• Journal of Korean Society of Water and Wastewater
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• v.27 no.3
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• pp.383-394
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• 2013

A sedimentation basin is used to remove suspended sediments which can cause abrasive and erosive wear on hydraulic turbines of hydropower plants. This sediment erosion not only decreases efficiency of the turbine but also increases maintenance costs. In this study, the three-dimensional numerical simulations were carried out on the overseas hydropower project. The simulations of flow and suspended sediment concentration were obtained using FLOW-3D computational fluid dynamics code. The simulations provide removal efficiency of a sedimentation basin based on particle sizes. The influence of baffles on the flow field and the removal efficiency of suspended sediments in the sedimentation basin has been investigated. This paper also provides the numerical simulations for sediment-induced density currents that may occur in the sedimentation basin. The simulation results indicate that the formation of density currents decreases the removal efficiency. When a baffle is installed in the sedimentation basin, the baffle provides intensive settling zones resulting in increasing the sediments settling. Thus the enhanced removal efficiency can be achieved by installing the baffle inside the sedimentation basin.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.99-104
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• 2008

Zeta potential, sedimentation bulk density and rheology in the dispersion system have been studied in terms of solid loading (40-55 vol%), and types of additives. Ammonium polymethacrylate, glycerol, ethoxylated acetylenic diol, and polyvinyl alcohol have been used as the dispersant, cryo-protectant, surfactant, and binder, respectively. Sedimentation density greatly increased upon adding dispersant; the effect was more pronounced with ionic alumina suspension compared with covalent silicon carbide. With further addition of cryo-protectant and surfactant to dispersant, the sedimentation density increased somewhat. The suspension viscosity generally behaviored in an opposite manner to the sedimentation density, i.e., high sedimentation gave low high-shear viscosity, indicative of low order structure formation in the suspended particles. Shear rate rheology in shear rate of $2-300\;sec^{-1}$ showed a shear thinning and its onset began at similar shear rate (${\sim}100\;sce^{-1}$), regardless of solid loading.

• Journal of Environmental Science International
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• v.15 no.12
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• pp.1177-1183
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• 2006

This study was carried out to evaluate effect of sludge characteristics (pH, SVI, anaerobic storage, wet density and growth phase) on the sedimentation of bulking sludge of paper manufacturing plant. The results showed that mix hulking sludge with sewage sludge (10-60%) caused the decrease of SVI, the settled sludge concentration was increased. Increase of anaerobic storage time (0 to 8 day) was increased SVI, sedimentation performance was deteriorated. The sedimentation was improved by addition of loess (0.2-5.0 g/L), because wet density of sludge was increased and SVI was decreased. At an exponential phase, the ratio of sedimented/growthed sludge concentration was decreased, the ratio was increased after stationary phase.

• Animal cells and systems
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• v.7 no.4
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• pp.295-301
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• 2003

Effects of the settlement density of germlings and canopy on settled germlings of Fucus serratus were investigated on the rocky shore of the Isle of Man. The survival of transplanted germlings was mainly determined by parent canopy rather than by initial settlement density of germlings. However, germling growth was greater at low density than at high density and enhanced by canopy removal. Recruitment by natural propagules was stimulated at high settlement density and maximal recruits occurred on caged slides under the canopy. On the experimental slides, tiny snails and sedimentation were ,found. The number of snails was positively related with the settlement density of germ lings indicating that they fed the germlings. Sedimentation and snail number were greater with canopy removal treatments than in canopy intact ones. These indicate that ,canopy sweeping gives benefits to germlings by removing sediment from substrata and protecting them from herbivores. In conclusion, the survival of settled F. serratus germlings is mainly determined by canopy sweeping and their growth is retarded in the presence of a canopy and at high settlement density.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.7
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• pp.726-731
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• 2005

Sedimentation is treated as the most important unit process in waterworks, and plays great role on turbidity removal efficiency. Rectangle sedimentation basin is the most widely accepted sedimentation process. But it has some problems with short-circuit flow and density flow caused by temperature and influent turbidity variation. To solve these problems, installation of rectification wall was suggested, but not generally fully accepted in field. Because hole of rectification wall cause jet flow. In this research, use of moving baffle was investigated. Moving baffle was designed to induce uniform velocity at every section of water flow. The baffle walls was made from soft fiber materials. The baffle walls with flow of sedimentation basin moves at same speed. It is like that it controls density flow and short-circuit flow and induce uniform velocity at every section of water flow in sedimentation basin. When moving baffle was operated retention time of sedimentation basin was extended to 1 hours. When it talked again and the effluent time of highest concentration of the chlorine ion from 100 minutes was extended to 160 minutes. Turbidity removal efficiency was tested with different operation modes(continuous and batch) with influent turbidity and retention time. It was revealed that turbidity removal efficiency carl be improved up to 36%(continuous mode) and 58%(batch mode) respectively. Consequently if moving baffle introduces in Rectangle sedimentation basin, it forecasts that the turbidity improvement above 30% will be possible.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.4
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• pp.107-113
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• 2009

This paper considers the influence of floc on the sedimentation rate for the cohesive material. The effects of floc density and size changes were also taking into consideration during the experiment. The settling velocity of a discrete floc was measured in a quiescent water column. Floc diameter and density were investigated using a modified Stokes equation with some constants such as water density, viscosity, material density and the floc fractal dimension $n_f$ obtained from the relationship between the floc diameter and the floc settling. The floc diameter of quartz and alumina increased at increasing initial concentrations. The floc size of quartz with increasing NaCl concentration varied between approximately 0.8 um to $10{\mu}m$. Floc density decreased as floc size increased. The floc settling velocity and the floc diameter have a straight line relationship on a logarithm. The floc fractal dimension nf was 2.65 with increasing of initial concentration and 2.93 with increasing of NaCl. The exponent n to predict the settling velocity was proposed and varied from 1 to 1.93.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.2
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• pp.191-200
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• 2004

DAF process has been designed considering raw water quality characteristics in Korea. Although direct filtration is usually operated, DAF is operated when the freshwater blooms occut or raw water turbidity become high. Pre-sedimentation iS prepared in case when raw water turbidity is very high by rainstorms. A main feature of this plant is that the operation mode can be changed (controlled) based on the characteristics of raw water to optimize the effluent quality and the operation costs. Treatment capacity (surface loading rate) and efficiency of DAF was found to be better than conventional sedimentation process. Moreover, low-density particles (algae and alum flocs) are easily separated while it is difficult to remove in sedimentation. One of the main concerns in adoption of DAF (Dissolved Air-Flotation) process is a high raw water turbidity problem. That is, DAF is not adequate for raw water, which is more turbid than 100NTU. In order to avoid this problem, pre-sedimentation basins are prepared in DAF plant to decrease the turbidity of DAF influent. For simulation of the actual operation, bench and full-scale tests were performed for highly turbid water conditions. Consequently, DAF process coupled with sedimentation is suggested that pre-sedimentation with optimum coagulation prior to DAF would be appropriate.

• Journal of the Korean Geotechnical Society
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• v.22 no.9
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• pp.5-14
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• 2006

Generally, the sediments contain significant water, clay, colloidal fraction and contaminants, and can result in soft strata with high initial void, and its potential hazards in subsurface environments exist. Electrokinetic technique has been used in sedimentation for volume reduction of slurry tailing wastes and in remediation for extraction of contaminants from contaminated soils. In this research, the coupled effects of sedimentation and remediation of contaminated sediments are focused using electrokinetic sedimentation and remediation techniques from experimental aspects. A series of laboratory experiments including variable conditions such as initial solid content of the specimen, concentration level of the contaminant, and magnitude of applied voltage are performed with the contaminated sediment specimens mixed with ethylene glycol. Commercially available high specification Kaolin was used to simulate slurried sediment. From the test results, the settlement of specimen increases with increasing of applied voltage and decreasing of solid content and contamination level. The density of specimen increases due to settlement of specimen in the process of electrokinetic sedimentation and decreases due to extraction of organic contaminant in the process of electrokinetic remediation.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.37 no.1
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• pp.24-32
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• 2004

A mathematical model is used to investigate nitrogen dynamics in the intensive aquaculture ponds in the western coast of Korea. Parameters associated with water quality, sediments and growing of shrimp (Fenneropenaeus chinensis) are measured to calibrate the model for feeding ponds A and B and storage ponds. The model describes the fate of nitrogen including loadings of ammonia from feeds, phytoplankton assimilation, nitrification, sedimentation, volatilization and discharge. The model obtains good agreements with the measured values of TAN $(NH_4,\;NH_3),\;NO(NO_2,\;NO_3)$ and Chl (chlorophyll a). Impacts of water exchange on TAN and Chl are investigated, showing that the range of 0.01-0.2 (/day) cannot effectively reduce TAN but reduces Chl. Nitrogen in the ponds A is removed by sedimentation $66\%,$ volatilization $8\%,$ discharge of particulate and dissolved $8\%.$ The pond B shows $56\%\;and\;26\%$ of sedimentation and volatilization, respectively, to yield $10\%.$ decrease and 8c/o increase compared to those in the pond A. While the pond A has larger area (1.02:0.66 ha) and same stocking density (0.025 md./L) at the beginning of culture, the pond B obtains higher stocking density (0.0065:0.0091 md./L), longer feeding period (103:121 day) and resultant higher shrimp production (1.15:2.13 t/ha/cycle) at harvest. This is possibly due to the hydraulic characteristics driven by paddlewheels. At low ratio of the low speed area and the pond area, the rate of sedimentation is high, while the rate of gas exchange is low. Thus, the measurement and model analysis suggest that water quality and shrimp production are positively correlated with the hydraulic characteristics in the shrimp ponds.

• KSBB Journal
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• v.9 no.5
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• pp.457-463
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• 1994

A new method that considers the pellet sedimentation characteristics for fungal cell concentration measurement was developed using optical density. Appropriate mixing of the pellet suspension almost homogeneously was tried to prevent the sedimentation of the pellet by a small magnetic bar in cuvette, giving a stable optical density. The linear relationship between optical density and the dry cell weight was obtained. However, different curved lines were observed according to the pellet size. Optical density couldn't be detectable in the size range of $355{\mu}m$above. It was concluded from the result that the use of optical density for measuring cell concentration in fungal broth became possible by considering the characteristics.