L^-1), surface air velocities (SAV; 1.1, 1.5, and 2.1 cm·sec^-1), and hydraulic residence times (HRT; 1, 3, and 6 min) at 16℃. Performance parameters such as daily solids removal rate and efficiency were measured, and a multi-regression model equation was developed accordingly. The daily solids removal rate and removal efficiency varied with the experimental conditions and ranged from 0.14-2.33 g-solids·m^-3-air·day^-1 and 8.9-96.7 %, respectively. Overall, the daily solids removal rate increased with increasing SS and SAV and decreasing HRT, whereas the removal efficiency increased with increasing SAV and HRT and decreasing SS. The daily solids removal rate (g-solids·m^-3-air·day^-1) of the foam fractionator for SAV (cm·sec^-1), SS (mg·L^-1) and HRT (min) were described by the following multi-regression model: Daily solids removal rate [f(z)]=-0.118+0.422SAV+0.094HRT+0.141SS (r²=0.873).

• Ocean and Polar Research
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• v.25 no.3
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• pp.269-275
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• 2003

Effects of different operating factors including superficial air velocity (SAV), hydraulic residence time (HRT), protein concentration, and foam overflow height on protein removal by a foam fractionator in simulated seawater aquaculture system were investigated. This experiment was conducted on batch and consecutive modes at different combinations of the affecting factors. The foam fractionator had a diameter of 20cm and a height of 120cm and the experiment was conducted with synthetic wastewater. In 5 consecutive trials, protein concentrations in culture tank water decreased faster when the foam fractionator was operated at higher SAVs and lower HRTs. In batch trials, protein removal rates increased with an increase in SAV but decreased with an increase in URT. Higher protein concentrations in the bulk solution resulted in higher protein removal rates. Protein concentrations in the collected foam condensates increased but the foam overflow rates decreased with the increase of foam overflow heights. The results of this experiment indicate that foam fractionation would be an effective way for protein removal in seawater aquaculture systems and the performance of the foam fractionator depends largely on the operating parameters, especially SAV.

• Journal of Korean Society on Water Environment
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• v.35 no.3
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• pp.248-256
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• 2019

Most of the lakes in Korea are artificial, and their limnological characteristics are significantly different from those of natural lakes in other countries. In this study, the relationship between trophic state parameters was investigated, based on summer average data of the upper layer, in 81 lakes in Korea, 2013-2017. Compared with trends of foreign natural lakes, chlorophyll a (Chl.a) concentration was slightly lower at the same total phosphorus (TP) concentration, and transparency (Secchi depth, SD) was noticeably lower at the same Chl.a concentration. This is because of excessive allochthonous loading of non-algal material during the monsoon period, and the reduction in phosphorus availability to algal growth, by light limitation and short hydraulic residence time. Considering these characteristics, we suggested site-specific thresholds of trophic state classification for Chl.a, TP and SD, based on annual average data at the upper layer of lakes ($3-10{\mu}g\;L^{-1}$ of Chl.a measured by UNESCO method; $13-33{\mu}g\;L^{-1}$ of TP; 1.6-3.2 m of SD for mesotrophic state class, respectively). The threshold value of TP for each trophic state class, corresponded to the upper value of previously reported range, and that of SD was out of the range. We suggested applying only TP and Chl.a in assessment of trophic state of lakes in Korea, excluding SD.

• Journal of Korea Society of Waste Management
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• v.34 no.5
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• pp.474-481
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• 2017

This study was conducted to investigate the effects of inoculum and carbon sources on anaerobic digestion characteristics. The treatments were combinations of inoculum (digestate of cattle manure and rumen fluid) with carbon sources (starch, cellulose, and xylan). Anaerobic digestion was performed in triplicate at $37^{\circ}C$ for 18 days at 100 rpm. Sampling was performed at 0, 1, 2, 3, 4, 5, 7, 9, 12, 15, and 18 days to measure pH, ammonia-N, volatile solids reduction, the cumulative methane content, and the cumulative methane production. There was a significant difference in methane content depending on the carbon source and there was a significant difference in pH, ammonia-N, methane production, and methane content depending on the inoculum (P < 0.05). The results of methane production were higher in the digestate of cattle manure treatment than in the rumen fluid treatment (P < 0.05). In this study, different digestive patterns depending on the type of carbon source could be used as basic research data to set the hydraulic residence time of anaerobic digestion facilities. In addition, the use of ruminal fluid as an inoculum may help accelerate the hydrolysis and acid production steps.

• Journal of Radiation Protection and Research
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• v.32 no.3
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• pp.117-122
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• 2007

The hydrodynamic behaviors of the clarifier with an interior baffle in a wastewater treatment plant was investigated by using a radiotracer $^{99m}Tc$(30 40 mCi) to verify the results of CFD(computational fluid dynamics) modelling in the previous study. The clarifier model was manufactured with consideration to the hydraulic similarity(1/21) of a real plant($L{\times}W{\times}H:2.6{\times}0.4{\times}0.2m$). By installation of an interior baffle to the clarifier, the strong density current at the bottom of the clarifier decreased substantially and increased the area of sludge settling zone, which were visualized successfully from the radiotracer experiment. Also the portion of short circuit stream changed from 48 % to 32 % and the mean residence time of sludge decreased from 940 sec to 810 sec, which corresponds to the results of CFD modelling. As a result, it is anticipated that radiotracer technology can be used as an important tool for designing new wastewater treatment plants and verifying their performances after structural modifications.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.11 no.6
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• pp.120-129
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• 2008

Removal rate of $NO_3-N$ and TN in a free water surface wetland system with litter layer on its bottom was compared with that without one. The system was established on floodplain in the down reach of the Gwangju Stream in 2001. Its dimensions were 31 meters in length and 12 meters in width. Water of the stream was funneled into it and its effluent was discharged back into the channel. Average litter layer of 9.6 cm was formed on its bottom in 2007. The layer and above-ground parts of reeds and cattails on the system were eliminated in Spring 2008. Volumes and water quality of inflow and outflow of the system were analyzed from May to November in 2007 and 2008, respectively. Inflow into the system both in 2007 and 2008 averaged approximately $40m^3/day$ and hydraulic residence time both in 2007 and 2008 was about 1.5 days. Average influent $NO_3-N$ concentration in 2007 and 2008 was 2.16 and 2.05 mg/L, respectively and influent TN concentration in 2007 and 2008 averaged 3.98 and 3.89 mg/L, respectively. With a 0.05 significance level, effluent temperatures, influent concentrations of $NO_3-N$ and TN, and stem numbers per square meter and height of the emergent plants showed no difference between the system with litter layer and without one. $NO_3-N$ removal in the system with litter layer and without it averaged 55.59 and 46.06%, respectively and TN retention averaged 57.24 and 48.97%, respectively. Both $NO_3-N$ and TN abatement rates in the system with litter layer were significantly high (p < 0.001) when compared with those without one. The wetland system having litter layer on its bottom was more efficient for $NO_3-N$ and TN retention than that without one.

• Journal of Korean Society on Water Environment
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• v.35 no.6
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• pp.557-566
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• 2019

Paldang is a river reservoir in the Midwest of Korea, which is a drinking water source for the metropolitan area. Since the Paldang Reservoir is shallow, and has a short hydraulic residence time, its water quality is directly impacted by two incoming rivers, the north Han River (NHR) and the south Han River (SHR). The NHR has different seasonal patterns of water temperature from the SHR because the NHR is greatly impacted by the discharge water from upstream dams. The electrical conductivity (EC) and other material concentrations of the SHR are usually higher than those of the NHR because its basin is limestone-based. The difference in water temperature in the two rivers causes density flow, and the distribution of the EC within the reservoir can be an indicator for monitoring density flow. From the vertical gradient of the EC at the dam site, from spring to fall, it was confirmed that the SHR flowed into the upper layer, and the NHR flowed into the lower layer, and vice versa at other times. The relative difference (RD) of the EC between the upper layer and the lower layer at the dam site was used as an indicator for density flow. The RD of the EC showed a very significant correlation with the RD of total organic carbon (r = 0.70, p < 0.001) and the RD of total nitrogen (r = 0.58, p < 0.01). This relationship is based on the assumption that the difference in electrical conductivity and water quality between the SHR and the NHR is constant. However, in many cases this assumption is inconsistent. Thus, further study is needed on more suitable indicators to evaluate the impact of density flow on water quality.

• KSBB Journal
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• v.14 no.1
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• pp.51-57
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• 1999

The immobilization of nitrifier consortium was carried out for the application to recirculating aquaculture system(RAS). The abilities of $NH_4^+$-N removal by immobilized nitrifier consortia prepared with boric acid treated, ethanol treated, ad freezing-thawing treated PVA beads at the concentration 15% were examined. To identify the possibility of applying the beads in the fluidized bed reactor, characteristics of beads were evaluated. The suitable bead was boric acid treated beads which had highest ammonia removal rate of 16.09 g/$m^3$/day. It took 12 days for nitrifier consortium immobilized beads to be stable for the removal of $NH_4^+$-N. Life spans of the beads were more than three months with aggressive aeration in the fluidized ed reactor when nitrifier consortia immobilized in PVA beads were used. In order to apply the nitrifier consortium immobilized beads to aquaculture facility, the continuous reactor was used for 49 days with synthetic aquacultural water containing 2 mg/L ammonia. The highest ammonia removal rate of 31.87 g/$m^3$/day was observed when hydraulic residence time was 0.6 hour(36min.).