Membrane Distillation Crystallization Applied to Brine Desalination: A Hierarchical Design Procedure

Electrodialysis desalination: The impact of solution flowrate (or Reynolds number) on fluid dynamics throughout membrane spacers

The incorporation of a spacer among membranes has a major influence on fluid dynamics and performance metrics. Spacers create feed channels and operate as turbulence promoters to increase mixing and reduce concentration/temperature polarization effects. However, spacer geometry remains unoptimized, and studies continue to investigate a wide range of commercial and custom-made spacer designs. The in-depth discussion of the present systematic review seeks to discover the influence of Reynolds number or solution flowrate on flow hydrodynamics throughout a spacer-filled channel. A fast-flowing solution sweeping one membrane's surface first, then the neighboring membrane's surface produces good mixing action, which does not happen commonly at laminar solution flowrates. A sufficient flowrate can suppress the polarization layer, which may normally require the utilization of a simple feed channel rather than complex spacer configurations. When a recirculation eddy occurs, it disrupts the continuous flow and effectively curves the linear fluid courses. The higher the flowrate, the better the membrane performance, the higher the critical flux (or recovery rate), and the lower the inherent limitations of spacer design, spacer shadow effect, poor channel hydrodynamics, and high concentration polarization. In fact, critical flow achieves an acceptable balance between improving flow dynamics and reducing the related trade-offs, such as pressure losses and the occurrence of concentration polarization throughout the cell. If the necessary technical flowrate is not used, the real concentration potential for transport is relatively limited at low velocities than would be predicted based on bulk concentrations. Electrodialysis stack therefore may suffer from the dissociation of water molecules. Next studies should consider that applying a higher flowrate results in greater process efficiency, increased mass transfer potential at the membrane interface, and reduced stack thermal and electrical resistance, where pressure drop should always be indicated as a consequence of the spacer and circumstances used, rather than a problem.

Membrane distillation crystallization technology for zero liquid discharge and resource recovery: Opportunities, challenges and futuristic perspectives

Water resources are getting limited, which emphasises the need for the reuse of wastewater. The conventional waste(water) treatment methods such as reverse osmosis (RO) and multi-effect distillation (MED) are rendered limited due to certain limitations. Moreover, the imposition of stringent environmental regulations in terms of zero liquid discharge (ZLD) of wastewater containing very high dissolved solids has assisted in developing technologies for the recovery of water and useful solids. Membrane distillation crystallization (MDCr) is an emerging hybrid technology synergising membrane distillation (MD) and crystallization, thus achieving ZLD. MDCr technology can be applied to desalinate seawater, treat nano-filtration, and RO reject brine and industrial wastewater to increase water recovery and yield useful solids. This manuscript focuses on recent advances in MDCr, emphasizing models that account for application in (waste)water treatment. MDCr has dual benefits, first the environmental conservation due to non-disposal of wastewater and second, resources recovery proving the proverb that waste is a misplaced resource. Limitations of standalone MD and crystallization are discussed to underline the evolution of MDCr. In this review, MDCr's ability and feasibility in the treatment of industrial wastewater are highlighted. This manuscript also examines the operational issues, including crystal deposition (scaling) on the membrane surface, pore wetting phenomenon and economic consequences (energy use and operating costs). Finally, opportunities and future prospects of the MDCr technology are discussed. MDCr technology can amplify natural resources availability by recovering freshwater and useful minerals from the waste stream, thus compensating for the relatively high cost of the technology.

Strategies to control product characteristics in simultaneous crystallization of NaCl and KCl from aqueous solution: seeding with NaCl and KCl

In this work we developed an approach for the simultaneous crystallization of NaCl and KCl from their aqueous solution by concomitantly seeding both salts. Results highlight the possibility of retrieving relatively pure solid fractions of each salt.

Membrane-based separation technologies: from polymeric materials to novel process: an outlook from China

During the past two decades, research on membrane and membrane-based separation process has developed rapidly in water treatment, gas separation, biomedicine, biotechnology, chemical manufacturing and separation process integration. In China, remarkable progresses on membrane preparation, process development and industrial application have been made with the burgeoning of the domestic economy. This review highlights the recent development of advanced membranes in China, such as smart membranes for molecular-recognizable separation, ion exchange membrane for chemical productions, antifouling membrane for liquid separation, high-performance gas separation membranes and the high-efficiency hybrid membrane separation process design, etc. Additionally, the applications of advanced membranes, relevant devices and process design strategy in chemical engineering related fields are discussed in detail. Finally, perspectives on the future research directions, key challenges and issues in membrane separation are concluded.