The Experts below are selected from a list of 9213 Experts worldwide ranked by ideXlab platform
Menachem Elimelech - One of the best experts on this subject based on the ideXlab platform.
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role of pressure in organic Fouling in forward osmosis and reverse osmosis
Journal of Membrane Science, 2015Co-Authors: Long D Nghiem, Menachem ElimelechAbstract:Fundamental understanding of membrane Fouling in osmosis-driven membrane processes is important for further deployment of this emerging technology in desalination and wastewater reuse. In this study, we investigated the role of pressure in organic Fouling and reversibility in forward osmosis (FO) and reverse osmosis (RO) using alginate as a model organic foulant. Varying contributions of pressure (i.e., osmotic versus hydraulic) to the overall driving force were realized in forward osmosis (FO), pressure-assisted FO (PFO), and reverse osmosis (RO) experiments, while the same total driving force for water permeation was applied. Confocal laser scanning microscopy was used to examine alginate Fouling Layer structure in the hydrated state, which informed two key parameters: Fouling Layer thickness and foulant volume. We observed that the resulting Fouling Layer became increasingly more compact in the order of FO, PFO, and RO experiments. Fouling Layer reversibility followed the same trend, with the highest and lowest reversibility observed for the FO and RO Fouling experiments, respectively. Possible mechanisms for Fouling Layer compaction in RO were discussed, including permeate drag force and foulant compressibility, as opposed to FO where only permeate drag force applies. Our findings suggest that pressure mechanistically alters the membrane Fouling Layer structure and Fouling reversibility, leading to higher Fouling reversibility in FO, where the driving force is osmotic pressure, than RO, where the driving force is hydraulic pressure.
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combined organic and colloidal Fouling in forward osmosis Fouling reversibility and the role of applied pressure
Journal of Membrane Science, 2014Co-Authors: Menachem Elimelech, Ho Kyong Shon, Seungkwan HongAbstract:Abstract In this study, we systematically investigated the propensity and reversibility of combined organic–colloidal Fouling in forward osmosis (FO) under various solution chemistries (pH and calcium ion concentrations) and applied hydraulic pressure on the feed side. Alginate, silica colloids, and their mixture (i.e., combined organic–colloidal) were used as model foulants. Our findings demonstrate that combined organic–colloidal foulants caused more rapid flux decline than the individual foulants due to the synergistic effect of alginate and silica colloids. As a result, much lower flux recovery was achieved by physical cleaning induced by increasing the cross-flow rate, in contrast to single foulants of which the Fouling Layer was easily removed under all solution conditions. Interestingly, less flux decline was observed at neutral pH for combined Fouling, while acidic conditions were favorable for alginate Fouling and basic solutions caused more silica Fouling, thereby providing clear evidence for the combined Fouling effect. It was also found that calcium ions enhanced water flux decline and induced the formation of less reversible combined organic–colloidal Fouling Layers. Lastly, the role of applied hydraulic pressure on the feed side in FO was examined to elucidate the mechanism of Fouling Layer formation, Fouling reversibility, and water flux recovery. Higher Fouling propensity and lower Fouling reversibility of combined organic–colloidal Fouling were observed in the presence of applied hydraulic pressure on the feed side. This observation suggests that the lower Fouling propensity and greater Fouling reversibility in FO compared to reverse osmosis (RO), are attributable to unpressurized operating conditions in FO.
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impact of organic and colloidal Fouling on trace organic contaminant rejection by forward osmosis role of initial permeate flux
Desalination, 2014Co-Authors: Long D Nghiem, William E Price, Menachem ElimelechAbstract:Abstract Fouling behaviour and its impact on the rejection of trace organic contaminants (TrOCs) by forward osmosis (FO) were investigated. Membrane Fouling was simulated using humic acid and colloidal particles as model foulants at different initial permeate water fluxes. Water flux decline was insignificant at an initial permeate flux of 9 L/m 2 h and the Fouling Layer was loose and fluid-like. By contrast, the water flux decline was substantial at an initial permeate flux of 20 L/m 2 h, resulting in the formation of a compact Fouling Layer. Water flux recovery after physical cleaning for both humic acid and colloidal particle fouled membranes was consistently higher at an initial permeate flux of 9 L/m 2 h compared to 20 L/m 2 h. The results suggest that the Fouling Layer structure varied from a fluid-like loose Layer at low initial permeate flux to a more cohesive and compact Layer at high initial permeate flux. We surmise that the fluid-like loose Layer formed at low initial permeate flux contributed to pore blockage and thus enhanced steric hindrance, thereby leading to an increase in TrOC rejection. By contrast, the cohesive and compact Fouling Layer formed at high initial permeate flux exacerbated cake-enhanced concentration polarisation, resulting in a decrease in TrOC rejection.
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Fouling control in a forward osmosis process integrating seawater desalination and wastewater reclamation
Journal of Membrane Science, 2013Co-Authors: Chanhee Boo, Menachem Elimelech, Seungkwan HongAbstract:A hybrid system that combines forward osmosis with a reverse osmosis seawater desalination process could reduce both energy requirements and environmental impacts by osmotic dilution of the seawater and concentrated brine with an impaired low salinity stream, such as treated wastewater effluent. In this study, we investigate the membrane Fouling behavior in forward osmosis under conditions simulating the osmotic dilution process and the use of hydrodynamic methods without the use of cleaning chemicals, to control membrane Fouling. Fouling runs with seawater or SWRO brine draw solution and deionized (DI) water feed solution showed insignificant water flux decline, which implies negligible effect of particulate and organic matter in the seawater/brine on Fouling of the FO membrane support Layer. Fouling of the membrane active Layer was evaluated by using an enriched synthetic wastewater effluent containing a mixture of inorganic and organic foulants, focusing on the impact of permeate drag force on Fouling Layer formation. Our results demonstrate that higher permeate water flux causes an increase in concentration build-up of foulants at the membrane surface, thereby forming a dense inorganic/organic combined Fouling Layer during FO Fouling runs. We also examined three hydrodynamic methods for minimizing FO membrane Fouling in the osmotic dilution process: (1) applying shear force on the membrane surface by increasing the cross-flow velocity, (2) using a feed-channel spacer to induce turbulence, and (3) employing pulsed flow to remove foulants from the membrane surface. Our results show that these hydrodynamic methods substantially reduce Fouling and flux decline rate.
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mechanisms of colloidal natural organic matter Fouling in ultrafiltration
Journal of Membrane Science, 2006Co-Authors: Ana Rita Costa, Maria Norberta De Pinho, Menachem ElimelechAbstract:The role of membrane pore size and solution chemistry in ultrafiltration (UF) membrane Fouling by colloidal natural organic matter (NOM) has been investigated. Fouling experiments were conducted with two laboratory-made cellulose acetate UF membranes, with estimated pore sizes of 2 and 10 nm, under identical hydrodynamic conditions. Flux decline with colloidal NOM was independent of pH and increased in the presence of calcium. The membrane pore size has been found to influence membrane flux decline. Permeate flux for the more permeable membrane (10 nm pore size) decreased faster than the flux of the tightest, less permeable membrane (2 nm pore size). The adhesion forces between the foulant (colloidal NOM) and the clean membrane, and between the foulant in bulk solution and foulant in the Fouling Layer, were determined by atomic force microscopy (AFM). Force measurements confirmed the Fouling trends with calcium ions. For a given solution chemistry, foulant–foulant adhesion was identical for both membranes, indicating that the more pronounced flux decline observed for the largest pore-size membrane was not related to differences in intermolecular chemical interactions among NOM molecules. At the earlier stage of filtration, the dominant Fouling mechanism was pore blocking for both membranes. For longer filtration times, there was a transition in the Fouling mechanism from pore blocking to cake formation. This transition occurred first for the more permeable membrane, indicating that colloidal NOM penetrates more readily into the pores of this membrane and that the relative size of colloidal NOM and the membrane pore influences the rate of pore blocking. The results further suggest that the structure of the Fouling Layer is dependent on the operating pressure. At high pressure, the compactness and specific resistance of the colloidal NOM Layer substantially increase, and thus, significantly affect the extent of flux decline.
Heng Liang - One of the best experts on this subject based on the ideXlab platform.
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biological pre treatments enhance gravity driven membrane filtration for the decentralized water supply linking extracellular polymeric substances formation to flux stabilization
Journal of Cleaner Production, 2018Co-Authors: Xiaobin Tang, Guibai Li, An Ding, Wouter Pronk, Jinlong Wang, Xiaoxiang Cheng, Christopher Ziemba, Jiajian Xing, Heng LiangAbstract:Abstract Gravity-driven membrane (GDM) filtration is a promising technology for decentralized drinking water treatment due to its low energy requirements and simple operation. The reduced flux observed in GDM systems relative to other membrane treatment techniques remains a vital obstacle to their wider application. With the goal of further improving membrane flux and permeate quality, three simple and practical technologies have been examined as pre-treatments for GDM systems, (i) slow filtration with granular activated carbon (GAC), expected to remove both biodegradable and non-biodegradable contaminants, (ii) slow filtration with modified fiber ball (MFB), expected to promote biodegradation of organic compounds and (iii) microfiltration (MF), expected to reject suspended substances and particles. Results indicated that stable permeability increased by approximately 230%, 150% and 100% in GDM systems employing GAC, MFB and MF pre-treatments compared to the control. The dissolved organic compounds (DOC) were removed by approximately 60% and 30% in GAC/GDM and MFB/GDM, while MF/GDM and GDM control were not effective at DOC removal. Correlations between the stable flux and extracellular polymeric substances (EPS) concentration (R 2 > 0.9) indicated that reduction of EPS should be responsible for the flux improvements. Tracing the fate of florescent foulants illustrated that the EPS was mainly secreted/converted by the microbes colonizing within the bio-Fouling Layer of the GDM system. During long-term filtration, assimilable organic compounds (AOC) which can serve as nutrients for the growth of microbes within the bio-Fouling Layer were efficiently consumed (>50%) by the biological pre-treatments. This reduction in AOC was linked with a reduction in the growth/activity of bacteria within the bio-Fouling Layer of GDM system and a reduction in EPS accumulation. Overall, biological pre-treatments can significantly enhance the flux and water quality produced by a GDM system without significantly increasing the operation and maintenance. These improvements in flux and water quality can hopefully spark wider adoption of GDM as an economical and environmentally-friendly technology for decentralized drinking water treatment.
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in situ coagulation versus pre coagulation for gravity driven membrane bioreactor during decentralized sewage treatment permeability stabilization Fouling Layer formation and biological activity
Water Research, 2017Co-Authors: An Ding, Jinlong Wang, Dachao Lin, Xiaobin Tang, Xiaoxiang Cheng, Nanqi Ren, Heng LiangAbstract:Abstract Gravity-driven membrane filtration systems are promising for decentralized sewage treatment due to their low energy consumption and low maintenance. However, the low stable permeability/flux is currently limiting their wider application. With the ultimate goal of increasing permeability, the aim of this study was to evaluate the effect of coagulation (in situ coagulation and pre-coagulation) on the performance of a gravity-driven membrane bioreactor (GDMBR) during treatment of synthetic sewage. Results show that in situ coagulation significantly increased permeability (more than two-fold); however, no stabilization of permeability occurred over the whole operation, when non-coagulated and pre-coagulated reactors were compared. The high permeability observed was attributed to the accumulated aluminium floc in the reactor, which prevented formation of fluorescent microbial metabolites (aromatic and tryptophan proteins, as well as fulvic acids), and further avoided membrane pore blocking. In addition, the surface porosity of the Fouling Layer was improved (from 11.2% to 32.4% for non-coagulated and in situ coagulated reactors). The unstable permeability was possibly associated with lower biological processes within the Fouling Layer. These might include lower adenosine triphosphate (ATP) content and lower fluorescent metabolites from the extracellular polymeric substances (EPS) caused by the accumulated Al (compared with the control). On the other hand, pre-coagulation improved the level of stable permeability compared with the control (80 versus 40 L/m2 h bar), mainly because pre-coagulation decreased the EPS content and also maintained high ATP content of the Fouling Layer. In addition, both coagulation processes reduced the total filtration resistance, mainly the hydraulically reversible resistance and cake Layer resistance, which could lower the cleaning frequency. Overall, coagulation could greatly increase the removal efficiency and improve the GDMBR permeability, which would make the process suitable for decentralized wastewater treatment.
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a low energy gravity driven membrane bioreactor system for grey water treatment permeability and removal performance of organics
Journal of Membrane Science, 2017Co-Authors: Heng Liang, An Ding, Ilona Szivak, Jacqueline Traber, Wouter PronkAbstract:Abstract Synthetic grey water was treated with a low-pressure gravity-driven membrane bioreactor (GDMBR) system. The system was operated without any direct shear at the membrane surface and without any cleaning or flushing. In order to reduce energy consumption, one reactor was operated without aeration and the results were compared with an aerated reactor. Although the dissolved oxygen content was low (0.4–0.6 mg/L) in the non-aerated system, a stable permeability was observed at a level of around 20 L/m2 h bar (flux of 1 L/m2 h). The Fouling resistance was dominated by the bio-Fouling Layer, which could be removed hydraulically. In comparison to the aerated system, the bio-Fouling Layer grown without aeration exhibited a lower biological activity, was thicker and had a lower surface roughness. Furthermore, the stable permeability of the aerated system was higher (40 L/m2 h bar), which could be explained by a lower content and load of extracellular polymeric substances (including extracellular polysaccharides and proteins). In comparison to filtration through a non-fouled membrane, the rejection of biopolymers and humic substances was strongly enhanced, which shows that the bio-Fouling Layer acts as a secondary membrane. The energy consumption was 0.02–0.04 kWh/m3, which is substantially less than for normal MBRs, and even less than for the traditional activated sludge process. These results show that grey water can be treated in a membrane reactor without any cleaning and flushing and even without any aeration, which makes the process suitable for decentralized wastewater treatment and considerably reduces the energy consumption.
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impact of aeration shear stress on permeate flux and Fouling Layer properties in a low pressure membrane bioreactor for the treatment of grey water
Journal of Membrane Science, 2016Co-Authors: Nicolas Derlon, Eberhard Morgenroth, Heng Liang, An Ding, Ilona Szivak, Wouter PronkAbstract:Abstract Two different aeration regimes were studied in a low pressure gravity driven membrane bioreactor without any flushing or (back-) washing. In one reactor, the aeration was positioned below the membrane module, thus exposing the membranes to aeration shear stress. A second reactor was operated at low shear stress by placing the aerator in a different compartment. Flux stabilization at 2.0 L/(m 2 h) occurred in the reactor with low shear stress while no flux stabilization was observed in the reactor with aeration shear stress, resulting in a flux of 0.5 L/(m 2 h) after 120 days. The thickness of the bio-Fouling Layer in the reactor with aeration shear was smaller (129 vs. 344 µm), which implies that shear stress resulted in a thinner, denser and less permeable bio-Fouling Layer. The results can be explained by differences in (1) the morphology of the bio-Fouling Layer and (2) the EPS contents (proteins and polysaccharides) in the bio-Fouling Layer. The low-shear system provides a suitable solution for decentralized grey water treatment, or other conditions where maintenance and energy consumption should be minimized. Furthermore, the results can contribute to decrease the energy consumption in MBR systems.
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hydraulic irreversibility of ultrafiltration membrane Fouling by humic acid effects of membrane properties and backwash water composition
Journal of Membrane Science, 2015Co-Authors: Haiqing Chang, Fangshu Qu, Huarong Yu, Kai Li, Guibai Li, Heng LiangAbstract:Abstract Five commercially available ultrafiltration (UF) membranes: polyethersulfone (PES, 100 kDa), polyvinylidene fluoride (PVDF, 100 kDa) and cellulose acetate (CA, 100, 30 and 10 kDa), were fouled with humic acid (HA) solutions and cleaned using various compositions of backwash water including ultrapure water, monovalent cations (Na + ), divalent cations (Ca 2+ ), an organic compound (HA) and UF permeate. The hydraulically irreversible Fouling and the hydraulic cleaning efficiency (HCE) for each combination of membrane and backwash water composition were analyzed. In summary, both the membrane properties and the backwash water composition affected hydraulically irreversible Fouling. The membrane properties significantly affected the total Fouling, and the HCE was primarily affected by the backwash water composition. Further, the adhesive free energy between HA and the membranes correlated well with the total Fouling. Ultrapure water was superior to UF permeate for backwashing, and the presence of appropriate components (e.g., Na + or HA) further improved the HCE; however, Ca 2+ exerted detrimental impacts on the HCE. In addition, the removal of the deposited HA was consistent with the amount of Ca 2+ released from the Fouling Layer during backwashing. Mechanistic analysis suggested that the backwashing process involves Fouling Layer swelling, ion exchange, electric double Layer release and competitive complexation.
Frank Lipnizki - One of the best experts on this subject based on the ideXlab platform.
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analysis of membrane Fouling by brunauer emmet teller nitrogen adsorption desorption technique
Scientific Reports, 2020Co-Authors: Tiina Virtanen, Gregor Rudolph, Anastasiia Lopatina, Basel Alrudainy, Herje Schagerlof, Liisa Puro, Mari Kallioinen, Frank LipnizkiAbstract:Membrane Fouling is the major factor limiting the wider applicability of the membrane-based technologies in water treatment and in separation and purification processes of biorefineries, pulp and paper industry, food industry and other sectors. Endeavors to prevent and minimize Fouling requires a deep understanding on the Fouling mechanisms and their relative effects. In this study, Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique was applied to get an insight into pore-level membrane Fouling phenomena occurring in ultrafiltration of wood-based streams. The Fouling of commercial polysulfone and polyethersulfone membranes by black liquor, thermomechanical pulping process water and pressurized hot-water extract was investigated with BET analysis, infrared spectroscopy, contact angle analysis and pure water permeability measurements. Particular emphasis was paid to the applicability of BET for membrane Fouling characterization. The formation of a Fouling Layer was detected as an increase in cumulative pore volumes and pore areas in the meso-pores region. Pore blocking was seen as disappearance of meso-pores and micro-pores. The results indicate that the presented approach of using BET analysis combined with IR spectroscopy can provide complementary information revealing both the structure of Fouling Layer and the chemical nature of foulants.
An Ding - One of the best experts on this subject based on the ideXlab platform.
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biological pre treatments enhance gravity driven membrane filtration for the decentralized water supply linking extracellular polymeric substances formation to flux stabilization
Journal of Cleaner Production, 2018Co-Authors: Xiaobin Tang, Guibai Li, An Ding, Wouter Pronk, Jinlong Wang, Xiaoxiang Cheng, Christopher Ziemba, Jiajian Xing, Heng LiangAbstract:Abstract Gravity-driven membrane (GDM) filtration is a promising technology for decentralized drinking water treatment due to its low energy requirements and simple operation. The reduced flux observed in GDM systems relative to other membrane treatment techniques remains a vital obstacle to their wider application. With the goal of further improving membrane flux and permeate quality, three simple and practical technologies have been examined as pre-treatments for GDM systems, (i) slow filtration with granular activated carbon (GAC), expected to remove both biodegradable and non-biodegradable contaminants, (ii) slow filtration with modified fiber ball (MFB), expected to promote biodegradation of organic compounds and (iii) microfiltration (MF), expected to reject suspended substances and particles. Results indicated that stable permeability increased by approximately 230%, 150% and 100% in GDM systems employing GAC, MFB and MF pre-treatments compared to the control. The dissolved organic compounds (DOC) were removed by approximately 60% and 30% in GAC/GDM and MFB/GDM, while MF/GDM and GDM control were not effective at DOC removal. Correlations between the stable flux and extracellular polymeric substances (EPS) concentration (R 2 > 0.9) indicated that reduction of EPS should be responsible for the flux improvements. Tracing the fate of florescent foulants illustrated that the EPS was mainly secreted/converted by the microbes colonizing within the bio-Fouling Layer of the GDM system. During long-term filtration, assimilable organic compounds (AOC) which can serve as nutrients for the growth of microbes within the bio-Fouling Layer were efficiently consumed (>50%) by the biological pre-treatments. This reduction in AOC was linked with a reduction in the growth/activity of bacteria within the bio-Fouling Layer of GDM system and a reduction in EPS accumulation. Overall, biological pre-treatments can significantly enhance the flux and water quality produced by a GDM system without significantly increasing the operation and maintenance. These improvements in flux and water quality can hopefully spark wider adoption of GDM as an economical and environmentally-friendly technology for decentralized drinking water treatment.
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in situ coagulation versus pre coagulation for gravity driven membrane bioreactor during decentralized sewage treatment permeability stabilization Fouling Layer formation and biological activity
Water Research, 2017Co-Authors: An Ding, Jinlong Wang, Dachao Lin, Xiaobin Tang, Xiaoxiang Cheng, Nanqi Ren, Heng LiangAbstract:Abstract Gravity-driven membrane filtration systems are promising for decentralized sewage treatment due to their low energy consumption and low maintenance. However, the low stable permeability/flux is currently limiting their wider application. With the ultimate goal of increasing permeability, the aim of this study was to evaluate the effect of coagulation (in situ coagulation and pre-coagulation) on the performance of a gravity-driven membrane bioreactor (GDMBR) during treatment of synthetic sewage. Results show that in situ coagulation significantly increased permeability (more than two-fold); however, no stabilization of permeability occurred over the whole operation, when non-coagulated and pre-coagulated reactors were compared. The high permeability observed was attributed to the accumulated aluminium floc in the reactor, which prevented formation of fluorescent microbial metabolites (aromatic and tryptophan proteins, as well as fulvic acids), and further avoided membrane pore blocking. In addition, the surface porosity of the Fouling Layer was improved (from 11.2% to 32.4% for non-coagulated and in situ coagulated reactors). The unstable permeability was possibly associated with lower biological processes within the Fouling Layer. These might include lower adenosine triphosphate (ATP) content and lower fluorescent metabolites from the extracellular polymeric substances (EPS) caused by the accumulated Al (compared with the control). On the other hand, pre-coagulation improved the level of stable permeability compared with the control (80 versus 40 L/m2 h bar), mainly because pre-coagulation decreased the EPS content and also maintained high ATP content of the Fouling Layer. In addition, both coagulation processes reduced the total filtration resistance, mainly the hydraulically reversible resistance and cake Layer resistance, which could lower the cleaning frequency. Overall, coagulation could greatly increase the removal efficiency and improve the GDMBR permeability, which would make the process suitable for decentralized wastewater treatment.
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a low energy gravity driven membrane bioreactor system for grey water treatment permeability and removal performance of organics
Journal of Membrane Science, 2017Co-Authors: Heng Liang, An Ding, Ilona Szivak, Jacqueline Traber, Wouter PronkAbstract:Abstract Synthetic grey water was treated with a low-pressure gravity-driven membrane bioreactor (GDMBR) system. The system was operated without any direct shear at the membrane surface and without any cleaning or flushing. In order to reduce energy consumption, one reactor was operated without aeration and the results were compared with an aerated reactor. Although the dissolved oxygen content was low (0.4–0.6 mg/L) in the non-aerated system, a stable permeability was observed at a level of around 20 L/m2 h bar (flux of 1 L/m2 h). The Fouling resistance was dominated by the bio-Fouling Layer, which could be removed hydraulically. In comparison to the aerated system, the bio-Fouling Layer grown without aeration exhibited a lower biological activity, was thicker and had a lower surface roughness. Furthermore, the stable permeability of the aerated system was higher (40 L/m2 h bar), which could be explained by a lower content and load of extracellular polymeric substances (including extracellular polysaccharides and proteins). In comparison to filtration through a non-fouled membrane, the rejection of biopolymers and humic substances was strongly enhanced, which shows that the bio-Fouling Layer acts as a secondary membrane. The energy consumption was 0.02–0.04 kWh/m3, which is substantially less than for normal MBRs, and even less than for the traditional activated sludge process. These results show that grey water can be treated in a membrane reactor without any cleaning and flushing and even without any aeration, which makes the process suitable for decentralized wastewater treatment and considerably reduces the energy consumption.
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impact of aeration shear stress on permeate flux and Fouling Layer properties in a low pressure membrane bioreactor for the treatment of grey water
Journal of Membrane Science, 2016Co-Authors: Nicolas Derlon, Eberhard Morgenroth, Heng Liang, An Ding, Ilona Szivak, Wouter PronkAbstract:Abstract Two different aeration regimes were studied in a low pressure gravity driven membrane bioreactor without any flushing or (back-) washing. In one reactor, the aeration was positioned below the membrane module, thus exposing the membranes to aeration shear stress. A second reactor was operated at low shear stress by placing the aerator in a different compartment. Flux stabilization at 2.0 L/(m 2 h) occurred in the reactor with low shear stress while no flux stabilization was observed in the reactor with aeration shear stress, resulting in a flux of 0.5 L/(m 2 h) after 120 days. The thickness of the bio-Fouling Layer in the reactor with aeration shear was smaller (129 vs. 344 µm), which implies that shear stress resulted in a thinner, denser and less permeable bio-Fouling Layer. The results can be explained by differences in (1) the morphology of the bio-Fouling Layer and (2) the EPS contents (proteins and polysaccharides) in the bio-Fouling Layer. The low-shear system provides a suitable solution for decentralized grey water treatment, or other conditions where maintenance and energy consumption should be minimized. Furthermore, the results can contribute to decrease the energy consumption in MBR systems.
Seungkwan Hong - One of the best experts on this subject based on the ideXlab platform.
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combined organic and colloidal Fouling in forward osmosis Fouling reversibility and the role of applied pressure
Journal of Membrane Science, 2014Co-Authors: Menachem Elimelech, Ho Kyong Shon, Seungkwan HongAbstract:Abstract In this study, we systematically investigated the propensity and reversibility of combined organic–colloidal Fouling in forward osmosis (FO) under various solution chemistries (pH and calcium ion concentrations) and applied hydraulic pressure on the feed side. Alginate, silica colloids, and their mixture (i.e., combined organic–colloidal) were used as model foulants. Our findings demonstrate that combined organic–colloidal foulants caused more rapid flux decline than the individual foulants due to the synergistic effect of alginate and silica colloids. As a result, much lower flux recovery was achieved by physical cleaning induced by increasing the cross-flow rate, in contrast to single foulants of which the Fouling Layer was easily removed under all solution conditions. Interestingly, less flux decline was observed at neutral pH for combined Fouling, while acidic conditions were favorable for alginate Fouling and basic solutions caused more silica Fouling, thereby providing clear evidence for the combined Fouling effect. It was also found that calcium ions enhanced water flux decline and induced the formation of less reversible combined organic–colloidal Fouling Layers. Lastly, the role of applied hydraulic pressure on the feed side in FO was examined to elucidate the mechanism of Fouling Layer formation, Fouling reversibility, and water flux recovery. Higher Fouling propensity and lower Fouling reversibility of combined organic–colloidal Fouling were observed in the presence of applied hydraulic pressure on the feed side. This observation suggests that the lower Fouling propensity and greater Fouling reversibility in FO compared to reverse osmosis (RO), are attributable to unpressurized operating conditions in FO.
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Fouling control in a forward osmosis process integrating seawater desalination and wastewater reclamation
Journal of Membrane Science, 2013Co-Authors: Chanhee Boo, Menachem Elimelech, Seungkwan HongAbstract:A hybrid system that combines forward osmosis with a reverse osmosis seawater desalination process could reduce both energy requirements and environmental impacts by osmotic dilution of the seawater and concentrated brine with an impaired low salinity stream, such as treated wastewater effluent. In this study, we investigate the membrane Fouling behavior in forward osmosis under conditions simulating the osmotic dilution process and the use of hydrodynamic methods without the use of cleaning chemicals, to control membrane Fouling. Fouling runs with seawater or SWRO brine draw solution and deionized (DI) water feed solution showed insignificant water flux decline, which implies negligible effect of particulate and organic matter in the seawater/brine on Fouling of the FO membrane support Layer. Fouling of the membrane active Layer was evaluated by using an enriched synthetic wastewater effluent containing a mixture of inorganic and organic foulants, focusing on the impact of permeate drag force on Fouling Layer formation. Our results demonstrate that higher permeate water flux causes an increase in concentration build-up of foulants at the membrane surface, thereby forming a dense inorganic/organic combined Fouling Layer during FO Fouling runs. We also examined three hydrodynamic methods for minimizing FO membrane Fouling in the osmotic dilution process: (1) applying shear force on the membrane surface by increasing the cross-flow velocity, (2) using a feed-channel spacer to induce turbulence, and (3) employing pulsed flow to remove foulants from the membrane surface. Our results show that these hydrodynamic methods substantially reduce Fouling and flux decline rate.
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chemical and physical aspects of natural organic matter nom Fouling of nanofiltration membranes
Journal of Membrane Science, 1997Co-Authors: Seungkwan Hong, Menachem ElimelechAbstract:The role of chemical and physical interactions in natural organic matter (NOM) Fouling of nanofiltration membranes is systematically investigated. Results of Fouling experiments with three humic acids demonstrate that membrane Fouling increases with increasing electrolyte (NaC1) concentration, decreasing solution pH, and addition of divalent cations (Ca2+). At fixed solution ionic strength, the presence of calcium ions, at concentrations typical of those found in natural waters, has a marked effect on membrane Fouling. Divalent cations interact specifically with humic carboxyl functional groups and, thus, substantially reduce humic charge and the electrostatic repulsion between humic macromolecules. Reduced NOM interchain repulsion results in increased NOM deposition on the membrane surface and formation of a densely packed Fouling Layer. In addition to the aforementioned chemical effects, results show that NOM Fouling rate increases substantially with increasing initial permeation rate. It is demonstrated that the rate of Fouling is controlled by an interplay between permeation drag and electrostatic double Layer repulsion; that is, NOM Fouling of NF membranes involves interrelationship (coupling) between physical and chemical interactions. The addition of a strong chelating agent (EDTA) to feed water reduces NOM Fouling significantly by removing free and NOM-complexed calcium ions. EDTA treatment of NOM-fouled membranes also improves the cleaning efficiency dramatically by disrupting the Fouling Layer structure through a ligand exchange reaction between EDTA and NOM-calcium complexes.