The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Menachem Elimelech - One of the best experts on this subject based on the ideXlab platform.

  • combined organic and Colloidal Fouling in forward osmosis Fouling reversibility and the role of applied pressure
    Journal of Membrane Science, 2014
    Co-Authors: Menachem Elimelech, Ho Kyong Shon, Seungkwan Hong
    Abstract:

    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.

  • impact of organic and Colloidal Fouling on trace organic contaminant rejection by forward osmosis role of initial permeate flux
    Desalination, 2014
    Co-Authors: Long D Nghiem, William E Price, Menachem Elimelech
    Abstract:

    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.

  • Colloidal Fouling in forward osmosis role of reverse salt diffusion
    Journal of Membrane Science, 2012
    Co-Authors: Chanhee Boo, Menachem Elimelech, Sangyoup Lee, Zhiyong Meng, Seungkwan Hong
    Abstract:

    a b s t r a c t 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.

  • synergistic effects in combined Fouling of a loose nanofiltration membrane by Colloidal materials and natural organic matter
    Journal of Membrane Science, 2006
    Co-Authors: Qilin Li, Menachem Elimelech
    Abstract:

    Abstract Fouling of nanofiltration (NF) membranes in water treatment and wastewater reuse applications is often caused by both Colloidal materials and dissolved organic matter. However, most past mechanistic studies on NF membrane Fouling have focused on either Colloidal Fouling or organic Fouling. In this study, the performance of a ‘loose’, low salt rejection NF membrane during combined Fouling by both Colloidal materials and dissolved natural organic matter (NOM) was compared with that during Colloidal Fouling and organic Fouling alone. A significant synergistic effect was observed during combined Fouling, manifested as considerably higher flux decline rate than what expected based on the sum of Colloidal and organic Fouling alone. Microscopic analysis of the colloid/organic foulant layer structure confirmed faster foulant accumulation on the membrane surface, indicating a mechanism of hindered back diffusion of Colloidal and organic foulants. The membrane flux decline during combined Fouling was also found to depend on solution chemistry and Colloidal particle size. Notably, the effects of these factors are different from those during Fouling by Colloidal materials or dissolved organic matter alone.

  • combined influence of natural organic matter nom and Colloidal particles on nanofiltration membrane Fouling
    Journal of Membrane Science, 2005
    Co-Authors: Menachem Elimelech
    Abstract:

    The combined influence of natural organic matter (NOM) and Colloidal particles on the Fouling of thin-film composite nanofiltration (NF) membranes is systematically investigated. Combined Fouling is compared to the individual Fouling behaviors (i.e., colloid or NOM alone) with respect to Fouling mechanisms and the effect of concentration factor (or recovery). Results demonstrate that (1) “cake-enhanced osmotic pressure” (CEOP) is a key Fouling mechanism for individual Colloidal Fouling, (2) NOM–calcium complexation is the dominant factor governing individual NOM Fouling, and (3) combined Fouling is affected by both CEOP and NOM–calcium complexation. The extent of flux decline for combined Fouling, however, is less than what inferred from additivity of the individual contributions of Colloidal and NOM Fouling to flux decline. This observation implies that the contributions of the Fouling mechanisms appear to be relatively less significant for combined Fouling compared to their separate influences on individual Colloidal and NOM Fouling. An increase in Colloidal stability in presence of NOM and the competition between colloids and NOM for calcium are likely explanations for this behavior. It is further shown that NF membrane salt rejection increases noticeably in case of combined Fouling compared to individual Colloidal Fouling due to the formation of an active rejecting layer by the accumulated NOM on the membrane surface. Results from combined Fouling runs involving EDTA treatment confirm that both CEOP and NOM–calcium complexation take place simultaneously.

A G Fane - One of the best experts on this subject based on the ideXlab platform.

  • a threshold flux phenomenon for Colloidal Fouling in reverse osmosis characterized by transmembrane pressure and electrical impedance spectroscopy
    Journal of Membrane Science, 2016
    Co-Authors: Lee Nuang Sim, A G Fane, Richard D Webster, H G L Coster
    Abstract:

    Abstract The dependence of membrane Fouling on flux has been investigated using silica as the model foulant in a crossflow membrane module operated at constant flux. Electrical impedance spectroscopy (EIS) was used to monitor the electrical properties of the Fouling process. We show that the nature of a flowing Colloidal suspension of silica on the membrane surface changes when a transition or threshold flux is reached. This transition was well-defined and was reflected in the changes of the slope of transmembrane pressure (TMP) with flux and the conductance of the diffusion polarization (DP) layer determined by EIS. The threshold flux increased with increasing crossflow velocity. The effect of a spacer in the feed channel was also investigated and the presence of spacer increased the threshold flux. The conductance of the diffusion polarization layer ( G DP ) derived from the low frequency region in the EIS was identified as the most important EIS parameter for signaling the onset of cake formation and the cake enhanced concentration polarization (CECP) effect. TMP measurements on their own provided limited information on these phenomena. The threshold flux was affected strongly by the crossflow velocity and this was also illustrated in the change in the minimum of the G DP with increasing flux. This study suggests that EIS could be applied “online” using a side-stream, 'canary' cell to continuously monitor a reverse osmosis system to ensure its operations remain below the threshold flux.

  • Colloidal metastability and membrane Fouling effects of crossflow velocity flux salinity and colloid concentration
    Journal of Membrane Science, 2014
    Co-Authors: S T V Sim, Tzyy Haur Chong, A H Taheri, W B Krantz, A G Fane
    Abstract:

    Microfiltration (MF) and ultrafiltration (UF) involving Colloidal suspensions are often involved in separations, concentration and clarification processes in the food and beverage as well as other industries. The increase in concentration near the membrane surface owing to concentration polarization can cause some part of a Colloidal Fouling layer to become metastable whereby it can undergo a higher order phase transition to a more dense gel. This was confirmed via deadend filtration studies wherein the Fouling layer thickness obtained from the transmembrane pressure (TMP) was compared with that determined directly via ultrasonic time-domain reflectometry (UTDR). Whereas entering this metastable state is thermodynamically driven, the transition from a Colloidal suspension to a more dense gel is a rate or kinetically driven process. This phase transition is manifest by a marked rate of increase in the TMP that occurs after an filtration time that is dependent on the flux. A ‘threshold transition flux’ is identified below which the time required for the phase transition can be considerably delayed. Since removing this dense gel layer via conventional cleaning protocols is more difficult, determining an operating strategy whereby this transition to a more dense gel can be delayed is clearly of interest for the optimal operation of MF and UF processes. To this end the effects of crossflow velocity, flux, salinity and Colloidal silica concentration on this metastability phenomenon are studied for a polyethersulfone UF membrane under crossflow and constant flux conditions. A lower crossflow velocity and higher flux, increased salinity and higher Colloidal silica concentration decrease the time required for the transition to a dense gel.

  • monitoring of Colloidal Fouling and its associated metastability using ultrasonic time domain reflectometry
    Journal of Membrane Science, 2012
    Co-Authors: Tzyy Haur Chong, William B Krantz, A G Fane
    Abstract:

    Abstract Ultrasonic Time Domain Reflectometry (UTDR) is used to monitor the deposition and physicochemical nature of Colloidal silica Fouling on a polyethersulfone ultrafiltration membrane under crossflow and constant flux conditions. The Fouling can be characterized by four stages based on the rate of increase of the transmembrane pressure (TMP): (1) an initial rapid increasing rate due to concentration polarization; (2) a slow constant rate; (3) a nonconstant increasing rate associated with metastability of the Colloidal silica; (4) a constant rapid rate associated with the foulant layer having a constant thickness. The destabilization of the Colloidal particles in the foulant layer during stage 3 is associated with an increase in the UTDR peak amplitude. During stage 4 the foulant layer thickness reaches a plateau value that decreases with increasing crossflow velocity. The rheological behavior of the foulant layer is described by the Bingham plastic model for which the yield stress can be obtained from the UTDR data. When membrane cleaning is done by switching from a Fouling to a non-Fouling feed solution, marked decreases in both the foulant layer thickness and TMP are observed. However, a residual tightly bound foulant layer remains on the membrane whose thickness, determined by UTDR, corroborates well with off-line scanning electron microscopy analysis.

  • investigations of the coupled effect of cake enhanced osmotic pressure and Colloidal Fouling in ro using crossflow sampler modified Fouling index ultrafiltration
    Desalination, 2011
    Co-Authors: Lee Nuang Sim, Vicki Chen, A G Fane
    Abstract:

    Abstract The aim of this study was to investigate the potential of using the resistivity and deposition rate data from Crossflow Sampler-Modified Fouling Index Ultrafiltration (CFS-MFIUF) measurements to determine the coupled effects of Colloidal Fouling and cake enhanced osmotic pressure (CEOP) effect. Cake filtration derived from CFS-MFIUF was combined with a CEOP model to predict the crossflow RO Fouling profile under constant flux filtration. The prediction based on resistivity, I′ from CFS-MFIUF measurement alone was found to underestimate the RO Fouling for high salinity solutions. However, when incorporating the mass information from the CFS-MFIUF test to account for the CEOP effect, the prediction showed good agreement with the TMP profile of the RO system. The results indicated that the CFS-MFIUF test which includes the CEOP effect is a very promising technique to provide an estimation of the RO Colloidal Fouling profile. When the changes of cake thickness and porosity throughout the filtration were considered, the predicted TMP profile based on the model clearly indicated a two-stage of Fouling profile which agreed well with the experimental data. Additional studies on the effects of cake thickness and porosity on CEOP highlighted the important influence of cake structure on CEOP.

  • Colloidal interactions and Fouling of nf and ro membranes a review
    Advances in Colloid and Interface Science, 2011
    Co-Authors: Chuyang Y Tang, Tzyy Haur Chong, A G Fane
    Abstract:

    Colloids are fine particles whose characteristic size falls within the rough size range of 1-1000 nm. In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability and often a deteriorated product water quality. There have been a large number of systematic studies on Colloidal Fouling of reverse osmosis (RO) and nanofiltration (NF) membranes in the last three decades, and the understanding of Colloidal Fouling has been significantly advanced. The current paper reviews the mechanisms and factors controlling Colloidal Fouling of both RO and NF membranes. Major Colloidal foulants (including both rigid inorganic colloids and organic macromolecules) and their properties are summarized. The deposition of such Colloidal particles on an RO or NF membrane forms a cake layer, which can adversely affect the membrane flux due to 1) the cake layer hydraulic resistance and/or 2) the cake-enhanced osmotic pressure. The effects of feedwater compositions, membrane properties, and hydrodynamic conditions are discussed in detail for inorganic colloids, natural organic matter, polysaccharides, and proteins. In general, these effects can be readily explained by considering the mass transfer near the membrane surface and the colloid-membrane (or colloid-colloid) interaction. The critical flux and limiting flux concepts, originally developed for Colloidal Fouling of porous membranes, are also applicable to RO and NF membranes. For small colloids (diameter≪100 nm), the limiting flux can result from two different mechanisms: 1) the diffusion-solubility (gel formation) controlled mechanism and 2) the surface interaction controlled mechanism. The former mechanism probably dominates for concentrated solutions, while the latter mechanism may be more important for dilute solutions. Future research needs on RO and NF Colloidal Fouling are also identified in the current paper.

Seungkwan Hong - One of the best experts on this subject based on the ideXlab platform.

  • nano Colloidal Fouling mechanisms in seawater reverse osmosis process evaluated by cake resistance simulator modified Fouling index nanofiltration
    Desalination, 2014
    Co-Authors: Younggil Ju, Seungkwan Hong
    Abstract:

    Abstract Fouling potentials caused by particulate matters are generally evaluated by Fouling index, such as SDI and MFI, widely used in RO membrane practices. However, these Fouling indices failed to predict the effect of nano-Colloidal sizes on flux decline, implying that Colloidal Fouling is too complex to be analyzed by simple Fouling index. Thus, in this study, nano-Colloidal Fouling mechanism in seawater reverse osmosis (SWRO) desalination was fundamentally investigated by employing new approach. Specifically, the specific cake resistance of Colloidal foulants was first determined by a novel method, cake resistance simulator-modified Fouling index nanofiltration (MFI-NF CRS ), which was conducted under operating pressure and solute environment similar to those of real SWRO desalination. Then Colloidal deposition and resulting cake-enhanced osmotic pressure (CEOP) were quantitatively assessed by fitting RO experimental data to the calculations from the CEOP model. The results clearly demonstrated that the flux decline caused Colloidal deposition in the SWRO process depended greatly on the CEOP. The newly developed methodology including MFI-NF CRS is expected to contribute significantly to better understand nano-Colloidal Fouling mechanisms and to accurately predict their Fouling potentials in the SWRO desalination.

  • combined organic and Colloidal Fouling in forward osmosis Fouling reversibility and the role of applied pressure
    Journal of Membrane Science, 2014
    Co-Authors: Menachem Elimelech, Ho Kyong Shon, Seungkwan Hong
    Abstract:

    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.

  • modeling of Colloidal Fouling in forward osmosis membrane effects of reverse draw solution permeation
    Desalination, 2013
    Co-Authors: Minkyu Park, Seungkwan Hong, Chanhee Boo, Jijung Lee, Shane A Snyder, Joon Ha Kim
    Abstract:

    Abstract A numerical model for predicting the flux decline due to Colloidal Fouling was developed for a forward osmosis (FO) membrane system. We derived the kinetic equation of the cake layer growth based on a first-order reaction and control volume approach. Based on the model simulation, it was found that the deposited particles on a membrane surface are proportional to the feed concentration and the permeate flux. Moreover, the simulation result reveals that the cake-enhanced osmotic pressure (CEOP) is a key factor diminishing the permeate flux for large Colloidal foulants. For small Colloidal foulants, the hydraulic resistance of the cake layer is dominant in flux decline at the beginning of the Fouling and CEOP increasingly become significant as Fouling progresses. The effects of the reverse draw solute permeation on the flux decline were also simulated. Interestingly, the increased reverse draw solute permeation obtained by increasing the solute permeability showed little effect on the flux decline. Contrarily, variation of the diffusivity significantly influenced the flux decline. Consequently, the numerical model developed in this paper suggests that the selection of draw solute for an FO membrane process should be carefully regarded, along with the Fouling mechanism.

  • Colloidal Fouling in forward osmosis role of reverse salt diffusion
    Journal of Membrane Science, 2012
    Co-Authors: Chanhee Boo, Menachem Elimelech, Sangyoup Lee, Zhiyong Meng, Seungkwan Hong
    Abstract:

    a b s t r a c t 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.

  • effect of cake layer structure on Colloidal Fouling in reverse osmosis membranes
    Desalination, 2008
    Co-Authors: Chanhyuk Park, Young Haeng Lee, Sang Hyup Lee, Seungkwan Hong
    Abstract:

    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 μm 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.

Tzyy Haur Chong - One of the best experts on this subject based on the ideXlab platform.

  • characterization of Colloidal Fouling in forward osmosis via ultrasonic time utdr and frequency domain reflectometry ufdr
    Journal of Membrane Science, 2020
    Co-Authors: Li Lai, William B Krantz, Lee Nuang Sim, Tzyy Haur Chong
    Abstract:

    Abstract Ultrasonic time- (UTDR) and frequency-domain reflectometry (UFDR) were applied to characterize internal and external Fouling in the forward osmosis (FO) process. Unlike RO applications, in which the transducer was placed above the membrane to detect external Fouling on the top surface of membrane, the transducer was placed below the membrane to enable detection of internal and external Fouling in an FO application. The amplitude changes and arrival-time shifts in UTDR were more sensitive than the flux decline as an indicator of FO Fouling. In the active-layer facing the feed solution (AL-FS) mode, the cake-layer thickness obtained via the differential UTDR signal agreed well with the mass-balance data. The Short-Time-Fourier-Transform (STFT) analysis permitted decomposing the non-overlapping peaks that revealed a significant decrease in the amplitudes of the high-frequency components due to the grain-scattering effect in the active-layer facing the draw solution (AL-DS) mode. In contrast, the frequency distribution remained unchanged in the AL-FS mode. The total reflected power (TRP) calculations for the arrival-times and principal peaks in the frequency-domain correlated well with the overall Fouling and internal Fouling, respectively.

  • integration of an anaerobic fluidized bed membrane bioreactor mbr with zeolite adsorption and reverse osmosis ro for municipal wastewater reclamation comparison with an anoxic aerobic mbr coupled with ro
    Chemosphere, 2020
    Co-Authors: Lee Nuang Sim, Tzyy Haur Chong, Yu Liu
    Abstract:

    Abstract This study compared the performance of an anaerobic fluidized bed membrane bioreactor (AFMBR)-zeolite adsorption-reverse osmosis (RO) system and an anoxic-aerobic MBR-RO system for municipal wastewater reclamation. Both MBR-RO systems were operated in parallel with the same operating conditions. The results showed that the MBR systems achieved excellent organic removals (>95%) and the anoxic-aerobic MBR could also remove ∼57% of soluble total nitrogen. Compared to the aerobic MBR, the AFMBR displayed better membrane performance with less energy consumption, attributed to effective membrane scouring by liquid-fluidized GAC particles. Furthermore, a zeolite column was employed to remove ammonia in the AFMBR permeate, which ensured comparable organic and nitrogen levels in the feeds to RO units in the two processes. Although less organic substances and microbial cells were accumulated on the RO membrane fed with AFMBR-zeolite column effluent, its Fouling rate (∼6.5 ± 2.2 bar/day) was significantly greater than that fed with anoxic-aerobic MBR permeate (∼1.1 ± 1.5 bar/day). This may be associated with more severe inorganic Colloidal Fouling on the RO membrane, illustrated by an electrical impedance spectroscopy Fouling monitoring system.

  • Colloidal metastability and membrane Fouling effects of crossflow velocity flux salinity and colloid concentration
    Journal of Membrane Science, 2014
    Co-Authors: S T V Sim, Tzyy Haur Chong, A H Taheri, W B Krantz, A G Fane
    Abstract:

    Microfiltration (MF) and ultrafiltration (UF) involving Colloidal suspensions are often involved in separations, concentration and clarification processes in the food and beverage as well as other industries. The increase in concentration near the membrane surface owing to concentration polarization can cause some part of a Colloidal Fouling layer to become metastable whereby it can undergo a higher order phase transition to a more dense gel. This was confirmed via deadend filtration studies wherein the Fouling layer thickness obtained from the transmembrane pressure (TMP) was compared with that determined directly via ultrasonic time-domain reflectometry (UTDR). Whereas entering this metastable state is thermodynamically driven, the transition from a Colloidal suspension to a more dense gel is a rate or kinetically driven process. This phase transition is manifest by a marked rate of increase in the TMP that occurs after an filtration time that is dependent on the flux. A ‘threshold transition flux’ is identified below which the time required for the phase transition can be considerably delayed. Since removing this dense gel layer via conventional cleaning protocols is more difficult, determining an operating strategy whereby this transition to a more dense gel can be delayed is clearly of interest for the optimal operation of MF and UF processes. To this end the effects of crossflow velocity, flux, salinity and Colloidal silica concentration on this metastability phenomenon are studied for a polyethersulfone UF membrane under crossflow and constant flux conditions. A lower crossflow velocity and higher flux, increased salinity and higher Colloidal silica concentration decrease the time required for the transition to a dense gel.

  • monitoring of Colloidal Fouling and its associated metastability using ultrasonic time domain reflectometry
    Journal of Membrane Science, 2012
    Co-Authors: Tzyy Haur Chong, William B Krantz, A G Fane
    Abstract:

    Abstract Ultrasonic Time Domain Reflectometry (UTDR) is used to monitor the deposition and physicochemical nature of Colloidal silica Fouling on a polyethersulfone ultrafiltration membrane under crossflow and constant flux conditions. The Fouling can be characterized by four stages based on the rate of increase of the transmembrane pressure (TMP): (1) an initial rapid increasing rate due to concentration polarization; (2) a slow constant rate; (3) a nonconstant increasing rate associated with metastability of the Colloidal silica; (4) a constant rapid rate associated with the foulant layer having a constant thickness. The destabilization of the Colloidal particles in the foulant layer during stage 3 is associated with an increase in the UTDR peak amplitude. During stage 4 the foulant layer thickness reaches a plateau value that decreases with increasing crossflow velocity. The rheological behavior of the foulant layer is described by the Bingham plastic model for which the yield stress can be obtained from the UTDR data. When membrane cleaning is done by switching from a Fouling to a non-Fouling feed solution, marked decreases in both the foulant layer thickness and TMP are observed. However, a residual tightly bound foulant layer remains on the membrane whose thickness, determined by UTDR, corroborates well with off-line scanning electron microscopy analysis.

  • Colloidal interactions and Fouling of nf and ro membranes a review
    Advances in Colloid and Interface Science, 2011
    Co-Authors: Chuyang Y Tang, Tzyy Haur Chong, A G Fane
    Abstract:

    Colloids are fine particles whose characteristic size falls within the rough size range of 1-1000 nm. In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability and often a deteriorated product water quality. There have been a large number of systematic studies on Colloidal Fouling of reverse osmosis (RO) and nanofiltration (NF) membranes in the last three decades, and the understanding of Colloidal Fouling has been significantly advanced. The current paper reviews the mechanisms and factors controlling Colloidal Fouling of both RO and NF membranes. Major Colloidal foulants (including both rigid inorganic colloids and organic macromolecules) and their properties are summarized. The deposition of such Colloidal particles on an RO or NF membrane forms a cake layer, which can adversely affect the membrane flux due to 1) the cake layer hydraulic resistance and/or 2) the cake-enhanced osmotic pressure. The effects of feedwater compositions, membrane properties, and hydrodynamic conditions are discussed in detail for inorganic colloids, natural organic matter, polysaccharides, and proteins. In general, these effects can be readily explained by considering the mass transfer near the membrane surface and the colloid-membrane (or colloid-colloid) interaction. The critical flux and limiting flux concepts, originally developed for Colloidal Fouling of porous membranes, are also applicable to RO and NF membranes. For small colloids (diameter≪100 nm), the limiting flux can result from two different mechanisms: 1) the diffusion-solubility (gel formation) controlled mechanism and 2) the surface interaction controlled mechanism. The former mechanism probably dominates for concentrated solutions, while the latter mechanism may be more important for dilute solutions. Future research needs on RO and NF Colloidal Fouling are also identified in the current paper.

Maria D Kennedy - One of the best experts on this subject based on the ideXlab platform.

  • the modified Fouling index ultrafiltration constant flux for assessing particulate Colloidal Fouling of ro systems
    Desalination, 2015
    Co-Authors: Sergio G Salinasrodriguez, Maria D Kennedy, Gary L Amy, Jan C Schippers
    Abstract:

    Reliable methods for measuring and predicting the Fouling potential of reverse osmosis (RO) feed water are important in preventing and diagnosing Fouling at the design stage, and for monitoring pre-treatment performance during plant operation. The Modified Fouling Index Ultrafiltration (MFI-UF) constant flux is a significant development with respect to assessing the Fouling potential of RO feed water. This research investigates (1) the variables influencing the MFI-UF test at constant flux filtration (membrane pore size, membrane material, flux rate); and (2) the application of MFI-UF into pre-treatment assessment and RO Fouling estimation. The dependency of MFI on flux, means that to assess accurately particulate Fouling in RO systems, the MFI should be measured at a flux similar to a RO system (close to 20 L/m2/h) or extrapolated from higher fluxes. The two studied membrane materials showed reproducible results; 10% for PES membranes and 6.3% for RC membranes. Deposition factors (amount of particles that remain on the surface of membrane) were measured in a full-scale plant ranging between 0.2 and 0.5. The concept of “safe MFI” is presented as a guideline for assessing pre-treatment for RO systems.

  • flux dependency of particulate Colloidal Fouling in seawater reverse osmosis systems
    Desalination and Water Treatment, 2012
    Co-Authors: Sergio G Salinasrodriguez, Maria D Kennedy, Gary L Amy, Jan C Schippers
    Abstract:

    Abstract Fouling is the main operational problem in seawater reverse osmosis systems (SWRO). Particulate Fouling is traditionally measured through the silt density index (SDI) and through the modified Fouling index (MFI). In recent years, ultrafiltration membranes were used successfully at constant flux – MFI-UF – to measure particulate/Colloidal Fouling potential and tested in sea water applications. Furthermore, constant flux operation allows predicting the rate of Fouling in RO systems. The objectives of this study are: (1) to measure the flux effect in MFI-UF with different membranes (100, 30 and 10 kDa) for raw seawater and pre-treated water before reverse osmosis in three different locations; (2) to study the particulate and Colloidal Fouling potential of seawater in reverse osmosis systems; (3) to project the increase in pressure due to cake resistance in reverse osmosis systems. In this research, flat ultrafiltration membranes (100, 50, 30 and 10 kDa) are used in a constant flux filtration mode to...

  • the fate of transparent exopolymer particles tep in integrated membrane systems removal through pre treatment processes and deposition on reverse osmosis membranes
    Water Research, 2009
    Co-Authors: Loreen O Villacorte, Maria D Kennedy, Gary L Amy, J C Schippers
    Abstract:

    Abstract The abundance of Transparent Exopolymer Particles (TEP) in surface waters has been unnoticed for many years until recently as a potential foulant in reverse osmosis systems. Recent studies indicate that TEP may cause organic and biological Fouling and may enhance particulate/Colloidal Fouling in reverse osmosis membranes. The presence of TEP was measured in the raw water, the pre-treatment processes and reverse osmosis (RO) systems of 6 integrated membrane installations. A spectrophotometric method was used to measure TEP in the particulate size range (>0.40 μm) and was extended to measure TEP in the Colloidal size range (0.05–0.40 μm). Ultrafiltration pre-treatment applied in 4 plants, totally removed particulate TEP while microfiltration systems (2 plants) and coagulation/sedimentation/rapid sand filtration systems (3 plants) partially removed this fraction. None of the pre-treatment systems investigated totally removed Colloidal TEP. Biopolymer analysis using LC–OCD showed consistency between Colloidal TEP and polysaccharide removal by UF pre-treatment and further verified the presence of TEP in the RO feedwater. TEP deposition in the RO system was determined after measuring total TEP concentrations in the RO feed and concentrate. The TEP deposition factors and specific deposition rates indicate that TEP accumulation had occurred in all plants investigated. This observation was verified by an autopsy of RO modules from two RO plants. Further improvement and verification of the (modified) TEP method, in particular the calibration, is necessary so that it can be employed to investigate the role of TEP in the Fouling of RO systems.