Search

The development and implementations of an integrated osmosis system (IOS) was discussed in this chapter. An IOS is comprised of the sequential stages of forward osmosis (FO), reverse osmosis (RO), and the related membranes. Performance and cost-effectiveness that cannot be easily achieved individually with the component systems can be achieved with IOS by optimally placing and using the desired properties of each membrane. IOS provides high diffusive and osmotic permeability, high rejection, low power consumption, and high mass transfer via the manipulation of convection, advection and diffusion, low concentration polarization gradients, low reverse salt flux, and effective restoration of performance after cleaning fouled membranes. The benefits of IOS include better permeate recovery and decreased volume of waste concentrate from RO processes or other elevated osmotic pressure solutions. The process of integrated osmosis first involves the use of a nanofiltration process to selectively harvest the solutes to achieve permeates with a reduced osmotic pressure. Then, the FO process is initialized to dewater the lowered osmotic pressure permeate in order to generate a dilute draw solution that serves as feed to the RO process. For the FO proses, RO permeate provides freshwater while the concentrate provides the draw solution. At the end of this chapter, an attempt is also made to show the research development and future direction of IOS, through hybrid membrane technology. The potential of the integrated systems to solve the world’s water crisis is more advantageous and economical compared to the individual systems.

Membrane distillation (MD) has proved worthwhile in treatment of hypersaline feeds demonstrating near complete rejection of dissolved solutes without any effect on the process conditions. This makes it potential treatment option for hypersaline oilfield produced water (PW) with salinity level far greater than that of seawater. Polymeric membranes have recently garnered more attention than their ceramic counterparts in oily wastewater treatment owing to ease of synthesis and relative cost advantage. However, lower mechanical durability and the propensity for fouling of these membranes due to presence of low surface energy organics in PW ultimately affects MD performance in its treatment. Studies elucidating the mechanism of fouling between PW feed and membranes in MD is scarcely reported in the literature. Various fouling mitigation approaches have shown promise towards the realization of MD as a viable option for PW treatment. Hybridization of MD, use of (super)hydrophobic MD membranes with feed pre-treatment using other technologies and/or membrane post-cleaning, integrated MD systems and recently omniphobic and Janus modifications of MD membranes have all been reported for treatment of PW showing more promise towards achieving ultrapure-distillate treatment. In this article, the performance of these polymeric MD membranes used in PW treatment in comparison to the other conventional treatment options as well as advances in MD as a cost-effective alternative for beneficial re-use of PW is reviewed, highlighting the areas requiring further study for this line of research. Because MD is still largely energy inefficient, several efforts to realize it as an all-round competitive technology focusing on long-term stability, brine handling capacity and potentials for cost savings with alternative and rather sustainable energy source are also discussed.

This study presents a facile approach to produce hydrophobic ceramic hollow fiber membranes (CHFMs) for membrane distillation (MD) desalination using the polymethylhydrosiloxane/tetraethylorthosilicate (PMHS/TEOS) hybrid material. The CHFM was modified via dip-coating with PMHS/TEOS hybrid solution followed by post-coating spinning to facilitate the formation of pores on the coating layer. The effects of ethanol and PMHS concentrations on the coating layer structure and hydrophobicity of the membranes were studied. CHFMs acquired hydrophobic properties after surface modification with the water contact angle values in the range of 108.2° to 124.1°. These membranes showed outstanding direct contact MD (DCMD) desalination performance with salt rejections of >99.98%. A flux of 6.7 L/m2h was achieved by the surface-modified CHFM when treating feed solution with a salinity of 35,000 ppm.

High wetting resistance and high permeate flux are crucial for membrane distillation (MD) to achieve a high performance. To achieve both of these qualities, this work focused on the fabrication of co-extruded dual-layer hollow fibre polyvinylidene fluoride nanocomposite membranes with hydrophobicity gradients. The nanocomposite membranes were incorporated with hydrophobised carbon-based nanoparticles, i.e. multi-walled carbon nanotube (MWCNT) and graphene nanoplatelet (GNP). The effect of different concentrations of nanoparticles (0, 1 and 2 wt%) on the properties and MD performance of the membranes were investigated. The outer layers of the nanocomposites membranes were more hydrophobic than the neat membrane, and the membrane containing 2 wt% of hydrophobised GNP exhibited the highest contact angle of 111.1°. All the inner layers of the membranes were found to be hydrophilic with contact angle of about 60°, thus proving that hydrophobicity gradients were achieved in the membranes. All the membranes had pore sizes and porosities around 0.1 μm and 21.8–42.9% respectively, which are suitable to be used in MD. The surface roughness and wetting resistance of all the nanocomposite membranes, especially the ones with GNP, were higher than the neat membrane and the values increased with increasing concentration of nanoparticles. These membrane characteristics had effects on the direct contact MD (DCMD) performance where all the nanocomposite membranes showed better flux than the neat membrane. The membrane incorporated with 2 wt% of hydrophobised GNP achieved the highest flux of 8.27 kg/(m2h). All the membranes achieved salt rejections of more than 99.9%.

Membrane distillation (MD) is a burgeoning membrane technology that has gained immense interest among membrane scientists worldwide. Despite a slow start, both the theoretical and experimental researches on MD, especially on desalination applications, have escalated significantly over the past few decades. Although the large-scale use of MD has not proliferated worldwide, the researches done thus far have helped us to understand the rudiments of MD and explore the potential areas capable of enhancing its commercial attractiveness. Membranes of very high quality, nearing the properties of an ideal membrane, will fuel the growth of this technology. An ideal membrane for MD is expected to have features such as high liquid entry pressure, low fouling rate, low thermal conductivity, high permeability and excellent mechanical strength. In that regard, ceramic membranes have been appreciated for their high tolerance to harsh conditions, however, their high cost has rendered them less favourable commercially. Polymeric membranes are seen as a plausible cheaper alternative and have dominated research done thus far on MD. This review aims to give a brief introduction to MD and a summary of the research efforts to acquire the desired properties in polymeric membranes used in MD for desalination purposes. Potential research directions are highlighted too.

A complete set of triple-layer (anode/electrolyte/cathode) hollow fiber for high temperature micro-tubular solid oxide fuel cell (MT-SOFC) consisting of nickel oxide (NiO) – yttria-stabilized zirconia (YSZ)/YSZ/lanthanum strontium manganite (LSM) – YSZ has been successfully fabricated in this study. A simplified fabrication technique of phase inversion-based co-extrusion/co-sintering has yielded a perfectly bounded sandwich structure with free-delamination and defect layers. The effect of co-sintering temperatures (1300 °C–1450 °C) on the morphologies, elemental distributions, electrolyte gas-tightness, mechanical strength, electrochemical performance and the impedance spectra test are well-inspected. The increase of co-sintering temperature has significant effects on the anode finger-like micro-channels shrinkage where the voids become very sharp-thin structure; and developing a thin gas-tight electrolyte layer. Whereas, rapid co-sintering rate (10 °C min−1) and large particle size of 3–5 μm (micron) of YSZ has hindered the formation of fully dense cathode layer resulting from higher co-sintering temperature. Correspondingly, with only 0.1116 Ωcm2 value of area-specific resistance (ASR), a maximum power density has increased from 0.34 W cm−2 to 0.75 W cm−2 with 1.05 V OCV at 700 °C when the co-sintering temperature ranging from 1400 °C to 1450 °C; which comparable with single-layer counterpart.