• 멤브레인
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• 제27권6호
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• pp.519-527
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• 2017

멤브레인 파울링은 지표수를 처리하는 저압 멤브레인 기술 적용의 확장에 있어 큰 장애가 된다. 따라서 파울링 제어를 위한 주기적인 수리학적 세정기술의 최적화는 매우 중요하다. 주기적인 수리학적 세정과 이와 연관된 파울링 현상에 관한 올바른 이해는 멤브레인 세정 전략을 최적화하기 위해 매우 유용할 수 있다. 실험적으로 측정한 투과도와 전통적인 Hermia 파울링 모델 예측 치의 비교를 통해, 본 연구에서는 합성 탁도유발 시료를 처리하는 가압식 멤브레인 공정에서 30분 여과와 정세정/역세정이 포함된 1분 세정조건을 바탕으로 6번의 운전사이클을 통해 발생하는 파울링 현상을 분석하고 이를 통해 지배적인 파울링 기작을 정량적으로 이해하고자 하였다. 단독 세정에서, 첫 번째 운전사이클에서 발생하는 파울링은 완전공극막힘 현상에 의해 주로 지배되었고 마지막 운전 사이클에서는 케이크 형성이 지배적인 파울링 기작으로 관찰되었다. 정세정과 역세정이 혼합된 경우, 파울링 속도는 감소하였으나 전반적으로 케이크 형성이 주 파울링 기작으로 관찰되었다.

• 상하수도학회지
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• 제17권4호
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• pp.534-541
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• 2003

Membrane processes are now frequently considered for application in drinking water treatment. The biggest impediment for applying membrane processes is fouling that comes from mass flux (such as particle and organic matter) to the membrane surface and its pores due to convection flow through the membrane. Natural organic matter (NOM) has been reported as the most detrimental foulant. Some research also indicated that particles were often the dominant cause of fouling. Therefore, both NOM and particle fouling need to be examined to better understand fouling in ultrafiltration. Two waters from natural sources, Lake Austin water and Missouri River water, were selected. Both waters are relatively hard waters but has significantly different particle concentrations, which will elucidate effects of particles on membrane fouling. Precipitative softening is traditionally designed to remove hardness ions in hard waters but it can also remove particles and organic matter. Therefore, the integrated water treatment with softening and ultrafiltration is proposed as a promising option for hard waters. The three levels of softening were used to represent different degrees of pretreatment to ultrafiltration in terms of organic matter (i.e., NOM fouling) and precipitates (i.e., particle fouling by further precipitation). Results showed that natural particles in Missouri River water was detrimental foulants of ultrafiltration. As the levels of softening were increased, NOM and particle removal was increased, and thus fouling was decreased. Direct images of the surface of the membranes by scanning electron microscopy allowed observation of the different properties of particles caught in fibril networks of natural organic matter.

• Nuclear Engineering and Technology
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• 제52권3호
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• pp.581-588
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• 2020

The membrane fouling is an important problem for FO applied to the radioactive wastewater treatment. The FO fouling characteristics for simulated radioactive wastewater treatment was investigated. On-line cleaning by deionized (DI) water and external cleaning by ultrasound and HCl were applied for the fouled membrane. The effectiveness and foulant removing amount by each-step cleaning were evaluated. The membrane fouling was divided into three stages. Co(II), Sr(II), Cs(I), Na(I) were all found deposited on both active and support layers of the membrane surface, resulting in membrane surface became rougher and more hydrophobic, which increased membrane resistance. On-line cleaning by DI water recovered the water flux to 69%. HCl removed more foulants than ultrasound.

• 상하수도학회지
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• 제34권2호
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• pp.115-125
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• 2020

This study was aimed to examine inorganic fouling and fouling reduction method in direct contact membrane distillation(DCMD) process. Synthetic seawater of NaCl solution with CaCO₃ and CaSO₄ was used for this purpose. It was found in this study that both CaCO₃ and CaSO₄ precipitates formed at the membrane surface. More fouling was observed with CaSO₄(anhydrite) and CaSO₄·0.5H₂O(bassanite) than CaSO₄·2H₂O(gypsum). CaCO₃ and gypsum were detected at the membrane surface when concentrates of SWRO(seawater reverse osmosis) were treated by the DCMD process, while gypsum was found with MED(multi effect distillation) concentrates. Air backwash(inside to out) was found more effective in fouling reduction than air scouring.

• 한국물환경학회지
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• 제29권4호
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• pp.559-567
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• 2013

In recent years, NF (nanofiltration) membrane has been receiving great attention for hardness removal and has begun to replace traditional lime soda ash softening process, particularly in Florida, USA, mainly due to less sludge production and easy operation. This study aimed to provide detailed surface characteristics of various commercial NF membranes by performing sophisticated surface analysis, which would help more fundamentally understand the performance of NF membranes. More specifically, a total of 7 NF membranes from top NF/RO manufacturers in the world were examined for basic performance tests, surface analysis, and fouling potential assessment. The results demonstrated that NF membranes are classified into two groups in terms of surface zeta potential; they are highly negatively charged ones, and neutral and/or less negatively charged ones. Their hydrophobicities, measured by contact angle, varied from hydrophilic to slightly hydrophobic ones. The AFM measurements showed various surface roughness, ranging from 23 nm (smooth) to 162 nm (rough) of average peak height. Lab-scale fouling experiments were performed using feedwater obtained from conventional water treatment plants in the province of Korea, and their results attempted to correlate to surface characteristics of NF membranes. However, unlike typical RO membranes, no clear correlation was found in this study, indicating that fouling mechanisms of NF membrane may be different from those of typical RO membranes, and both cake deposition and pore blocking mechanisms should be considered simultaneously.

• 상하수도학회지
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• 제19권5호
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• pp.632-638
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• 2005

Membrane fouling index such as Silt Density Index (SDI) and Modified Fouling Index (MFI) is an important parameter in design of the integrated RO/NF membrane processes for drinking water treatment. In this study, the effect of particle, membrane and feed water characteristics on membrane fouling index were investigated systematically. Higher fouling index values were observed when filtering suspensions with smaller particle size and higher feed particle concentration. Larger membrane resistance due to smaller pore size resulted in an increased membrane fouling index. The variations of feed water hardness and TDS concentrations did not show any impact on fouling index, suggesting that there were no significant colloidal interactions among particles and thus the porosity of particle cake layer accumulated on the membrane surface could be assumed to be 0.36 according to random packing density. Based on the experimental observations, fundamental membrane fouling index model was developed using Happel Cell. The effect of primary model parameters including particle size ($a_p$), particle concentration ($C_o$), membrane resistance ($R_m$), were accurately assessed without any fitting parameters, and the prediction of membrane fouling index such as MFI exhibited very good agreement with the experimental results.

• 상하수도학회지
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• 제31권5호
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• pp.389-395
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• 2017

In this paper, we investigate the characteristics of membrane fouling caused by water temperature in the Membrane bioreactor(MBR) process and try to derive the membrane fouling control by chemical enhanced backwashing(CEB). The extracellular polymeric substances(EPS) concentration was analyzed according to the water temperature in the MBR, and the membrane fouling characteristics were investigated according to the conditions, with sludge & without sludge, through a lab-scale reactor. As shown in the existing literature the fouling resistance rate was increased within sludge with the water temperature was lowered. However, in the lab-scale test using the synthetic wastewater, the fouling resistance increased with the water temperature. This is because that the protein of the EPS was more easily adsorbed on the membrane surface due to the increase of entropy due to the structural rearrangement of the protein inside the protein as the water temperature increases. In order to control membrane fouling, we tried to derive the cleaning characteristics of CEB by using sodium hypochlorite(NaOCl). We selected the condition with the chemicals and the retention time, and the higher the water temperature and the chemical concentration are the higher the efficiencies. It is considered that the increasing temperature accelerated the chemical reaction such as protein peptide binding and hydrolysis, so that the attached proteinaceous structure was dissolved and the frequency of the reaction collision with the protein with the chemical agent becomes higher. These results suggest that the MBRs operation focus on the fouling control of cake layer on membrane surface in low temperatures. On the other hand, the higher the water temperature is the more the operation strategies of fouling control by soluble EPS adsorption are needed.

• 대한조선학회논문집
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• 제53권5호
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• pp.400-409
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• 2016

In recent, shipping companies have made an enormous effort to improve the operation of vessel in various approaches, due to recession of shipping market and increasing competition among shipping companies. One of important parameters for improving the efficiency of vessel is the resistance performance that consist of friction and residual resistance. Especially, it is recognized that the friction resistance tends to be affected by conditions of vessel’s surface and occupies approximately 70~90% of the total resistance for slow speed ships. In general, the surface of vessel is covered with various type of paint to reduce fouling and corrosion. As time goes by, however, it is so hull roughness would be increased by fouling over the wetted surface that anti-fouling paints, such as CDP(Controlled Depletion Paint), Tin-Free SPC(Self Polishing Co-polymer) or Foul Release, are applied evenly on the hull surface. Nevertheless, these anti-fouling paints could not prevent fouling absolutely. A fundamental study on evaluating ship resistance performance variation due to hull roughness has been performed using a commercial software, Star-CCM+, which solves the continuity and Navier-Stokes equations for incompressible and viscous flow. The results of present simulation for plate are compared with some experimental data available and the effect of surface roughness to ship resistance performance is discussed.

• 해양환경안전학회지
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• 제22권1호
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• pp.123-128
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• 2016

프로펠러 표면의 생물 부착이 프로펠러 성능에 상당한 영향을 미치지만 프로펠러 표면 거칠기와 관련된 연구는 상대적으로 선체 표면에 비하여 많지 않다. 본 연구에서는 Schultz(2007)가 발표한 Granville's similarity-law scaling 절차에 기초하여 실선 7 m 크기의 탱커 프로펠러에 표면 부착물 상태가 서로 다른 3가지 경우를 고려하여 프로펠러 단독 효율의 감소의 변화를 Lifting surface code를 사용하여 수치적 계산을 수행하여 효율을 비교하였다. 본 논문에서의 결과는 표면 거칠기가 큰 석회질 부착물($k_s=0.001$)은 선박 설계 속도(J=0.5)에서 최대 15 %의 프로펠러 효율 감소를 보였음을 확인하였으며 이는 선박 운항 시 생물 부착에 의한 효율 감소에 대한 평가가 고려되어야 한다는 점을 나타내고 있다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
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• pp.89-89
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• 2012