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The sustainability of global clean and safe water supply is one of the grand challenges facing the world. Membrane technology based on polymeric membranes is one of the most important and widely recognized technologies for desalination and wastewater treatment. While polymeric membranes are known to be plagued with some bottlenecks, the technical progress and the accompanying knowledge in inorganic membrane development have grown inexorably to solve some of the underlying issues. Aside from the conventionally used ceramic membranes which based on metal oxides, nanostructures such as zeolites, metal organic frameworks and carbon based materials have sparked enormous interest in the preparation of inorganic membranes owing to their tunable nanoscaled structural properties that can render excellent rejection and/or ultrafast water transport. This review provides insights into the physico-chemical properties and fabrication approaches of different classes of inorganic membranes. The transport mechanisms that are associated to their unique structural features are also discussed. Furthermore, the performance evaluation of these inorganic membranes in a wide spectrum of desalination and wastewater treatment applications are also elaborated. Finally, the challenges in the development of inorganic membrane for practical commercial application are identified and the future perspectives are presented. [ABSTRACT FROM AUTHOR]

Multidisciplinary, innovative and high values development of high performance, cost-effective and environmentally acceptable separation systems is highly desired to tackle the sustainability challenges that facing current desalination technology. Owing to their versatility and immense potentials to evolve scientific and technical innovations, nanotechnology is probably one of the most prominent strategies that has gained growing scientific and public recognition to provide solutions that can extend the limits of sustainability in membrane desalination technology. This short review provides a brief insight into the roles and prospective of nanotechnology, particularly the nano-enabled membrane technology, to serve as a key element to render feasible solutions for sustainable development in membrane desalination technology. The contribution also highlights the strategies of transforming risk and challenges of this cutting edge technology into competitive advantage in order to timely and efficiently drive values in enhancing the desalination performance, profits and sustainability. The applications of nanomaterials and nanocomposite in membrane desalination are anticipated to foster untapped initiatives and innovation in fundamental science, engineering and technology to spearhead the new wave of leading edge sustainable membrane desalination technology. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a thermal-driven membrane separation process which recently garners interest from academic and industry due to its low energy requirements and the ability to integrate with renewable energy. In this work, two different additives, i.e. polyethersulfone (PES) and ethylene glycol (EG), were added into dope solutions consisting of polyvinylidene fluoride (PVDF) and 1-methyl-2-pyrrolidone (NMP) to prepare membranes for MD applications. The membranes were characterized with respect to thickness, pore size, porosity, and water contact angle using scanning electron microscope and water contact goniometer. Compared with the membranes made from pure PVDF and PVDF–EG system, it is found that PVDF–EG–PES membrane displayed improved characteristics i.e. having optimum porosity, large pore size, and thin membrane thickness coupled with finger-like structure extended from both inner and outer layers of the membrane. In addition to this, the permeate flux of PVDF–EG–PES membrane during MD application was also reported to be the highest among all the membranes studied when tested under same process conditions. With respect to membrane performance stability, the results showed that PVDF–EG–PES membrane could achieve a very consistent permeate flux while maintaining high NaCl rejection throughout 20 h operation, indicating the potential of this membrane in MD process. [ABSTRACT FROM PUBLISHER]

Advanced science and technology based on graphene-based nanomaterials is experiencing a rapid rate of change in the performance capabilities to substitute or serve as alternative approaches for the existing technologies. In the context of water treatment, more particularly in field of desalination, significant numbers of breakthroughs have been achieved to drive accelerated change for ceaseless capability improvements. In this contribution, the unique features of graphene-based nanomaterials that have generated tremendous interest among the material researchers are described along with their potential applications in desalination. Another aim of this paper is to provide comprehensive scientific progress of these nanomaterials in order to explore the challenges and opportunities of graphene-based nanomaterials in advancing current desalination technology. Finally, a future prospective on how this rapidly emerging field may evolve from short to medium and long term is highlighted and the outlooks regarding the technological challenges, economical implication and toxicological impact of graphene-based nanomaterials on the environment are briefly discussed. As this novel carbon nanostructured material will certainly offer exciting and tunable features for desalination technology, it is anticipated that by grabbing the approaching opportunities and tackling the encountered challenges, these astonishing materials could very well make clean water more accessible around the globe. [ABSTRACT FROM AUTHOR]

Access to clean water resource continues to be the most urgent and pressing global issue where hiking economic and ecological needs have urged for more water-efficient technologies. Membrane-based separations for desalination are playing an increasingly important role to provide adequate water resources of desirable quality for a wide spectrum of designated applications. The engagement of multidisciplinary research areas into the commercial membrane and membrane systems offers an opportunity to refine and optimise current techniques as well as provides new insight and novel methods of purifying water. The advancement of material science and engineering reveals the potentials to solve real-world practical problems and heighten the current technologies. This review highlights some of the latest notable achievements of novel advanced membrane materials and emerging membrane processes for water solution. The unique characteristics of advanced membranes and emerging membrane processes in leading the state-of-the-art desalination are presented. Lastly, the future directions for research, development and commercialization of membrane and membrane processes are critically discussed. It is expected that, the promising and well-adapted characteristics possessed by the novel membranes and advanced membrane processes can provide meaningful inspiration for breakthrough technologies and solutions where soon they will be translated into exploitable innovations in industries. [ABSTRACT FROM AUTHOR]

Reverse osmosis (RO) based desalination is one of the most important and widely recognized technologies for production of fresh water from saline water. Since its conception and initiation, a significant development has been witnessed in this technology w.r.t. materials, synthesis techniques, modification and modules over the last few decades. The working of a RO plant inclusive of the pretreatment and post-treatment procedures has been briefly discussed in the article. The main objective of this review is to highlight the historical milestones achieved in RO technology in terms of membrane performance, the developments seen over the last few years and the challenges perceived. The material properties of the membrane dominate the performance of a RO process. The emergence of nano-technology and biomimetic RO membranes as the futuristic tools is capable of revolutionizing the entire RO process. Hence the development of nano-structured membranes involving thin film nano-composite membranes, carbon-nanotube membranes and aquaporin-based membranes has been focussed in detail. The problems associated with a RO process such as scaling, brine disposal and boron removal are briefed and the measures adopted to address the same have been discussed. [ABSTRACT FROM AUTHOR]

Water scarcity is a global issue that needs to be urgently addressed to alleviate its adverse impacts on social and economic development. Desalination has been touted as an attractive alternative that can sustainably provide freshwater, particularly when there is no better option to augment water supplies. Tremendous research innovations and evolutions have been made to improve desalination processes in various aspects. Hybridization of two of more desalination processes has been recognized as a promising approach to tackle the inherent disadvantages of conventional desalination processes in regards of energy consumption, water productivity and environmental impacts. While there remains a huge demand for thermal-based desalination particularly in the Middle East region, it is timely to provide a review to look into the progresses made in the hybridization of thermal-based desalination processes. The opportunities for further advancement in the hybridization of thermal-based desalination processes are also proposed. The driving forces for the hybridization of these processes include energy saving, increased freshwater production and improved flexibility in tapping renewable energy. The design and configurations, performances and optimizations have been made in the hybridizations of thermal-thermal or thermal-membrane desalination. Thermal-based hybrid desalination system represents the future trend of commercial scale desalination operations. • The hybridizations of thermal-based desalination processes are reviewed. • thermal-thermal and thermal-membrane based hybridizations demonstrate economic feasibilities and synergistic advantages. • Thermal-based hybrid system outperformed the standalone counterparts in various aspects. • Thermal-based hybrid system is the future trend of commercial scale desalination operations. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have been classified as promising membrane materials for ultimate and efficient water desalination attributed by its diversified structures, tunable chemical functionalities and pore structures that serve as additional water channels. MOF-integrated membranes have been successfully prepared and applied for desalination process via different membrane processes; namely reverse osmosis (RO), forward osmosis (FO), nanofiltration (NF) and membrane distillation (MD). While there are reviews on the applications of MOFs-based membranes for water purification, herein, we present a comprehensive review of recent progress of different types of MOFs-integrated membranes, with emphasis placed on water desalination. This review focuses on membrane requirements for different membrane processes, the development of suitable MOFs for water application, different approaches of designing MOFs-based membranes, prior of discussion on the recent progress of MOFs-integrated membranes for desalination using different types of membrane processes. Lastly, insights and perspectives are suggested in terms of future research directions and development challenges. • The tunable features making MOFs as promising materials for membrane fabrication/modification for desalination process. • Application of MOFs membranes is influenced by water stability, pore size, aperture window cage and dispersibility. • MOF-integrated membranes is the promising candidate to address the trade-off effects of membrane selectivity and permeability. • Different types of MOF-integrated membranes that can be applied in RO, NF, FO and MD for desalination process. • Some fundamental and technical aspects have to be addressed to realize the potential benefits of MOF-integrated membranes. [ABSTRACT FROM AUTHOR]

• Review on new/modified IP techniques for defect-less TFN membrane fabrication. • Important characteristics of nanofillers to generate PA layer with high integrity. • Effects of nanomaterials on membrane physicochemical properties and performances. Thin film composite (TFC) reverse osmosis (RO) membrane has been dominating commercial desalination process for several decades since its inception in the 1970s. Despite the ability of generating high quality water at promising water permeability, the commercial TFC RO membrane is still susceptible to fouling and chlorine attack which lead to performance instability as a function of operation time. Over the past decade, the prowess of nanomaterials integration in overcoming the drawbacks of conventional TFC membrane has been proven by many research studies and this has led to the significant progress of thin film nanocomposite (TFN) membrane development. However, it remains a great challenge in integrating the inorganic nanomaterials with the polyamide (PA) selective layer of TFN membrane due to the incompatibility between organic and inorganic materials and the uneven distribution of nanomaterials. In view of this, this article intends to critically review various fabrication techniques that have been developed or modified to incorporate nanofillers within or atop PA layer for the development of TFN membranes. In addition, the essential characteristics of nanofillers in order to achieve good integration with PA layer as well as their impacts in improving membrane performance with respect to water flux, rejection, antifouling, antibacterial and chlorine stability are also reviewed. We hope this review article could provide insights to researchers in fabricating defect-free TFN RO membranes for enhanced water desalination. [ABSTRACT FROM AUTHOR]

Abstract In this study, thin film nanocomposite (TFN) membranes were fabricated by incorporating highly hydrophilic halloysite nanotubes (HNTs) and self-synthesized graphitic carbon nitride (g-C 3 N 4) nanoparticles into polysulfone-based substrate and interfacially polymerized polyamide top layer, respectively. The TFN membranes were evaluated for their performance in forward osmosis (FO) applications. The XRD, ATR-FTIR, FESEM and TEM results confirmed the successful synthesis of g-C 3 N 4 nanoparticles. The effects of nanomaterials incorporation were investigated in terms of membrane surface morphology, hydrophilicity and separation performance. When 0.05 wt/v% of g-C 3 N 4 was added to the polyamide layer, the membrane surface contact angle was significantly reduced from 68° in the control membrane (TFN0.0) to <10° in the TFN membrane (TFN0.05), leading to high water flux of 18.88 L/m2·h (approximately 270% higher than the TFN0.0 membrane). The results have proven the predominant effect of the polyamide layer modification compared to the support modification towards FO performance enhancement. The water flux decline for the TFN0.0 and TFN0.05 membranes after a prolonged time of 1200 min was only 12% for the TFN0.05 while TFN0.0 membrane experienced 24% reduction. In addition, fouling resistance of the membranes assessed by BSA revealed that the flux of TFN0.0 has reduced by 54% after 1200 min, meanwhile TFN0.05 recorded a reduction of approximately 30%. The findings confirmed the effectiveness of g-C 3 N 4 as a promising surface modifier for polyamide layer to simultaneously contribute to flux enhancement and increased anti-fouling properties. Highlights • HNT and g-C 3 N 4 were incorporated into the PSf substrate and PA layer of TFN FO membranes. • Superhydrophilic PA layer surface was attained with the incorporation of g-C 3 N 4. • Desalination performances of TFN FO membranes surpassed that of TFC and commercial membranes. • The anti-fouling property has been greatly enhanced. [ABSTRACT FROM AUTHOR]

In this work, green silica-based ceramic hollow fiber membranes (CHFMs) derived from rice husk ash waste were successfully prepared via phase inversion and sintering technique. Prior to the fabrication, rice husk waste was converted into amorphous and crystalline silica-based rice husk ash (ARHA and CRHA). The surface of CHFMs could be easily modified to become hydrophobic by grafting with a fluoroalkylsilane (FAS) agent. The CHFMs were characterized before and after grafting using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), measurement of contact angle and liquid entry pressure of water (LEPw), and three-point bending test. The pore size and the porosity of the membrane surface were also evaluated using mercury intrusion porosimetry (MIP). Lotus-leaf structure formed at the surface of HFMs by grafting, leading to a high contact angle of >150°. Direct contact membrane distillation (DCMD) performance of membrane after grafting was conducted for 200 h using the synthetic seawater of various NaCl concentrations at different feed temperatures. The experimental results show that the permeate flux decreased with the increasing feed concentration, whereas it was enhanced with the increasing feed temperature. A high water flux of 38.2 kg/m 2 h and salt rejection up to 99.9% were obtained by CHFM prepared from CRHA (CHFM/CRHA). [ABSTRACT FROM AUTHOR]

Water scarcity at global level has called for attentions to establish new and innovative technologies that can be tapped to provide sustainable solutions to water crisis. Membrane-based desalination has been acknowledged as one of the promising approaches to resolve the global challenges. Currently, different membrane-based technologies have been deployed worldwide for clean water production. However, despite the great advances made in terms of the permeate flux and rejection, the practical application of membrane for desalination is still limited by the inevitable membrane fouling issue. Membrane fouling is known to be the major culprit to the elevated operating costs due to the deterioration of permeate flux, increasing transmembrane pressure, and frequent chemical cleaning which shorten the membrane's lifespan. This review provides insights into the recent advancement in mitigating membrane desalination fouling. The fouling control strategies which encompass the efforts made in the novel membrane development, feed water pretreatment, and membrane cleaning are highlighted. The advantages and limitations of these techniques are discussed and reviewed based on a substantial number of up-to-date literatures. [ABSTRACT FROM AUTHOR]

Airgap membrane distillation (AGMD) is an efficient configuration employed widely for the solar membrane distillation desalination process. In the present work, 1-D Knudsen and molecular transport (KMT) model has been developed to investigate the performance of the flat sheet PVDF membrane. A new solution algorithm for the co-current and counter-current flow regime has been designed to solve the heat and mass transfer equations iteratively for a single-stage AGMD module. The feed temperature, feed flow rate, airgap size, salinity, membrane porosity and module length were varied and compared with experimental results. The increase in feed temperature from 40 °C to 80 °C resulted in 10.38 times increase in flux for co-current flow and 11.05 times for counter-current flow. The maximum permeate flux at 80 °C was 8.668 kg/m2h and 8.871 kg/m2h for the co-current and counter-current processes, respectively. Optimizing the feed temperature, flow rate, and membrane length using RSM suggests 80 °C, 1.528 LPM and 10 m as the optimum operating condition. An AGMD module of size 0.8 m width and 10 m length under the optimum operating condition exhibited a freshwater yield of 8.73 kg/h by consuming 24.98 kWh/m3 of specific energy, and the water production cost would be around $2.25/m3. • A 1-D theoretical model is developed for AGMD and solved iteratively • The model is validated using the results obtained from the lab scale experimental setup • The feed water temperature, flow rate and membrane length are the key parameters that affects its performance • RSM is used for the optimization of the process to minimize the water production cost [ABSTRACT FROM AUTHOR]

Two hybrid photooxidation systems consisting of two different reactors; photocatalytic reactor-ultrafiltration (PR-UF) and photocatalytic membrane reactor (PMR) have been investigated and compared for photolysis and separation of oily water. In both, oily water was irradiated by ultraviolet (UV) light. In PR, UV irradiation was made on the TiO 2 photocatalyst suspended in oily water, followed by ultrafiltration (UF) to remove TiO 2 particles and hydrocarbon residues. On the other hand, TiO 2 was immobilized on the halloysite nanotube (HNT) and embedded in the UF membrane in PMR. In both systems, hydrocarbon concentration, chemical oxygen demand (COD), total dissolved solid (TDS), and hydrocarbon concentration were measured at each step of photooxydation and filtration. In UF, membrane flux, reduction in solute concentration, flux decline and flux recovery by backwashing were investigated. The experimental results showed that the reduction in TOC by PR-UF was ~ 10% higher than PMR. On the other hand, reduction in hydrocarbon concentration, COD and TDS was higher for PMR. The TiO 2 concentration in UF permeate was 8 ppm and 0.2 ppm, respectively, for PR-UF and PMR. [ABSTRACT FROM AUTHOR]

In this work, titanate nanotubes (TNTs) were self-synthesized and amino functionalized to produce titanate nanotubes (NH 2 -TNTs) for thin film nanocomposite (TFN) reverse osmosis (RO) membrane fabrication. The novel RO membranes were fabricated by embedding NH 2 -TNTs of different quantities into polyamide (PA) layer. The nanotubular morphology of NH 2 -TNTs was studied using TEM while FTIR was employed to confirm the reaction of TNTs with [1-(2-amino-ethyl)-3-aminopropyl] trimethoxysilane. The effect of NH 2 -TNTs on the PA layer of TFN with respect to surface morphology, separation performance and antifouling properties was thoroughly investigated and discussed. The presence of NH 2 -TNTs in PA layer was verified using XPS while the “leaf-like” outgrowth morphology of PA layer was observed using FESEM. Results showed that the TFN membrane with 0.05% NH 2 -TNTs embedded was the most promising membrane as it exhibited 93% higher water flux than the control thin film composite (TFC) membrane, without compensating NaCl rejection. In terms of organic fouling tendency, the TFN0.05 membrane also showed higher tolerance compared to the control membrane during RO process. Furthermore, as high as 94% of the water flux of TFN0.05 was able to retrieve by a simple water rinse process, which suggests that organic fouling in TFN0.05 is highly reversible. [ABSTRACT FROM AUTHOR]

Over several decades, membrane transport has developed into established field in membrane science and technology. Two different approaches i.e., irreversible thermodynamic model (ITM) and solution diffusion model (SDM) has been thoroughly discussed in the literatures however due to its simplicity and applicability in the area of reverse osmosis desalination membrane, only SDM is chosen and discussed in this work. Recent experimental works are systematically presented for directly or indirectly validating the model. [ABSTRACT FROM AUTHOR]

In this study, a new type of thin film nanocomposite (TFN) forward osmosis (FO) membranes was prepared by incorporating different quantities of halloysite nanotubes (HNTs) into the polyamide layer via interfacial polymerization. The FO performance of all fabricated TFN membranes in terms of water permeability and reverse solute flux was compared and the best performing membrane which showed good balance between permeability and solute flux, among all, was selected for further organic fouling investigation. Using 10 mM NaCl concentration in feed solution and draw solution of 2 M NaCl, the TFN membrane that was embedded with 0.05% HNTs (i.e. TFN0.05) was identified as the best performing membrane due to its high water permeability and low reverse solute flux. Confirmed by the results of BSA removal in the presence of Ca 2 + , the TFN0.05 membrane also exhibited significantly higher fouling resistance compared to a typical TFC membrane. As an indication to the TFN0.05 fouling reversibility, it was found that > 96% permeate flux could be recovered after a simple water rinse process. Overall, it can be concluded that the addition of an appropriate amount of HNTs into the polyamide layer can remarkably improve the antifouling affinity of conventional TFC membranes for FO applications. [ABSTRACT FROM AUTHOR]

Freshwater scarcity is one of the grand challenges that has posed threats to the global economy, societal stability and ecosystem balance. Desalination has been long recognized as an effective approach for fresh water production from seawater and brackish water. Forward osmosis (FO) is currently one of the most studied technologies for seawater and brackish water desalination due to its intrinsic advantages compared to reverse osmosis. On the other hand, membrane distillation (MD) is an emerging technology to offer a potentially cost effective thermally-driven desalination process, especially when coupled with waste heat and solar thermal. One major and inevitable challenge for FO and MD is membrane fouling. For decades, fouling and its related topics have gained extensive attention from the desalination communities and various strategies have been implemented to tackle this long standing issue. In this contribution, the fouling mitigation strategies in terms of pretreatment, membrane surface modification and operating conditions for both FO and MD processes are comprehensively reviewed. • FO and MD are emerging technologies for desalination. • A review focuses on fouling mitigation strategies in FO and MD for desalination. • Membrane modification and operating conditions play important roles in fouling mitigation. [ABSTRACT FROM AUTHOR]