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Polyvinylidene fluoride (PVDF) electrospun nanofibrous membranes (ENMs), consolidated with a heatpress process and of various thicknesses were fabricated and tested in a DCMD cell at five different operating conditions. Membranes as thin as 27 μm were sufficiently robust for evaluation and gave a transmembrane flux as high as 60 L/h m 2 . An analytical model was created to estimate the optimal membrane thickness for DCMD operations. It is found that the value of optimal thickness increases with reduced heat transfer coefficients; decreased feed inlet temperature; increased membrane permeability; and increased salinity. Even for 10% NaCl the predicted optimum was estimated to be 13 μm which was too thin for experimental confirmation. Based upon this analysis but with due allowance for the variation of heat transfer coefficients with temperature dependent physical properties a single Matlab model was created to fit the five sets of data. With the introduction of a structural derivation factor, which reflected the experimentally determined variation of porosity and pore size with thickness, the model was found to fit the data very well. [ABSTRACT FROM AUTHOR]

To separate oil/water mixtures and emlusions, superwetting membranes have been developed via synergy between surface chemistry and topography. However, challenges remain as most of them exhibit unsatisfactory performance, limited strength and durability. Herein, we report a novel membrane with switchable super-wettability for oil and water. This novel composite membrane was developed by electrospinning a hierarchically porous polyvinylidene fluoride (PVDF)-silica composite nano/micro-beaded top layer and a PVDF nanofibrous intermediate layer on a non-woven support. The surface of the composite membrane was modified to exhibit high surface free energy. The membrane is in-air superamphiphilic, underwater superoleophobic and under-oil superhydrophobic. It can treat various types of oil/water mixtures, from simple layered solutions to emulsions (including surfactant-free or surfactant-stabilized oil-in-water and water-in-oil emulsions) without external driving force or under an ultralow pressure (0.1 bar) in a cross-flow filtration process. It shows a flux up to 2000 L/m 2 h and high separation efficiency (> 99.99% in terms of water and oil purities in the permeation) in the cross-flow filtration process. The membrane also exhibits an excellent robustness under harsh conditions, including strong acidic or alkaline solutions, hot water and petroleum. In addition, it presents remarkable antifouling and easy-cleaning properties, which were demonstrated in a 50-h continuous operation. [ABSTRACT FROM AUTHOR]

Recent studies have proved the advantages of novel composite membranes in the extractive membrane bioreactor (EMBR) for recalcitrant organic wastewater treatment. However, more systematic research into membrane properties and mass transfer effects are required. This study investigates the role of internal concentration polarization (ICP), including concentrated and diluted ICP, in an aqueous-aqueous extractive process, and the coupled effects of membrane roughness and hydrodynamic conditions on membrane performance in both cross-flow EMBR (CF-EMBR) and submerged EMBR (S-EMBR) processes. To study these factors, a nanofibrous composite membrane with a four-tiered structure, consisting of a dense polydimethylsiloxane (PDMS) selective layer, a polyvinylidene fluoride (PVDF) nanofibrous sublayer, a non-woven mechanical support and a rough micro/nano-beaded layer, has been developed for the EMBR by electrospinning and spray-coating. A diluted ICP, which occurred when the selective layer faces receiving water (SL-R w ), was less severe than a concentrated ICP in the selective layer facing feed (SL-F) orientation. It resulted in higher overall membrane mass transfer coefficients ( k 0 's) in the SL-R w mode during the aqueous-aqueous extractive tests. In addition, less biofilm was observed on the smooth PDMS surface after 14-days CF-EMBR and S-EMBR operations in the selective layer facing biomedium (SL-R bio ) mode. In contrast, in the SL-F mode during EMBR operations, the ridges and valleys on the membrane surface were able to provide a more favourable micro-environment for microorganisms and protect them from external stresses. The mature micro-colonies that developed in the SL-F mode clogged the membrane support and enhanced concentrated ICP, resulting in a significant reduction of k 0 's by more than 58%. Moreover, as the shear force on the membrane surface due to up-flow of air bubbles in the S-EMBR could mitigate the biofilm attachment, the most effective biofilm control strategy found in this study was to operate the nanofibrous composite membrane in the S-EMBR configuration with a smooth selective layer facing the biomedium. This effectively decreased the amounts of protein by 86%, polysaccharides by 88% and total suspended solids (TSS) by 89% in the biofilms on membrane surface, and achieved the highest stable k 0 of 7.0 × 10 −7 m/s. [ABSTRACT FROM AUTHOR]