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© 2002 Elsevier Science B.V. Postdoctoral grant from Universidad Complutense of Madrid by M.A. Izquierdo Gil and support from the Danish Directorate for Development are gratefully acknowledged., Membrane distillation (MD) has a great potential as a concentration process for temperature labile liquids such as fruit juices, etc. Besides water, also aroma compounds will permeate through the membrane depending on their volatility and how the MD process is operated on the permeate side.In this paper, an experimental and theoretical investigation of the influence of concentration polarisation and temperature polarisation on the flux and selectivity of binary aqueous mixtures of ethanol is presented for vacuum membrane distillation (VMD) processes. Experimental results include changes of the following parameters: nature of solutions, membrane material and pore size, feed temperature, recirculation flow rate. One method was proposed in order to evaluate the concentration polarisation effects from the fit of the experimental data. General models taking into account Knudsen and viscous flows were proposed, but viscous contribution resulted to be negligible under our operating conditions. Therefore, theoretical fluxes were estimated using Knudsen model and a good agreement between them and the experimental ones was found., Danish Directorate for Development, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V. The present work was performed at the Department of Nuclear Methods and Process Engineering, Institute of Nuclear Chemistry and Technology Warsaw and was financially supported by FP6 European Funds under Marie Curie project: AMERAC no. MTKDCT-2004-509226. The authors acknowledge this financial support., The factorial design of experiments and desirability function approach has been applied for multiresponse optimization in pervaporation separation process. Two organic aqueous solutions were considered as model mixtures, water/acetonitrile and water/ethanol mixtures. Two responses have been employed in multi-response optimization of pervaporation, total permeate flux and organic selectivity. The effects of three experimental factors (feed temperature, initial concentration of organic compound in feed solution, and downstream pressure) on the pervaporation responses have been investigated. The experiments were performed according to a 21 full factorial experimental design. The factorial models have been obtained from experimental design and validated statistically by analysis of variance (ANOVA). The spatial representations of the response functions were drawn together with the corresponding contour line plots. Factorial models have been used to develop the overall desirability function. In addition, the overlap contour plots were presented to identify the desirability zone and to determine the optimum point. The optimal operating conditions were found to be, in the case of water/acetonitrile mixture, a feed temperature of 55 degrees C, an initial concentration of 6.58% and a downstream pressure of 13.99 kPa, while for water/ethanol mixture a feed temperature of 55 degrees C, an initial concentration of 4.53% and a downstream pressure of 9.57 kPa. Under such optimum conditions it was observed experimentally an improvement of both the total permeate flux and selectivity., FP6 European Funds, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 Elsevier Ltd. Economical support from the CICYT is acknowledged., In the membrane distillation (MD) literature, the heat transfer coefficients of the boundary layers are usually estimated from well known heat transfer empirical correlations developed for non-porous and rigid heat exchangers. A difference between the mechanism of heat transfer in MD systems, which is coupled with transmembrane mass transfer, and the mechanism of heat transfer in "pure" heat exchangers is expected to exist. Vacuum membrane distillation has been experimentally studied in a capillary membrane module and the heat transfer coefficients have been evaluated in both the lumen and the shell side of the membrane module. A critical review of the most frequently used heat transfer empirical correlations in MD systems is presented. Finally, the experimental results obtained in this paper are compared to those of literature, in order to test their applicability in membrane distillation systems., CICYT, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier B.V. Postdoctoral grant from Universidad Complutense of Madrid to M.A. Izquierdo-Gil, Project PB-98-07-88 (CYCYT, Spain) and support from the Danish Directorate for Development are gratefully acknowledged, Vacuum membrane distillation (VMD) has been studied as a separation process to remove volatile organic compounds from aqueous streams. A vapour pressure difference across a microporous hydrophobic membrane is the driving force for the mass transport through the membrane pores (this transport takes place in vapour phase). The vapour pressure difference is obtained in VMD processes by applying a vacuum on one side of the membrane. The membrane acts as a mere support for the liquid-vapour equilibrium. The evaporation of the liquid stream takes place on the feed side of the membrane, and the condensation on the permeate side of the membrane. The paper focus on aroma stripping using VMD; factors influencing flux and separation performance using selected model aroma compounds have been studied. Mainly the following parameters have been examined-aroma compounds: activity coefficient/vapour pressure values; membrane type: PTFE/PP/PVDF; feed flow rate; feed temperature. A comparison is made between different thermodynamic models for calculating the vapour-liquid equilibrium at the membrane/pore interface., CICYT (Spain), Danish Directorate for Development, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

At present, both energy and water are predominantly supplied through the burning of fossil fuels. Going forward, new demand (and the replacement of retiring assets) is increasingly being met by sustainable technologies—largely driven by solar energy. This PhD thesis aimed to address two pressing Sustainable Development Goals, set out by the United Nations, ‘affordable and clean energy’ and ‘clean water’, by developing solar-driven desalination (D) technologies using two different approaches: ‘direct solar-desalination’ and ‘indirect solar-desalination’. The first approach used feedwater heated directly by a solar thermal collector for vacuum membrane distillation (VMD) for a small residential scale. In contrast, the second approach targeted the indirect use of energy from a concentrated solar power (CSP) plant via more well-established desalination processes for large-scale applications. In the first approach, this thesis successfully designed and manufactured the first hollow fiber-based multi-effect VMD that can internally recover the latent heat of the permeate vapor between effects using metallic hollow helical baffles, reducing the energy consumption by more than 60% and producing up to 20 L/h at less than 2 USD per cubic meter of freshwater. In the second approach, detailed numerical simulations found that replacing the power block’s condenser with a multi-effect distillation (MED) system can significantly improve the CSP plant’s payback period by 5% – 13% but at the expense of reducing the thermal efficiency by 7% – 11.5%. Another solution is to utilize some of the generated electricity from the CSP plant to operate reverse osmosis (either on-site or at a facility near the coast); however, this was found to hurt the plant’s revenue since some of the valuable electricity generated is consumed by the RO plant, instead of being sold to the grid. Another CSP-D solution is to replace the conventional steam Rankine cycle with a supercritical CO2 cycle, which can pr

Membrane distillation is a promising technique for numerous applications, namely in desalination, wastewater treatment, food, textile and chemical industry. Vacuum membrane distillation (VMD) offers numerous advantages in terms of flux, thermal efficiency and relevance for specific products. On the other hand, direct contact membrane distillation (DCMD) is the most studied configuration and it is preferred due to its conceptual simplicity. The literature is addressing their performance considering mainly the transmembrane flux, which is leading to a lack of full understanding of the phenomena behind each configuration. In this work, the concentration of carbonate solutions using vacuum and direct contact membrane distillation is performed, and results are analyzed by the flux and the overall mass transfer coefficient. This analysis has allowed the evaluation of the real performance of each configuration by keeping the effect of the driving force out of the discussion. The results reveal higher and more stable mass transfer coefficients in VMD, and a much more significant impact of concentration in DCMD. Thus, even though DCMD presents a very attractive configuration in terms of simplicity, its performance is poorer in comparison with VMD.

This thesis constitutes a part of the "IMPRESS" project which is aiming at the production of bio-plastics by utilizing hemicellulosic hydrolysates. The hydrolysate stream, after following the steps of acid hydrolysis and neutralization, consists of monosaccharides (C5/C6 sugars), salt and sugar degradation products. The C5/C6 sugars need to be concentrated by a factor of 10 to be purified afterwards in downstream processes. Evaporation has been the most dominant technology in the sugar treatment sector, however the current study aimed to investigate tubular nanofiltration (NF) and vacuum membrane distillation (VMD) units for concentrating the C5/C6 sugars, as more sustainable alternatives. Synthetic solutions with C5/C6 sugars and salt were used to assess the performance of the NF and MD membranes in terms of sugar and salt rejection before the experiments with the real hydrolysate solution. Among the different NF and MD membranes, the one that met the C5/C6 sugar rejection requirements (>90 %) during the synthetic solution experiments was tested for concentrating the C5/C6 sugars. The most suitable technology for concentrating the C5/C6 sugars was also assessed for its energy consumption. Additionally, single filtration tests were conducted to characterize the NF membranes, while surface tension and contact angle measurements were performed to predict the membrane wetting phenomena during the VMD operation. Based on the C5/C6 sugar rejection values (range of 22-81 %) obtained with ceramic and polymeric NF membranes, it was deduced that the tubular NF membranes were not capable of meeting the C5/C6 sugar concentration goals. The polymeric membranes performed better than the ceramic ones in terms of C5/C6 sugar rejection, with a maximum sugar rejection of 81 %. However, the polymeric membranes were found to be more prone to fouling, showing a maximum decrease of 34 % in the water permeability after 4 hours of operation with the hydrolysate solution. Additionally

Energy and clean water demand is on rise due to population and economic growth. Since solar energy resources are ubiquitous around the world, hybrid energy-water technologies driven by low-grade thermal energy represent a potential way to meet this demand while minimizing environmental impacts. Membrane distillation (MD) technology is particularly well-suited to remote/off-grid applications due to its modularity and ability to treat high salinity water with low fouling potential. Compared to other MD configurations, when high permeate flux and gain output ratio are required, a Vacuum Membrane Distillation (VMD) can be employed. However, unlike multi-effect distillation and multi-stage flash, VMD systems have not yet been fully optimized for specific heat consumption (SHC) or water recovery rate (RR). In this study, a techno-economic assessment, using the Chemical Engineering Plant Cost Index (CEPCI) method, of single versus multi-stage VMD configurations with respect to these aspects was carried out. Single stage VMD was considered as the baseline configuration. The effect of brine recirculation on the SHC is examined for the proposed multi-stage configurations. It was found that for a VMD process, brine recirculation is the most effective method to reuse the brine heat, which resulted in reducing the SHC by 60%. Moreover, single stage VMD with brine recirculation was found to be superior than multi-stage configurations achieving the lowest SHC and LCOW. As an understanding of the VMD technology, this work represents the first step in critically evaluating the performance of alternative VMD multi-stage configurations to aid in module design, scale-up and process optimization.

In today’s industry ammonia is produced on a large scale, and is used in the production of fertilisers, cleaning products and much more. Eventually the ammonia enters our wastewater, either directly or through urine. This is then removed with conventional nitrifying-denitrifying treatment or with Anammox. That process consumes energy and does not recover the ammonia. Therefore, the goal of the ‘From Pollutant to Power’ project, of which this thesis is a part, is to achieve a paradigm shift for ammonia to become an energy resource instead of a wastewater pollutant. The objective of the project is to recover ammonia and use it in a solid oxide fuel cell (SOFC) to produce energy. To do this, a vapour with at least a mass percentage of ammonia (m%NH3) of 5% is needed. The energy produced with the SOFC can then be used to cover the energy need for the extraction of ammonia. The SOFC can produce 4.2MJ·kg-N-1 of thermal energy and 8.4 MJ·kg-N-1 of electrical energy. This study examines the use of vacuum membrane stripping (VMS) to strip ammonia from wastewater. The research objective is to go from using VMS to recover ammonia from synthetic wastewater to strip ammonia from real wastewater, in order to produce ammonia fuel for a SOFC. To accomplish this, some knowledge gaps need to be filled. First, methods need to be found that concentrate the permeate more than previously possible with the VMS to reach the desired m%NH3 in the permeate. Therefore, the effect of the cross-flow of the feed side was investigated and how to concentrate the permeate vapour with the help of condensation. Next, the effect of contaminants on the VMS process was examined by looking at the effect of salts in the wastewater and testing with real industrial ammonia-rich wastewater from amide production, which contains some organics. The final issue to consider was whether this process would be feasible in terms of energy; therefore, an energy balance was made. Multiple experimental tests, From Pollutant to Power, Civil Engineering

In today’s industry ammonia is produced on a large scale, and is used in the production of fertilisers, cleaning products and much more. Eventually the ammonia enters our wastewater, either directly or through urine. This is then removed with conventional nitrifying-denitrifying treatment or with Anammox. That process consumes energy and does not recover the ammonia. Therefore, the goal of the ‘From Pollutant to Power’ project, of which this thesis is a part, is to achieve a paradigm shift for ammonia to become an energy resource instead of a wastewater pollutant. The objective of the project is to recover ammonia and use it in a solid oxide fuel cell (SOFC) to produce energy. To do this, a vapour with at least a mass percentage of ammonia (m%NH3) of 5% is needed. The energy produced with the SOFC can then be used to cover the energy need for the extraction of ammonia. The SOFC can produce 4.2MJ·kg-N-1 of thermal energy and 8.4 MJ·kg-N-1 of electrical energy. This study examines the use of vacuum membrane stripping (VMS) to strip ammonia from wastewater. The research objective is to go from using VMS to recover ammonia from synthetic wastewater to strip ammonia from real wastewater, in order to produce ammonia fuel for a SOFC. To accomplish this, some knowledge gaps need to be filled. First, methods need to be found that concentrate the permeate more than previously possible with the VMS to reach the desired m%NH3 in the permeate. Therefore, the effect of the cross-flow of the feed side was investigated and how to concentrate the permeate vapour with the help of condensation. Next, the effect of contaminants on the VMS process was examined by looking at the effect of salts in the wastewater and testing with real industrial ammonia-rich wastewater from amide production, which contains some organics. The final issue to consider was whether this process would be feasible in terms of energy; therefore, an energy balance was made. Multiple experimental tests, From Pollutant to Power, Civil Engineering

The influence of feed temperature and total ammonia nitrogen concentration on permeate quantity and quality in a vacuum membrane distillation process has been researched in order to determine the suitability of membrane distillation in an energy producing system including a solid oxide fuel cell.

The influence of feed temperature and total ammonia nitrogen concentration on permeate quantity and quality in a vacuum membrane distillation process has been researched in order to determine the suitability of membrane distillation in an energy producing system including a solid oxide fuel cell.

Sustained water scarcity conditions due to increased fresh water demand necessitates water authorities to consider alternatives for supplementary water supply. Water recycling in a sustainable manner is increasingly being practiced around the world for protection of water resources. Abundantly available brackish water sources with suitable treatment can be used for recycling purposes. On the other hand, grey water recycling has been accepted due to the quantity and quality of this source compared to sewage. A typical household’s grey water contains approximately 70% of the domestic wastewater and its TDS, COD and TOC concentrations are 49.7, 39.7 and 38.3% less than medium sewage. Grey water treatment for reuse will not only decrease the rate of fresh water consumption in urban areas but also will reduce the pressure on wastewater treatment plants. These substantial improvements are obtainable by means of an appropriate treatment technology in a sustainable and efficient manner. Water is also closely interconnected with energy. Water extraction, treatment, transport and distribution all requires energy. In regard with the exigent situations predicted for water and energy in future as well as their interactions, the potential of solar powered treatment technologies are investigated as an attractive and promising solutions. This research compared three innovative solar-based treatment systems from a selection of a broad range of technologies that have been used for brackish and grey water treatment. The treatment systems were assessed through a multi-criteria decision analysis method embedding twelve sustainability indicators under three major criteria. Pairwise comparison of indicators and selected systems revealed that the solar powered vacuum membrane distillation (SVMD) system was the most sustainable technology option for both brackish and grey water treatment based on economic, environmental and social pillars.

Sustained water scarcity conditions due to increased fresh water demand necessitates water authorities to consider alternatives for supplementary water supply. Water recycling in a sustainable manner is increasingly being practiced around the world for protection of water resources. Abundantly available brackish water sources with suitable treatment can be used for recycling purposes. On the other hand, grey water recycling has been accepted due to the quantity and quality of this source compared to sewage. A typical household’s grey water contains approximately 70% of the domestic wastewater and its TDS, COD and TOC concentrations are 49.7, 39.7 and 38.3% less than medium sewage. Grey water treatment for reuse will not only decrease the rate of fresh water consumption in urban areas but also will reduce the pressure on wastewater treatment plants. These substantial improvements are obtainable by means of an appropriate treatment technology in a sustainable and efficient manner. Water is also closely interconnected with energy. Water extraction, treatment, transport and distribution all requires energy. In regard with the exigent situations predicted for water and energy in future as well as their interactions, the potential of solar powered treatment technologies are investigated as an attractive and promising solutions. This research compared three innovative solar-based treatment systems from a selection of a broad range of technologies that have been used for brackish and grey water treatment. The treatment systems were assessed through a multi-criteria decision analysis method embedding twelve sustainability indicators under three major criteria. Pairwise comparison of indicators and selected systems revealed that the solar powered vacuum membrane distillation (SVMD) system was the most sustainable technology option for both brackish and grey water treatment based on economic, environmental and social pillars.

Sustained water scarcity conditions due to increased fresh water demand necessitates water authorities to consider alternatives for supplementary water supply. Water recycling in a sustainable manner is increasingly being practiced around the world for protection of water resources. Abundantly available brackish water sources with suitable treatment can be used for recycling purposes. On the other hand, grey water recycling has been accepted due to the quantity and quality of this source compared to sewage. A typical household’s grey water contains approximately 70% of the domestic wastewater and its TDS, COD and TOC concentrations are 49.7, 39.7 and 38.3% less than medium sewage. Grey water treatment for reuse will not only decrease the rate of fresh water consumption in urban areas but also will reduce the pressure on wastewater treatment plants. These substantial improvements are obtainable by means of an appropriate treatment technology in a sustainable and efficient manner. Water is also closely interconnected with energy. Water extraction, treatment, transport and distribution all requires energy. In regard with the exigent situations predicted for water and energy in future as well as their interactions, the potential of solar powered treatment technologies are investigated as an attractive and promising solutions. This research compared three innovative solar-based treatment systems from a selection of a broad range of technologies that have been used for brackish and grey water treatment. The treatment systems were assessed through a multi-criteria decision analysis method embedding twelve sustainability indicators under three major criteria. Pairwise comparison of indicators and selected systems revealed that the solar powered vacuum membrane distillation (SVMD) system was the most sustainable technology option for both brackish and grey water treatment based on economic, environmental and social pillars.

The influence of temperature (10–45°C), feed flow rate (300–500L/h) and sweeping gas flow rate (1.2–2m3/h) on the recovery of berry fruit juice aroma compounds by sweeping gas membrane distillation (SGMD) was examined on an aroma model solution and on black currant juice in a lab scale membrane distillation set up. The data were compared to recovery of the aroma compounds by vacuum membrane distillation (VMD). The flux of SGMD increased with an increase in temperature, feed flow rate or sweeping gas flow rate. Increased temperature and feed flow rate also increased the concentration factors (Cpermeate/Cfeed) of the aroma compounds. At 45°C the most volatile and hydrophobic aroma compounds obtained the highest concentration factors: 12.1–9.3 (black currant juice) and 17.2–12.8 (model solution). With black currant juice a volume reduction of 13.7% (vol.%) at 45°C, 400L/h, resulted in an aroma recovery of 73–84vol.% for the most volatile compounds. Compared to VMD, the aroma recovery with SGMD was less influenced by the feed flow rate but more influenced by the temperature. Higher fluxes were achieved during concentration by VMD and this reduced the operation time, which in turn reduced the degradation of anthocyanins and polyphenolic compounds in the juice. Industrial relevanceHigh temperature evaporation is the most widely used industrial technique for aroma recovery and concentration of juices, but membrane distillation (MD) may provide for gentler aroma stripping and lower energy consumption. This study gives important clues about the fate of berry juice aroma compounds and polyphenols during concentration by MD, and identifies the main factors influencing the aroma recovery efficiency with MD. Both SGMD and VMD are promising techniques for gentle stripping of berry juice aroma compounds and deserve further consideration as alternative techniques for gentle aroma stripping in industrial fruit juice processing.

The influence of temperature (10–45°C), feed flow rate (300–500L/h) and sweeping gas flow rate (1.2–2m3/h) on the recovery of berry fruit juice aroma compounds by sweeping gas membrane distillation (SGMD) was examined on an aroma model solution and on black currant juice in a lab scale membrane distillation set up. The data were compared to recovery of the aroma compounds by vacuum membrane distillation (VMD). The flux of SGMD increased with an increase in temperature, feed flow rate or sweeping gas flow rate. Increased temperature and feed flow rate also increased the concentration factors (Cpermeate/Cfeed) of the aroma compounds. At 45°C the most volatile and hydrophobic aroma compounds obtained the highest concentration factors: 12.1–9.3 (black currant juice) and 17.2–12.8 (model solution). With black currant juice a volume reduction of 13.7% (vol.%) at 45°C, 400L/h, resulted in an aroma recovery of 73–84vol.% for the most volatile compounds. Compared to VMD, the aroma recovery with SGMD was less influenced by the feed flow rate but more influenced by the temperature. Higher fluxes were achieved during concentration by VMD and this reduced the operation time, which in turn reduced the degradation of anthocyanins and polyphenolic compounds in the juice. Industrial relevanceHigh temperature evaporation is the most widely used industrial technique for aroma recovery and concentration of juices, but membrane distillation (MD) may provide for gentler aroma stripping and lower energy consumption. This study gives important clues about the fate of berry juice aroma compounds and polyphenols during concentration by MD, and identifies the main factors influencing the aroma recovery efficiency with MD. Both SGMD and VMD are promising techniques for gentle stripping of berry juice aroma compounds and deserve further consideration as alternative techniques for gentle aroma stripping in industrial fruit juice processing.

Vacuum membrane distillation (VMD) has been studied as a separation process to remove volatile organic compounds from aqueous streams. A vapour pressure difference across a microporous hydrophobic membrane is the driving force for the mass transport through the membrane pores (this transport takes place in vapour phase). The vapour pressure difference is obtained in VMD processes by applying a vacuum on one side of the membrane. The membrane acts as a mere support for the liquid-vapour equilibrium. The evaporation of the liquid stream takes place on the feed side of the membrane, and the condensation on the permeate side of the membrane. The paper focus on aroma stripping using VMD; factors influencing flux and separation performance using selected model aroma compounds have been studied. Mainly the following parameters have been examined-aroma compounds: activity coefficient/vapour pressure values; membrane type: PTFE/PP/PVDF; feed flow rate; feed temperature. A comparison is made between different thermodynamic models for calculating the vapour-liquid equilibrium at the membrane/pore interface. (C) 2004 Elsevier B.V. All rights reserved.