• KSBB Journal
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• 제5권1호
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• pp.25-35
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• 1990

In the Xanthan gum fermentation by Xanthomonas campestris there are problems of the large energy consumption by long fermentation time, the mass transfer of oxygen and nutrients by high viscous fermentation broth. In this study, the media optimization and the fed batch fermentation were carried out to decrease fermentation time and increase Xanthan gum yield. The $O_2$ uptake rate (OUR) and $CO_2$ evolution rate(CER) which were obtained from the analysis of fermentation exit gas using a gas chromatograph were investigated. As a result, the fermentation time decreased at optimal assimilable nitrogen concentration but increased at poor or rich assimilable nitrogen concentration, the Xanthan gum biosynthesis was stimulated under the limited condition of assimilable nitrogen source and the optimum fermentation medium was obtained as follow; Glucose=30g / l, Peptone=8.0g / l, $K_2HPO_4=2.0g/l$, $MgS0_47H_2O=10g/l$, Sodium acetate=20g/l, Sodium pyruvate=0.5g/1. As the agitation speed and nitrogen concentration increased, the $O_2$ uptake rate and $CO_2$ evolution rate increased. The OUR and CER were 37.3mmol $O_2/\;l$ hr and 20.2 mmol $CO_2/\;L$ hr at peptone 11g / l and agitation speed 990RPM, respectively. In fed batch fermentation, the final concentration of Xanthan gum was enhanced up to 29g / l.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제23회 추계학술대회 논문집
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• pp.178-183
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• 2004

액체산소 탱크 내에서의 열적 성층화(thermal stratification) 현상은 대기로부터의 열 투입과 탱크 내에서의 극저온 액체의 열적 비평형에 의해 발생된다. 열적 성층화 현상은 벤트 시스템, 탱크 단열. 펌프 설계에 영향을 미치게 되므로 정교한 해석 및 시험적 검증이 필요하다. 본 논문에서는 side-wall에서의 열 투입에 의해 발생되는 경계층 유동을 해석적 방법으로 1차원 모델링하여 시간에 따른 성충화 부피의 증가 및 탱크 내에서의 높이에 따른 온도 분포를 묘사한다.

• Environmental Engineering Research
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• 제23권4호
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• pp.345-353
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• 2018

This paper summarizes results of research on the electrochemical (EC) degradation of disinfection by-products (DBPs) and iodine-containing contrast media (ICMs), with the focus on EC reductive dehalogenation. The efficiency of EC dehalogenation of DBPs increases with the number of halogen atoms in an individual DBP species. EC reductive cleavage of bromine from parent DBPs is faster than that of chlorine. EC data and quantum chemical modeling indicate that the EC reduction of iodine-containing DBPs (I-DBPs) is characterized by the formation of active iodine that reacts with the organic substrate. The occurrence of ICMs has attracted attention due to their association with the generation of I-DBPs. Indirect EC oxidation of ICMs using anodes that produce reactive oxygen species can result in a complete degradation of these compounds yet I-DBPs are formed in the process. Reductive EC deiodination of ICMs is rapid and its overall rate is diffusion-controlled yet I-DBPs are also produced in this reaction. Further progress in practically feasible EC methods to remove DBPs, ICMs and other trace-level organic contaminants requires the development of novel electrocatalytic materials, elimination of mass transfer limitations via innovative design of 3D electrodes and EC reactors, and further progress in the understanding of intrinsic mechanisms of EC reactions of DBPs and TrOC at EC interfaces.

• 한국수정란이식학회지
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• 제32권3호
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• pp.123-130
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• 2017

This study was conducted to investigate the effects of alpha-lipoic acid (aLA) as an antioxidant that decrease the reactive oxygen species (ROS) in bovine embryonic development. Slaughterhouse derived bovine immature oocytes were collected and 4 different concentrations (0, 5, 10 and 20 mM) of aLA was supplemented in bovine in vitro maturation (IVM) medium. After 20 hrs of IVM, maturation rates, levels of ROS and glutathione (GSH), and further embryonic development after parthenogenetic activation (PA) and in vitro fertilization (IVF) was investigated according to aLA concentrations. Maturation rate was significantly higher in 10 mM group than other groups (80.5% vs. 62.9, 73.9, 64.2%; P<0.05). In the levels of ROS and GSH in matured oocytes as an indicator of oocyte quality, significantly better results were shown in 5 and 10 mM groups compared with other 2 groups. After IVM, significantly higher rates of blastocyst formation were shown in 10 mM groups in both of PA (27.9% vs. 18.8, 22.3, 14.2%; P<0.05) and IVF (32.6% vs. 23.9, 27.3, 16.2%; P<0.05) embryos. In addition, significantly more cell total cell number and higher inner cell mass ratio in 10 mM PA and IVP blastocysts showed developmental competence in 10 uM groups. Therefore, based on the entire data from this study, using $10{\mu}M$ of aLA confirmed to be the optimal concentration for bovine oocyte maturation and embryonic development.

• 한국미생물·생명공학회지
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• 제48권3호
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• pp.344-357
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• 2020

Streptococcus zooepidemicus 유래의 세포외 고분자물질인 히알루론산(hyaluronic acid) (HA)을 대량 생산하기 위해, 균주 개량, 생산배지 및 배양공정 개발에 관한 연구를 수행하였다. HA 고생산성 변이주를 선별하기 위해 약 99%의 사멸률을 보이는 ethylmethane sulfonate (EMS) 처리조건을 적용해서, 지속적인 random screening 방법으로 고생산성, 고안정성의 변이주들을 선별할 수 있었다. HA를 고농도로 생산하기 위해서는, 이 균주의 생화학 및 배양생리적 특성에 기반한 최적 배지개발이 필수적이라고 판단하여, one-factor-at-a-time (OFAT), full factorial design (FFD), steepest ascent method (SAM) 및 response surface method (RSM) (반응표면분석법)을 순차적으로 적용하여 통계적 배지 최적화 실험을 수행하였다. 최적 배지조성에서 플라스크 배양에 의한 HA 생산성은 5.38 g/l로서, 이전 배지(3.54 g/l)에 비해 약 52% 향상된 생산량을 얻을 수 있었다. 또한 선별된 우량균주와 최적화된 생산배지를 이용하여 5 L 발효조에서 배양공정 최적화 연구를 수행하였다. 이 균주의 생리학적 특성을 고려할 때, HA 생산성을 높이기 위해서는 (배양 중 HA 축적으로 인해 고점도를 띠는) 배양액으로의 충분한 용존산소 공급이 매우 중요한 요인인 것으로 판단되었다. 따라서 용존산소 공급과 밀접하게 관련있는 발효조의 교반시스템(교반 날개 종류, 크기 및 배치 등) 및 교반속도에 대한 최적화 연구를 수행하였다. 그 결과, 교반축 하부에는 Rushton turbine-type, 상부에는 marine-type의 확장된 교반날개(기존 대비 직경 1.3배 확장)가 설치된 경우, 450 rpm에서 강화된 혼합력과 충분한 용존산소 공급으로 인해 HA 생산성이 기존 플라스크 배양 대비 약 1.8배(9.79 vs. 5.38 g/l) 더 높은 것으로 확인되었다. 최종적으로 HA 배양공정의 scale-up 가능성을 확인하기 위해, pilot 규모의 50 L 발효조 배양을 최대 300 rpm의 교반속도에서 수행하였다. 처음으로 시도한 50 L 배양임에도 불구하고, HA 최대 생산성 면에서 볼 때, 5 L 발효조 결과와 거의 동일한 수준(98.5%) (9.11 vs 9.25 g/l)의 생산량을 얻을 수 있었다. 반면 지수기 성장단계인 배양 15시간까지의 50 L 배양의 HA 평균생산속도(r_p)는 0.46 g/l/hr로서 0.62 g/l/hr인 5 L 배양 대비 약 74% 정도에 머무는 것으로 나타났다. 따라서 생산 발효조의 scale-up 시, 생산균주의 전단응력 민감성(shear damage)을 함께 고려하면서, 산소전달계수(k_La)를 기반으로 하는 교반시스템에 대한 체계적인 연구가 진행된다면, HA 생산속도도 증가될 수 있는 긍정적인 결과를 얻을 수 있을 것으로 기대된다.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2000년도 춘계학술발표대회
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• pp.89-91
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• 2000

Polynuclear aromatic hydrocarbon (PAH) compounds are highly carcinogenic chemicals and common groundwater contaminants that are observed to persist in soils. The adherence and slow release of PAHs in soil is an obstacle to remediation and complicates the assessment of cleanup standards and risks. Biological degradation of PAHs in soil has been an area of active research because biological treatment may be less costly than conventional pumping technologies or excavation and thermal treatment. Biological degradation also offers the advantage to transform PAHs into non-toxic products such as biomass and carbon dioxide. Ample evidence exists for aerobic biodegradation of PAHs and many bacteria capable of degrading PAHs have been isolated and characterized. However, the microbial degradation of PAHs in sediments is impaired due to the anaerobic conditions that result from the typically high oxygen demand of the organic material present in the soil, the low solubility of oxygen in water, and the slow mass transfer of oxygen from overlying water to the soil environment. For these reasons, anaerobic microbial degradation technologies could help alleviate sediment PAH contamination and offer significant advantages for cost-efficient in-situ treatment. But very little is known about the potential for anaerobic degradation of PAHs in field soils. The objectives of this research were to assess: (1) the potential for biodegradation of PAH in field aged soils under denitrification conditions, (2) to assess the potential for biodegradation of naphthalene in soil microcosms under denitrifying conditions, and (3) to assess for the existence of microorganisms in field sediments capable of degrading naphthalene via denitrification. Two kinds of soils were used in this research: Harbor Point sediment (HPS-2) and Milwaukee Harbor sediment (MHS). Results presented in this seminar indicate possible degradation of PAHs in soil under denitrifying conditions. During the two months of anaerobic degradation, total PAH removal was modest probably due to both the low availability of the PAHs and competition with other more easily degradable sources of carbon in the sediments. For both Harbor Point sediment (HPS-2) and Milwaukee Harbor sediment (MHS), PAH reduction was confined to 3- and 4-ring PAHs. Comparing PAH reductions during two months of aerobic and anaerobic biotreatment of MHS, it was found that extent of PAHreduction for anaerobic treatment was compatible with that for aerobic treatment. Interestingly, removal of PAHs from sediment particle classes (by size and density) followed similar trends for aerobic and anaerobic treatment of MHS. The majority of the PAHs removed during biotreatment came from the clay/silt fraction. In an earlier study it was shown that PAHs associated with the clay/silt fraction in MHS were more available than PAHs associated with coal-derived fraction. Therefore, although total PAH reductions were small, the removal of PAHs from the more easily available sediment fraction (clay/silt) may result in a significant environmental benefit owing to a reduction in total PAH bioavailability. By using naphthalene as a model PAH compound, biodegradation of naphthalene under denitrifying condition was assessed in microcosms containing MHS. Naphthalene spiked into MHS was degraded below detection limit within 20 days with the accompanying reduction of nitrate. With repeated addition of naphthalene and nitrate, naphthalene degradation under nitrate reducing conditions was stable over one month. Nitrite, one of the intermediates of denitrification was detected during the incubation. Also the denitrification activity of the enrichment culture from MHS slurries was verified by monitoring the production of nitrogen gas in solid fluorescence denitrification medium. Microorganisms capable of degrading naphthalene via denitrification were isolated from this enrichment culture.

• 분석과학
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• 제10권1호
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• pp.66-74
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• 1997

지름 2.54cm, 길이 10cm인 유리관에 tyrosinase(EC. 1.14.18.1)를 입자의 크기 $550{\mu}m$인 탄소에 고정시켜 충진하고, 페놀과 산소를 기질로 사용하여 tyrosinase의 반응 특성을 조사하기 위해 axial dispersion 모델을 제안하였다. 본 논문에서 페놀의 농도는 55.5mM로 고정시키고 산소(2.7ppm, 5.4ppm, 그리고 9.5ppm)와 유속 (1~3mL/s)을 변화시키면서 탄소에 고정된 tyrosinase의 반응을 관찰하였다. 또한, Damkolher수를 계산하고 분산 특성과 식으로부터 효소반응 속도 및 분산의 영향을 예측하기 위해 수치적 해석을 하였다. 연구 결과 물질저항은 주로 외부 전달과 내부확산이었으며, 제안된 모델에서 Biot수는 64.25였다. 페놀은 1.0mL/s 정도의 느린 속도에서 산소의 농도가 높을수록 높은 전환율을 나타내었다. 한편, axial dispersion 모델과 plug flow 모델의 비교에서는 모두 같은 전환율을 나타내어 axial dispersion 모델이 반응속도와 무관함을 알 수 있었다.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2002년도 춘계 학술발표회 논문집
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• pp.227-234
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• 2002

With the increasing environmental consideration and stricter regulations, gasification of waste is considered to be more attractive technology than conventional incineration for energy recovery as well as material recycling. The experiment for combustible waste mixed with plastic and cellulosic materials was performed in the fixed bed gasifier to investigate the gasification behavior with the operating conditions. Waste pelletized with a diameter of 2~3cm and 5cm of length was gasified at the temperature range of 1100~145$0^{\circ}C$. It was shown that the composition of H$_2$ was in the range of 30~40% and CO 15~30% depending upon oxygen/waste ratio. Casification of waste due to thermoplastic property from mixed plastic melting and thermal cracking shows a prominent difference from that of coal or coke. It was desirable to maintain the top temperature up to foot to ensure the mass transfer and uniform reaction through the packed bed. As the bed height was increased, the formation of H$_2$ and CO was increased whilst $CO_2$ decreased by the char-$CO_2$ reaction and plastic cracking. From the experimental results, the cold gas efficiency was around 61% and heating values of product gases were in the range of 2800~3200㎉/Nm3.

• 한국환경보건학회지
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• 제40권2호
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• pp.147-156
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• 2014

Objectives: This study was carried out to examine whether the apparent photolysis with or without sensitizers [NaOH and humic acid (HA)] was prompted photodegradation of polychlorinated biphenyl (PCB) in aqueous solution. Methods: PCBs photodegradation occurred using fluorescence black lamps at ${\lambda}_{max}=300nm$. PCB congeners were exposed in 10 ppm HA or 0.05N NaOH solutions, to investigate the decreasing profile of PCB concentration with time. The PCBs were then analyzed by gas chromatography/mass spectrometry (GC-MS). Reductive degradation profile of PCB congeners in the presence of both sensitizers under oxygen-saturated protic conditions was described using the wind-rose diagrams. Results: Use of HA or NaOH decreased PCB concentration with time in the dark and on irradiation, indicating that photolysis underwent through reductive dechlorination through energy transfer and possibly with reactive oxygens. The dechlorination was marked by a chromatographic shift, observed in the GC-MS plots. Therefore it is logical to assume that increasing the dose of sensitizers would increase the photodegradation rates of PCBs. The half-lives of pentachloro-PCB (penta-3) in 0.05N NaOH and 10 ppm HA were estimated at about 47 hours and 39 hours, respectively, under the same experimental conditions of photolysis. It was found that the rate of photolysis of pentachloro-PCB in aqueous solution followed apparent first-order kinetics compared to other congeners. Conclusion: Photochemical degradation (using 328 nm UV light) of penta- and hexa-PCBs in HA or alkaline solution is a viable method for pretreatment method. The results are helpful for the further comprehension of the reaction mechanism for photolytic dechlorination of PCBs in aquatic system.

• 한국수소및신에너지학회논문집
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• 제29권1호
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• pp.41-55
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• 2018

General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.