• 제어로봇시스템학회:학술대회논문집
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• 1990.10a
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• pp.550-555
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• 1990

In the VSS control, reaching phase and chattering problem are the main disadvantages. A simple nonlinear sliding surface is proposed to cope with the reaching phase. The chattering problem is alleviated by almost continuous control with the compensation using the infinite closed loop.

• Journal of Environmental Science International
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• v.9 no.1
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• pp.75-80
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• 2000

Kinetic data for the acid phase anaerobic digestion were presented in this study and the constants were determined with acid production rate and gas production rate. Process models based on continuous culture theory were used to describe the characteristics of the acid forming microorganisms and to enable further development toward utilization of the process in a more rational manner. Acid phase digestion can be separated with appropriate manipulation of hydraulic retention time in anaerobic digestion. Kinetic analysis of data from the various hydraulic retention times using a phase specific model obtained form the acid phase indicated maximum specific growth rate of 0.40/h, saturation constant of 2,000mgCOD.$\ell$, yield coefficient of 0.35 mgVSS/msCOD utilized and decay constant of 0.04/h for the acid production rate. Similar analysis of data for the gas production rate indicated maximum specific growth rate of 0.003/h, saturation constant of 2,200mgCOD/$\ell$, yield coefficient of 0.035 mgVSS/mgCOD utilized and decay constant of 0.06/h.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.1
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• pp.43-50
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• 1989

In this paper we present a new approach to control system design for multivariable systems using a sliding mode. In the applications of variable structure system (VSS) theory to multivariable systems, there exist some difficulties such as how to determine switching gains and how to reduce chattering phenomena in input and state trajectories. To cope with these drawbacks we introduce switching dynamics instead of switching logics to obtain the sliding mode. Consequently, we can obtain the new design approach which is much simpler than the VSS theory, And there do not exist chattering phenomena in this method because the obtained control inputs are continuous. Hierarchical control concepts are used to the control system design. Numerical examples are discussed as illustrations.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.3
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• pp.228-236
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• 1989

The theroy of variable structure control system (VSS) is applied to the position control for DC servo-motors. In order to use the microcomputer as a control device, the principles of VSS for the continuous-time system are extended to the discrete-time system. A new switching law is proposed to achieve the reduction of chattering. It adds a new switching structure to the conventional switching sturctures. This switching region is set near and including the conventional switching curve. The new algorithm is obtained for single-input second order system, and applied to the position control of a DC servo-motor. Experimental results show that the transient behavior is improved due to the reduction of chattering and good robustness properties are demonstrated.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.2
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• pp.195-206
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• 2014

Immobilization of anaerobic ammonium oxidizing bacteria has been studied to enhance the biomass retention of the slowly growing bacteria and the process stability. The purpose of this study was to compare the nitrogen removal efficiency of granular and immobilized anammox bacteria with poly vinyl alcohol and alginate. The specific anammox activity of the granular, homoginized and immobilized anammox bacteria were $0.016{\pm}0.0002gN/gVSS/d$, $0.011{\pm}0.001gN/gVSS/d$ and $0.007{\pm}0.0005gN/gVSS/d$, respectively. Although the activity decreased to 43.7 % of the original one due to low pH and $O_2$ exposure during the homogination and the immobilization, it was rapidly recovered within 7 days in the following continuous culture. When synthetic T-N concentrations of 100, 200, 400, 800 mg/L were fed, the immobilized anammox bacteria showed higher nitrogen removal efficiencies at all operational conditions than those of granular anammox bacteria. When the sludge retention time was shorten below 30.7 days and the reject water was fed, the nitrite removal efficiency of the granular anammox bacteria dropped to 8 % of the initial value, while that of the immobilized anammox bacteria was maintained over 95 % of the initial one. The immobilization with poly vinyl alcohol and alginate would be a feasible method to improve the performance and stability of the anammox process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4B
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• pp.421-426
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• 2006

The effect of initial concentration of ammonium ion ($N_0$) and active nitrifiers ($X_0$) on nitrification was examined by continuous monitoring of the ammonium removal rate. The concentration of the active nitrifiers in the culture sludge, measured by the oxygen uptake rate (OUR), was found to be 42.8% of the culture sludge. Experiments were carried out under different ratios of $N_0/X_0$, viz., 0.025 to 0.493. The results from this study show that the oxidation rate was similar under the same $N_0/X_0$ ratio despite different initial concentration of ammonium ion ($N_0$) and active nitrifiers ($X_0$). Moreover, the Contois kinetic expression which includes biomass concentration, was found to describe the mechanism behind nitrification process. The ammonium oxidation rate ($q_{Nmax}$) and half saturation constant per unit activated nitrifiers ($K_N{^{\prime}}$) were theoretically determined using the Contois expression. These values were found to be 4.32 gN/gVSS/day and 0.013 gN/gVSS respectively.

• Journal of Microbiology and Biotechnology
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• v.27 no.10
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• pp.1798-1807
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• 2017

The differentiations in nitrogen-converting activity and microbial community structure between granular size fractions in a continuous completely autotrophic nitrogen removal over nitrite (CANON) reactor, having a superior specific nitrogen removal rate of $0.24g/(g\;VSS{\cdot}h)$, were investigated by batch tests and high-throughput pyrosequencing analysis, respectively. Results revealed that a high dissolved oxygen concentration (>1.8 mg/l) could result in efficient nitrite accumulation with small granules (0.2-0.6 mm in diameter), because aerobic ammonium-oxidizing bacteria (genus Nitrosomonas) predominated therein. Meanwhile, intermediate size granules (1.4-2.0 mm in diameter) showed the highest nitrogen removal activity of $40.4mg/(g\;VSS{\cdot}h)$ under sufficient oxygen supply, corresponding to the relative abundance ratio of aerobic to anaerobic ammonium-oxidizing bacteria (genus Candidatus Kuenenia) of 5.7. Additionally, a dual substrate competition for oxygen and nitrite would be considered as the main mechanism for repression of nitrite-oxidizing bacteria, and the few Nitrospira spp. did not remarkably affect the overall performance of the reactor. Because all the granular size fractions could accomplish the CANON process independently under oxygen limiting conditions, maintaining a diversity of granular size would facilitate the stability of the suspended growth CANON system.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.269-275
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• 1993

The performance of Upflow Anaerobic Sludge Blanket(UASB) reactor for treatment of corn starch wastewater was investigated using continuous and batch experiment. Results showed that the corn starch wastewater had different characteristics in terms of biodegradability and methane potential, depending on the manufacturing precess. COD removal efficiencies were maintained over 70% up to the loading rate of 3.2 kg $COD/m^3{\cdot}day$ and the maximum gas production rate was about 55 l/day, equivalent to 3.5 l/day per liter of reactor volume, at the loading rate of 8.4 kg $COD/m^3{\cdot}day$. In the anaerobic serum bottle test(SBT) carried out along with continuous operation, the sludge activity was found to increase from 0.03 to 0.53 g $COD-CH_4/g\;VSS{\cdot}day$ as granular sludges were developed in 130 days operation. SBT gave valuable informations on the characteristics of wastewaters to be treated as well as on the sludge activity. The overall morphological characteristics of granular sludges cultivated on corn starch wastewaters were similar to those cultivated on various organic industrial wastewaters such as distillery and sugar.

• Journal of the Korea Organic Resources Recycling Association
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• v.19 no.2
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• pp.22-27
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• 2011

This study was performed to find out the optimum condition for hydrogen production by changing mixture ratio from 3:7(food waste water : swine wastewater) without pre-treatment of food wastewater and swine wastewater using a continuous reaction process. It was confirmed that hydrogen generation according to pH is the highest in a condition of pH 5.5, and that the optimum pH for hydrogen production in case of mixing food wastewater with swine wastewater is 5.5 through this. Hydrogen generation according to HRT showed high hydrogen generation rate in case of 4 days rather than 3 days, and this involves largely in vitality of hydrogen producing bacteria according to variation of the HRT value, so it is judged that HRT also acts as an important factor to hydrogen producing bacteria. The organic removal efficiency recorded a removal efficiency of maximum TS 52%, VS 71%, TSS 83% and VSS 89% at the 6th day of operation, and it was confirmed that organic removal efficiency is possible even through an hydrogen production process.