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A vacuum membrane distillation bioreactor (VMDBR) by permeate fractional condensation and mechanical vapor compression with PTFE membrane was developed for bioethanol production. Cell concentration of 11.5 g/L, glucose consumption rate of 5.2 g/L/h and ethanol productivity of 2.3 g/L/h could be obtained with fermentation continues lasting for 140 h. Membrane flux of over 10 kg/m 2 /h could be obtained for model solution separation. Higher temperature and flow rate could promote membrane separation. Membrane flux could be reduced to about 2000 g/m 2 /h with fermentation proceeding owing to the deposited cell on membrane surface. The membrane separation performance could be resumed by water rinse. High ethanol concentration of 421 g/L could be obtained by permeate fractional condensation with the process separation factor increased to 19.2. Energy of only 14 MJ/kg was required in VMDBR and the energy consumption would be reduced further if the compressed vapor could be used to heat the feed., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The vacuum membrane distillation (VMD) is a promising technology for lots of applications. To solve the membrane fouling and wetting problems, in this paper, a novel ZnO nanorods 1 H,1 H,2 H,2 H-perfluorodecyltriethoxysilane (PDTS) modified poly(vinylidene fluoride) (PVDF) membrane with a micro/nanoscale hierarchical structure and a superhydrophobic surface has been prepared and applied to the VMD process for distilling highly salty water, for the first time. Among these, a pyrolysis-adhesion method is created to obtain the ZnO seeds and fasten them on the PVDF substrate firmly. The novel modified membrane shows a stable superhydrophobic surface with a water contact angle of 152°, easy cleaning property, excellent thermal and mechanical stability, because of the Cassie's state caused by pocketing much air in the hydrophobized ZnO nanorods, the low surface energy of PDTS coating, and the strong adhesion between ZnO nanorods and PVDF membrane, which has built an ideal structure for VMD application. After 8 h VMD of 200 g L -1 NaCl solution, compared to the virgin PVDF membrane, the novel membrane shows a similar permeate flux but a much higher quality permeated liquid because of its unique antifouling and antiwetting caused by the several microns gap between the feed and the membrane. Due to its easy cleaning property, the novel membrane also exhibits an excellent reusability.

Four main tasks were presented: (i) ceramic membrane functionalization (TiO 2 5 kDa and 300 kDa), (ii) extended material characterization (physicochemistry and tribology) of pristine and modified ceramic samples, (iii) evaluation of chemical and mechanical stability, and finally (iv) assessment of membrane efficiency in vacuum membrane distillation applied for volatile organic compounds (VOCs) removal from water. Highly efficient molecular grafting with four types of perfluoroalkylsilanes and one nonfluorinated agent was developed. Materials with controllable tribological and physicochemical properties were achieved. The most meaningful finding is associated with the applicability of fluorinated and nonfluorinated grafting agents. The results of contact angle, hysteresis of contact angle, sliding angle, and critical surface tension as well as Young's modulus, nanohardness, and adhesion force for grafting by these two modifiers are comparable. This provides insight into the potential applicability of environmental friendly hydrophobic and superhydrophobic surfaces. The achieved hydrophobic membranes were very effective in the removal of VOCs (butanol, methyl-tert-butyl ether, and ethyl acetate) from binary aqueous solutions in vacuum membrane distillation. The correlation between membrane effectiveness and separated solvent polarity was compared in terms of material properties and resistance to the wetting (kinetics of wetting and in-depth liquid penetration). Material properties were interpreted considering Zisman theory and using Kao diagram. The significant influence of surface chemistry on the membrane performance was noticed (5 kDa, influence of hydrophobic nanolayer and separation controlled by solution-diffusion model; 300 kDa, no impact of surface chemistry and separation controlled by liquid-vapor equilibrium).

Membrane distillation (MD) is a promising separation technique capable of being used in the desalination of marine and brackish water. Poly(vinylidene fluoride) (PVDF) flat sheet nano-composite membranes were surface modified by coating with electro-spun PVDF nano-fibres to increase the surface hydrophobicity. For this purpose, the nano-composite membrane containing 7 wt.% superhydrophobic SiO2 nano-particles, which showed the highest flux in our previous work, was first subjected to pore size augmentation by increasing the concentration of the pore forming agent (Di-ionized water). Then, the prepared flat sheet membranes were subjected to nanofibres coating by electro-spinning. The uncoated and coated composite fabricated membranes were characterized using contact angle, liquid entry pressure of water, and scanning electron microscopy. The membranes were further tested for 6 h desalination by direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD), with a 3.5 wt.% synthetic NaClaq as the feed. In DCMD the feed liquid and permeate side temperature were maintained at 27.5 °C and 15 °C, respectively. For VMD, the feed liquid temperature was 27 °C and a vacuum of 94.8 kPa was applied on the permeate side. The maximum permeate flux achieved was 3.2 kg/m(2).h for VMD and 6.5 kg/m(2).h for DCMD. The salt rejection obtained was higher than 99.98%. The coated membranes showed a more stable flux than the uncoated membranes indicating that the double layered membranes have great potential in solving the pore wetting problem in MD., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Water pollution of volatile organic compounds (VOCs) was a serious environment problem. Vacuum membrane distillation (VMD) was an environmental friendly membrane separation technology to treat VOCs wastewater. Aqueous binary mixtures of ethyl acetate were treated by VMD process. Comparisons were made between different membrane modules for investigating the influence of channel on the membrane separation performance. Three kinds of channel presented different useful area, shape, width, and depth. The arc flow channel was more easier to reduce resistance than square flow channel. Operation parameters influencing flux and separation performance were examined: feed-flow rate, feed concentration, vacuum degree, and feed temperature. Vacuum degree and feed temperature had more significant influence on membrane flux and separation factor than other parameters. The effect of membrane type on separation properties was also investigated, the smaller pore membrane was better for increasing the separation factor. Three membrane modules with various channels were used for experiments. VMD is very suitable for low concentration of aqueous solution VOC separation and better experimental separation performance could be obtained. [ABSTRACT FROM AUTHOR]

The polyvinylidene fluoride hollow fiber hydrophobic membrane was applied in vacuum membrane distillation (VMD) process for the treatment of reverse osmosis-concentrated wastewater from a steel plant. The effects of pretreatment methods on the CODcr removal, the performance and membrane fouling of VMD process were studied. The morphology and composition of the fouling layer were studied by scanning electron microscope and energy dispersive spectroscopy, respectively. The reason for the flux declination in VMD process was discussed. The results showed that the CODcr removal reached 40%, and the flux of VMD process was increased after the pretreatment of coagulation and ultrafiltration, when the concentration factor reached eight, the flux of VMD process using properly pretreated solution was 30% higher than that using un-pretreated solution as the feed. The membrane surface morphology and elemental analysis testified that the fouling of membrane surface was obviously alleviated by pretreatment. [ABSTRACT FROM AUTHOR]

The fluid flow in a rectangular channel is observed by a high-speed fluid field display system, and the fluid appearances under different operate parameters are presented pictorially. Numerical simulations are performed to investigate brine desalination by vacuum membrane distillation (VMD) with three different channel configurations (rectangular, serpentine and spiral) to compare the effect of channel configuration on the process. The results obtained from simulation are analysed from the viewpoint of field synergy. This study concludes that better field synergy leads to better membrane permeability flux. The spiral channel shows the best performance in enhancing heat transfer and increasing the synergy. Increasing the co-direction component of the multi-field could enhance the transfer process. The numerical simulation results are consistent with experimental results. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a thermally driven membrane process using porous hydrophobic membranes. MD has been investigated as an alternative desalination technology due to its advantages over multi-stage flash (MSF) and reverse osmosis (RO). Nevertheless, it is difficult to design and optimize the MD systems under various conditions, because both thermal and hydrodynamic effects play an important role. Therefore, this study focused on performance analysis of MD systems in different configurations. Direct contact MD (DCMD) and vacuum MD (VMD) were experimentally compared using laboratory-scale systems. A simple model was also applied to analyze the difference between two configurations theoretically. Experimental results indicated that permeate flux in DCMD and VMD were sensitive to the operating conditions. Using same membranes, two MD systems showed different flux behaviors. The influences of operating parameters for DCMD and VMD on overall efficiency were also investigated. The model results also confirmed the difference between these two systems theoretically. [ABSTRACT FROM AUTHOR]

Low sugar concentration and the presence of various inhibitors are the major challenges associated with lignocellulosic hydrolyzates as a fermentation broth. Vacuum membrane distillation (VMD) process can be used to concentrate sugars and remove inhibitors (furans) efficiently, but it's not desirable for the removal of less volatile inhibitors such as acetic acid. In this study, a VMD-adsorption process was proposed to improve the removal of acetic acid, achieving simultaneous concentration and detoxification of lignocellulosic hydrolyzates by one step process. Results showed that sugars were concentrated with high rejections (>98%) and little sugar loss (<2%), with the significant reduction in nearly total furans (99.7%) and acetic acid (83.5%) under optimal operation conditions. Fermentation results showed the ethanol production of hydrolyzates concentrated and detoxified using the VMD-adsorption method were approximately 10-fold greater than from untreated hydrolyzates., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Vacuum membrane distillation, like any membrane distillation process, is a thermally driven process in which the convective mass transfer is the dominant mechanism for mass transfer. The driving force is maintained by applying vacuum at the downstream side to keep the pressure at this side below the equilibrium vapor pressure (see Fig. 1). The membrane in this process is a physical support for the vapor-liquid interface and does not affect the selectivity associated with the vapor-liquid equilibrium. Vacuum membrane distillation has the potential to be one of the most common techniques, in environmental engineering, used to separate dilute aqueous mixtures, such as in the removal of ethanol from fermentation broth to prevent the inhibition of the microorganisms used in fermentation, and for the removal of trace concentrations of VOC''s. In addition to that, VMD can be used when the feed contains non-volatile salt as in desalination. The objective of this article is to determine the most important mass transfer resistance in vacuum membrane distillation in the case of removal of trace VOC''s. Simple criteria used without the need to solve the mathematical model. [Copyright &y& Elsevier]