• 한국물환경학회지
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• 제21권3호
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• pp.230-235
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• 2005

The main purpose of the flocculation process is to make flocs bigger to be removed easily in the following processes. The flow pattern and mixing intensity have a great influence on flocculation. In this study, the flow pattern was examined by a hydraulic tracer-test, where 3 water treatment plants having $800,000m^3/d$, $44,000m^3/d$ and $40,000m^3/d$ were employed. Also, the settling test was conducted to find out the relationship between the mixing intensity and the settling ability of flocs. The hydraulic tracer-test was conducted for the various flocculation processes that have different structures of flocculation basins. In the result, the retention time distribution (RTD) curves for the flocculation processes were quite different. In case of the inappropriate structure of the flocculation basin, the flow is not even so that the floc does not grow enough. To find out the relationship between mixing intensity and settleability of flocs, G-values were calculated and the settling test was conducted for two flocculation basins which have the same conditions except the G-value. For the flocculation basin with uneven G-value, the floc settleability was revealed poor. On the other hand, the flocculation basin with even G-value, the settleability was better than the previous one. From these experimental results, it is confirmed that the flow pattern is closely related to the structure of the flocculation basin and the settleability is affected by mixing intensity. Therefore the flow pattern and the strength of the mixing intensity should be examined sufficiently to design and operate flocculation basin.

• 상하수도학회지
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• 제23권6호
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• pp.865-870
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• 2009

In this study, the adequacy of Reynolds numbers and Froude numbers derived from about sixty domestic water treatment plants (WTPs) were analyzed in order to estimate the characteristics of hydraulic behavior within the rectangular shaped sedimentation basins used widely. From the results of analysis, most of domestic WTPs have satisfied the criteria regulated as that Reynolds number should less than 1,000(dimensionless). On the other hand, they have not been able to satisfy the Froude number criteria, which should be higher than $1.0{\times}10^{-6}$. The reasons why most of domestic WTPs could not satisfy the criteria are that its criteria basis has been not only inadequate, but also the concept of external flow occurred around a settling particle has been ignored. Accordingly, this study proved the feasibility of Archimedes number, which indicates the ratio between particle Reynolds number and Froude number, to evaluate the hydraulic efficiency and its function of scale factor.

• 한국물환경학회지
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• 제20권5호
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• pp.534-538
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• 2004

Granulation characteristics have been studied with an aerobic sequencing batch reactor(SBR). Organic loading of 2.46kg COD/$m^3$/day followed by 4.14kg COD/$m^3$/day had been applied to the lab-scale SBR with a very short settling time during the operating cycle. The granulation proceeded to the diameter range of 3 to 5 mm with MLSS concentration of 12,000mg/L at 45th days of operation while COD removal efficiency remained almost consistent after the granule formation. It has been noticed that aerobic granulation under the higher loading with a very short settling time seemed to be due to the microbial selection of better flocculating species.

• 상하수도학회지
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• 제27권2호
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• pp.207-214
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• 2013

To evaluate characteristics of water quality in Jeju, a study was implemented for Han stream and retention ponds. Inflow water quality of retention ponds was heavily dependent on precedent rainfall, and no pesticide was detected due to the little artificial pollution sources. A smooth settling efficiency curve was noticed because heavy particles were already settled down in front of the retention pond. There were weak relationships between retention time and water quality, and this can be attributable to high concentration of pollutants influx at peak inflow. In addition, as Han stream retention pond has a role of groundwater recharge, inflow control based on water quality as well as quantity is needed to maximize pollutant removal at the retention ponds.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2020년도 전력전자학술대회
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• pp.160-162
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• 2020

A control technique for the auxiliary buck/boost converter is proposed herein to improve the load transient response of the buck converter. The proposed technique improves the system efficiency by enabling the soft switching operation of the auxiliary converter. The design guidelines for achieving capacitor charge balance for the output capacitor during the transient are also presented herein. The experimental results revealed that the output voltage undershoot and settling time during the load step-up transient were 40 mV and 14 ㎲, respectively, and the output voltage overshoot and settling time during the load step-down transient were 35 mV and 21 ㎲, respectively. The performance and effectiveness of the proposed technique were experimentally verified using a prototype buck converter with a 15-V input, 3.3-V output, and 200-kHz switching frequency.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3139-3143
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• 2007

The objective of this paper was to investigate the mixing characteristics of an three-stage inline coagulant mixing system experimentally. Wastewater samples of pH 8.5 and initial turbidity 1,000NTU were taken from a site of tunneling work. At the constant dosage, 0.36mL/L, of polymer as coagulant aids, the coagulation efficiency with the dosage of PAC as coagulant was about 4${\sim}$6% at 10 minutes after sampling. In the case of 2 different velocity gradient conditions, the efficiency of turbidity removal was increased about 6.5${\sim}$8% with increasing the dosage of coagulant while, the efficiency was increased about 20${\sim}$21.5% with increasing the dosage of coagulant aids. The efficiency of turbidity removal with the settling time after sampling was about 90% after 1 minute, and the efficiency was about 95% after 5 minutes.

• 한국토양환경학회지
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• 제2권1호
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• pp.73-81
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• 1997

고속도로에서 흘러오는 빗물의 양을 조절하고 환경오염을 최소화하기 위해 프랑스 일부 고속도로변에 간이정화시설을 설치하였다. 중금속에 의해 오염된 입자를 제거하기 위해 설치된 간이정화시설의 효과를 평가하기 위해서 오를레앙 남쪽 20km지점의 "Les Ardilleres" 지역의 A-71고속도로변에 위치한 간이정화시설을 선정하였다. Muller (1979)와 Helz (1976)에 의해 각각 도입된 index of geoaccumulation와 enrichment factor를 이용하여 오염된 도로변 토양과 간이정화시설에서 채취한 부유퇴적물의 중금속오염 정도를 정량화하여 평가하였다. 기대한 데로, 도로변 토양의 오염은 매우 심각한 반면에 부유퇴적물의 오염은 미약하였다. 간이정화시설의 부유퇴적물은 카드뮴오염만이 진행되고 있으며 이 결과는 인위적인 오염과 자연적인 농집현상에 기인된 것이다. 부유퇴적물에 수반되어 간이정화시설에 유입되는 중금속의 추정량은 하루 납 0.9g, 아연 2.1g, 카드뮴 6mg이다. 자동차통행에 의해 배출된 납과 아연의 양과 간이정화시설에 유입된 것을 비교한 tentative mass balance 결과 고속도로상에 오염된 납과 아연의 약 5~11% 만이 빗물에 의해 간이정화 시설에 운반되어 유입되었다. 간이정화시설의 효율을 높이기 위한 제안이 제시되었다.제안이 제시되었다.

• 대한환경공학회지
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• 제39권5호
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• pp.229-236
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• 2017

국내에서 설치 운영 중인 D정수장의 장방형 침전지를 대상으로 설계유량($15,864m^3/day$)과 운영유량($33,333m^3/day$))에 대하여 CFD 해석 방법을 사용하여 침전지의 유동특성 및 tracer 모의를 수행하였으며, 침전지의 유입부로 유입되는 플럭을 입자로 가정하여 모사하는 Lagrangin 기법을 적용하여 침전지의 효율을 검토하였다. 그 결과 침전지내 흐름을 plug flow 영역으로 만들기 위한 평균 속도값을 0.00193 m/s, 0.00417 m/s로 도출되었다. 또한 각 유량 조건에 대해 Tracer test를 모의한 결과 ${\beta}$(유효접촉인자) 값은 각각 0.51, 0.46, Morrill Index값은 각각 6.05와 3.21, 단락류 Index는 0.54와 0.34로 나타났다.

• 상하수도학회지
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• 제23권5호
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• pp.573-581
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• 2009

In the case that the average velocity within rectangular-shaped sedimentation basin is less than 1.5cm/sec, and Froude number less than $10^{-6}$, it can not be expected that the longitudinal baffle improves the sedimentation efficiency. Also, since relatively lower velocity increases the effect of geostrophic body force, asymmetric flow pattern on a plane occurs within the basin. From the results of CFD (Computational Fluid Dynamics) simulation, in the case that the highest velocity within rectangular-shaped sedimentation basin is over 1.5cm/sec, and Froude number over $10^{-6}$, it can be expected that the longitudinal baffle installed within rectangular-shaped sedimentation basin improves the sedimentation efficiency.

• International journal of advanced smart convergence
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• 제9권1호
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• pp.19-28
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• 2020

We studied the on-site treatment of soil contaminated by heavy metals and petroleum was tested using relocatable soil washing equipment for greater remediation efficiency. Different combinations of pH and solid/liquid ratio were tested to determine the optimum balance, settling on values of 5 and 1:2, respectively. Next, soils containing Pb, Hg, and petroleum were further tested to assess the optimum number of washing cycles. The remediation efficiency of Pb and Hg in soil contaminated solely by heavy metals was 90.1% and 86.4% after three and two washings, respectively. The remediation efficiency of petroleum in soil contaminated solely by petroleum was 98.8% after one washing. When soil contaminated by both heavy metals and petroleum was cleaned, up to 91.0% of Pb, 86.9% of Hg, and 96.1% of petroleum was removed after two, one, and one washings, respectively. We conducted all remediation efficiencies and concentration reductions satisfied the standard threshold for soil contamination in South Korea.