This research proposes an optimal flushing operation technique in an effort to prevent secondary water pollutions and accidents in aged pipes, and to improve the cleaning effect of unidirectional flushing. Water flow directions were analyzed using EPANET 2.0, while flushing and air scouring experiments in forward and reverse directions were performed in the field. In 42 experiments, average residual chlorine concentration and turbidity were improved after cleaning compared to before cleaning. It was found that even when the same cleaning method was used, further improvement of cleaning effect was possible by applying air injection and reverse direction cleaning techniques. By means of one-way ANOVA(Analysis of variance), it was also possible to statistically verify the need of actively utilizing air injection and reverse direction cleaning. Based on correlation between turbidity and TSS, the total amount of suspended solids removal was estimated for 874 flushing operations and 194 air scouring operations. The result showed that air scouring used more discharge water than flushing by an average of 4.9 m3 yet with larger amounts of suspended solids removal by an average of 145.9 g. The result of analysis on turbidity values from 887 flushing operations showed low cleaning effect of unidirectional flushing for the pipes with diameters over 300 mm. In addition, the turbidity values measured during cleaning showed an increasing tendency as pipe age increased. The methodology and results of this research are expected to contribute to the efficient maintenance and improvement of water quality in water distribution networks. Follow-up research involving the measurement of water quality at regular time intervals during cleaning would allow a more accurate comparison of discharge water quality characteristics and cleaning effects between different cleaning methods. To this end, it is considered necessary to develop a standardized manual that can be used in the field and to provide relevant trainings.

A membrane module including grid was designed and introduced to MBR (membrane bio-reactor) for the purpose of better control of membrane fouling. It could be anticipated that the grid enhances the shear force of fluid-air mixture into the membrane surface by even-distributing the fluid-air to the membrane module. As MLSS concentration, packing density which is expressed in the ratio of the housing and the cross-sectional area of membrane fibers (Am/At) and air-flow rate were changed, membrane foulings were checked by monitoring fouling resistances. The total fouling resistance (Rc+Rf) without grid installation (i.e., control) was 2.13×1012 m-1 , whereas it was reduced to 1.69×1012 m-1 after the grid was installed. Regardless of the grid installation, the Rc+Rf increased as the packing density increased from 0.09 to 0.28, however, the increment of resistance for the grid installation was less than that of the control. Increase in the air flow rate did not always guarantee the reduction of fouling resistance, indicating that the higher air flow rate can partially de-flocculate the activated sludge flocs, which led to severer membrane fouling. Consequently, installation of grids inside the housing have brought a beneficial effect on membrane fouling and optimum air flow rate is important to keep the membrane lowering fouling.

Single-staged anaerobic fluidized ceramic membrane bioreactor (AFCMBR) was operated at 25oC for the treatment of low-strength synthetic wastewater with chemical oxygen demand averaging 260 mg/L. Tubular ceramic membrane consisting of aluminun dioxide (Al2O3) with 0.5 μm pore size was used. Overall COD removal was achieved as 87-95% with effluent COD concentration of 15-30 mg/L at hydraulic retention time (HRT) ranging from 1 to 3 hr depending upon permeate flux. Maintenance cleaning with NaOCl solution improved GAC scouring to reduce biofouling effectively, which allowed TMP less than 0.15 bar at 20 L/m2.hr. Energy required to operate the AFCMBR was reduced to 0.038 Kwh/m3 at 17 L/m2.hr, which was about 17% of the electrical energy converted by methane produced by AFCMBR.

Deposits discharged through the cleaning mainly were cement mortar, bitumen paintings and rust pieces, and fragments of perforation, stones and gravels. Deposits were more removed through swabbing pig cleaning rather than air scouring cleaning on the whole. However, air scouring cleaning were not influenced by the constraint conditions such as a change in the diameter or the presence of the valve in water mains compare to swabbing pig cleaning. So, it was thought that air scouring cleaning might be more favorable to water distribution network cleaning in the future. After the cleaning, water quality including residual chlorine and turbidity also was improved because of the removal of a significant amount of the deposits. Therefore, if the cleaning is continuously and regularly implemented in water mains, it is expected that it will help to recover the reliability and to preserve the health of water quality.

The main objective of this research is to study feasibility for applying metal membrane to remove particles from air scouring membrane backwash water. Also, the research was conducted to investigate the influence of polyamine coagulation on floc growth in membrane backwash water as pretreatment for removal particles. From the results of experiments for evaluating the influence of polyamine coagulation on floc growth, it was investigated that particles in the rage of 2~50 μm grew up to 30~5,000 μm. In addition, all six metal membranes showed lower removal efficiency, which was 0.87~13.89%, in the case of no polyamine coagulant. On the other hand, in the case of injecting polyamine coagulant, those did extremely high efficiency in 56~92%. From the SEM(Scanning Electron Microscope) images of filtered wiremesh and metal foam membrane, sieve effects were predominant for liquid solid separation in wiremesh and adsorption and diffusion capture effects were predominant in metal foam membrane.

Solvent-free low foaming scouring agents (LFSC) were prepared by blending of 2-ethylhexylaminoethyl sulfate (2-EHAS), POE(10) octadecylbenzyl- ammonium chloride (POBAC) and Sedlan FF-200 (FF-200). As the results of several tests, 2-EHAS/POBAC/FF-200/water (8g/12g/20g/60g) mixture (LFSC-5) showed good cleaning power, penetrating ability and stability to alkali, and gave less problem in water pollution. The foaming power of LFSC-5 measured by Ross and Miles method was 8mm foam height immediately after foaming, and that measured by Ross and Clark method was less than 300mm foam height at 30℃, and 18mm at 80℃. As a result, LFSC-5 proved a good low foaming scouring agent for fiber.

Low foaming scouring agents (LSSA) were prepared by blending of amine salt of dodecylbenzene sulfone, poly (PO-b-EO) glycol, Newpol PP-2000, MJU-100, ethylene glycol and organic solvent. As the results of several tests, LSSA-2 showed good scouring effect, penetrating ability and emulsifiability, and showed not much water pollution. The foaming power of LSSA-2 measured by Ross & Miles method was 11mm foam height immediately after foaming. And the foaming power of LSSA-2 measured by Ross & Clark method were less than 310mm foam height at 30℃, 17mm at 80℃. As a result, LSSA-2 was proved as a good foaming scouring agent.

본 연구는 하상재료의 종류와 유속에 따른 세굴변화에 대한 연구를 진행하였고, 유속, 구성방법 및 재료와 세굴에 대한 상관관계를 정의하여 호안 및 제방의 운용성을 검토하고자 실험을 통한 연구를 진행하였다. 본 연구의 실험에 사용된 재료는 제방에 사용되고 있는 재료로 모래, 황토를 이용 하였다. 실험실규모 고속수로에서 다양한 계측장비들을 이용하여 유속의 변화에 따른 재료의 세굴을 측정하였다. 이를 통해 세굴 전·후의 재료변 화를 수치적으로 분석하였다. 고유속흐름에서 하상재료에 따라 세굴의 정도를 비교·평가하여 안정성에 대한 연구도 진행하였다. 실험 결과 모래의 경우 응집력이 매우 약하여 1.0 m/s 이하에서도 40% 이상의 재료가 유실이 되고 황토의 경우 모래보다 유속이 빠른 2 m/s 이상에서도 6% 이하 의 재료가 유실이 되었다. 재료가 유실된 이유중 하나는 강한 응집력으로 건조균열이 발생하여 세굴에 취약한 결과를 보였다. 본 연구에서는 이러한 건조균열의 발생부터 재료가 유실되는 현상을 제거하는 방법부터 재료에 대한 구성과 유실정도를 평가 하였다.

해양구조물의 말뚝기초 주변에서 일어나는 세굴 현상은 구조물을 불안정하게 만들고 구조물의 기능을 잃게 만들기도 한다. 기초 주변에서 발생하는 와류는 세굴의 주된 요인이며, 그것은 유동조건, 지반조건, 기초의 형태 등에 영향을 받는다. 세굴에 의해서 해양구조물 기초말뚝의 근입깊이가 감소하면 지지력이 감소하고 구조물에 큰 변위가 일어나 결국 구조물의 붕괴로 이어지기도 한다. 본 연구에서는 해양구조물 주변에서의 세굴심을 예측하기 위해 STAR-CCM+라는 3차원 상용 CFD 소프트웨어를 이용하였다. 해저면을 높은 동점성계수와 밀도를 갖는 유체로 가정하여 VOF multiphase 모델을 이용한 세굴심 예측이 가능하도록 하였다. 이 모델은 RANS (Reynolds Averaged Navier-Stokes) 방정식 기반의 k-Є 난류모델을 해석하여 세굴심을 산정한다. 모델의 신뢰성을 확보하기 위해 실험 논문과의 비교가 이루어졌으며 유사성을 발견할 수 있었다.

본 연구에서는 수리실험을 실시하여 만곡부의 흐름특성과 만곡부에서의 교각 주위 국부세굴형상, 최대 국부세굴심 등을 분석하였다. 또한, 기존의 세굴보호공법 중 원환에 의한 보호공법을 만곡부에 적용하여 세굴감소효과를 분석하였다. 180' 만곡수로에 대해 이동상 실험결과 본 실험조건에서는 최대 횡방향 하상경사가 150' 단면에서 발생하였으며, 원환에 의한 세굴감소효과는 유로 직선부에서 최대 40%, 만곡부에서는 150' 단면 외측의 경우 최대 44%의 감소효과