• Membrane and Water Treatment
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• 제7권5호
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• pp.433-449
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• 2016

The successful application of cleaning protocols is vital for optimized filtration processes. A series of experiments with an ultrafiltration ceramic tubular membrane were carried out for the foulants dextran and carboxymethyl cellulose. Firstly, the impact on fouling of concentration changes was investigated with the increase in resistance being used as the key parameter. In the second phase, removal of reversible fouling was also investigated by employing intermittent rinsing consisting of a cold water rinse followed by a hot one. A comparative analysis for both foulants is reported. Across a range of concentrations and for both foulants, the reduction in resistance due to rinsing was found to depend upon concentration (C); it changed as $C^n$ where n was found to be 0.3. A plausible semi-theoretical explanation is given. Thirdly, for both foulants, the application of a combination of strong alkaline solutions with oxidizing agent (mainly sodium hypochlorite) followed by acid was found to be appropriate for cleaning of the ceramic membrane. The effect of increased temperature for cleaning agents followed by a warm water rinse contributed positively to the cleaning capability.

• 대한환경공학회지
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• 제34권9호
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• pp.637-643
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• 2012

본 연구에서는 300 kDa 공경의 세라믹막을 이용하여 재이용 원수인 하수 2차 방류수를 처리하여 가역 및 비가역 막오염비율을 연구하였다. 이를 위하여 운전조건인 막간차압을 변화시킬 때의 각 막오염을 수치적으로 계산하고 F-EEM과 SEC분석을 시행하였다. 또한 탁도, TOC 및 UV254를 측정하여 수질의 안정성을 평가하였다. 막간차압이 낮을수록 비가역 막오염에서 가역 막오염으로의 형성이 증가하였으며, 이는 주로 분자량이 큰 단백질 성분으로 인한 것으로 나타났다. 또한 하수 2차 처리수에는 다양한 분자량의 오염물이 함유되어 있으나 상대적으로 0.5 kDa 이하의 작은 분자량을 가지는 오염물이 가장 많았으며, 그 다음으로는 12 kDa 이상의 물질이 많았다. 300 kDa의 세라믹막은 주로 6 kDa 이상의 물질을 제거하였으며, 막간차압이 낮을수록 12 kDa 이상의 고분자 물질과 1 kDa 이하 물질이 가역 막오염으로 형성되는 것으로 나타났다.

• 상하수도학회지
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• 제32권2호
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• pp.77-87
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• 2018

In this study, the effects of operating conditions on the formation of reversible and irreversible fouling were investigated in the filtration using ceramic membrane for water treatment process. The effect of coagulation pretreatment on fouling formation was also evaluated by comparing the performance of membrane filtration both with and without addition of coagulant. A resistance-in-series-model was applied for the analysis of membrane fouling. Total resistance (RT) and internal fouling resistance (Rf) increased in the membrane filtration process without coagulation as membrane flux and feed water concentrations increased. Internal fouling resistance, which was not recovered by physical cleaning, was more than 70% of the total resistance at the range of the membrane flux more than $5m^3/m^2{\cdot}day$. In the combined process with coagulation, the cake layer resistance (Rc) increased to about 30-80% of total resistance. As the cake layer formed by coagulation floc was easily removed by physical cleaning, the recovery rate by physical cleaning was 54~90%. It was confirmed from the results that the combined process was more efficient to recover the filtration performance by physical cleaning due to higher formation ratio of reversible fouling, resulted in the mitigation of the frequency of chemical cleaning.

• Environmental Engineering Research
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• 제24권2호
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• pp.298-308
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• 2019

This work deals with the membrane fouling mode and the unclogging in seawater ultrafiltration process. The identification of the fouling mechanism by modeling the experimental flux decline was performed using both the classical models of Hermia and the combined models of Bolton. The results show that Bolton models did not bring more precise information than the Hermia's and the flux decline can be described by one of the four Hermia's models since the backwash interval is ${\leq}60$ min. An experimental screening study has been then conducted to choose among 5 parameters (backwash interval, duration, pulses and the flow-rate or injected hypochlorite concentration) those that are the most influential on the fouling and the net water production. It has emerged that fouling is mainly affected by the backwash interval; its prolongation from 30 to 60 min engenders an increase in the reversible fouling and a decrease in the irreversible fouling. This later is also significantly reduced when the hypochlorite concentration increases from 4.5 to 10 ppm. Moreover, the net water production significantly increases with increasing the filtration duration up to 60 min and decreases with decreasing the backwash duration and backwash flow-rate from 10 to 40 s and from 15 to ${\geq}20L.min^{-1}$, respectively.

• Membrane and Water Treatment
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• 제8권5호
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• pp.499-515
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• 2017

The purpose of this study was to investigate membrane fouling caused by microalgal cells in submerged membrane systems consisting of polymeric and ceramic microfiltration membranes. In this study, one polymeric (flat-sheet, pore size: $0.2{\mu}m$) and two ceramic (flat-sheet, pore size: $0.2{\mu}m$ and cylindrical, pore size: $1{\mu}m$) membranes were used. Physical cleaning was performed with water and air to determine the potential for reversible and irreversible membrane fouling. The study results showed that substantial irreversible membrane fouling (after four filtration cycles, irreversible fouling degree 27% (cleaning with water) and 38% (cleaning with air)) occurs in the polymeric membrane. In cleaning studies performed using water and air on ceramic membranes, it was observed that compressed air was more effective (recovery rate: 87-91%) for membrane cleaning. The harvesting performance of the membranes was examined through critical flux experiments. The critical flux values for polymeric membrane with a pore size of $0.20{\mu}m$ and ceramic membranes with a pore size of $0.20{\mu}m$ and $1{\mu}m$ were ${\leq}95L/m^2hour$, ${\leq}70L/m^2hour$ and ${\leq}55L/m^2hour$, respectively. It was determined that critical flux varies depending on the membrane material and the pore size. To obtain more information on membrane fouling caused by microalgal cells, the characterization of the fouled polymeric membrane was performed. This study concluded that ceramic membranes with a pore size of $0.2-1{\mu}m$ in the submerged membrane system could be efficiently used for microalgae harvesting by cleaning the membrane with compressed air at regular intervals.

• 한국물환경학회지
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• 제33권4호
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• pp.403-408
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• 2017

In these days, wastewater reclamation and seawater desalination play essential role in addressing the challenge of worldwide water scarcity. Particularly, reverse osmosis (RO) for seawater desalination process is commonly used due to less energy consumption than conventional thermodynamic systems. However, membrane fouling and electrical energy consumption during operation of RO system for seawater desalination haver continued to be a obstruction to its application. In this study, therefore, wastewater secondary effluent is used for osmotic dilution of seawater. Firstly, fouling behaviour of RO by simulating wastewater effluent in osmotic dilution process was measured and we calculated energy consumption of overall desalination process by theoretical equations and commercial program. Our results reveal that RO membrane fouling can be efficiently controlled by pre-treatment systems such as nano filtration (NF) or forward osmosis (FO) process. Especially FO system for osmotic dilution process is a non-pressurized membrane system and, therefore, the operating energy consumption of overall desalination system was the lowest. Moreover, fouling layer on FO membrane is comparatively weak and reversible enough to be disrupted by physical cleaning. Thus, RO system with low salinity feed water through FO process is possible as a less energy consuming desalination system with efficient membrane fouling control.

• 상하수도학회지
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• 제23권4호
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• pp.459-469
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• 2009

It is well known that coagulation pretreatment can reduce foulants prior to membrane filtration. The purpose of this research was to investigate the effects of coagulation on fouling of ceramic microfiltration membrane($0.1 {\mu}m$) using pilot plant of $150m^3/day/train$ capacity. Train A membrane system has pretreatment process of ozonation and coagulation while train B has only coagulation. Two types of coagulation operation were investigated: back mixer(rapid mixing with or without slow mixing) which is a conventional mechanically stirred mixer and an inline static mixer. Ozone dose rate for train A was 1 mg/L and ozone contact time was 12 min. The coagulation dose(PACl 10% as $Al_2O_3$) rate was changed 20~40 mg/L according to experimental schedule. In this experimental conditions, the coagulation of back mixer type with rapid mixing(GT=72,000) and slow mixing(GT=45,000) was the best effective in reduction of ceramic membrane fouling regardless preozonation. Especially, the effect of inline static mixer was sensitive to change in water quality. Ozonation mainly affected irreversible fouling rather than reversible fouling in accordance with less adsorption of NOM on the membrane surface. Thus, the increase rate of the nomalized TMP(trans membrane pressure) at $25^{\circ}C$ for train A was relatively lower than that of train B under same coagulation process with same coagulant dosage. The best performance of ceramic membrane appeared in case of combined process with ozonation, therefore this integrated process is able to archive less coagulant dosing and secure a stability of ceramic membrane system.

• 상하수도학회지
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• 제27권3호
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• pp.363-371
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• 2013

In this study, effect of activated carbon size on flux and fouling of membrane was investigated on activated carbon and membrane hybrid system. The activated carbon was prepared with crushing and screening. The activated carbon was named by A100, B100, A200, B200, A325 and B325 due to size of activated carbon. The permeability for A100, B100, A200 and B200 showed no significant difference. However, the permeability for A325 and B325 was decreased rapidly and was lowed due to increase the concentration of NOM. Main resistance for A100, B100, A200 and B200 was identified as irreversible fouling. However main resistance for A325 and B325 was identified as reversible fouling. The smaller activated carbon adsorbs NOM faster than bigger particles, which can show high permeability at early stage of the operation and then showed faster decrease of permeability at end of the operation.

• 상하수도학회지
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• 제31권2호
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• pp.161-168
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• 2017

Microfiltration (MF) and Ultrafiltration (UF) membrane processes capable of producing highly purified water have been extensively applied as a pretreatment process in the wastewater reuse field with the improvement of membrane properties and resistance, development of operating protocols, and improvement of technologies of backwashing and physicochemical cleaning, and improvement of scale and antifoulants. However, despite of the development of membrane production and process technologies, fouling still remains unresolved. This study confirmed that foulants such as polysaccharides, proteins and humic substances existed in final treated effluent (secondary effluent) by fluorescence excitation emission matrix (FEEM) and fourier transform infrared spectroscopy (FTIR) analysis. In addition, when constructing ozone oxidation and coagulation processes as a hybrid process, the removal efficiency was 5.8%, 6.9%, 5.9%, and 28.2% higher than that of the single process using coagulation in turbidity, color, dissolved organic carbon (DOC), and UV254, respectively. The reversible and irreversible resistances in applying the hybrid process consisting of ozone oxidation and coagulation processes were lower than those in applying ozone oxidation and coagulation processes separately in UF membrane process. Therefore, it is considered possible to apply ozonation/coagulation as a pretreatment process for stable wastewater reuse by and then contributing to the reduction of fouling when calculating the optimal conditions for ozone oxidation and coagulation and then to applying them to membrane processes.

• 멤브레인
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• 제32권6호
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• pp.390-400
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• 2022

나노여과막(NF)은 식품가공, 제약 등 폐수는 물론 지자체 하수처리시설에서 배출되는 폐수 처리에 있어 훨씬 낮은 압력으로 운용이 가능해 역삼투막(RO)보다 인기가 높다. NF막의 경우 분리 메커니즘은 투과확산 기작과 더불어 RO 박막보다 낮은 가교밀도로 인한 체거름 메커니즘이다. 막 오염은 세라믹 막과 달리 고분자 막의 경우 나노 여과 공정의 고질적인 문제 중 하나이다. 이러한 문제를 해결하기 위해 차아염소산나트륨을 사용한 멤브레인 세척이 이루어진다. 폴리머 멤브레인에 비해 세라믹 멤브레인은 이러한 화합물에 매우 안정적이다. 본 리뷰에서는 NF 프로세스에 의한 폐수 처리의 다양한 유형의 세라믹 막 적용에 대해 논의한다.