• Journal of Korean Society of Water and Wastewater
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• v.26 no.6
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• pp.779-786
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• 2012

The degradation of 2-chlorophenol(2-CP) by various AOPs(Advanced Oxidation Processes) including the photo-Fenton process has been examined. In sole $Fe^{2+}$, UV or $H_2O_2$ process without combination, low removal efficiencies have been achieved. But the photo-Fenton process showed higher removal efficiency for degradation of 2-chlorophenol than those of other AOPs including the Fenton process and the UV processes. In the photo-Fenton process, the optimal experimental conditions of 2-chlorophenol degradation were obtained at pH 3 and the $Fe^{2+}/H_2O_2$molar ratio of 1. Also the 2-chlorophenol removal efficiency increased with decreasing of the initial 2-chlorophenol concentration. 3-chlorocatechol and chlorohydroquinone were identified as photo-Fenton reaction intermediates, and a degradation pathway of 2-chlorophenol in the aqueous phase during the photo-Fenton reaction was proposed.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.1
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• pp.31-38
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• 2013

The degradation of 4-chlorophenol(4-CP) by various AOPs(Advanced Oxidation Processes) with continuous feeding of $H_2O_2$, including the ultraviolet/hydrogen peroxide, the Fenton and the photo-Fenton process has been investigated. The photo-Fenton process showed the highest removal efficiency for degradation of 4-chlorophenol than those of other AOPs including the Fenton process and the combined UV process with continuous feeding of $H_2O_2$. In the photo-Fenton process, the optimal experimental condition for 4-CP degradation was obtained at pH 3. Also the 4-CP removal efficiency increased with decreasing of the initial 4-CP concentration. 4-chlorocatechol and 4-chlororesorcinol were identified as photo-Fenton reaction intermediates, and the degradation pathways of 4-CP in the aqueous phase during the photo-Fenton reaction were proposed.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.1
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• pp.27-37
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• 2021

Tetracycline is one of the most commonly used as antibiotics for the livestock industry and it is still widely used nowadays. Tetracycline and its metabolites are excreted with excrement, which is difficult to completely removed with conventional sewage treatment, therefore it is apprehended that the tetracycline-resistant bacteria occurs. In this study, the oxidant named ferrate(VI) was used to degrade the tetracycline and investigate the reaction between ferrate(VI) and tetracycline under various aqueous conditions. The highest degradation efficiency of tetracycline occurred in basic condition (pH 10.1 ± 0.1) because of the pKa values of tetracycline and ferrate(VI). The results also showed the effect of water temperature on the degradation of tetracycline was not significant. In addition, the dosage of ferrate(VI) was higher, the degradation of tetracycline and the self-degradation of ferrate(VI) also higher, finally the efficiency of ferrate(VI) was lower. The results said that the various mechanisms effects the reaction of ferrate(VI) oxidation, it required the consideration of the characteristics of the target compound for optimal degradation efficiency. Additionally, intermediate products were detected with LC/MS/MS and three degradation pathways were proposed.

• Journal of Microbiology and Biotechnology
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• v.23 no.6
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• pp.864-871
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• 2013

The recombinant strain P. pastoris GS115-lccC was used to produce laccase with high activity. Factors influencing laccase expression, such as pH, methanol concentration, copper concentration, peptone concentration, shaker rotate speed, and medium volume were investigated. Under the optimal conditions, laccase activity reached 12,344 U/L on day 15. The recombinant enzyme was purified by precipitating and dialyzing to electrophoretic homogeneity, and was estimated to have a molecular mass of about 58 kDa. When guaiacol was the substrate, the laccase showed the highest activity at pH 5.0 and was stable when the pH was 4.5~6.0. The optimal temperature for the laccase to oxidize guaiacol was $60^{\circ}C$, but it was not stable at high temperature. The enzyme could remain stable at $30^{\circ}C$ for 5 days. The recombinant laccase was used to degrade chlorpyrifos in several laccase/mediator systems. Among three synthetic mediators (ABTS, HBT, VA) and three natural mediators (vanillin, 2,6-DMP, and guaiacol), vanillin showed the most enhancement on degradation of chlorpyrifos. Both laccase and vanillin were responsible for the degradation of chlorpyrifos. A higher dosage of vanillin may promote a higher level of degradation of chlorpyrifos, and the 2-step addition of vanillin led to 98% chlorpyrifos degradation. The degradation of chlorpyrifos was faster in the L/V system ($k_{obs}$ = 0.151) than that in the buffer solution ($k_{obs}$ = 0.028).

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.372-378
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• 2018

Life management technology is required as the failure risk of aged power transformers increases. Asset management technology is developed to evaluate the remaining life, establish the replacement strategies, and decide the optimal investment based on the reliability and economy of power transformers. The remaining life assessment uses data such as installation, operation, maintenance, refurbishment, and failure of power transformers. The optimal investment also uses data such as maintenance, outage, and social costs. To develop the asset management system for power transformers, determining the degradation parameters related to the aging of power transformers and evaluating the condition of power transformers using these parameters are important. In this study, since 1983, 110,000 Dissolved Gas Analysis (DGA) data have been analyzed to determine the degradation parameters related to the aging of power transformers. The alarm rates of combustible gases ($H_2$, $C_2H_2$, $C_2H_4$, $CH_4$, and $C_2H_6$), TCG, CO, and $CO_2$ were analyzed. The end of life and failure rate (bathtub curve) of power transformers were also calculated based on the failure data from 1981 to 2014. The DGA gases related to discharge, overheating, and insulation degradation were determined based on alarm and failure rates. $C_2H_2$, $C_2H_6$, and $CO_2$ were discharge, oxidation, and insulation degradation parameters related to the aging of power transformers.

• KEPCO Journal on Electric Power and Energy
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• v.3 no.1
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• pp.23-28
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• 2017

The life management technology becomes important as the failure risk of the aged power transformers increases. Asset management technology, therefore, has been developed to evaluate the remaining life and build replacement strategies of power transformers, which enables an optimal investment decisions based on reliability and economic feasibility. The remaining life assessment technology uses data related to such as installation, operation, maintenance, refurbishment, and disposed history of power transformers. The optimal investment decision additionally uses data related to failure and social costs. To develop the asset management technology in power transformers, it is important to find deterioration parameters directly indicating degradation of power transformers. In this study, 110,000 DGA data during the past 35 years have been analyzed in order to find the deterioration parameters related to the degradation of power transformers. The alarm rates of combustible gases ($H_2$, $C_2H_2$, $C_2H_4$, $CH_4$, $C_2H_6$), TCG CO, and $CO_2$ were analyzed as deterioration parameters. The origin of the gas was discussed in connection with discharge, overheating and insulation aging.

• Journal of Environmental Health Sciences
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• v.33 no.5
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• pp.462-469
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• 2007

Isolation and application of oil-degradation microbes from the oil-contaminated soil and the determination of optimal operation conditions about the peat moss, the addition for the oil-biodegradation. After all experiments, we have acquired three important conclusions: First, we found out the 4 microbes, Pseudomonas fluorescens, Pseudomonas aeruinosa, Kurtia sp., Bacillus ceres, with excellent capability for the oil-degradation; Second, the optimal operating conditions of the peat moss for TPH treatment were pH $7{\sim}8$, temperature $25{\sim}30^{\circ}C$, water content 20%, mixing 2 times/ day, addition volume 2%; Third, in case of the application to the oil-contaminated soil with 4 mixed microbes, the removal efficiency of TPH was increased from 54% to 83% in oil-contaminated soil and from 65% to 85% in oil-contaminated soil with the peat moss.

• Journal of Microbiology and Biotechnology
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• v.28 no.6
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• pp.909-916
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• 2018

Previously, a cytosolic trehalase (TreH) from the hyperthermophilic archaeon Sulfolobus acidocaldarius was reported; however, the gene responsible for the trehalase activity was not identified. Two genes, saci_1816 and saci_1250, that encode the glycoside hydrolase family 15 type glucoamylase-like proteins in S. acidocaldarius were targeted and expressed in Escherichia coli, and their abilities to hydrolyze trehalose were examined. Recombinant Saci_1816 hydrolyzed trehalose exclusively without any help from a cofactor. The mass spectrometric analysis of partially purified native TreH also confirmed that Saci_1816 was involved in proteins exhibiting trehalase activity. Optimal trehalose hydrolysis activity of the recombinant Saci_1816 was observed at pH 4.0 and $60^{\circ}C$. The pH dependence of the recombinant enzyme was similar to that of the native enzyme, but its optimal temperature was $20-25^{\circ}C$ lower, and its thermostability was also slightly reduced. From the biochemical and structural results, Saci_1816 was identified as a trehalase responsible for trehalose degradation in S. acidocaldarius. Identification of the treH gene confirms that the degradation of trehalose in Sulfolobus species occurs via the TreH pathway.

• KSBB Journal
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• v.32 no.2
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• pp.96-102
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• 2017

The lignocellulose that is a major component of spent coffee ground was degraded and saccharified. To implement the spent coffee, after several pre-treatments, inoculation of Phanerochaete chrysosporium and solid-state fermentation were conducted. The optimal temperature of the enzymes (lignin peroxidase, manganese peroxidase, xylanase, laccase, and cellulase) for degradation of lignocellulose by P. chrysosporium was found. We also measured the maximum activity of enzymes (lignin peroxidase 0.15 IU/mL, manganese peroxidase 0.90 IU/mL, laccase 0.11 IU/mL, cellulase 5.87 IU/mL, carboxymethyl cellulase 9.52 IU/mL, xylanase 1.16 IU/mL) used for the process. As a result, 4.73 mg/mL of reduced sugar was obtained and 61.02% of lignin was degraded by solid state fermentation of P. chrysosporium on spent coffee ground.

• Journal of Microbiology and Biotechnology
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• v.13 no.2
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• pp.309-312
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• 2003

A bacterial strain NB01, isolated from wastewater, was found to utilize nitrobenzene (NB) as the sole source of nitrogen, carbon, and energy. The strain was classified as a member of a high G+C Gram-positive group and identified as Mycobacterium chelonae based on an analysis of its 16S rRNA gene sequence. The strain grew on NB with a concomitant release of about 63% of the total available nitrogen as ammonia, suggesting a reductive degradation mechanism. The optimal pH and temperature for degradation were PH 7.0-8.0 and $30^{\circ}C$, respectively. The cell growth was retarded at NB concentrations above 1.8 mM. The degradation of NB followed Michaelis-Menten kinetics within the tolerance range, and the $K_m$ and maximum specific removal rate for NB were 0.33 mM and $11.04\;h^{-1}$, respectively.