Membrane Distillation (MD) is based on the evaporation of a hot feed through a microporous and hydrophobic membrane. Thermal energy is needed to heat the feed up to the desired temperature during the ...process. Therefore, improvements of the thermal performance of MD are important to apply this technology at large scale. The Special Issue “Thermal Performance of Membrane Distillation” focuses on the recent research efforts made in this direction, covering both the development of new membranes and the optimization of the process.
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•A novel submerged vacuum membrane distillation module that utilizes solar energy is developed.•Solar evacuated tube collectors are used as the feed container.•The system achieved a ...stable water production under different scenarios (weather profiles).•Feed agitation enhanced the water production rate by 22%.
Submerged membrane distillation (S-MD) has been proposed as an alternative to conventional cross-flow MD systems to desalinate hypersaline water. In conventional S-MD systems, the hydrophobic membrane is submerged in the feed water tank that is directly heated by an electric heating element, eliminating the need for feed pumping. In this study, a solar-heated submerged vacuum membrane distillation (S-VMD) system that uses an evacuated tube collector as the feed container is proposed. Indoor tests under steady-state operating conditions and daily outdoor tests under ambient weather conditions were conducted to investigate the system’s functionality. The effect of two agitation techniques (aeration and internal circulation) to reduce temperature and concentration polarizations were studied. The daily performance tests revealed that the solar-heated S-VMD system can achieve a permeate flux of 5.9–11.1 kg·m−2·h−1 depending on solar intensity. The permeate flux was enhanced by 9% under aeration and by 22% under circulation in the outdoor tests. The water production per solar absorbing area can be as high as 0.96 kg·m−2·h−1. The system maintained a stable permeate flux and excellent water quality over a long-term operation. The small-scale system can provide fresh water in remote areas with limited natural resources.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
It is well known that the mass flux (J) and the membrane thermal efficiency (η) of membrane distillation increase with the feed flow temperature. A comprehensive laminar and turbulent flow model for ...simulating and evaluating the performance of direct contact membrane distillation (DCMD) when operated at inlet feed temperature (Tf,i) from 80°C to 180°C, higher than the customary maximum of ~80°C, was developed and used to explain and assess the performance of such high temperature DCMD, as well as the potential associated problems of the needed higher operating pressure, and provide knowledge useful for their future design and optimization. Some of the key results are that raising Tf,i from 80°C to 180°C, increases J 9.4-fold, and η 2.1-fold, and decreases the specific energy consumption (SEC) 2.9-fold. Raising the flow Reynolds number from 1200 to 7000 increases J 2.6-fold and η by 15%, but SEC increases 2.3-fold. The needed system pressurization does not affect the process performance significantly. The higher operating temperatures also provide more practical opportunities for heat recovery, which could significantly further raise overall system efficiency.
•High temperature membrane distillation•High temperature membrane water desalination•Numerical analysis of high temperature membrane distillation•Membrane properties effects in high temperature membrane distillation•High temperature direct contact membrane distillation
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Six Hyflon/PVDF composite membranes were prepared and tested in membrane distillation.•MD performance was related to membranes structure.•Pore size, porosity, LEP, contact angle and thickness ...influence membrane performance.
Membrane distillation (MD) is a promising technology for the treatment of highly saline waters. However, there are few microporous hydrophobic membranes, available as hollow fibers and flat sheets, properly manufactured for MD. In the present paper, highly hydrophobic Hyflon/PVDF composite hollow fiber membranes were prepared by coating three kinds of Hyflon AD on poly(vinylidene fluoride) (PVDF) membranes. The PVDF hollow fiber membranes were prepared via two different techniques (i.e. NIPS and TIPS). The six different Hyflon AD/PVDF composite membranes were characterized and tested in MD, both in direct contact (DCMD) and vacuum (VMD) configuration. The testing of the membranes in VMD showed that the performance of the different membranes was, as expected, strongly dependent on pore size, porosity, liquid entry pressure (LEP) and contact angle (Φ). DCMD experiments revealed that another parameter influencing the membrane performance is the thickness because it allows reducing the heat loss due to conduction through the membrane.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Pilot-scale VMD plant with 8.0 m3/d production was developed.•Design scheme and schematic of VMD pilot plant were detailed.•High DF of 104.85 for Cs and high CF of 110.3 were ...achieved.•Detailed evaluation of energy efficiency through STEC and GOR was conducted.•Heat loss of pilot-scale membrane module as heat pinch effect was analyzed.
A pilot-scale vacuum membrane distillation (VMD) demonstration plant for decontamination of radioactive wastewater with 8.0 m3/d water production was developed. The design scheme, main components and functions of VMD pilot plant were detailed. Effects of operational parameters on permeate flux, gain output ratio (GOR) and decontamination factor (DF) of simulated radioactive wastewater were analyzed. As feed temperature increased from 70℃ to 90℃, permeate flux grew exponentially from 1.59 kg/(m2·h) to 6.82 kg/(m2·h). High DF 104.85 of Cs+ and high concentration factor (CF) 110.3 of simulated radioactive wastewater were reached with stable permeate flux in pilot-plant-scale. DF of Cs+ and GOR were relatively stable under various operation conditions. The outlet temperature of membrane modules increased with the growth of flow rate, bringing about 9 °C temperature difference between 2 m3/h and 14 m3/h at the same inlet temperature of 70 °C. The significant heat loss in radial direction as temperature polarization and in axial direction as the heat pinch effect in hollow fiber membrane modules are the main issues for large-scale MD plant. This study demonstrates a remarkable potential of VMD for decontamination of radioactive wastewater and provides an integrated design of VMD pilot-scale plant.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Solar-powered membrane distillation (SP-MD) is examined as a promising renewable solution in the desalination and water treatment industry. In this study, an innovative direct contact membrane ...distillation (DCMD) module to directly utilize solar thermal energy is proposed. While previous studies focused more on utilizing solar energy indirectly (i.e. to heat the feed water outside the MD module), the proposed system integrates hollow fiber membranes inside evacuated tube solar collectors in order to achieve a more compact system. The performance of the direct SP-MD module is measured first indoors in a bench-scale experiment, and then tested outdoors under sunlight. Results show that applying radiation directly can enhance the efficiency and permeate flux up to 17% compared to the same process when radiation is not applied under the same operating conditions. The daily operation of a stand-alone, directly heated SP-MD unit equipped with 0.035 m2 membrane area achieved a permeate flux of 2.2 to 6.5 kg·m−2·h−1 depending on solar intensity.
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•A novel direct contact membrane distillation module to directly utilize solar energy is demonstrated.•Hollow fiber membranes are integrated within a solar evacuated tube collector.•Indoor and outdoor experiments were carried out.•The permeate flux varied between 2.2 and 6.5 kg·m−2·h−1 when tested under ambient sunlight.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Co3O4/NCDs-PVDF (CN-PVDF) membrane was first applied in membrane distillation.•Effect of photo-Fenton on the physical and chemical properties of HA-Ca2+ was studied.•Effect of ...photo-Fenton on the interaction mode between HA-Ca2+ and the membrane was studied.•Fouling resistance and interface cleaning of CN-PVDF membrane was investigated.
Membrane distillation (MD), boasting high interception efficiency and low operational pressures, emerges as an innovative membrane technology. However, the occurrence of membrane fouling due to interaction between natural organic matter (NOM) and inorganic ions during the MD process curtails water purification efficiency, thereby constraining its potential applications. To address this quandary, this study integrates sulfate radical-based advanced oxidation processes (SR-AOPs) into MD technology to bolster membrane fouling control. A straightforward hydrothermal method coupled with vacuum filtration was employed to synthesize a Co3O4/Nitrogen-modified carbon quantum dots (NCDs)/PVDF (CN-PVDF) membrane for the first time, which was utilized in the MD treatment of simulated humic acid (HA) wastewater. Under visible light irradiation (1.9 kW/m2), CN-PVDF membrane activation of peroxymonosulfate (PMS) effectively altered the chemical attributes of the MD feed solution and reduced organic matter concentration. Moreover, it dismantled the carboxyl sites on HA that interact with Ca2+, consequently attenuating the formation of organic–inorganic complex pollutants. The XDLVO analysis showcased that photo-Fenton oxidation led to a diminishment in pollutant hydrophobicity, correlating with a 17.59 kT reduction in pollutant-membrane adsorption and a 7.47 kT amplification in adhesion barriers. This strategy transformed the initial two-stage fouling mode into a singular one, which significantly decreased the flux decline and the fouling layer thickness. Furthermore, the CN-PVDF membrane demonstrated self-cleaning capabilities via photo-Fenton. This study advances an innovative approach to bolster the fouling resistance of MD membranes and provides substantial theoretical support for the integration of SR-AOPs and MD technologies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Membrane distillation (MD) is a promising technology for treating saline industrial wastewater, but current hydrophobic MD membranes suffer significant wetting issues due to contaminants commonly ...present in wastewater. In this study, we report an effective method to fabricate a polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) electrospun nanofiber membrane with improved anti-wetting property against low-surface-tension substances. Without surface activation, the pristine electrospun nanofiber PVDF-HFP membrane with intrinsic re-entrant structure was directly fluorinated by 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (FDTS) employing vapor deposition (VD). The fluorinated membrane exhibited excellent surface omniphobicity with high water and ethanol contact angle of 154.1 ± 0.1° and 122.6 ± 1.7°, respectively. The fluorinated membrane showed highly stable omniphobicity and mechanical properties at harsh conditions such as ultrasonic, boiling water, acid and base treatment. More importantly, the resultant omniphobic membrane exhibited robust wetting resistance to the saline feed containing sodium dodecyl sulfate (SDS, 0.4 mM) in an 8-h dynamic direct contact MD (DCMD) test. This study provides an effective and benign approach to fabricate omniphobic nanofiber membranes which have great potential in treating saline wastewater containing low surface tension substances.
•An omniphobic electrospun nanofiber membrane was fabricated by an effective method.•No need to activate the surface and creat secondary re-entrant structures before fluorination.•The fluorination was on the basis of physical interaction between PVDF-HFP and FDTS.•The obtained omniphobicity was very stable under harsh conditions.•The omniphobic membrane showed the robust anti-wetting property to surfactants in DCMD.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The DCMD technology for wastewater treatment is very promising. However, it is easily suffered by membrane fouling and wetting. In this study, a Janus membrane was fabricated by coating ...polyvinylamine (PVAM) and gallic acid (GA) onto one side of a PVDF composite membrane, which another side is covered with POTS-SiO2. The PVAM and GA side could bind water to form a hydration layer, thus repel the contaminants. The POTS-SiO2 side was superhydrophobicity and prevented the membrane wetting. Finally, The Janus membrane presented exceptional performance in separating salt containing emulsified oil by DCMD. It kept a stable flux of 17.0 ± 0.2 Kg·m−2·h−1 and a low level conductivity of 0.60 ± 0.02 μS/cm in the cold side during the 36 h DCMD procedure, compared with the pristine PVDF membrane and the PVDF/POTS-SiO2 membrane. The results presented simultaneously antifouling and antiwetting properties of the Janus membrane. While the Janus membrane can be well used in desalination of emulsified oil containing salt, it has a great potential for application to treat other complex wastewater.
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•A Janus membrane was prepared via asymmetric modified process.•The Janus membrane presented simultaneous wetting resistant and antifouling performances.•The Janus membrane maintained stable flux and ultra-low conductivity in 36 h DCMD.•The Janus membrane showed great potential in treating complicated water or wastewater.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
