• Journal of Environmental Health Sciences
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• v.24 no.2
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• pp.9-19
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• 1998

Laboratory experiments were carried out to investigate the performance of anaerobic sequencing batch reactor(ASBR) for digestion of a municipal sludge. Each cycle of the ASBR comprised feeding, two-or three-day reaction, one-day thickening, and withdrawal. The reactors were operated at an HRT of 10days and 5days with an equivalent organic loading rate of 0.8-1.54 gVS/l/d, 1.81-3.56 gVS/l/d at 35$\circ$C, respectively. Solids accumulation was remarkable in the ASBR during start-up period, and directly affected by settleable solids in the feed sludge. Floatation thickening occured in the ASBRs, and Solids profiles at the end of thickening step dramatically changed at solid-liquid interface. Slight difference in solids concentrations was observed within thickened sludge bed. Efficiencies through floatation thickening were comparable to that of additional thickening of the completely mixed control reactor. Average solids concentrations in the ASBRs were 2.2-2.6 times higher than that in the control throughout the total operation period. The dehydrogenase activity had a strong correlation with the solids concentration. Organics removals based on clarified effluent of the ASBRs were consistently above 86%. Remarkable increase in equivalent gas production of 27-52% was observed at the ASBRs compared with the control though the control and ASBRs showed similiar effluent quality. Thus, digestion of a municipal sludge was possible using the ASBR in spite of high concentration of solids in the sludge.

• Ecology and Resilient Infrastructure
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• v.4 no.4
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• pp.226-236
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• 2017

In this study, we aimed to analyze the characteristics of water quality variation at Kyeongan Stream for a decade and to investigate by the flow-loading equation. The correlation analysis of water quality parameters and the influence factors were examined by statistical analysis. The characteristics of water quality variation showed that the fluctuations in $BOD_5$, $COD_{Mn}$ and TOC were repeated from year to year. TN and TP were decreased by year. By the flow-loading equation, the concentrations of $BOD_5$, $COD_{Mn}$, TOC and TN were decreased when the flow rate was on the rise. However, the flow did not affect the concentration of TP. According to correlation analysis, $BOD_5$ was highly correlated with $COD_{Mn}$ and TOC with the correlation coefficients of 0.890 (p<0.01) and 0.721 (p<0.01). The result of factor analysis, we identified that the water quality in Kyeongan Stream has been highly influenced by the organic matter index, followed by nitrogenous substance depending on the seasonal variations and the influx of suspended solid in accordance with the increase of flow.

• Journal of the Korea Organic Resources Recycling Association
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• v.8 no.2
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• pp.130-139
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• 2000

Serial basic tests were conducted for the determination of fundamental kinetics and for the actual application of kinetic parameter to food waste digestion with precise measurement of methane production under a thermophilic condition. The effects of food particle size, sodium ion concentration, and volatile solid (VS) loading rate on the anaerobic thermophilic food waste digestion process were investigated. Results of serial test for the determination of fundamental kinetic coefficients showed the value of k (maximum substrate utilization rate coefficient) and KS (half-saturation coefficient) as $0.24hr^{-1}$ and $700mg/{\ell}$, respectively, for non-inhibiting organic loading range. No inhibition effect was shown until $5g/{\ell}$ of sodium ion concentration was applied to a serum bottle reactor. However, the volume of methane gas was decreased gradually when the concentrations of more than $5g/{\ell}$ of sodium ion applied. All sizes of food waste particle showed the same constants (A : 0.45) but the maximum substrate utilization rate constant ($k_{HA}$) was inversely proportional to particle size. As an average particle size increased from 1.02 mm to 2.14 mm, $k_{HA}$ decreased from $0.0033hr^{-1}$ to $0.0015hr^{-1}$. The result reveals that particle size is one of the most important factors in anaerobic food waste digestion. There was no inhibition effect of sodium ion when VS loading rate was $30g/{\ell}$. And maximum injection concentration of VS loading rate was determined about $40g/{\ell}$.

• Environmental Engineering Research
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• v.25 no.1
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• pp.1-17
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• 2020

With benefits to the human health, environment, economy, and energy, anaerobic digestion (AD) systems have attracted remarkable attention within the scientific community. Anaerobic digestion system is created from (bio)reactors to perform a series of bi-metabolism steps including hydrolysis/acidogenesis, acetogenesis, and methanogenesis. By considering the physical separation of the digestion steps above, AD systems can be classified into single-stage (all digestion steps in one reactor) and multi-stage (digestion steps in various reactors). Operation of the AD systems does not only depend on the type of digestion system but also relies on the interaction among growth factors (temperature, pH, and nutrients), the type of reactor, and operating parameters (retention time, organic loading rate). However, these interactions were often reviewed inadequately for the single-stage digestion systems. Therefore, this paper aims to provide a comprehensive review of both single-stage and multi-stage systems as well as the influence of the growth factors, operating conditions, and the type of reactor on them. From those points, the advantages, disadvantages, and application range of each system are well understood.

• Journal of Korean Society of Water and Wastewater
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• v.8 no.1
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• pp.1-8
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• 1994

Laboratory experiments were conducted to investigate the effect of digestion temperature on the settleability and dewaterability of anaerobically digested sludge. The digesters were operated at a hydraulic retention time of 20 days with a loading rate of 0.63~0.66kg volatile solids per cubic meter per day at the temperature of $35^{\circ}C$ and $55^{\circ}C$. A mixed primary and secondary municipal sludge was used as a feed. The interface height of the sludge during settling test was recorded to identify settleability. As a measure of dewaterability of the sludge, specific resistance and capillary suction time were also measured with and without chemical conditioning. Higher digestion efficiency was obtained at $55^{\circ}C$ than $35^{\circ}C$. However, the settleability and dewaterability of the sludge at $35^{\circ}C$ were quite higher than those of the sludge digested at $55^{\circ}C$. The optimum dosages of ferric chloride for sludge conditioning were 0.4% and 0.6% at $35^{\circ}C$ and $55^{\circ}C$, respectively. The filtrate COD of the sludge digested at $55^{\circ}C$ was higher than at $35^{\circ}C$, which means that poor dewaterability of the sludge result in high filtrate COD.

• Journal of the Korean Society of Combustion
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• v.14 no.4
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• pp.1-6
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• 2009

Analysis of the internal state of the blast furnace is necessary to predict and to control the operating conditions. Especially, it is important to develop models of the blast furnace to predict the cohesive zone because shape of the cohesive zone influences overall operating conditions of blast furnace such as gas flow, chemical reactions and temperature. Because many previous blast furnace models have assumed cohesive zone to be fixed, it was not possible to evaluate the shape change of cohesive zone in relation with operating conditions such as PCR, blast condition, and production rate. In this study, an axi-symmetric 2-dimensional steady state model is proposed to simulate blast furnace processes. In this model, cohesive zone is determined by the solid temperature. Finite volume method is employed for numerical simulation. To find location of the cohesive zone, entire calculation procedure is iterated until converged. Through this approach, shape of the cohesive zone, velocity and temperature within the furnace are predicted from the model.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.1
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• pp.42-48
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• 2011

To define ice as a solid material, mathematical and physical characteristics and their application examples are investigated for several materials' yield functions which include isotropic elastic, isotropic elastic-plastic, classical Drucker-Prager, Drucker-Prager Cap, Heinonen's elliptic, Derradji-Aouat's elliptic, and crushable foam models. Taking into account brittle failure mode of ice subject to high loading rate or extremely low temperature, isotropic elastic model can be better practicable than isotropic elastic-plastic model. If a failure criterion can be properly determined, the elastic model will provide relatively practicable impact force history from ice-hull interactions. On the other hand, it is thought that the soil models can better predict the ice spalling mechanism, since they contain both terms of shear stress-induced and hydrostatic stress-induced failures in the yield function.

• Structural Engineering and Mechanics
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• v.55 no.4
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• pp.857-869
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• 2015

The aluminum 7075-T6 is known as an alloy widely used in aircraft structural applications, which does not exhibit strain rate sensitivity during dynamic compressive tests. Despite mechanical importance of the material, there is not enough attention to determine appropriate sample dimensions such as a sample diameter relative to the device bar diameter and sample length to diameter (L/D) ratio for dynamic tests and how these two parameters can change mechanical behaviors of the sample under dynamic loading condition. In this study, various samples which have different diameters of 31.8, 25.4, 15.9, and 9.5 mm and sample L/D ratios of 2.0, 1.5, 1.0, 0.5, and 0.25 were tested using Split Hopkinson Pressure Bar (SHPB), as this testing device is proper to characterize mechanical behaviors of solid materials at high strain rates. The mechanical behavior of this alloy was examined under ${\sim}200-5,500s^{-1}$ dynamic strain rate. Aluminum samples of 2.0, 1.5 and 1.0 of L/D ratios were well fitted into the stress-strain curve, Madison and Green's diagram, regardless of the sample diameters. Also, the 0.5 and 0.25 L/D ratio samples having the diameter of 31.8 and 25.4 mm followed the stress-strain curve. As results, larger samples (31.8 and 25.4 mm) in diameters followed the stress-strain curve regardless of the L/D ratios, whereas the 0.5 and 0.25 L/D ratios of small diameter sample (15.9 and 9.5 mm) did not follow the stress-strain diagram but significantly deviate from the diagram. Our results indicate that the L/D ratio is important determinant in stress-strain responses under the SHPB test when the sample diameter is small relative to the test bar diameter (31.8 mm), but when sample diameter is close to the bar diameter, L/D ratio does not significantly affect the stress-strain responses. This suggests that the areal mismatch (non-contact area of the testing bar) between the sample and the bar can misrepresent mechanical behaviors of the aluminum 7075-T6 at the dynamic loading condition.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.1
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• pp.17-25
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• 2003

Treatment with implants of single tooth missing cases is both functional and esthetic. Although the success rate of single-tooth implant treatments is increasing, sometimes it makes some problems. Problems with single-tooth implant treatments include soft tissue complications, abutment screw fracture, and most commonly, abutment screw loosening, and these involve the instability of the dental implant-superstructure interface. This study investigated and compared dental implant screw joint micromotion of various implant system with external connection or internal connection when tested under simulated clinical loading, Six groups (N=5) were assessed: (1) Branemark AurAdapt (Nobel Biocare, Goteborg, Sweden), (2) Branemark EsthetiCone (Nobel Biocare, Goteborg, Sweden), (3) Neoplant Conical (Neobiotec, Korea), (4) Neoplant UCLA (Neobiotec, Korea), (5) Neoplant 5.5mm Solid (Neobiotec, Korea), and (6) ITI SynOcta (Institute Straumann, Waldenburg, Switzerland). Six identical frameworks were fabricated. Abutment screws were tightened to 32-35 Ncm and occlusal screw were tightened to 15-20 Ncm with an electronic torque controller. A mechanical testing machine applied a compressive cyclic load of 20kg at 10Hz to a contact point on each implant crown. Strain gauge recorded the micromotion of the screw joint interface once a second. Data were selected at 1, 500, 5,000, 10,000, 20,000, 30,000, 40,000 and 50,000 cycle and 2-way ANOVA test was performed to assess the statistical significance. The results of this study were as follows; The micromotion of the implant-superstructure in the interface increased gradually through 50,000 cycles for all implant systems. In the case of the micromotion according to cycle increase, Neoplant Conical and Neoplant UCLA system exhibited significantly increasing micromotion at the implant-superstructure interface (p<0.05), but others not significant. In the case of the micromotion of the implant-superstructure interface at 50,000 cycle, the largest micromotion were recorded in the Branemark EsthetiCone, sequently followed by Neoplant Conical, Neoplant UCLA, Branemark AurAdapt, ITI SynOcta and Neplant Solid. Internal connection system showed smaller micromotion than external connection system. Specially, Neoplant Solid with internal connection system exhibited significantly smaller micromotion than other implant systems except ITI SynOcta with same internal connection system (p<0.05). In the case of external connection, Branemark EsthetiCone and Neoplant Conical system with abutment showed significantly larger micromotion than Branemark AurAdapt without abutment (p<0.05).

• Clean Technology
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• v.25 no.4
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• pp.302-310
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• 2019

A constructed wetland with the aerobic tank and anaerobic/anoxic tank connected in series was employed in order to treat highly polluted stream water. The aerobic tank was maintained aerobic with a continuous supply of air through the natural air draft system. Five pilot plants having different residence times were employed together to obtain parameters for the best performances of the wetland. BOD and COD removals at the aerobic tank followed the first order kinetics. COD removal rate constants were slightly lower than BOD. The temperature dependence of COD (θ = 1.0079) and BOD (θ = 1.0083) was almost the same, but the temperature dependence (θ_N) of T-N removal was 1.0189. The SS removal rate was as high as 98% and the removal efficiency showed a tendency to increase with increasing hydraulic loading rate (Q/A). The main mechanism of BOD and COD removal at the anaerobic/anoxic tank was entirely different from that of the aerobic tank. BOD and COD were supplied as the carbon source for biological denitrification. T-P was believed to be removed though the cation exchange between orthophosphate and gravels within the anaerobic and anoxic tanks. The wetland could successfully be operated without being blocked by the filtered solid which subsequently decomposed at an extremely fast rate.