Membrane Distillation Applications Research Articles

A novel janus membrane modified by MXene for enhanced anti-fouling and anti-wetting in direct contact membrane distillation

Membrane fouling and wetting limit the applications of membrane distillation (MD) for wastewater treatment, especially when treating the wastewater with a high concentration of low surface tension substances such as oil and surfactants. In this paper, virgin polyvinylidene fluoride (PVDF) membrane was modified by polydimethylsiloxane (PDMS) to enhance anti-wetting ability. Then a thin polydopamine (PDA) layer was coated as a reaction platform for further modification. Polyethyleneimine (PEI) was cross-linked with PDA to form a uniform and stable layer, through hydrogen bonds and electrostatic interaction to immobilize hydrophilic MXene, which formed a Janus MXene-PVDF membrane. The MXene layer was the key for superoleophobicity and high liquid entry pressure (LEP) of membrane, capable of mitigating membrane fouling and wetting when dealing with low surface tension wastewater (LSTW). From the experiments results, pristine PVDF membrane showed severe fouling and wetting with flux decline and salt leakage during treatment of LSTW (surfactants containing water, oil-in-water emulsion and sodium dodecyl sulfate stabilized oil-in-water emulsion). However, under the same conditions, the Janus MXene-PVDF membrane exhibited remarkably stable flux (9.3 kg m−2h−1, 9.1 kg m−2h−1, 10.2 kg m−2h−1) and salt rejection (almost 99.9%) after 15 h operation. Excellent fouling and wetting resistance of MXene-PVDF membrane was mainly attributed to its superhydrophilic and superoleophobic top surface (in-air water contact angle: 30.2°, under-water oil contact angle: 169.9°) and hydrophobic substrate (in-air water contact angle: 130.8°), together with high LEP value (91.1 Kpa). This study provides a viable route to fabricated a Janus membrane with outstanding fouling and wetting resistance for LSTW, oily wastewater and it has great potential for sewage treatment in the future.

Comparison of omniphobic membranes and Janus membranes with a dense hydrophilic surface layer for robust membrane distillation

Membrane wetting, fouling, and scaling are three prominent challenges that limit membrane distillation (MD) applications. To overcome these challenges, novel MD membranes including omniphobic membranes and Janus membranes with a dense hydrophilic surface layer have been developed. In this study, we fabricated an omniphobic membrane and a Janus membrane composed of a dense polyvinyl alcohol (PVA) surface layer and a polyvinylidene fluoride (PVDF) substrate. The two membranes have been compared in MD experiments with different feeds. Furthermore, the working mechanisms of the two membranes have been elucidated. As a result, neither the omniphobic MD membrane nor the Janus MD membrane can resolve all three challenges at the same time. Specifically, both the omniphobic MD membrane and Janus MD membrane can resist wetting but via different working mechanisms. From breakthrough pressure (BP) determinations with an ethanol-water mixture (i.e., a low-surface-tension liquid), the omniphobic MD membrane resists wetting as its LEP (82.0 ± 9.2 kPa) is larger than the transmembrane pressure in the MD operation, while the Janus MD membrane resists wetting because the huge capillary pressure (550 ± 50 kPa) in the dense hydrophilic surface layer retains the wetting solution. The omniphobic MD membrane is prone to oil fouling because of the strong underwater hydrophobic attraction between the membrane surface and the mineral oil droplets, while the Janus MD membrane can substantially mitigate fouling due to the lack of attraction between the mineral oil droplets and the hydrophilic membrane surface. The omniphobic MD membrane exhibits outstanding scaling resistance because minerals can hardly precipitate and/or crystalize on the membrane surface, while the Janus MD membrane was susceptible to scaling due to the precipitation and/or crystallization of minerals inside the hydrophilic surface layer. Therefore, the selection of MD membranes should depend on the feed constituents. Overall, our study provides important guidelines for the future development of robust MD membranes.

Designing triple-layer superhydrophobic/hydrophobic/hydrophilic nanofibrous membrane via electrohydrodynamic technique for enhanced anti-fouling and anti-wetting in wastewater treatment by membrane distillation

Developing high-performance membranes for membrane distillation (MD) to treat highly saline industrial wastewater is of great significance. In this work, a superhydrophobic/hydrophobic/hydrophilic triple-layer membrane combining an electrosprayed superhydrophobic top layer, an electrospun hydrophobic nanofibrous intermediate layer and a hydrophilic microporous membrane substrate was fabricated by using electrohydrodynamic techniques. The top superhydrophobic surface possesses a unique surface morphology composing of hydrophobic SiO2-polymer microbeads with nanoscaled protrusions and interconnected thin nanofibers, which contributed to the enhanced water flux for desalination in direct contact MD. By tuning the concentrations of hydrophobic SiO2 nanoparticles and polyvinylidene fluoride-co-hexafluoropropylene for electrospraying the top layer, the triple-layer membrane showed both enhanced anti-fouling and anti-wetting properties due to the reduced liquid-solid contact area and stable Cassie-Baxter state. The triple-layer membrane exhibited stable MD performances when using real seawater and industrial flue gas desulfurization wastewater as the feed solutions, while no obvious fouling and wetting being observed even at 60% water recovery. This study provides an effective approach for fabricating a high-performance triple-layer superhydrophobic/hydrophobic/hydrophilic membrane for potential practical MD applications for industrial wastewater treatment.

Hydrophobic modification of alumina-based tubular ceramic surface and its characterisation

An alumina-based ceramic tubular support surface has been modified with commercially available organosilanes to impart hydrophobic characteristics for its possible application in membrane distillation applications. These membranes were fired at higher temperatures; hence, limited hydroxyl groups were present on the ceramic support surface for coupling with organosilanes. A suitable layer of silica sol was coated to increase the availability of hydroxyl groups before hydrophobic agents. It was observed that providing the intermediate layer enhanced the gripping of silanes with support as well as durability of the hydrophobic membrane increased. The water contact of the hydrophobic surface was 143° and remains unaltered even at 80 °C for 96 h. EDX spectrum showed the presence of silanes on the surface and the XPS depth profile showed a coating of 100 nm. The liquid entry pressure of the membrane was observed as 2.1–2.2 kg/cm2 which is comparable with the commercially available polymeric hydrophobic membranes. The developed hydrophobic membranes may be used for desalination applications.

Fabrication of polystyrene (PS)/cyclohexanol-based carbon nanotubes (CNTs) mixed matrix membranes for vacuum membrane distillation application

In this work, for the first time, carbon nanotubes (CNTs) with hydrophobic nature were used as an appropriate nanofiller to fabricate polystyrene (PS)/CNTs mixed matrix membranes (MMMs) for vacuum membrane distillation (VMD) application, successfully. At first, the effect of PS concentration on performance of the prepared membranes was investigated. As a novelty, the performance of the back of the neat PS membranes was also evaluated. Subsequently, at optimized PS concentration (15 wt%), the effect of CNTs content on the PS/CNTs MMMs performance was investigated. FESEM, FTIR, AFM, Tensile strength and water contact angle analyzes were performed to characterize the prepared MMMs. Increased porosity and average pore size and improved mechanical properties were observed for PS/CNTs MMMs compared to the neat PS membranes. It was found that the cyclohexanol-based CNTs with high hydrophobicity and unique physicochemical properties could improve the prepared MMMs performance in VMD application. On the other hand, the oxygen atom in cyclohexanol structure facilitates dispersion of CNTs in organic solvents and polymeric matrices and also improves the CNTs transport properties. Compared to the optimized PS membrane with water contact angle (WCA) of 80.21° and flux of 2.5 L/m2.h, the performance of the PS/CNTs MMM incorporated with 1 wt% of the raw CNTs (optimum membrane) with WCA of 91.64° and water flux of 34.78 L/m2.h improved, significantly. Also, it was found that liquid entry pressure (LEP) of the PS/CNTs MMMs is higher than that of the neat PS membranes. Finally, to study the influences of some operating parameters on the optimized PS/CNTs MMM performance, Taguchi experimental design method was applied.

Scale Up and Validation of Novel Tri-Bore PVDF Hollow Fiber Membranes for Membrane Distillation Application in Desalination and Industrial Wastewater Recycling.

Novel tri-bore polyvinylidene difluoride (PVDF) hollow fiber membranes (TBHF) were scaled-up for fabrication on industrial-scale hollow fiber spinning equipment, with the objective of validating the membrane technology for membrane distillation (MD) applications in areas such as desalination, resource recovery, and zero liquid discharge. The membrane chemistry and spinning processes were adapted from a previously reported method and optimized to suit large-scale production processes with the objective of translating the technology from lab scale to pilot scale and eventual commercialization. The membrane process was successfully optimized in small 1.5 kg batches and scaled-up to 20 kg and 50 kg batch sizes with good reproducibility of membrane properties. The membranes were then assembled into 0.5-inch and 2-inch modules of different lengths and evaluated in direct contact membrane distillation (DCMD) mode, as well as vacuum membrane distillation (VMD) mode. The 0.5-inch modules had a permeate flux >10 L m−2 h−1, whereas the 2-inch module flux dropped significantly to <2 L m−2 h−1 according to testing with 3.5 wt.% NaCl feed. Several optimization trials were carried out to improve the DCMD and VMD flux to >5 L m−2 h−1, whereas the salt rejection consistently remained ≥99.9%.

Enhanced properties of PVDF nanofibrous membrane with liquid-like coating for membrane distillation

Grafted poly(dimethyl siloxane) (PDMS) or fluorinated chains as liquid-like films have drawn much attention recently to render the substrate self-cleaning and lyophobic characteristics. Herein, novel PVDF nanofibrous membrane with liquid-like coating was facilely fabricated via one-step co-deposition of TiO2 nanoparticles (TiNPs) and a macromolecular coupling agent with PDMS side chains for membrane distillation. The fabricated PDMS-based coating and TiO2 nanoclusters distributed uniformly on the surface rendered the membrane both superhydrophobic (water contact angles as high as 150.4°) and slippery (water sliding angles as low as 4.5°) characteristics. Membrane distillation (MD) experiments showed that the coated membrane is highly effective in mitigating membrane scaling and wetting via hindering foulant deposition and fouling-releasing mechanisms, while simultaneously maintaining a permeability of as high as 34.5 L·m−2·h−1 and a selectivity of >99.99%. These results are competitive when compared with those of typical commercial membranes and related PVDF nanofibrous membranes, which makes the coated membrane a promising candidate for durable MD applications.

Facile preparation of omniphobic PDTS-ZnO-PVDF membrane with excellent anti-wetting property in direct contact membrane distillation (DCMD)

Membrane distillation (MD) is a promising hybrid thermal/membrane desalination process to treat high salinity industrial wastewater with near-complete rejection of nonvolatile solutes. However, MD membrane still suffers the membrane wetting, which largely affects the desalination performance. In this study, a facile method includes one-step in-situ growth of ZnO nanorods and dip coating of low surface energy 1H,1H,2H,2H-perfluorodecytriethoxysilane (PDTS) was applied to fabricate omniphobic membrane (FZnO-PVDF) with excellent anti-wetting performance. The anti-wetting performance of FZnO-PVDF membrane was systemically evaluated by treating pure water, feed with surfactant and sparingly soluble salts for the first time. Theoretical analysis such as numerical simulation, dynamic liquid entry pressure (LEP) changes and nucleation condition was carried out to explain its anti-wetting mechanism. Results showed that FZnO-PVDF membrane displayed high contact angles towards water droplets with (∼121.1°) or without alcohol (∼164.9°), and low sliding angle for water (10.6°). The resultant membrane not only exhibited excellent resistance for surfactant-induced membrane wetting towards 0.6 mM sodium dodecyl sulfate (SDS) due to its enhanced LEP value (225 kPa), but also remarkable resistance for scaling-induced membrane wetting because of the high energy barrier for CaSO4 heterogeneous nucleation (34.2 mJ mol−1) and slip boundary condition of membrane. This study provides valuable insights for fabricating omniphobic membrane and comprehending its anti-wetting property in MD application.

Hydrophobic silica sand ceramic hollow fiber membrane for desalination via direct contact membrane distillation

A porous hollow fibre ceramic membrane derived from a low-cost natural material (silica sand) and fabricated by combine phase inversion and sintering technique followed by fluoroalkylsilane (FAS17) grafting to improve its hydrophobicity is reported in this study. Prior to the subjection of the silica sand ceramic hollow fibre membrane (SSCHFM) to a desalination performance test via direct contact membrane distillation (DCMD), characterization studies were performed on the SSCHFM before and after grafting using different characterization techniques, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), 3-points bending, water liquid entry pressure (LEPw), and water contact angle measurement. Mercury porosimetry analysis (MIP) was also used to determine the pore size distribution and porosity of the SSCHFM. The grafting process caused an increasing of the contact angle from 0° to 142.5° ± 2.0, and LEPw value of (2.6 ± 0.4 bar) was achieved. AFM images showed an increment in the surface roughness of the grafted SSCHFM from 0.305 µm to 0.375 μm, with a slight decrease in the average pore size and porosity from 0.17 µm and 17% to 0.12 µm and 14.7% respectively. After the grafting process, the performance of the membrane in DCMD was evaluated on a salt solution for 32 h at different NaCl concentrations (8,16, 24, 32 and 40) g/L, feed flow rates and feed temperatures. The results showed a decrease in the permeate flux at increasing feed concentration, but the reverse was at higher feed flow rates and feed temperatures. The surface-modified membrane recorded a water flux value of 35 kg/m2.h and 100% salt rejection. The results indicate that the hydrophobic hollow fibre ceramic membranes derived from silica sand have significant potential to be developed for membrane distillation application in water purification and reclamation.

Synergy of feed-side aeration and super slippery interface in membrane distillation for enhanced water flux and scaling mitigation

Membrane distillation (MD) is an acknowledged promising technology for desalinating hypersaline brine, and as such can be a suitable candidate to further concentrate the seawater discharged from reverse osmosis process. Mineral scaling represents a major constraint against the application of MD for further desalination of concentrated seawater, especially when considering CaSO4 (gypsum) and NaCl. Up until now, it has been difficult to rely solely on membrane modification to mitigate CaSO4 scaling. Permeate-side aeration can lessen CaSO4 scaling, but does not permit to increase the water flux. Herein, we proposed the synergy of feed-side aeration and super slippery interface to perform concentrated seawater desalination via direct contact membrane distillation. The results of this study show that this synergistic effect could significantly increase the water flux, which was approximately 1.5 times higher in comparison to the membrane without aeration. Moreover, the synergistic effect effectively alleviates the complex scaling of concentrated seawater, achieving 90 wt% water recovery rate. Based on the observed results, we elucidated the mechanisms governing the enhanced water flux and scaling mitigation driven by the synergistic effect. In addition, we studied the optimal working condition for this system, unveiling that low-intensity large bubbles are more suitable as they lead to a better equilibrium between the economics and functionality of the process.

Flat sheet metakaolin ceramic membrane for water desalination via direct contact membrane distillation

Abstract Hydrophobic metakaolin-based flat sheet membrane was developed via phase inversion and sintering technique and modified through 1H,1H,2H,2H-perfluorooctyltriethoxysilane grafting agents. The prepared membrane was characterized by different techniques such as XRD, FTIR, SEM, contact angle, porosity, and mechanical strength. Their results indicated that the wettability, structural, and mechanical properties of the prepared membrane confirm the suitability of the material for membrane distillation (MD) application. The prepared metakaolin-based flat sheet membrane acquired hydrophobic properties after surface modification with the water contact angle values of 113.2° to 143.3°. Afterward, the membrane performance was tested for different sodium chloride aqueous solutions (synthetic seawater) and various operating parameters (feed temperature, feed flow rate) using direct contact membrane distillation (DCMD). Based on the findings, the prepared membrane at metakaolin loading of 45 wt.% and sintered at 1,300 °C was achieved the best performance with &amp;gt;95% salt rejection and permeate flux of 6.58 ± 0.3 L/m2 · h at feed temperature of 80 °C, feed concentration of 35 g/L, and feed flow rate of 60 L/h. It can be concluded that further optimization of membrane porosity, mechanical, and surface properties is required to maximize the permeate flux and salt rejection.

Mitigating membrane wetting in the treatment of unconventional oil and gas wastewater by membrane distillation: A comparison of pretreatment with omniphobic membrane

The treatment of unconventional oil and gas (UOG) wastewater by membrane distillation (MD) is a promising alternative to disposal via deep-well injection for UOG wastewater management. However, MD has been constrained by membrane pore wetting, which could be induced by surfactants that are commonly used in hydraulic fracturing fluids. Herein, we investigated and compared two strategies, namely pretreatment via coagulation-adsorption and the use of omniphobic membranes, for wetting mitigation in MD treatment of UOG wastewater from the Denver-Julesburg Basin, Colorado. Both strategies were able to mitigate membrane wetting, but pretreatment exhibited better treatment efficiency than the use of omniphobic membranes that was subject to significant membrane fouling. Membrane characterization using scanning electron microscopy, energy dispersive X-ray spectroscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy demonstrated the effective reduction of membrane fouling and scaling after pretreatment. Further, ultrahigh pressure liquid chromatography (UHPLC) coupled with quadrupole time-of-flight mass spectrometry (LC/QToF/MS) was performed to investigate the efficacy of pretreatment in removing surfactants. Pretreatment was found to be highly efficient at removing polyethylene glycol (PEG) and polypropylene glycol (PPG) surfactant classes, which were likely responsible for membrane wetting. Our findings suggest that pretreatment could have comparable or even better effectiveness than omniphobic membranes for improving MD treatment of UOG wastewater with high wetting potential. Comparative investigations on these two wetting mitigation strategies are valuable for rational selection of appropriate strategies to promote practical applications of MD to industrial wastewater treatment. • Membrane wetting occurs in MD treatment of UOG wastewater. • Pretreatment and omniphobic membranes as wetting mitigation strategies. • Pretreatment outperforms omniphobic membranes. • Key surfactant classes removed by pretreatment are identified.

Book Review: Advanced and Hybrid Membranes for Wastewater Treatment

The interesting part of this recent published book is that it offers better understanding on the mechanism of wastewater treatment for membrane technologies, current information about technologies and limitation of wastewater treatment, recent discovered solutions from experts for wastewater treatment and information on weaknesses and solution to membrane technologies. There are 10 chapters in which wrote by the membrane expertise covering the recent progress and development of the various membrane technologies towards water and wastewater treatment. In chapter 1, overview of wastewater treatment including conventional treatment such as ion-exchange, coagulation-flocculation and adsorption has been discussed. At the end of the chapter, membrane technology and its advantages has been introduced. Chapter 2 discussed the conventional technology stated in Chapter 1 in detail. In the chapter, the advantages and disadvantages of the conventional technologies has also been stated. Example of the advantages are including depending on pH and slow process. Chapter 3 provide an insight in the recent advanced separation technology for wastewater treatment such as hybrid adsorption-separation application that can be achieved by membrane technology and membrane distillation application. Meanwhile, Chapter 4 addressed in detail the recent progress of adsorptive ultrafiltration mixed matrix membrane for heavy metals removal such as zinc, nickel and chromium. In chapter 5, photocatalytic membrane has been introduced in the chapter with the brief mechanism on the photocatalytic activity has also been explained. Chapter 6 focussed on the membrane distillation for wastewater treatment. In the chapter, various membrane distillation type has been stated with example of recent works such as direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), vapour membrane distillation (VMD) and sweeping gas membrane distillation (SGMD). In Chapter 7, integrated forward osmosis processes have been described such as FO-MD, FO-RO or both. Chapter 8 introduced ceramic membrane technology to the readers in the book with new alternative material in production of low-cost ceramic membrane. In Chapter 9, recent works on metal organic framework (MOF) including MOF membrane for wastewater separation has been explained. In the last Chapter 10, some potential solution to overcome weaknesses of advanced membranes technologies for wastewater treatment are also discussed. Future recommendation for these technologies is also discussed at the end of the book. This book focused on the collection of recent progress related to advanced membrane technologies towards water and wastewater treatment, for example forward osmosis and membrane distillation. This book has been written by membrane experts from Malaysia and India, providing an insight of recent progress on advanced membrane technologies. This book will be the vital references for the researchers, students, membrane technologist, membrane manufacturer and academicians. Some improvement can be made by adding several interesting topics such as incorporation of waste inorganic materials into polymeric membranes and commercial ceramic membrane that made up from alumina and titania. In addition, some integrated technologies combining two advanced membrane technologies such as integrated forward osmosis and membrane distillation can be interesting if discussed.

Construction of superhydrophobic micro/nano-structure surface on polypropylene hollow fiber membrane and its application in membrane distillation

Construction of superhydrophobic micro/nano-structure surface on polypropylene hollow fiber membrane and its application in membrane distillation

Membrane Scaling and Wetting in Membrane Distillation: Mitigation Roles Played by Humic Substances.

Membrane scaling and wetting severely hinder practical applications of membrane distillation (MD) for hypersaline water/wastewater treatment. In this regard, the effects of feedwater constituents are still not well understood. Herein, we investigated how humic acid (HA) influenced gypsum-induced membrane scaling and wetting during MD desalination. At low concentrations (5-20 mg L-1), HA notably mitigated membrane scaling and wetting. The morphological characterization of scaled membranes revealed that the antiwetting behavior could be ascribed to the formation of a compact and protective gypsum/HA scale layer, which blocked the flow channel of scaling ions and suppressed the intrusion of scale particles into membrane pores. Based on the comprehensive analysis of the scaling process, the formation of the scale layer was related to the heterogeneous crystallization of gypsum on the membrane surface. Moreover, deprotonated HA interfered with the heterogeneous crystallization process by inhibiting the formation of gypsum nuclei and altering the orientation of crystal growth, thus delaying membrane scaling and altering the morphology of the scale layer. Thermodynamic and kinetic analyses further demonstrated the mitigation mechanism of HA. Furthermore, improved fouling reversibility and antiwetting ability in synthetic seawater treatment endowed by HA were observed. This study provides new insight into the roles played by the organic constituents of water/wastewater during membrane desalination, providing a valuable reference for developing novel strategies to improve the performance of MD.

Membrane distillation for wastewater treatment: Current trends, challenges and prospects of dense membrane distillation

Membrane distillation (MD) has excellent potential for wastewater treatment, and studies on this subject have increased recently. The unique features of MD to pass only volatile component through the pores has led to the exploration of hybrid MD, particularly membrane distillation bioreactor (MDBR) and osmotic membrane bioreactor-membrane distillation (OMBR-MD). Fouling and wetting are recognised as drawbacks in particular applications despite the excellent performance. The application of classical porous MD is highlighted as the main concern that leads to poor separation performances. This review highlights the possibility of applying dense membrane to push forward MD applications for wastewater treatment. The development of self-standing and composite dense MD and their performances in applications of wastewater treatment are summarized and discussed. The operational parameters affecting MD performance in the treatment of various types of feed are presented to analyze the robustness and the critical shortcomings of dense MD for wastewater treatment. Challenges, such as the trade-off between mechanical integrity and permeate flux, lack of studies using real wastewater for long-term operation, stability of the dense membrane against rigorous operation conditions, complicated fabrication methods, and the use of harsh chemicals during the fabrication of dense MD membranes are elaborated for further improvement in the development of dense MD membranes for wastewater treatment.

Robust reduced graphene oxide composite membranes for enhanced anti-wetting property in membrane distillation

The application of membrane distillation (MD) has been severely limited by membrane wetting, particularly when treating feed solutions having contaminants with low surface energy. Herein, inspired by the special anti-wetting properties of the graphene-based membrane, a simple and scalable approach has been developed to fabricate the anti-wetting composite membranes with a reduced graphene oxide (rGO) skin layer and a microporous polytetrafluoroethylene (PTFE) substrate. The anti-wetting mechanism of rGO was investigated using a quartz crystal microbalance with dissipation and also fluorescence microscope. The prepared rGO-PTFE composite membrane exhibited outstanding MD performance with high water flux of about 60 L·m−2 h−1, excellent salt rejection (>99.9%) and robust anti-wetting properties when desalinating a 3.5 wt% NaCl feed solution with 0.8 mM sodium dodecyl sulfate (SDS) for 66 h at the temperature difference of 40 °C. Moreover, the rGO-PTFE composite membrane achieved an ultrahigh water flux of about 149 LMH and perfect salt rejection (100%) at a temperature difference of 60 °C, which is 1.2–3.5 times as high as the flux of the reported MD membranes. Our research provides a robust rGO composite membrane with high flux and anti-wetting properties in MD and offers some insightful understanding about the anti-wetting mechanism of rGO against SDS and water.

Effect of Solvent and Copolymer Loading in Synthesizing Hybrid Pvdf-Ptfe Membranes for Vacuum Membrane Distillation Application

Effect of Solvent and Copolymer Loading in Synthesizing Hybrid Pvdf-Ptfe Membranes for Vacuum Membrane Distillation Application

Noninvasive Real-Time Monitoring of Wetting Progression in Membrane Distillation Using Impedance Spectroscopy.

Membrane distillation (MD) is a promising technology for the treatment of high salinity wastewater using a hydrophobic membrane; however, the occurrence of wetting due to surfactants in polluted or low surface tension liquid impedes MD application. Common monitoring approaches, such as conductivity and flux measurement, cannot explain the wetting phenomenon that occurs during the wetting process in detail. Recently, impedance spectroscopy has been proposed for early wetting detection, as it depends on the change of water/air composition in the membrane pores. An earlier and larger variation was observed with precise signal detection. In this study, we proposed an analytical approach to estimate the wetting front, which is the average feed intrusion distance, by the impedance value recorded in real-time operation. With this proposed approach, the wetting mechanism in the presence of a surfactant and the effect of pore size on a commercial polyvinylidene fluoride membrane could be quantified, which cannot be explained in detail using conductivity and flux measurements.

Membrane cleaning in membrane distillation of reverse osmosis concentrate generated in landfill leachate treatment.

As a thermally induced membrane separation process, membrane distillation (MD) has drawn more and more attention to the advantages of treating hypersaline wastewaters, especially the concentrate from the reverse osmosis (RO) process. One of the major obstacles in widespread MD application is the membrane fouling. We investigated the feasibility of direct contact membrane distillation (DCMD) for landfill leachate reverse osmosis concentrate (LFLRO) brine treatment and systematically assessed the efficiency of chemical cleaning for DCMD after processing LFLRO brine. The results showed that 80% water recovery rate was achieved when processing the LFLRO brine by DCMD, but membrane fouling occurred during the DCMD process, and manifested as the decreasing of permeate flux and the increasing of permeate conductivity. Analysis revealed that the serious flux reduction was primarily caused by the fouling layer, which consisted of organic matter and inorganic salts. Five cleaning methods were investigated for membrane cleaning, including hydrogen chloride (HCl)-sodium hydroxide (NaOH), ethylene diamine tetraacetic acid (EDTA)-NaOH, citric acid, sodium hypochlorite (NaClO) and sodium dodecyl sulphate (SDS) cleaning. Among the chemical cleaning methods investigated, the 3 wt.% SDS cleaning showed the best efficiency at recovering the performance of fouled membranes.