• Journal of Microbiology and Biotechnology
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• v.15 no.5
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• pp.946-951
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• 2005

Biodegradation of the endocrine-disrupting chemical di-n-butyl phthalate (DBP) was investigated using a bacterium, Pseudomonas fluorescens B-1, isolated from mangrove sediment. The effects of temperature, pH, salinity, and oxygen availability on DBP degradation were studied. Degradation of DBP was monitored by solid-phase extraction using reversed-phase HPLC and UV detection. The major metabolites of DBP degradation were identified as mono-n-butyl phthalate and phthalic acid by gas chromatography-mass spectrometry (GC-MS) and a pathway of degradation was proposed. Degradation by P. fluorescens B-1 conformed to first-order kinetics. Degradation of DBP was also tested in seawater by inoculating P. fluorescens B-1, and complete degradation of an initial concentration of $100{\mu}g/l$ was achieved in 144 h. These results suggest that DBP is readily degraded by bacteria in natural environments.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.169-176
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• 2001

The sediment at the majority of fishery harbors located on the east coast of Korea are affccted by the waves and wave-induced currents as the main external force. And the surroundings of the harbors are composed of sandy beaches. Because many harbors are small and their entrances are located in the wave¬breaking zone, they suffer severe siltation and topographical changes. In order to solve the problems, we have to understand the mechanism through estimations and accurate reproduction of the harbor siltation phenomenon. We suggest economically substantial countermeasures for harbor siltation in the small fishery harbors and investigate the preventive effects using a numerical simulation technique.

• Journal of Ocean Engineering and Technology
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• v.20 no.4 s.71
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• pp.58-63
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• 2006

When the costal zone surrounded by a breakwater has a narrow vertical opening, currents in the vicinity of a narrow entrance can result in a jet flow, coinciding with the tide. Such a Tidal-Jet Generator(TJG) can change the water mass distribution and transport processes in the domain of influence of the jet. Also, it can decrease the residual time of them. In the present study, the water purification utilizing tidal jets in the coastal zone over constant bathymetry are estimated numerically, using a finite-difference numerical scheme, named the NS-MAC-TIDE method, which isbased on the fully 3D Navier-stokes(NS) equations. The shear velocity near the inlet of the TJG are predicted from the flow field simulation, and are assessed qualitatively with the development of scouring or sediment that is caused by the change of diffusion or sweeping flowup from the seabed of sediment particles. Finally, through solving a transport equation of concentration, the residual time related on mass transport processes and the flushing mechanism for water purification are investigated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.644-653
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• 2018

Landslides occur frequently due to the effects of heavy rainfall and typhoons caused by climate change. Erosion control measures are needed to effectively prevent landslide damage. In order to improve their efficiency, it is necessary to quantitatively measure the sediment discharge from the mountain stream. In this study, a load cell sensor was installed in a mountain stream and the measured values were compared according to the applicability and load test type in the mountain stream. The result of the load test showed that the effect of the loading type (load test 1, 2) was low at average (loadings) of 0.4kgf and 0.6kgf at sites 1 and 2, respectively. The load factor was also derived by regression analysis to increase the accuracy of the measured values. According to the results of the load factor (normalized) to the load-cell measurement value, the output value increased by 14.8% and 24.6% in sites 1 and 2, respectively, and was calculated to be similar to the reference value. The load cell sensor enabled us to quantitatively estimate the amount of sediment discharge in the mountain stream through time series analysis with the water level and rainfall information. If the monitoring is carried out for a long time, it can be used to find the sediment discharge mechanism for the mountain stream. In addition, applying sensors such as load-cells to a mountain stream is expected to contribute to the development of related industries, such as the manufacturing of measurement sensors.

• Journal of the Korean Geosynthetics Society
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• v.12 no.4
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• pp.123-131
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• 2013

The patents trends registered in korea, the USA, Japan and Europe were analyzed to forecast the direction of R&D for the technology of sediment disaster. As a result of portfolio analysis, the number of patents in Korea have continued to rise, but have been placed behind the other countries. The level of technology of each country was investigated. In the survey technology and sensing technology, the Korean and USA situations were classified as a period of growth, and the Japanese situation was classified as a period of decline. In the control technology and protection technology, Korean situation was classified as a period of growth, and the Japanese situation was classified as a period of decline. As a result of analysis for a direction of R&D using blank technologies, standardization of analysis technologies for mechanism, fusion techniques between ICT and conventional techniques, development of eco-friendly materials and evaluation of structure should be developed by R&D in Korea.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.595-605
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• 1994

The field observations. data analyses and numerical experiments are performed to investigate the short and long term beach deformation mechanisms in Haeundae beach. The schematic diagrams of deposition and erosion mechanism due to the attack of typhoons are described from the analysis on the beach widths and profiles. The short term beach deformation depends strongly on the characteristics of incident waves and wave-induced currents. The main incident wave and the calibration parameters of the shoreline change model are determined using the beach width data. Beacause the main incident wave approaches obliquly from the SE direction, the net westward longshore sediment transport occurs. Therefore the unbalance of longshore sediment budget in the east of the beach where the sediment source dose not exist causes a beach erosion. On the other hand, the deposited sand in the west is lost offshore by the storm wave action.

• Journal of Microbiology and Biotechnology
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• v.13 no.3
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• pp.366-372
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• 2003

The production of microbiologically enriched cultures that degrade cis- 1,2-dichloroethylene(DCE) under anaerobic conditions was investigated. Among 80 environmental samples, 19 displayed significant degradation of $10{\mu}M$ cis-DCE during 1 month of anaerobic incubation, and one sediment sample collected at a landfill area (Nanji-do, Seoul, Korea) showed the greatest degradation ($94\%$). When this sediment culture was subcultured repeatedly, the ability to degrade cis-DCE gradually decreased. However, under Fe(III)-reducing conditions, cis-DCE degradation by the subculture was found to be maintained effectively. In the Fe(III)-reducing subculture, vinyl chloride (VC) was also degraded at the same extent as cis-DCE No accumulation of VC during the cis-DCE degradation was observed. Thus, Fe(III)-reducing microbes might be involved in the anaerobic degradation of the chlorinated ethenes. However, the subcultures established with Fe(III) could function even in the absence of Fe(III), showing that the degradation of cis-DCE and VC was not directly coupled with the Fe(III) reduction. Consequently, the two series of enrichment cultures could not be obtained that degrade both cis-DCE and VC in the presence or absence of Fe(III). Considering the lack of VC accumulation, both cultures reported herein may involve interesting mechanism(s) for the microbial remediation of environments contaminated with chlorinated ethenes. A number of fermentative reducers (microbes) which are known to reduce Fe(III) during their anaerobic growth are potential candidates involved in cir-DCE degradation in the presence and absence of Fe(III).

• 한국해양학회지
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• v.25 no.1
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• pp.26-35
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• 1990

Sound velocities and attenuation coefficients of marine surface sediments were calculated from insitu acoustic experiments on 4 nearshore areas off Pohang, Pusan Yeosu, and Kunsan around the Korean Peninsula. The relationship between these values and physical properties of sediments was examined and attenuation mechanism was analysed using the estimated gas content. Sound velocities and attenuation coefficients ranging from 1470 to 1616 m/sec and 0.0565 to 0.6604 dB/kHz-m, respectively, are well related to sediment types. The attenuation coefficient is maximum in coarse silts, and the sound velocity increases with density. The gas content estimated less than 8 ppm increases with the decreasing sediment grain size. When the sediment size is greater than fine sand, sound attenuation is mostly due to friction losses, and probably negligible viscous loss remains unchanged with the varying physical properties of sediments. The maximum attenuation in coarse silts result from both friction loss and cohesion of finer sediments between the contacts of silt grains. The cohesion begins to be the dominant dissipative process with decreasing grain size from medium and fine silts.

• The Korean Journal of Quaternary Research
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• v.5 no.1
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• pp.33-45
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• 1991

Sand bars associated with strong tidal currents are well developed in the subtidal zone near the Kokunsan islands. Tidal currents measured at sand bar in the area show an asymmetry in magnitude between flood and ebb currents. At the southern flank of the sand bar the currents are flood-dominant whereas the currents are ebb-dominant at the northern flank. The asymmetry is more distinctive as the currents become stronger during spring tide. Moreover, the flood-dominance along the southern flank is stronger than the ebb-dominance along the northern flank. Thus the flood current is more affective to the sand bar. The sandy bottom sediment is mostly transported as bedload by the tidal currents. The magnitude asymmetry of the tidal currents results in a net sediment movement in one direction. The direction is onshore in the south and offshore in the north, which may result in a net counterlookwise rotation of the sands around the sand bar. However, the sand bar may migrate towards onshore due to the more affective flood current in the south. The irregular V-shaped outline of the sand bar in the south also seem to reflect the strong effect of flood current.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.4
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• pp.209-220
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• 2019

Even though the scale of hard structures for beach stabilization should carefully be determined such that these structures do not interrupt the great yearly circulation process of beach sediment in which the self-healing ability of natural beach takes places, massive hard structures such as the submerged breakwater of wide-width are frequently deployed as the beach stabilization measures. On this rationale, asymmetric ripple mat by Irie et al. (1994) can be the alternatives for beach stabilization due to its small scale to replace the preferred submerged breaker of wide-width. The effectiveness of asymmetric ripple mat is determined by how effectively the vortices enforced at the contraction part of flow area over the mat traps the sediment moving toward the offshore by the run-down. In order to verify this hypothesis, we carry out the numerical simulations based on the Navier-Stokes equation and the physically-based morphology model. Numerical results show that the asymmetric ripple mat effectively capture the sediment by forced vortex enforced at the apex of asymmetric ripple mat, and bring these trapped sediments back to the beach, which has been regarded to be the driving mechanism of beach stabilization effect of asymmetric ripple mat.