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International audience; The control of biofouling is required to improve membranes performances for water filtration. In this context, developing bioinspired approaches to modify membranes and give them antifouling properties is an interesting alternative. In this study, we elaborated new anti-biofouling membranes by coating them with vanillin, a natural bioactive molecule acting as a Quorum Sensing Inhibitor (QSI). First, the adsorption of vanillin by filtration was optimized to obtain homogeneous surface modifications. The modified membranes were then characterized in terms of physical-chemical properties: the results showed that they were more hydrophobic and exhibited a 14% decrease in pure water flux. Then, their anti-fouling properties were evaluated using complementary multiscale characterization methodologies; AFM single-cell experiments showed that vanillin adsorption had an effect on both the probability of bacterial cells to adhere to the surface, and on the force of adhesion. Direct EFM and SEM observation and adhesion assays further confirmed the effect of vanillin-modified membranes at the population-scale which showed a decrease in the bacterial coverage rate up to 50%. Altogether, it confirms the multifunctionality of vanillin-coated membranes against biofouling: reduction of bacterial initial adhesion by changing the membranes surface properties and reduction of biofilm formation by quorum sensing inhibition

International audience; While membrane bioreactors (MBR) have been broadly applied to wastewater treatment, membrane ageing studies have focused mainly on: (i) understanding the chemical action of sodium hypochlorite or (ii) monitoring ageing in direct filtration facilities (drinking water, groundwater, etc.). Thus, a comprehensive investigation under full-scale MBR operating conditions is still required. In the present study, polyvinylidene difluoride (PVDF) hollow fibers were sampled from a full-scale MBR in northern Paris during 7 years of operation. In addition, pristine membranes were aged at bench scale by single soaking in hypochlorite solution at a concentration and pH similar to MBR cleaning protocols. Both bench-scale- and full-scale-aged hollow fibers were characterized using similar analytical methods to assess the contributions of chemical action and operating conditions to the ageing process. At bench scale, membranes experienced no changes in mechanical resistance, but intrinsic permeability (i) first increased as a result of the hydrophilic agent oxidation, i.e., polyvinyl pyrrolidone (PVP), increasing porosity with the appearance of small pores (diameter 20 nm), and (ii) then the structure seemed to collapse and permeability decreased as a result. By contrast, membranes aged at full scale experienced a 46% decline in maximum tensile strength probably due to mechanical stress induced by aeration conditions in MBR. Besides, permeability increased for the whole period as a result of a more pronounced oxidation/dislodgement of PVP molecules leading to higher porosity and the appearance of bigger pores (diameter 40 nm). These changes favored irreversible fouling in contrast to bench-scale ageing. Therefore, bench-scale ageing is not completely representative of full-scale ageing and membrane autopsies must be preferred to this end. However, permeability and PVP content measurements may be applied after cleaning as in situ nondestructive tools in full-scale MBR to monitor membrane ageing. Plant operators should be aware that a continuous increase in intrinsic permeability may favor irreversible fouling accumulation demanding more frequent chemical cleanings.

International audience; Sub-stoichiometric titanium oxide (TiOx) reactive electrochemical membrane (REM) were integrated for the first time as anode in the electro-Fenton (EF) process. Hydroxyl radicals (•OH) were produced both in the retentate from Fenton's reaction and at the REM from anodic oxidation (AO). Optimal mass transport conditions were implemented because of convection-enhanced mass transport of (i) organic pollutants towards the REM surface during filtration and (ii) dissolved 02 towards cathode active sites owing to the use of a 3D carbon felt cathode in flow-through configuration for H202 generation. The efficiency of the REM/EF process was much higher than EF or REM used as standalone processes. For instance, taking paracetamol as target pollutant, (67 ± 2)% removal of 55 mg L - i of initial TOC was achieved with a high mineralization current efficiency (MCE) of ( 43 ± 1)%. By comparison, standalone REM and EF processes achieved only 47% (MCE = 30%) and 31 % (MCE = 20%) of TOC removal, respectively. By monitoring TOC removal both in retentate and permeate, the effect of homogeneous oxidation in the bulk retentate and heterogeneous oxidation at the REM could be observed separately. It was thus highlighted that the efficiency of AO might be affected by the presence of • OH and Fe2 + in the bulk. It was also emphasized a synergistic effect related to the formation of carboxylic acids in the bulk retentate that are more easily mineralized at the REM where both • OH-mediated oxidation and direct electron transfer occur.

International audience

International audience; Fenton oxidation is one of the promising advanced oxidation processes for the efficient elimination of pharmaceuticals from wastewater. The strong oxidation ability of this process is attributed to the generation of highly reactive hydroxyl radicals (radical dotOH) in the solution. In the present study, heterogeneous micro-sized zeolite catalysts that contain iron have been used in the Fenton-like process. This process enables operation in a wide pH range and facilitates the reuse of catalysts. Indeed, the coupling of the heterogeneous Fenton reaction with membrane filtration will ensure catalyst retention in the effluent compartment during the continuous water treatment. This study then investigated the fouling control strategies and membrane long-term stability in the heterogeneous Fenton reactor. During the filtration of the zeolite catalyst suspension, the critical flux for irreversible fouling was determined. One of the strategies to control membrane fouling can then be to choose an operating flux below this critical flux. In the case where a flux value above the critical flux is chosen, the results demonstrated total efficiency of hydrodynamic backwashing to eliminate hydraulically reversible fouling. Concerning the question of polymeric membrane long-term stability, it has been demonstrated that due to contact with the Fenton medium, membrane material undergoes oxidation and polymeric chain scissions. This latter is strongly linked to the decline in the mechanical resistance of membranes. In the tested conditions, despite the degradation to membrane material, the critical flux for irreversible fouling remained unchanged on aged membranes.

International audience; The oxidation ability of two prominent eco‐friendly electrochemical advanced oxidation processes (EAOPs), namely anodic oxidation with H2O2 generation (AO‐H2O2) and electro‐Fenton (EF) for complete abatement of acidic solution of 4‐aminophenazone (4‐APZ) has been investigated using conductive boron‐doped diamond (BDD) and sub‐stoichiometric titanium oxide (Ti4O7) anodes and carbon‐felt cathode. The higher performance of EF compared to AO‐H2O2 with either anode was demonstrated. In all trials, 4‐APZ was completely destroyed, following pseudo first‐order kinetics with the rate constant values increasing with applied current and higher values attained with BDD compared to Ti4O7 anode at similar conditions. The absolute rate constant for the reaction between 4‐APZ and hydroxyl radicals was found to be 3.9±0.2×109 L mol−1 s−1. Complete mineralization could be attained with BDD anode, whereas Ti4O7 anode only showed excellent mineralization up to 94 % TOC removal. Therefore, Ti4O7 anode can constitutes a promising anode material thanks to its lower manufacturing cost. Inorganic ions like NO3− and HCO3− at concentration up to 25 mM has no effect on mineralization efficiency during AO‐H2O2, but the presence of Cl− even at lower concentration of 10 mM significantly reduced the TOC removal efficiency. The toxicity of the solution sharply increased at initial stage of treatment, corresponding to the formation of cyclic by‐products but their conversion to carboxylic acids due to longer treatment time involved a sharp toxicity decrease, thus ensuring overall detoxification.

International audience; This paper deals with an experimental and modelling study on the electrochemical oxidation of refractory pharmaceuticals using a boron-doped diamond (BDD) anode. Different parameters have been investigated, such as the role of salts (sulfates), the presence of other organics, and the influence of applied current intensity. Ciprofloxacin (CIP), Sulfamethoxazole (SMX) and Salbutamol (SALBU) were used for models of pharmaceuticals, and urea as a model for a common organic. The complete removal of pharmaceuticals was observed in all electrolyses under galvanostatic conditions. The presence of common organic waste or other pharmaceutical has no significant impact on the degradation of the CIP target molecule. A mathematical model predicting the temporal concentration variation of organics with electroxidation time has been developed. In this model, different oxidation pathways have been considered: the transfer of electrons (direct oxidation) or of oxygen atoms via the reaction with either hydroxyl radicals or/and with strong electrogenerated oxidants. Excellent correlation with experiments is obtained under all experimental conditions.

International audience; Electro-oxidation processes are promising options for the removal of organic pollutants from water. The major appeal of these technologies is the possibility to avoid the addition of chemical reagents. However, a major limitation is associated with slow mass transfer that reduces the efficiency and hinders the potential for large-scale application of these technologies. Therefore, improving the reactor configuration is currently one of the most important areas for research and development. The recent development of a reactive electrochemical membrane (REM) as a flow-through electrode has proven to be a breakthrough innovation, leading to both high electrochemically active surface area and convection-enhanced mass transport of pollutants. This review summarizes the current state of the art on REMs for the electro-oxidation of organic compounds by anodic oxidation. Specific focuses on the electroactive surface area, mass transport, reactivity, fouling and stability of REMs are included. Recent advances in the development of sub-stoichiometric titanium oxide REMs as anodes have been made. These electrodes possess high electrical conductivity, reactivity (generation of •OH), chemical/electrochemical stability, and suitable pore structure that allows for efficient mass transport. Further development of REMs strongly relies on the development of materials with suitable physico-chemical characteristics that produce electrodes with efficient mass transport properties, high electroactive surface area, high reactivity and long-term stability.

International audience; Refractory pharmaceuticals remain in biologically treated wastewater and are continuously discharged into aquatic systems due to their limited biodegradability. Electrochemical oxidation is promising for the treatment of such refractory compounds, in particular using a boron doped diamond (BDD) anode. This study investigates the role of salts, such as sulfates and chlorides in the electrochemical treatment of wastewater. The presence of sulfates accelerated the removal of ciprofloxacin and sulfamethoxazole, but had no effect on the oxidation of salbutamol. This comparison highlights the selectivity of the reaction between organics and sulfate radicals. The addition of chlorides into the solution led to a remarkably-faster degradation of ciprofloxacin. However, incomplete mineralization was observed at high current densities due to the significant formation of halogenated organic compounds (AOX). The formation of refractory and toxic compounds such as ClO4− and AOX can be limited under the control of (i) applied current intensity and (ii) duration of electrolysis. Electrochemical oxidation of concentrated biologically-treated hospital wastewater investigated the excellent removal of biorefractory pharmaceuticals and confirmed the acceleration effect of salts on pharmaceutical degradation.

International audience; The objective of the present work is to correlate the evolution of membrane characteristics due to contact with hypochlorite used as cleaning agent to its selectivity towards model solutes. Accelerated ageing experiments were performed by soaking the membrane at ambient temperature in hypochlorite solutions. The total free chlorine concentration of these solutions was fixed at 350 ppm and the pH at 8. The model solute selected was T500 Dextran. The experimental results demonstrated that hypochlorite induced membrane degradation, on one hand modified the solutes–membrane interactions increasing irreversible fouling and, on the other hand, lowered the selectivity. These results have been correlated with the modification of the pore size distribution following a protocol in which fouling did not affect membrane characterization. The most probable scenario of distribution evolution over degradation process was an increase of the pore radius of the initial population, accompanied by a decrease in their number, coupled with the appearance of defects, whose radius increased with the progress of the degradation.

International audience; The way in which bacterial communities colonize flow in porous media is of importance but basic knowledge on the dynamic of these phenomena is still missing. The aim of this work is to develop microfluidic experiments in order to progress in the understanding of bacteria capture in filters and membranes. PDMS microfluidic devices mimicking filtration processes have been developed to allow a direct dynamic observation of bacteria across 10 or 20 micrometers width microchannels. When filtered in such devices, bacteria behave surprisingly: Escherichia coli, Pseudomonas aeruginosa or Staphylococcus aureus accumulate in the downstream zone of the filter and form large streamers which oscillate in the flow. In this study streamer formation is put in evidence for bacteria suspension in non nutritive conditions in less than one hour. This result is totally different from the one observed in same system with "inert" particles or dead bacteria which are captured in the bottleneck zone and are accumulated in the upstream zone. Observations within different flow geometries (straight channels, connected channels, staggered row pillars) show that the bacteria streamer development is influenced by the flow configuration and, particularly by the presence of tortuosity within the microchannels zone. These results are discussed at the light of 3D flow simulations. In confined systems and in laminar flow there is secondary flow (z-velocities) superimposed to the streamwise motion (in xy plane). The presence of the secondary flow in the microsystems has an effect on the bacterial adhesion. A scenario in three steps is established to describe the formation of the streamers and to explain the positive effect of tortuous flow on the development kinetics.

A pilot-scale study was performed to assess variations of reverse osmosis (RO) membrane water permeance ( A ) and salt retention ( R obs ) induced by chlorination and to compare them with those observed at the lab-scale. A chlorination protocol was adapted to expose only the surface active layer (an aromatic polyamide) of a composite RO membrane to consecutive free chlorine doses ranging from 40 to 4000 ppm h, at pH 6.9. Along the long-term filtration of seawater, performed with a 4" spiral wound RO module, we monitored the variations of A , the decrease of R obs and the rate of increase of A with time, and found them quantitatively similar to those reported in previous studies performed at the lab-scale under accelerated exposure conditions. The elemental analysis of the feed and permeate streams revealed that the rejection of divalent ions remained constant (ca. 100%), irrespective of the free chlorine dose reached, whereas the rejection of monovalent ions of the seawater (mainly sodium, chloride and bromide ions) decreased as the exposure dose increased. Overall, transposing the characterization procedure to the pilot-scale further supports that chlorination of PA, under pH conditions usually found in desalination plants (6.9 to 8.0), is controlled by the concentration of HOCl, as observed from elemental analysis of the surface by XPS.

International audience; In water treatment by microfiltration and ultrafiltration, a major concern is the integrity loss or failure of membrane induced by onsite operations, potentially leading to permeate water contamination. This study aims to provide a better understanding of the phenomena responsible for membrane damage by analyzing its causes and effects. The role of sodium hypochlorite exposure conditions and the impact of mechanical stress on membrane characteristics were investigated. Monitoring of hydraulic response, mechanical properties and the evolution of the chemical structure showed, on multiple scales, strong indications of membrane chemical degradation, involving radical mechanisms, accelerated by tensile stress application.

International audience; Water (A) and solute (B) permeability of aromatic polyamide (PA) reverse osmosis membranes (RO) were monitored under varying applied pressure, solute nature and concentration to assess their evolution after exposure of the membrane to free chlorine. Above a threshold value of 400 ppm h HOCl water permeability was influenced by permeation conditions during both filtration of ultrapure water (UP water) and reverse osmosis of salts performed sequentially. Water permeability decreased during the filtration of UP water performed at a constant applied pressure of 60 bar. During the reverse osmosis of an electrolyte solution, performed at a constant permeation flux of 31 L h¯¹ m¯², A was observed to increase continuously with time, e.g. up to a factor of 3 after exposure to 3120 ppm h HOCl, most severe dose used. Differences in the charge density of mono- and divalent cations did not influence the rate of increase of A with time, which was however shown to depend on salt flux and ascribed to a diffusion limited relaxation process presumed to occur within the dense hydrated PA network. The relative and opposite impact of applied pressure and of salt permeation highlighted the importance in distinguishing conditions under which the water permeability (A) of a chlorinated membrane is measured, whether during the filtration of UP water or of a salt.

International audience; The decomposition of diethyl phthalate (DEP) in water using UV–H2O2 process was investigated in this paper. DEP cannot be effectively removed by UV radiation and H2O2 oxidation alone, while UV–H2O2 combination process proved to be effective and could degrade this compound completely. With initial concentration about 1.0 mg/L, more than 98.6% of DEP can be removed at time of 60 min under intensity of UV radiation of 133.9 μW/cm2 and H2O2 dosage of 20 mg/L. The effects of applied H2O2 dose, UV radiation intensity, water temperature and initial concentration of DEP on the degradation of DEP have been examined in this study. Degradation mechanisms of DEP with hydroxyl radicals oxidation also have been discussed. Removal rate of DEP was sensitive to the operational parameters. A simple kinetic model is proposed which confirms to pseudo-first order reaction. There is a linear relationship between rate constant k and UV intensity and H2O2 concentration.

Despite a long history of development, the hemodialysis procedure (artificial kidney) still possesses some limitations, such as loss of the initial properties of the membrane due to fouling and poor removal of the middle sized uremic toxins. The present study is part of an European project named BioArt the aim of which was to overcome these limitations. In that objective, one of the partners of BioArt project reported on the development of the novel promising concept of double layer membrane with embedded adsorptive particles. A thorough characterization of the new membrane was then necessary, more precisely the extent to which mixed matrix layer can improve the removal of the uremic toxins from various groups needed to be evaluated, as well as the propensity of the membrane material to become fouled. The studies of the fouling phenomena are conventionally performed at the macro scale (bundle of hollow fibers) without insights of what is happening at the scale of an isolated fiber. Therefore, the primary aim of the present Thesis was to transfer the research of the protein-induced membrane fouling from the macro to the micro scale. A novel transparent microfluidics device with the polymeric membrane inside has been developed and applied for the filtration of model proteins: bovine serum albumin (BSA) and a-lactalbumin. Thanks to the coupling of the microchip with the fluorescent microscopy, different patterns of protein deposition on the membrane surface were observed and related to the variations in the hydrodynamic conditions inside the microchip. It was found that at certain conditions one may observe the difference in protein accumulation in the inlet, the middle, and the outlet of the channel while at other conditions this effect vanishes. Additionally, the unexpected phenomena of a-lactalbumin aggregation was observed over the course of filtration. The location and shape of the aggregates were also dependent on the hydrodynamic conditions and the applied transmembrane pressure. Aiming to address the problem of membrane design optimization for the enhancement of the middle molecules elimination from the bloodstream, a mathematical model, which accounts for the presence of adsorptive particles inside the complex double-layer membrane, has been proposed. The objective of the model was to understand the interplay of three solute removal mechanisms: convection, diffusion, and adsorption. The model allows predicting the influence of various parameters such as molecule diffusivity, membrane thickness, the presence of convection, content of adsorptive particles on the flux intensification across the membrane. The developed model seems to be a useful tool, which may be applied to design optimized membranes for the removal of toxins.; Malgré une longue histoire de développement, l'hémodialyse (rein artificiel) possède encore quelques limitations, telles que la perte des propriétés initiales de la membrane en cours de traitement à cause du colmatage et la mauvaise élimination des toxines urémiques de taille moyenne. La présente étude fait partie d'un projet européen nommé BioArt dont le but est d'apporter des solutions à ces limites. Dans cet objectif, l'un des partenaires du projet a proposé le développement d'un nouveau concept de membrane double couche au sein de laquelle sont incorporées des particules adsorbantes. Une caractérisation complète de cette nouvelle membrane était alors nécessaire, plus précisément l'impact de la matrice mixte sur l'élimination des toxines urémiques de divers groupes devait être évalué, ainsi que la propension du matériau membranaire à se colmater. Les études des phénomènes de colmatage sont classiquement menées à l'échelle macroscopique (faisceau de fibres creuses) sans analyse à l'échelle d'une fibre isolée. Le but premier de la présente thèse a alors été de proposer un dispositif permettant une étude du colmatage membranaire induit par la protéine à l'échelle microscopique. Un dispositif microfluidique transparent dans lequel la membrane polymère est insérée a été élaboré et mis en œuvre pour la filtration des protéines modèles : l'albumine de sérum bovin (BSA) et l'a-lactalbumine. Grâce au couplage avec la microscopie de fluorescence, différents modes d'adsorption des protéines sur la surface de la membrane ont été observés et liés aux variations des conditions hydrodynamiques à l'intérieur de la puce. Il a été constaté, sous certaines conditions, une différence dans l'accumulation de protéines entre l'entrée, le centre et la sortie du canal tandis que dans d'autres conditions cet effet s'annule. En outre, un phénomène inattendu, l'agrégation de l'a-lactalbumine, a été observé au cours de la filtration. La localisation dans le canal et la forme des agrégats dépendent également des conditions hydrodynamiques et de la pression transmembranaire appliquée. Dans le but d'optimiser la conception de la membrane vis à vis de son aptitude à éliminer des molécules de taille moyenne de la circulation sanguine, un modèle mathématique a été proposé. L'objectif du modèle était, en prenant en compte la présence de particules adsorbantes à l'intérieur de la membrane double couche, de rendre compte de la combinaison des trois mécanismes d'élimination du soluté : la convection, la diffusion et l'adsorption. Le modèle permet de prédire l'influence de divers paramètres tels que la diffusivité de la molécule, l'épaisseur de la membrane, la présence de la convection, la charge en particules adsorbantes, sur l'intensification des flux à travers la membrane. Le modèle semble être un outil utile pouvant être appliqué à l'optimisation de membranes pour l'élimination des toxines.