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Now showing items 1 - 16 of 67

  • Evaluation of membrane-based desalting processes for RO brine treatment

    Lee, Songbok   Kim, Youngjin   Kim, Albert S.   Hong, Seungkwan  

    Membrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20-30 degrees C. The applicability of RO, FO, and MD was further tested with real brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Foulant analysis suggested that CaCO3 scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3 scaling, however, had only small impact on flux behavior in MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat (below 50-70 degrees C) is available.
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  • Nanoscale Pillar-Enhanced Tribological Surfaces as Antifouling Membranes

    Choi, Wansuk   Chan, Edwin P.   Park, Jong-Hyun   Ahn, Won-Gi   Jung, Hyun Wook   Hong, Seungkwan   Lee, Jong Suk   Han, Ji-Young   Park, Sangpil   Ko, Doo-Hyun   Lee, Jung-Hyun  

    We present a nonconventional membrane surface modification approach that utilizes surface topography to manipulate the tribology of foulant accumulation on water desalination membranes via imprinting of submicron titanium dioxide (TiO2) pillar patterns onto the molecularly structured, flat membrane surface. This versatile approach overcomes the constraint of the conventional approach relying on interfacial polymerization that inevitably leads to the formation of ill-defined surface topography. Compared to the nonpatterned membranes, the patterned membranes showed significantly improved fouling resistance for both organic protein and bacterial foulants. The use of hydrophilic TiO2 as a pattern material increases the membrane hydrophilicity, imparting improved chemical antifouling resistance to the membrane. Fouling behavior was also interpreted in terms of the topographical effect depending on the relative size of foulants to the pattern dimension. In addition, computational fluid dynamics simulation suggests that the enhanced antifouling of the patterned membrane is attributed to the enhancement in overall and local shear stress at the fluid TiO2 pattern interface.
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  • Colloidal fouling in forward osmosis: Role of reverse salt diffusion

    Boo, Chanhee   Lee, Sangyoup   Elimelech, Menachem   Meng, Zhiyong   Hong, Seungkwan  

    Colloidal fouling behavior in forward osmosis (FO) was investigated, focusing on the role of reverse salt diffusion. Two suspensions of silica nanoparticles, with average particle diameters of 24 and 139 nm, were used as model colloidal foulants. To verify the effect of reverse salt diffusion on the colloidal fouling behavior, NaCl and LaCl3 were employed as draw solutions because they exhibit different reverse diffusion rates. Our results suggest that in colloidal fouling of FO, salts diffuse from the draw to the feed solution and accumulate within the colloidal fouling layer that forms on the membrane surface. The accumulated salts result in a marked acceleration of cake-enhanced osmotic pressure (CEOP), which reduces the net osmotic driving force for permeate water flux. Fouling was not observed with the small, 24-nm particles because of the lack of substantial cake formation, but was notable for the 139-nm particles and for a feed containing a mixture of the 24 and 139 nm particles. Our findings further indicate that colloidal fouling is enhanced under solution conditions (ionic strength and pH) within the colloidal cake layer that promote aggregation or destabilization of the silica particles. Colloidal fouling reversibility was also examined by varying the cross-flow velocity during the FO fouling runs. We showed that in the absence of colloidal particle destabilization/aggregation, the permeate flux during colloidal fouling in FO recovered almost completely when the cross-flow velocity was increased from 8.5 to 25.6 cm/s. Our results suggest that reverse salt diffusion in FO is a key mechanism that controls colloidal fouling behavior as well as fouling reversibility. Therefore, minimization of reverse salt diffusion through the selection of proper draw solutes and optimization of FO membrane selectivity are important for minimizing colloidal fouling as well as enhancing FO operation efficiency. (C) 2011 Elsevier B.V. All rights reserved.
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  • Treatment of medical radioactive liquid waste using Forward Osmosis (FO) membrane process

    Lee, Songbok   Kim, Youngjin   Park, Jungmi   Shon, Ho Kyong   Hong, Seungkwan  

    d The use of forward osmosis (FO) for concentrating radioactive liquid waste from radiation therapy rooms in hospitals was systematically investigated in this study. The removal of natural and radioactive iodine using FO was first investigated with varying pHs and draw solutions (DSs) to identify the optimal conditions for FO concentration. Results showed that FO had a successful rejection rate for both natural and radioactive iodine (I-125) of up to 99.3%. This high rejection rate was achieved at a high pH, mainly due to electric repulsion between iodine and membrane. Higher iodine removal by FO was also attained with a DS that exhibits a reverse salt flux (RSF) adequate to hinder iodine transport. Following this, actual radioactive medical liquid waste was collected and concentrated using FO under these optimal conditions. The radionuclides in the medical waste (I-131) were removed effectively, but the water recovery rate was limited due to severe membrane fouling. To enhance the recovery rate, hydraulic washing was applied, but this had only limited success due to combined organic-inorganic fouling of the FO membrane. Finally, the effect of FO concentration on the reduction of septic tank volume was simulated as a function of recovery rate. To our knowledge, this study is the first attempt to explore the potential of FO technology for treating radioactive waste, and thus could be expanded to the de-watering of the radioactive liquid wastes from a variety of sources, such as nuclear power plants.
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  • Retardation of wetting for membrane distillation by adjusting major components of seawater

    Kim, Hye-Won   Yun, Taekgeun   Hong, Seungkwan   Lee, Seockheon   Jeong, Seongpil  

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  • Comparison of bacterial communities of biofilms formed on different membrane surfaces.

    Lee, Sang-Hoon   Hong, Ted Inpyo   Kim, Bongchul   Hong, Seungkwan   Park, Hee-Deung  

    Bacterial biofilm communities formed on different membrane surfaces were investigated based on 16S rRNA gene sequence analysis. The biofilm communities were distinct from those of mixed-liquor and consisted mainly of Beta- and Gammaproteobacteria. Sequences of Xathomonas and Aquabacterium were mostly retrieved from the biofilm samples rather than from the mixed liquor. Furthermore, statistical analyses demonstrated the importance of a physico-chemical property of membrane, surface roughness, in structuring the bacterial biofilm communities. =20
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  • Measurements of assimilable organic carbon (AOC) in high saline conditions using P17

    Mun, Eunjeong   Lee, Sangyoup   Kim, Inhyuk   Kwon, Boksoon   Park, Heedueng   Hong, Seungkwan  

    Biofouling caused by the deposition or growth of microorganisms on the membrane surface is one of the major concerns in nanofiltration (NF) and reverse osmosis (RO) processes. Assimilable organic carbon (AOC) has been a useful index to assess the growth potential of bacteria. In the case of drinking water, the AOC assay method has been widely applied to estimate growth or regrowth potential of bacteria in distribution and storage systems. However, studies on AOC measurement for high salinity water samples such as brackish water and seawater are rather scarce. The objective of this research is to investigate the influence of water salinity on the conventional AOC assay method. AOC samples with different salt concentrations were prepared by varying NaCl concentration from 0 to 35,000 mg/L, while the acetate concentration was held at 100 mu g/L. The number of cells produced in water samples was measured by the heterotrophic plate count (HPC) method using R2A agar. The result showed that the cell production of Pseudomonas fluorescens strain P17 and Spirillum strain NOX decreased with increasing salinity. Especially, the growth of Spirillum strain NOX was noticeably influenced by water salinity. To further observe the relation between acetate concentration and cell production in high salinity water, organic-free saline water samples were prepared by spiking NaCl in deionized (DI) water. The organic-free saline water samples were enriched with acetate of which concentration was varied to be 0-1,000 mu g/L (as acetate). Also, P. fluorescens strain P17 was adjusted to high total dissolved solids (TDS) condition prior to being injected into the saline water samples. The result demonstrated that the amount of microorganisms increased with increasing acetate concentration. Although AOC measurement of saline water using Spirillum strain NOX seemed unacceptable, it was suggested that P. fluorescens strain P17 has the possibility to be used in measuring AOC in saline water. Moreover, the yield factor was altered as a result of reflecting salinity impact as the growth number of P. fluorescens strain P17 was unstable with high saline condition.
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  • Fouling evaluation and mechanisms in a FO-RO hybrid process for direct potable reuse

    Choi, Byeong Gyu   Kim, David Inhyuk   Hong, Seungkwan  

    A forward osmosis (FO) and reverse osmosis (RO) hybrid process was examined for sustainable direct potable reuse (DPR) of wastewater through integration with seawater desalination. Using real wastewater secondary effluent, feasibility of the FO-RO system for DPR was systematically assessed by investigating fouling behavior and its reversibility and evaluating the quality of produced water. Its technical advantages were further verified by the ease of fouling control. The results for the silt density index (SDI) and the modified fouling index (MFI) clearly demonstrated that FO significantly alleviated the potential of subsequent RO membrane fouling, leading to sustainable RO operation for wastewater reuse. Permeate water flux in FO was significantly recovered by physical cleaning. However, biopolymer-like substances was persistently accumulated on the FO membrane surface even after repeated cleaning, suggesting that pretreatment for removal of such substances causing irreversible fouling are required for long-term operation of the FO-RO process. Lastly, the final product water satisfied all 58 components of the quality standards for drinking water in Korea, confirming that the double barrier provided by the FO and RO membranes was adequate for DPR. (C) 2016 Elsevier B.V. All rights reserved.
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  • Comparison of fouling behavior in forward osmosis (FO) and reverse osmosis (RO)

    Lee, Sangyoup   Boo, Chanhee   Elimelech, Menachem   Hong, Seungkwan  

    Fouling behaviors during forward osmosis (FO) and reverse osmosis (RO) are compared. Alginate, humic acid, and bovine serum albumin (BSA) are used as model organic foulants, and two suspensions of silica colloids of different sizes are chosen as model particulate foulants. To allow meaningful comparison of fouling behavior, identical hydrodynamic operating conditions (i.e., initial permeate flux and cross-flow velocity) and feed water chemistries (i.e., pH, ionic strength, and calcium concentration) are employed during FO and RO fouling runs. The observed flux-decline behavior in FO changed dramatically with the type of organic foulant, size of colloidal foulant, and the type of the draw solution employed to generate the osmotic driving force. Based on these experimental data and the systematic comparisons of fouling behaviors of FO and RO, we provide new insights into the mechanisms governing FO fouling. In FO, reverse diffusion of salt from the draw solution to the feed side exacerbates the cake-enhanced osmotic pressure within the fouling layer. The elevated osmotic pressure near the membrane surface on the feed side leads to a substantial drop in the net osmotic driving force and, thus, significant decline of permeate flux. Our results further suggest that the structure (i.e., thickness and compactness) of the fouling layers of FO and RO is quite different. By varying the cross-flow velocity during the organic fouling runs, we were able to examine the fouling reversibility in FO and RO. The permeate flux during organic fouling in FO recovered almost completely with increasing cross-flow velocity, while no noticeable change was observed for the RO system. Our results suggest that organic fouling in FO could be controlled effectively by optimizing the hydrodynamics in the feed stream without employing chemical cleaning. (C) 2010 Elsevier B.V. All rights reserved.
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  • Understanding possible underlying mechanism in declining germicidal efficiency of UV-LED reactor

    Lee, Hyunkyung   Jin, Yongxun   Hong, Seungkwan  

    Since ultraviolet light emitting diodes (UV-LEDs) have emerged as an alternative light source for UV disinfection systems, enhancement of reactor performance is a demanding challenge to promote its practical application in water treatment process. This study explored the underlying mechanism of the inefficiency observed in flow-through mode UV disinfection tests to improve the light utilization of UV-LED applications. In particular, the disinfection performance of UV-LED reactors was evaluated using two different flow channel types, reservoir and pathway systems, in order to elucidate the impact of physical circumstances on germicidal efficiency as the light profile was adjusted. Overall, a significant reduction in germicidal efficiency was observed when exposure time was prolonged or a mixing chamber was integrated. Zeta analysis revealed that the repulsion rate between microorganisms decreased with UV fluence transfer, and that change might cause the shielding effect of UV delivery to target microorganisms. In line with the above findings, the reduction in efficiency intensified when opportunities for microbial collision increased. Thus, UV induced microbial aggregation was implicated as being a disinfection hindering factor, exerting its effect through uneven UV illumination. Ultimately, the results refuted the prevailing belief that UV has a cumulative effect. We found that the reservoir system achieved worse performance than the pathway system despite it providing 15 times higher UV fluence: the differences in germicidal efficiency were 1-log, 1.4-log and 1.7-log in the cases of P.aeruginosa, E.coli and S.aureus, respectively.
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  • Effect of cake layer structure on colloidal fouling in reverse osmosis membranes

    Park, Chanhyuk   Lee, Young Haeng   Lee, Sanghyup   Hong, Seungkwan  

    A series of reverse osmosis (RO) membrane filtration experiments was performed systematically in order to investigate the effects of various hydrodynamic and physicochemical operational parameters on a cake layer formation in colloidal and particulate suspensions. Bench-scale fouling experiments with a thin-film composite RO membrane were performed at various combinations of trans-membrane pressure (TMP), cross-flow velocity (CFV), particle size, pH, and ionic strength. In this study, silica particles with two different mean diameters of 0.1 and 3.0 mu m were used as model colloids. Membrane filtration experiments with colloidal suspensions under various hydrodynamic operating conditions resulted that more significant permeate flux decline was observed as TMP increased and CFV decreased, which was attributed to the higher accumulative mass of particles on the membrane surface. Results of fouling experiments under various physicochemical operating conditions demonstrated that the rate of flux decline decreased significantly with an increase of the ionic strength as well as particle size, while the flux decline rate did not vary when solution pH changed. The experimentally measured cake layer thickness increased with a decrease in particle size and solution ionic strength. Furthermore, the model estimation of cake layer thickness by using a cake filtration theory based on the hydraulic resistance of membrane and cake layer was performed under various ionic strength conditions. The primary model parameters including accumulated mass and specific cake resistance were calculated from the cake layer resistance. This result indicated that the formation of cake layer could be closely related with solution water chemistry. The model estimated cake layer thickness values were in good agreement with the experimentally measured values.
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  • Biofouling of reverse osmosis membranes: Microbial quorum sensing and fouling propensity

    Kim, Sejin   Lee, Sangyoup   Hong, Seungkwan   Oh, Youngsook   Seoul, Mijin   Kweon, Jihyang   Kim, Taehyun  

    Fouled RO membranes from a real water treatment plant were analyzed biochemically to investigate the role of quorum sensing in controlling the rate and the extent of biofilm formation on the membrane surface. The results showed that 60%, of bacterial species found on the fouled membrane surface contribute to biofilm formation through the active intraspecies as well as interspecies communication. It was confirmed that N-acylated homoserine lactones (AHL) produced from microorganisms involved in the quorum sensing transferred bacterial signal. In addition, flow field-flow fractionation (Fl-FFF) analyses demonstrated that most microorganisms contributing to biofilm formation through quorum sensing exhibited favorable adsorption on the membrane surfaces. The skewness values of these microorganisms were noticeably greater than those of organic macromolecules (i.e., natural organic matter) and particles. The study suggests that biochemical control of interfering quorum sensing could be an effective alternative to control biofilm formation and, thus, the reduction in biofouling of RO membranes.
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  • A new approach to the characterization of reverse osmosis membrane by dynamic hysteresis

    Lee, Eunsu   Lee, Sangyoup   Hong, Seungkwan  

    Physical aspects of dynamic hysteresis for characterizing reverse osmosis (RO) membranes have been investigated. Dynamic hysteresis was used as a parameter of showing physical surface characteristics of RO membranes. Automated microbalance was utilized to determine dynamic hysteresis based on the Wilhelmy plate method. Dynamic hysteresis determined with non-polar liquid was related to physical surface characteristics including surface roughness and heterogeneity determined by atomic force microscopy imaging and analysis. A remarkable correlation between dynamic hysteresis and surface heterogeneity was obtained when non-polar liquid was used during the measurements. Dynamic hysteresis increased as the surface heterogeneity of RO membrane increased.
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  • Boron transport in forward osmosis: Measurements, mechanisms, and comparison with reverse osmosis

    Kim, Changwoo   Lee, Sangyoup   Shon, Ho Kyong   Elimelech, Menachem   Hong, Seungkwan  

    The physical and chemical factors affecting boron solute flux behavior and membrane transport mechanisms in forward osmosis (FO) have been systematically investigated. Boron solute flux behavior in FO was further compared with that in reverse osmosis (RO) by employing identical plate-and-frame cells and membranes under the same filtration conditions. The influence of draw solution pH, draw solution type, and membrane orientation on boron solute flux was examined for FO, and the effects of water flux, cross-flow velocity, feed water boron concentration, and solution pH on boron solute flux were examined for both FO and RO. Results show that reverse salt diffusion, a unique feature of FO, is a key mechanism governing boron solute flux in FO. Boron solute flux through the FO membrane was inversely proportional to the degree of reverse salt diffusion by draw solution. The higher boron rejection observed in FO compared to RO is also attributed to reverse salt diffusion in FO. It is also shown that membrane orientation in FO plays an important role, affecting boron solute flux due to different degrees of internal concentration polarization. In both FO and RO, boron solute flux increased with increasing water flux. However, the influence of water flux on boron solute flux was less significantin FO than RO. Furthermore, boron solute flux decreased with increasing feed water pH due to the conversion of the neutral boric acid to borate anions. The findings provide new insight into the mechanisms and factors controlling boron solute transport in FO. (c) 2012 Elsevier B.V. All rights reserved.
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  • Evaluation on suitability of osmotic dewatering through forward osmosis (FO) for xylose concentration

    Kim, David Inhyuk   Choi, Jongmoon   Hong, Seungkwan  

    Forward osmosis (FO) has great potential for sustainable osmotic dewatering, which can attain several goals including low energy use, high water recovery, and low membrane fouling. However, this technology still involves critical issues that should be explored to achieve successful functioning of osmotic dehydration process, such as feed characteristics, FO membrane performance, and draw solution selection. In this study, the effectiveness of FO for osmotic dehydration was demonstrated by adopting xylose solution as model feed. Aside from current energy intensive evaporation methods, this widely used sweetener needs an advanced and energy-efficient concentration method such as FO. The stable performance showed xylose can be sustainably concentrated with a consistently high dewatering rate, whereas the recovery rate using a pressure-driven membrane system was constrained by the bursting pressure of nanofiltration membrane. Lastly, high-quality of concentrated product can be obtained by selecting a suitable draw solution of which its reversely diffused salts barely affect the xylose solution or are used to enhance the xylose quality. Employing Poly (aspartic acid) sodium salt or sugar-based solutes as draw help to preserve the purity of enriched xylose. These results suggest that FO can provide a feasible solution for food processing which requires product concentration through dewatering while preserving and improving its quality.
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  • Environmental and economic impacts of fertilizer drawn forward osmosis and nanofiltration hybrid system

    Kim, Jung Eun   Phuntsho, Sherub   Chekli, Laura   Hong, Seungkwan   Ghaffour, Noreddine   Leiknes, TorOve   Choi, Joon Yong   Shon, Ho Kyong  

    Environmental and economic impacts of the fertilizer drawn forward osmosis (FDFO) and nanofiltration (NF) hybrid system were conducted and compared with conventional reverse osmosis (RO) hybrid scenarios using microfiltration (MF) or ultrafiltration (UF) as a pre-treatment process. The results showed that the FDFO-NF hybrid system using thin film composite forward osmosis (TFC) FO membrane has less environmental impact than conventional RO hybrid systems due to lower consumption of energy and cleaning chemicals. The energy requirement for the treatment of mine impaired water by the FDFO-NF hybrid system was 1.08 kWh/m(3), which is 13.6% less energy than an MF-RO and 21% less than UF-RO under similar initial feed solution. In a closed-loop system, the FDFO-NF hybrid system using a TFC FO membrane with an optimum NF recovery rate of 84% had the lowest unit operating expenditure of AUD $0.41/m(3). Besides, given the current relatively high price and low flux performance of the cellulose triacetate and TFC FO membranes, the FDFO-NF hybrid system still holds opportunities to reduce operating expenditure further. Optimizing NF recovery rates and improving the water flux of the membrane would decrease the unit OPEX costs, although the TFC FO membrane would be less sensitive to this effect.
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