• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.171-176
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• 2000

Bioremediation of hazardous hydrophobic organic compounds, such as polycyclic aromatic hydrocarbons (PAHs), is a major environmental concern due to their toxic and carcinogenic properties. Due to their hydrophobicity, the hydrophobic organic compounds are mainly associated with the soil organic matter or nonaqueous-phase liquids. A major question concerns the relationships between biodegradation and sorption. This work develops and utilizes a non- steady state model for evaluating the interactions between sorption and biodegradation of phenanthrene, a 3-ring PAH compound, in soil-slurry systems. The model includes sorption/desorption of a target compound, its utilization by microorganisms as a primary substrate existing in the dissolved phase and/or the sorbed phase in biomass and soil, oxygen transfer, and oxygen utilization as an electron acceptor. Biodegradation tests with phenanthrene were conducted in liquid and soil-slurry systems. The soil-slurry tests were performed with very different mass transfer rate: fast mass transfer in a flask test at 150 rpm, and slow mass transfer in a roller-bottle test at 2 rpm. In the slurry tests, phenanthrene was degraded more rapidly than in liquid tests, but with a similar rate in both slurry systems. Modeling analyses with several hypotheses indicate that a model without biodegradation of compound sorbed to the soil was not able to account for the rapid degradation of phenanthrene, particularly in the roller bottle slurry test. Reduced mass-transfer resistance to bacteria attached to the soil is the most likely phenomenon accounting for rapid sorbed-phase biodegradation.

• KSBB Journal
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• v.9 no.2
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• pp.211-223
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• 1994

In fermentations with a 4-liter stirred tank bioreactor, a better than two-fold enhancement of the gas-liquid mass transfer coefficient$(k_La)$ in the celite-immobilized fungal cultures of Tolypocladium in flatum over the parallel conventional free-cell was observed at identical biomass concentrations, despite the higher specific oxygen uptake rate of the immobilized fungi during exponential growth. As a result oxygen sufficient conditions, i. e., dissolve oxygen(D.O.) concentrations exceeding 75% air saturation, could be maintained throughout exponential growth period of the immobilized culture, in contrast to the suspended fungal culture, whose D.O. levels fell below 50% air saturation. A linear monotonic dependence of $k_La$ upon impeller agitaion rate was found for both immobilized and conventional cultivation modes over a range of 250 to 550rpm, the slope being a function of biomass concentration for the free but not for the immobilized cell system In contrasts oxygen transfer rate was a much weaker function of aeration rate up to about 2.5 vvm for both culture configurations. Above this level, aeration rate had no further effect on the mass transfer. In addition, the immobilized cultures sustained good morphological and physiological states, leading to almost two times higher cyclosporln A (CyA) productivity overt the parallel free cell system. These experiments suggest that the celite-immobilized fungal system in a stirred tank reactor has considerable promise for scaling up cyclosporin A production in terms of high-density cultivation.

• Applied Chemistry for Engineering
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• v.4 no.1
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• pp.153-161
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• 1993

Cathodic oxygen reduction kinetics on $La_{0.9}Sr_{0.1}MnO_3$ electrode have been examined at $700-900^{\circ}C$ under various oxygen partial pressures. AC impedance and current interruption techniques were employed for the determination of charge transfer resistances for electrochemical oxygen reduction. The $R_{ct}$ values obtained from two different methods were very close each other for $La_{0.9}Sr_{0.1}MnO_3$ electrode. Activation energy for the electrochemical oxygen reduction was found to be 174kJ/mol under atmospheric oxygen pressure. $R_{ct}$ measurements as a function of oxygen partial pressure indicate that the rate-determining step for the electrochemical oxygen reduction on $La_{0.9}Sr_{0.1}MnO_3$ electrode is the charge transfer process.

• Microbiology and Biotechnology Letters
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• v.20 no.4
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• pp.445-450
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• 1992

An enhancement of the oxygen transfer rate in a 1$\ell$ bioreactor for mammalian cell culture by using a silicone rubber tubing as an oxygenator was investigated. When the silicone membrane was used to supply oxygen to the culture broth, the oxygen transfer coefficients ($k_{\iota}a$) measured in deionized-distilled water were markedly increased. Effect of surface aeration without the tubing aeration was very low under $1.0hr^{-1}$ of $k_{\iota}a$. The enhancing effects of agitation rates on $k_{\iota}a$ were much more effective than those of aeration rates. The increase of $k_{\iota}a$ with increasing tube length was observed as a result of the large surface area for oxygen supply. However, 2 m of the tube length was adequate for a 1$\ell$ vessel. The larger blade type of impeller was effective to enhance the kLa values because of its high mixing intensity. In culture medium supplemented with 5% serum, kLa values were reduced to approximately 40% probably due to the viscosity. We also obtained the normal cell concentration of $5{\times}10^6$ cells/m$\ell$ of HepG2 on microcarriers, which could be achieved in a typical bioreactor for animal cell culture.

• Transactions of the Korean hydrogen and new energy society
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• v.12 no.3
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• pp.231-238
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• 2001

Electrocatalytic activity of palladium for hydrogen oxidation and reduction was studied using AC impedance method. The system under study was arranged in electrolytic mode consisting of Pd electrode under study, Pt counter electrode and Nafion electrolyte between them. Two types of Pd electrodes were used - carbon-supported Pd (Pd/C) and Pd foil electrode. Pd/C anode contacting pure hydrogen showed a steady decrease of charge transfer resistance with the increase of anodic overpotential, which is an opposite trend to that found with Pd foil anode. But Pd foil cathode also exhibited a decrease of the resistance with the increase of cathodic overpotential. The relationship between imposition of overpotential and subsequent change of the charge transfer resistance is determined by the ratio of the rate of faradaic process to the rate of mass transportation; if mass transfer limitation holds, increase of overpotential accompanies the increase of charge transfer resistance. Regardless of the physical type of Pd electrode, the anode contacting hydrogen/oxygen gas mixture did not reveal any independent arc originated from local anodic oxygen reduction.

• Korean Chemical Engineering Research
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• v.59 no.2
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• pp.276-280
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• 2021

The oxygen transfer rate at the liquid surface of the reciprocally shaking vessel was studied. The required power of the reciprocally shaking vessel was not proportional to the shaking frequency, unlike the rotational shaking vessel, and the liquid level suddenly fluctuated greatly at a certain frequency as the flow pattern in the vessel was a left and right wave flow different from that of the rotational shaking that has a rotational flow. The effect of the shaking frequency on the required power in the reciprocally shaking vessel was very complex, such as less power required than the rotational shaking vessel when the shaking frequency is more than 3 s-1, but the required power for the range of the generated rotational flow in the reciprocally shaking vessel could be correlated with the equation that was reported for the rotational shaking vessel. The kLa (mass transfer capacity coefficient) in the reciprocally shaking vessel also increased in a complex pattern because the required power for shaking was not consumed in a simple pattern, unlike kLa in the rotational shaking vessel, which increases linearly with increasing frequency. The kLa of the reciprocally shaking vessel was larger than the kLa of the rotational shaking vessel, and as the kLa value increased, the difference between them increased sharply. As a result, the oxygen transfer rate in the reciprocal motion was greater than that of the rotational motion, and could be correlated with the required power per unit volume.

• Bulletin of the Korean Chemical Society
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• v.16 no.1
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• pp.21-26
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• 1995

Electrochemical reduction of oxygen has been carried out at glassy carbon electrode and carbon ultramicroelectrode, the surface of which is modified with a new Co(Ⅱ)-Schiff base complex, Co(Ⅱ)-3,4-bis(salicylidene diimine)toluene in 1 M KOH solution. The results obtained from cyclic voltammetric and chronoamperometric experiments are consistent with the formation of the reasonably stable superoxide ions as a primary electron transfer reaction product. The exchange rate constant obtained for oxygen reduction is about 0.02 cm/s.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.267-270
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• 2005

We investigate the spectral energy distributions (SEDs) of low mass-loss rate O-rich asymptotic giant branch (AGB) stars using the infrared observational data including the Infrared Space Observatory (ISO) data. Comparing the results of detailed radiative transfer model calculations with observations, we find that the dust formation temperature is much lower than 1000 K for standard dust shell models. We find that the superwind model with a density-enhanced region can be a possible alternative dust shell model for LMOA stars.

• KSBB Journal
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• v.13 no.6
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• pp.700-705
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• 1998

Studies were made to investigate effects of the scale-up of stirred tank bioreactors on cell growth and alkaloids production for suspension cultures of Eschscholtzia californica. In the 1.5 L STR, cell lysis was observed at 110 rpm or higher agitation speed. The agitation speed of 30 L STR was 43.7 rpm to maintain the same shear stress developed in 1.5 L STR of 100 rpm. As a result of scale-up from 1.5 L to 30 L STR, the specific growth rate was decreased from 0.12 to 0.07 day-1. The alkaloids productivity was also decreased from 0.24 to 0.14 mg/L-day. Changes of mixing performance and oxygen transfer were studied to explain the decrease of cell growth and alkaloids production. Decreased oxygen transfer rate coefficient(KLa) and increased mixing time by the scale-up was observed at various aeration rates.

• Bulletin of the Korean Chemical Society
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• v.18 no.11
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• pp.1175-1179
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• 1997

The adsorption of oxygen on ZnO was monitored by measuring the capacitance of two contacting crystals which have depletion layers originated from the interaction between oxygen and ZnO at 298 K-473 K. An admission of oxygen to the sample induced an irreversible increase in the depth and the amount of adsorbed oxygen was less than 0.001 monolayer in the experimental condition. The relation between pressure of oxygen and variation of the depth was tested from the view point of Langmuir or Freundlich isotherm. Using Hall effect measurement and kinetic experiment, a model equation on the adsorption process was proposed. From the results, it was suggested that oxygen adsorption depended on the rate of electron transfer from ZnO to oxygen while the amount of adsorbed oxygen was kinetically restricted by the height of surface potential barrier.