Simulation d’une filtration liquide en canal poreux fermé à une extrémité avec prise en compte de la formation du dépôt

La formation d’un dépôt de filtration ainsi que les performances de filtration associées ont été étudiées par CFD en utilisant un maillage mobile. Des lois expérimentales décrivant la porosité et la perméabilité du dépôt ont été intégrées au modèle. Ces lois ont été obtenues à partir de la mesure d’épaisseur de dépôt in situ par nappe laser. L’effet d’une perméabilité membranaire non uniforme sur la distribution spatiale du dépôt a ensuite été étudié

Caractérisation In-Situ de dépôts formés en filtration membranaire de suspensions particulaires et de biofluides (intéraction entre structure locale et performances du procédé)

Le colmatage membranaire demeure l un des verrous majeurs des bioréacteurs à membrane (BAM). Ces travaux visent à apporter une contribution à la compréhension de la dynamique de structuration de dépôts complexes formés lors de la filtration frontale de (bio)fluides et son impact sur les performances de filtration. Pour cela, différents outils permettant la mesure in-situ des propriétés structurelles locales des dépôts ont été utilisés de manière à pouvoir relier ces propriétés aux performances globales de filtration. Les propriétés électrocinétiques des dépôts ont également été étudiées. Deux méthodes, l une optique et l autre acoustique, ont été utilisées pour caractériser les propriétés structurelles locales des dépôts (épaisseur, cinétique de croissance). Dans un premier temps, les épaisseurs obtenues par les méthodes optiques et acoustiques ont été comparées. Il a été montré que, dans le cas de dépôts peu poreux, les deux méthodes conduisent aux mêmes épaisseurs de dépôts. Dans le cas de dépôts plus poreux, ces deux méthodes permettent l obtention de données complémentaires à deux niveaux de profondeur différents au sein du dépôt. L influence des conditions opératoires sur la structuration de dépôts de particules modèles a ensuite été étudiée. Grâce à la méthode optique il a été montré que, quelles que soient les conditions opératoires, il existe une variation temporelle des propriétés du dépôt. De plus, une répartition non homogène du dépôt à la surface de la membrane peut également exister, favorisée par de faibles répulsions entre particules. Enfin, l applicabilité des différentes méthodes au cas des biofluides issus de BAM a été évaluée. La structure de dépôts complexes constitués lors de la filtration de ces biofluides a ensuite été étudiée. La compressibilité des dépôts, mise en évidence à l échelle globale par suivi des performances de filtration, a également été observée à l échelle locale : l épaisseur du dépôt décroît avec une augmentation de la PTM. De plus, à l échelle locale, une variabilité spatiale des propriétés du dépôt a été mise en évidence. Afin de contrôler la compressibilité des dépôts l impact de l ajout de particules au sein du biofluide a été évaluéMembrane fouling is one of the major drawbacks of membrane bioreactors. This study is thus a contribution to the understanding of the dynamic structuring of complex deposits build-up during dead-end filtration of complex biofluids. Several tools were used to perform in-situ characterization of cake layer structural properties at local scale and to link them to global filtration performances. The electrokinetics properties of the deposit were also investigated. An optical and an acoustic method were used to measure local cake thickness and growth kinetics. The thicknesses given by the two methods were first compared. It was shown that for compact deposits the two different methods lead to the same thickness of the deposit. For more porous deposits, these two methods allow to obtain complementary data at two different depths of the deposits. The influence of operating conditions on cake layer structuring during filtration of modelled particles was evaluated. Using the optical method it was shown that, whatever the operating conditions, the cake structure is not constant in time. Furthermore, a spatial variability of the cake layer thickness might exist especially in the case of weak particle-particle repulsion. Finally, it has been investigated whether the different methods could be applied or not to the case of biofluid filtration. The structural properties of the complex deposits built up during diluted activated sludge filtration were investigated. Cake compressibility was observed at global scale by a monitoring of process performances and was also observed at local scale: cake thickness decreases as TMP increases. Furthermore, at local scale, a spatial variability of deposit structure was found. Particle addition into the biofluid was assessed in order to mitigate compressibility effectsTOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Rheological study of sludge of membranes bioreactors for water treatment: protocol, limitations and link with the filtration

The submerged membranes bio-reactors (sMBR) are more and more visible in the field of waste water treatment. The membrane fouling, that causes a drastic fall of the performances, can be limited by the application of a swarm of bubbles close to the membrane surfaces. This aeration as a major factor of the energetic expense of these processes, lets numerous studies to focus on the understanding of the mechanisms linking the bubbles swarm with fouling.. In this background, the rheological tools appeared to be useful to understand the behaviour of sludge under shear stress. In order to be sure to get significant results, we used three types of rheological measurements: i) the influence of shear rate on shear stress; ii) the influence of upward then downward stages of shear stress on viscosity; iii) the influence of the alternation of two stages of shear stress with implementation times identical to those of sMBR aeration. Besides a viscoplastic behaviour previously observed, a phenomenon of hysteresis appeared. The transparent upper plan used on the rheometer exhibited formations of aggregative structures “in roll”. Sludges of a sMBR using different sequencing of aeration are compared: the developed protocols enabled to differentiate those sludges, with characteristic results depending on mechanical applications. The aim of this work is, eventually, to propose some correlations between usual characteristics of the process and aeration operating parameters, in order to propose an aeration policy improving energetic performances

Réutilisation des eaux usées épurées par association de procédés biologiques et membranaires

Les procédés de réutilisation des eaux usées doivent être robustes, fiables et rentables pour que leur utilisation se démocratise et devienne complémentaire des traitements des eaux de surface. Le couplage d un procédé biologique et de procédés membranaires représente une solution prometteuse pour répondre à ces challenges. Cette étude se focalise sur l impact des conditions de fonctionnement du procédé secondaire (en particulier par bioréacteur à membrane BAM) sur le colmatage du procédé tertiaire de nanofiltration (NF) ou d osmose inverse (OI) ainsi que sur le devenir des micropolluants et microorganismes tout au long de la chaine de traitement. Dans un premier temps, des expériences à court terme de filtration avec différentes membrane NF et d OI ont été réalisées afin de caractériser les interactions entre effluents secondaires et membranes. Il a ainsi été observé de très fortes rétentions de tous les micropolluants ciblés par la Directive Cadre Européenne. En termes de colmatage, la chute de flux de l OI, essentiellement liée pour ces essais de courte durée à une augmentation de pression osmotique puis à un dépôt de cristaux minéraux, peut être maîtrisée en contrôlant le pH et la concentration en carbonate et phosphate de l effluent secondaire. Par ailleurs, des chutes de flux plus importantes sont observées lors des filtrations réalisées avec les membranes de NF qui sont plus sensibles au colmatage irréversible. Dans un second temps, l optimisation de la filière de traitement des eaux usées urbaines couplant un bioréacteur à membranes à un procédé d OI a été réalisée à partir d une unité pilote fonctionnant en continu. La sélection de conditions opératoires adéquates a permis de faire fonctionner le procédé d OI pendant plus de quatre mois sans qu aucune maintenance ne soit réalisée. Une faible chute de flux de l OI, linéaire sur toute la période de filtration, essentiellement dû à l adsorption de molécules organiques à la surface de la membrane, a été observée. Sur l ensemble de la période d essais, la filière BAM/OI permet d obtenir un abattement optimal en micropolluants présents. Lorsque des micropolluants sont injectés à des concentrations plus élevées (simulation d une brusque dégradation de la qualité des eaux en entrée de filière) dans le bioréacteur, une chute de l activité de la biomasse couplée à un relargage de produits microbiens solubles peut être observée. Néanmoins, ces pics de pollution n ont eu aucun impact sur le colmatage de la membrane du BAM ni sur celle de l OI. La filière BAM-OI permet donc de garantir un taux de rejet élevé et une productivité d environ 15 L.h-1.m2 quelles que soient les fluctuations de la composition de l eau usée urbaine à traiter.In order to be competitive compare to surface water treatments, wastewater reuse needs robust, reliable and profitable combination of technologies. The combination of bioreactors and membrane processes seems to be a promising solution to these challenges. This study focus on the impact of the operating conditions of the secondary treatment (particularly the membrane bioreactor (MBR)) on the nanofiltration (NF) and reverse osmosis (RO) tertiary treatments as well as the fate of micropollutants and microorganisms along the treatment line. Firstly, short term filtration experiments with various NF and RO membranes were performed in order to characterize the interactions between secondary treatment effluents (STE) and membranes. High retentions of micropollutants listed by the European water framework directive were observed. During these short term experiments, RO flux decline is mainly due to an increase of osmotic pressure and then a precipitation of salts that can be solved by controlling the pH and thus the carbonate and phosphate concentration of the STE. In addition, higher flux declines are observed with NF because of a higher irreversible fouling behavior. Secondly, continuous long term tests were performed on a pilot unit combining a MBR and a RO processes. The appropriate selection of operating conditions allowed treating wastewater during more than four months without any maintenance. A linear low flux decline, mainly due to adsorption of organic molecules at the membrane surface was observed. During this filtration period, the MBR/RO process presented very high micropollutant retentions. When micropollutants are injected at higher concentration (simulation of sudden fluctuation of feed composition) into the MBR, a drop of biomass activity combined with soluble microbial products release can be observed. Nevertheless, these peaks of pollution did not cause any additional fouling of MBR as well as RO membranes. MBR/RO process is then a reliable technology that can guaranty high retention and productivity (around 15 L.h-1.m-2) whatever the fluctuations of the feed composition.TOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Modeling equations and dataset of model parameters for ultrafiltration membrane fabrication

In the related research article, entitled “A generic process modeling ‒ LCA approach for UF membrane fabrication: Application to cellulose acetate membranes” [1], a generic model is described and used to obtain the list of material and energy flows as a function of operating conditions for ultrafiltration (UF) hollow fibers preparation by non-solvent induced phase separation. In this data article, equations of the model, a dataset of model parameters and modelled data are detailed. modeling equations are developed from material and energy balances for each unit operation (i.e. from polymer solution mixing to module conditioning) based on an industrial membrane fabrication process of UF cellulose acetate modules. These equations may be reused as such or adapted to other membrane materials and industrial practices. The dataset of model parameters relates to industrial on-site measurements and scientific literature for the existing cellulose-based module. The modelled data corresponds to a reference situation for which hollow fibers (inner and outer diameters equal to 0.93 mm and 1.67 mm, respectively) are fabricated from a polymer solution composition of 20 wt.% of cellulose triacetate, 78 wt.% N-methyl-2-pyrrolidone and 2 wt.% lithium chloride

A generic process modelling – LCA approach for UF membrane fabrication: Application to cellulose acetate membranes

The purpose of the research is to elaborate and implement a decision-making tool for greener membrane fabrication. The scientific novelty put forth in this study is the generic process modelling – LCA approach applied to the field. The resulting parameterized model allows to obtain material and energy flows as a function of operating conditions for ultrafiltration hollow fibers prepared by non-solvent induced phase separation. Its modular configuration allows for flexibility and adaptation to various membrane materials and industrial practices. Contributions of inputs on environmental impacts can be assessed, as well as the influence of operating conditions. Results for cellulose acetate membranes show major contributions of NMP (i.e. solvent) and glycerol (i.e. pre-conditioning liquid). Improvement strategies for environmental mitigation include acting on glycerol-related operating conditions and are to be considered within the geographic context of membrane fabrication; further technical and economic feasibility studies would embed these strategies in a full eco-design approach. Such a methodology and results should be taken into account for the elaboration of “green membranes” whatever the application and coupled with the impact of membrane use and end-of-life

A metrics-based approach to preparing sustainable membranes: application to ultrafiltration

The purpose of the research is to make a first step towards rationalizing green polymeric membrane preparation. A holistic methodological approach based on metrics that consider technical, environmental, health and safety issues have been suggested to assess sustainability of membrane preparation. Metrics have been applied to solvent substitution in a non-solvent induced phase separation process. The flammability hazard of three shortlisted alternative solvents has substituted the reprotoxicity hazard of common solvents. The ultrafiltration cellulose diacetate membranes prepared with methyl lactate as solvent have a greater renewable intensity and require a lower number of solvents for their preparation. Trade-offs between use of resources (polymer, solvent, energy…) and membrane properties are inevitable. Further socio-economic, risk and life cycle analysis are crucial to fully integrate ecodesign in membrane preparation

Attempts, Successes, and Failures of Distance Learning in the Time of COVID-19

Over 1.7 billion students around the world have had their education disrupted by the spread of the Coronavirus disease worldwide. Schools and universities have not faced this level of disruption since World War II. The COVID-19 pandemic presented a colossal challenge for teachers to urgently and massively adapt all their classes to distance learning in order to maintain educational continuity with the same quality. Even if some teachers and certain classes were ready to face the situation, a large majority had to adapt their teaching and learning in a very short time without training, with insufficient bandwidth, and with little preparation. This unexpected and rapid transition to online learning has led to a multiplication of teachers’ strategies for distance learning in lectures, tutorials, project groups, lab works, and assessments. The purpose of this paper is to present the feedback from students and teachers who participated in the lockdown semester of two different groups of a 5-year program in Chemistry, Environment and Chemical Engineering (100 students) at INSA Toulouse (France). The analysis has highlighted some great successes and some failures in the solutions proposed. Consequently, some guidelines can be given to help us all to learn the lessons of such a singular experience in order to face the unexpected future with more knowledge and more successful distance learning. Teachers have shown very strong resilience during this crisis, at the cost of significant personal commitment. They admit that they have learned more about distance education in two months than in the last 10 years

Procédé hybride de coagulation/ultrafiltration pour la potabilisation des eaux de surface

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Engineering of an MBR supernatant fouling layer by fine particles addition: A possible way to control cake compressibility

International audienc