Special Issue "Membrane Distillation Process"

A special issue of Membranes (ISSN 2077-0375). This special issue belongs to the section "Membrane Engineering and Applications".

Deadline for manuscript submissions: 20 December 2019.

Special Issue Editor

Dr. Alessandra Criscuoli
E-Mail Website
Guest Editor
Institute on Membrane Technology, Rende, Italy
Interests: Membrane Contactors; Membrane Distillation; Integrated Membrane Systems; Water and Wastewater Treatment; Desalination; Energetic and Exergetic analysis

Special Issue Information

Dear Colleagues,

The water stress that we have been experiencing in the last few years is pushing towards the development of new technologies for the purification and recovery of water.

Membrane Distillation (MD) is based on the use of hydrophobic microporous membranes that prevent the passage of aqueous feed as liquid through the micropores, allowing the transport of water vapor and volatiles only, thanks to a difference of partial pressures established across the membrane. In this way, high-purity distillates can be produced starting from a variety of aqueous streams, like effluents coming from textile/agrofood/pharmaceutical industry, olive mill wastewaters, waters contaminated by heavy metals, sea, and brackish waters. Some studies on the application of MD for the purification of radioactive wastewaters and of urine have also been carried out.

With respect to Reverse Osmosis (RO), which is limited by the osmotic pressure and sometimes shows low rejection values for elements like As(III) and Boron, MD is able to produce fresh water from high-concentrated streams and provides 100% theoretical rejections for all non-volatiles present into the aqueous feeds.

Despite these advantages, MD is far from a significant application at industrial scale, due to some still pending issues:

  • need of developing membranes with high hydrophobicity and liquid entry pressure values, able to be stable when treating real streams in long-term runs;
  • need of developing modules with reduced thermal and mass transfer resistances;
  • need of reducing the specific thermal energy consumption.

Research on the above-mentioned points are in progress, including the use of renewable energies to cover the thermal demand of the system and the integration of MD with other membrane units, in order to improve the overall performance of the processes.

The aim of this Special Issue is to provide an overview of the last results obtained in the field for overcoming MD drawbacks and boosting its implementation at a large scale.

Dr. Alessandra Criscuoli
Guest Editor

Manuscript Submission Information

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Keywords

  • Membrane Distillation
  • Water and Wastewater Treatment
  • Desalination
  • Hydrophobic Membranes
  • Specific Thermal Energy Consumption
  • Renewable Energies
  • Integrated Membrane Operations

Published Papers (8 papers)

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Research

Open AccessArticle
Concentration of 1,3-dimethyl-2-imidazolidinone in Aqueous Solutions by Sweeping Gas Membrane Distillation: From Bench to Industrial Scale
Membranes 2019, 9(12), 158; https://doi.org/10.3390/membranes9120158 - 26 Nov 2019
Abstract
Sweeping gas membrane distillation (SGMD) is a useful option for dehydration of aqueous solvent solutions. This study investigated the technical viability and competitiveness of the use of SGMD to concentrate aqueous solutions of 1,3-dimethyl-2-imidazolidinone (DMI), a dipolar aprotic solvent. The concentration from 30% [...] Read more.
Sweeping gas membrane distillation (SGMD) is a useful option for dehydration of aqueous solvent solutions. This study investigated the technical viability and competitiveness of the use of SGMD to concentrate aqueous solutions of 1,3-dimethyl-2-imidazolidinone (DMI), a dipolar aprotic solvent. The concentration from 30% to 50% of aqueous DMI solutions was attained in a bench installation with Liqui-Cel SuperPhobic® hollow-fiber membranes. The selected membranes resulted in low vapor flux (below 0.15 kg/h·m2) but were also effective for minimization of DMI losses through the membranes, since these losses were maintained below 1% of the evaporated water flux. This fact implied that more than 99.2% of the DMI fed to the system was recovered in the produced concentrated solution. The influence of temperature and flowrate of the feed and sweep gas streams was analyzed to develop simple empirical models that represented the vapor permeation and DMI losses through the hollow-fiber membranes. The proposed models were successfully applied to the scaling-up of the process with a preliminary multi-objective optimization of the process based on the simultaneous minimization of the total membrane area, the heat requirement and the air consumption. Maximal feed temperature and air flowrate (and the corresponding high operation costs) were optimal conditions, but the excessive membrane area required implied an uncompetitive alternative for direct industrial application. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessArticle
Characterization and Assessment of a Novel Plate and Frame MD Module for Single Pass Wastewater Concentration–FEED Gap Air Gap Membrane Distillation
Membranes 2019, 9(9), 118; https://doi.org/10.3390/membranes9090118 - 06 Sep 2019
Abstract
Membrane distillation (MD) is an up and coming technology for concentration and separation on the verge of reaching commercialization. One of the remaining boundaries is the lack of available full-scale MD modules and systems suitable to meet the requirements of potential industrial applications. [...] Read more.
Membrane distillation (MD) is an up and coming technology for concentration and separation on the verge of reaching commercialization. One of the remaining boundaries is the lack of available full-scale MD modules and systems suitable to meet the requirements of potential industrial applications. In this work a new type of feed gap air gap MD (FGAGMD) plate and frame module is introduced, designed and characterized with tap water and NaCl–H2O solution. The main feature of the new channel configuration is the separation of the heating and cooling channel from the feed channel, enabling a very high recovery ratio in a single pass. Key performance indicators (KPIs) such as flux, gained output ratio (GOR), recovery ratio and thermal efficiency are used to analyze the performance of the novel module concept within this work. A recovery rate of 93% was reached with tap water and between 32–53% with salt solutions ranging between 117 and 214 g NaCl/kg solution with this particular prototype module. Other than recovery ratio, the KPIs of the FGAGMD are similar to those of an air gap membrane distillation (AGMD) channel configuration. From the experimental results, furthermore, a new MD KPI was defined as the ratio of heating and cooling flow to feed flow. This RF ratio can be used for optimization of the module design and efficiency. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessArticle
CFD Investigation of Spacer-Filled Channels for Membrane Distillation
Membranes 2019, 9(8), 91; https://doi.org/10.3390/membranes9080091 - 25 Jul 2019
Abstract
The membrane distillation (MD) process for water desalination is affected by temperature polarization, which reduces the driving force and the efficiency of the process. To counteract this phenomenon, spacer-filled channels are used, which enhance mixing and heat transfer but also cause higher pressure [...] Read more.
The membrane distillation (MD) process for water desalination is affected by temperature polarization, which reduces the driving force and the efficiency of the process. To counteract this phenomenon, spacer-filled channels are used, which enhance mixing and heat transfer but also cause higher pressure drops. Therefore, in the design of MD modules, the choice of the spacer is crucial for process efficiency. In the present work, different overlapped spacers are investigated by computational fluid dynamics (CFD) and results are compared with experiments carried out with thermochromic liquid crystals (TLC). Results are reported for different flow attack angles and for Reynolds numbers (Re) ranging from ~200 to ~800. A good qualitative agreement between simulations and experiments can be observed for the areal distribution of the normalized heat transfer coefficient. Trends of the average heat transfer coefficient are reported as functions of Re for the geometries investigated, thus providing the basis for CFD-based correlations to be used in higher-scale process models. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessArticle
Evaluation of Permeate Quality in Pilot Scale Membrane Distillation Systems
Membranes 2019, 9(6), 69; https://doi.org/10.3390/membranes9060069 - 05 Jun 2019
Cited by 2
Abstract
In this work, the salinity of permeate obtained with membrane distillation (MD) in pilot scale systems was analyzed. Experiments were performed with three different spiral-wound commercial modules, one from Solar Spring with 10 m2 surface membrane area and two from Aquastill with [...] Read more.
In this work, the salinity of permeate obtained with membrane distillation (MD) in pilot scale systems was analyzed. Experiments were performed with three different spiral-wound commercial modules, one from Solar Spring with 10 m2 surface membrane area and two from Aquastill with 7.2 and 24 m2. Intermittent operation meant that high permeate conductivity was measured in the beginning of each experiment, which was gradually decreasing until reaching a constant value (3–143 µS·cm−1 for seawater feed). The final quality reached did not depend on operating conditions, only the time it took to reach it. This can be because the permeate flux dilutes the minimal feed leak taking place through pinholes in the membranes. Larger feed leak through the membrane was observed when operating in vacuum-enhanced air-gap MD configuration (V-AGMD), which is compatible with this explanation. However, for the increase of feed leak with salinity (up to 1.8 M), a conclusive explanation cannot be given. Pore wetting due to crystallization is discarded because the high permeate quality was recovered after washing with distilled water. More studies at higher salinities and also at membrane level are required to investigate this. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessArticle
The Influence of Talc Addition on the Performance of Polypropylene Membranes Formed by TIPS Method
Membranes 2019, 9(5), 63; https://doi.org/10.3390/membranes9050063 - 14 May 2019
Abstract
The effect of talc addition on the morphology of capillary membranes formed by a thermally induced phase separation (TIPS) method was investigated in the presented work. The usability of such formed membranes for membrane distillation was evaluated. Two types of commercial capillary polypropylene [...] Read more.
The effect of talc addition on the morphology of capillary membranes formed by a thermally induced phase separation (TIPS) method was investigated in the presented work. The usability of such formed membranes for membrane distillation was evaluated. Two types of commercial capillary polypropylene membranes, fabricated for microfiltration process, were applied in the studies. A linear arrangement of polymer chains was obtained in the walls of membranes formed without a talc addition. In the case of membranes blended with talc, the linear structure was disordered, and a more porous structure was obtained. The changes in morphology enhanced the mechanical properties of blended membranes, and their lower thermal degradation was observed during 350 h of membrane distillation studies. Long-term studies confirmed the stability of talc dispersion in the membrane matrix. A leaching of talc from polypropylene (PP) membranes was not found during the membrane distillation (MD) process. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessFeature PaperArticle
Triple-Layer Nanofiber Membranes for Treating High Salinity Brines Using Direct Contact Membrane Distillation
Membranes 2019, 9(5), 60; https://doi.org/10.3390/membranes9050060 - 06 May 2019
Cited by 1
Abstract
A composite, three-layered membrane for membrane distillation was prepared from electrospun polyvinylidene fluoride (PVDF) nanofibers supported by commercial polyethersulfone (PES) nanofiber based nonwoven from E.I. duPont de Nemours company (DuPont). The membranes were tested in direct contact membrane distillation (DCMD) using a 5.0 [...] Read more.
A composite, three-layered membrane for membrane distillation was prepared from electrospun polyvinylidene fluoride (PVDF) nanofibers supported by commercial polyethersulfone (PES) nanofiber based nonwoven from E.I. duPont de Nemours company (DuPont). The membranes were tested in direct contact membrane distillation (DCMD) using a 5.0 M sodium chloride brine as a feed solution. The triple layer membrane combines the hydrophobicity of PVDF and the robustness of the PES. The triple layer membrane demonstrated excellent performance in DCMD (i.e., relatively high water flux compared to the commercial PVDF membrane and a complete salt rejection of the brine) with mechanical properties imparted by the PES layer. This work is the first to demonstrate the use of a commercially produced nanofiber nonwoven for membrane distillation. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessArticle
Concentrating of Sugar Syrup in Bioethanol Production Using Sweeping Gas Membrane Distillation
Membranes 2019, 9(5), 59; https://doi.org/10.3390/membranes9050059 - 01 May 2019
Abstract
Membrane distillation (MD) is a relatively new and underdeveloped separation process which can be classified as a green technology. However, in order to investigate its dark points, sensitivity analysis and optimization studies are critical. In this work, a number of MD experiments were [...] Read more.
Membrane distillation (MD) is a relatively new and underdeveloped separation process which can be classified as a green technology. However, in order to investigate its dark points, sensitivity analysis and optimization studies are critical. In this work, a number of MD experiments were performed for concentrating glucose syrup using a sweeping gas membrane distillation (SGMD) process as a critical step in bioethanol production. The experimental design method was the Taguchi orthogonal array (an L9 orthogonal one) methodology. The experimental results showed the effects of various operating variables, including temperature (45, 55, and 65 °C), flow rate (200, 400, and 600 ml/min) and glucose concentration (10, 30, and 50 g/l) of the feed stream, as well as sweeping gas flow rate (4, 10, and 16 standard cubic feet per hour (SCFH)) on the permeate flux. The main effects of the operating variables were reported. An ANOVA analysis showed that the most and the least influenced variables were feed temperature and feed flow rate, each one with 62.1% and 6.1% contributions, respectively. The glucose rejection was measured at 99% for all experiments. Results indicated that the SGMD process could be considered as a versatile and clean process in the sugar concentration step of the bioethanol production. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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Open AccessArticle
Treatment of Flue Gas Desulfurization Wastewater by an Integrated Membrane-Based Process for Approaching Zero Liquid Discharge
Membranes 2018, 8(4), 117; https://doi.org/10.3390/membranes8040117 - 26 Nov 2018
Cited by 1
Abstract
An integrated membrane process for the treatment of wastewaters from a flue gas desulfurization (FGD) plant was implemented on a laboratory scale to reduce their salt content and to produce a water stream to be recycled in the power industry. The process is [...] Read more.
An integrated membrane process for the treatment of wastewaters from a flue gas desulfurization (FGD) plant was implemented on a laboratory scale to reduce their salt content and to produce a water stream to be recycled in the power industry. The process is based on a preliminary pretreatment of FGD wastewaters, which includes chemical softening and ultrafiltration (UF) to remove Ca2+ and Mg2+ ions as well as organic compounds. The pretreated wastewaters were submitted to a reverse osmosis (RO) step to separate salts from water. The RO retentate was finally submitted to a membrane distillation (MD) step to extract more water, thus increasing the total water recovery factor while producing a high-purity permeate stream. The performance of RO and MD membranes was evaluated by calculating salts rejection, permeate flux, fouling index, and water recovery. The investigated integrated system allowed a total recovery factor of about 94% to be reached, with a consequent reduction of the volume of FGD wastewater to be disposed, and an MD permeate stream with an electrical conductivity of 80 μS/cm, able to be reused in the power plant, with a saving in fresh water demand. Full article
(This article belongs to the Special Issue Membrane Distillation Process)
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