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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]

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]

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]

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]

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]