Fluxes and behaviors of groundwater-borne nutrients in the ocean

조형미 서울대학교 대학원 2017 국내박사

Submarine groundwater discharge (SGD) into coastal waters is an important pathway for transporting nutrients to the ocean. Although the fluxes of SGD and associated nutrient discharge to the ocean at local and regional scales have been well studied, detailed estimates and models of SGD-related nutrient inputs to coastal waters on a global scale are few in number. Therefore, in this study, the global magnitude of SGD and its associated nutrient fluxes into the global ocean were estimated using a radium isotope (228Ra). The re-estimated magnitude of global SGD flux was approximately 1–1.5 times the river discharge and SGD-derived nutrient fluxes were comparable to the river-driven fluxes to the global ocean. These results imply that SGD is a critical source of nutrients to the ocean and therefore plays a critical role in marine productivity. Nutrient fluxes through SGD can be calculated by multiplying the endmember concentrations of nutrients in groundwater by the SGD flux. However, groundwater nutrient concentrations are altered through biogeochemical reactions in the subterranean estuary (STE), where mixing between groundwater and aquifer solids occurs, prior to entering the ocean. Furthermore, the adsorption and desorption behaviors of silicon (Si) and phosphorus (P) in the STE have not been investigated although these processes influence Si and P fluxes through SGD. Based on laboratory experiments, rapid desorption of P (5–20 μmol/L) occurred from the sediment columns when Si was 40−90% removed in the initial stage within the first 24 hours. These results suggest that Si adsorption can result in significant P desorption from sediments in the STE into seeping groundwater. Nutrient inputs via SGD play a significant role in nutrient cycling and primary productivity in the coastal ocean. This study based on seasonal sampling campaigns shows that SGD plays a critical but different role in nutrient budgets and stoichiometry in coastal waters off a volcanic island depending on open-ocean nutrient conditions. When bay seawater was influenced by the N-limited Tsushima Current, SGD was the major source of DIN in N-limited bay waters. SGD was also the absolute source of DIP in P-depleted bay waters that were influenced by P-limited Changjiang River diluted water (CDW). In addition, excessive inputs of nutrients from SGD resulted in an almost complete transfer of SGD-derived nutrients to the open ocean during the season in which a large flux of SGD occurs.

Malate Dehydrogenase-Mediated Activation of Nε-Lysine Acetyltransferase Modulates Metabolic Flux

김건 서울대학교 대학원 2025 국내석사

Flux-dependent signal transduction systems enable bacteria to sense intracellular metabolic fluxes and adapt their physiology to environmental changes. Although flux-dependent regulatory systems are increasingly recognized for their impact on cellular physiology, the molecular details of how these systems function remain poorly understood. In Escherichia coli, the interconversion of malate and oxaloacetate in the tricarboxylic acid (TCA) cycle, catalyzed by malate dehydrogenase (Mdh), is influenced by extracellular environmental conditions. Although prior research has explored how external factors regulate the directionality of the TCA cycle, the specific contribution of Mdh to the modulation of metabolic flux has remained largely unexplored. This study was conducted to elucidate the role of Mdh as a key sensor of TCA cycle flux in E. coli. We identified Protein Acetyltransferase Z (PatZ), a known acetyltransferase in E. coli, as a novel interaction partner of Mdh. Their binding was confirmed by ligand fishing, binding test, and isothermal titration calorimetry. Structural modeling by AlphaFold3 predicted a 2:1 binding stoichiometry, where two Mdh bind to a single PatZ. Additionally, the predicted model identified Histidine 511 of PatZ as a critical residue for the interaction between the two proteins, which was validated by site-directed mutagenesis and binding assays. Furthermore, we identified that the metabolites NADH and ATP attenuate the Mdh-PatZ interaction, implying that this protein complex is involved in metabolite-sensitive regulation and may function as a metabolic flux sensor. Analysis of the effect of the interaction between the two proteins revealed that PatZ had no significant effect on the enzymatic activity of Mdh. Interestingly, Mdh was found to enhance the acetyltransferase activity of PatZ. Furthermore, phenotypic analysis showed that the PatZ mutant strain defective in Mdh binding exhibited a growth curve similar to that of the catalytically inactive PatZ mutant strain. This finding indicates that Mdh not only enhances the enzymatic activity of PatZ but also plays an additional regulatory role. These findings suggest that Mdh functions not only as a metabolic enzyme in the TCA cycle but also as a sensor of the intracellular redox state, regulating the enzymatic activity of PatZ in a flux-dependent manner. Mdh likely influences the acetylation state of downstream targets by modulating the acetyltransferase activity of PatZ, thereby contributing to metabolic regulation. This study thus reveals a potential mechanism of flux-dependent signal transduction in bacteria. Considering the evolutionary conservation of Mdh across diverse organisms, these findings may provide broader insights into metabolic flux regulation in other biological systems. Flux-dependent signal transduction systems은 박테리아가 세포 내부의 대사 흐름을 감지하고, 환경 변화에 신속하게 적응할 수 있도록 한다. 이러한 흐름 의존적 조절 시스템의 중요성은 점차 부각되고 있지만, 작동 원리는 아직 명확히 규명되지 않았다. Escherichia coli에서 tricarboxylic acid (TCA) 회로 내 말산과 옥살로아세트산 간의 가역적 전환 반응은 말산탈수소화효소(Malate dehydrogenase, Mdh)에 의해 촉매되며, 외부 환경에 따라 전환 방향을 결정하는 것으로 알려졌다. 지금까지의 연구는 TCA 회로의 방향성이 외부 요인에 의해 어떻게 조절되는지에 초점을 맞추어 왔으나, Mdh가 대사 흐름을 조절하는 데 있어서의 역할과 중요성에 대한 연구는 아직 부족한 상황이다. 이에 E. coli에서 Mdh가 TCA 회로의 흐름을 조절하는 주요 조절자로서의 역할에 대해 확인하고자 하였다. 본 연구에서 E. coli에서 아세틸전이효소로 알려진 단백질 아세틸전이효소 Z(Protein Acetyltransferase Z, PatZ)가 Mdh와 상호작용하는 단백질임을 처음으로 확인하였다. 이들 간의 결합은 ligand fishing 실험, protein binding 실험, 등온 적정 열량 측정법 등을 통해 검증되었다. Alphafold3를 이용한 구조 예측에서 Mdh와 PatZ가 2대 1의 결합 비를 이루며 복합체를 형성함을 확인하였다. 예측된 모델을 바탕으로 PatZ 단백질의 Histidine 511번 잔기가 두 단백질 간 상호작용에 관여하는 중요한 아미노산 잔기임을 확인하였으며, 이는 protein binding 실험을 통해 검증되었다. 나아가 protein binding 실험으로 NADH와 ATP 등의 대사산물이 Mdh와 PatZ 간 상호작용을 특이적으로 약화시킨다는 사실을 확인하였다. 마지막으로, 효소 활성 확인 실험, western blot, DTNB 실험을 통해 PatZ는 Mdh에 영향을 미치지 않지만, Mdh는 PatZ의 아세틸전이효소 활성을 증가시키는 것으로 확인되었다. 이러한 결과는 Mdh가 단순히 TCA 회로의 대사 담당 효소로 기능할 뿐만 아니라, 세포 내 산화 및 환원 상태를 감지하여 효소 활성을 대사 흐름 의존적으로 조절하는 조절자로서 기능할 수 있음을 시사한다. Mdh가 PatZ의 아세틸전이효소 활성을 조절함으로써 아세틸조효소A 합성효소(acetyl-CoA synthetase)와 같은 하위 단백질들의 아세틸화 상태에 영향을 미치는 등의 대사 조절에 영향을 미칠 것으로 보인다. 본 연구는 박테리아에서 새로운 flux-dependent signal transduction system의 기작을 제시하며, Mdh가 다양한 생물에서 진화적으로 보존되어 있다는 점에서 다른 생명체에서도 이러한 조절 시스템에 대한 통찰을 제공할 수 있다.

MF 공정에서 유입수 오존농도가 플럭스와 처리수 수질에 미치는 영향

조세현 서울시립대학교 대학원 2009 국내석사

Advanced water treatment is now widely applied to many drinking water treatment plants in order to deal with the problems such as taste and odor, pathogen, disinfection by-products (DBPs), and toxic chemicals. Membrane filtration process has high effectiveness in turbidity and pathogenic microorganisms in the water treatment process. Membrane application in surface water treatment also provides many advantages over conventional treatment such as energy consumption and area. One of the most significant issues affecting the development of membrane applications in drinking water treatment is membrane fouling. Membrane fouling results in poor membrane performance by decreasing the permeate flux and increasing the transmembrane pressure (TMP). Ozone is well-known of its high performance in oxidation and high effectiveness in color and odor removal. Several studies report that preozonation can eliminate the complication of the chemical structures and aromaticity in influent water. Therefore, in this study, the effect of ozonation on suppressing membrane fouling was investigated by dosing ozone in the membrane feed water using surface water. The increase of membrane filtration flux and water quality variation were observed for the study. The raw water used in this research was obtained from Han river intake station located in Seoul. The pilot plant consisted of ozone generator, ozone injector and ozone resistant MF module. Ozone was injected by a ejector. The material of membrane was PVDF (polyvinylidenefluoride). Outside-in filtration was carried out by cross-flow with the transmembrane pressure(TMP) of 0.4 bar. The combined ozonation-MF system was operated with a cycle of filtration (28.5 min), backwashing (1 min) and drain (0.5 min). The analysis of water quality was carried out for each sample taken at (a) raw water, (b) circulation tank, (c) feed of the MF with ozone, (d) permeate of the MF, respectively. MF system was operated with 0.4, 0.6, 0.8 and 1.0 bar of feed pressure and 0.2 bar of the concentrate pressure. The specific flux declined in the range of 162.4~66.1, 183.0~62.3, 184.2~61.0 and 174.3~47.5 L/㎥·hr·bar at the TMP of 0.3, 0.4, 0.5 and 0.6 bar respectively. The flux was declined to 50% of initial flux after 14.3 hr, 11.6 hr, 8.4 hr and 6.2 hr respectively. Cumulative permeate productions up to 50% of initial flux were 90.6L, 107.5L, 98.4L and 83.7L respectively. Thus, economical TMP was estimated to be 0.4 bar. Thus, MF system and hybrid system was operated at 0.4 bar of TMP. When 2 to 5 mg/L of ozone was injected, the concentration of ozone in permeate was maintained 0.1 to 0.5 mg/L. Improvement of flux was observed to be 1.3 to 2.3 times for 2 to 5 mg/L of injection of ozone comparing with no-ozone. More than 0.3 mg/L of residual ozone concentration in the permeate was needed for high flux in membrane system. During the experimental period, the hybrid system was maintained at 90% of the initial permeate flux. And turbidity of permeate was below 0.06 NTU. The removal efficiencies of TOC and DOC by MF system were 27.3%, 25.1% respectively, while those of the hybrid system were 29.9%, 27.8% respectively. The removal efficiencies of UV_(254) and THMFP by MF system was 65.7%, 32.3% respectively. However, those of the hybrid system was 77.4%, 44.0%. This results indicated that larger organic compounds in the water changed to lower molecular weight compounds or to hydrophilic matters with oxidation by residual ozone. The raw water had similar proportions of hydrophilic(HPI) and hydrophobic(HPO) fraction. However after ozonation and MF filtration, the HPO decreased and HPI increased. THMs decline of permeate came from this effect in the hybrid system. From the results, hybrid system consisted of ozonation and MF membrane showed high performance at improvement of membrane fouling and water quality. 현재 기존 정수처리공정의 대부분은 응집-침전-모래여과-염소소독으로 구성되어 있어 맛·냄새 물질, 병원성 미생물, 소독부산물(disinfection by products, DBPs), 미량 유기물질의 제어에 어려움이 있다. 이러한 문제를 해결하기위해 다양한 고도정수처리 공정들이 소개되고 있으며 오존, 활성탄, 막 분리 공정 등이 국내외 정수장에 도입되고 있다. 고도처리기술로서 막 분리공정은 우수한 탁질 제거와 병원성 미생물에 대한 안전성 확보, 처리시설의 소형화 및 자동화 등 여러 장점을 갖추고 있어 기존에 설치된 재래식 처리공정을 대신하여 사용할 수 있는 간결하고 유지관리가 용이한 처리공정이라 할 수 있다. 그러나 막 여과 기술의 문제점 중 하나는 막 오염(fouling)에 의한 여과유속(flux)의 감소 또는 막간차압(trans membrane pressure, TMP)의 상승으로 낮은 생산성과 처리수량의 시간적 변동과 같은 수공급 문제 그리고 잦은 세정, 막의 교체와 전력사용량의 증가 등의 문제가 발생한다. 오존처리는 강력한 살균 및 산화기능을 가지고 있어 원수에 포함되어 있는 박테리아나 바이러스를 살균 및 불활성화 시킬 수 있으며, 유기물질 구조를 변경시키고 분자량을 저감시킨다. 본 연구에서는 이러한 오존의 강력한 산화력을 이용해 막 오염을 줄이고자 MF 막 여과의 전처리로 막 유입수에 오존을 주입하였다. 내 오존성의 PVDF 재질의 가압식 국산막을 이용하여 막 표면에까지 오존을 잔류시킴으로서 막 오염을 저감시키고자 하였으며, 생산성 향상과 수질을 확인하였다. 그 결과는 다음과 같다. 막 유입수에 오존 주입 농도를 2~5 mg/L로 변화시켰을 때 투과수 내 용존 오존농도는 0.1~0.5 mg/L로 나타났으며, 주입농도를 증가시킬수록 용존 오존농도는 증가하는 경향을 보이며 보다 높은 flux로 여과가 가능하였다. 유입수 내에 존재하는 막 오염물질과 막 표면에 축적된 오염물질을 오존이 저분자화, 친수화 및 산화시키고 fouling 속도를 감소시킨 것으로 판단된다. 오존을 주입하지 않은 경우와 비교하여 오존을 막 유입수에 주입하였을 때, flux는 1.3~2.3 배의 증가를 보였다. 2배 이상의 flux를 얻고자 한다면 4 mg/L 이상으로 주입하여야 한다. fouling을 제어하기 위한 용존 오존의 효과를 생각해보면 막 표면에까지 오존을 잔류시키기 위해서 주입량 보다는 투과수 내에 용존 오존농도로 제어하는 것이 효과적이다. 막 유입수에 오존을 주입하여 투과수내 0.3 mg/L 이상의 용존 오존농도를 유지하면서 연속 자동운전 하였을 때 0.06 NTU 이하의 안정된 유츌수를 보이며, 초기 flux의 90%에 해당하는 고 flux 여과가 가능하였다. MF system과 비교하여 hybrid system은 역세모드를 실시하지 않고 여과모드만 지속하였을 경우 10시간 운전시 초기 flux의 20%가 향상되었고, 역세모드를 실시한 자동운전의 경우 10시간 운전시 21%, 60시간 운전시 42%가 향상되었다. hybrid system의 여과 초기 flux 감소가 적음에도 불구하고 여과 모드에서 감소한 flux의 역세에 의한 회복율은 각각 54.6%, 56.1%로 hybrid system에서 더 높은 회복을 보였다. 공정에 대한 수질에 있어서 MF system과 hybrid system에서 TOC, DOC는 모두 25~30%의 제거율을 나타내지만 hybrid system에서 UV_(254)와 THMFP의 경우 제거율은 각각 77%, 44%로 잔류 오존에 의해 수중 유기물이 저분자화 또는 친수화 된 것으로 보이며 MF system 보다 높은 제거율을 보였다. NOM 성상 변화 분석에서 원수의 친수성, 소수성 분율이 비슷하였으나 오존처리와 막 여과를 통하여 hydrophobic fraction(HPO)과 transphilic fraction(TPI)은 감소하고 hydrophilic fraction(HPI)은 약간 증가하였다. 높지 않은 유기물 제거를 감안하면 NOM의 일부 제거되고 나머지는 친수성 부분으로 전환된 것으로, 이러한 NOM 성상의 변화는 trihalomethanes(TMHs)의 생성을 다소 감소시킨 것으로 판단된다. 이상의 결과를 통해 MF 막 유입수에 오존을 주입하는 hybrid system에서 투과수의 잔류 오존농도에 따른 투과 flux 향상은 수중 유기물과 주입된 오존의 작용, 막 표면에서의 침적된 오염물질과 오존의 상호작용으로 판단된다. 따라서 MF 막 유입수에 오존을 주입하는 hybrid system은 MF 막의 fouling 감소와 수질 개선에 효과적인 것을 알 수 있었다.

수반중성자속을 사용한 몬테칼로 분산감소인자 민감도 분석

곽민수 서울대학교 대학원 2012 국내석사

몬테칼로 계산에서 수반해는 측정하고자 하는 목표함수에 대한 중요도로 해석될 수 있고, 분산감소기법에 사용되는 인자를 결정하는 데 쓰일 수 있다. 본 연구는 공간-에너지 의존 수반해를 이용하여 가중치 윈도우 기법의 가중치 하한한계값을 공간-에너지 의존적으로 지정함으로써 몬테칼로 계산의 효율성을 증대시키는 데 있어서, 분산감소 인자에 대한 계산효율의 민감도를 조사하고, 수반중성자속으로부터 분산감소인자를 생성하는 몇 가지 방법을 제안하고 소스모드 계산과 증배계수 계산 문제에 적용시켜 그 효과에 대해서 평가한다. FDM(Finite Difference Method)을 이용하여 공간-에너지 의존 수반해를 구하고, 수반해의 역수를 가중평균하여 기존의 implicit capture에서 통용되던 가중치 하한한계값과 동일하도록 가중치 윈도우 기법의 가중치 하한 한계값을 설정한다. 여기서, 수반해를 가중평균할 때 사용하는 함수로는 공간-에너지에 의존하지 않는 임의의 상수값을 사용하는 방법과 공간-에너지 기반의 중성자속, 중성자밀도, 목표반응율 등을 사용할 수 있다. 수반해를 이용하여 공간-에너지 의존적 가중치 하한값을 설정한 계산은 가중 방식에 따라 효과가 다르며 여전히 최적의 분산감소인자가 존재할 가능성을 남기지만, 기존의 획일적 가중치 하한 한계값을 설정한 계산에 비해 몬테칼로 계산의 효율성을 증대시킬 수 있다. 1차원 고에너지 중성자 차폐문제와 1차원 TBM 삼중수소 증식문제에 적용시켜 반응율 측정에 대한 몬테칼로 계산이 기존의 Implicit capture를 사용하였을 때 보다 개선된 것을 보이고, 2차원 7군 표준검증 문제인 C5G7와 OPR1000 2차원 문제에 대해 적용시켜 증배계수 계산에 대한 개선된 분산감소능력을 입증한다. In Mote Carlo neutronic calculation, adjoint flux can be considered as an important function with regarded to the destination function which is to be calculated. Also, It can be used to determining a parameter for variance reduction calculation. On the background of determining a lower parameter of weight window technique by using space-energy dependent adjoint flux, this study aims to present a number of method to determine lower parameter of weight window technique from a space-energy dependent adjoint flux, and to analysis the sensitivity of variance reduction performance on source mode and criticality mode calculation along with the suggested methods for determining the variance reduction parameter. As regarded to the step of determining lower parameter of weight window technique used in this study, obtain a weighted average of inversed space-energy dependent adjoint flux; the adjoint flux is pre-obtained from FDM(Finite Difference Method) calculation. Then, multiplied constant can be obtained, which makes the averaged value be equivalent to the lower parameter which is commonly used in Implicit Capture method. For the weighting factor used in weighted averaging of inversed adjoint flux, it can be used that space-energy dependent neutron flux, neutron population, reaction rate, and even space-energy independent constant. Using the variance reduction techniques parameterized from an adjoint flux shows different performance between methods to make the parameter from adjoint flux. Also it still leaves a open possibility to show an improved performance by changing the parameter. Though, one benefit is guaranteed that variance reduction techniques using a adjoint flux shows an improved performance compared to commonly using Implicit Capture method which use a constant parameter not space-energy dependent adjoint flux. To demonstrate the performance of variance reduction with adjoint flux, performs source mode calculations of 1-dimensional 7group high energy neutron shielding problem and 1-dimensional 47group TBM(Test Blanket Module) problem. For the criticality mode calculation, calculations of 2-dimensional 7group C5G7 from IAEA and 2-dimensional 7group OPR1000 problem is carried out.

CaO-Fe2O3-CaF2系 Flux의 Injection에 의한 熔銑의 脫燐에 對한 硏究

이광근 全南大學校 1986 국내석사

최근에 CaO계 flux 대신에 soda계 flux에 의한 脫P와 脫S가 연구되고 있지만 CaO계 flux는 자원이 풍부하므로 비용과 에너지 절감면에서 유리하다. 본 연구에서는 1350℃에서 CaO-Fe₂O₃-CaF₂ fluxes을 취입한 후 산소가스를 상취하여 flux 조성, 산소유량, 초기 Si 함량, 염기도, 첨가제의 영향을 조사한 결과는 다음과 같다. 1) 염기도가 0.3에서 flux중의 Fe₂O₃량이 증가하거나 일정한 조성에서 산소유량이 증가함에 따라 脫P率은 증가하였으며 脫C率은 15% 내로 脫C率이 증가함에 따라 脫P率도 증가하였다. 2) 초기 Si함량이 감소함에 따라 최종 P함량도 감소하였다. 3) 염기도가 증가할수록 脫P率은 증가하였고 염기도가 2.8에서는 脫P반응이 脫Mn반응보다 우선하였고 엽기도가 0.8에서는 脫Mn반응이 脫P 반응보다 우선하였다. 4) 8wt% CaF₂ 대신에 같은 양의 MnO₂을 첨가할 경우에 脫P率은 거의 같았다. It has been studied currently that soda-based fluxes are usable for dephosphorization and desulfurization of pig iron in stead of CaO - based fluxes. But, our country is abundant in resource of lime , and so the usage of CaO based fluxes should be favorable from the points of view of cost and energy-saving. This paper deals with the effect of flux composition, oxygen blowing rate, initial silicon content, basicity and other flux on dephosphorization of molten pig iron by injection of CaO - Fe_2 O_3- CaF_2 fluxes and top blowing of oxgen gas at 1350°C The results are as follows 1. In the theoretical basicity's 0.8, the degree of dephosphorization increased with Fe_2 O_3 powder of fluxes at constant oxygen blowing rate or oxygen blowing rate at constant fluxes composition. The extent of decarburization is below 15 % and the degree of dephosphorization increased with the degree of decarburization. 2. The final phosphorus content was lower with the low initiul silicon content. 3. The degree of dephosphorization increased with the basicity. At 2.8 basicity the reation of dephosphorization preferred to the reaction of mangornese oxidation. At 0.8 basicity the reaction of manganese oxidation proferred to the reaction of dephosphorization. 4. When the dephosphorization agent of 8% Mn0_2 and 8% CaF_2 was injected of 16 % CaF_2, the degree of dephosphorization was almost the same.

Critical Flux Behavior and Mass Transport in Fouling of Forward Osmosis Membrane Filtration

Thanh-Tin Nguyen 광주과학기술원 대학원 2021 국내박사

Forward osmosis (FO) membrane process has emerged as a promising technology for application in desalination and water treatment. The integrated FO-RO process could carry out both desalination and water treatment simultaneously if seawater and wastewater (WW) are employed in the FO membrane process. However, fouling can be an anticipated and inevitable issue in the FO process. Membrane fouling is closely related to the concept of the critical flux. This concept has been well applied in the pressure driven membrane process. Nevertheless, hitherto, little attention has been directed to the role of the critical flux of osmotically driven processes (FO) in controlling membrane. Therefore, a systematic study on the critical flux of FO is necessary for fouling control in wastewater reuse and desalination. This work not only focus on the comprehensive evaluation of critical flux behavior-based membrane fouling control for wastewater reuse and desalination but also validate mass transport in fouling of FO membrane. The structure of the thesis is divided into 5 specific tasks. In Task 1 (Chapter III), the existence of critical flux concept in the FO process has been successfully demonstrated through a reliable stepping method (DS concentration stepping). The critical flux behavior in the FO processes was evidently affected by the foulant type and the membrane type. PA-TFC membrane outperformed the CTA membrane in terms of critical flux, which suggests that the former might be favored for practical applications. Organic fouling (organic macromolecules types e.g., polysaccharide, humic acid, protein and their initial concentration) need to be paid attention as they cause serious fouling. This fact is considered in Task 2 (Chapter IV). A comprehensive assessment of PA-TFC FO critical flux behavior for a variety of organic fouling types and concentrations was carried out. Based on these critical values, guidelines for fouling control, of relevance to wastewaters, are proposed. Importantly, the operational flux and complex mixtures had strong influence on the morphology of organic fouling layer. These conditions led to the formation of a cohesive and compact cake layer. This task confirmed that plant operation below the critical flux can still generate a small degree of fouling but this fouling is reversible and reversibility is vital for the minimization of chemical cleaning. A threshold value of 25 LMH was preliminarily proposed for fouling control, at which beneficial energy consumption can be obtained. Since the flux decline in FO membrane is due to the couple effect of concentration polarizations and fouling, the Task 3 (Chapter V) has been directed towards a quantitative evaluation of the synergistic outcome of concentration polarizations (CPs) and Cake-Enhanced concentration polarization (C-ECP) on overall FO performance. In this task, a good foundation for an understanding of transport phenomena and fouling in the FO process has been achieved. As the results, operation at an initial 34 LMH favored the formation of a thicker and more compact cake layer which resulted in significant increase in both cake structural parameter (four-fold) and cake layer enhanced concentration polarization (ten-fold). After 40 h operation without physical cleaning the additional effect of cake layer enhanced concentration polarization and fouling resistance consumed 25% of the total driving force; the significant internal concentration polarization still had the greatest impact. In contrast operation at the lower flux of 25 LMH generated less fouling with a lower cake structural parameter (119 µm). The resultant flux decline was only 3%. Understanding the insightful impact of divalent cations mass transport on the complex organic fouling of forward osmosis (FO) membrane is vital when seawater/brine is utilized in a FO hybrid process. In this Task 4 (Chapter VI), the work deeply focused on quantifying the influence of divalent cations on not only critical flux but also the organic fouling mechanism. The presence of divalent cations in aqueous solutions caused a decrease in critical flux values. The fouling mechanism is mainly governed by intermolecular and ion-mediated interactions. The findings suggested the interaction of divalent cations with organic matters close to the membrane surface is more noticeable than that in the feed solution. These interactions combined with an operation at the flux ≥ 30 LMH led to the formation of a compact and cohesive cake layer (4.8 -9.1 µm) where the great divalent cations were deposited on membrane surface after 30 h operation (Ca2+: 162.13 - 256.72 g/m2, Mg2+: 182.60 - 374.38 g/m2). In contrast, 21 LMH below critical value exhibited minor fouling with a very thin cake layer (0.5 µm) and minimized deposited divalent cations (Ca2+: 79.47 g/m2, Mg2+: 46.65 g/m2). Overall, the extended operation of 30 h suggested 16-21 LMH were threshold values for FO fouling control. For a real practical application, the optimal operating condition under critical flux-based fouling control need to explored. Therefore, the task 5 (Chapter VII) was carried out. In this chapter, we investigated the effect of hydrodynamic conditions on the change of critical/threshold flux. The study comprehensively evaluated different cross-flow velocity (CFV) in the feed side and draw side, being 6.66, 9.99, 12.32, 19.98 cm/s. It was found that the hydrodynamic conditions i.e., different CFV of both sides had a certain impact on the change of the critical/threshold behavior. Critical flux values were ranged 13-18 LMH, depending on choosing hydrodynamic condition. However, to reduce membrane cost, the study indicated that threshold flux should be recommended for a guideline in which it exhibited higher critical values (24-25 LMH). Overall, for a thin film composite membrane and wastewater with a foulant concentration of 160 mg/L an operation of CFV in feed/ CFV in the draw ratio of 1.5-2 is a recommended value to attain the fouling control but retaining a high critical/threshold values.

자속구속형 고온초전도 전류제한기의 설계 및 특성 해석

임성훈 全北大學校 2003 국내박사

The flux-lock type high-Tc superconducting fault current limiters (HTSC-FCLs) have been fabricated and their current limiting characteristics have been investigated. It was confirmed from experiments that the flux-lock type HTSC-FCL could improve both the quench characteristics and the transport capacity compared with the resistive type HTSC-FCL, namely, the independent operation of HTSC element. The flux-lock type HTSC-FCL is expected to be advantageous for the induction of simultaneous quench in case of series connection of HTSC elements. YBa_(2)Cu_(3)O_(7)-(YBCO) thin film was used a s the current limiting element of the flux-lock type HTSC-FCL, which was fabricated by etching the YBCO thin film into 2 mm wide and 420 mm long meander line consisting of fourteen stripes with different length. The solenoidal coil for the application of magnetic field, the flux-lock reactor and the circuit for control of current in coil 3 during a fault period were fabricated and integrated into the flux-lock type HTSC-FCL after testing their operations. The operational characteristics of the flux-lock type HTSC-FCL due to the direction of winding by coil 1 and 2 were analyzed and the fault current limiting characteristics through the quench distribution of HTSC element were investigated and compared with the case of the independent operation of HTSC element. The effect of the 3rd winding in the flux-lock type HTSC-FCL on the fault current limiting characteristics, which was originally installed for the application of magnetic field into HTSC element, was investigated. With the analysis for the limiting impedance and the current limiting ratio, the fault current limiting characteristics of the flux-lock type HTSC-FCL using series resonance between the magnetic field coil and the phase adjusting capacitor in the 3rd winding were investigated. The effects of magnetic field application on the resistance of HTSC element a s well a s the fault current limiting characteristics for the flux-lock type HTSC-FCL were analyzed. The fault current limiting experiments using a control circuit for the control of current flowing at the 3rd winding were performed. It was shown that the fault current limiting levels could be controlled by the switching operation of the control circuit. From the analysis for the results obtained by the experiments and the simulations for the fault current limiting characteristics of the flux-lock type HTSC-FCL, the conclusions were found as follows : 1. The different fault current limiting operations due to the direction of winding by coil 1 and 2 could be observed and the initial limiting current could be adjusted by the inductances of coil 1 and 2. In case of subtractive polarity winding, the initial limiting current was increased from 17 A to 22 A a s the number of turns in coil 2 was increased from 14 turns to 28 turns. On the other hand, in case of additive polarity winding, the initial limiting current was decreased from 9.44 A to 4.68 A. The values of the measured initial limiting current well agreed with ones calculated. The quench time of the flux-lock type HTSC-FCL with the subtractive polarity winding in fault condition was reduced two times compared with the independent operation of HTSC element. However, quench time of the flux-lock type HTSC-FCL with the additive polarity winding had no difference compared with the independent operation of HTSC element. 2. The limiting impedance of the flux-lock type HTSC-FCL with the 3rd winding was lower than that of the flux-lock type HTSC-FCL without the 3rd winding, which led to an increase of fault current. It was observed that the current flowing at the 3rd winding during a fault time caused the current of coil 1 to increase. Therefore, the fault current, which was equal to the sum of currents in coil 1 and coil 2, increased. However, the introduction of the 3rd winding into the flux-lock type HTSC-FCL prevented the saturation of an iron core and the reduction of the limiting impedance, which is expected to be the required part for the HTSC-FCL using iron core. 3. The limiting impedance and the current limiting ratio were expressed a s the function of both the quench power of HTSC element and the inductance of coil 1 for two cases : the flux-lock type HTSC-FCL without the 3rd winding and the flux-lock type HTSC-FCL applying the series resonance into the 3rd winding. From the comparison of two cases, the limiting impedance and the current limiting ratio of the flux-lock type HTSC-FCL without the 3rd winding were more improved than those of the flux-lock type HTSC-FCL applying the series resonance into the 3rd winding a s the quench power and the inductance of coil 1 increased. 4. The problem of continuous increase of the limited fault current for the flux-lock type HTSC-FCL applying series resonance into the 3rd winding after the fault current limiting operation occured could be solved by setting the resonance frequency near the power supply frequency, not exact its one. Resistance increase of HTSC element in the flux-lock type HTSC FCL applying the series resonance into the 3rd winding resulted from the mutual flux between coil 1 and coil 2, not the application of magnetic field into HTSC element in case of the subtractive polarity winding. The increase of current for the generation of larger magnetic field rather resulted in the increase of the fault current. 5. The fault current limiting levels could be adjusted by the switching operation of control circuit installed at the 3rd winding, which started to be operated by a program immediately after the current of coil 3 flowed at the moment of a fault. The control circuit was expected to be an required component of the flux-lock type HTSC-FCL with the 3rd winding for the adjustment of the fault current limiting levels a s well as the magnetic field applying into HTSC element.

Predicting flux of volatile fatty acids in membrane distillation

신보라 세종대학교 대학원 2024 국내박사

The aim of this study is to develop a model for predicting the initial flux of VFAs and water in solutions containing mixed VFAs. Volatile fatty acids (VFAs) are recognized as available resources, being low molecular weight organic acids containing a carboxylic group. VFAs are used as acidifiers in the food industry, and they have a wide range of applications in industries, such as pharmaceuticals and chemical manufacturing. Instead of extracting VFAs from new petroleum sources, they can be recovered from wastewater (such as effluent of anaerobic hydrogen fermentation or condensate from food waste drying processes) and utilized. To recover VFAs from waste resources, it is necessary to calculate the mass transport rate through flux prediction. Predicting the initial flux of VFAs can be utilized to forecast the performance (recovery rate of VFAs, mass transport of VFAs, and quality of the permeate solution) in the DCMD when valuable VFAs are recovered or separated from wastewater. To achieve this goal, the first study derived the Nusselt (Nu) equation to improve the water flux model, while the second and third studies proposed new models to predict the flux of VFAs. In Chapter 2, the aim of this study is to determine the Nusselt number (Nu) for predicting the water flux in the direct contact membrane distillation (DCMD) process. The temperature of the bulk solution and the membrane surface differ due to the heat transfer coefficient. The temperature polarization coefficient (TPC) is the difference in the temperature between the bulk solution and the membrane’s surface. It is essential to determine the temperature of the membrane’s surface using the heat transfer coefficient, which can be calculated using the Nusselt number, in order to predict the flux. The heat transfer coefficient varies due to various factors, which include the membrane characteristics, operating conditions, module configurations, and the overall system designs. The heat transfer coefficient varies depending on the characteristics of each system. It is necessary to derive an empirical equation for the system that was used in this study via research. One influential factor among the factors that are related to the heat transfer is the cross flow velocity (CFV). This study therefore conducted distillation experiments under various CFV and temperature conditions. A new Nusselt number equation was derived using the experimental results. The accuracy of the flux prediction was evaluated by conducting distillation experiments under different conditions. A thorough statistical analysis confirmed a precise match between the observed flux and the flux that was predicted flux using the empirical Nu equation. In Chapter 3, Parameters affecting the flux of VFAs were identified. Their relationship was confirmed experimentally. Acetic acid, butyric acid, and valeric acid were selected as the target compounds because they have different Henry's constants and hydrophobicity. The ionization of and acid solution varies depending on the pH. The MD tests were performed under various pH conditions. The flux of VFAs was observed to vary depending on the pH. The flux of VFAs was found to be proportional to the ionization fraction (𝛼0) of the feed solution. Therefore, the model was developed to reflect the ionization fraction. An empirical formula was derived to predict the flux of VFAs using experimental data. A statistical analysis supported that the flux predicted by the model fitted very well with the observed flux. Additionally, experiments were performed with acid solutions of various concentrations. The concentration range applicable to the derived empirical formula was validated. The developed model can provide further insight into the relationship between flux and pH. In Chapter 4, the aim of this study is to develop a model to predict the initial flux of volatile fatty acids (VFAs) mixtures using the direct contact membrane distillation (DCMD), focusing on understanding the interaction between the acids and improving a previous model to better suit the VFAs mixtures. The experiments investigated the influence of acids in the VFAs mixture. It was verified whether the ionization fraction of VFAs, even in multi-acid solutions, is proportionate to the flux. The correction coefficient and the overall mass transfer coefficient were introduced to enhance the model that previously used an empirical equation. The correction coefficients were derived, reflecting the interaction between acids and the hydrophobic membrane in the VFAs mixtures. Furthermore, the Nu equation derived in Chapter 2 was utilized to predict the water flux in VFAs mixtures. A random factor experiment was conducted to verify the accuracy of the prediction model. Additionally, the sum of each VFA transport can be estimated and expressed using a common water quality measure, chemical oxygen demand. The modeling work can provide further insights into the relationship among the flux, ionization, hydrophobicity, and the interactions among acids.

계절적 빈산소에 따른 진해만의 메탄 거동 연구 : 용존 메탄농도와 flux의 변화 양상을 중심으로

김서영 부산대학교 대학원 2021 국내석사

빈산소는 연안 메탄의 생성과 소비를 변화시켜 대기로의 메탄 flux에 영향을 줄 가능성이 크다. 계절적 빈산소를 겪고 있는 진해만에서 메탄 거동과 Budget 변화를 확인하기 위해 시기별 메탄 농도와 flux를 정량화하였다. 빈산소 시기 퇴적층-수층 메탄 flux는 100배 이상 증가하였으며(각 6, 1900µmol m-2 day-1) 수층-대기 메탄 flux는 약 2배, 저층 메탄 농도는 약 10배 이상 증가하는 양상을 보였다(각 190, 420µmol m-2 day-1; 각 22, 230nM). 빈산소 시기 (8월) 퇴적층에서 혐기성 호흡과정이 표층으로 이동되는 Shoaling의 형성 여부는 황화수소 농도가 최대로 검출되는 깊이의 변화로 확인되었다. Shoaling에 의한 수층과 메탄생성구간 사이 거리의 짧아짐은 메탄생성구간으로 유입되는 유기물을 증가시켜 메탄의 생성을 촉진시킨다. 또한 생성된 메탄이 수층으로 이동하는 거리가 짧아지기 때문에 산화에 의한 소비가 감소할 것이다. 생성 증가와 소비 감소의 복합적인 작용은 퇴적층-수층 메탄 flux와 용존 메탄을 증가시킬 수 있고, 이는 수층-대기 메탄 flux의 증가를 일으킨 것으로 추정된다. 본 연구에서는 빈산소 시기 축적된 메탄의 성층 해소에 따른 방출을 관측하지는 못하여 추정한 대기로의 메탄 flux값이 과소 평가되었을 가능성이 있다. 본 연구에서 빈산소로 인한 연안의 메탄 flux 증가를 확인하였고 향후 여러 연안 환경에서 산소조건에 따른 메탄 생성 연구의 필요성을 보여주었다

무불소계 mold flux의 결정화 및 전열특성

최순용 연세대학교 대학원 2005 국내석사

In continuous casting of steel, mold fluxes have a decisive effect on both the efficiency of the continuous casting process and the surface quality of the steel product. The surface quality of the steel product depends on the viscosity and heat transfer of infiltrated mold flux. The lubrication between the mold wall and the solidified shell depends on the viscosity of infiltrated mold flux and heat transfer is also regulated by the properties of the mold flux infiltrating the gap. Mold fluxes usually contain the following major constituents: CaO-Al2O3-SiO2-Na2O-CaF2. These mold fluxes lie in the pseudo-wollastonite area within the ternary diagram CaO-SiO2-Al2O3. Among the chemical composition of mold flux, the main role of fluorine(F) is the control of viscosity and heat transfer by controlling the crystallization rate of mold flux. This is very important for production of the high quality steel product and for improving the efficiency of the continuous casting process. However, the fluorine in mold flux tends to damage both the continuous casting facilities and the environment of the earth. The corrosion in continuous casting facilities is considered to be caused by a decrease in pH in the secondary cooling water on contact with the mold flux films. Therefore mold fluxes containing fluorine are considered to have a great influence on corrosion of continuous casting facilities. In the near future, the discharge of fluorine is expected to be limited by the global environmental regulation of soil and water quality. Therefore, elimination of fluorine in the mold flux is considered to be an urgent necessity. In this work, high viscosity type and low viscosity type F-free mold fluxes were prepared based on the glass system CaO-SiO2-Al2O3-Na2O -MgO, with the addition of B2O3 orand Li2O as substitute materials for fluorine. Then, the addition effect of B2O3 and Li2O on properties of the mold flux, such as viscosity and thermal conductivity, was examined. Also, the influence of the basicity(CaOSiO2) on the crystallization behavior of mold flux was studied by DTA isothermalnon-isothermal method and single hot thermocouple technique(SHTT). As a results, Physical properties of prepared F-free mold flux were similar to the commercial mold flux and we find the adequate application possibility in continuous casting of steel. 용강 제조 시 사용되는 연속주조용 mold flux의 성분 중 불소는 점도 및 응고온도를 효과적으로 감소시키는 첨가제로서 널리 사용되고 있다. 불소는 mold flux의 성능향상을 위해 매우 효과적인 첨가제이지만, 연속주조 공정 중 주편을 냉각시키기 위하여 사용되는 냉각수내로 혼입되어 연속주조 설비의 부식을 야기할 뿐 아니라 폐수로 혼입되어 환경공해를 유발한다. 따라서 이러한 불소 사용에 따른 문제점을 개선함과 동시에 연속주조 시 우수한 품질의 강을 제조할 수 있는 무불소계 mold flux를 탐색하여, 요구되는 특성의 비교평가를 함으로써 기존 mold flux와 유사한 점도, 열전도도 및 결정화 경향을 갖는 무불소계 mold flux를 개발 및 적용가능성을 검토하였다. 고점도형 무불소계 mold flux 조성(CaO-SiO2-Al2O3-Na2O-B2O3계) 중 최적조성은 CaOSiO2=1.3, CaO:40.98wt%, SiO2:31.62wt%, MgO:3.5wt%, Al2O3:5.4wt%, Na2O:8.5wt%, B2O3:10wt% (Ua2-1)으로 극저탄소강 적용을 목표로 설계한 저염기도 고점도 mold flux로서 점도가 2.55poise, 열전도도는 1.043Wm·K(glass), 1.287Wm·K(crystalline)로 극저탄소강에 적합하다. 결정화기구는 DTA 등온비등온 모두 bulk nucleation 및 확산에 의한 3차원 결정성장 기구며, 활성화에너지는 57.56±5.19KJmol이다. 현장 시험적용 결과 실제 극저탄소강 저속 연주공정에 불소함유 기존 mold flux(KG-02)를 Ua2-1로 대체하여 약 2,000ton의 제품을 생산한 결과, 기존 제품과 비교하여 표면결함, 주문외 발생, SEN(Submerged Entry Nozzle) 용손 등에서 모두 불소함유 기존 mold flux보다 우수한 특성을 나타내었다. 저점도형 무불소 mold flux 개발을 위해 설계된 L series 조성(CaO-SiO2-Al2O3-Na2O-B2O3계)은 1300℃ 에서의 고온점도가 0.44~1.23 poise로 저점도형 무불소 산화물계 조성확보가 가능하였다. 최적조성은 CaOSiO2=1.4, CaO:42.35wt%, SiO2:30.25wt%, MgO:1.5wt%, Al2O3:2.4wt% Na2O:11.5wt%, B2O3=10wt%, Li2O=2wt% (L3)이며, 점도가 1.07poise, 유동온도가 1100℃, 열전도도는 1.17Wm·K(glass), 1.70Wm·K(crystalline)로 상용 mold flux인 KE와 가장 유사한 값을 나타냈으며, 결정화기구는 bulk nucleation 및 확산에 의한 3차원 결정성장 기구로 상용 mold flux와 동일하였다. 따라서 실제공정에의 적용가능성은 충분하다고 판단된다.