• Geomechanics and Engineering
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• v.35 no.4
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• pp.385-393
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• 2023

To analyze the consolidation with horizontal sand drains, the plane strain consolidation model under multi-ramp loading is established, and its corresponding analytical solution is derived by using the separation of variables method. The proposed solution is verified by the field measurement data and finite element results. Then, the effects of the loading mode and stress distribution on consolidation and dissipation of pore pressure are investigated. At the same time, the influence of hydraulic conductivity and thickness of sand blankets on soil consolidation are also analyzed. The results show that the loading mode has a significant effect on both the soil consolidation rate and generation-dissipation process of pore water pressure. In contrast, the influence of stress distribution on pore pressure dissipation is obvious, while its influence on soil consolidation rate is negligible. To guarantee the fully drained condition of the sand blanket, the ratio of hydraulic conductivity of the sand blanket to that of clay layer k_d/k_v should range from 1.0×10⁴ to 1.0×10⁶ with soil width varying from 100 m to 1000 m. A larger soil width correspondingly needs a greater value of kd/kv to make sure that the pore water can flow through the sand blanket smoothly with little resistance. When the soil width is relatively small (e.g., less than 100 m), the effect of thickness of the sand blanket on soil consolidation is insignificant. And its influence appears obvious gradually with the increase of the soil width.

• Journal of Animal Science and Technology
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• v.45 no.4
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• pp.641-648
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• 2003

In a batch mode treatment process, which electrolyzes the wastewater after derivation of N-P crystal formation and recovery, the characteristics of pollutant removal induced with the changes of loading rate and hydraulic retention time were studied. $MgCl_2$ was used as Mg source for the formation of struvite and the molar ratio of $MgCl_2$ to $PO_4^{3-}$ in influent was 1.3. When analyzing the average treatment efficiencies and removal characteristics obtained from four separate operations (Run I, II, III, IV), removal efficiencies of PO43- was not function of its loading rate. Under a condition of sufficient aeration and Mg source provided, over 88% of $PO_4^{3-}$ was eliminated by the formation of MAP without any pH adjustment, in spite of loading rate variation. An optimum-loading rate of NH4-N to achieve high removal efficiency was approximately $100g/m^3/d$. Below that loading rate, the removal of NH4-N was proportional to the loading rate into the system, and hence stable and high removal efficiency, over 90%, was achieved. However, when the loading rate increased over that rate, removal efficiency began to drop and fluctuate. Removal efficiency of TOCs was dependant upon the hydraulic retention time ($r^2$=0.97), not upon the loading rate. Stable and high color removal (94%) was obtained with 2 days of HRT in electrolysis reactor.

• Journal of Korean Society on Water Environment
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• v.16 no.4
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• pp.523-532
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• 2000

The purpose of this study was to investigate the effects of the hydraulic retention time (HRT) and organic loading rate (OLR) on microbial characteristics and treatment efficiency in sewage treatment using aerated submerged biological filter (ASBF) reactor. This reactor combines biodegradation of organic substrates by fixed biomass with a physical separation of biomass by filtration in a single reactor. Both simulated wastewater and domestic wastewater were used as feed solutions. The experimental conditions were a temperature of 17 to $27^{\circ}C$, a hydraulic retention time of 1 to 9hr, an organic loading rate of 0.47 to $3.84kg\;BOD/m^3{\cdot}day$ in ASBF reactor. This equipment could obtain a stable effluent quality in spite of high variation of influent loading rate. Total biomass concentration. biofilm thickness and biofilm mass increased an exponential function according to the increasing OLR. The relationships between water content and biofilm density were in inverse proportion. The percentage of backwash water to influent flow was almost 9%. The separation efficiency of biomass was the percentage of 91 to 92 in ASBF reactor. The sludge production rates in feed solutions of simulated wastewater and domestic wastewater were 0.14~0.26 kg VSS/kg BODrem, 0.43~0.48 kg VSS/kg BODrem, respectively.

• Journal of Korean Society of Water and Wastewater
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• v.11 no.1
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• pp.33-41
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• 1997

An attempt was made to enhance anaerobic treatment efficiency by adopting the anaerobic sequencing batch reactor(ASBR) process at a thermophilic temperature. Operational characteristics of the ASBR process were studied using laboratory scale reactors and concentrated organic wastewater composed of soluble starch and essential nutrients. Effects of fill to react ratio (F/R) were examined in the Phase I experiment, where the equivalent hydraulic retention time(HRT) was maintained at 5 days with the influent COD of 10g/L. A continuous stirred tank reactor(CSTR) was operated in parallel as a reference. Treatment efficiency was higher for the ASBRs because of continuous accumulation of volatile suspended solids(VSS) compared to the CSTR. However, the rate of gas production and organic removal per unit VSS in the ASBRs was much lower than the CSTR. This was caused by reduced methane fermentation due to accumulation of volatile acids(VA), especially for the case of low F/R, during the fill period. When the F/R was high, maximum VA was low and the VA decreased in short period. Consequently, more stable operation was possible with higher F/R. Effects of hydraulic loading rate on the efficiency was studied in the Phase II experiment, where the organic loading rate was elevated to 3333mg/L-d with the F/R of 0.12. Reduction of organic removal along with rapid increase of VA was observed and the stability of reaction was seriously impaired, when the influent COD was doubled. However, operation of the ASBR was quite stable, when the hydraulic loading rate was doubled and a cycle time was adjusted to 12 hour. It is essential to avoid rapid accumulation of VA during the fill period in order to maintain operational stability of the ASBR.

• Computers and Concrete
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• v.20 no.3
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• pp.339-350
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• 2017

Dynamic behaviours of reinforced concrete (RC) bending beams subjected to monotonic loading with different loading rates were studied. A dynamic experiment was carried out with the electro-hydraulic servo system manufactured by MTS (Mechanical Testing and Simulation) Systems Corporation to study the effect of loading rates on the mechanical behaviours of RC beams. The monotonic displacement control loading, with loading rates of 0.1 mm/s, 0.5 mm/s, 1 mm/s, 5 mm/s and 10 mm/s, was imposed. According to the test results, the effects of loading rates on the failure model and load-displacement curve of RC beams were investigated. The influences of loading rates on the cracking, ultimate, yield and failure strengths and displacements, ductility and dissipated energy capability of RC beams were studied. Then, the three-dimensional finite element models of RC beams, with the rate-dependent DP (Drucker-Prager) model of concrete and three rate-dependent model of steel reinforcement, were described and verified using the experimental results. Finally, the dynamic mechanical behaviours and deformation behaviours of the numerical results were compared with those of the experimental results.

• Journal of Korean Society on Water Environment
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• v.29 no.6
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• pp.808-812
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• 2013

A new type of microbial fuel cell (MFC) with anaerobic membrane filter was designed to produce bioelectricity and to treat domestic sewage at relatively high organic loading rate (OLR) of $6.25kgCOD/m^3/day$ and short hydraulic retention time (HRT) of 1.9 h. A following aeration system was applied to ensure effluent water quality in continuous operation. Glucose was supplemented to increase the influent concentration of domestic sewage. Influent substrate of 95% was removed via the MFC and following aeration system and the corresponding maximum power density was $25.6mW/m^3$. External resistor of $200{\Omega}$ and air-cathode system contributed better MFC performance comparing to $2000{\Omega}$ and dissolved oxygen as a catholyte.

• Journal of Korean Society on Water Environment
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• v.25 no.1
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• pp.159-166
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• 2009

This study has been attempted to generate electricity, while simultaneously treating artificial organic wastewater using both batch and continuous microbial fuel cells (MFCs). In the batch MFC, current-voltage curve showed an onset potential of -0.69 V vs. Ag/AgCl. The potential range between this potential and 0 potential displayed an available voltage for an automatic production of electric energy and glucose, which was oxidized and treated at the same time. The 486 mg/L glucose solution showed the maximum power of $30mW/m^2$ and the maximum current density of $75mA/m^2$ shown in the power curve. As a result, discharging of the cell containing COD 423 mg/L at the constant current density of $60mA/m^2$ showed a continuous electricity generation for about 22 hours that dropped rapidly due to dissipating of organic material. Total electric energy production was 18.0 Wh. While discharging, the pH change was low and dropped from pH 6.53 to 6.20 then increased to 6.47, then stabilized at this charge. The COD treatment efficiency was found to be 72%. In the continuous MFC, COD removal tends to increase as the hydraulic retention time is increased. At one day of hydraulic retention time as the maximum value reaches the COD removal efficiency, power production rate and power production rate per COD removal that were obtained were 68.8%, $14mW/m^2$, and $20.8mW/m^2/g$ CODrm, respectively. In the continuous MFC, the power production rate per COD removal increases as the hydraulic retention time is increased and decreases as the organic loading rate is increased. At the values lower than an organic loading rate of $1kgCOD/m^3/d$, the values higher than about $18.1mW/m^2/g$ CODrm could be obtained.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.2
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• pp.261-272
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• 2013

Algae boom (Red tide) in south coastal area of Korea has been appeared several times during a decade. If algae boom appears in the desalination plant, media filter and UF filter are clogged quickly, and the plant should be shutdown. In general, Algae can be removed from water by flotation better than by sedimentation, because of the low density of algal cell. The purpose of this study conducts the CFD simulation of DAF flotation basin to apply the design of the dissolved air flotation with ball filter in the Test Bed for SWRO desalination plant. In this study, Eulerian-Eulerian multiphase model was applied to simulate the behavior of air bubbles and seawater. Density difference model and gravity were used. But de-sludge process and mass transfer between air bubbles and seawater were ignored. Main parameter is hydraulic loading rate which is varied from 20 m/hr to 27.5 m/hr. Geometry of flotation basin were changed to improve the DAF performance. According to the result of this study, the increase of hydraulic loading rate causes that the flow in the separation basin is widely affected and the concentration of air is increased. The flow pattern in the contact zone of flotation basin is greatly affected by the location of nozzle header. When the nozzle header was installed not the bottom of the contact zone but the above, the opportunity of contact between influent and recycle flow was increased.

• Computers and Concrete
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• v.24 no.6
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• pp.527-539
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• 2019

In this paper, the fracture characteristics of concrete specimens with different notch depths under three-point flexural loads are studied by finite element and fracture mechanics methods. Firstly, the concrete beams (the size is 700×100×150 mm) with different notch depths (a=30 mm, 45 mm, 60 mm and 75 mm respectively) are tested to study the influence of notch depths on the mechanical properties of concrete. Subsequently, the concrete beams with notch depth of 60 mm are loaded at different loading rates to study the influence of loading rates on the fracture characteristics, and digital image correlation (DIC) is used to monitor the strain nephogram at different loading rates. The test results show that the flexural characteristics of the beams are influenced by notch depths, and the bearing capacity and ductility of the concrete decrease with the increase of notch depths. Moreover, the peak load of concrete beam gradually increases with the increase of loading rate. Then, the fracture energy of the beams is accurately calculated by tail-modeling method and the bilinear softening constitutive model of fracture behavior is determined by using the modified fracture energy. Finally, the bilinear softening constitutive function is embedded into the finite element (FE) model for numerical simulation. Through the comparison of the test results and finite element analysis, the bilinear softening model determined by the tail-modeling method can be used to predict the fracture behavior of concrete beams under different notch depths and loading rates.

• Journal of Korean Society on Water Environment
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• v.35 no.6
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• pp.567-573
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• 2019

DABF(Dissolve Air Flotation with Ball Filter) is developed as the DAF with the addition of a fiber ball at the lower part of the DAF. The DABF with a capacity of 4,500 ㎥/h was constructed at Gijang SWRO plant in Busan. Since the ball filter has high filtration rate, the loading rate of DABF was designed from 20 to 42 ㎥/h/㎡. When one DABF basin is in the back washing mode, the loading rate of other two DABF basins is increased to 42 ㎥/h/㎡. Turbidity at the BF outlet in DABF is <2 NTU at turbidity of 5-10 NTU at the BF inlet. If there is no algae bloom and turbidity is low in raw seawater, only BF in DABF is operated and meets <2 NTU at the BF outlet. Even if BF is operated at high hydraulic loading rates, no significant differential pressure increases and reduction in the turbidity removal rate is minimal in a day. Thus, DABF is the pre-treatment technology that provides stable water quality even with BF onlyoperation without DAF operation. Compared with the DAF, DABF requires additional facilities such as valves, piping, and drainage systems for backwashing the BF. But in terms of footprint and operating costs, DABF has more advantages than DAF. With DABF application, the load of the downstream filtration equipment is decreased so that the capacity of the filtration equipment can be reduced. Also, if the downstream filtration equipment is to be maintained the same regardless of DABF, the operating cost of DABF is less than DAF.