Membranes

An aerated membrane reactor (25 L working volume) equipped with 1.5 m² hollow-fiber module was designed and operated using synthetic greywater for household water reuse. Activated sludge (MBR), activated carbon (PAC), zeolite (ZEO) and iron hydroxide (GEH) were added in separate experiments to optimize membrane hydraulic performance and removal efficiency of organics. The use of additives improved permeate quality (in terms of Chemical Oxygen Demand—COD) compared to the direct membrane filtration mode of operation. GEH and MBR were efficient for phosphorus removal, which was not the case for PAC and ZEO. No significant improvement of membrane flux was recorded when PAC, ZEO or GEH were added inside the membrane tank. The MBR system displayed optimum performance during medium-term operation, with COD removal efficiency 85% and permeate flux between 40 and 25 L m⁻² h⁻¹. The capital costs of the proposed technology were around 300 € and the operational costs below 80 € yr⁻¹, rendering the process feasible at household level. Greywater treatment systems for household applications are still on their infancy; however, this trend is expected to change due public perception towards circular economy, water conservation and reuse. Full article

Chronic wounds complicated with biofilm formed by pathogens remain one of the most significant challenges of contemporary medicine. The application of topical antiseptic solutions against wound biofilm has been gaining increasing interest among clinical practitioners and scientific researchers. This paper compares the activity of polyhexanide-, octenidine- and hypochlorite/hypochlorous acid-based antiseptics against biofilm formed by clinical strains of Candida albicans, Staphylococcus aureus and Pseudomonas aeruginosa. The analyses included both standard techniques utilizing polystyrene plates and self-designed biocellulose-based models in which a biofilm formed by pathogens was formed on an elastic, fibrinous surface covered with a fibroblast layer. The obtained results show high antibiofilm activity of polihexanide- and octenidine-based antiseptics and lack or weak antibiofilm activity of hypochlorite-based antiseptic of total chlorine content equal to 80 parts per million. The data presented in this paper indicate that polihexanide- or octenidine-based antiseptics are highly useful in the treatment of biofilm, while hypochlorite-based antiseptics with low chlorine content may be applied for wound rinsing but not when specific antibiofilm activity is required. Full article

Groundwater contamination by chlorinated hydrocarbons represents a particularly difficult separation to achieve and very little is published on the subject. In this paper, we explore the potential for the removal of chlorinated volatile and non-volatile organics from a site in Bedfordshire UK. The compounds of interest include trichloroethylene (TCE), tetrachloroethylene (PCE), cis-1,2-dichloroethylene (DCE), 2,2-dichloropropane (DCP) and vinyl chloride (VC). The separations were first tested in the laboratory. Microfiltration membranes were of no use in this separation. Nanofiltration membranes performed well and rejections of 70–93% were observed for synthetic solutions and up to 100% for real groundwater samples. Site trials were limited by space and power availability, which resulted in a maximum operating pressure of only 3 bar. Under these conditions, the nanofiltration membrane removed organic materials, but failed to remove VOCs to any significant extent. Initial results with a reverse osmosis membrane were positive, with 93% removal of the VOCs. However, subsequent samples taken demonstrated little removal. Several hypotheses were presented to explain this behavior and the most likely cause of the issue was fouling leading to adsorption of the VOCs onto the membrane and allowing passage through the membrane matrix. Full article

In this study, the use of composite track-etched membranes (TeMs) based on polyethylene terephthalate (PET) and electrolessly deposited silver microtubes (MTs) for the decomposition of toxic phenothiazine cationic dye, methylene blue (MB), under visible light was investigated. The structure and composition of the composite membranes were elucidated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction technique. Under visible light irradiation, composite membrane with embedded silver MTs (Ag/PET) displayed high photocatalytic efficiency. The effects of various parameters such as initial dye concentration, temperature, and sample exposure time on the photocatalytic degradation process were studied. The decomposition reaction of MB was found to follow the Langmuir–Hinshelwood mechanism and a pseudo-first-order kinetic model. The degradation kinetics of MB accelerated with increasing temperature and activation energy, E_a, was calculated to be 20.6 kJ/mol. The reusability of the catalyst was also investigated for 11 consecutive runs without any activation and regeneration procedures. The Ag/PET composite performed at high degradation efficiency of over 68% after 11 consecutive uses. Full article

The effects of green processes in hybrid polydimethylsiloxane (PDMS) membranes on CO₂ separation have received little attention to date. The effective CO₂ separation of the membranes is believed to be controlled by the reaction and curing process. In this study, hybrid PDMS membranes were fabricated on ceramic substrates using the water-in-emulsion method and evaluated for their gas transport properties. The effects of the tetraethylorthosilicate (TEOS) concentration and curing temperature on the morphology and CO₂ separation performance were investigated. The viscosity measurement showed that, at specific reaction times, it is benefit beneficial to fabricate the symmetric hybrid PDMS membranes with a uniform and dense selective layer on the substrate. Moreover, the a high TEOS concentration can decrease the reaction time and obtain create the a fully crosslinked structure, allowing more efficient CO₂/N₂ separation. The separation performance was furtherly improved with in the membrane prepared at a high curing temperature of 120 °C. The developed membrane shows excellent CO₂/N₂ separation with a CO₂ permeance of 27.7 ± 1.3 GPU and a CO₂/N₂ selectivity of 10.3 ± 0.3. Moreover, the membrane shows a stable gas separation performance of up to 5 bar of pressure. Full article

Membrane-based processes are considered a promising separation method for many chemical and environmental applications such as pervaporation and gas separation. Numerous polymeric membranes have been used for these processes due to their good transport properties, ease of fabrication, and relatively low fabrication cost per unit membrane area. However, these types of membranes are suffering from the trade-off between permeability and selectivity. Mixed-matrix membranes, comprising a filler phase embedded into a polymer matrix, have emerged in an attempt to partly overcome some of the limitations of conventional polymer and inorganic membranes. Among them, membranes incorporating tubular fillers are new nanomaterials having the potential to transcend Robeson’s upper bound. Aligning nanotubes in the host polymer matrix in the permeation direction could lead to a significant improvement in membrane permeability. However, although much effort has been devoted to experimentally evaluating nanotube mixed-matrix membranes, their modelling is mostly based on early theories for mass transport in composite membranes. In this study, the effective permeability of mixed-matrix membranes with tubular fillers was estimated from the steady-state concentration profile within the membrane, calculated by solving the Fick diffusion equation numerically. Using this approach, the effects of various structural parameters, including the tubular filler volume fraction, orientation, length-to-diameter aspect ratio, and permeability ratio were assessed. Enhanced relative permeability was obtained with vertically aligned nanotubes. The relative permeability increased with the filler-polymer permeability ratio, filler volume fraction, and the length-to-diameter aspect ratio. For water-butanol separation, mixed-matrix membranes using polydimethylsiloxane with nanotubes did not lead to performance enhancement in terms of permeability and selectivity. The results were then compared with analytical prediction models such as the Maxwell, Hamilton-Crosser and Kang-Jones-Nair (KJN) models. Overall, this work presents a useful tool for understanding and designing mixed-matrix membranes with tubular fillers. Full article

In many instances, one or more components of a pharmaceutical or cosmetic formulation is an oil. The aims of this study were two-fold. First, to examine the potential of preferential uptake of one oily vehicle component over another into a model barrier membrane (silicone) from blended vehicles (comprising two from the common excipients isohexadecane (IHD), hexadecane (HD), isopropyl myristate (IPM), oleic acid (OA) and liquid paraffin). Second, to study the effect of membrane-vehicle interactions on the diffusion of model permeants (caffeine (CF), methyl paraben (MP) and butyl paraben (BP)) from blended vehicles. Selective sorption and partition of some oils (especially IHD and IPM) at the expense of other oils (such as OA) was demonstrated to take place. For example, the membrane composition of IHD was enriched compared to a donor solution of IHD-OA: 41%, 63% and 82% IHD, compared to donor solution composition of 25%, 50% and 75% IHD, respectively. Pre-soaking the membrane in IHD, HD or LP, rather than phosphate buffer, enhanced the flux of MP through the membrane by 2.6, 1.7 and 1.3 times, respectively. The preferential sorption of individual oil components from mixtures altered the barrier properties of silicone membrane, and enhanced the permeation of CF, MP and BP, which are typically co-formulated in topical products. Full article

The CO₂ separation from flue gas based on membrane technology has drawn great attention in the last few decades. In this work, polyetherimide (PEI) hollow fibers were fabricated by using a dry-jet-wet spinning technique. Subsequently, the composite hollow fiber membranes were prepared by dip coating of polydimethylsiloxane (PDMS) selective layer on the outer surface of PEI hollow fibers. The hollow fibers spun from various spinning conditions were fully characterized. The influence of hollow fiber substrates on the CO₂/N₂ separation performance of PDMS/PEI composite membranes was estimated by gas permeance and ideal selectivity. The prepared composite membrane where the hollow fiber substrate was spun from 20 wt% of dope solution, 12 mL/min of bore fluid (water) flow rate exhibited the highest ideal selectivity equal to 21.3 with CO₂ permeance of 59 GPU. It was found that the dope concentration, bore fluid flow rate and bore fluid composition affect the porous structure, surface morphology and dimension of hollow fibers. The bore fluid composition significantly influenced the gas permeance and ideal selectivity of the PDMS/PEI composite membrane. The prepared PDMS/PEI composite membranes possess comparable CO₂/N₂ separation performance to literature ones. Full article

Cranberries, mainly processed as juice, have garnered interest over the past decade due to their high content of phytochemical compounds related to promising health benefits. To meet consumer expectations, a juice clarification step is usually incorporated to remove suspended solids. The use of pectinolytic enzyme and membrane processes are commonly applied to the production of clarified juices, but no studies have been done on cranberry juice. In this study, the effects of 60 (D60) and 120 min (D120) of depectinization by pectinolytic enzymes coupled to clarification by ultrafiltration (UF) (membrane molecular weight cut-off (MWCO) of 50, 100 and 500 kDa) was evaluated on the filtration performance, membrane fouling and cranberry juice composition. Compared to fresh juice, depectinization for 60 and 120 min reduced the UF duration by 16.7 and 20 min, respectively. The best filtration performance, in terms of permeate fluxes, was obtained with the 500 kDa MWCO UF membrane despite the highest total flux decline (41.5 to 57.6%). The fouling layer at the membrane surface was composed of polyphenols and anthocyanins. Compared to fresh juice, anthocyanin decreased (44% and 58% for D60 and D120, respectively) in depectinized juices whereas proanthocyanidin (PAC) content increased by 16%. In view of the industrial application, a 60 min depectinization coupled to clarification by a 500 kDa UF membrane could be viewed as a good compromise between the enhancement of filtration performance and the loss of polyphenols and their fouling at the membrane surface. Full article

The increasing adoption of ultra-low pressure (ULP) membrane systems for drinking water treatment in small rural communities is currently hindered by a limited number of studies on module design. Detailed knowledge on both intrinsic membrane transport properties and fluid hydrodynamics within the module is essential in understanding ULP performance prediction, mass transfer analysis for scaling-up between lab-scale and industrial scale research. In comparison to hollow fiber membranes, flat sheet membranes present certain advantages such as simple manufacture, sheet replacement for cleaning, moderate packing density and low to moderate energy usage. In the present case study, a numerical model using computational fluid dynamics (CFD) of a novel custom flat sheet membrane module has been designed in 3D to predict fluid flow conditions. The permeate flux through the membrane decreased with an increase in spacer curviness from 2.81 L/m²h for no (0%) curviness to 2.73 L/m²h for full (100%) curviness. A parametric analysis on configuration variables was carried out to determine the optimum design variables and no significant influence of spacer inflow or outflow thickness on the fluid flow were observed. The numerical model provides the necessary information on the role of geometrical and operating parameters for fabricating a module prototype where access to technical expertise is limited. Full article

Experimental surface pressure ($\mathsf{\pi }$) and electric surface potential ($\Delta \mathrm{V}$) isotherms were measured for membrane lipids, including the following phosphatidylcholines (PCs)—1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC); 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC); 1,2-diarachidoyl-sn-glycero-3-phosphocholine (DAPC); and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). In addition, other phospholipids, such as phosphatidylethanolamines (represented by 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE)) and sphingolipids (represented by N-(hexadecanoyl)-sphing-4-enine-1-phosphocholine (SM)) were also studied. The experimental apparent dipole moments (${\mathsf{\mu }}_{\mathrm{A}}^{\exp }$) of the abovementioned lipids were determined using the Helmholtz equation. The particular contributions to the apparent dipole moments of the investigated molecules connected with their polar (${\mathsf{\mu }}_{\perp }^{\mathrm{p}}$) and apolar parts (${\mathsf{\mu }}_{\perp }^{\mathrm{a}}$) were theoretically calculated for geometrically optimized systems. Using a three-layer capacitor model, introducing the group’s apparent dipole moments (calculated herein) and adopting values from other papers to account for the reorientation of water molecules (${\mathsf{\mu }}_{\perp }^{\mathrm{w}}/{\mathsf{\epsilon }}_{\mathrm{w}}$), as well as the for the local dielectric permittivity in the vicinity of the polar (${\mathsf{\epsilon }}_{\mathrm{p}}$) and apolar (${\mathsf{\epsilon }}_{\mathrm{a}}$) groups, the apparent dipole moments of the investigated molecules were calculated (${\mathsf{\mu }}_{\mathrm{A}}^{\mathrm{calc}}$). Since the comparison of the two values (experimental and calculated) resulted in large discrepancies, we developed a new methodology that correlates the results from density functional theory (DFT) molecular modeling with experimentally determined values using multiple linear regression. From the fitted model, the following contributions to the apparent dipole moments were determined: ${\mathsf{\mu }}_{\perp }^{\mathrm{w}}/{\mathsf{\epsilon }}_{\mathrm{w}}=-1.8\pm 1.4 D$; ${\mathsf{\epsilon }}_{\mathrm{p}}=10.2\pm 7.0$ and ${\mathsf{\epsilon }}_{\mathrm{a}}=0.95\pm 0.52$). Local dielectric permittivity in the vicinity of apolar groups (${\mathsf{\epsilon }}_{\mathrm{a}}$) is much lower compared to that in the vicinity of polar moieties (${\mathsf{\epsilon }}_{\mathrm{p}}$), which is in line with the tendency observed by other authors studying simple molecules with small polar groups. A much higher value for the contributions from the reorientation of water molecules (${\mathsf{\mu }}_{\perp }^{\mathrm{w}}/{\mathsf{\epsilon }}_{\mathrm{w}}$) has been interpreted as resulting from bulky and strongly hydrated polar groups of phospholipids. Full article

Human bestrophin-1 protein (hBest1) is a transmembrane channel associated with the calcium-dependent transport of chloride ions in the retinal pigment epithelium as well as with the transport of glutamate and GABA in nerve cells. Interactions between hBest1, sphingomyelins, phosphatidylcholines and cholesterol are crucial for hBest1 association with cell membrane domains and its biological functions. As cholesterol plays a key role in the formation of lipid rafts, motional ordering of lipids and modeling/remodeling of the lateral membrane structure, we examined the effect of different cholesterol concentrations on the surface tension of hBest1/POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and hBest1/SM Langmuir monolayers in the presence/absence of Ca²⁺ ions using surface pressure measurements and Brewster angle microscopy studies. Here, we report that cholesterol: (1) has negligible condensing effect on pure hBest1 monolayers detected mainly in the presence of Ca²⁺ ions, and; (2) induces a condensing effect on composite hBest1/POPC and hBest1/SM monolayers. These results offer evidence for the significance of intermolecular protein–lipid interactions for the conformational dynamics of hBest1 and its biological functions as multimeric ion channel. Full article

In this study, we focused on obtaining polysulfone-polyurethane (PSF-PUR) blend partly degradable hollow fiber membranes (HFMs) with different compositions while maintaining a constant PSF:PUR = 8:2 weight ratio. It was carried out through hydrolysis, and evaluation of the properties and morphology before and after the hydrolysis process while maintaining a constant cut-off. The obtained membranes were examined for changes in ultrafiltration coefficient (UFC), retention, weight loss, morphology assessment using scanning electron microscopy (SEM) and MeMoExplorer™ Software, as well as using the Fourier-transform infrared spectroscopy (FT-IR) method. The results of the study showed an increase in the UFC value after the hydrolysis process, changes in retention, mass loss, and FT-IR spectra. The evaluation in MeMoExplorer™ Software showed the changes in membranes’ morphology. It was confirmed that polyurethane (PUR) was partially degraded, the percentage of ester bonds has an influence on the degradation process, and PUR can be used as a pore precursor instead of superbly known polymers. Full article

In this study, a magnetic/polyetherimide-acrylonitrile composite nanofiber membrane with effective adsorption of nickel ions in an aqueous solution was created using a simple electrospinning method. Iron oxide nanoparticles (NPs) were stirred and ultrasonically dispersed into a polyetherimide-acrylonitrile solution to create a homogenous NPs suspension, which was placed in an electrospinning machine to produce a uniform and smooth nanofiber composite membrane. Nanoparticle incorporation into this membrane was confirmed using scanning electron microscope, energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and NPs aqueous stability from a leaching test. The high adsorption capability of the membrane on nickel ions was attributed to the combination of magnetic NPs, polyetherimide-acrylonitrile matrix, and the nanostructure of the membrane. A membrane containing magnetic NPs demonstrated the maximum adsorption capabilities (102 mg/g) of nickel ions in an aqueous solution. Various kinetic and isotherm models were applied to understand the adsorption behavior, such as pseudo-second-order kinetic and Langmuir isotherm models. A polyetherimide-acrylonitrile composite nanofiber membrane containing magnetic NPs could be used as an environmentally friendly and nontoxic adsorbent for the removal of nickel ions in an aqueous medium due to its ease of preparation and use and stability in aqueous mediums. Full article

Polymer membranes, having improved conductivity with enhanced thermal and chemical stability, are desirable for proton exchange membranes fuel cell application. Hence, poly(benzophenone)s membranes (SI-PBP) containing super gas-phase acidic sulfonyl imide groups have been prepared from 2,5-dichlorobenzophenone (DCBP) monomer by C-C coupling polymerization using Ni (0) catalyst. The entirely aromatic C-C coupled polymer backbones of the SI-PBP membranes provide exceptional dimensional stability with rational ion exchange capacity (IEC) from 1.85 to 2.30 mS/cm. The as-synthesized SI-PBP membranes provide enhanced proton conductivity (107.07 mS/cm) compared to Nafion 211^® (104.5 mS/cm). The notable thermal and chemical stability of the SI-PBP membranes have been assessed by the thermogravimetric analysis (TGA) and Fenton’s test, respectively. The well distinct surface morphology of the SI-PBP membranes has been confirmed by the atomic force microscopy (AFM). These results of SI-PBP membranes comply with all the requirements for fuel cell applications. Full article

In the era of antibiotic resistance, there is an urgent need for efficient antibiotic therapies to fight bacterial infections. Cationic antimicrobial peptides (CAMP) are promising lead compounds given their membrane-targeted mechanism of action, and high affinity towards the anionic composition of bacterial membranes. We present a new CAMP, W-BP100, derived from the highly active BP100, holding an additional tryptophan at the N-terminus. W-BP100 showed a broader antibacterial activity, demonstrating a potent activity against Gram-positive strains. Revealing a high partition constant towards anionic over zwitterionic large unilamellar vesicles and inducing membrane saturation at a high peptide/lipid ratio, W-BP100 has a preferential location for hydrophobic environments. Contrary to BP100, almost no aggregation of anionic vesicles is observed around saturation conditions and at higher concentrations no aggregation is observed. With these results, it is possible to state that with the incorporation of a single tryptophan to the N-terminus, a highly active peptide was obtained due to the π–electron system of tryptophan, resulting in negatively charged clouds, that participate in cation–π interactions with lysine residues. Furthermore, we propose that W-BP100 action can be achieved by electrostatic interactions followed by peptide translocation. Full article

Cake-enhanced concentration polarization (CECP) has been ascribed as the main cause of flux decline in dead-end filtration. An unfamiliar approach was used to investigate the role of CECP effects in the fouling of a nanofiltration membrane (NF-270) that poorly reject salts. Membrane–foulant affinity interaction energies were calculated from measured contact angles of foulants and membrane coupons based on the van der Waals/acid–base approach, and linked to resistance due to adsorption (R_a). In addition, other fouling mechanisms and resistance parameters were investigated using model organic and colloidal foulants. After selection, the foulants and membranes were characterized for various properties, and fouling experiments were conducted under controlled conditions. The fouled membranes were further characterized to gain more understanding of the fouling layer properties and flux decline mechanisms. Sodium alginate and latex greatly reduced membrane permeate flux as the flux declined by 86% and 59%, respectively, while there was minor flux decline when aluminum oxide was used as model foulant (<15% flux decline). More flux decline was noted when fouling was conducted with a combination of organic and colloidal foulants. Contrary to other studies, the addition of calcium did not seem to influence individual and combined fouling trends. Foulants adsorbed more on the membrane surface as the membrane–foulant affinity interactions became more attractive and pore blocking by the foulants was not important for these experiments. Hydraulic resistance due to cake formation (R_c) had a higher contributing effect on flux decline, while CECP effects were not substantial. Full article

The acceleration of inactivating viable cells of Escherichia coli (E. coli), by using new direct and indirect innovative methods, is the targeted method of using an atmospheric pressure plasma jet (APPJ) operated by an AC high-voltage power source with variable frequency up to 60 kHz and voltage ranging from 2.5 to 25 kV. Discharges using dry argon (0% O₂) discharges and different wet argon discharges using admixtures with O₂/Ar ratios ranging from 0.25% to 1.5% were studied. The combined effects of dry and wet argon discharges, direct and indirect exposure using a mesh controller, and hollow magnets were studied to reach a complete bacterial inactivation in short application times. Survival curves showed that the inactivation rate increased as the wettability increased. The application of magnetized non-thermal plasma discharge with a 1.5% wetness ratio causes a fast inactivation rate of microbes on surfaces, and a dramatic decrease of the residual survival of the bacterial ratio due to an increase in the jet width and the enhanced ability of fast transport of the charges to viable cells, especially at the edge of the Petri dish. The membrane damage of E. coli mechanism factors in the activation process by APPJ is discussed. Full article

Wafer-enhanced electrodeionization (WE-EDI) is an electrically driven separations technology that occurs under the influence of an applied electric field and heavily depends on ion exchange resin chemistry. Unlike filtration processes, WE-EDI can be used to selectively remove ions even from high concentration systems. Because every excess ion transported increases the operating costs, the selective separation offered by WE-EDI can provide a more energy-efficient and cost-effective process, especially for highly concentrated salt solutions. This work reports the performance comparison of four commonly used cation exchange resins (Amberlite IR120 Na⁺, Amberlite IRP 69, Dowex MAC 3 H⁺, and Amberlite CG 50) and their influence on the current efficiency and selectivity for the removal of cations from a highly concentrated salt stream. The current efficiencies were high for all the resin types studied. Results also revealed that weak cation exchange resins favor the transport of the monovalent ion (Na⁺) while strong cation exchange resins either had no strong preference or preferred to transport the divalent ions (Ca²⁺ and Mg²⁺). Moreover, the strong cation exchange resins in powder form generally performed better in wafers than those in the bead form for the selective removal of divalent ions (selectivity > 1). To further understand the impact of particle size, resins in the bead form were ground into a powder. After grinding the strong cation resins displayed similar behavior (more consistent current efficiency and preference for transporting divalent ions) to the strong cation resins in powder form. This indicates the importance of resin size in the performance of wafers. Full article