Approche intégrée du dessalement d'eau de mer :\ud Distillation membranaire sous vide pour la réduction des rejets salins et possibilités de\ud couplage avec l'énergie solaire

Le problème de pénurie en eau potable se pose encore de nos jours dans de nombreux pays. Du fait\ud de l’importance de la ressource en eau présente dans les océans, la solution du dessalement de l’eau\ud de mer est en constant progrès. Ce dessalement se fait actuellement majoritairement par osmose\ud inverse. Cependant, ce procédé membranaire est limité en facteur de concentration en raison de la\ud pression osmotique de l’eau de mer qui augmente avec la concentration en sels. Il en résulte des\ud volumes importants de rejets salins dans l’eau de mer ce qui perturbe l’équilibre du milieu naturel. Une\ud approche originale a été proposée dans le cadre du projet européen MEDINA afin de réduire ces\ud rejets. Il s’agit de l’utilisation du procédé de distillation membranaire sous vide (DMV) au sein d’une\ud filière intégrée d’OI. En effet, la DMV permet d’opérer à de fortes concentrations en sels et elle peut\ud également être couplée avec l’énergie solaire dans un objectif d’économie d’énergie.\ud La démarche adoptée dans cette étude consiste à étudier l’utilisation de la DMV pour des eaux très\ud concentrées en sels, à la fois des eaux synthétiques mais aussi des eaux réelles (eaux de mer et\ud rétentats d’osmose inverse). Une double approche à la fois expérimentale (à l’aide d’un pilote à\ud échelle laboratoire) et théorique (par un outil de modélisation) a été utilisée.\ud Les résultats ont montré l’intérêt de la DMV pour la surconcentration des rétentats d’OI. En effet, la\ud DMV peut travailler à des fortes concentrations en sels jusqu’à 300 g.L-1 tout en maintenant des flux\ud de perméat encore importants (7 L.h-1.m-2) et un perméat avec une très faible salinité (taux de rejet en\ud sels de 99,96 %). Les volumes de rejets peuvent ainsi être réduits par 5 et le taux de conversion\ud augmente jusqu’à presque 90 %. Les phénomènes de colmatage (cristallin, organique et biologique)\ud sont également limités. Des dépôts de cristaux de sels ont pu être observés et analysés. Des\ud mécanismes de cristallisation ont été proposés mettant en évidence le rôle majeur du calcium.\ud Le couplage de la DMV avec des technologies solaires thermiques permet une réduction importante\ud de la demande énergétique. Les utilisations d’étangs solaires à gradient de salinité et de collecteurs\ud solaires thermiques ont été comparées et ont montré les potentialités intéressantes des collecteurs\ud solaires thermiques en termes de température atteinte et donc de flux de perméat. ---------------------------------------------------------------------------------------------------------------------------------------------------------------- The lack of potable water is still a problem in many countries. Considering the nearly endless water\ud resource in the oceans, seawater desalination is an increasing attractive solution. Reverse Osmosis\ud (RO) desalination is the main technology used nowadays. However, RO is limited in recovery factor\ud due to the osmotic pressure which increases with salinity. It results high brine volume rejected directly\ud in seawater which induces environmental perturbations. An innovative approach was proposed in the\ud frame of the European project MEDINA in order to reduce these brines: the use of vacuum membrane\ud distillation (VMD) in an integrated RO desalination process. Indeed, VMD allows operating at high salt\ud concentration and can be coupled with solar thermal energy in order to reduce energy requirement.\ud The present work consisted in studying use of VMD for highly salty concentrated waters, both for\ud synthetic and real waters (seawater and RO retentate). An experimental approach was used with a\ud lab-scale pilot plant completed by a theorical approach with a modelling tool.\ud Results show the interest of VMD for the overconcentration of RO retentates. Indeed, VMD can be\ud operated at high salt concentration up to 300 g.L-1 maintaining still high permeate fluxes (7 L.h-1.m-2)\ud and nearly pure permeate (salt rejection of 99.96 %). Brine volumes can so be reduced by 5 and\ud recovery factor increased up to nearly 90 %. Fouling (organic, scaling or bio-fouling) is limited. Salt\ud crystal deposit has been observed and analysed. Precipitation mechanisms have been proposed,\ud mainly with the crucial part of the calcium.\ud VMD coupling with solar thermal technologies allow an important reduction of the energy requirement.\ud Use of salinity gradient solar ponds and solar thermal collectors have been compared and have shown\ud the potentialities of using solar thermal collector in order to obtain high temperatures and so high\ud permeate fluxes\u

Polymeric membranes for treatment of produced water on offshore plateform

Introduction Phase separation using non-solvent coagulation of a polymer solution is the most widespread industrial process to manufacture membranes. Large solvent quantity is then use that it complicates the overall process and may lead to environmental and health problems. Knowing that polymer concentration is usually in the range 15-20 % and coagulation and washing baths require to be often renewed, large amounts of aqueous solutions must be treated. For instance 10 m2 of ultrafiltration membrane need about 1 to 1.5 kg of solvent. Our objective in this proposal is to develop a novel process for membrane mass production in agreement with the principles of green chemistry. The main technical and economic output of using water instead organic solvents should consist in a simplification of the manufacturing process by lowering wastes and recycling. Environmental outputs will be a safer process, more economic on atoms, limiting the wastes and applicable to renewable naturally-occurring polymers. Please click Additional Files below to see the full abstract

Approche intégrée du dessalement d eau de mer (Distillation membranaire sous vide pour la réduction des rejets salins et possibilités de couplage avec l énergie solaire)

Le problème de pénurie en eau potable se pose encore de nos jours dans de nombreux pays. Du fait de l importance de la ressource en eau présente dans les océans, la solution du dessalement de l eau de mer est en constant progrès. Ce dessalement se fait actuellement majoritairement par osmose inverse. Cependant, ce procédé membranaire est limité en facteur de concentration en raison de la pression osmotique de l eau de mer qui augmente avec la concentration en sels. Il en résulte des volumes importants de rejets salins dans l eau de mer ce qui perturbe l équilibre du milieu naturel. Une approche originale a été proposée dans le cadre du projet européen MEDINA afin de réduire ces rejets. Il s agit de l utilisation du procédé de distillation membranaire sous vide (DMV) au sein d une filière intégrée d OI. En effet, la DMV permet d opérer à de fortes concentrations en sels et elle peut également être couplée avec l énergie solaire dans un objectif d économie d énergie. La démarche adoptée dans cette étude consiste à étudier l utilisation de la DMV pour des eaux très concentrées en sels, à la fois des eaux synthétiques mais aussi des eaux réelles (eaux de mer et rétentats d osmose inverse). Une double approche à la fois expérimentale (à l aide d un pilote à échelle laboratoire) et théorique (par un outil de modélisation) a été utilisée. Les résultats ont montré l intérêt de la DMV pour la surconcentration des rétentats d OI. En effet, la DMV peut travailler à des fortes concentrations en sels jusqu à 300 g.L-1 tout en maintenant des flux de perméat encore importants (7 L.h-1.m-2) et un perméat avec une très faible salinité (taux de rejet en sels de 99,96 %). Les volumes de rejets peuvent ainsi être réduits par 5 et le taux de conversion augmente jusqu à presque 90 %. Les phénomènes de colmatage (cristallin, organique et biologique) sont également limités. Des dépôts de cristaux de sels ont pu être observés et analysés. Des mécanismes de cristallisation ont été proposés mettant en évidence le rôle majeur du calcium. Le couplage de la DMV avec des technologies solaires thermiques permet une réduction importante de la demande énergétique. Les utilisations d étangs solaires à gradient de salinité et de collecteurs solaires thermiques ont été comparées et ont montré les potentialités intéressantes des collecteurs solaires thermiques en termes de température atteinte et donc de flux de perméatThe lack of potable water is still a problem in many countries. Considering the nearly endless water resource in the oceans, seawater desalination is an increasing attractive solution. Reverse Osmosis (RO) desalination is the main technology used nowadays. However, RO is limited in recovery factor due to the osmotic pressure which increases with salinity. It results high brine volume rejected directly in seawater which induces environmental perturbations. An innovative approach was proposed in the frame of the European project MEDINA in order to reduce these brines: the use of vacuum membrane distillation (VMD) in an integrated RO desalination process. Indeed, VMD allows operating at high salt concentration and can be coupled with solar thermal energy in order to reduce energy requirement. The present work consisted in studying use of VMD for highly salty concentrated waters, both for synthetic and real waters (seawater and RO retentate). An experimental approach was used with a lab-scale pilot plant completed by a theorical approach with a modelling tool. Results show the interest of VMD for the overconcentration of RO retentates. Indeed, VMD can be operated at high salt concentration up to 300 g.L-1 maintaining still high permeate fluxes (7 L.h-1.m-2) and nearly pure permeate (salt rejection of 99.96 %). Brine volumes can so be reduced by 5 and recovery factor increased up to nearly 90 %. Fouling (organic, scaling or bio-fouling) is limited. Salt crystal deposit has been observed and analysed. Precipitation mechanisms have been proposed, mainly with the crucial part of the calcium. VMD coupling with solar thermal technologies allow an important reduction of the energy requirement. Use of salinity gradient solar ponds and solar thermal collectors have been compared and have shown the potentialities of using solar thermal collector in order to obtain high temperatures and so high permeate fluxesTOULOUSE-INSA (315552106) / SudocSudocFranceF

Response to the letter-to-the-editor entitled “Comments on ‘Evaluation of systems coupling vacuum membrane distillation and solar energy for seawater desalination”’

International audienc

Evaluation of systems coupling vacuum membrane distillation and solar energy for seawater desalination

International audienceVacuum membrane distillation (VMD) is a hybrid membrane-evaporative process which has been shown to be of interest for seawater desalination. The main drawback of this process is the relatively high energy requirement linked to the need to heat the feed water. A way to solve this problem could be the use of a renewable source such as solar energy to provide the heat energy required. Two solutions of solar energy use are investigated in this paper: salinity gradient solar ponds (SGSP) and solar collectors (SC). For each solution, two configurations were studied. The first was based on pre-heating the feed seawater before the membrane process while the second used a membrane module directly coupled with solar energy, i.e. a membrane submerged in an SGSP or an SC integrated at the surface of the membrane module. VMD process simulations were carried out for the four different configurations with VMD modelling software previously developed and adapted to the different combinations. Simulation results showed that immersing the membrane module directly in an SGSP could induce marked concentration and temperature polarisation phenomena that reduced fluxes. Turbulence had to be created in the feed seawater to reduce polarisations and this option was difficult to combine with an SGSP. The most interesting solution seemed to be the use of SC. High fluxes of 140 L h(-1) m(-2) could be reached (for a vacuum pressure of 500 Pa and a membrane with a Knudsen permeability of 1.85 x 10(-5) s mol(1/2) m(-1) kg(-1/2)). (C) 2010 Elsevier B.V. All rights reserved

Vacuum membrane distillation of seawater reverse osmosis brines

International audienceSeawater desalination by Reverse Osmosis (RO) is an interesting solution for drinking water production. However, because of limitation by the osmotic pressure, a high recovery factor is not attainable. Consequently, large volumes of brines are discharged into the sea and the flow rate produced (permeate) is limited. In this paper, Vacuum Membrane Distillation (VMD) is considered as a complementary process to RO to further concentrate RO brines and increase the global recovery of the process. VMD is an evaporative technology that uses a membrane to support the liquid-vapour interface and enhance the contact area between liquid and vapour in comparison with conventional distillation. This study focuses on VMD for the treatment of RO brines. Simulations were performed to optimise the operating conditions and were completed by bench-scale experiments using actual RO brines and synthetic solutions up to a salt concentration of 300 g L(-1). Operating conditions such as a highly permeable membrane, high feed temperature, low permeate pressure and a turbulent fluid regime allowed high permeate fluxes to be obtained even for a very high salt concentration (300 g L(-1)). For the membrane studied, temperature and concentration polarisation were shown to have little effect on permeate flux. After 6 to 8 h, no organic fouling or biofouling was observed for RO brines. At high salt concentrations, scaling occurred (mainly due to calcium precipitation) but had only a limited impact on the permeate flux (24% decrease for a permeate specific volume of 43L m(-2) for the highest concentration of salt). Calcium carbonate and calcium sulphate precipitated first due to their low solubility and formed mixed crystal deposits on the membrane surface. These phenomena only occurred on the membrane surface and did not totally cover the pores. The crystals were easily removed simply by washing the membrane with water. A global recovery factor of 89% can be obtained by coupling RO and VMD. (C) 2010 Elsevier Ltd. All rights reserved

A new method for permeability measurement of hydrophobic membranes in Vacuum Membrane Distillation process

In this paper, a new method for permeability measurement of hydrophobic membranes used in Vacuum Membrane Distillation, instead of common measurement methods, was proposed. As VMD is a pressure and temperature driven process, the idea of this work is to propose a new water vapour permeability measurement method based on variation of feed temperature at a fixed vacuum pressure. This new method showed a greater stability and simplicity than the existing pressure variation method by not only allowing a wide range of feed temperature (25 degrees C divided by 60 degrees C) to be scanned continuously, but also avoiding fluctuations of the system as observed in the pressure variation test. Permeabilities of two different kinds of hydrophobic membranes were measured by this new method and also by the existing pressure variation test. A comparison between these two methods was also presented to assess the feasibility and applicability of this new method. (C) 2013 Elsevier Ltd. All rights reserved

Hollow-Fiber Membrane Contactor for Biogas Recovery from Real Anaerobic Membrane Bioreactor Permeate

International audienceThis study demonstrates the application of hollow-fiber membrane contactors (HFMCs) for the recovery of biogas from the ultrafiltration permeate of an anaerobic membrane bioreactor (AnMBR) and synthetic effluents of pure and mixed CH4 and CO2. The developed membrane degassing setup was coupled with a pilot-scale AnMBR fed with synthetic domestic effluent working at 25 °C. The membrane degassing unit was able to recover 93% of the total dissolved CH4 and 83% of the dissolved CO2 in the first two hours of permeate recirculation. The initial recovery rates were very high (0.21 mg CH4 L−1 min−1 and 8.43 mg CO2 L−1 min−1) and the membrane was able to achieve a degassing efficiency of 95.7% for CH4 and 76.2% for CO2, at a gas to liquid ratio of 1. A higher mass transfer coefficient of CH4 was found in all experimental and theoretical evaluations compared to CO2. This could also be confirmed from the higher transmembrane mass transport resistance to CO2 rather than CH4 found in this work. A strong dependency of the selective gas transport on the gas and liquid side hydrodynamics was observed. An increase in the liquid flow rate and gas flow rate favored CH4 transport and CO2 transport, respectively, over each component. The results confirmed the effectiveness of the collective AnMBR and membrane degassing setup for biogas recovery. Still, additional work is required to improve the membrane contactor’s performance for biogas recovery during long-term operation

Asymmetric Solvent-Annealed Triblock Terpolymer Thick Films Topped by a Hexagonal Perforated Lamellar Nanostructure

International audienceAsymmetric and nanostructured polystyrene-block-poly(2-vinyl pyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO or SVEO, S:V:EO ≈ 56:34:10, M ∼ 79.5 kg.mol–1 and Đ ∼ 1.05) thick films blended with 20 wt % of a short PS homopolymer (hPS, M ∼ 10.5 kg.mol–1 and Đ ∼ 1.09) were achieved by combining the non-solvent induced phase separation (NIPS) process with a solvent vapor annealing (SVA) treatment. Here, the NIPS step allows for the formation of a highly-permeable sponge-like substructure topped by a dense thin layer exhibiting poorly-ordered nanopores while the subsequent SVA treatment enables to reconstruct the material top surface into a porous monolayer of well-ordered hexagonal perforated lamellae (HPL). This optimized film architecture generated by NIPS-SVA showed a mean water permeability of 860 L h–1 m–2 bar–1, which is roughly twice time higher than the flux measured through NIPS made PS-b-P2VP-b-PEO/hPS materials having poorly-ordered nanopores. The post-SVA treatment also revealed as a powerful tool to tailor the thickness of the nanostructure formed within the blended material since monoliths entirely composed of a HPL phase were produced by increasing the time of exposure to a chloroform stream. The water flux of such PS-b-P2VP-b-PEO/hPS monoliths was found to be an order of magnitude lower than that of their asymmetric film homologues

Phase separated structures of concentrated polymer solutioons

International audiencePhase separation of concentrated homopolymer solutions is both of fundamental interest (the large difference in viscosity/elasticity of the two phases can lead to unusual behaviors) and of practical importance (novel porous structures can be made by this process). I will first review how 2D phase-field simulations (Fig.1) reveal the influence of the mobility dependance with concentration for capturing features of phase separation like growth laws. On the experimental side I will examine various water-soluble polymers and show how anomalous phase diagrams seem to be closely connected to unusual features of arrested-like phase separation as evidenced by light scattering and confocal microscopy. Thin films of these polymer solutions were used for making membranes (Fig. 2), avoiding the use of organic solvents. The case of homo-polyelectrolytes is also of great interest since the theory is still controversial, as I will briefly recall. First results will be presented about phase separation upon changes in salt concentration, polymer concentration and temperature for a polyelectrolyte whose structure is also promising for membranes