Joule-heating membranes: Do they really work for membrane distillation processes?

Effect of coagulation pretreatment on membrane distillation process for desalination of recirculating cooling water

The growing scarcity of fresh water is driving the implementation of wastewater treatment and water reuse on an increasingly large scale. Various methods have been developed and used for water reuse from wastewater; however, the membrane distillation (MD) process, as a promising separation technology, has recently gained more attention. The MD process is a non-isothermal membrane-based separation used in various applications, especially for desalination and water/wastewater treatment. Compared with other separation processes, the MD process possesses several unique characteristics such as total (100%) rejection, intensive to feed concentration, mild operating conditions as well as stable performance at high contaminant concentrations. Due to the high fresh water demand in recent years, extensive researches have been devoted to the MD process in areas of water/wastewater treatment. The present paper offers a comprehensive MD state of the art review covering the MD applications for wastewater treatment and water reuse.

Membrane processes with outstanding advantages have been developed over the past three decades and could be used for oily wastewater treatment applications, effectively. Nowadays, forward osmosis (FO) and membrane distillation (MD) processes, as two essential membrane processes have received considerable attention, for oily wastewater treatment applications. The excellence of MD and FO processes compared to other membrane processes is their cost-effectiveness and capability to remove smaller oil drops with lower energy consumption. Membrane fouling as a challenge with decreasing separation efficiency has hindered the commercialization of FO and MD processes. Therefore, developing new FO and MD membranes with lower fouling tendency is very important for water treatment applications especially for oily wastewater treatment. In this chapter, after bibliographic analysis, the conventional methods developed for treating various types of oily wastewaters are reviewed, in brief. Then, various membrane processes with particular emphasis on their challenges and advances in oily wastewater treatment applications are presented. Afterward, focusing on FO and MD processes, the current materials used to fabricate proper membranes for FO and MD processes are discussed.

Feasibility of membrane distillation process for potable water reuse: A barrier for dissolved organic matters and pharmaceuticals

ABSTRACTPloy(vinylidene fluoride)–polytetrafluoroethylene nanofibrous membrane fabrication and direct contact membrane distillation (DCMD) process were simulated and optimized by response surface methodology (RSM). Analysis of variance was applied to develop and verify the models that predict the objectives. The three‐dimensional response surfaces of different objectives were obtained. Results showed that the membrane with thickness of 70.7 μm, contact angle of 146.2°, and liquid entry pressure of 53.5 kPa was obtained within investigated experimental range under the optimum electrospinning conditions. Rejection rate of 99.99% and the permeate flux of 67.5 kg m−2 h−1 were gained under the optimum membrane distillation (MD) process parameters. The actual and predicted values show good consistency verifying the accuracy of the models. In addition, an overall investigation of the influence of heat‐press temperature on the morphological and mechanical properties of electrospun membrane was carried out. Results indicated that electrospinning process and MD performance can be enhanced after the corresponding variables were optimized by RSM. This study provides a scientific way to optimize the electrospinning and DCMD parameters. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47125.

Application of fluoroalkylsilanes (FAS) grafted ceramic membranes in membrane distillation process of NaCl solutions

An integrated forward osmosis (FO)-membrane distillation (MD) process is promising for the treatment and resource recovery from municipal wastewater. As higher temperature is applied in MD, it could affect the performance of both FO and MD units. This study aimed to investigate the effects of the type of draw solution (DS) and feed solution (FS) such as ammonium solution or municipal wastewater containing ammonium at higher temperatures on membrane treatment performance. It is found that higher FS and DS temperatures resulted in a higher water flux and a higher RSF with either NaCl or glucose as DS due to the increased diffusivity and reduced viscosity of DS. However, the water flux increased by 23–35% at elevated temperatures with glucose as DS, higher than that with NaCl as DS (8–19%), while the reverse solute flux (RSF) increase rate with NaCl as DS was two times higher than that with glucose as DS. In addition, the use of NaCl as DS at higher temperatures such as 50 and FS at 42 °C resulted in increased forward ammonium permeation from the FS to the DS, whereas ammonium was completely rejected with glucose as DS at all operating temperatures. Reducing pH or lowering the temperature of DS could improve ammonium rejection and minimize ammonia escape to the recovered water, but extra cost or reduced MD performance could be led to. Therefore, the results suggest that in an integrated FO-MD process with DS at higher temperatures such as 50 °C, glucose is better than NaCl as DS. Furthermore, a simplified heat balance estimation suggests that internal heat recovery in the FO-MD system is very necessary for treating municipal wastewater treatment. This study sheds light on the selection of DS in an integrated FO-MD process with elevated temperature of both FS and DS for the treatment of wastewater containing ammonium. In addition, this study highlights the necessity of internal heat recovery in the integrated FO-MD system.

Simulation of Heat and Mass Transfer in Direct Contact Membranedistillation (md): The Effect of Membrane Pore Space Description

Fertilizer-driven FO and MD integrated process for shale gas produced water treatment: Draw solution evaluation and PAC enhancement

Fouling and wetting in the membrane distillation driven wastewater reclamation process – A review

Membrane distillation for sustainable wastewater treatment

The thermal and mechanical stability of different capillary polypropylene (PP) membranes used in the membrane distillation (MD) process were investigated. Membranes differed in storage time from the manufacturing (from 1 to 8 years). Small changes in polymers crystallinity, melting temperature (T m ) and crystallization temperature (T c ) were detected as the storage time of membranes increased. This can be assigned to the crystal growth in amorphous phase of PP. However, independently on the storage time the brand-new membranes were found to be flexible and elastic and capable to bending without fracture. The MD process was carried out either continuously or continuously/periodically. Distilled water and NaCl solutions were used as feeds in MD process. It was found that PP membranes are loosing their flexibility and become brittle during long-term usage in MD modules, and as a consequence, they show susceptibility to cracking and fracture. These effects were more significant when NaCl solutions were used as feeds.

Membrane distillation (MD) is an evaporation/condensation process of volatile components through a hydrophobic porous membrane. The maintenance of gas phase inside the membrane pores is a fundamental condition required to carry out the MD process. A hydrophobic nature of the membrane prevents liquid penetration into the pores. Membranes having these properties are prepared from polymers with a low value of the surface energy, such as polypropylene (PP), polytetrafluoroethylene (PTFE) or polyvinilidene fluoride (PVDF) (Alklaibi & Lior, 2005; Bonyadi & Chung, 2009, Gryta & Barancewicz, 2010). Similar to other distillation processes also MD requires energy for water evaporation. The hydrodynamic conditions occurring in the membrane modules influence on the heat and mass transfers, and have a significant effect on the MD process efficiency. The MD separation mechanism is based on vapour/liquid equilibrium of a liquid mixture. For solutions containing non-volatile solutes only the water vapour is transferred through the membrane; hence, the obtained distillate comprises demineralized water (Alklaibi & Lior, 2004; Gryta, 2005a; Schneider et al., 1988). However, when the feed contains various volatile components, they are also transferred through the membranes to the distillate (ElBourawi et al., 2006; Gryta, 2010a; Gryta et al., 2006a). Based on this separation mechanism, the major application areas of MD include water treatment technology, seawater desalination, production of high purity water and the concentration of aqueous solutions (El-Bourawi et al., 2006; Drioli et al., 2004, Gryta, 2006a, 2010b; Karakulski et al., 2006; Martinez-Diez & Vazquez-Gonzalez, 1999; Srisurichan et al., 2005; Teoh et al., 2008). A few modes of MD process are known: direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), sweeping gas membrane distillation (SGMD), vacuum membrane distillation (VMD) and osmotic membrane distillation (OMD). These variants differ in the manner of permeate collection, the mass transfer mechanism through the membrane, and the reason for driving force formation (Alklaibi & Lior, 2005; Gryta, 2005a). The most frequently studied and described mode of MD process is a DCMD variant. In this case the surfaces of the membrane are in a direct contact with the two liquid phases, hot feed and cold distillate (Fig. 1). The DCMD process proceeds at atmospheric pressure and at temperatures that are much lower than the normal boiling point of the feed solutions. This allows the utilization of solar heat or so-called waste heat, e.g. the condensate from turbines or heat exchangers (Banat & Jwaied, 2008; Bui et al., 2010; Li & Sirkar, 2004).

The influence of draw ratio on the structure and properties of poly(tetrafluoroethylene-cohexafluoropropylene)(FEP) hollow fiber membrane which was fabricated by melt-spinning stretching(MS) method was investigated in this article.The primary FEP hollow fiber membrane structure was compact while the porous structure occurs after stretching.Furthermore,the increase of membrane draw ratios induced the obvious increase of membrane porosity and the N2flux while the decrease of the liquid entrance pressure(LEP).Meanwhile,the FEP hollow fiber membrane was applied to the vacuum membrane distillation(VMD) process to compared with M-S PP hollow fiber membrane which was the commercial product.The results show that the hydrophobic properties,LEP and mechanical strength of FEP hollow fiber membrane was better than PP hollow fiber membrane.The strong and stable of hydrophobic properties enabled the FEP membrane unpenetrated,which kept the desalination rate maintain up to 99%.The larger inner diameter(about 0.74 mm) of FEP hollow fiber membrane induced the use of internal pressure VMD type which brought about the higher VMD flux when the feed temperature increased.

A technique which can be adapted effectively for water treatment or water desalination in industrial applications is the Distillation done by Membrane Distillation (MD) process, due to its lower potential energy consumption and simplicity. The improvements are made on MD has been experimentally tested to the desalination process. The efficiency of the membrane is tested and this process can be employed to the arid areas where the fresh water sources and electric power is low. The experiment was handled by varying the inlet permeate concentration and the flow rate of the salt in the feed. An analysis of the changes in various parameters such as the temperatures of permeate (outlet) and product, flow rate of the product, permeate flux, pH, conductivity was made. The goal of this work is to exploit the usage of suitable membrane for a sustainable water recovery from a wastewater source.