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In view of the proliferating applications involving membrane-based separation, the inevitable membrane fouling phenomenon is well-studied. However, the influence of foulant shape on membrane fouling remained incompletely understood. Therefore, the goal of this study was to investigate the fouling behaviors by three different shapes of latex particles (namely, peanut, pear and sphere) with similar mean diameters in the range of 3.5–3.8 μm. External and internal fouling were studied using polycarbonate track-etched (PCTE) membranes with nominal pore sizes of 2 and 8 μm, respectively. Flux data were taken, and fouling models, optical coherence tomography (OCT) and field-emission scanning electron microscope were employed. Regarding external membrane fouling, the sphere-shaped particles displayed the worst flux decline, which is tied to the greatest tendency to deposit on the membrane pores, as revealed by the network fouling model. As for internal fouling, the flux decline curves were more similar among the particle types. The fouling model shows the sphere-shaped particles gave the densest internal cake, which caused slightly steeper flux decline in the latter part of the filtration. Furthermore, OCT indicates that the highest fouling fractions at 7.5 μm below the membrane were exhibited for the peanut-shaped particles, which is due to the preferential vertical orientation resulting in deeper penetration. Results here highlight the non-negligible influence of foulant particle shape, which warrants further understanding and accounting for membrane fouling studies. [Display omitted] • Used OCT to reveal influence of foulant particle shape on membrane fouling. • Spheres were more prone to pore-blockage and thus gave worst flux decline. • Non-spherical particles gave less dense internal cakes due to rotational effects. • Peanut-shaped particles penetrated deeper due to preferential vertical orientation. • Particle shape affected flux decline more when external fouling was dominant. [ABSTRACT FROM AUTHOR]

The Derjaguin-Landau-Verwey-Overbeek (DLVO) model, as well as the extended model (XDLVO), is popularly employed to quantify the interfacial interactions underlying membrane fouling. However, disagreements between membrane fouling extent and the interaction energies derived from DLVO or XDLVO models have been reported, which suggests gaps in the understanding. This study demonstrates that the DLVO approximation methods for predicting the interfacial foulant-membrane interaction are sensitive to the boundary condition assumptions (e.g., constant charge versus constant potential). In particular, while both the Poisson-Boltzmann (P–B) and linear superposition approximation (LSA) equations can quantify the electrostatics (EL) interaction energy component, the former assumes constant potential, while the latter additionally considers constant charge scenarios. The relative accuracy of these two equations were evaluated here. For dead-end filtration tests, flux decline trends, OCT analysis results and fouling model parameters were obtained. Regarding fouling of pristine PCTE membrane by latex particles of opposite charge signs, both the P–B and LSA equations contribute to predict relative fouling extents correctly. However, for the case of the BPEI-coated membrane, the P–B equation failed whereas the LSA equation gave good agreements. For cross-flow filtration tests in organic solvents, LSA also out-performed the P–B equation in providing more accurate predictions of membrane fouling. The results here highlight the shortcomings in the commonly used P–B equation and are expected to be potentially valuable in the development of better approximations for quantifying interfacial interaction energies. [Display omitted] • Both P–B and LSA equations predict fouling of pristine membrane by latex correctly. • Only LSA predict affinity between coated membrane layer and latex correctly. • Superiority of LSA also applies to fouling in organic solvents. • P–B equation is more limited due to underlying constant-potential assumption. • Boundary condition assumptions need to be considered in use of DLVO model. [ABSTRACT FROM AUTHOR]

Membrane fouling in organic solvent environments remains poorly explored despite its significance in chemical and pharmaceutical industries. This study uses molecular dynamics (MD) simulations and experiments to explore lysozyme fouling in water, as well as four organic solvent environments, namely, 30 % v/v and 50 % v/v isopropyl alcohol (IPA), and 30 % v/v and 50 % v/v dimethyl sulfoxide (DMSO). Experimentally, flux declines were least with IPA and worst with DMSO. Biased simulations indicate the worst fouling in DMSO is tied to the most attractive lysozyme-membrane energy in the presence of DMSO. However, the relative attractive energies for IPA and water do not agree with the relative flux declines, indicating other factors are more influential when the interaction energies are similar. To understand the gentler flux decline for IPA despite the more attractive lysozyme-membrane energy, radial distribution functions (RDFs) were obtained from unbiased simulations. Analyss of the water and solvent films around both the membrane and the lysozyme molecule reveal that the denser water film around both entities induced by the presence of IPA serves as a barrier for fouling and thus leads to less flux decline. The results underscore the complexity of fouling in organic solvent systems, cautioning against direct use of the understanding based on aqueous systems. [Display omitted] • Membrane fouling by lysozyme in water, IPA and DMSO studied. • Flux decline worst in DMSO and least in IPA. • Worst fouling in DMSO tied to most significant lysozyme-membrane attraction. • Least fouling in IPA tied to denser water film around membrane and lysozyme. • Both biased and unbiased molecular dynamics simulations needed for full explanation. [ABSTRACT FROM AUTHOR]

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules. [Display omitted] • Operating under AL-FS orientation is preferred as a strategy for better fouling control. • Integrally skinned asymmetric hollow fiber membranes were developed for AL-FS orientation in PRO. • The membranes achieved sustainable power production when wastewater was employed. • The volumetric power density was predicted to yield promising solution for practical application. [ABSTRACT FROM AUTHOR]

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules. [Display omitted] • Operating under AL-FS orientation is preferred as a strategy for better fouling control. • Integrally skinned asymmetric hollow fiber membranes were developed for AL-FS orientation in PRO. • The membranes achieved sustainable power production when wastewater was employed. • The volumetric power density was predicted to yield promising solution for practical application. [ABSTRACT FROM AUTHOR]

The current study aimed to understand both external and internal membrane fouling by three proteins with different net charges, namely, negatively charged pepsin and bovine serum albumin (BSA), as well as positively charged lysozyme. Polycarbonate track-etched (PCTE) membranes were used. Per electrostatic attraction, the flux decline was the worst for lysozyme, which is attributed by the fouling model to the greatest pore blockage (α) and pore constriction (β), and by field-emission scanning electron microscope (FESEM) and optical coherence tomography (OCT) to the most extensive external fouling. Between pepsin and BSA, BSA gave worse flux decline despite its more negative net charge. The fouling model indicates that BSA gave greater pore blockage (α) and denser internal cake (R c / R m), while the quartz crystal microbalance with dissipation (QCM-D) indicates a rigid cake structure. Notably, despite monotonic flux decline with filtration, the OCT fouling voxel trends show significant fluctuations, which has not been reported before and thus signify the unique behavior of protein foulants in straight-through pores. Specifically, the trends below and above the −4.5 μm layer (i.e., 4.5 μm below the feed-membrane interface) are perfectly opposite, indicating the non-uniform protein deposits slipping downwards in the membrane pores as filtration progressed. The dynamic movements of the protein cakes unveiled here warrant more understanding in future studies. • Surprising fluctuations of OCT fouled voxels despite monotonically decreasing flux. • Dynamic downward motion of fouled protein deposit in the straight-through pores. • Delayed fluctuations by BSA tied to densest and most rigid cake. • Worst flux decline by lysozyme due to high pore blockage and pore constriction. [ABSTRACT FROM AUTHOR]

Membrane fouling, which is a key obstacle in implementing membrane technology, has been studied extensively for aqueous feeds. With increasing interests in organic solvent applications, a corresponding effort on understanding membrane fouling is warranted. This study employs molecular dynamics simulations to unveil the mechanisms underlying the different adsorption behaviors of dextran onto a polyacrylonitrile (PAN) membrane in three polar and protic solvents, namely, water, formamide and ethanol. The dextran-membrane separation distance is the lowest for water, followed by ethanol then formamide, which agrees with the worse flux decline for water relative to formamide observed experimentally. The greatest adsorption tendency in water is tied to the most attractive dextran-membrane interaction. On the other hand, the lower adsorption tendency in formamide and ethanol is linked to enhanced solvation of the dextran molecule and membrane, which deters dextran adsorption onto the membrane. Specifically, formamide, which leads to the least adsorption, exhibits the most attractive solvent-dextran and solvent-membrane interaction energies, the highest solvent-accessible surface area (SASA) for dextran, and also the highest density of solvent molecules in the solvation shell closest to the membrane. As for ethanol, it gives the highest density of solvent molecules in the solvation shell closest to a part of the dextran. The solvation of foulant and membrane by water deviates from that by other similarly polar and protic solvents, which has important implications in membrane fouling and highlights the need for enhancing the understanding of membrane fouling behaviors in organic solvents. [Display omitted] • Adsorption tendency of dextran on membrane is greatest in water and least in formamide. • Dextran-membrane interaction is most attractive in water. • Solvent-dextran and solvent-membrane interactions are most attractive in formamide. • Competitive solvent and dextran adsorption onto membrane governs fouling. • Greater solvation of foulant and membrane in ethanol and formamide reduces fouling. [ABSTRACT FROM AUTHOR]