• Solar Energy
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• v.17 no.4
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• pp.13-22
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• 1997

Drag reduction produced by the dilute solution of polymer under turbulent flow in a rotating disk apparatus(RDA) was investigated in this study for the purpose of potential application to the Ocean Thermal Energy Conversion(OTEC) system. Four different molecular weights of poly(ethylene oxide)(PEO) were used as drag reducing additives, and synthetic seawater was adopted as a solvent. Experiments were undertaken to observe the dependence of drag reduction on various factors such as polymer molecular weight, polymer concentration and the rotating speed of the disk. The concentration dependence on the drag reduction of this polymer system was shown to obey an empirical drag reduction equation of the Virk's universal correlation.

• Journal of Wetlands Research
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• v.12 no.2
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• pp.47-57
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• 2010

The purpose of this study is to investigate the seasonal variation of water quality parameters in Suncheon bay. We investigated at fifteen stations from October 2008to July 2009. picoplankton The salinity in the bay ranged from 8.8 to 31.9psu, DO ranged from 6.34 to 11.84 mg/L and the pH ranged from 7.80 to 8.34. The mean concentration of suspended solids ranged from 52.1 to 104.0 mg/L and COD concentration ranged from 2.27 to 5.33 mg/L. The total coliform group ranged from 6 to 37CFU. The concentrations of COD and total coliform group were relatively higher in the upper part of the Suncheon bay than lower one. The concentrations of nutrients such as nitrogen, phosphorus, silicate were also higher in the upper part of the bay, because the large amount of fresh water was inflowed into the bay from the Dong stream and Isa stream. Because the N/P ratio was ranged from 4.54 to 9.61 in this study, the limiting nutrients was nitrogen in the Suncheon bay comparing to the Redfield ratio.

• ALGAE
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• v.28 no.2
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• pp.173-183
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• 2013

Sodium hypochlorite (NaOCl) is widely used to disinfect seawater in power plant cooling systems in order to reduce biofouling, and in ballast water treatment systems to prevent transport of exotic marine species. While the toxicity of NaOCl is expected to increase by ongoing ocean acidification, and many experimental studies have shown how algal calcification, photosynthesis and growth respond to ocean acidification, no studies have investigated the relationship between NaOCl toxicity and increased $CO_2$. Therefore, we investigated whether the impacts of NaOCl on survival, chlorophyll a (Chl-a), and effective quantum yield in three marine phytoplankton belonging to different taxonomic classes are increased under high $CO_2$ levels. Our results show that all biological parameters of the three species decreased under increasing NaOCl concentration, but increasing $CO_2$ concentration alone (from 450 to 715 ${\mu}atm$) had no effect on any of these parameters in the organisms. However, due to the synergistic effects between NaOCl and $CO_2$, the survival and Chl-a content in two of the species, Thalassiosira eccentrica and Heterosigma akashiwo, were significantly reduced under high $CO_2$ when NaOCl was also elevated. The results show that combined exposure to high $CO_2$ and NaOCl results in increasing toxicity of NaOCl in some marine phytoplankton. Consequently, greater caution with use of NaOCl will be required, as its use is widespread in coastal waters.

• Journal of fish pathology
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• v.12 no.1
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• pp.42-48
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• 1999

The disinfectant effects of total residual oxidants (TROs) produced by ozonization of natural sea water were investigated against fish pathogenic bacteria isolated from flounder and red seabream. The concentration of 0.1 mg TROs/liter was stable for 20 min in filtered natural seawater, and those of 0.3 and 0.5 mg TROs/liter were also stable for more 1 hr. Disinfectant effects of TRO against Edwardsiella tarda, Vibrio sp., Streptococcus sp. and Staphylococcus sp. were observed with a concentration of 0.1 mg/liter for 180 sec, and the treatment killed more than 99.9% of bacterial cells. With TROs of 0.3 to 0.5 mg/ liter, the viable cells of the bacteria were reduced by more than 99.99% in 60 sec.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.4
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• pp.285-292
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• 2021

Osmotic power is to produce electric power by using the chemical potential of two flows with the difference of salinity. Water permeates through a semipermeable membrane from a low concentration feed solution to a high concentration draw solution due to osmotic pressure. In a pressure retarded osmosis (PRO) process, river water and wastewater are commonly used as low salinity feed solution, whereas seawater and brine from the SWRO plant are employed as draw solution. During the PRO process using wastewater effluent as feed solution, PRO membrane fouling is usually caused by the convective or diffusive transport of PRO which is the most critical step of PRO membrane in order to prevent membrane fouling. The main objective of this study is to assess the PRO membrane fouling reduction by pretreatment to remove organic matter using coagulation-UF membrane process. The experimental results obtained from the pretreatment test showed that the optimum ferric chloride and PAC dosage for removal of organic matter applied for the coagulation and adsorption process was 50 mg/L as FeCl₃ (optimum pH 5.5). Coagulation-UF pretreatment process was higher removal efficiency of organic matter, as also resulting in the substantial improvement of water flux of PRO membrane.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.1
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• pp.93-100
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• 2021

Forward osmosis (FO) process is a chemical potential driven process, where highly concentrated draw solution (DS) is used to take water through semi-permeable membrane from feed solution (FS) with lower concentration. Recently, commercial FO membrane modules have been developed so that full-scale FO process can be applied to seawater desalination or water reuse. In order to design a real-scale FO plant, the performance prediction of FO membrane modules installed in the plant is essential. Especially, the flux prediction is the most important task because the amount of diluted draw solution and concentrate solution flowing out of FO modules can be expected from the flux. Through a previous study, a theoretical based FO module model to predict flux was developed. However it needs an intensive numerical calculation work and a fitting process to reflect a complex module geometry. The idea of this work is to introduce deep learning to predict flux of FO membrane modules using 116 experimental data set, which include six input variables (flow rate, pressure, and ion concentration of DS and FS) and one output variable (flux). The procedure of optimizing a deep learning model to minimize prediction error and overfitting problem was developed and tested. The optimized deep learning model (error of 3.87%) was found to predict flux better than the theoretical based FO module model (error of 10.13%) in the data set which were not used in machine learning.

• Membrane Journal
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• v.33 no.3
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• pp.87-93
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• 2023

Electrodialysis (ED) is essential in separating ions through an ion exchange membrane. The disposal of brine generated from seawater desalination is a primary environmental concern, and its recycling through membrane separation technology is highly efficient. Alkali is produced by several chemical industries such as leather, electroplating, dyeing, and smelting, etc. A high concentration of alkali in the waste needs treatment before releasing into the environment as it is highly corrosive and has a chemical oxygen demand (COD) value. The concentration of calcium and magnesium is almost double in brine and is the perfect candidate for carbon dioxide adsorption, a major environmental pollutant. Sodium hydroxide is essential for the metal carbonation process which, is easily produced by the bipolar membrane electrodialysis process. Various strategies are available for its recovery, like reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and ED. This review discusses the ED process by ion exchange membrane for alkali recovery are discussed.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.1
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• pp.1-8
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• 2015

To evaluate accuracy and precision of determination of total alkalinity ($Alk_T$) and carbon dioxide ($TCO_2$) derived from present study, experiment was applied with $CO_2$ CRM (Batch 132, Scripps Institution of Oceanography; $Alk_T=2229.24{\pm}0.39{\mu}mol/kg$, $TCO_2=2032.65{\pm}0.45{\mu}mol/kg$). As the result, average concentration of $Alk_T$ and $TCO_2$ was $2354.09{\mu}mol/kg$ (~5.6% difference with $CO_2$ CRM) and $2089.60{\mu}mol/kg$ (~2.3% difference with $CO_2$ CRM), respectively. For previous method (Gran Titration) by addition $NaHCO_3$ to deionized water($Alk_T$ $2023.33{\mu}mol/kg$), average concentration was $2193.39{\mu}mol/kg$ (sd=57.15, n=7). Whereas, average concentration was $2017.02{\mu}mol/kg$ (sd=10.98, n=7) for the present study. Recovery yield experiments of total alkalinity in deionized water and seawater were implemented by addition of $NaHCO_3$. The recovery yield of deionized water in the range 0 to $4952.39{\mu}mol/kg$ was 100.8% ($R^2$=0.999), and seawater in the range 0 to $2041.32{\mu}mol/kg$ was 102.3% ($R^2$=0.999). Comparison of $pCO_2$ sensor (PSI $CO_2-Pro^{TM}$) with present method showed very meaningful correlation coefficient ($R^2$=0.977) in the range of 427 to $705{\mu}atm$ and 9.16 to $15.24{\mu}mol/kg$ throught elapsed time for two weeks. Field experiment of diurnal variation of total carbon dioxide was accomplished at Sachon harbor in the coastal waters of East Sea of Korea. Concentration of $Alk_T$ and $TCO_2$ was increased during night, and decreased during daylight hours. The results showed mirror type between $TCO_2$ and dissolved oxygen, which was attributable to photosynthesis and respiration of phytoplankton. Also, open ocean field study was performed to obtain vertical profile of $Alk_T$ and $TCO_2$ in C-C zone (Clarion-Clipperton Fracture Zone), Northeastern Pacific. Average concentrations of $Alk_T$ in the surface mixed layer (0~60 m) and deeper layer below 200 m were $2422.38{\mu}mol/kg$ (sd=78.73, n=20) and $2465.87{\mu}mol/kg$ (sd=57.68, n=103), respectively. And average concentrations of $TCO_2$ were $2134.47{\mu}mol/kg$ (sd=65.4, n=20) and $2431.87{\mu}mol/kg$ (sd=65.02, n=103) in the same depth ranges such as $Alk_T$. Vertical distributions of $Alk_T$ and $TCO_2$ concentrations tended to increase with depth, and analyzed concentrations showed slightly higher than those of previous studies in this area.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.2
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• pp.111-120
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• 2003

To describe dinoflagellate cysts from Gwangyang Bay, surface sediment samples were collected at 20 sites by the TFO core sampler on 24 August 2001, in coupled with a phytoplankton investigation by surface seawater sampling. More than 17 genera, 36 species of dinoflagellate cysts were Identified from the sediment samples of Gwangyang Bay, consisting of 14 species of gonyaulacoid, 14 species of protoperidinioid, 3 species of diplopsalid, 2 species of gymnodinioid, 1 species of tuberculodinioid and calciodinellid, respectively. Cyst concentrations in Gwangyang Bay varied from 115 to 2,188 cysts/g, and generally increased toward a western part of the study area. The highest cyst concentration was observed at St. 11 located in the northwestern region with 11 genera and 19 species(2,188 cysts/g), while the lowest value with 6 genera and 9 species(115 cysts/g) was observed at St. 3 located in the center of the study area. The predominant dinoflagellate cyst was Spiniferites bulloideus, followed by Alexandrium sp., Brigantedinium simplex and S. delicatus. The motile forms of eight dinoflagellate cysts recorded in the sediment samples were also observed in the seawater: Polykrikos swartzii/kofoidii complex, Scripssiella trochoidea, Protoperidinium claudicans(cyst name: Votadinium spinosum), P. pentagonum(: Trinovantedinium capitatum capitatum), P. conicum(: Selenopemphix quanta), P. leonis(: Quinquecuspis concretum), P. conicoides(: Brigantedinium simplex), Gonyaulax spp.(: Spiniferites spp.). In this study, heterotrophic dinoflagellate cysts show the highest concentration at St. 6 where the highest density of diatoms simultaneously observed from surface water sample. This result suggests that the grazing of heterotrophic dinoflagellates on the diatoms in high concentration caused the higher concentration of heterotrophic dinoflagellate cysts.

• Journal of Wetlands Research
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• v.18 no.1
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• pp.58-67
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• 2016

This study was performed to investigate the long-term changes in water quality and benthic ecology around the Nakdong River Estuary. The effect of the estuarine barrage on the ecosystem was also evaluated. The water quality was interpreted using the field survey (2013 and 2014) and monitoring data (MOE, 1989~2013) and the macrobenthic-fauna was investigated through analysis of the field survey data (2014) and literatures review (1985~2013). The long-term variation of water quality of Nakdong River generally showed increased nutrient concentration with decreased discharge, while abrupt influence of the barrage construction was not observed. However, the nutrient and organic matter concentration inside the barrage distinctly was higher than the concentration outside the barrage because the mixing of fresh and seawater was limited by the barrage. Especially, in the period of low discharge during winter, the Chlorophyll-a concentration clearly increased more in the downstream inside the barrage, showing the barrage effect. In other words, stagnant effect caused by barrage construction had an effect on the water quality degradation in dry seasons. As for the benthic ecology inside barrage after barrage construction, molluscans and brackish-water crustaceans disappeared. Outside the barrage, benthic ecosystem has deteriorated and the small-sized organic indicative species like Prionospio membranacea, Pseudopolydora kempi, Sinocorophium sinensis became dominant due to several construction such as Myeong-Gi Bridge, Airport construction, industrial complex after the Nakdong barrage construction.