La microfiltration est largement utilisée pour la clarification, la stabilisation et la concentration de nombreuses suspensions à base de fruits (jus de fruits, agro-déchets, vin, etc.). Malgré ses divers avantages, la microfiltration présente néanmoins un inconvénient majeur qui est le phénomène de colmatage qui s’installe pendant l’opération de filtration et entraîne une diminution de la perméabilité membranaire. Si de nombreux mécanismes de colmatage (adsorption, blocage de pores, etc.) sont observés pendant la filtration de suspensions polydisperses comme les jus de fruits ou certains coproduits liquides, le dépôt de particules sur la membrane est souvent supposé être le mécanisme limitant. La formation de ce dépôt est fortement dépendante de l’équilibre entre forces convectives (imposées par le flux de perméat), qui attirent les particules de la suspension à proximité de la membrane, et forces de rétrotransport, qui éloignent les particules de la surface membranaire. La stratégie la plus employée pour maitriser le colmatage membranaire par dépôt est la filtration tangentielle qui permet d’imposer de forts cisaillements à la surface membranaire qui favorisent les mécanismes de rétrotransport des particules. Si cette stratégie de maîtrise du colmatage est amplement utilisée à l’échelle industrielle pour la microfiltration des suspensions à base de fruits, elle nécessite des coûts d’investissement et de fonctionnement non négligeables qui limitent son implantation aux industries présentant de fortes capacités de production et d’investissement. Au regard de cela, l’utilisation d’une configuration de filtration à membranes immergées pour la microfiltration de suspensions à base de fruits pourrait être une alternative intéressante. Cette configuration repose sur l’immersion de la membrane (modules plans ou fibres creuses) dans la suspension à filtrer, et est associée à un mode de filtration externe-interne, frontal ou quasi-frontale. Si l’absence de conditions hydrodynamiques intenses au voisinage de la membrane est associée à des flux relativement bas, les nombreux avantages de ce mode opératoire (coûts de fonctionnement réduits, simplicité opérationnelle, forte compacité, etc.) pourraient favoriser son emploi par les petits producteurs de jus de fruits et/ou les industries de valorisation des coproduits présentant des capacités limitées d’investissement et enclins à minimiser leurs couts opérationnels. Ce travail a ainsi étudié pour la première fois la possibilité d’utiliser un tel système pour la microfiltration de suspensions à base de fruits variées (jus de fruits et coproduits vinicoles). Ce travail de thèse a ciblé ainsi plusieurs objectifs : (i) caractériser le potentiel et le comportement colmatant de suspensions à base de fruits, en lien avec les caractéristiques physicochimiques propres à chaque suspension et au regard de leur filtration par membranes immergées, (ii) étudier des performances d’un système de microfiltration de suspensions à base de fruits par membranes immergées, performances en termes de productivité et de sélectivité et enfin (iii) dégager des pistes de réflexion qui conduiraient à une choix pertinent de conditions de filtration (mode immergé ou tangentiel) pour un type de suspension ciblé. Ce travail fournit ainsi des résultats d’identification de paramètres physico-chimiques clefs qui pourraient constituer un premier guide pour le choix de la configuration membranaire la plus adaptée au produit, permettant d’assurer une productivité acceptable lors de la microfiltration de suspensions à base de fruits. / Microfiltration is widely used to ensure clarification, stabilization, and concentration of various fruit-based suspensions (e.g. fruit juices, food by-products, wine). However, the performances of membrane filtration remain highly challenged by membrane fouling. During microfiltration of polydisperse suspensions, such as fruit-based suspensions, membrane fouling is generally associated to the deposition of particles on the membrane layer. This type of fouling is mainly governed by the equilibrium between convective forces (permeate flow), leading particles to flow towards the membrane, and back-transport forces, removing particles away from the membrane surface. The filtration performances depend strongly on this equilibrium, which is mostly governed by the hydrodynamic conditions of the filtration process and the particles size distribution of the suspension. In food industries, cross-flow microfiltration is generally used to limit membrane fouling. In this configuration, high cross-flow velocities are applied in order to enhance the back-transport forces limiting the deposition of foulant materials on the membrane surface. However, this working mode is well known to be highly energy consuming and might not always be relevant depending on the suspension characteristics. In the light of this, using immersed membranes configuration for the microfiltration of fruit-based suspensions might be an interesting alternative, especially for small producers with limiting investment capacity. In this configuration, widely used in other fields, the membranes are immersed in the suspension and filtration is performed in operating conditions close to that of dead-end filtration with limited back-transport forces and low operating costs. However, the performances of this filtration configuration remain little studied for the microfiltration of fruit-based suspensions. In this respect, this work investigated for the first time the possibility of using immersed membranes configuration for the microfiltration of various fruit-based suspensions (fruit juices and winery byproducts). Firstly, a characterization of the fouling potential of various suspensions during their microfiltration using immersed membranes filtration was performed in relation with their physicochemical properties (particle size distribution). Then, this work allowed highlighting the promising performances of immersed membranes configuration when used for the microfiltration of fruit-based suspensions, in terms of productivity and in terms of selectivity (clarification, concentration of bioactive compounds). Finally, it allowed drawing preliminary results about the relation between the physicochemical characteristics of a suspension and its fouling behavior while using (i) immersed membranes filtration or (ii) conventional cross-flow filtration. These results might be of great interest for the identification of relevant physicochemical parameters to predict the usefulness of using high cross-flow velocity to prevent membrane fouling during the microfiltration of fruit-based suspensions.

Les eaux usées peuvent possiblement être traitées par un système membrane intégré et combinant les procédés de bioréacteur à membrane (BAM) et d’osmose inverse (OI) pour une élimination efficace des micropolluants en vue de la réutilisation des eaux. Cependant, le rejet des concentrats d’OI dans l’environnement pourraient représenter un danger en raison de la toxicité de certains de leurs composés (micropolluants, sels, matières organiques). Une des solutions possibles peut être de recycler le concentrat d’OI vers le BAM. Néanmoins, une étude approfondie s’impose pour une telle configuration car le recyclage mettrait en jeu la recirculation de matière organique non biodégradable, ou de fortes concentrations en sels ou micropolluants, qui pourraient finalement engendrer, directement ou indirectement, un colmatage de la membrane ainsi qu’une modification de l’activité bactérienne dans le BAM. Les effets du recyclage de concentrat d’OI sur les performances de BAM ont été étudiés de deux différentes manières, en distinguant les effets à court-terme (ou court temps de contact) et les effets à long-terme (ou long temps de contact). Les résultats montrent qu’après un temps de contact de 3 heures entre le concentrat et les boues, les concentrations en protéines et polysaccharides dans le surnageant restent inchangées par rapport au début de l’opération. Une analyse HPLC-SEC a permis d’étudier les effets du concentrat d’OI sur la production de matières microbiennes solubles de types protéique. Un pic de concentration en substances protéiques ayant une masse moléculaire de 10 à 100 kDa a été observé dans le surnageant juste après l’addition du concentrat d’OI. Le pouvoir colmatant des boues n’a lui pas été modifié après l’injection du concentrat d’OI. Cette observation ouvre sur la possibilité de développer une opération d’OI comme traitement tertiaire en aval du BAM. La combinaison BAM-OI pourrait donc être une solution envisageable pour traiter le concentrat d’OI. Pour les longs temps de contact, les résultats ont montré que l’impact de l’effluent toxique (concentrat d’OI) sur les boues dépendait du rendement de l’opération d’OI et des caractéristiques du concentrat. Les mêmes tendances ont été observées quelle que soit la composition du concentrat en sels et en matière organique, puisqu’une augmentation de la concentration en protéine a été mise en évidence. L’effet du recyclage du concentrat d’OI a aussi été étudié à différents débits et avec différentes caractéristiques. Les effets sur les performances globales du BAM ainsi que sur son colmatage ont plus particulièrement été investigués. Le taux d’abattement en termes de Demande Chimique en Oxygène (DCO) est, dans tous les cas, supérieur à 93 %, quel que soit le débit de recyclage. Des résultats similaires ont été obtenus en termes de Carbone Organique Dissous. De plus, l’efficacité de la nitrification n’a pas été affectée en présence de concentrat d’OI dans le BAM. L’analyse HPLC-SEC a révélé un pic important de concentration en composés protéiques dans le surnageant, avec des masses moléculaires comprises entre 10 et 100 kDa et entre 100 et 1000 kDa. Par conséquent, une augmentation significative du pouvoir colmatant des boues a été observée et attribuée à la présence de protéines. Par ailleurs, le recyclage du concentrait d’OI n’a pas eu d’effet sur l’élimination de la carbamazépine et du diclofenac dans le BAM. Au contraire, l’élimination du ketoprofene a légèrement baissé, en passant de 94 à 72 %. Enfin, l’effet du recyclage de concentrat d’OI sur la biodégradation a été révélé comme insignifiant, ce qui indique que le recyclage du concentrat d’OI pourrait être une bonne alternative pour réduire les concentrats d’OI et limiter leur rejet dans l’environnement. / Wastewater effluents can be treated by an integrated membrane system combining membrane bioreactors (MBR) and reverse osmosis (RO) for effective removal of micropollutants in the field of high-quality water reuse. However, discharging the RO concentrate waste stream directly into the natural environment could lead to serious problems due to the toxic components contained in the concentrates (micropollutants, salts, organic matter). A possible solution could be the recirculation of RO concentrate waste to the MBR. However, such an operation should be studied in detail since the recirculation of non-biodegradable organic matter or high concentrations of salts and micropollutants could directly or indirectly contribute to MBR membrane fouling and modification of the biodegradation activity. The effects of RO concentrate recirculation on the MBR performances were investigated in two different ways of contact, i.e. short term peak contact and long-term continuous contact at various operating conditions. The results demonstrated that after 3 hours of contact time between the sludge and concentrate, the same values of both protein and polysaccharide concentrations were found in the supernatant, compared to that at the beginning of the reactor. HPLC-SEC analysis was employed to study the effects of RO concentrate on the production of protein-like SMPs. A significant peak of protein-like substances with a molecular size of 10-100 kDa was observed immediately in the supernatant after the addition of RO concentrate. Besides, no significant change was found of the sludge fouling propensity after the injection of RO concentrate into the activated sludge. This finding proposes the opportunities to develop RO process as a tertiary treatment of the membrane bioreactor (MBR), hence, the integrated MBR - RO concept with the RO concentrate recirculation to the MBR might be a solution to treat the concentrate waste stream produced by RO. During the long-term continuous contact, the results demonstrated that the impact of the toxic flow on activated sludge depends on the recovery of the RO step and the characteristics of the concentrate but the same trends were observed whatever the organic matter and salt contents of the concentrates: the concentration of proteins increased. The effects of the reverse osmosis concentrate recirculation, at different flow rates and with different characteristics, to the MBR were investigated. Their impacts on MBR global performances, especially the MBR fouling were evaluated. The removal efficiencies of chemical oxygen demand (COD) at the different flow rates of concentrate were greater than 93%. Similar results for the dissolved organic carbon removal efficiency were found in the MBR. Additionally, the presence of RO concentrate in the MBR did not inhibit the nitrification process. HPLC-SEC analysis employed to study the effects of RO concentrate on the production of protein-like SMPs demonstrated a significant peak of protein-like substances corresponding to 10-100 kDa and 100-1000 kDa molecules in the supernatant. Thus a significant increase of sludge fouling propensity was observed, which could be attributed to the increased quantity of protein-like substances. Furthermore, the recirculation of RO concentrate to the MBR did not significantly affect the removal of carbamazepine and diclofenac in the MBR. Meanwhile, the removal rate of ketoprofen was impacted slightly by the RO concentrate recycling to the MBR (from 94 to 72%). Finally, the effect of the concentrate on sludge activity was studied and no significant effect was observed on biodegradation, indicating that the return of the concentrate to the MBR could be a good alternative for the reduction of concentrate quantities before disposal to the environment.

La microfiltration est un procédé baro-membranaire largement utilisé pour stabiliser et clarifier les jus de fruits ou pour concentrer leur fraction pulpeuse. Toutefois le colmatage membranaire limite la productivité économique du procédé. Même si de nombreuses études ont été menées pour comprendre et limiter le colmatage, aucun véritable outil n'est aujourd'hui disponible pour prévoir la filtrabilité d'un jus de fruits. Le développement de ce type d'outils prévisionnels est pourtant essentiel pour faciliter l'optimisation des conditions de filtration et pour une meilleure maitrise du colmatage membranaire. Dans ce contexte, l'étude a été axée sur l'identification de nouveaux critères de filtrabilité des jus de fruits au travers de la compréhension et de la caractérisation des mécanismes de colmatage qui interviennent.En choisissant le jus d'orange comme modèle, une approche statistique a permis, dans un premier temps, une sélection rapide et pertinente des caractéristiques physico-chimiques des jus de fruits directement corrélées à leur filtrabilité, à savoir la matière sèche totale, l'extrait sec soluble, le pH, la conductivité et la granulométrie. Ensuite, des stratégies expérimentales complémentaires basées sur des filtrations à l'échelle du laboratoire ont été proposées pour identifier les différentes fractions colmatantes en fonction de leur taille ainsi que les mécanismes de colmatage associés. Ces stratégies novatrices ont permis d'étudier le pouvoir colmatant du jus d'orange en prenant en compte toute sa complexité et de proposer par la suite des cartographies de composés colmatants. Ces cartographies s'avèrent particulièrement intéressantes pour anticiper le comportement colmatant des jus de fruits sans avoir recours à des filtrations longues et coûteuses à grande échelle. Les résultats ont montré que le phénomène le plus important qui régit le colmatage membranaire global au cours de la filtration du jus d'orange semble être le colmatage externe par dépôt. Les objectifs de la dernière partie du travail, ont été de considérer plus fortement le caractère complexe et hétérogène des jus de fruits, pouvant les conduire à des changements brutaux de comportement lors de leur filtration. Pour cela des mesures rhéologiques en mode dynamique couplées à une stratégie d'isolement spécifique des différentes fractions colmatantes du jus d'orange ont été menées pour déterminer le comportement viscoélastique de la fraction insoluble du jus d'orange au cours de sa concentration. Les observations ont montré que les énergies des interactions entre les particules insolubles sont des fonctions croissantes de la concentration de la fraction insoluble et dépendent de la taille des particules. De plus, la transition vers un comportement « solide » du jus d'orange semble être favorisée par la présence des fractions particulaire et supra-colloïdale. Ces observations sont cohérentes avec le mécanisme de colmatage prédominant dû à l'accumulation de ces fractions à la surface de la membrane. La confrontation de nouvelles études de filtrabilité à l'échelle du laboratoire avec la performance de la filtration à grande échelle permettra de généraliser les stratégies proposées pour prédire la performance de la filtration de nouveaux jus de fruits. / Microfiltration is a pressure driven process successfully used to clarify and stabilize fruit juices or to concentrate their pulpy fraction. However, membrane fouling remains the critical factor governing the overall economic productivity of this process. Even if, many studies have been made to understand and limit membrane fouling, to date, there stills a lack of predicting tools to evaluate the filterability of fruit juices. However, it is interesting to develop practical and efficient tools for the prediction of fruit juices filterability in order to adapt and optimize filtration conditions to the fouling behavior of the filtered juice. In this respect, this study focused on the identification of new criteria of fruit juices filterability through the comprehension and the characterization of the potential fouling mechanisms.First, orange juice was chosen as test matrix and a statistical approach was used to select simple and relevant physico-chemical characteristics of this juice in relation with its filterability, namely dry matter, TSS, pH, conductivity, and particles size. Later, additional experimental strategies based on filtration tests at lab-scale were developed to identify the relevant size-classes of foulant compounds and related fouling mechanisms. These innovative strategies allowed studying the fouling potential of orange juice with the consideration of its complexity and proposing cartographies of foulant compounds. These cartographies are particularly interesting to anticipate the fouling behavior of fruit juices without any costly filtration operation at large scale. Moreover, results showed that external fouling seems to be the predominant fouling mechanism governing the overall membrane fouling during orange juice filtration. Finally, the aim of the last part of the work was to highlight the role of the complex and heterogeneous nature of fruit juices in their unexpected behavior during their filtration. For this purpose, the viscoelastic behavior of orange juice suspended solids during their concentration was obtained from rheological measurements in dynamic mode coupled with specific isolation of orange juice foulant fractions. Results showed that the energy of the interactions between juice particles increased as the suspended solids concentration increased and depends on the particles size. Furthermore, the solid-like behavior of the juice was enhanced by the presence of supra-colloids and large particles. These observations are in accordance with the predominant fouling mechanism that is due to the accumulation of these fruit fractions on the membrane surface. The confrontation of new filterability studies at laboratory scale with the performance of large-scale filtration will enable to generalize the proposed strategies to predict the performance of filtration of new fruit juices.

Nitrogen is the major component of biosphere. Paradoxically, nitrogen pollution is the concern globally. Ammonia pollution is due to its unceasing rejection into nature such as groundwater, current water and the atmosphere. This phenomenon constitutes a threat for the humanity, land and aquatic flora, and consequently disturbs the balance of natural ecosystem. Recently, that situation has lead to develop various techniques and/or technologies for ammonia removal from municipal and industrial wastewaters. Particularly in the environmental biotechnology area, two main objectives were recently aimed in many research activities: the development of new configurations of competitive bioreactors and the monitoring of partial nitrification process, which are the fundamental basis of this thesis project. In this study, the partial ammonium oxidation process, also called nitrite route, was studied in a 60 litre jet-loop submerged membrane bioreactor pilot plant. The research was organized around six chapters. An exhaustive literature review of the state-of- art of the biological nitrification process and the membrane technologies was performed. The materials and measurement methods were presented. The colorimetric method, the chromatography analysis, the biomass estimation by the suspended solids (SS), the aggregates size measurement, the gas holdup, the gas-liquid mass transfer, the bubbles gas diameter determination, the medium rheology aspects, etc., and the complete equipment of the bioreactor were studied in detail. The plant automation functioning was also studied. Membrane module (Mitsubishi Sterapore-L) characterization was carried out and three characteristic parameters were estimated: the membrane intrinsic resistance Rm, the membrane permeability Lp and the membrane porosity εm. Estimations revealed good agreement between experimental results and theoretical methods based on the Darcys law and the Carman-Kozeny law applicable in microfiltration system. Hydrodynamics and aeration aspects were studied. The mixing in the jet-loop system was characterized by the mixing time (tmix) and the circulation time (tc), respectively. The results showed that the characteristic times (tmix and tc) decrease with an increase in input gas flowrate and the circulated liquid flowrate. A model correlation involving the air and the combined liquid effects was proposed to describe the circulation time evolution. The classical non-steady state clean water test was used to determine the gas-liquid mass transfer coefficient (kLa). It was found to be influenced by the combined action of air and recirculated-liquid flowrates and a correlation has been proposed to describe their influence. The interpretation of kLa results and the system mixing data showed that the developed reactor corresponds to a near perfect mixing tank. This criterion was satisfactorily verified by literature data. The gas holdup (εg) was directly measured by the volume expansion method. In the absence of liquid circulation, εg ranged between 1 and 4% for the investigated range of gas liquid superficial velocities. It was found to increase linearly with the air superficial velocity, which corresponds to the bubbly flow regime. However, in the presence of liquid flowrate, εg slightly increased (from 1 to 6%) with increase in the superficial liquid velocity. A model has been proposed to correlate εg and the air and the recirculated-liquid velocities. The average diameter of the bubbles gas (dB) in the system was also estimated by the Leibson theoretical model based on the Reynolds number at the orifice of the gas distributor. Finally, biological aspects were studied. Respirometry measurements were conducted to characterize the process medium. The mass transfer, the gas holdup and the medium viscosity were determined. The obtained data allowed estimating the α factor and the β factor, respectively. The interaction of the growth of microorganisms into the process and the membrane performance was also investigated and a correlation model was proposed to describe membrane fouling with time. The optimal conditions for ammonium partial oxidation were determined using process monitoring and simulation. Dissolved oxygen (DO), temperature (T) and hydraulic retention time (HRT) were selected to achieve a high nitrite accumulation in the system. The results obtained showed that the selected parameters should be fixed at DO ≈ 2 mgO2.l-1, HRT ≈ 6 7 h and T = 30°C, respectively. The partial nitrification was simulated by the use of the TwoPopNitrification model included into the BioWin 2.2 software. For these simulations, a sequencing ammonia oxidation assumption was adopted: the nitrozation followed by the nitration step, respectively. The corresponding kinetics and stoichiometric constants were estimated by combining literature data and experimental nitrification results. For these estimates, the ammonium oxidation was monitored on several process samples taken at different times. The estimates were also delivered by monitoring the ammonium oxidation on the process operated in the batch mode. The plotting of simulations and experimental results revealed good agreement. In order to investigate the process performance in terms of biological stability, a long time period (≈ 600 days) was simulated. The results showed that a high stable nitrite accumulation (> 95%) could be achieved when the above optimal conditions are imposed to the system. However, after a long time, the accumulated nitrite is converted into nitrate and then the system is disrupted. For the simulated experimental conditions, the process disruption period was located between 180 and 350 days. At this period, a corresponding theoretical purge flowrate was found to range between 0.15 10-3 m3.d-1 and 3.0 10-3 m3.d-1. Simulations also showed that increasing the purge flowrate decreases the sludge retention time and then favours nitrite accumulation into the process. That is an interesting strategy to increase the performance of the biological partial nitrification process.