Fabrication of thin film composite poly(amide)-carbon-nanotube supported membranes for enhanced performance in osmotically driven desalination systems

Advanced Polymeric Nanocomposite Membranes for Water and Wastewater Treatment: A Comprehensive Review

Nanomaterials have been extensively used in polymer nanocomposite membranes due to the inclusion of unique features that enhance water and wastewater treatment performance. Compared to the pristine membranes, the incorporation of nanomodifiers not only improves membrane performance (water permeability, salt rejection, contaminant removal, selectivity), but also the intrinsic properties (hydrophilicity, porosity, antifouling properties, antimicrobial properties, mechanical, thermal, and chemical stability) of these membranes. This review focuses on applications of different types of nanomaterials: zero-dimensional (metal/metal oxide nanoparticles), one-dimensional (carbon nanotubes), two-dimensional (graphene and associated structures), and three-dimensional (zeolites and associated frameworks) nanomaterials combined with polymers towards novel polymeric nanocomposites for water and wastewater treatment applications. This review will show that combinations of nanomaterials and polymers impart enhanced features into the pristine membrane; however, the underlying issues associated with the modification processes and environmental impact of these membranes are less obvious. This review also highlights the utility of computational methods toward understanding the structural and functional properties of the membranes. Here, we highlight the fabrication methods, advantages, challenges, environmental impact, and future scope of these advanced polymeric nanocomposite membrane based systems for water and wastewater treatment applications.

Study of Membranes with Nanotubes to Enhance Osmosis Desalination Efficiency by Using Machine Learning towards Sustainable Water Management

Water resources management is one of the most important issues nowadays. The necessity of sustainable management of water resources, as well as finding a solution to the water shortage crisis, is a question of our survival on our planet. One of the most important ways to solve this problem is to use water purification systems for wastewater resources, and one of the most necessary reasons for the research of water desalination systems and their development is the problem related to water scarcity and the crisis in the world that has arisen because of it. The present study employs a carbon nanotube-containing nanocomposite to enhance membrane performance. Additionally, the rise in flow brought on by a reduction in the membrane's clogging surface was investigated. The filtration of brackish water using synthetic polyamide reverse osmosis nanocomposite membrane, which has an electroconductivity of 4000 Ds/cm, helped the study achieve its goal. In order to improve porosity and hydrophilicity, the modified raw, multi-walled carbon nanotube membrane was implanted using the polymerization process. Every 30 min, the rates of water flow and rejection were evaluated. The study's findings demonstrated that the membranes have soft hydrophilic surfaces, and by varying concentrations of nanocomposite materials in a prescribed way, the water flux increased up to 30.8 L/m²h, which was notable when compared to the water flux of the straightforward polyamide membranes. Our findings revealed that nanocomposite membranes significantly decreased fouling and clogging, and that the rejection rate was greater than 97 percent for all pyrrole-based membranes. Finally, an artificial neural network is utilized to propose a predictive model for predicting flux through membranes. The model benefits hyperparameter tuning, so it has the best performance among all the studied models. The model has a mean absolute error of 1.36% and an R² of 0.98.

Progress in osmotic membrane bioreactors research: Contaminant removal, microbial community and bioenergy production in wastewater

Renewable energy, water conservation, and environmental protection are the most important challenges today. Osmotic membrane bioreactor (OMBR) is an innovative process showing superior performance in bioenergy production, eliminating contaminants, and low fouling tendency. However, salinity build-up is the main drawback of this process. Identifying the microbial community can improve the process in bioenergy production and contaminant treatment. This review aims to study the recent progress and challenges of OMBRs in contaminant removal, microbial communities and bioenergy production. OMBRs are widely reported to remove over 80% of total organic carbon, PO₄^3-, NH₄⁺ and emerging contaminants from wastewater. The most important microbial phyla for both hydrogen and methane production in OMBR are Firmicutes, Proteobacteria and Bacteroidetes. Firmicutes' dominance in anaerobic processes is considerably increased from usually 20% at the beginning to 80% under stable condition. Overall, OMBR process has great potential to be applied for simultaneous bioenergy production and wastewater treatment.

Comparison of Nanofiltration with Reverse Osmosis in Reclaiming Tertiary Treated Municipal Wastewater for Irrigation Purposes

This study compares the performance of nanofiltration (NF) and reverse osmosis (RO) for the reclamation of ultrafiltered municipal wastewater for irrigation of food crops. RO and NF technologies were evaluated at different applied pressures; the performance of each technology was evaluated in terms of water flux, recovery rate, specific energy consumption and quality of permeate. It was found that the permeate from the reverse osmosis (RO) process complied with Food and Agriculture Organization (FAO) standards at pressures applied between 10 and 18 bar. At an applied pressure of 20 bar, the permeate quality did not comply with irrigation water standards in terms of chloride, sodium and calcium concentration. It was found that nanofiltration process was not suitable for the reclamation of wastewater as the concentration of chloride, sodium and calcium exceeded the allowable limits at all applied pressures. In the reverse osmosis process, the highest recovery rate was 36%, which was achieved at a pressure of 16 bar. The specific energy consumption at this applied pressure was 0.56 kWh/m³. The lowest specific energy of 0.46 kWh/m³ was achieved at an applied pressure of 12 bar with a water recovery rate of 32.7%.

ON/OFF Switchable Nanocomposite Membranes for Separations

Although water, air, and other resources are abundant on earth, they have been subjected to strict environmental regulations. This is because of their limitation of availability for human consumption. In the separation industry, the membrane system was introduced to increase the amount of resources available to mankind. Experts used an easy-to-use polymeric material to design several membranes with porous structures for wastewater treatment, gas separation, and chemical removal; consequently, they succeeded in obtaining positive results. However, past polymeric membranes exhibited a chronic drawback such that it was difficult to simultaneously augment the permeate flux and improve its selectivity toward certain substances. Because of the trade-off relationship that existed between permeability and selectivity, the membrane efficiency was not very good; consequently, the cost-effectiveness was significantly hindered because there was no other alternative than to replace the membrane in order to maintain its initial characteristics steadily. This review begins with the introduction of a polymer nanocomposite (PNC) membrane that has been designed to solve the chronic problem of polymeric membranes; subsequently, the stimuli-responsive PNC membrane is elucidated, which has established itself as a popular topic among researchers in the separation industry for several decades. Furthermore, we have listed the different types and examples of stimuli-responsive PNC membranes, which can be switched by external stimuli, while discussing the future direction of the membrane separation industry.

Effect of Anisotropy of Cellulose Nanocrystal Suspensions on Stratification, Domain Structure Formation, and Structural Colors

Outstanding optical and mechanical properties can be obtained from hierarchical assemblies of nanoparticles. Herein, the formation of helically ordered, chiral nematic films obtained from aqueous suspensions of cellulose nanocrystals (CNCs) were studied as a function of the initial suspension state. Specifically, nanoparticle organization and the structural colors displayed by the resultant dry films were investigated as a function of the anisotropic volume fraction (AVF), which depended on the initial CNC concentration and equilibration time. The development of structural color and the extent of macroscopic stratification were studied by optical and scanning electron microscopy as well as UV-vis spectroscopy. Overall, suspensions above the critical threshold required for formation of liquid crystals resulted in CNC films assembled with longer ranged order, more homogeneous pitches along the cross sections, and narrower specific absorption bands. This effect was more pronounced for the suspensions that were closer to equilibrium prior to drying. Thus, we show that high AVF and more extensive phase separation in CNC suspensions resulted in large, long-range ordered chiral nematic domains in dried films. Additionally, the average CNC aspect ratio and size distribution in the two separated phases were measured and correlated to the formation of structured domains in the dried assemblies.

Highly Permeable Thin-Film Composite Forward Osmosis Membrane Based on Carbon Nanotube Hollow Fiber Scaffold with Electrically Enhanced Fouling Resistance

Forward osmosis (FO) is an emerging approach in water treatment, but its application is restricted by severe internal concentration polarization (ICP) and low flux. In this work, a self-sustained carbon nanotube hollow fiber scaffold supported polyamide thin film composite (CNT TFC-FO) membrane was first proposed with high porosity, good hydrophilicity and excellent electro-conductivity. It showed a specific structure parameter as low as 126 μm, suggesting its weakened ICP. Against a pure water feed using 2.0 M NaCl draw solution, its fluxes were 4.7 and 3.6 times as high as those of the commercial cellulose triacetate TFC-FO membrane in the FO and pressure retarded osmosis (PRO) modes, respectively. Meanwhile, the membrane showed excellent electrically assisted resistance to organic and microbial fouling. Its flux was improved by about 50% during oil-water simulation separation under 2.0 V voltage. These results indicate that the CNT TFC-FO membrane opens up a frontier for stably and effectively recycling potable water from electrochemical FO process.

A review on organic–inorganic hybrid nanocomposite membranes: a versatile tool to overcome the barriers of forward osmosis

Forward osmosis (FO) processes have recently attracted increasing attention and show great potential as a low-energy separation technology for water regeneration and seawater desalination. However, a number of challenges, such as internal concentration polarization, membrane fouling, and the trade-off effect, limit the scaleup and industrial practicality of FO. Hence, a versatile method is needed to address these problems and fabricate ideal FO membranes. Among the many methods, incorporating polymeric FO membranes with inorganic nanomaterials is widely used and effective and is reviewed in this paper. The properties of FO membranes can be improved and meet the demands of various applications with the incorporation of nanomaterials. This review presents the actualities and advantages of organic–inorganic hybrid nanocomposite FO membranes. Nanomaterials applied in the FO field, such as carbon nanotubes, graphene oxide, halloysite nanotubes, silica and Ag nanoparticles, are classified and compared in this review. The effects of modification methods on the performance of nanocomposite FO membranes, including blending, in situ interfacial polymerization, surface grafting and layer-by-layer assembly, are also reviewed. The outlook section discusses the prospects of organic–inorganic hybrid nanocomposite FO membranes and advanced nanotechnologies available for FO processes. This discussion may provide new opportunities for developing novel FO membranes with high performance.

Nanocomposite forward osmosis (FO) membranes have attracted increasing attentions recently and showed great comprehensive performance. Various modification methods have been employed to incorporate inorganic nanomaterials to FO membranes.

Integrating seawater desalination and wastewater reclamation forward osmosis process using thin-film composite mixed matrix membrane with functionalized carbon nanotube blended polyethersulfone support layer

Thin-film composite mixed matrix membrane (TFC MMM) with functionalized carbon nanotube (fCNT) blended in polyethersulfone (PES) support layer was synthesized via interfacial polymerization and phase inversion. This membrane was firstly tested in lab-scale integrating seawater desalination and wastewater reclamation forward osmosis (FO) process. Water flux of TFC MMM was increased by 72% compared to that of TFC membrane due to enhanced hydrophilicity. Although TFC MMM showed lower water flux than TFC commercial membrane, enhanced reverse salt flux selectivity (RSFS) of TFC MMM was observed compared to TFC membrane (15% higher) and TFC commercial membrane (4% higher), representing membrane permselectivity. Under effluent organic matter (EfOM) fouling test, 16% less normalized flux decline of TFC MMM was observed compared to TFC membrane. There was 8% less decline of TFC MMM compared to TFC commercial membrane due to fCNT effect on repulsive foulant-membrane interaction enhancement, caused by negatively charged membrane surface. After 10 min physical cleaning, TFC MMM displayed higher recovered normalized flux than TFC membrane (6%) and TFC commercial membrane (4%); this was also supported by visualized characterization of fouling layer. This study presents application of TFC MMM to integrated seawater desalination and wastewater reclamation FO process for the first time. It can be concluded that EfOM fouling of TFC MMM was suppressed due to repulsive foulant-membrane interaction.

Insights into Surface Interactions between Metal Organic Frameworks and Gases during Transient Adsorption and Diffusion by In-Situ Small Angle X-ray Scattering

The fabrication of molecular gas sieving materials with specific affinities for a single gas species and able to store large quantities of materials at a low or atmospheric pressure is desperately required to reduce the adverse effects of coal and oil usage in carbon capture. Fundamental understanding of the dynamic adsorption of gas, the diffusion mechanisms across thin film membranes, and the impact of interfaces play a vital role in developing these materials. In this work, single gas permeation tests across micro-porous membrane materials, based on metal organic framework crystals grown on the surface of carbon nanotubes (ZiF-8@CNT), were performed for the first time in-situ at the Australian Synchrotron on the small angle X-ray scattering beamline in order to reveal molecular sieving mechanisms and gas adsorption within the material. The results show that specific chemi-sorption of CO₂ across the ZiF-8 crystal lattices affected the morphology and unit cell parameters, while the sieving of other noble or noble like gases across the ZiF-8@CNT membranes was found to largely follow Knudsen diffusion. This work demonstrates for the first time a novel and effective technique to assess molecular diffusion at the nano-scale across sub-nano-porous materials by probing molecular flexibility across crystal lattice and single cell units.

Efficiently Combining Water Reuse and Desalination through Forward Osmosis-Reverse Osmosis (FO-RO) Hybrids: A Critical Review

Forward osmosis (FO) is a promising membrane technology to combine seawater desalination and water reuse. More specifically, in a FO-reverse osmosis (RO) hybrid process, high quality water recovered from the wastewater stream is used to dilute seawater before RO treatment. As such, lower desalination energy needs and/or water augmentation can be obtained while delivering safe water for direct potable reuse thanks to the double dense membrane barrier protection. Typically, FO-RO hybrid can be a credible alternative to new desalination facilities or to implementation of stand-alone water reuse schemes. However, apart from the societal (public perception of water reuse for potable application) and water management challenges (proximity of wastewater and desalination plants), FO-RO hybrid has to overcome technical limitation such as low FO permeation flux to become economically attractive. Recent developments (i.e., improved FO membranes, use of pressure assisted osmosis, PAO) demonstrated significant improvement in water flux. However, flux improvement is associated with drawbacks, such as increased fouling behaviour, lower rejection of trace organic compounds (TrOCs) in PAO operation, and limitation in FO membrane mechanical resistance, which need to be better considered. To support successful implementation of FO-RO hybrid in the industry, further work is required regarding up-scaling to apprehend full-scale challenges in term of mass transfer limitation, pressure drop, fouling and cleaning strategies on a module scale. In addition, refined economics assessment is expected to integrate fouling and other maintenance costs/savings of the FO/PAO-RO hybrid systems, as well as cost savings from any treatment step avoided in the water recycling.

Alginate fouling reduction of functionalized carbon nanotube blended cellulose acetate membrane in forward osmosis

Functionalized multi-walled carbon nanotube blended cellulose acetate (fCNT-CA) membranes were synthesized for forward osmosis (FO) through phase inversion. The membranes were characterized through SEM, FTIR, and water contact angle measurement. AFM was utilized to investigate alginate fouling mechanism on the membrane. It reveals that the fCNT contributes to advance alginate fouling resistance in FO (57% less normalized water flux decline for 1% fCNT-CA membrane was observed than that for bare CA membrane), due to enhanced electrostatic repulsion between the membrane and the alginate foulant. Furthermore, it was found that the fCNT-CA membranes became more hydrophilic due to carboxylic groups in functionalized carbon nanotube, resulting in approximately 50% higher water-permeated flux than bare CA membrane. This study presents not only the fabrication of fCNT-CA membrane and its application to FO, but also the quantification of the beneficial role of fCNT with respect to alginate fouling in FO.

Chlorine resistant glutaraldehyde crosslinked polyelectrolyte multilayer membranes for desalination

Crosslinked polyelectrolyte multilayer membranes are synthesized with salt rejection values approaching those of commercial desalination membranes, but with increased chlorine resistance. The membranes are fabricated directly onto porous commercial substrates. Subsequent crosslinking of the polycation layers with glutaraldehyde leads to NaCl rejections of up to 97%, while the incorporation of a highly sulfonated polysulfone polyanion leads to high chlorine resistance.

Preparation and characterization of thin-film composite membrane with nanowire-modified support for forward osmosis process

Internal concentration polarization (ICP) in forward osmosis (FO) process is a characteristic problem for asymmetric thin-film composite (TFC) FO membrane which leads to lower water flux. To mitigate the ICP effect, modification of the substrates’ properties has been one of the most effective methods. A new polyethersulfone-based ultrafiltration membrane with increased surface porosity and high water flux was recently produced by incorporating Zn₂GeO₄ nanowires. The composite membrane was used as a substrate for the fabrication of TFC FO membrane, by coating a thin layer of polyamide on top of the substrate. The substrate and the nanowires were characterized by a range of techniques such as SEM, XRD, and contact angle goniometry. The water permeability and molecular weight cut-offs (MWCO) of the substrate; and the FO performance of the TFC membrane were also determined. The Zn₂GeO₄-modified membrane showed ~45% increase in water permeability and NaCl salt rejection of 80% under RO mode. In FO mode, the ratio of water flux to reverse solute flux was also improved. However, lower FO flux was obtained which could be due to ICP. The result shows that Zn₂GO₄ nanowire may be used as a modifier to the substrate to improve the quality of the polyamide layer on the substrate to improve the flux and selectivity, but not as effective in reducing ICP. This work demonstrates that the incorporation of nanomaterials to the membrane substrate may be an alternative approach to improve the formation of polyamide skin layer to achieve better FO performance.