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Membrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20–30°C. The applicability of RO, FO, and MD was further tested with real brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Foulant analysis suggested that CaCO3scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3scaling, however, had only small impact on flux behavior in MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat (below 50–70°C) is available. [ABSTRACT FROM PUBLISHER]

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-NFCRS), 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-NFCRS is expected to contribute significantly to better understand nano-colloidal fouling mechanisms and to accurately predict their fouling potentials in the SWRO desalination. [Copyright &y& Elsevier]

Ultrasound was used to improve a forward osmosis (FO) sludge dewatering process for the control of fouling by deposited sludge flocs. FO was able to concentrate activated sludge from a real-scale wastewater reclamation plant. However, the flux decline indicated a severe fouling phenomenon. To mitigate this FO fouling, ultrasound radiation using a novel cell configuration was applied. However, the application of continuous radiation unexpectedly resulted in more severe fouling. Fluorescence excitation-emission matrix (FEEM) spectroscopy showed that longer ultrasound radiation applications caused high organic release from sludge flocs. Confocal scanning laser microscopy (CLSM) clearly identified a thicker organic fouling layer on the FO membrane surface. Ultrasound cleaning was optimized for radiation length and improved by the integration of flushing. Specifically, the combination of ultrasound and flushing caused a flux loss recovery of 70% or more. This work demonstrated the possibility of ultrasound cleaning as a fouling control method for FO sludge dewatering applications. [ABSTRACT FROM AUTHOR]

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

Pressure retarded osmosis (PRO) operated with active layer facing feed solution (AL-FS), in contrary to typical PRO membrane orientation (active layer facing draw solution, AL-DS), has a strong potential for sustainable power generation from salinity gradient energy with low membrane fouling. The feasibility of PRO in AL-FS mode was first examined by verifying less membrane deformation and insignificant shadow effect under pressurized PRO operation. The simulation of such PRO process showed that its low power density due to internal concentration polarization could be improved through reducing structural parameter of the support layer. Fouling experiments using synthetic wastewater clearly demonstrated that severe fouling observed with PRO operation at AL-DS was greatly reduced by switching PRO membrane orientation to AL-FS. Lastly, specific energy consumption of a PRO-RO hybrid process was assessed to be favorable in view of both power density and membrane fouling, suggesting that economically feasible power generation as well as effective water treatment can be achieved by operating PRO in the AL-FS orientation. [ABSTRACT FROM AUTHOR]

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]

In this study, the fouling propensity of a hybrid ceramic membrane bioreactor (CMBR)-reverse osmosis (RO) process was investigated over a prolonged period using real textile wastewater effluent. Additionally, the effectiveness of in-situ ozonation for fouling mitigation was investigated. The results revealed that the CMBR-RO system achieved approximately 99.8 % removal of chemical oxygen demand and 97.4 % removal of total nitrogen. Despite this, soluble extracellular polymeric substances, particularly biopolymers and humics-like substances, remained in the system, resulting in irreversible fouling on the ultrafiltration (UF) membrane. The implementation of in-situ ozonation notably reduced ceramic membrane fouling by enhancing the filterability of larger macromolecules and eliminating inorganic/organic foulants from the membrane surface. Multiple modified fouling indexes were also utilized to evaluate the fouling potential of the RO feed water through size fractionation. It is worth noting that ozonation could pose a potential risk for subsequent RO membrane fouling due to the formation of low molecular weight neutrals, acids, and calcium- or silica- related inorganic-organic complexes. Overall, the integrated CMBR-RO system with in-situ ozonation exhibited excellent performance in producing clean water, achieving nearly 100 % removal of 20 Aromatic Amines. These findings underscore the viability of the CMBR-RO system as a practical and sustainable choice for the reclamation of textile wastewater. [Display omitted] • Biopolymers and humics-like substances led to irreversible fouling • In-situ ozonation significantly improved the filterability of larger macromolecules • LMW molecules induced by ozone poses a potential risk for subsequent RO • The hybrid process removed almost 100% of 20 AAs in final water [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Membrane processes have attracted considerable attention in the field of water treatment because of their excellent compactness, convenient operation and management, and relatively low energy consumption. However, fouling is a significant technical challenge. Electrically conductive membrane (ECM) technology has recently emerged as a promising alternative owing to its novel and effective mechanisms and outstanding fouling control efficiency. However, because ECM technology is still in the early stages of research, its maturity is low, and fundamental research on the mechanism is insufficient. In this critical review, the mechanisms of the ECM for fouling control were systematically elucidated and categorized as electrochemical oxidation and reduction, electrostatic interactions, and electrolysis. Subsequently, an extensive and comprehensive literature survey of ECM applications was conducted. The current state of the application and performance of ECM technology was evaluated. The operation and modification strategies of ECM research are discussed based on an accurate understanding and evaluation of the fundamental mechanisms and level of actual application of ECM technology for fouling control. Consequently, topics for future academic research and practical applications of the ECM are proposed. [Display omitted] • Fundamental mechanisms of ECM for fouling control are described and categorized. • Performances of ECM application to membrane processes are analyzed. • Recent operation and modification strategies of ECM are discussed. • Future directions for ECM research and applications are proposed. [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: In order to evaluate the effect of membrane surface properties on the initial stage of biofouling, in the reverse osmosis (RO) membrane process, initial bacterial adhesion and biofilm formation experiments were performed under no filtration condition. In this study, five commercialized polyamide thin-film composite RO membranes (SW30HRLE, SW30HR (Dow FilmTec Co., USA), TM820 (Toray Co., Japan), RE-BE, RE-FE (Woongjin Chemical Co., Korea)) were chosen and their surface properties such as surface charge, roughness, hydrophobicity and surface morphology were measured. For examining initial bacterial adhesion, a flow channel reactor was employed for 3h, while for examining a biofilm formation, the CDC reactor was employed for 48h. Pseudomonas aeruginosa PAO1 tagged with GFP was selected as a model bacterial strain. Major findings in this study indicate that although the initial bacterial cell adhesion in a flow channel reactor indicated more bacterial cells attachment on the membrane surface with higher hydrophobicity, the extent of biofilm grown in CDC reactor for 48h became similar regardless of the difference of the membrane surface properties, indicating that the membrane surface properties become a less important factor affecting the biofilm growth on the membrane surface. This finding will be helpful in improving the understanding of biofouling issue occurring in the real RO membrane system, although practical implication is somewhat limited since this study was performed under no filtration condition. [Copyright &y& Elsevier]

• Electrolysis-based, in situ microbubble generation mitigates membrane fouling. • Nickel foam is an ideal material for in situ, interfacial microbubble generation. • Rapid (<5 min) and complete flux recovery is demonstrated for all model foulants. • Process stability is demonstrated for many fouling cycles and long operation times. • Orders of magnitude more efficient compared to conventional cleaning strategies. For membrane-based, water treatment technologies, fouling remains a significant challenge for pressure-driven processes. While many antifouling strategies have been proposed, there remains significant room for improved efficiency. Direct application of microbubbles (MBs) at a membrane surface offers a promising approach for managing interfacial fouling through continuous physical interaction(s). Despite such potential, to date, integration and optimization of in-situ generated MBs at the membrane interface that are both highly antifouling with minimal energy inputs and unwanted side reactions remains mostly outstanding. Here we demonstrate the application of conductive, porous nickel foam for electrolysis-based generation of hydrogen microbubbles at an ultra-filtration (UF) membrane interface, which significantly mitigates membrane fouling for a range of model foulants. System characterization and optimization includes comparison of metal foams (Ni, Cu, Ti), faradic efficiencies, hydrogen evolution reaction (HER) curves, cyclic voltammetry, and quantification of hydrogen gas flux and bubble size, as a function of applied current. When optimized, we report rapid (<5 min) and near complete (∼99 %) flux recovery for three classes of foulants, including calcium alginate, humic acid (HA), and SiO 2 particles. For all, the described MB-based approach is orders of magnitude more energy efficient when compared to conventional cleaning strategies. Finally, we demonstrate the MB-based regeneration/cleaning process is stable and repeatable for ten cycles and also highly effective for a challenge water (as a model oilfield brine). Taken together, this work presents a novel and efficient approach for the application of in-situ electrically generated MBs to support sustainable pressure-driven membrane processes. [ABSTRACT FROM AUTHOR]

Wetting by fouling is phenomenon specific to membrane distillation (MD) and are regarded as challenges to the seawater membrane distillation (SWMD) process. To understand fouling and wetting, the influence of Mg and Sr crystals, which can potentially cause scaling, as well as Ca crystals deposited on the membrane surface were investigated. Mg(OH) 2 and CaSO 4 had significant impact on fouling and wetting. Even if CaCO 3 and SrSO 4 had no effects on fouling and wetting as single salts, CaCO 3 and CaSO 4 were dominant in synthetic seawater without Mg(OH) 2. However, the occurrence of Mg(OH) 2 scales became a cause for concern if Ca ion was removed from seawater for the prevention of fouling and wetting. Therefore, Mg as well as Ca should be removed for proper fouling and wetting control. NaOH/Na 2 CO 3 softening was used for the removal of Ca and Mg ions. In addition, based on the inhibition effects of Mg ions on Ca scales, a new pretreatment method involving the injection of MgCl 2 to increase the Mg /Ca ratio was examined. Image 1 • Wetting in MD process using a seawater was observed by visualization system. • Wetting by Mg(OH) 2 occurred during the MD process was firstly suggested. • Retardation of the wetting in MD process was achieved by a Mg addition to the feed. • The SrCO 3 scalant was formed when major components of seawater were removed. • The CaCO 3 and CaSO 4 scalants resulted in the partial and full wettings, respectively. [ABSTRACT FROM AUTHOR]

Preoxidation is gaining spotlight in the mitigation of ultrafiltration (UF) membrane fouling caused by algal organic matter (AOM). Although it is known to be beneficial in freshwater, its applicability in seawater treatment has barely been explored. This study first evaluated the effect of UV/permonosulfate (PMS) oxidation for UF process against marine harmful algal blooms (HAB). The transition of AOM released from Pseudo Nitzchia was investigated which produces a neurotoxin, domoic acid (DA). Specifically, UV light emitting diodes (LED) were employed as UV source. The results indicated UV-LED/PMS treatment effectively reduces the fouling potential of AOM. However, the participation of abundant chloride ions generated free chlorine and disinfection byproducts, thus, PMS addition below 0.5 mM was suggested for seawater applications. With respect to PMS 0.5 mM, TOC and cake layer resistance were reduced by 10% and 85%, respectively, and this was followed by significant improvements in water permeability, flux reversibility and permeate quality of UF process. Furthermore, PMS exhibited significant reactivity for decomposing DA achieving rapid disappearance of 1 ppm of DA within a minute. The aforementioned results encourage the use of PMS as a bulk oxidant in seawater treatment to simultaneously mitigate membrane fouling and improve permeate quality. Unlabelled Image • The impact of UV-LED/PMS preoxidation was assessed against marine AOM fouling. • Despite abundant Cl− ions, it was effective to be applied in seawater condition. • Preoxidation greatly mitigated both reversible and irreversible UF membrane fouling. • UV-LED/PMS preoxidation is also beneficial to reduce toxic substance, domoic acid. • To control moderate amounts of free Cl and THMs, [PMS] < 0.5 mM was suggested. [ABSTRACT FROM AUTHOR]

Membrane fouling is an inevitable phenomenon and common issue in Reverse Osmosis (RO) membrane systems used for water reclamation. Severe membrane fouling in RO system could consequently increases the operation cost as it requires frequent membrane chemical cleaning process thus consuming more chemical agents and shorten lifespan of RO membrane module. In this study, potential foulants of RO membranes that are used at Sydney's urban wastewater recycling facility which treated for domestic and commercial wastewaters, were investigated via membrane autopsy method. The three-year-old spiral wound RO membrane modules were taken from the site for membrane autopsy and to investigate major fouling factors as well as in-depth study of fouling mechanisms throughout various characterization methods. Additionally, a flux recovery rate of fouled RO membranes via the chemical cleaning was also examined using different kind of chemical cleaning agents to find a most effective chemical cleaning combination. • Three-year-old RO membranes in WWTP were conducted membrane autopsy. • Membrane fouling factors were investigated using various analysis methods. • Effective chemical cleaning condition was found via variety use of cleaning agents. • Organic fouling on the membrane was predominant by protein and polysaccharides. • Mg and Na were the primary components of the foulants on the membrane. [ABSTRACT FROM AUTHOR]

[Display omitted] • ECMC was applied to mitigate fouling induced by flue gas during CO 2 stripping. • The surface modification improved the conductivity and stripping performance of ECMs. • ECMC mitigated fouling by electrostatic repulsion in foulants at low concentrations. • High voltage which occurs oxidation was necessary to prevent fouling in harsh conditions. • ECMC reduced the total energy consumption per CO 2 amount in stripping process. Carbon capture utilization & storage (CCUS) process is a promising technology for reducing greenhouse gas emissions. However, the biggest challenge in commercializing CCUS is reducing energy consumption during the CO 2 stripping stage. Membrane contactors have been developed to reduce energy consumption and improve CO 2 stripping performance. However, traditional polymer-based membranes are vulnerable to damage by combustion residues such as oil and grease. To address this problem, electrically conductive membranes (ECMs) have been developed to enable efficient electrochemical reactions for anti-fouling purposes. This study investigated the anti-fouling performance of an electrically conductive membrane contactor (ECMC) for CO 2 stripping. Surface modification with a two-layered ECM resulted in the superior electrical conductivity and CO 2 stripping flux compared to other ECMs. Electrostatic repulsion effectively mitigated fouling by 92.1 % compared to non-charged ECMC by preventing the attachment of oil and grease, but it was not observed a significant effect in high oil and grease concentrations. The electrochemical oxidation process when applying a high voltage improved anti-fouling performance, and the O 2 sweep gas mode greatly maintained the CO 2 stripping flux at 95.2 % with high oil and grease concentrations. Furthermore, the feasibility of the ECMC was demonstrated by comparing the predicted total energy consumption per CO 2 amount under actual operating conditions. In conclusion, ECMC improved the energy efficiency of CO 2 stripping by providing high anti-fouling performance in CCUS. [ABSTRACT FROM AUTHOR]

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]

Abstract A visualization system was designed for a real-time observation of scales during direct contact membrane distillation (DCMD). The system was composed of a MD module, a camera and light sources. Firstly, visibility of the scales with the system and correlation between detected spots and wetting were assessed during the MD process using a polyvinylidene fluoride (PVDF) 0.45 μm membrane. The white spots were observed in the captured images from the visualization system and got broader with the electrical conductivity (EC) increase in permeate. It was verified that the spots indicated the pores blocked by the CaSO 4 scales. The wetting occurred through the white spots if the pressure was applied. Therefore, the high wetting potential area could be identified with the suggested visualization system during the MD operation in real-time. The visualization system was applied to the MD process under different permeate temperatures (20 and 55 °C). The visualization system successfully detected the pore blocking related with different scale formation according to the temperatures at the membrane surface. Graphical abstract Unlabelled Image Highlights • The visualization system was suggested for the detection of the scales in real-time. • The scales in the pores and on the surface were detected using the system. • The suggested system enabled to provide temporal and spatial information on scales. • The different wettability was successfully distinguished by the system. [ABSTRACT FROM AUTHOR]

Abstract Several fouling indexes, such as silt density index (SDI), have been applied in the reverse osmosis (RO) process to predict the fouling tendency, design the pretreatment process, and optimize the cleaning cycles. However, the forward osmosis (FO) process has no reliable method, as yet, that relates fouling with its performance. This study utilized the concept of fouling reversibility to develop a fouling index for the FO process simulation. The osmotically driven reversibility index (ORI) was determined by measuring the flux recovery after the physical cleaning or flushing cycle. The protocols of ORI measurement were developed systematically by determining the proper operation mode, cross-flow velocity for physical cleaning, and draw solution type and concentration. The applicability of ORI was examined by investigating the FO process in treating secondary effluents from various full-scale wastewater treatment plants. The results demonstrated that the normalized final flux by fouling in FO was closely correlated to the ORI measurements with high statistical reliability (R2 = 0.84). After conducting a long-term stable FO operation, it is deduced that the ORI is a useful evaluation parameter for continuous FO and its cleaning cycles in which periodic flushing is normally utilized to exploit and enhance the fouling reversibility of FO. Graphical abstract fx1 Highlights • An osmotically-driven reversibility index (ORI) was developed for FO process. • ORI simulates FO fouling reversibility and its operational protocol was constructed. • High correlation of ORI and FO fouling was obtained using various real wastewaters. • ORI is a useful evaluation parameter for continuous FO and its cleaning cycles. [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 use of forward osmosis (FO) for concentrating radioactive liquid waste from radiation therapy rooms in hospitals was systematically investigated in this study. The removal of natural and radioactive iodine using FO was first investigated with varying pHs and draw solutions (DSs) to identify the optimal conditions for FO concentration. Results showed that FO had a successful rejection rate for both natural and radioactive iodine ( 125 I) of up to 99.3%. This high rejection rate was achieved at a high pH, mainly due to electric repulsion between iodine and membrane. Higher iodine removal by FO was also attained with a DS that exhibits a reverse salt flux (RSF) adequate to hinder iodine transport. Following this, actual radioactive medical liquid waste was collected and concentrated using FO under these optimal conditions. The radionuclides in the medical waste ( 131 I) were removed effectively, but the water recovery rate was limited due to severe membrane fouling. To enhance the recovery rate, hydraulic washing was applied, but this had only limited success due to combined organic-inorganic fouling of the FO membrane. Finally, the effect of FO concentration on the reduction of septic tank volume was simulated as a function of recovery rate. To our knowledge, this study is the first attempt to explore the potential of FO technology for treating radioactive waste, and thus could be expanded to the dewatering of the radioactive liquid wastes from a variety of sources, such as nuclear power plants. [ABSTRACT FROM AUTHOR]

An osmotic dilution process of forward osmosis (FO) and reverse osmosis (RO) was applied at pilot-scale to integrate wastewater treatment with seawater desalination in a coal-fired power plant. FO was osmotically driven by seawater used as cooling water. FO-treated wastewater was diluted with seawater and then further processed by RO. Seasonal variation in water flux, fouling behavior and reversibility, and energy consumption in both FO and RO were systematically evaluated during 5 months of pilot operation. The FO water flux, which declined due to the organic fouling induced by the wastewater from the coal-fired power plant, was readily recovered by physical cleaning. The integrated FO-RO dilution process was able to reduce the RO fouling potential through FO treatment of wastewater, significantly decreasing SDI value to 1.5 ± 0.1. This study also reported energy consumption data, to our knowledge for the first time, at pilot scale operation of FO-RO dilution process, and showed that total energy consumption for desalinating the diluted feed, including wastewater reclamation by FO, was 15% less than that of typical seawater desalination by RO. The results of this FO-RO pilot study demonstrated that sustainable FO-RO operation can be achieved in the treatment of power plant wastewater owing to easy fouling control, low energy consumption, and superior final water quality. [ABSTRACT FROM AUTHOR]

Recently, a modified fouling index (MFI) is published on ASTM, and thus, is expected to become a standard method for evaluating fouling potential, as a supplement to silt density index (SDI). Employing membranes with smaller pore size in MFI measurements has been continuously suggested in many previous studies. However, there was a lack of practical studies verifying the usefulness of MFI. In this study, the applicability of multiple MFIs (i.e., MFI 0.45 , MFI-UF 100 kDa and MFI-UF 10 kDa ) were evaluated at a full-scale UF/RO seawater desalination plant located in the Middle East. For a year, MFIs were measured with RO feed water and the results were correlated with increments in differential pressure (DP) of RO process. Regression analysis was conducted in order to find out whether the fouling index could predict RO performance deterioration. The observed MFIs clearly showed correlation with DP variation, while SDI and water quality parameters (e.g. turbidity and UV 254 ) exhibited relatively low accordance. Particularly, MFI-UF 100 kDa was the most sensitive, indicating that colloidal fouling is the main cause of fouling in SWRO desalination. The regression results were reconfirmed through specific events where feed water quality was severely changed due to red tide or ship movement at intake. These events provided unconventional feed water characteristics, but similar trend was observed that MFI-UF 100 kDa was most sensitive. The application of MFI in an actual plant provided valuable contribution for the further advancement of MFI measurements. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD), often integrated with crystallization (MDC), is an attractive treatment option for shale gas produced water (SGPW) because of its ability to handle high salinity as well as the inherent geothermal heat available to this process. To evaluate the feasibility of applying MD process for SGPW treatment, membrane fouling and wetting, which are barrier to its practical application, were systematically examined by varying organic and inorganic constituents, simulating the SGPW from Marcellus shale (USA). The liquid entry pressure (LEP) was first measured to predict the possibility of wetting by the chemical constituents of SGPW, and then a series of lab-scale MD and MDC experiments were performed to elucidate membrane wetting mechanisms. The results revealed that membrane wetting became more pronounced in the presence of oil and grease. The inorganic scaling induced by multivalent ions, such as barium and calcium in SGPW, also enhanced membrane wettability and led to poor permeate water quality. By integrating with crystallization, scalant loading was reduced properly and thus membrane wetting was mitigated effectively. As a result, adopting this MDC process increased total recovery up to 62.5%. Our experimental observations demonstrated that MD could be sustainably operated for SGPW treatment through optimized crystallization for scaling removal as well as effective pre-treatment for organic removal. [ABSTRACT FROM AUTHOR]

In this study, a novel hollow fiber nanofiltration (HFNF) was investigated for treating real Cijengkol river water in Indonesia. Ultrafiltration (UF) pretreatment was performed to evaluate the effect of UF on the HFNF performance. The water quality of the raw water and permeate of the UF, HFNF, and UF-HFNF hybrid was first characterized. UF could remove only solids, while both nanofiltration (NF) and the UF-NF hybrid achieved a high removal efficiency for impurities in river water, meeting the standards for drinking water quality. However, severe organic fouling occurred in the HFNF membranes. To effectively control organic fouling, various cleaning methods were investigated, and then the analyses of gel permeation chromatography (GPC) and fluorescence excitation emission matrix (FEEM) were conducted on backwashing wastewater to identify the cleaning mechanism. First, hydraulic flushing and backwashing were evaluated, and both methods achieved higher than 90% efficiency particularly for high-molecular-weight organic foulants (>1000 Da). However, the cleaning efficiency decreased during long-term operation because of the low removal efficiency of low-molecular-weight (LMW) organics. Hence, chemically enhanced backwashing (CEBW) (i.e., 5 ppm and 10 ppm NaOCl) was employed to enhance the cleaning efficiency. The results showed that membrane fouling was easily controlled by CEBW with 95% removal efficiency. To reduce the usage of chemicals, CO 2 scouring, and CO 2 nucleation backwashing were also examined. CO 2 nucleation backwashing exhibited a better efficiency than CO 2 scouring because of the additional effect of CO 2 nucleation on the HFNF membrane surface. Interestingly, a relatively high removal efficiency for fulvic acid-like organic fouling was observed in both CEBW and CO 2 nucleation backwashing, whereas tryptophan and tyrosine-like proteins, soluble microbial products (SMPs), and humic-like organics were hardly removed by acidic condition (pH < 6.5) or high shear force, leading to a low cleaning efficiency of CO 2 nucleation backwashing. [Display omitted] • Indonesia river water was treated by novel hollow fiber nanofiltration membrane. • The dominant membrane fouling was due to low molecular weight organic fouling. • Periodical hydraulic backwashing and CO 2 scouring can replace pretreatment. • Hydraulic backwashing removes only high molecular weight organic foulants. • Chemical and CO 2 backwashing can remove low molecular weight organic fouling. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) are a major barrier to the stable and efficient operation of seawater reverse osmosis (SWRO) desalination plants. Although the intensity varies regionally, the occurrence of HABs impairs plant operation through severe particulate, organic, and biological fouling of both pretreatment and RO systems. As a result, considerable effort has been put into developing and optimizing pre-treatment techniques to mitigate these problems. This study reviews the historical changes and current status of pretreatment applications based on >110 datasets for large SWRO desalination plants. Chronological analysis underscores the increasing trend in the operation of dissolved air flotation and ultrafiltration systems since severe HABs in the Middle East from 2008 to 2009. The impact of HAB characteristics on system performance was also analyzed, and the efficiency of current pretreatment systems for the removal of HABs was evaluated, along with proposals for operational guidelines. Finally, future strategies for i) intelligent monitoring and prediction of HABs, ii) improvement of unit processes for the removal of algal organic matter, and iii) utilization of algal biomass to alleviate environmental impact were systematically delineated for smarter, safer, and greener operation of future SWRO desalination plants in response to the occurrence of HABs. [Display omitted] • Review on the impact of harmful algal blooms (HABs) on seawater desalination • Analysis of >110 datasets of full-scale SWRO desalination plants • Historical trends and current practice of pretreatment applications • Guidelines for pretreatment operation under HABs occurrences • Future operational directions for smarter, safer and greener desalination practice [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) demonstrates enormous potential to treat high salinity water due to its unique rejection mechanism; however, fouling and wetting continue to be major technical challenges in high recovery conditions due to the concentration of contaminants. Electrical repulsion with electrically conductive membranes shows promise to address fouling and wetting, as it prevents contaminants from accessing the membrane surface. Improvements to electrical conductivity and hydrophobicity occurred using a multi-layered single-wall carbon nanotube (SWCNT) coating on a polyvinylidene fluoride (PVDF) membrane without MD performance degradation. These results were identified by analyzing cyclic voltammetry, electrochemical impedance spectroscopy, and direct contact angle. An experimental and theoretical evaluation on the feasibility of using electrical repulsion with the SWCNT/PVDF membrane to address the fouling and wetting of the MD was carried out. This evaluation was undertaken using a series of fouling/wetting experiments and repulsive force calculations. The results confirmed that fouling and wetting in the MD process were effectively mitigated by electrical repulsion with the SWCNT/PVDF membrane, allowing more than twice the operation time without any performance degradation; this was despite the low applied voltage and long-term operational conditions. The experimental observations demonstrated that electrical repulsion with the SWCNT/PVDF membrane potentially facilitates sustainable MD operations with high recovery conditions. [Display omitted] • Electric repulsion with SWCNT modification was investigated. • SWCNT modification increased hydrophobicity and conductivity of MD membrane. • Electric repulsion has effectively mitigated fouling and wetting with low voltage applied. • Fouling and wetting mitigation mechanism was examined by calculating repulsive force. • SWCNT/polyvinylidene fluoride membrane was stable in long-term with low voltage. [ABSTRACT FROM AUTHOR]

Current fouling indices typically employed in RO practices, such as silt density index (SDI) and modified fouling index (MFI), have suffered greatly from their inability to predict actual fouling potential primarily due to the erroneous interpretation of fouling mechanisms. Our findings clearly demonstrated that the effect of pore blocking should be excluded during fouling index measurements to simulate real RO applications. Thus, new concept of cake fouling index (CFI) was developed in order to accurately evaluate true fouling cake layer resistance. Specifically, the CFI was determined through consecutive filtration tests by subtracting the flux decline of the secondary filtration from that of the first one to eliminate the effect of pore blocking. The results proved that CFI better predicts the degree of fouling rate in RO experiments than MFI. It was also revealed that it could be utilized as a useful tool for identifying and evaluating the fouling mechanisms. Through a comparison of MFI and CFI, it was shown that pore blocking was enhanced as much as cake formation when pH decreased, while divalent cations (Ca 2+ ) increased only cake formation on the membrane surface. This newly developed index refining existing MFI method is expected to provide more precise information about RO membrane fouling, especially for the design of effective pretreatment processes. [ABSTRACT FROM AUTHOR]

The chemical heterogeneity (charge distribution) of polyamide reverse osmosis (RO) membrane surfaces and its influence on membrane fouling were investigated using atomic force microscopy (AFM). Negatively charged carboxyl modified latex (CML) and positively charged aliphatic amine latex (AAL) particles were employed to make AFM colloidal probes. The adhesive forces were significantly higher with the AAL probe due to negatively charged membrane surfaces. The chemical heterogeneity measured by AFM colloidal probes indicated that RO membranes could have chemically heterogeneous surfaces even if they exhibited similar average surface properties including zeta potential, contact angle and surface roughness. By performing fouling experiments with two commercial RO membranes of different chemical heterogeneities, it was demonstrated that RO membrane with high chemical heterogeneity was more prone to fouling, suggesting that surface charge distribution is one of the key factors governing RO membrane fouling. Consequently, surface chemical heterogeneity provides a new tool for accessing membrane fouling mechanisms and a novel concept for developing fouling resistant RO membranes. [ABSTRACT FROM AUTHOR]

A hybrid process of pressure retarded osmosis (PRO) and reverse osmosis (RO) has a great potential for successfully integrating wastewater reclamation with seawater desalination, which can achieve several operational goals simultaneously including augmenting water resources, providing multiple barriers for wastewater purification, seawater dilution for lowering energy use as well as capital cost, osmotic power generation, and less environmental impact. The low energy use of a PRO–RO process was demonstrated by assessing specific energy consumption (SEC). However, a substantial flux decline was observed owing to the susceptibility of PRO to membrane fouling. Particularly, inorganic fouling was pronounced within the support layer, which was hardly reversible by hydrodynamic methods such as physical flushing and osmotic backwashing. Lastly, the anti-scaling pretreatment was shown to be very effective for lessening inorganic scaling within the support layer, suggesting that a PRO–RO hybrid process could be successfully applied with optimized fouling control strategies in PRO. [ABSTRACT FROM AUTHOR]

Organic fouling mechanisms in forward osmosis (FO) were systematically investigated at varying feed and draw temperatures. The effect of temperature variation on FO performance was first examined without foulants. When draw temperature increased, internal concentration polarization (ICP) decreased, which caused water flux to increase. Water flux was also improved with increasing feed temperature due to water permeability increased by decreased viscosity. Thus it can be deduced that water flux enhancement was induced by combined effects of reduced ICP and enhanced water permeability. A series of fouling experiments was then elaborately designed to fundamentally elucidate organic fouling mechanisms. Results demonstrated that organic fouling was significantly influenced by convective and diffusive organic transports induced by increasing temperature. Faster flux decline was observed with increasing draw temperature, primarily due to increased permeation drag. When increasing feed temperature, FO membrane was less fouled, attributing to enhanced organic back diffusion from membrane surface as well as increased organic solubility. Furthermore, fouling became more severe above certain critical flux at which organic convection by permeation drag dominated fouling mechanism as seen with escalating both temperatures simultaneously. Findings from this study can be utilized beneficially when FO temperature may be varied and needs to be optimized. [ABSTRACT FROM AUTHOR]

This study elucidates the physicochemical mechanisms of monovalent and multivalent inorganic scaling and suggests an optimal cleaning strategy for efficient membrane distillation (MD) operation. Three distinct stages of MD inorganic scaling were clearly identified by i) experimentally measuring transient flux, ii) rejection behavior resulted from the deposition of a scale, and iii) SEM-EDX analysis of the membrane. During stage 1, no scale was found over the membrane surface showing almost stable water flux and permeate conductivity. In stage 2, the onset of inorganic scaling resulted in the deposition of scaling on some parts of the membrane surface, partially covering the membrane pores, which lead to a sudden reduction in the water flux despite a steady solute rejection. However, as scaling expands into the pore in final stage 3, the permeate conductivity increased, indicating a reduction in rejection. Then, the pores were completely blocked, and the water flux reached almost zero. To simulate this scaling formation more fundamentally, the saturation index (SI) and supersaturation (S) concepts were introduced. The type and timing of scaling were successfully predicted by the SI value, and the amount of scaling was accurately estimated by the S value. Moreover, through the analysis of this physicochemical mechanism of inorganic scaling, an optimal cleaning strategy for sustainable MD operation was proposed. [Display omitted] • The physicochemical mechanism of inorganic scaling was identified as three distinct stages. • The scaling formation on MD performance was confirmed at each stage. • The scaling formation was simulated by using supersaturation (S) concepts. • The type and timing of scaling were predicted by the proposed saturation index. • A cleaning strategy and fouling mechanism for sustainable MD operation were elucidated. [ABSTRACT FROM AUTHOR]

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. [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: 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 139nm, 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 139nm 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 25.6cm/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. [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: Fouling behaviors during forward osmosis (FO) and reverse osmosis (RO) are compared. Alginate, humic acid, and bovine serum albumin (BSA) are used as model organic foulants, and two suspensions of silica colloids of different sizes are chosen as model particulate foulants. To allow meaningful comparison of fouling behavior, identical hydrodynamic operating conditions (i.e., initial permeate flux and cross-flow velocity) and feed water chemistries (i.e., pH, ionic strength, and calcium concentration) are employed during FO and RO fouling runs. The observed flux-decline behavior in FO changed dramatically with the type of organic foulant, size of colloidal foulant, and the type of the draw solution employed to generate the osmotic driving force. Based on these experimental data and the systematic comparisons of fouling behaviors of FO and RO, we provide new insights into the mechanisms governing FO fouling. In FO, reverse diffusion of salt from the draw solution to the feed side exacerbates the cake-enhanced osmotic pressure within the fouling layer. The elevated osmotic pressure near the membrane surface on the feed side leads to a substantial drop in the net osmotic driving force and, thus, significant decline of permeate flux. Our results further suggest that the structure (i.e., thickness and compactness) of the fouling layers of FO and RO is quite different. By varying the cross-flow velocity during the organic fouling runs, we were able to examine the fouling reversibility in FO and RO. The permeate flux during organic fouling in FO recovered almost completely with increasing cross-flow velocity, while no noticeable change was observed for the RO system. Our results suggest that organic fouling in FO could be controlled effectively by optimizing the hydrodynamics in the feed stream without employing chemical cleaning. [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]

In this study, the impacts of three feed spacer design parameters; thickness, porosity and architecture, on the cleaning efficiency of ultrafiltration (UF) membranes were studied, both in backwash and relaxation cleaning modes, using sodium alginate solution dosed with CaCl 2 as the process feed. Both commercial, net-type spacers and 3D-printed spacers based on triply periodic minimal surfaces (TPMS) architectures were utilized in the study. Increased spacer thickness and porosity were found to increase the cleaning resistance of the membrane, while TPMS spacers were found to yield a lower cleaning resistance than net-type spacers, even with the latter being thicker. The root causes of these observations were analyzed based on resistance analysis of the fouling layer on the membranes. To do that, overall, residual, reversible and irreversible fouling resistances were quantified at the end of a 20-cleaning cycle test. Statistical correlations were then established between these resistances and spacer properties. The results showed that the consequential impacts of spacer design on the shear stresses, created by the feed flow on the fouling layer, underscore the observed fouling mechanism and the consequent cleaning efficiency. The spacer design can impact these shear stresses through its hydraulic diameter and spacer-membrane contact area. When the spacer design leads to lower shear stresses, a cake filtration mechanism prevails, a more irreversible fouling occurs and more challenging cleaning becomes. A recently published work on combined intermediate pore blockage and cake filtration model for fouling was used to construe these observations. • Impacts of spacer properties on membrane backwash and relaxation is assessed. • Net-type spacers and triply periodic minimal surface (TPMS) spacers studied. • Statistical correlation between spacer design and fouling resistances determined. • Effect of spacer architecture on pore blockage and irreversible fouling evaluated. • Relationship between spacer design and fouling mechanism established. [ABSTRACT FROM AUTHOR]