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Copyright of Industrial Water Treatment is the property of CNOOC Tianjin Chemical Research & Design Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to solve the problems of low separation efficiency and poor operation stability in the process of industrial sulfuric acid waste treatment, a concentration and recovery system of hollow fiber vacuum membrane distillation based on polytetrafluoroethylene (PTFE) was proposed. Experiments on concentration of sulfuric acid waste by vacuum membrane distillation under different working conditions were carried out to study the influence of operation parameters on the water production characteristic of the system. The results showed that the membrane flux decreased with the increase of feed concentration and vacuum side pressure, while increased with the increase of feed temperature and feed velocity. In addition, the system operated continuously for 10 days under the conditions of feed concentration of 2%, feed temperature of 80 ℃ and feed velocity of 1.0 m/s, the membrane flux of the system decreased slightly, and the fluctuation range of condensed water conductivity was 11-13 μS/cm, which was much lower than that of tap water (200 μS/cm), and the separation efficiency was as high as 99.9%. The system had excellent operation stability and could achieve high purity separation of sulfuric acid waste, which had a broad application prospect.

In order to solve the problems of low separation efficiency and high energy consumption in the industrial wastewater treatment, a combined system of mechanical vapor recompression and hollow fiber vacuum membrane distillation was constructed. The operational characteristics of the coupled system were investigated, and experimental studies were conducted on the evaporation of ammonium chloride solution under different feed conditions and long-term operation. The results indicated that as ammonium chloride mass concentration, feed temperature, feed flow rate and vacuum side pressure were 5%, 75 ℃, 10 m3/h and 24 kPa, the freshwater production ratio, freshwater conductivity, separation efficiency and specific heating energy consumption(SHEC) were obtained as 45.9 kg/h, 11.9 μS/cm, 99.9% and 118.5 kW·h/t. In addition, the increase of ammonium chloride mass concentration decreased the freshwater production ratio and increased the SHEC, while the increase of feed temperature and feed flow rate increased the freshwater production ratio and decreased the SHEC. After 240 h of long term operation, membrane fouling did not significantly affect the freshwater quality, but reduced the freshwater production ratio. The water production rate was restored to 96.1% of the original through membrane cleaning. The system can separate the ammonia chloride solution with high efficiency and has a broad application prospect.

Copyright of Industrial Water Treatment is the property of CNOOC Tianjin Chemical Research & Design Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present study aims to evaluate the performance of porous hydrophobic Polyvinylidene fluoride − Polytetrafluoroethylene (PVDF-PTFE) composite membranes for desalination by vacuum membrane distillation (VMD) technique. The effect of operating parameters such as feed NaCl concentration (10,000 to 40,000 mg/L), feed temperature (50 °C to 80 °C), and downstream pressure (80 to 120 mmHg) on water permeation rate was studied. The increase in feed temperature enhanced the water permeation rate due to a rise in driving force across the membrane. For a constant downstream pressure of 80 mmHg, feed temperature of 80 °C and feed flow rate of 80 L/h, the membrane exhibited a maximum water flux of 3 kg/m2h with 99.86% salt rejection when aqueous NaCl concentration of 10,000 mg/L was charged as feed. Membrane characterization was performed using various analytical tools to determine physico-chemical properties such as pore size, structural elucidation, thermal stability, crystallinity, and hydrophobicity of the membrane material. Further, a temperature and concentration polarization coefficient-based analysis was performed by solving the mass and heat transport model equations using MATLAB software. The proposed research study promotes the application of VMD for recovering potable water from highly saline sea/brackish water and alleviates brine disposal issues. [ABSTRACT FROM AUTHOR]

This paper deals with a numerical study of heat and mass transfer in a vacuum membrane distillation unit used for desalination. The governing equations expressing the conservation of mass, momentum, energy, and species for the saline solution with coupled boundary conditions, as well as the mass and energy balances on the membrane sides, were solved numerically. The slip boundary condition due to the membrane's hydrophobicity was also taken into consideration. The numerical model was validated with available experimental data and found to be in good agreement. The effects of operational parameters on pure water production and temperature polarization were presented and discussed. A comparison between three flat-sheet membranes commonly used in vacuum membrane distillation was conducted under the same operating conditions. In addition, a comparison between the Nusselt and Sherwood numbers obtained in this study and correlations commonly used in the literature was conducted, which revealed remarkable deviations between models along the channel. The impact of the heat and mass transfer coefficients on the transmembrane permeate mass flux variation is found to be important. [ABSTRACT FROM AUTHOR]

This study simulates a solar-powered reverse osmosis (RO) system integrated with vacuum membrane distillation (VMD) for desalination brine treatment. The models were simulated using the Simulink package and MATLAB. The water production, energy consumption data, and the energy generation of 100 solar panels for the best location in Saudi Arabia were calculated to demonstrate this integration. The optimal yearly tilt was 28.5°, and the monthly tilts were found to be ranging from 5.2° to 51.9°. utilising the optimal monthly tilts and the sun tracking system resulted in a 6.46% and 40.3% increases in the power generated throughout the year, respectively. The specific electrical energy consumption was found to be ranging from 4.61 to 5.11 kWh/m3 for the RO process, and the specific thermal energy consumption was found to be ranging from 152 to 202.4 kWh/m3 for the VMD. The overall recovery ranged between 43.5 and 48.2% using the RO system and a mere 11.22% to 13.64% using the VMD system, resulting in a combined recovery ranging from 54.7 to 61.9%, with total production ranging from 7595 to 9611 m3 of freshwater per year. The results attained in this study are greatly beneficial to both acadmic and desalination industries and future researchers aiming with the brine treatment process to reach zero liquid discharge (ZLD) or minimal liquid discharge (MLD). [ABSTRACT FROM AUTHOR]

Vacuum membrane distillation (VMD) is an attractive method for water desalination due to its high pure water permeability under lower operating temperatures, resulting in less energy consumption, lower heat loss via conduction through the membrane surface, and negligible heat transfer by conduction due to the low pressure on the permeate side. The aim of this study is to establish a comprehensive numerical model that describes the water vapor transfer across a hydrophobic micro-porous membrane in single-stage and multi-stage VMD processes for seawater desalination. The numerical predictions are compared to previous experimental data, and a good correlation is observed. The investigation also conducted a sensitivity analysis of process variables and membrane specifications on VMD performance, as well as an assessment of the impact of temperature and concentration polarization. The obtained results showed that the permeation flux reached 18.42 kg/m²·h at 35 g/L feed concentration, 65°C feed temperature, 50 L/h feed flow rate, and 3 kPa vacuum pressure. Moreover, the findings revealed that feed temperature was the most significant factor, while feed flow rate was the least important in determining permeation flux. Additionally, the results indicated that the structure and porosity of support materials play important roles in determining the performance of VMD process. Finally, results confirmed that temperature polarization had a more significant effect on the reduction of permeate flux than concentration polarization. [ABSTRACT FROM AUTHOR]

This study presents a theoretical model based on integrated heat and mass transfer in a vacuum membrane distillation module. The vacuum membrane distillation is being investigated using a parametric analysis with the objective of investigating the influence of operating parameters on process performance. The study considers various factors associated with VMD operation, such as feed inlet temperature, feed inlet flowrate, and vacuum pressure. Two key performance metrics, namely permeate flux and gained output ratio (GOR), are employed to evaluate the system's performance. The results reveal that raising the feed temperature and flowrate results in improved output flux and GOR. Nevertheless, the impact of changing the feed temperature on performance enhancement surpasses that of adjusting the feed flowrate. Furthermore, decreasing the pressure in the permeate channel, thereby achieving higher vacuum levels, significantly improves the permeate flux, particularly at lower feed temperatures. However, this productivity increase comes at the expense of increased heat loss and reduced GOR. Additionally, all the parameters investigated demonstrate substantial effects on the permeate flux, while their influences on the GOR are negligible. [ABSTRACT FROM AUTHOR]

Vacuum membrane distillation (VMD) is a compelling technique for desalinating water because it exhibits superior pure water permeability at lower operating temperatures compared to other membrane distillation technologies. This leads to reduced energy consumption, lower heat loss via conduction across the membrane surface, and minimal heat transfer through conduction due to the low pressure on the permeate side. Detailed modelling of heat and mass transfer in VMD is essential for optimizing the process as it provides valuable insights that contribute to the advancement and successful implementation of seawater desalination using VMD technology. The aim of this study is to establish a comprehensive numerical model that describes the water vapor transfer across a hydrophobic micro-porous membrane in single-stage and multi-stage VMD processes for seawater desalination. The numerical predictions were compared to experimental data in addition to numerical computations based on an existing literature database, and good agreement has been found. The investigation also conducted a sensitivity analysis of process variables and membrane specifications on the VMD performance, as well as an assessment of the impact of temperature and concentration polarization. The obtained results showed that the permeation flux reached 18.42 kg/m2·h at 35 g/L feed concentration, 65 °C feed temperature, 50 L/h feed flow rate, and 3 kPa vacuum pressure. Moreover, the findings revealed that the feed temperature was the most significant factor, while the feed flow rate was the least important in determining the permeation flux. Additionally, the findings suggested that the effectiveness of the VMD process heavily relies on the composition and permeability of the support materials. Finally, the results confirmed that temperature polarization had a more significant effect on the reduction of the permeate flux than the concentration polarization. [ABSTRACT FROM AUTHOR]

China is the world’s largest producer and exporter of concentrated apple juice (CAJ). However, traditional concentration methods such as vacuum evaporation (VE) and freeze concentration cause the loss of essential nutrients and heat-sensitive components with high energy consumption. A green and effective technique is thus desired for juice concentration to improve product quality and sustainability. In this study, a hybrid forward osmosis–membrane distillation (FO–MD) process was explored for the concentration of apple juice using sodium lactate (L-NaLa) as a renewable draw solute. As a result, commercial apple juice could be concentrated up to 65 °Brix by the FO process with an average flux of 2.5 L·m−2·h−1. Most of the nutritional and volatile compounds were well retained in this process, while a significant deterioration in product quality was observed in products obtained by VE concentration. It was also found that membrane fouling in the FO concentration process was reversible, and a periodical UP water flush could remove most of the contaminants on the membrane surface to achieve a flux restoration of more than 95%. In addition, the L-NaLa draw solution could be regenerated by a vacuum membrane distillation (VMD) process with an average flux of around 7.87 L∙m−2∙h−1 for multiple reuse, which further enhanced the long-term sustainability of the hybrid process.

Membrane distillation (MD) is considered a promising technology for desalination. In the MD process, membrane pores are easily contaminated and wetted, which will degrade the permeate flux and salt rejection of the membrane. In this work, SiC ceramic membranes were used as the supports, and an Al2O3 micro-nano structure was constructed on its surface. The surface energy of Al2O3@SiC micro-nano composite membranes was reduced by organosilane grafting modification. The effective deposition of Al2O3 nanoflowers on the membrane surface increased membrane roughness and enhanced the anti-fouling and anti-wetting properties of the membranes. Simultaneously, the presence of nanoflowers also regulated the pore structures and thus decreased the membrane pore size. In addition, the effects of Al2(SO4)3 concentration and sintering temperature on the surface morphology and performance of the membranes were investigated in detail. It was demonstrated that the water contact angle of the resulting membrane was 152.4°, which was higher than that of the pristine membrane (138.8°). In the treatment of saline water containing 35 g/L of NaCl, the permeate flux was about 11.1 kg⋅m−2⋅h−1 and the salt rejection was above 99.9%. Note that the pristine ceramic membrane cannot be employed for MD due to its larger membrane pore size. This work provides a new method for preparing superhydrophobic ceramic membranes for MD.

Membrane distillation (MD) is a process driven by the vapor pressure difference dependent on temperature variation, utilizing a hydrophobic porous membrane. MD operates at low pressure and temperature, exhibiting resilience to osmotic pressure. However, a challenge arises as the membrane performance diminishes due to temperature polarization (TP) occurring on the membrane surface. The vacuum MD process leverages the application of a vacuum to generate a higher vapor pressure difference, enhancing the flux and mitigating TP issues. Nevertheless, membrane fouling leads to decreased performance, causing membrane wetting and reducing the ion removal efficiency. This study investigates membrane fouling phenomena induced by various silica nanoparticle sizes (400, 900, and 1300 nm). The patterns of membrane fouling, as indicated by the flux reduction, vary depending on the particle size. Distinct MD performances are observed with changes in the feed water temperature and flow rate. When examining the membrane fouling mechanism for particles with a porosity resembling actual particulate materials, a fouling form similar to the solid type is noted. Therefore, this study elucidates the impact of particulate matter on membrane fouling under diverse conditions.

The direct integration of membrane distillation and solar energy collection in a single module is a promising technology for autonomous seawater desalination in remote regions; however, the modeling and design of such modules are challenging because of the coupling of the radial and longitudinal heat and mass transfers. In a previous study, we provided as a first modeling approach a hollow fiber solar collector vacuum membrane distillation (VMD) module, considering a constant temperature at the shell side and a pure water feed. Here, a full model is developed to describe the coupled effects of the solar collector and a hollow fiber VMD module operating in an outside/in mode with saline water. The model considers all the main phenomena (membrane distillation, temperature and concentration polarization, absorption of solar radiation and energy balances over the solar collector, radial and longitudinal heat and mass transfer, seawater properties, and more than 30 variables). Applied to simulate the behavior of a semi-industrial-scale module, it allows the influence of solar radiation on the performance/limits of the integrated module to be discussed based on the radial and longitudinal profiles and heat flows. The model can be used to identify key points in the module design to better utilize solar radiation and manage heat flows.

This paper addresses a retrofitting vacuum membrane distillation (VMD) setup to reduce the accumulated pressure inside the permeated side. This modification is necessary to extend the operation of the VMD to extreme operation conditions of higher hot water temperatures. This modification, denoted as a hybrid configuration, proposes the injection of a cold water stream into the VMD cell without mixing it with the permeate. Energy and exergy efficiency analyses were performed to assess the effectiveness of the hybrid configuration. The performance of the modified system indicated an improvement in terms of permeate flux (J), the gain output ratio (GOR), and the utilitarian exergetic efficiency (ηex,u), which reach up to two and three times that of the base configuration of the VMD system. However, the exergetic efficiency (ηex) of the hybrid system showed marginal improvement compared to the base case over the tested range of hot water temperatures. This is because the enhanced vapor production is penalized by excess energy consumption. Moreover, the highest exergy destruction percentages occurred in the operational components (e.g., heater and chillers) which fall in the range of 19.0–68.9%. The exergy destruction percentage in the original components (e.g., the VMD cell and condenser) did not exceed 8.3%. Furthermore, this study indicated that the hybrid configuration requires additional tuning and optimization to perform efficiently over wide operating conditions.

In this study, we developed a comprehensive two-dimensional computational fluid dynamics (CFD) model using COMSOL™ Multiphysics to describe and simulate heat transfer, mass transfer and fluid flow in the flat sheet vacuum membrane distillation (VMD) under laminar flow conditions. A combination of Knudsen and Poiseuille flow was applied to study mass transfer across the membrane. The effect of variation of Reynolds number, inlet feed temperature and degree of vacuum on different parameters (mass flux, temperature polarization coefficient- TPC, concentration polarisation, heat transfer coefficient) was studied. There was a positive impact of the Reynolds number (50–200) on mass flux (13.15%), heat transfer coefficient (2.64%) and TPC (1.42%), while CPC decreased by 56.63%. The increment in the heat transfer coefficient was due to fluid mixing on the feed side, while the increment in the TPC was due to a higher temperature gradient across the membrane surfaces. The increment in the feed temperature (323–343 K) resulted in an increase in mass flux by 132.9%, while TPC decreased from 0.98 to 0.90. The degree of vacuum (640–750 mm Hg) increased mass flux and heat transfer coefficient by 72.52 and 425.83%, respectively, while the TPC decreased by 8.81%. The feed temperature was the most sensitive parameter with respect to mass flux. The developed CFD model was validated with in-house experimental results with reasonable accuracy. HIGHLIGHTS Comprehensive 2D CFD model developed using COMSOL to simulate heat transfer, mass transfer and fluid flow in VMD.; CFD model used to determine the temperature and concentration polarization at the membrane surface.; The effect of Reynolds number, feed temperature, and vacuum degree on VMD performance parameters were studied.; Combination of Knudsen and Poiseuille flow was applied to study mass transfer across the membrane.;

Brackish water has attracted increasing attention as a promising source to augment fresh water supply in many areas around the world. However, the ubiquitously high content of arsenic in brackish water presents a vexing technical challenge to reverse osmosis (RO) desalination plants. In this study, an integrated RO/vacuum membrane distillation (VMD) process was investigated for enhanced As(III) removal and water recoveries of brackish water desalination without requirement of pre-oxidation step as in other conventional treatment processes. The experimental results demonstrate that As(III) removal and water flux of the single RO process were profoundly affected by the conditions of the brackish water feed and the process water recovery. At pH 10, the As(III) removal maximized at 90%, and sharply dropped to below 80% as the process water recovery exceeded 70%. Exceeding the process water recovery of 70% also significantly reduced the RO process water flux. On the other hand, the VMD process was able to further treat concentrated RO brines with a 100% As(III) removal and stable water flux. Thanks to advantage of VMD, the integrated RO/VMD process at the global water recovery of 95.5% achieved adequate global As(III) removal, bringing the As(III) concentration in the product water down to below the 10-ppb allowable maximum limit. [ABSTRACT FROM AUTHOR]

Numerical simulations were carried out to assess the technical and economic feasibility of a solar water desalination system that has a novel hybrid Concentrating Photovoltaic Thermal (CPVT) collector coupled with a Vacuum Membrane Distillation (VMD) process. A special characteristic of this CPVT is its triangular receiver with PV cells facing the reflecting surface. This type of receiver has the advantage of generating more electricity with less PV surface area and great potential to be used to hybridize conventional parabolic thermal collectors. TRNSYS was employed to analyze the annual performance of the CPVT-VMD system evaluating parameters such as solar fraction, specific permeate production and specific energy production for different coastal cities. In the dynamic simulations, local annual weather data and specific information about the characteristics and operating conditions of a real CPVT collector and a VMD module were considered. From the parametric analysis the optimal surface area of collectors and the input temperature of the VDM module were determined. A maximum specific permeate of 218.410 m 3/m2VMD for Acapulco, MX, and a minimum of 170.365 m 3/m2VMD for Singapore, SG, were achieved for the proposed CPVT-VMD system of four solar collectors with an operating set temperature of 55 °C. An economic profit was found after 7 years for Acapulco city, which showed great potential to use solar energy from hybrid CPVT collectors for a VMD process to provide freshwater in coastal cities. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a viable technology and potential candidate for desalination of hypersaline wastewater. Nevertheless, MD membranes with high flux and superior antiwetting ability face a significant challenge for realizing high-efficient desalination. Herein, polyvinylidene fluoride (PVDF) hydrophobic porous membranes are fabricated by non-solvent induced phase separation. The structure of PVDF membranes, such as pore type, size, porosity, and surface hydrophobicity, can be well tuned over a wide range via adjusting phase separation conditions. To enhance the robustness of PVDF membrane, hydrophobized halloysite nanotubes (HNTs) are blended for membrane fabrication. The enhanced mechanical strength of membrane increases wetting resistance via inhibiting pore deformation and LEP reduction during salt crystals growth. In the treatment of hypersaline wastewater (70 g∙L−1) containing 3 g∙L−1 CaCl 2 and 3 g∙L−1 Na 2 SO 4 via VMD, the HNTs/PVDF membrane with 50 wt% HNTs shows a high flux of 54 L∙m−2∙h−1, over 99.99 % NaCl rejection, and outstanding stability for 100 h. Our work not only offers a novel strategy to enhance wetting resistance of MD membranes for hypersaline wastewater treatment, but also demonstrates that the mechanical strength of membranes also significantly influences antiwetting ability of MD membranes. [Display omitted] • Halloysite nanotubes are blended to enhance mechanical strength of PVDF membranes. • Robust membrane can improve the wetting resistance by inhibiting pore deformation. • The membrane exhibits both high flux (54 L∙m−2∙h−1) and NaCl rejection (> 99.99 %). • The membrane sustains > 100 h using a 7 wt% NaCl solution as the feed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The PVDF membranes with high aspect ratio and stable microstructures were prepared. • The peeling process was added to the traditional template method membrane. • The membrane exhibited excellent long-term stability in concentration test. • A model of the full VMD process with coupled heat-mass-flow was developed. In recent years, membrane distillation (MD) has emerged as an effective solution to mitigate the high energy consumption associated with conventional fermentable sugar concentration processes. However, the inherent low mechanical strength of traditional organic membrane surfaces can result in issues related to membrane wetting during long-term MD experiments. In this work, superhydrophobic PVDF/MWCNTs (multi-walled carbon nanotubes) distillation membranes with high mechanical strength were prepared by a combination of templating and co-blending techniques. The process involved peeling the semi-gelation membrane from a sandpaper template, subsequently forming a high aspect ratio microstructure on the membrane surface via tearing and pulling. Additionally, the incorporation of MWCNTs further bolstered the mechanical strength of the membrane. At a peeling time of 90 s and a MWCNTs content of 0.08 wt%, the distillation membrane exhibited an impressive water contact angle of 153.2°, indicating it possess exceptional hydrophobicity while maintaining high mechanical strength. The separation performance of the prepared distillation membranes has been inspected by conducting both experimental analyses and computational fluid dynamics (CFD) modeling of the entire MD process. An appropriate elevation in both feed flow rate and temperature could effectively mitigate the problem of temperature and concentration polarization on the membrane surface. PVDF/MWCNTs distillation membrane demonstrated a modest reduction in permeate flux of about 11.69 % and a stable rejection rate exceeding 99.95 % throughout a 100-hour operational period, and it required only 15 h to concentration of aqueous glucose solution to 100 g/L, significantly enhancing the efficiency of the process. This study also employed a combination of experiments and simulations to optimizes the process conditions guiding the vacuum membrane distillation (VMD) process and could provide guidance for the future application of membrane distillation in the concentration of sugar solutions. [ABSTRACT FROM AUTHOR]

Vacuum membrane distillation (VMD) has attracted increasing interest for various applications besides seawater desalination. Experimental testing of membrane technologies such as VMD on a pilot or large scale can be laborious and costly. Machine learning techniques can be a valuable tool for predicting membrane performance on such scales. In this work, a novel hybrid model was developed based on incorporating a spotted hyena optimizer (SHO) with support vector machine (SVR) to predict the flux pressure in VMD. The SVR–SHO hybrid model was validated with experimental data and benchmarked against other machine learning tools such as artificial neural networks (ANNs), classical SVR, and multiple linear regression (MLR). The results show that the SVR–SHO predicted flux pressure with high accuracy with a correlation coefficient (R) of 0.94. However, other models showed a lower prediction accuracy than SVR–SHO with R-values ranging from 0.801 to 0.902. Global sensitivity analysis was applied to interpret the obtained result, revealing that feed temperature was the most influential operating parameter on flux, with a relative importance score of 52.71 compared to 17.69, 17.16, and 14.44 for feed flowrate, vacuum pressure intensity, and feed concentration, respectively.

In this paper, an integrated system based on low-concentrated photovoltaic/thermal (LCPV/T) technology and efficient vacuum membrane distillation (VMD) seawater desalination utilizing the energy of solar is established. Through a theoretical analysis and a series of experiments, this paper explores the temperature change of a single VMD process, and the variation trend of single-day membrane flux with solar irradiation and temperature parameters. In addition, the changes in solar irradiation, temperatures of the integrated system, membrane flux, and thermoelectric properties in different seasons are also analyzed. A mathematical model was established to calculate the relationship between membrane flux and temperature difference. The experimental results show that the membrane flux of VMD is 2.73 L/(m2·h); the simulated seawater can achieve a desalination rate of 99.9%. After economic analysis, the operating incomes of the system under sunny weather conditions in different seasons were all positive. [ABSTRACT FROM AUTHOR]

With the rapid development of traditional Chinese medicine (TCM) industry, the treatment of TCM wastewater has become an important environmental issue. Among them, TCM processing cleaning wastewater is suitable for recovering high-quality water resources from it due to its low chemical oxygen demand (COD). Compared with pressure driven membrane process, Membrane distillation (MD) can yield highly purified distillate under mild operating conditions. Therefore, this work aims to evaluate the effects of feed temperature, feed flow, osmotic side vacuum degree and membrane material on the treatment of cleaning wastewater from TCM processing. Besides, the fouling of membrane in MD process and the efficiency of chemical cleaning on fouling removal were also investigated. The results show that it is feasible to recover high-quality water from traditional Chinese medicine processing cleaning wastewater by VMD. Compared with feed, COD in permeate decreased by 99%. During the 10 h experiment, the flux of both membranes decreased slightly due to the accumulation of fouling layer on the membrane surface. Chemical cleaning, especially alkali as cleaning agent can effectively remove the fouling layer. [Display omitted] • VMD can recover high quality water from the cleaning wastewater of traditional Chinese medicine processing. • The flux and thermal efficiency were significantly affected by temperature and vacuum. • The flux decrease occurred due to the formation of fouling layer. • Contact angle and rejection recovery of contaminated membranes can be achieved by NaOH cleaning. • PTFE membranes are more suitable than PVDF ones for long-term operation due to higher flux and anti wetting ability. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Tiangong University is the property of Journal of Tianjin Polytechnic University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Membrane material plays an important role in the membrane distillation technology. However, traditional membrane materials such as polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) and PP have existing membrane pollution and membrane infiltration problems, which limit further development of the membrane distillation technology. To solve these problems, the 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) has been added to the PTFE solution to create a novel super-hydrophobic PFDTES-PTFE membrane. A series of characterizations and characterization techniques have accordingly been used to study the structure and performance of the prepared membranes, such as atomic force microscope (AFM), water contact angle (WCA) measurements, liquid entry pressure (LEP) tests, vacuum membrane distillation (VMD) experiments, etc. The AFM analysis indicated a decreased roughness of the PFDTES-PTFE membrane. Moreover, the WCA of the membrane was increased from 131.3° to 137.5°, and the LEP increased by 33.3%, which indicated that the PFDTES-PTFE membrane showed excellent hydrophobicity and anti-wetting performances. What is more, the mean pore size was reduced from 269.6 to 205.0 nm, but there was a minor difference in film thickness. Furthermore, the VMD tests were implemented to evaluate the performance of the original and modified membranes with aspect to wetting. Compared to the pristine membrane, the modified PTFE membrane showed a slight decrease in membrane flux in the VMD process. However, the modified membrane kept a stable membrane flux about 0.932 L/(m2·h) with a salt rejection values of 99.8% after distillation for 3 h. In a word, the present study has proposed a new method to extend the membrane life, in favor of further developments of the membrane technology for islands and reef fields. [ABSTRACT FROM AUTHOR]

This paper focused on employing a vacuum membrane distillation system (VMD) driven by mechanical vapor recompression to achieve the sulfuric acid waste recovery. After establishing the mathematical models with the thermodynamic first and second laws considered simultaneously, the effects of critical parameters on the mass and heat transfer processes were first investigated. Furthermore, the effects of membrane area on thermodynamic characteristic of the system were explored. The simulation results showed that decreasing feed concentration or increasing feed temperature, feed velocity and permeate side pressure could strengthen heat and mass transfer process. Furthermore, increasing membrane area caused the total power consumption to exhibit a decline first followed by a rise and the exergy efficiency to exhibit a first rise followed by a decline. There was an optimal membrane area of 60 m² that minimized the total power to 10.04 kW and maximized the exergy efficiency to 19.06% at a feed concentration of 5%, feed temperature of 358.15 K, feed velocity of 1.0 m·s–1 and evaporation rate of 200 kg·h–1. The research results provide reference and technical support for the treatment of industrial waste acid. [ABSTRACT FROM AUTHOR]

This work was focussed on synthesizing a polyvinylidene fluoride (PVDF)–polytetrafluoroethylene (PTFE) hybrid flat sheet membrane using a nonhazardous solvent dimethyl sulfoxide (DMSO) for ethanol–water separation via vacuum membrane distillation (VMD). The base polymer (PVDF) concentrations were varied from 12 wt% to 16 wt% and the copolymer (PTFE) loading were ranged from 1 wt% to 2 wt% (e.g., 1.0 wt%, 1.5 wt%, and 2.0 wt%). The morphological characteristics, porosity, and contact angle (CA) were examined for the synthesized membranes. An increased CA was observed when PTFE loading was increased in the dope solution. The addition of PTFE to the dope solution efficiently diminished the formation of micro voids and increased the hydrophobicity of the membrane with improved characteristics. Membrane pore size, porosity, and thickness increased significantly from 0.17 µm to 0.21 µm, 48.37% to 67.79%, and 79.31 µm to 107.62 µm, respectively, within the studied range. A pure PVDF membrane CA of 88° was increased to 117.3° for 2 wt% loaded PTFE in PVDF. The synthesis of PVDF–PTFE hybrid membranes that used DMSO as a solvent and distilled water as a nonsolvent in a coagulation bath appears to be viable for membrane preparation via phase inversion to provide a reliable and sustainable separation process with a safer environment. The performance of the synthesized membrane was studied for flux and the separation factor. The maximum ethanol flux and separation factor obtained were 11 kg/m2/h and 7.0, respectively. This work suggests that the PVDF–PTFE hybrid flat sheet membranes could be used for ethanol separation in VMD. [ABSTRACT FROM AUTHOR]

Perfluoropolymer membranes are widely used because of their good environmental adaptability. Herein, the ultrafine fibrous FEP porous membranes were fabricated with electrospinning-sintered technology. The effects of PVA content and sintering temperature on the fabricated membranes' morphologies and properties were investigated. The results indicate that a kind of dimensionally stable network structure was formed in the obtained ultrafine fibrous FEP porous membranes after sintering the nascent ultrafine fibrous FEP/PVA membranes. The optimal sintering conditions were obtained by comparing the membranes' performance in terms of membrane morphology, hydrophobicity, mechanical strength, and porosity. When the sintering temperature was 300 °C for 10 min, the porosity, water contact angle, and liquid entry pressure of the membrane were 62.7%, 124.2° ± 2.1°, and 0.18 MPa, respectively. Moreover, the ultrafine fibrous FEP porous membrane at the optimal sintering conditions was tested in vacuum membrane distillation with a permeate flux of 15.1 L·m−2·h−1 and a salt rejection of 97.99%. Consequently, the ultrafine fibrous FEP porous membrane might be applied in the seawater desalination field. [ABSTRACT FROM AUTHOR]

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• A robust PP-SiO 2 -TiO 2 -PDA composite membrane with light-absorbing properties was prepared. • The photothermal effect induced by black PDA significantly enhances evaporation efficiency. • The PP-TiO 2 -SiO 2 -PDA composite membrane improved desalination performance in membrane distillation. • The porosity of the PP-TiO 2 -SiO 2 -PDA composite membrane (72%) is slightly higher than that of the original PP membrane. A robust silica-titania polydopamine composite membrane was fabricated adding a photothermal polydopamine coating to the surface of polypropylene membrane for photothermal vacuum membrane distillation. Detailly, the surface of an inert PP membrane was modified with atomically controllable titanium and silicon to enhance the hydroxyl groups on the membrane surface, then, a photothermal effect layer of polydopamine was generated on the composite membrane surface through the self-polymerization reaction of dopamine. The polydopamine coating has significant light absorption and heating properties, and it can act as a local heater when exposed to light sources. This local heating effect significantly raises the temperature at the membrane interface, creating a thermal gradient that drives the evaporation of water molecules. Specifically, we quantitatively analyzed the three reasons (surface energy, free radicals, and photothermal effect) for the increase in evaporation rate of the pristion PP membrane caused by the membrane composite membrane. Among these reasons, the photothermal effect caused by black polydopamine is the most important factor for improving evaporation efficiency. The dark-illumination alternating experiment revealed that the PP-TiO 2 -SiO 2 -PDA composite membrane delivered a noteworthy enhancement in vacuum membrane distillation performance (approximately 40%), while the improvement of the PP membrane was only 1.7%. [ABSTRACT FROM AUTHOR]

Conductive heating vacuum membrane distillation (CHVMD) is an emerging desalination technology. By heating the membrane surface with a heat carrier, it solves the issue of temperature polarization inherent in the membrane distillation process. However, additional research is needed to understand its heat and mass transfer. Herein, aluminum heat carrier was enhanced by incorporating graphene (GPE) and hydrophobic silica (SiO 2) nanoparticles, and the effects of these heat carriers on heat and mass transfer were discussed. Results showed that the graphene-modified heat carrier had a higher infrared emissivity, effectively enhancing radiative heat dissipation and increasing the internal temperature by 1.8 ℃. The SiO 2 nanoparticles improved the evaporation efficiency of feed by altering the liquid surface curvature, resulting in an 11.5 % increase in flux. Additionally, the flux increased to 12.1 L/(m2·h), and the specific energy consumption decreased by 20 % using GPE/SiO 2 composite-modified heat carrier. Furthermore, the modified carrier demonstrated a notable 23.3 % increase in thermal efficiency. This feat was made possible by the innovative double-sided heat carrier modification, forming a dual liquid layer structure upon contact with the feed. These results highlight the effectiveness of the modification heat carrier enhancing the CHVMD system's heat and mass transfer. • Modified heat carriers were prepared for conductive heating vacuum membrane distillation process. • Using graphene coating heat carriers increased the internal temperature of the MD module by 1.8 ℃. • The heat carrier with SiO 2 nanoparticles raised water vapor pressure and causing an 11.5 % flux rise. • GPE/SiO 2 -Al heat carrier achieved the thermal efficiency of 91.9 %. [ABSTRACT FROM AUTHOR]

In this work, a bench-scale vacuum membrane distillation crystallization (VMDC) system coupled with microbubble aeration (MBA) was developed for treating high-salinity feed brine. Herein, the effect of seeding dose on membrane fouling and wetting control in the VMDC system was studied by using synthetic saturated calcium sulfate solution. The results showed that introducing gypsum seeds at a dose of 0.5 g/L effectively restricted membrane fouling and wetting. Subsequently, seeding-induced crystallization coupled with MBA was employed to investigate the control effect on membrane fouling and wetting during VMDC with simulated high-salinity feed brine treatment. As 0.5 g/L gypsum seeds were directly added at 7 h in the VMDC experiment while employing MBA, membrane fouling and wetting were effectively controlled. Finally, the mechanism behind the control of membrane fouling and wetting was elucidated during VMDC operation by integrating seeding-induced crystallization with MBA. This could be ascribed to the synergic effect of gypsum seeds and microbubbles in bulk solution. In brief, this work offers a promising approach to control membrane fouling and wetting during concentrating high-salinity wastewater by VMD. [Display omitted] • A novel approach to control membrane fouling and wetting was proposed. • Seeding-induced crystallization inhibited the occurrence of membrane pore wetting. • Membrane scaling control was enhanced by integrating seeding-induced crystallization with microbubble aeration. [ABSTRACT FROM AUTHOR]

Numerical simulations were carried out to assess the technical and economic feasibility of a solar water desalination system that has a novel hybrid Concentrating Photovoltaic Thermal (CPVT) collector coupled with a Vacuum Membrane Distillation (VMD) process. A special characteristic of this CPVT is its triangular receiver with PV cells facing the reflecting surface. This type of receiver has the advantage of generating more electricity with less PV surface area and great potential to be used to hybridize conventional parabolic thermal collectors. TRNSYS was employed to analyze the annual performance of the CPVT-VMD system evaluating parameters such as solar fraction, specific permeate production and specific energy production for different coastal cities. In the dynamic simulations, local annual weather data and specific information about the characteristics and operating conditions of a real CPVT collector and a VMD module were considered. From the parametric analysis the optimal surface area of collectors and the input temperature of the VDM module were determined. A maximum specific permeate of 218.410 m 3/m2VMD for Acapulco, MX, and a minimum of 170.365 m 3/m2VMD for Singapore, SG, were achieved for the proposed CPVT-VMD system of four solar collectors with an operating set temperature of 55 °C. An economic profit was found after 7 years for Acapulco city, which showed great potential to use solar energy from hybrid CPVT collectors for a VMD process to provide freshwater in coastal cities.

Membrane distillation seawater desalination technology has received widespread attention. However, this technology has problems such as high energy consumption and high initial temperature requirements. A membrane distillation seawater desalination system integrated with low-concentrating photovoltaic/thermal (LCPV/T-MD) modules was designed. With the help of concentrating photovoltaic panels and solar collectors, the working fluid required for membrane distillation is cascaded heating to obtain distilled fresh water. The integrated LCPV/T-MD mathematical model the hybrid experimental system were established, and the thermal, electrical performance, and water yield were analyzed. The results show that the greater Δ P , the lower of the salinity c , and the higher the inlet water temperature T in , the greater the water yield. The LCPV/T-STC heating subsystem can heat the water temperature above 60 °C, and then auxiliary heating by heating rod can meet the requirements of MD system for inlet water temperature. In the experiment, the thermal efficiency and the electrical efficiency of the system can reach 56.2% and 15.9%, respectively. The GOR of the total LCPV/T-MD system can reach 0.69, and the MD subsystem water yield can reach 0.579 L/(h·m2). The findings can provide guidance for the further study of membrane distillation. • A membrane distillation module with low concentrating photovoltaic/thermal system was designed. • Both pressure difference and inlet saline water temperature have positive influence on water yield and GOR. • The outlet water temperature of LCPV/T-STC can meet the requirement of the MD subsystem inlet water temperature. • The maximum thermal and electrical efficiency reach 56.2% and 15.9%, the experimental water yield gets 0.579 L/(h m2). [ABSTRACT FROM AUTHOR]

This study focuses on modeling the mass transfer process in the vacuum membrane distillation method (commonly used for radioactive wastewater) by means of artificial neural networks (ANNs). For this purpose, the permeate flux is modeled as a function of four system parameters (pollutant type, feed temperature, permeate temperature, and permeate pressure). To determine the best suitable model for the considered system, several structures of ANNs were analyzed. The results obtained indicated that a feed forward multilayer perceptron neural networks with a hidden layer and ten neurons in hidden layer and with determination of coefficient of 0.975 and maximum root mean squared error of 1.83% can predict the permeate flux with desirable accuracy. [ABSTRACT FROM AUTHOR]

In this paper, an integrated system based on low-concentrated photovoltaic/thermal (LCPV/T) technology and efficient vacuum membrane distillation (VMD) seawater desalination utilizing the energy of solar is established. Through a theoretical analysis and a series of experiments, this paper explores the temperature change of a single VMD process, and the variation trend of single-day membrane flux with solar irradiation and temperature parameters. In addition, the changes in solar irradiation, temperatures of the integrated system, membrane flux, and thermoelectric properties in different seasons are also analyzed. A mathematical model was established to calculate the relationship between membrane flux and temperature difference. The experimental results show that the membrane flux of VMD is 2.73 L/(m2·h); the simulated seawater can achieve a desalination rate of 99.9%. After economic analysis, the operating incomes of the system under sunny weather conditions in different seasons were all positive.

Seawater desalination using conventional vacuum membrane distillation is facing a grave problem of high specific heat consumption (SHC). In order to deal with this issue, energy of the saline feed is recovered in multi-stage vacuum membrane distillation (MSVMD). The present study is aimed to analyze the energetics of MSVMD in terms of SHC, gained output ratio (GOR), and specific membrane area (SMA) as a function of process parameters. An attempt was made to determine the optimum number of stages for the maximum permeate productivity. Further, the impact of multi-staging on MSVMD energetics was also analyzed. A drop in cumulative SHC, GOR, and SMA was found with the corresponding rise in feed inlet temperature. Rising saline feed flowrates enhanced the cumulative SHC and GOR, however, it declined the SMA. The economics of MSVMD in terms of levelized cost of water (LCOW) were also investigated. It was observed that the permeate enhancing conditions such as a rising saline feed temperature from 60°C to 100°C depreciates the LCOW by about 57 USD/m³. Similarly, a decline in the LCOW was noticed with a surge in saline feed flowrate and vacuum pressure. Multi-staging initially dropped the LCOW, but it was found that after a certain number of stages, further addition would cause an upsurge in the LCOW. [ABSTRACT FROM AUTHOR]

Recently, the seawater and brackish water desalination process have gained widespread attention due to the scarcity of drinking water. Among several membrane distillation (MD) methods for desalination, vacuum membrane distillation (VMD), and direct contact membrane distillation (DCMD) are mostly focused techniques. However, there are several technical issues associated with these techniques that have a negative impact on their performance. The most influential of them are temperature polarization (TP) and concentration polarization (CP) that reduces the permeate flux significantly. A state-of-the-art review is presented to gain a clear understanding of, the impact of both the TP and CP on various performance parameters and methods to overcome these obstacles. The main focus is on the causes of TP and CP, theoretical models, experimental key findings for TP and CP, and their impact on the performance of VMD and DCMD. For DCMD, the value of TPC for channels with spacers falls in the range of 0.9–0.97, whereas for flow channels without spacers, the TPC was in the range of 0.57–0.76. Finally, different methods are discussed to overcome the TP and CP. [ABSTRACT FROM AUTHOR]

• A novel VMD-Fenton oxidation process was proposed to treat the low-level radioactive organic wastewater. • The wastewater can meet the national standards for direct discharge after treatment. • The weak hydrogen bonds between PTFE membrane and contaminants were found to cause the reversible membrane fouling. During the production of UO 2 kernel for the high temperature gas-cooled nuclear reactor, a large amount of low-level radioactive organic wastewater (LLROW) containing ammonia, uranium and organic compounds are generated. The current treatment process is suffered from the production of radioactive solid wastes, low adsorption efficiency of organic matters and the frequent membrane fouling during RO process. In this study, vacuum membrane distillation (VMD)-Fenton oxidation process was developed for the deep purification of the LLROW. The process parameters were optimized and the system performance was evaluated. As a result, all major contaminates such as uranium, NH 3 -N, TN and COD could meet the GB8978-1996 (secondary standard) and GB/T31962-2015 (B standard) for direct discharge. The membrane fouling was also studied by membrane autopsy as well as the quantum calculation. It was found that weak hydrogen bonds were formed between PTFE membrane and contaminants while the membrane fouling could be recovered by 0.1 M HCl cleaning. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) has received ample recognition for treating complex wastewater, including hypersaline oil and gas (O&G) produced water (PW). Rigorous water quality assessment is critical in evaluating PW treatment because PW consists of numerous contaminants beyond the targets listed in general discharge and reuse standards. This study evaluated a novel photocatalytic membrane distillation (PMD) process, with and without a UV light source, against a standard vacuum membrane distillation (VMD) process for treating PW, utilizing targeted analyses and a non-targeted chemical identification workflow coupled with toxicity predictions. PMD with UV light resulted in better removals of dissolved organic carbon, ammoniacal nitrogen, and conductivity. Targeted organic analyses identified only trace amounts of acetone and 2-butanone in distillates. According to non-targeted analysis, the number of suspects reduced from 65 in feed to 25–30 across all distillate samples. Certain physicochemical properties of compounds influenced contaminant rejection in different MD configurations. According to preliminary toxicity predictions, VMD, PMD with and without UV distillate samples, respectively contained 21, 22, and 23 suspects associated with critical toxicity concerns. Overall, non-targeted analysis together with toxicity prediction provides a competent supportive tool to assess treatment efficiency and potential impacts on public health and the environment during PW reuse. [Display omitted] • Non-targeted chemical screening tools were used to evaluate treated produced water. • Fates of different suspect compounds were studied. • Photocatalytic membrane distillation resulted in better removal of dissolved organics. • Human health and environment-based concerns of suspect compounds were discussed. • Non-targeted chemical screening is helpful in identifying critical target analytes. [ABSTRACT FROM AUTHOR]

Membrane distillation has emerged as a promising technique for treating high-saline water. However, the process suffers from drawbacks such as wettability and fouling due to insufficient hydrophobicity of the membrane material. A practical approach for preparing hydrophobic membranes should involve improving surface roughness and chemistry manipulation. Herein, we explored chemical grafting of different functional groups viz. 1-(4-vinyl benzyl)azepane, N-(4-vinyl benzyl)decan-1-amine and 3-(triethoxysilyl)-N-(4-vinyl benzyl) propane-1-amine on polyvinylidene fluoride side chain to improve the hydrophobic characteristics and vacuum distillation performance (permeate flux and salt rejection). The successful grafting of hydrophobic functional groups on the polyvinylidene fluoride side chain was confirmed by spectral analysis such as 1H nuclear magnetic resonance, Attenuated total reflectance-Fourier transformation infrared spectroscopy, and X-ray photoelectron spectroscopy. The synthesised membranes were further characterised using morphology techniques (scanning electron microscopy, atomic force microscopy) for hydrophobicity (water contact angle, liquid entry pressure) and thermal and mechanical stability. The desalination performance of membranes was assessed by varying feed concentration (2–8 % NaCl) and feed temperature (30–75 °C). The 3-aminopropyltriethoxysilane grafted vinyl benzyl polyvinylidene fluoride membrane exhibited the highest flux (20.35 L m−2 h−1), salt rejection (99.99 %) at 4 % NaCl feed concentration and 60 °C feed temperature attributed to a well-arranged large number of pores and its hydrophobicity. The 3-aminopropyltriethoxysilane grafted membrane exhibited the highest anti-fouling characteristic. Further, high flux and salt rejection of the synthesised membranes for vacuum membrane distillation operation were compared to membranes reported in the literature, demonstrating its potential for high saline water desalination. [Display omitted] • Flat-sheet side chain chemical grafted PVDF membranes were prepared via NIPS. • Effect of feed concentration, and temperature; and anti-fouling characteristics of the membranes were studied. • M-APTES membrane exhibited the highest flux, salt rejection and anti-fouling characteristics. [ABSTRACT FROM AUTHOR]

• A Janus PTFE composite membrane was fabricated via a LbL method. • The membrane surface wettability and morphology were facilely manipulated. • The membrane has excellent scaling-, fouling- and wetting-resistances in MD. • The possible mechanism of scaling and fouling resistance was analyzed deeply. Development of membranes with robust anti-scaling and anti-fouling properties are highly required for vacuum membrane distillation (VMD) of saline solution. Therefore, we proposed a facile and benign strategy to construct a polytetrafluoroethylene (PTFE)-based membrane with an asymmetric surface wetting Janus structure consisting of a hydrophobic PTFE substrate and a thin hydrophilic hydrogel-like coating layer. The coated layer was made of the ionic cross-linked alginate and chitosan networks through electrostatic interaction and hydrogen bonding. Owing to the favorable swelling behavior and reduced water evaporation enthalpy of hydrogel top layer, the Janus composite membranes (noted as PTFE@CS/SAH) maintained the stable vapor flux of 32 L m−2 h−1 at 50 °C. Notably, the PTFE@CS/SAH sustained stable desalination efficiency for the treatment of challenging saline solution containing mineral oil or surfactant. Moreover, the long-term VMD operation test demonstrated that PTFE@CS/SAH exhibited strong scaling- and organic fouling- resistance facing simulated seawater. The simultaneous anti-scaling and anti-fouling mechanism of PTFE@CS/SAH have been systematically investigated and summarized as the synergistic effect of dense hydration layer, favorable electrostatic interaction as well as the robust capillary pressure imparted by coating layer. This work brings fresh insights for the controllable design and construction of Janus structured membranes for VMD application. [ABSTRACT FROM AUTHOR]

The vacuum membrane distillation (VMD) process was applied to separate ethanol from a simulated ethanol–water solution using a commercial polytetrafluoroethylene (PTFE) membrane. The presence of ethanol in the ethanol–water solution with a 2 wt.% ethanol concentration at a temperature above 40 °C during the MD process may result in membrane failure due to an increase in the chance of the PTFE membrane wetting at high temperatures. Therefore, the operating temperature in this study was not higher than 35 °C, with an initial ethanol concentration up to 10 wt.%. This work focuses on optimizing the VMD operating parameters using the Taguchi technique based on an analysis of variance (ANOVA). It was found that the feed temperature was the most-affected parameter, leading to a significant increase in the permeation flux of the PTFE membrane. Our results also showed that the permeate flux was reported at about 24.145 kg/m2·h, with a separation factor of 8.6 of the permeate under the operating conditions of 2 wt.%, 30 °C, 60 mm Hg(abs), and 0.6 L/min feed (concentration, temperature, permeate vacuum pressure, and flow rate, respectively). The initial feed concentration, vacuum pressure, and feed flow rate have a lower impact on the permeation flux.

In this paper, exergoeconomic and exergoenvironmental analyses of a solar vacuum membrane distillation (VMD) desalination system were performed to evaluate the cost of exergy destruction and the environmental impact of each component of the desalination system. The analysis permits the identification and evaluation of inefficiencies in the plant as well as the determination of the most environmental friendly process components and opportunities for design improvements. The results showed that the solar collector has the largest irreversibility and cost of exergy destruction. Therefore, it is a very important component for improving solar VMD plant performance. In addition, it will be profitable to reduce exergy losses in the membrane module even at the expense of increased investment costs since the dominant factor in the total cost rate for this component is the cost of exergy destruction. Whereas, it would be advantageous to reduce capital costs in the condenser since it has a relatively high exergoeconomic performance. On the other hand, exergoeconomic factor and exergy efficiency for the heat exchanger are found to be 49.02% and 96.59%, respectively, indicating that the exergy and exergoeconomic performance of this component is satisfactory. Finally, the results revealed that the largest potential for reducing the overall environmental impact of the solar VMD system is associated with the solar collector, the membrane module, the condenser, and the heat exchanger. [ABSTRACT FROM AUTHOR]

Water recovery by membrane distillation (MD) is an attractive alternative to existing urine treatment systems because it could improve the water recovery rate and reliability in space missions. However, there are few studies of urine MD, particularly on the removal of the remaining contaminants from distillate water and the assessment of its long-term performance. In this study, the influences of various operation parameters on distillate water quality and operation stability were investigated in batch mode. The low pH of feedstock reduced the conductivity and total ammonium nitrogen (TAN) in distillate water because the low pH promoted the ionization of ammonia to ammonium ions. However, the low pH also facilitated the formation of free chlorine hydride, which resulted in the minor deterioration of the conductivity in the distillate due to the increasing volatility of chlorine hydride in the feedstock. Thirty batches of vacuum membrane distillation (VMD) experiments demonstrated that the permeate flux and the distillate water quality slightly decreased due to the small range of membrane wetting but still maintained an over 94.2% and 95.8% removal efficiency of the total organic carbon (TOC) and TAN, and the conductivity was −1 in the distillate water after 30 test batches. VMD is a feasible option for urine treatment in space missions.

Hollow fiber membranes were produced from a commercial polyvinylidene fluoride (PVDF) polymer, Kynar HSV 900, with a unique sandwich structure consisting of two sponge-like layers connected to the outer and inner skin layers while the middle layer comprises macrovoids. The sponge-like layer allows the membrane to have good mechanical strength even at low skin thickness and favors water vapor transportation during vacuum membrane distillation (VMD). The middle layer with macrovoids helps to significantly reduce the trans-membrane resistance during water vapor transportation from the feed side to the permeate side. Together, these novel structural characteristics are expected to render the PVDF hollow fiber membranes more efficient in terms of vapor flux as well as mechanical integrity. Using the chemistry and process conditions adopted from previous work, we were able to scale up the membrane fabrication from a laboratory scale of 1.5 kg to a manufacturing scale of 50 kg with consistent membrane performance. The produced PVDF membrane, with a liquid entry pressure (LEPw) of >3 bar and a pure water flux of >30 L/m2·hr (LMH) under VMD conditions at 70–80 °C, is perfectly suitable for next-generation high-efficiency membranes for desalination and industrial wastewater applications. The technology translation efforts, including membrane and module scale-up as well as the preliminary pilot-scale validation study, are discussed in detail in this paper.