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International audience; In this work, we present an integrated dynamic cross-flow electro-Fenton (DCF-EF) system for the treatment of the pharmaceutical, acetaminophen (paracetamol), in aqueous medium. A carbonaceous electrocatalytic membrane was used as cathode, allowing the continuous production of H2O2 during EF in dynamic filtration mode. The transmembrane pressure (TMP) and current were the two driving forces of the system, whose influence strongly affected the global efficiency. It was found that H2O2 production from the electrochemical reduction of dissolved O2 was favoured at higher TMP values as a consequence of an increase of the O2 partial pressure, and higher H2O2 amounts entailed an increase in the efficiency of the process. Current also had a positive effect on H2O2 production and acetaminophen degradation and mineralization efficiencies up to an optimal value. Complete degradation of the drug and 44% mineralization were achieved under optimal conditions (2.0 bar and 100 mA). On the other hand, the results pointed out that the use of a Ti4O7 rod as counter electrode (anode) had an important contribution to the mineralization of the acetaminophen’s solutions owing to the formation of hydroxyl radicals (OH) on its surface, which highlighted the oxidative power of this anode material. The oxidation mechanisms involved during the process were assessed by electrochemical measurements with both electrodes (carbon membrane and Ti4O7 rod), and a degradation pathway for paracetamol oxidation was proposed based on the identification of the main aromatic and aliphatic degradation by-products. This DCF-EF process is presented as a potential alternative for water treatment and reuse in which the integration of membrane and electrochemical technologies brings together separation science and advanced oxidation.

International audience

International audience; Reactive Electrochemical Membrane (REM) prepared from carbothermal reduction of TiO2 is used for the mineralization of biorefractory pollutants during filtration operation. The mixture of Ti4O7 and Ti5O9 Magnéli phases ensures the high reactivity of the membrane for organic compound oxidation through •OH mediated oxidation and direct electron transfer. In cross-flow filtration mode, convection-enhanced mass transport of pollutants can be achieved from the high membrane permeability (3300 LMH bar-1). Mineralization efficiency of oxalic acid, paracetamol and phenol was assessed as regards to current density, transmembrane pressure and feed concentration. Unprecedented high removal rates of total organic carbon and mineralization current efficiency were achieved after a single passage through the REM, e.g. 47 g m-2 h-1 - 72% and 6.7 g m-2 h-1 - 47% for oxalic acid and paracetamol, respectively, at 15 mA cm-2. However, two mechanisms have to be considered for optimization of the process. When the TOC flux is too high with respect to the current density, aromatic compounds polymerize in the REM layer where only direct electron transfer occurs. This phenomenon decreases the oxidation efficiency and/or increases REM fouling. Besides, O2 bubbles sweeping at high permeate flux promotes O2 gas generation, with adverse effect on oxidation efficiency.

Hollow fiber membrane contactors with ionic liquids are promising alternatives to traditional spray towers and amines for carbon dioxide absorption. Ionic liquids have emerged as new alternative solvents because of their zero emission features compared with amines. The aim of this work was to compare fibers based on PVDF and different additives, as well as fibers including two different ionic liquids. On the one hand, 1-ethyl-3-methylimidazolium ethyl sulfate [emim][EtSO4] presents physical absorption, and on the other hand, 1-ethyl-3-methylimidazolium acetate [emim][Ac] presents chemical absorption. To compare the fibers under study, the thickness of the composite fiber was examined using scanning electron microscopy (SEM). The mechanical properties and the bubble point were also evaluated. Permeability tests were conducted, and the gas permeation of the composite hollow fibers was measured using pure CO2. Laboratory-made stainless steel modules were used for the tests. All of the above tests were performed with the fibers in both wet and dry conditions. It was determined that the fibers with the ionic liquid immobilized would be promising for CO2 capture because the CO2 permeance significantly increased. Namely, D+[emim][EtSO4] achieved a 43% increase compared with the fibers without the addition of the ionic liquid, resulting in a CO2 permeance value of 57040NL/(hm2bar), which is higher than the values reported in the literature for PVDF. Moreover, the overall mass transfer coefficient for CO2 capture using the D+[emim][Ac] fibers also presented highly competitive values. This research has been funded by the Spanish Ministry Economy and Competitiveness (Projects ENE2010-14828 and CTQ2013-48280-C3-1-R).

Reactive Electrochemical Membrane (REM) prepared from carbothermal reduction of TiO

Among the available membranes, dense polymer composite hollow-fiber membranes are promising for gas permeation applications coupled with the use of gas/liquid contactors, but they are also used in other membrane processes such as pervaporation. This study focuses on a coating process, starting from a polymer solution, to control the thickness and regularity of the coated polymer. The thickness of the liquid film coated onto a fiber is related to the coating velocity, the physical and chemical properties of the liquid, and the coating geometry. Depending on the dominating forces, several regimes are defined: two unstable regimes, in which a thin and regular polymer layer cannot be produced, and two stable regimes, which are of interest for reaching our objectives at the laboratory or industrial scale. The theoretical laws were compared to experimental coatings with solutions of poly(trimethylsilyl)propyne (PTMSP) dissolved in cyclohexane coated onto poly(ether sulfone) (PES) hollow fibers. The viscosities, surface tensions, and densities of the solutions used were measured. The experimental thicknesses of coated polymer layers were compared to values calculated from Landau’s law, which describes the thickness behavior in the viscocapillary regime. The results showed good behavior agreement, but the experimental thickness was underestimated by the calculations. Four different kinds of composite membranes were prepared using two different porous supports (MicroPES and Oxyphan) and two different permeable polymers (PTMSP and Teflon AF2400) for coating. The obtained composites hollow fibers were characterized. All four presented low-energy surfaces with no wetting phenomena. They also exhibited high CO2 and N2 permeabilities with CO2/N2 selectivities between 3.4 and 2.5. The mechanical properties of the composites remained stable except for composites based on PES affected by the drying step during the coating process.

Poly(vinylidene fluoride) (PVDF) hollow fiber membranes were obtained by the phase inversion technique. The influence of internal coagulant viscosity (0.001 to 3 Pa s) and air gap (0.6 to 86.4 cm) on the structure and mechanical resistance of the fibers was studied. A “sponge-like” structure free of macrovoids was obtained by using polyvinyl alcohol (PVA) with N-methyl pyrrolidinone and water as internal coagulant (viscosity 3 Pa s). The effect of the air-gap was studied in order to control the structure and obtain mechanically resistant membranes with tensile strength at break between 2.2 and 54.3 N/mm2 and pure water permeability ranging from 4 to 199 Lh−1m−2bar−1. CO2 permeability of these membranes was measured and found to be in the range of 365 to 53200 NLh−1m−2bar−1. The “Dusty Gas” model (DGM) was used to calculate the pore size of the membranes from CO2 permeability experiments, obtaining pore radius values going from 0.6 to 10.8 µm. Results from modeling were compared with pore sizes observed in...

International audience; Drinking water production plants using membrane filtration processes report membrane failure issues. According to the literature, membrane degradation is often induced by exposure to sodium hypochlorite, an oxidant widely used during in-place cleanings. The present study focused on quantifying the effect of membrane exposure mode to hypochlorite on properties modifications of a PES/PVP ultrafiltration membrane widely used for drinking water production. For this purpose effects of sodium hypochlorite concentration, contact duration and exposure mode (static or dynamic) were investigated. The pH of the hypochlorite solution was set to 8 as it was demonstrated in numerous previous works that the pH range 7–8 leads to the most severe modification in the membrane characteristics. Membrane degradation was monitored at molecular scale by attenuated total reflectance infrared spectroscopy and at macroscopic scale by pure water permeability and elongation at break measurements. The results obtained in static (soaking) and dynamic (filtration and filtration/backwashing cycles) hypochlorite exposure modes indicated that PES/PVP membrane degradation progress was predominantly governed by hypochlorite oxidation rate. In the tested conditions, mechanical stress (pressure differentials) did not significantly contribute to membrane ageing. The correlation between molecular and macroscopic characterizations demonstrated that PVP degradation is responsible for the membrane integrity loss. A linear relationship between the loss of ductility of the membrane and the progress of the PVP degradation was obtained whatever the exposure mode. Thanks to experiments conducted at various hypochlorite concentrations and exposure durations, the hypochlorite dose parameter (hypochlorite concentration times contact time), widely used in the literature, was demonstrated to be inappropriate to describe the degradation rate: the hypochlorite concentration impact was shown to be dominating the exposure time's one on the degradation rate.

New nanofiltration membranes have been developed by UV-photografting. Sodium p -styrene sulfonate (NaSS) and [2-(acryloyloxy)ethyl]trimethyl ammonium chloride (AC) were used for the modification of a polysulfone ultrafiltration membrane. The membrane cut-off was estimated. The grafted membranes were evaluated for the removal of six different dyes according to their charge in the aim of reusing the water in the process house. The effects of various parameters such as dye class, pressure, pH and the presence of salt were evaluated. It was observed that the newly developed membranes showed acceptable performance both in terms of flux and rejection. Dye retention was higher than 96% and hydraulic permeability was 0.48–0.56 m 3 m −2 day −1 at 0.4 MPa. The influence of pH and salt on the performance of membranes in terms of fouling and retention was established and compared to a commercial membrane (Desal 5 DK).

International audience; The main objective of this study is to develop a new formula for a diet mayonnaise-like sauce without cholesterol. Emulsifying power is provided by the use of soy lecithin and the total fat content was limited to 16%. Droplet size measurement of employed mayonnaise samples at different times show that the largest diameter of fat does not exceed 18.5 µm with a yield stress of 56.1 Pa. Results of stability to centrifugation reveal that the absence of the supernatant oily layer ensures the stability of the emulsion. Using the experimental design method, the number of trials can be limited to a number of 16 experiments, and best formulation of the mayonnaise (without cholesterol) was obtained.

A new way to prepare nanofiltration membranes, consisting of in-line external modification of the skin of a polysulfone ultrafiltration hollow fibre skin, is described. The paper presents a continuous process (dip-coating followed by photografting) and the influence of the operating conditions on the membrane characteristics. This study is focused on a simplified model based on the evaluation of the two sources of monomer available for grafting: one is monomer contained in the thin film drawn from the dip bath, second is contained in the pores of the membrane. The results show that two extreme types of modification can be produced, depending on the experimental conditions: a high rate coupled with a short dip contact time leads essentially to an external grafting whereas a low rate coupled with a long dip residence time leads essentially to an “in pore” grafting.

An in-line coagulation (without settling)/UF process has been studied to improve membrane performance and water quality for surface water treatment. Using coagulation before UF increases permeate quality; the extent of dissolved organic matter removal is controlled by the coagulation step. Efficient coagulation conditions for a coagulation/settling process can be applied for the in-line coagulation/UF process and membrane fouling is reduced. Floc cake resistance is lower than resistance due to the unsettled floc and the uncoagulated organics. For an inside-out hollow-fiber system, the impact of coagulation dose depends on filtration mode: for instance, in cross-flow with a feed-and-bleed configuration, a reduction of coagulant dose induces an increase of the mass transfer resistance even in quasi-stable hydrodynamic operating conditions.

The in-line coagulation/ultrafiltration (UF) combined process has been studied in order to improve membrane performance for the treatment of surface water with high organic content. Ultrafiltration experiments were performed using cellulose derivative hollow-fibre membranes with ferric chloride as coagulant. The efficacy of adding coagulant just before the membrane module depends on the filtration mode, the process configuration and the module design. In dead-end mode, permeation flux of 70 l/hm2 can be maintained, but high backwash frequency (low recovery) is necessary to prevent plugging. Cross-flow filtration was effective in reducing fouling and allows operation at higher permeation flux. In cross-flow filtration, the feed-and-bleed configuration (single stage continuous process) appears promising to reduce backwash frequencies: for a recovery of 95% and at a permeation flux of 120 l/h.m2, quasi-steady transmembrane pressure can be maintained with a low fouling rate (10 kPa in 400 min.). In cross-flow filtration, the use of curved modules with Dean vortices reduces the fouling rate by a factor of 2 compared with a conventional straight module.

The performance of several designs of curved membrane modules with Dean vortices was compared through experiments using a colloidal bentonite suspension and cellulose acetate hollow-fibre ultrafiltration (UF) membranes. The different module geometries were: straight, helically coiled, twisted and sinusoidal, or meander-shaped. The experiments show a remarkable increase in mass transfer in curved modules as compared to conventional straight ones. Comparisons were made for modules equipped with the same hollow fibres and the same Dean number (De) for a given Reynolds number (Re). At the same Dean number, all the curved geometries gave the same limiting permeate flux. A mass transfer correlation relating limiting UF flux with the mean wall shear stress has been obtained.

Secondary flows known as Dean vortices, that appear in a curved pipe due to centrifugal force, are found to reduce concentration polarisation and fouling and increase membrane permeation rates. The influence of Dean vortices on mass transfer is studied in membrane filtration. The experimental study consists in filtering suspensions of baker's yeast with ultrafiltration hollow fibre membranes, arranged in straight or coiled modules. The effect of different operating parameters is tested: flow velocity, suspension concentration and module geometry. It is found that secondary flow enhances membrane permeation by a factor of up to 5. Moreover, an energy analysis shows that for the same energy consumption, the permeate flux obtained in a coiled module is still far greater than that in a straight module.

International audience; The presence of pores larger than a micron, known as macrovoids, in polymeric membranes is particular lydetrimental for membrane structural integrity and mechanical properties. The theoretical modelling and physical understanding of the mechanisms of initiation and growth of the macrovoids, notably in order to determine processing conditions that would allow to make macrovoids free membranes, have been the subject of a vast literature and a restill controversial. However, experimental data on macrovoids, that could help to discriminate between several ideas are scarce and have been essentially obtained using 2D imaging systems. A very large number of observations are then needed to obtain statistically significant results and the limitation to 2D images does not permitto access to an accurate description of the macroporous structure. In this work, anX-raytomography system was used to image the 3D porous structure of hollow fibre membranes with a spatial resolution of one micron. Image analysis tools have been developed to accurately characterise them acrovoid shapes and spatial distribution on the membrane outer and inner skins as a function of some of the spinning process conditions (concentration of solvent into the bore and airgap length). The main purpose is there fore to quantify effects of some processing conditions on the macroporous structure of a hollow fibre membrane. Also, such an accurate characterisation of the macrovoids spatial distribution and 3D shape, as well as their variations with the process experimental conditions, help to shed light on macrovoids initiation and growth mechanisms.

International audience; A helically wound hollow-fibre (or tubular) membrane module was studied in an oxygenation operation with water flowing in the laminar regime inside the tube. Data are compared with a conventional module where straight hollow-fibre membranes are in parallel alignment. In the former design, the results are analyzed taking into account the formation of secondary flow (Dean vortices) and a new mass transfer correlation is presented. In the latter design, results are consistent with the Lévêque equation. It is shown that the presence of vortices gives better performance in terms of oxygen transfer. Improvement factors were in the range of 2 to 4.

International audience; New hollow fibre nanofiltration membranes have been developed by UV-photografting using sodium p-styrene sulfonate (NaSS) as a vinyl monomer. The influence of different parameters on the grafting process such as irradiation time, quantity of received UV energy by the membrane and addition of photoinitiator, on the performances and the characteristics of the membranes were examined. The molecular weight cut-off of the grafted hollow fibres was estimated using different PEG solutions. The grafted membranes were also evaluated for the removal of different anionic dyes (Acid, Direct and Reactive dyes) with an aim to reuse the dye and the water in the process house. It is observed that the newly developed hollow-fibre membranes show performances which are close to that of an “ideal” membrane adapted to the treatment of dye effluents. For example, a negatively charged hollow fibre with a 4500 Da cut-off can be used to concentrate a saline direct red 80 solution with a high flux (15 × 10−5 l h−1 m−2 Pa−1 (15 l h−1 m−2 bar−1)), a high dye rejection (R > 97%) and a salt retention lower than 2%.

International audience; The use of air in backwash of hollow-fiber modules was investigated experimentally from bench to full scale. Modules operated in a dead-end and outside-in mode: they were fouled by either a bentonite suspension or a raw river water and then backwashed in presence of air. The air was injected into the retentate compartment either in combination with a reversed permeate flux or together with feed water after a brief permeate back flow. Results indicate that the cake layer is instantaneously lifted off by the reversed permeate flux and is concentrated in the free volume of the module. To remove it from the module and recover the feed concentration, this volume has to be rinsed with a volume at least three times as big. The air, by its piston-like action, improves material removal and reduces the volume of concentrated foulant to be flushed. So the backwash time is reduced and its efficiency is improved. An optimum air flow rate can be found that is independent of the water flow rate used to flush the module free-volume.

Coiled and straight hollow-fibre modules have been built and tested; the permeate flux obtained in ultrafiltration with these two geometries is compared for two feeds: a colloidal bentonite suspension and a dextran solution. In the case of colloidal suspensions, the secondary flows induced by the coiled geometry allow fouling to be reduced and the permeate flux is multiplied by a factor of up to 2. An empirical relationship is proposed to express the limiting flux of permeate as a function of both the velocity and some geometrical parameters of the coiled modules. Analogous results are obtained during the ultrafiltration of dextran. It is also shown that under certain conditions almost no deposit was formed; the permeate flux under these conditions is three times higher for coiled modules than for straight ones. For a given energy expenditure and ultrafiltration process, the gain in permeate flux can reach a factor of 1.8.

International audience; Mass transfer in ultrafiltration for water and wastewater treatment is improved by Dean vortices. With this secondary flow, which appears in a coiled hollow-fibre module, the shear stress is higher than in a straight module and is a maximum near the external wall of the coiled tube. As a consequence, concentration polarisation and cake deposition are reduced and the limiting flux in ultrafiltration of model fluids (bentonite and yeast suspensions) and activated sludge is improved by up to 5 times. The effect of the hydrodynamic conditions and feed concentration is tested. An energy analysis shows that an improvement in permeate flux is found at a given energy consumption.

International audience; Ultrafiltration in a hollow-fiber module operating with outside-in and dead-end flow at a constant flow rate was simulated using a model that takes into account the longitudinal pressure drops inside the fibers and within the fiber bundle. The model considers both the filtration phase during which the membrane is fouled by the formation of a filter cake and the backwash phase in which it is cleaned, so as to predict the net rate of production of the module during an operating cycle.The results show that there is a combination of packing density and fiber diameter that gives a maximum net flow rate. Furthermore, this model allows the influence of operating conditions and feed properties on the module performance to be estimated. This can be used to determine how operating parameters must be modified when there is a change in the feed properties.

The alleviation of environmental problems is one of the biggest challenges of technology today. The development and implantation of new separation processes may result in a “green” industrial revolution. Membrane technology has many advantages to offer in this respect. Membrane contactors are commonly hollow fibre devices used as substitutes for packed towers. As such, they are alternative industrial configurations for carrying out gas absorption or stripping and liquid-liquid extraction. This paper is limited to gas-liquid contactors. In the case of oxygenation of water, a resistance-in-series model with two resistances, the membrane and the liquid film resistance, was used to describe the oxygen transfer process. An induction of secondary flows is used to decrease the mass transfer resistance in the liquid phase and increase the oxygen flux. The study was based on a comparison between straight modules and coiled modules. For straight modules, the results are consistent with the Leveque correlation. For coiled modules mass transfer coefficients were found to be two to four times higher than for straight modules and a new mass transfer correlation is presented.