• Journal of Environmental Impact Assessment
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• v.24 no.3
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• pp.278-286
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• 2015

Pilot scale system was designed to identify the growth and movement of algae, depending on environmental changes(retention time, nutrient concentration, etc) in Gangjeong-Goryeong Weir of the Nakdong River. Considering the stability of algal culture and easy observation of algal growth, pilot scale system was made of transparent acrylic material(3 sets of flexible cylindrical water tanks with 1 m diameter and 4 m height). Auxiliary equipments include light intercepter, water inflow device for different water depth and storage of reclaimed water. The retention time was 2 days(before construction of weir; treatment 1), 8 days(after construction of weir, 2013; treatment 2) and 30 days(2014; treatment 3). According to the water temperature of treatment 1 were similar by depth, treatment 3 showed a difference between the surface(0 m) and bottom(4 m) more than $3^{\circ}C$. DO, pH showed relatively high in the surface than the bottom. Nutrients showed eutrophic condition in all experiments. The Chlrophyll-a concentration of the treatment 1 showed a relatively lower value than the Chlrophyll-a concentration of the treatment 2 and 3. Therefore, the retention time was considered to influence the growth of phytoplankton.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.1
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• pp.15-25
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• 2006

This study was initiated to evaluate the effect of HRT(hydraulic retention time) on removal efficiencies of organic matter (C), nitrogen(N) and phosphorus(P) in municipal wastewater for suspenced-growth processes(MLE; Modified Ludzack-Ettinger) and hybrid process(Modified-Dephanox). M-Dephanox process was designed to improve the performance of Dephanox process on denitrification efficiency. As the results, removal efficiencies of C, N and P in M-Dephanox process, which is hybrid process, were higher than those in MLE, which is suspended-growth process. Especially, nitrification inhibition of MLE was observed more severely than M-Dephanox as hydraulic retention time was reduced from 6 hr to 3.5 hr. Nitrification in nitrification reactors on M-Dephanox, at short HRT, was so excellent that ammonia nitrogen removal efficiency in nitrification reactors of M-Dephanox was about 92% at 1.59 hr of HRT of nitrification reactors, however, nitrification in nitrification reactors on M-Dephanox was affected severely by organic matter entering to nitrification reactors from downstream settler. It was observed that reducing of HRT in whole process resulted from reducing of HRT in nitrification reactors on M-Dephanox.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.3
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• pp.405-415
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• 2000

Experiments for autotrophic denitrification were performed using an upf10w reac1.or packed with sulfur particles as an electron donor. The influent $NO_3{^-}$-N concentration was kept almost constant, but the hydraulic retention time(HRT) and temperature varied. Results of the research showed that the denitrification efficiency and gas generation rate decreased as the HRT and temperature were reduced. During the HRT effect experiment, alkalinities of 3.44~5.71g, with an average of 4.67 g which is close to the theoretical value of 4.57g were consumed for each gram of $NO_3{^-}$-N removed. During the temperature effect experiment, however, the values were 6.58~13.41 g with an average of 9.12 g which is almost twice the theoretical value Denitrification along the length of the reactor appeared to be a first-order reaction with a reaction rate constant of 0.1648/hr. On the other hand, the sulfate generation showed a zero-order reaction with a reaction rate constant of 241/hr. There was some discrepancy in the nitrogen mass balance between the theoretical and measured values, requiring further researches.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.2
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• pp.229-234
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• 2007

In the present work, the sequencing batch reactor process of two-sludge type was optimized. The effects of solid retention time, hydraulic retention time, length of biosorption phase and temperature variation were investigated, respectively. In the T-N removal, the long solid retention time was favored. It was speculated that SCOD biosorption efficiency was higher in long solid retention time than in short solid retention time. In the comparison of hydraulic retention time, the removal efficiency of $NH_4^+-N$ and T-N were almost same in all applied hydraulic retention times which were 8 hr, 10 hr and 15 hr. It was observed that there was no need to have the hydraulic retention time more than 20 min in biosorption phase for enhancement of T-N removal efficiency. An experimental comparison of removal efficiencies with different temperature conditions was carried out. Decrease of temperature didn't affect the performance of the process, however, phosphorus removal efficiency was a little higher at low temperature than high temperature. Consequently, the process developed in this study was much amenable to wastewater treatment which was conducted in the low temperature and high loading rate.

• The Journal of the Korea Contents Association
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• v.16 no.7
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• pp.146-153
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• 2016

This work studies the equilibrium behavior of customers and optimal pricing strategies of the sever in a continuous-time M/M/1 queueing system. In this work, we consider two pricing models. The first one is called the ex-ante payment scheme where the server charges a flat price for all services, and the second one is called the ex-post payment scheme where the server charges a price that is proportional to the time a customer spends in the system. In each pricing model, the departing customer receives the reward that is inversely proportional to his/her sojourn time. The server should make the optimal pricing decisions in order to maximize its expected profit per unit time in each payment scheme. This work also investigates customer's equilibrium joining or balking behaviors under server's optimal pricing strategies. Numerical experiments are conducted to help the server best select one between two pricing models.

• Korean Journal of Ecology and Environment
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• v.35 no.2 s.98
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• pp.133-140
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• 2002

This study was performed in lab scaled oxidation pond. The removal efficiency of pollutant on the influence of changes of hydraulic retention time and pond style was investigated. The correlation between organic removal efficiency and dissolved oxygen concentration on algal photosynthesis showed the light time revealed a higher relationship more than the dark time, and the squares of the correlation coefficient of 15 days retention time were higher than that of 5 days in single pond. The variation of dissolved oxygen concentration of a series pond was from 4.2 to 19.8 mg/l under 5 days retention time, the concentration of dissolved oxygen increased with increasing step of series pond. Between the single pond and a series of pond system, a series of pond system showed better organic removal efficiency. Average removal efficiency range of $TBOD_5$ and $SBOD_5$ was $49{\sim}83%$ and $87{\sim}92%$, respectively. Algae should be removed appropriately to increase the removal efficiency of organic matter.

• Proceedings of the KAIS Fall Conference
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• 2002.05a
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• pp.260-263
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• 2002

이 연구는 과량의 유분(dodecane)으로 오염된 토양을 효율적으로 정화시키기 위한 화학적 토양세정(soil flushing)에서 알코올 성분에 의한 유동성을 고찰한 것이다. 탄소수가 다른 알코올 (methanol, ethanol, butanol)과 Tween-80 계면활성제를 세정용액으로 사용하여 혼합비, 조용매 종류 및 체류시간에 따른 세정결과를 도시하였다. 조용매 사용시 세척효율은 최대 94%(Butanol/Tween-80(w/w)=0.1) 이었다. 체류시간의 연장은 재흡착되는 admicelle의 증가로 말미암아 세정효율을 감소시키는 것으로 나타났다.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2001.11a
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• pp.77-79
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• 2001

본 연구에서는 전기분해에 의한 양식장 배출수중의 유기물질 및 암모니아를 전류밀도, 전극간격에 따른 제거 특성을 살펴보았다. 전극간격 및 전류밀도에 따른 제거효율은 전극간격이 가까울수록, 전류밀도가 클수록 제거효율은 증가하였다 유기물질은 107.5A/$m^2$의 전류밀도에서 반응기 체류시간 8분동안 98.5%, 암모니아는 전류밀도를 107.15A/$m^2$로 유지하고, 간격을 변화시키면서 반응기 체류시간 120sec동안 암모니아의 제거율을 보면 92.6%의 제거효율을 나타내었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.149.2-149.2
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• 2014

진공용기를 배기하기 시작하면 짧은 시간 동안은 공기의 배기가 주를 이루지만 그 후에는 표면 방출 기체의 배기가 이어지고 표면방출 기체의 대부분은 물이라는 것은 누구나 알고 있는 사실이다. 그러나 배기 계산을 할 때는 막상 물 보다는 공기의 일부로 생각하거나 수분을 다른 기체들과 유사하게 다루는 것에 익숙해져 있다. 이런 계산 결과는 실제 상황을 재현하지 못할 뿐만 아니라 일반적으로 배기능력을 과대평가하게 만들어서 공정 계획대로 진공 시스템을 운전하는 것을 불가능하게 만든다. 물은 일반적인 기체와는 성격이 아주 다르다. 다른 기 체 분자들의 흡착 에너지가 ~0.3 eV이고 기름분자가 ~1 eV 정도인 것에 반해 물은 0.55 eV 내외로 상온에서도 비교적 흡착을 잘하고 또 적당히 방출도 일어나는 특별한 특성 때문에 용기 압력을 지배하면서도 신속한 배기를 방해한다. 만일 이런 물의 흡착률 및 방출률을 제대로 수치화할 수 있다면 배기 계산을 훨씬 현실화할 수 있다. 물의 흡착률은 물분자의 부착계수가 지배하고 방출률은 체류시간에 의해 결정되지만 표면상태에 따라 천차만별이므로 얼마라고 확정하기 어렵다. 우선 이번에는 물의 부착계수 최대값을 0.1 정도로 잡고 흡착량에 따라 직선적으로 줄어드는 것으로 가정하며, 물의 표면 체류시간도 몇 가지 값으로 가정해서 0-D 입자 평형 계산을 수행하여 특정 시스템에서 얻은 실험 결과와 비교하려고 한다. 앞으로 몬테카를로 방법과 연계하여 3차원적 분석을 할 수 있는 코드로 발전시켜 나갈 예정이다.

• Journal of Korea Water Resources Association
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• v.54 no.7
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• pp.495-507
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• 2021

With the recent industrial development, accidental pollution in riverine environments has frequently occurred. It is thus necessary to simulate pollutant transport and dispersion using water quality models for predicting pollutant residence times. In this study, we conducted a field experiment in a meandering reach of the Sum River, South Korea, to validate the field applicability and prediction accuracy of RAMS+ (River Analysis and Modeling System+), which is a two-dimensional (2D) stream flow/water quality analysis program. As a result of the simulation, the flow analysis model HDM-2Di and the water quality analysis model CTM-2D-TX accurately simulated the 2D flow characteristics, and transport and mixing behaviors of the pollutant tracer, respectively. In particular, CTM-2D-TX adequately reproduced the elongation of the pollutant cloud, caused by the storage effect associated with local low-velocity zones. Furthermore, the transport model effectively simulated the secondary flow-driven lateral mixing at the meander bend via 2D dispersion coefficients. We calculated the residence time for the critical concentration, and it was elucidated that the calculated residence times are spatially heterogeneous, even in the channel-width direction. The findings of this study suggest that the 2D water quality model could be the accidental pollution analysis tool more efficient and accurate than one-dimensional models, which cannot produce the 2D information such as the 2D residence time distribution.