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Abstract: A series of filtration experiments was performed systematically to investigate physical and chemical factors affecting the efficiency of backwashing during microfiltration of colloidal suspensions. In this study, all experiments were conducted in dead-end filtration mode utilizing an outside-in, hollow-fiber module with a nominal pore size of 0.1 μm. Silica particles (mean diameter = 0.14 μm) were used as model colloids. Using a flux decline model based on the Happel''s cell for the hydraulic resistance of the particle layer, the cake structure was determined from experimental fouling data and then correlated to backwash efficiency. Modeling of experimental data revealed no noticeable changes in cake layer structure when feed particle concentration and operating pressure increased. Specifically, the packing density of the cake layer (1-cake porosity) in the cake layer ranged from 0.66 to 0.67, which corresponds well to random packing density. However, the particle packing density increased drastically with ionic strength. The results of backwashing experiments demonstrated that the efficiency of backwashing decreased significantly with increasing solution ionic strength, while backwash efficiency did not vary when particle concentration and operating pressure increased. This finding suggests that backwash efficiency is closely related to the structure of the cake layer formed during particle filtration. More densely packed cake layers were formed under high ionic strength, and consequently less flux was recovered per given backwash volume during backwashing. [Copyright &y& Elsevier]

Pressure assisted osmosis (PAO) has been recently suggested as a way to overcome the current limitations of forward osmosis (FO), since water flux can be increased by additional hydraulic driving force. To validate its feasibility more fundamentally, the effect of hydraulic pressure combined with osmotically driven FO process was evaluated experimentally, and compared with theoretical modeling. Four different FO and NF membranes were selected and their performance characteristics were determined by both RO- and FO-based methods, since PAO is a simultaneous osmotic- and pressure-driven membrane process. The degree of enhancing water flux and reducing reverse solute flux (RSF) in the PAO process clearly differed according to the membrane type and their performance parameters. Modeling PAO performance, using the values of A, B, and S determined from both RO- and FO-based methods, often failed to exactly match experimental observations, particularly for thin film composite (TFC) FO membranes, suggesting that PAO membrane performance parameters are apparently pressure-dependent. Discernible compaction in the support layer of TFC FO membranes was identified and confirmed by FO tests at different operating modes and SEM analysis, partially explaining large variations in S values under pressurized PAO operation and thus resulting large deviation from theoretical predictions. [ABSTRACT FROM AUTHOR]

To advance cost-effective strategies for developing flat-sheet ceramic microfiltration membranes, the feasibility of using waste mineral-based materials as a ceramic membrane in engineered membrane bioreactor systems (MBRs) for treating low-strength domestic wastewater was evaluated. The ceramic membrane support layers that had effectively been fabricated with pyrophyllite and alumina were sintered at 1350 °C, and subsequently coated with alumina powder suspension to achieve a narrow pore size distribution. Membrane surface properties were characterized to understand the membrane fouling phenomenon in ceramic MBRs (CMBRs). Consistently high organic removal efficiency could be achieved under all investigated hydraulic retention times (HRTs) in the CMBRs. The physico-chemical sludge properties were measured to evaluate design parameters affecting membrane fouling for the CMBR. We further evaluated the performance of pyrophyllite-alumina composite ceramic membranes in a pilot-scale CMBR plant, with 1 m 3 /d capacity that was constructed at an actual water resource recovery facility (WRRF), to improve nitrogen removal and produce high quality effluent through a combined process of modified Ludzack-Ettinger (MLE) and CMBR (MLE/CMBR). The MLE/CMBR was operated successfully up to 20 LMH, with the final effluent chemical oxygen demand (COD) being maintained below 16.3 mg/L. [ABSTRACT FROM AUTHOR]

Nanofiltration (NF) membrane has been increasingly applied for brackish water treatment and often integrated to conventional water treatment consisting of coagulation, sedimentation, and filtration (CSF) processes. In this study, the corrosion potential of NF treated water was examined in lab-scale corrosion loop tests, and the optimum design of NF process blended with CSF treated water was proposed for iron pipe corrosion prevention. Severe iron corrosion was observed when exposed to NF treated water, which was manifested by more negative values of Langelier saturation index (LSI), mainly due to high removal of hardness (Ca 2 + ) and alkalinity (HCO 3 − ). Thus it was suggested that high corrosion potential by NF could be controlled by blending with CSF treated water. SEM, XRD, and XRF analyses clearly identified reduced corrosion, evidenced by less iron oxyhydroxides and more calcium carbonate on iron pipe surface, with decreasing NF treated water in blending. NF process simulation also demonstrated the improved stability of blended waters by decreasing flux and increasing recovery. Lastly, the LSI model reflecting blending ratio and NF membrane performance was newly developed for the design and operation of NF blending systems in order to lower the corrosion risk of pipe distribution systems through optimizing NF operating conditions. [ABSTRACT FROM AUTHOR]

A novel method to determine reverse draw and forward feed solute fluxes in forward osmosis (FO) membrane was developed to analyze FO performance more accurately. Specifically, apparent draw solute permeability (B d ) and feed solute permeability (B f ) were proposed, instead of relying on single solute permeability (B). Our results clearly demonstrated that both draw and feed fluxes were not well predicted with the solute permeability (B) measured by RO mode experiment, typically employed in FO membrane characterization. In this study, the draw and feed solute permeabilities were evaluated independently by the experimental protocols which simulated actual FO operation more closely. Much better agreement between experimental observations and theoretical predictions was obtained when both B d and B f were applied for the analysis of draw and feed solute fluxes, respectively. Thus, the utilization of apparent draw and feed solute permeabilities provides more precise assessment of draw solute loss and permeate water quality, which are very important for FO membrane process design and operation. [ABSTRACT FROM AUTHOR]

Abstract: Fertiliser-drawn forward osmosis (FDFO) desalination has been recently studied as one feasible application of forward osmosis (FO) for irrigation. In this study, the potential of membrane scaling in the FDFO process has been investigated during the desalination of brackish groundwater (BGW). While most fertilisers containing monovalent ions did not result in any scaling when used as an FO draw solution (DS), diammonium phosphate (DAP or (NH4)2HPO4) resulted in significant scaling, which contributed to severe flux decline. Membrane autopsy using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD) analysis indicated that the reverse diffusion of DAP from the DS to the feed solution was primarily responsible for scale formation during the FDFO process. Physical cleaning of the membrane with deionised water at varying crossflow velocities was employed to evaluate the reversibility of membrane scaling and the extent of flux recovery. For the membrane scaled using DAP as DS, 80–90% of the original flux was recovered when the crossflow velocity for physical cleaning was the same as the crossflow velocity during FDFO desalination. However, when a higher crossflow velocity or Reynolds number was used, the flux was recovered almost completely, irrespective of the DS concentration used. This study underscores the importance of selecting a suitable fertiliser for FDFO desalination of brackish groundwater to avoid membrane scaling and severe flux decline. [Copyright &y& Elsevier]

Fouling behavior along the length of membrane module was systematically investigated by performing simple modeling and lab-scale experiments of forward osmosis (FO) membrane process. The flux distribution model developed in this study showed a good agreement with experimental results, validating the robustness of the model. This model demonstrated, as expected, that the permeate flux decreased along the membrane channel due to decreasing osmotic pressure differential across the FO membrane. A series of fouling experiments were conducted under the draw and feed solutions at various recoveries simulated by the model. The simulated fouling experiments revealed that higher organic (alginate) fouling and thus more flux decline were observed at the last section of a membrane channel, as foulants in feed solution became more concentrated. Furthermore, the water flux in FO process declined more severely as the recovery increased due to more foulants transported to membrane surface with elevated solute concentrations at higher recovery, which created favorable solution environments for organic adsorption. The fouling reversibility also decreased at the last section of the membrane channel, suggesting that fouling distribution on FO membrane along the module should be carefully examined to improve overall cleaning efficiency. Lastly, it was found that such fouling distribution observed with co-current flow operation became less pronounced in counter-current flow operation of FO membrane process. [ABSTRACT FROM AUTHOR]

Abstract: The influence of pH and calcium ion concentrations on the organic fouling of reverse osmosis (RO) membranes was investigated under two distinguished ionic strengths representing surface water (i.e., 10mM) and seawater conditions (i.e., 600mM). Variations in flux decline with respect to the feed water pH and calcium concentrations under these ionic environments were compared. Organic foulants deposited on the membrane surface were collected and characterized in terms of specific UVA (SUVA) and fluorescence excitation and emission matrix (FEEM) in conjunction with XAD-8/4 resin fractionation. Flux-decline curves obtained by various feed water pH and calcium concentrations under the low ionic strength condition were quite different with each other, while flux-decline curves obtained at the seawater-level ionic strength was almost identical regardless of variations in the feed water pH and calcium concentration. SUVA and FEEM results showed that the characteristics of organic matters attached on the membrane surface at high ionic strengths were significantly different from those at low ionic strengths. SUVA values and FEEM images indicated that organic foulants at the seawater-level ionic strength were mostly hydrophobic. Consequently, enhanced hydrophobic interaction dominantly controlled the rate and the extent of organic fouling at seawater-level ionic strength where the impacts of feed water pH and calcium were significantly masked. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract Highly enriched grapefruit juice is expected to be obtained through forward osmosis (FO) without degradation of its nutrients. However, this technology is facing several key issues that must be explored to validate the suitability of FO as a dewatering process, namely, membrane performance testing, fouling control, and product quality assessment. In this work, grapefruit juice was dewatered using a commercial thin-film composite FO membrane that exhibited stable performance. The simulation results also suggested that the dewatering could be further enhanced by improving the S value of the current TFC FO membrane. Severe membrane fouling was observed, and it was predominantly due to suspended particles larger than 0.45 μm, such as pectin. However, sustainable osmotic dewatering operation could be attained by implementing appropriate fouling control strategies, such as separating large-sized particles by sedimentation or centrifugation prior to osmosis and recovering the declined water flux by physical cleaning. The dehydrated feed exhibited no significant loss of nutritional value, suggesting that the FO membrane dewatered the juice effectively while retaining its constituents. In addition, the FO process could be further improved to obtain enhanced-quality grapefruit juice by applying pressure to the feed stream or employing a sugar-based draw solution such as glucose. Graphical abstract Image 1 Highlights • This work probed the challenging issues in osmotic dewatering of grapefruit juice. • Stable flux induced by TFC FO membrane can be improved further by reducing S value. • The severe fouling by particulate substances was alleviated by their separation. • Hydraulic flushing well restored the declined flux caused by dissolved matters. • Applying pressure or adopting glucose further reduced the reversely diffused salts. [ABSTRACT FROM AUTHOR]

In ultrapure water (UPW) production, ultraviolet (UV) radiation is an effective process for reducing microorganisms and organic matter. An increasing trend of reusing the spent UPW further encourages the adoption of UV at the upstream of reverse osmosis (RO) to mitigate membrane fouling and to enhance water quality. In this study, UV technology, both low and medium pressure lamps, was assessed for RO pretreatment in UPW production. The fouling potential of problematic pollutants (e.g., silica and IPA) was evaluated pre and post UV treatment based on fouling index under constant flux mode. We found that the rejection rate of IPA was enhanced up to 80% and thus reduced the organic fouling potential in RO. On the contrary, for inorganic nano-particle such as silica, a significant increase in fouling potential after UV exposure was observed. Zeta and small angle X-ray scattering analysis implied that this fouling potential transition was derived from silica particle agglomeration under UV radiation. The RO fouling tests corroborated findings from fouling index measurements, showing severe flux decline after UV radiation. This research provides new insight for UPW production design by revealing the influence of UV on inorganic and organic pollutants during the reclamation of spent UPW. [ABSTRACT FROM AUTHOR]

The feasibility of an anaerobic ceramic membrane bioreactor (AnCMBR) was investigated by comparison with a conventional anaerobic membrane bioreactor (AnMBR). With regard to treatment performance, the AnCMBR achieved higher organic removal rates than the AnMBR because the ceramic membranes retained a high concentration of biomass in the reactor. Despite a high mixed liquor suspended solid (MLSS) concentration, the AnCMBR exhibited lower membrane fouling. To elucidate effects of sludge properties on membrane fouling in the AnCMBR and AnMBR, soluble microbial products (SMPs) and extracellular polymeric substances (EPSs) were analyzed. The SMP and EPS concentrations in the AnCMBR were higher than in the AnMBR. This may be because some suspended solids bio-degraded and likely released protein-like SMPs in the AnCMBR. Hydrophobicity and surface charges were analyzed; the sludge in the AnCMBR was found to be more hydrophobic and less negative than in the AnMBR because protein was abundant in the AnCMBR. Despite the adverse properties of the sludge in the AnCMBR, it showed more stable filtration performance than the AnMBR. This is because the alumina-based ceramic membrane had a superhydrophilic surface and could thus mitigate membrane fouling by hydrophilic-hydrophobic repulsion. The findings from this study have significant implications for extending the application of AnCMBRs to, for example, treatment of high-strength organic waste such as food waste or livestock manure. [ABSTRACT FROM AUTHOR]

The performance of pressure retarded osmosis (PRO) membrane, characterized by water and solute permeability ( A and B ) and the structural parameter ( S ), was analyzed by a new method designed to simulate the PRO process more closely. Compared to conventional approaches to membrane characterization using reverse osmosis (RO)/forward osmosis (FO), the newly developed method using a single PRO experiment better predicted PRO process performance, particularly when high pressure was applied on the draw side. It was clearly demonstrated that apparent B value increased with increasing draw pressure. This characterization method was also used to evaluate PRO membrane performance in the presence of organic matter, such as alginate or xanthan, in draw solutions. Organic matter in draw solutions reduced the apparent B value, which could result in less draw solute loss in PRO processes. Our experimental observations clearly suggested that PRO membrane processes should be analyzed and predicted by methods like the one presented which simulate actual PRO operating conditions, particularly the hydraulic pressure applied to draw solutions. [ABSTRACT FROM AUTHOR]

Abstract: Forward osmosis (FO) is an emerging technology that has received much global interest due to its potential applications in wastewater reclamation and seawater desalination. One of the major challenges to overcome is the detrimental effects of concentration polarization (CP), which reduce the effective osmotic pressure driving force and thus decrease productivity of the FO process. In this study, pressure assisted osmosis (PAO) was investigated as a method to increase the effective driving force and water flux by combining an osmotic pressure driving force with an additional hydraulic pressure. Experiments were carried out to examine the efficiency of the PAO process using a bench-scale setup specially designed to prevent membrane deformation under the applied hydraulic pressure. Results showed that PAO water flux increased with increasing the applied hydraulic pressure in FO mode (i.e., active layer facing the feed solution). The measured water fluxes were in good agreement with predictions based on a model developed to describe the water flux in PAO operation. However, the PAO water flux was lower than model predictions in PRO mode (i.e., active layer facing the draw solution). This observation is attributed to the spacer ‘shadow effect’ and the resulting reduction in the effective membrane area by the spacers. The results also showed that reverse solute flux decreased with increasing the applied hydraulic pressure in both FO and PRO modes. Although applying hydraulic pressure to FO increases energy consumption, the higher water flux in PAO reduces the number of membrane modules for the FO process. In addition, control of the driving force is easier in PAO than FO, leading to flexibility in system design and operation. Based on these results, a possible combination of FO and RO system with PAO was proposed for allowing higher energy efficiency in seawater desalination. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: The surface characteristics of reverse osmosis membranes and their relation to membrane fouling are systematically investigated by measuring membrane dynamic hysteresis based on the Wilhelmy plate method. Dynamic hysteresis represents the difference between the forces applied to a membrane surface when it is advanced into and withdrawn from a liquid or solution. Our results demonstrate that the chemical surface heterogeneity of various RO membranes could be quantified by measuring their dynamic hysteresis. The chemical heterogeneity was mostly related to the distribution of surface charge rather than average zeta potential. There was a remarkable correlation between the chemical surface heterogeneity and membrane dynamic hysteresis. It was clearly shown that dynamic hysteresis varied substantially with respect to the solution chemistry of test solutions. The dynamic hysteresis of RO membranes measured in the presence of organic foulants was further related to the flux-decline rate determined from bench-scale fouling experiments. It was found that higher flux-decline rate was obtained for RO membranes with larger dynamic hysteresis. Based on the results in this study, it is demonstrated that dynamic hysteresis measurements can be a promising tool for characterizing membrane surfaces as well as assessing membrane fouling. [ABSTRACT FROM AUTHOR]

Abstract: The adhesion property of Pseudomonas putida on reverse osmosis (RO) membranes was systematically investigated using the asymmetrical flow field-flow fractionation (AsFl-FFF). The adhesion of P. putida on two different RO membranes was investigated by varying the salt concentration of carrier solution to evaluate the effect of ionic strengths and membrane characteristics on the biofouling potential of RO membranes. The elution peak in terms of peak retention time and area obtained from AsFl-FFF analysis was used to evaluate the adhesion tendency of P. putida under different solution ionic conditions. Results showed that P. putida was favorably attached to RO membranes at higher ionic strengths. Hydrophobic RO membrane exhibited more adhesive property to P. putida compared to the tested hydrophilic membrane under the lower ionic strength condition. The effect of solution ionic strength on the adhesion tendency was more influential than membrane characteristics. In addition, the influence of ionic strength variation on adhesion tendency was more sensitive to hydrophilic membranes than hydrophobic membranes. [ABSTRACT FROM AUTHOR]

Abstract: A new approach to evaluate the fouling potential of feed waters for reverse osmosis (RO) and nanofiltration (NF) practices was systematically investigated. A multiple membrane array system (MMAS) was developed, in which microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes were connected in series. This system was designed to separate the target foulants in the feed water and evaluate the fouling potential of a targeted foulant. More specifically, particulate, colloids, and organic matters were separated by MF, UF, and NF membranes in a consecutive manner, and the modified fouling index (MFI) was measured during each separation. The resulting three MFI values are Particle-MFI, Colloid-MFI, and Organic-MFI, and presented schematically in a triangle manner. The results demonstrated that fouling potentials of various feed waters (e.g., seawaters pretreated by various pretreatment options as well as raw seawater) evaluated by the MMAS were much more accurate and informative compared to those predicted by conventional silt density index (SDI) and single MFI. The fouling potentials determined by the MMAS precisely reflected changes in feed water quality by different pretreatment options (i.e., sand filtration, microfiltration, and ultrafiltration), while SDI measurements were not sensitive enough to detect these variations. It was also shown that the fouling potentials evaluated by the MMAS were well correlated with the actual flux-decline rates determined by lab-scale RO fouling experiments simulating seawater desalination, suggesting that the MMAS could provide a better way to predict fouling potential and guidance to select proper pretreatment processes. [ABSTRACT FROM AUTHOR]

Abstract: In this study, various foulants are tested with the conventional fouling indexes such as silt density index (SDI) and modified fouling index (MFI) under high TDS conditions to evaluate the practical appliance of these indexes for RO desalination. A new approach for developing a more realistic fouling index is investigated based on flow field-flow fraction (Fl-FFF) analysis. The results showed that the SDI and MFI for the feed waters containing the particulate foulants larger than the pore size of the membranes used in SDI and MFI measurements were not significantly affected by the feed water salinity. This is due to the fact that the main fouling mechanism is the deposition of particles on the membrane surface and, hence, the cake filtration controls the permeate flux. In case of the particles as well as organics smaller than the pore size of the membranes, the SDI and MFI failed to accurately predict the fouling potential of feed waters with high salinity. In addition, the characteristics of membrane (i.e., hydrophobicity) also played an important role in determining membrane performance. Based on the results from Fl-FFF analyses, it was demonstrated that both qualitative and quantitative assessments of fouling potential of feed waters with different foulants and TDS conditions were possible. [Copyright &y& Elsevier]

Abstract: Recent studies have shown that the rougher, less negatively charged, and more hydrophobic membranes are prone to organic fouling. These surface characteristics of RO membranes, however, have been usually determined at very low TDS conditions, while seawater contains ten to thousand times more TDS than surface and even brackish waters. In this study, three aromatic polyamide thin-fi lm composite (TFC) RO membranes were characterized for chemical and physical properties. Membrane characterization was performed under both the low (i.e., 10 mg/L) and high (i.e., 35,000 mg/L) TDS conditions to see how these surface characteristics are aff ected by seawater-level TDS. Results showed that both the chemical and physical surface properties were altered signifi cantly under the high TDS condition with becoming more favorable to membrane fouling, namely, less negatively charged, more hydrophobic, and rougher. Mechanisms responsible for these changes such as charge screening and osmotic swelling are delineated. The way of changing in surface characteristics under the high TDS condition was substantially diff erent with respect to the surface characteristics determined at the low TDS condition. It was confi rmed that the chemical and physical properties were interrelated and, thus, variations in chemical properties with respect to the solution chemistry applied led to changes in physical properties and vice versa. [Copyright &y& Elsevier]

Abstract: A membrane fouling index such as the silt density index (SDI) and modified fouling index (MFI) is an important parameter in design and operation of reverse osmosis (RO) and nanofiltration (NF) membrane processes for desalination. Nevertheless, SDI and MFI often fail to predict actual membrane fouling due to their limited capability to measure fouling potential by colloidal deposition and organic adsorption. In this study, a novel method to determine fouling index was attempted using a set of different membrane filters for better prediction of RO/NF fouling potential. Three MF/UF membranes were used for MFI tests in order to increase sensitivity to fouling potential of particles, hydrophobic organics, and sub-micron colloids. The fouling indices determined using different membrane filters were compared with RO filtration results. Experimental results indicated that fouling indices using different test membranes showed variable results for untreated and pretreated waters. Nevertheless, no single method was sufficient for accurate measurement of fouling potential. Accordingly, a new fouling index (CFI: combined fouling index) was developed by combining various fouling indices. The CFI exhibited good agreement with experimental data compared with other fouling indices such as SDI, MFI, and MFI–UF. [Copyright &y& Elsevier]