There have been tremendous advances in membrane distillation (MD) since the concept was introduced in 1961: new membrane designs and process configurations have emerged, and its commercial viability has been evaluated in several pilot-scale studies. However, its high energy consumption has hindered its commercialization. One of the most promising ways to overcome this obstacle is to develop more energy-efficient membrane modules. The MD research community has therefore developed diverse new module configurations for hollow fiber and flat sheet membranes that increase the thermal energy efficiency of MD by minimizing thermal polarization, increasing mass transfer across the membrane, and improving heat recovery from the condensed vapor. This review summarizes the progress that has been made in the design of hollow fiber and flat sheet membrane modules for MD applications. It begins with a brief introduction to MD and its configurations before describing developments in module fabrication and highlighting key areas where further research is needed. 

Progress in module design for membrane distillation

Preparation of reduced graphene oxide-carbon nanotubes membranes for conductive heating membrane distillation treatment of humic acid

Membrane distillation (MD) is a thermal-based membrane operation with high potential for the treatment of aqueous streams. However, its implementation is limited and only few examples of MD pilots can be found in desalination. One of the reasons behind this is that MD requires thermal energy for promoting the evaporation of water, which implies higher energy consumption with respect to pressure-driven membrane operations, like reverse osmosis (RO). Recently, among the different methods investigated to improve the thermal efficiency of MD, attempts for obtaining a localized heating of the feed, close to the membrane surface, were carried out. This work reviews experimental activities on the topic, dealing with both modified membranes, used under solar irradiation or coupled to an electric source, and specifically designed heated modules. The main results are reported and points of action for further optimization are identified. In particular, although at an early stage, this type of approach led to improvements in membrane flux and to a reduction of energy consumption with respect to conventional MD. Nevertheless, long tests to ensure a stable performance time, the optimization of operating conditions, the development of methods to control fouling issues, and the identification of the best module design, together with the scale-up of membranes/modules developed, represent the main research efforts needed for future implementation of localized heating strategy.

/pdf/localized-heating-to-improve-the-thermal-efficiency-of-3iixpti1.pdf

Localized Heating to Improve the Thermal Efficiency of Membrane Distillation Systems

Membrane distillation (MD) is an emerging technology for the brine desalination. Directly heating feed liquid at the membrane-water interface for improving the performance of MD has been demonstrated, while the problem of membrane scaling remained. Herein, carbon nanotube-based electroactive membranes were prepared and characterized by a variety of methods. It was then used in a conductive heating vacuum membrane distillation system. We firstly increased the flux by optimizing system configuration, placing a spacer in the feed channel, and setting vent holes on the thermal conducting layer. Then, aiming at silicates and sulfates scaling in MD, the electroactive membranes and titanium were used as working electrodes and the counter electrode, respectively, to discuss the electrochemical anti-scaling performance and mechanism. Results showed that the silicate scale on the membrane surface can be effectively cleaned by using the electroactive membrane as the cathode and applying a potential of -5V to destroy the structure of the silicate through an electrochemical reaction. With the electroactive membrane as the anode, the scaling of calcium sulfate can be mitigated by providing a continuous potential through electrostatic repulsion. This paper may provide further insights into inorganic scaling control in conductive heating vacuum membrane distillation process. • Carbon nanotube based electroactive membranes were prepared • A conductive heating vacuum membrane distillation system was optimized • Electroactive membrane was used as an electrode to alleviate scaling • Electrochemical anti-scaling mechanisms on silicates and sulfates were elucidated 

Enhance the anti-scaling performance of conductive heating vacuum membrane distillation by carbon nanotube-based electroactive membrane

Contribution of graphene oxide (GO)-containing polydimethylsiloxane (PDMS) binder to the surface modification of electrospun PVDF membrane towards development of photothermal vacuum membrane distillation (PVMD)

Membrane distillation (MD) is a thermally driven desalination process that has excellent application prospects in seawater desalination or hypersaline wastewater treatment, while severe temperature polarization (TP) and the resulting relatively high energy consumption have become principal challenges limiting the commercial application of MD. Therefore, the design of novel systems to overcome the shortage of conventional MD requires urgent attention. Here, we developed three surface heating vacuum membrane distillation systems, namely, SHVMD-1, SHVMD-2, and SHVMD-3, according to the different positions of the thermal conducting layer in the cell. The distillate flux, TP, and energy performance of these systems under different operating conditions were investigated. All three systems showed stable performance, with a salt rejection >99.98% for 35 g/L NaCl, and the highest flux was close to 9 L/m2·h. The temperature polarization coefficients were higher than unity in SHVMD-2 and SHVMD-3 systems, and the SHVMD-2 system produced the lowest specific energy consumption and the highest thermal efficiency. In addition, we tested the intermittent surface heating process, which can further improve energy performance through reducing specific electrical energy consumption in vacuum membrane distillation. This paper provides a simple and efficient membrane system for the desalination of brines.

Enhanced Performance of Membrane Distillation Using Surface Heating Process.

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Enhanced Performance of Membrane Distillation Using Surface Heating Process.