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This work aimed at characterizing the viscoelastic behavior and the fouling propensity of orange juice matrices composed of concentrated suspended particles (CSP) with defined size distributions. Small-, medium- and large-CSP (respectively colloids, supra-colloids and large particles) were first isolated and then mixed together according to a mixture design. The shear moduli, the specific resistance to filtration and the compressibility factor of isolated CSP and CSP mixtures were quantified. Small-, medium- and large-CSP were characterized by viscoelastic properties with a predominant solid-like behavior. The deposit layer of large-CSP had the highest shear moduli, while small-CSP presented the highest specific resistance to filtration. Small-, medium- and large-CSP deposit layers were considered as compressible matrices. The rheological behavior and the fouling propensity of mixtures of small-, medium- and large-CSP were analyzed using ternary diagrams. These diagrams revealed that the small-, medium- and large-CSP proportions modulated differently the shear moduli and the fouling propensity of CSP mixtures. Indeed, the solid-like behavior was strongly influenced by large-CSP proportions, the specific resistance to filtration depended mainly on the CSP size polydispersity, while small- or medium-CSP proportions had a major influence on the compressibility factor.

This work studies the role of dispersing and dispersed phases in the rheological properties of fruit juices during concentration operations. A special focus was given to the behavior of the dispersed phase (SS) when it is concentrated singly or simultaneously with the dispersing phase (TSS). The experimental strategy consisted in the characterization of the viscoelastic properties and the flow behavior of various orange juice suspensions containing different concentrations of soluble and suspended insoluble compounds. Results showed that the presence of solutes in the dispersing phase increases the cohesion energies between the particles of the dispersed phase and governs their viscoelastic behavior. As for the flow behavior, the concentration of dispersed particles proved to be the parameter controlling the consistency indexes in the TSS domain between 0% and 30%. Furthermore, results reveal a TSS threshold around 40%, at which great physical alterations may occur to the dispersed phase. This study provides new knowledge concerning the distinctive role of the dispersing and the dispersed phases in the viscoelastic properties and flow behavior of fruit juices. This information could be useful to predict and control the rheological behavior of fruit juices during concentration operations such as vacuum concentration and microfiltration.

This study proposed to investigate the impact of ripening on the physical properties of mango purees. An extensive study of the particle size and rheological properties of mango purees and their dispersed phase was performed using particle size measurements, small deformation rheology, and an innovative technology combining simultaneous rheometry and in situ FTIR spectroscopy. The results revealed a sharp decrease in the solid-like behavior of mango purees, as well as in the energy of cohesion of their dispersed phase during the first 10 days of ripening, leading to a weakening of their gel-structure. The size of suspended insoluble solids in the purees continued to decrease until 15 days of ripening. According to the spectral fingerprints, it was possible to identify some changes in the purees' sugar content occurring upon the physical changes during ripening. The highest sucrose and lowest fructose contents were observed in purees obtained during the first 10 days of ripening, in comparison with the following days. Based on the twin physical and spectral fingerprints, purees obtained from the early days of ripening (

International audience; The aim of this study was to evaluate the potential effect of tributyltin (TBT) on the performance of suspended-growth biological processes. The influence of TBT was evaluated for (i) the endogenous and exogenous respirations of heterotrophic micro-organisms in laboratory-scale batch reactors, taken from a municipal wastewater treatment plant and (ii) chemical oxygen demand (COD) removal, sludge production and oxygen consumption of a pilot-sale membrane bioreactor (MBR) system inoculated with heterotrophic micro-organisms taken from a MBR system. The batch experiments showed that the presence of TBT was likely to modify the activity of bacterial populations in endogenous conditions. The increase in endogenous oxygen needs suggested an increase in the maintenance requirements, essentially to manage the chemical stress induced by the presence of TBT. If the addition of TBT did not perturb COD removal in an MBR system, it limited sludge production and increased oxygen requirements; it is assumed that these modifications were linked with the necessity for the biomass to adapt in this stressful environment, as reflected by an increase in the maintenance requirements. These results emphasised that the respiratory activity of the bacterial cultures was modified by the presence of TBT, in the sense that an excess of oxygen was required to adapt to this chemical stress.; Le but de cette étude était d'évaluer l'effet potentiel du tributylétain (TBT) sur la performance des processus biologiques à croissance suspendue. L'influence du TBT a été évaluée pour (i) les respirations endogène et exogène de micro-organismes hétérotrophes dans des réacteurs batch à l'échelle du laboratoire, provenant d'une station d'épuration municipale et (ii) l'élimination de la demande chimique en oxygène (DCO), la production de boues et la consommation d'oxygène d'un système pilote de bioréacteur à membrane (MBR) inoculé avec des micro-organismes hétérotrophes provenant d'un système MBR. Les expériences en batch ont montré que la présence de TBT était susceptible de modifier l'activité des populations bactériennes en conditions endogènes. L'augmentation des besoins endogènes en oxygène a suggéré une augmentation des besoins de maintenance, essentiellement pour gérer le stress chimique induit par la présence de TBT. Si l'ajout de TBT n'a pas perturbé l'élimination de la DCO dans un système MBR, il a limité la production de boues et augmenté les besoins en oxygène ; on suppose que ces modifications sont liées à la nécessité pour la biomasse de s'adapter dans cet environnement stressant, comme le reflète l'augmentation des besoins de maintenance. Ces résultats ont souligné que l'activité respiratoire des cultures bactériennes était modifiée par la présence de TBT, dans le sens où un excès d'oxygène était nécessaire pour s'adapter à ce stress chimique.

Mango has an abundant production leading to important post-harvest losses. Mango processing is an alternative to reduce these losses. Nowadays, the lack of instrumental tools suitable to sort mangos according to their ability to be processed into products with specific quality is a main setback for their processing. The aim of this study was to develop new tools, mainly non-destructive, to sort easily fresh mangos according to their maturity stage and to the specific properties of their purees. To this end, an innovative experimental strategy combining textural, rheological and physico-chemical analyses was proposed to characterize mangos and their purees. Results showed that mango firmness is a great indicator of mango heterogeneity and has an important impact on the properties of mango purees. A non-destructive compression test was reliable to measure accurately mango firmness and to anticipate rheological and particles size properties of mango purees.

The objective of this work was to describe the dispersion state of flavonoids (i.e. naringin and narirutin) in the press liquor obtained after filtration-compression of fresh citrus (grapefruit) peels. An original methodology for the quantification of the dispersion, based on a size fractionation, and its evolution over time was proposed. Three fractions were identified: (i) a particulate fraction, (ii) a large-colloidal fraction and (iii) a small-colloidal and soluble fraction. Narirutin and naringin were initially found on small-colloidal/soluble form. During time, an aggregation of the compounds present in the press liquor, revealed by turbidity measurements, was observed. This aggregation resulted in an increase of the particulate fraction, at the expense of the colloidal one. This aggregation seemed to trap naringin, that progressively appeared in the particulate fraction, although that no evolution of narirutin location was observed. The tendency to sediment of the formed aggregates was evaluated, by a Turbiscan® optical analyser, in the objective of their future isolation. The stability study of the press liquor over time showed that this suspension was physically stable; the aggregates/flocs were not able to settle at room temperature, certainly because of interparticle repulsion or other reasons as low floc density, porous floc structure, etc.

Initiative of waste treatment has to be based on user-friendly technologies, using robust, cost-effective and low-energy consuming processes. The global objective of this study was to reduce technical steps for the extraction of flavonoids (naringin and narirutin) from citrus peel (grapefruit peel). After a first fresh peel grinding, the relevance of a simple filtration-compression, as a first downstream process, of the obtained slurry was studied. An optimization of this solid-liquid separation was proposed and the impact of a pectinolytic enzymatic treatment, resulting potentially in a larger release of flavonoids, was investigated. The results demonstrated that a preliminary step of filtration-compression, directly realized on fresh grinded peels as downstream processing for flavonoids extraction could be pertinent and that the enzymatic treatment improved the slurry filterability. An optimal separation was obtained with a transmembrane pressure of 5 bar, leading to highest extractable liquid phase volume and to an extraction around 80% of naringin and narirutin. A modelling of the filtration step, essential for the scaling of a filtration-compression process on site, was proposed. An originality of this work was to identify the dispersion state of the flavonoids within the liquid phase, capital identification for a relevant choice of the subsequent extraction step of these compounds.

Microfiltration is widely used to ensure the a thermal stabilization, clarification 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. To prevent membrane fouling, cross-flow filtration is generally performed. Nevertheless, this intensive working mode is considered as highly energy consuming due to the intensive pumping required to circulate the suspension at high velocities. In the light of this, immersed membranes configurations have been developed in many fields, as they allow working in energy-friendly operating conditions. Thus, this work investigated for the first time the performances of an immersed membranes configuration for fruit-based suspensions microfiltration, in terms of productivity (membrane fouling, permeate flux) and selectivity (clarification, concentration of bioactive compounds). This study focused on three fruit-based suspensions: a grapefruit juice and two winery by-products. Concerning the process selectivity, pilot-scale experiments showed that immersed membranes filtration allowed producing retentate and permeate of quality as least as good as the one related to conventional cross-flow filtration. Concerning the process productivity, cross-flow filtration allowed reaching higher fluxes compared to immersed membranes filtration, in accordance with the conventional order of magnitude specific to each configuration. Immersed membranes configuration could find interesting applications within small production units of fruit juices and/or industries dealing with the valorization of low added-value byproducts thanks to its various advantages (high compactness, easy handling and mobility, low investment and operational costs).

A high molecular weight chitosan was chemically modified to quantitatively incorporate quaternary ammonium groups. Its efficiency was evaluated in the liquid-solid separation for various liquors, and compared with the one of a polyelectrolyte usually used for this utilization. The performance of the liquid-solid separation was estimated through the determination of two parameters measured after the screening- settling of the mixture liquor/flocculating agent: the separation efficiency (EV) and the TS removal efficiency (ETS). Apart for liquor 6, TS removal was always better after an addition of functionalized chitosan. Furthermore, whatever the type of liquor, the distribution was modified by an increased presence of high-size particles when functionalized chitosan was added. Moreover, chitosan addition tended to homogenize the size of the particles, which could facilitate the choice of the liquid-solid separation process. This homogenization was particularly observed for the liquor initially highly dispersed in size, i.e. liquors 1, 4, 6 and 8.

Biomass concentrations 2 to 5 times higher than in a conventional activated sludge (CAS) process can be achieved in a membrane bioreactor system (MBR). These non–conventional operating conditions, i.e. high sludge concentration, can induce different sludge characteristics and dewatering aptitude, essential parameters for the optimization of the sludge post–treatment, like mechanical dewatering. The objective of this work is to study the dewatering behavior of MBR sludge, and particularly the influence of high total suspended solids concentration, on viscosity and on the key dewaterability indicators. Operating conditions are chosen to obtain MBR sludge with constant characteristics, except TSS concentration. The results confirm that the sludge viscosity is dependent on the TSS concentration. The high viscosity obtained for high TSS concentration can be unfavorable to an efficient mixing in the MBR unit, as well as to acceptable membrane permeability. However, good settleability is obtained with high TSS concentration although the sludge presents high compressibility property and a large part of bound water. This large part of bound water seems to not disturb the sludge filterability, which stays relatively good in comparison with CAS. Consequently, high–TSS concentration in MBR system can be coherent with an efficient sludge post–treatment.

Despite the several advantages of microfiltration, applications of this separation technique in fruit juice industries have been challenged by its low economical productivity due to membrane fouling. Although several studies aimed to identify operating conditions (e.g. juice pretreatment, crossflow filtration mode, etc.) to achieve acceptable performances, only few studies focused on the fouling propensity of fruit juices and on the identification of their foulant compounds. The aim of this work was to evaluate the fouling behavior of two orange juices and focused on the identification of relevant size-classes of foulant particles. Lab-scale filtration tests were carried out in conjunction with juice size-fractionation with the aim of quantifying the resistance to filtration of the juices. Based on a resistance-in-series approach, size-cartographies of foulant particles that are juice and membrane-specific were built. These cartographies were provided for two mineral membranes M 1.2 and M 0.2 with different average pore diameters (1.2 and 0.2 μm). M 1.2 results showed that the fouling is mainly external for both juices and due to particles larger than 2 µm. In contrast, results concerning M 0.2 filtration tests showed that four different size-classes of fruit juices compounds are involved in different fouling mechanisms. Moreover, the hydraulic reversibility of the fouling mechanisms was evaluated through the impact of shear rate on the measured resistances. It was seen that the fouling was mainly reversible when M 1.2 was used for both juices filtration while it was not the case when juices were filtered with M 0.2 . This information would be interesting to choose the appropriate strategy in order to enhance the microfiltration of these juices at large scale. Moreover, the proposed size-cartography strategy would greatly satisfy the industrial demand for practical tool to identify the different size-classes of compounds governing the overall membrane fouling.

The objective of this paper is (i) to investigate correlations between MBR membrane fouling and MBR sludge physical properties, and (ii) to develop the parameters for control membrane fouling especially physical properties in term of dewatering parameters. The experiments are performed in a submerged membrane bioreactor, in sub-critical flux conditions. The physical sludge characteristic is studied for two running periods, characterized by different organic loads (VLR) and/or solid retention times (SRT). The physical sludge characteristics (SMP, SCOD, CST, SRF, viscosity and SVI) are quantified and correlated with the fouling rate. The soluble fraction is the major parameter affecting physical sludge characteristics, with the polymeric linkage. The CST can be a reliable parameter to predict the extent of second stage membrane fouling rate in MBR filtration and can be useful for monitoring the MBR system.

The objective of this research is to study the effect of the substrate/biomass ratio (F/M) on the performance of two immersed membrane bioreactors operating, respectively with a sequential (SMBR) or a continuous (CMBR) mode. A synthetic organic substrate was selected to analyse the mixed culture behaviour and an average 1 g COD L −1 day −1 volumetric organic load was imposed in both MBRs. Each system worked during a 150 days operational period without any sludge extraction. In both cases, the global performance was relevant due to the porous membrane selectivity and to the high reactors biomass concentration. In fact, the COD removal efficiency was more than 94%, and the permeate free from suspended solids with a turbidity lower than 0.5 NTU. Due to non-continuous conditions, the SMBR system appeared hardly less successful than the CMBR system, with a COD effluent concentration and a sludge production, respectively equal to 125 mg COD L −1 and 0.092 g COD P g COD T −1 which are approximately twice higher than in CMBR system. These differences are presumably linked with the very high instantaneous F/M ratios imposed on the SMBR system during the feed periods (from 12 g COD g MLVSS −1 day −1 at the beginning of the experiment to 2.5 g COD g MLVSS −1 day −1 at the end of the operation). These brief high F/M ratios could favour a cell replication behaviour which is generally linked to important microbial soluble compounds production (soluble COD) and unfortunately associated with an accumulation of products coming from cell lysis (sludge production). Despite these observations, the SMBR system appears as an appropriate solution in case of non-continuous wastewater productions as often observed on industrial sites.

The main objective of this study is to evaluate the performance and the structure of the microbial community of a submerged membrane bioreactor (MBR) for seafood processing wastewater treatment and reuse. This system was operated continuously under favourable biological conditions, with complete biomass retention. In terms of organic removal and membrane performance, the MBR had a good efficiency to treat high strength with organic loading variation characteristic of real seafood processing wastewater. The overall results showed the importance of ecological microbial compositions in each stage of development that were different in MBR in comparison with conventional activated sludge. The MBR sludge could tolerate real stresses such as salinity and variation of COD and SS inlet in a wide range, with always good removal efficiencies in terms of BOD and COD. At the beginning period, bulking sludge was present. After 700 h of operation, the sludge characteristics not only showed healthy floc formations and good settling, but also confirmed the stable state of the system without overgrowth filamentous bacteria. In evaluating the fouling potential of membrane by cake filtration theory, it was found that soluble substances, soluble microbial products and/or residual organics play a key role in inducing membrane fouling. The αW values of the soluble fraction were three times higher than those of the particulates of bacterial floc.

The aim of this work is to analyse the biological performances of two immersed membranes bioreactors focusing on the biomass adaptation to complex substrate degradation and the performance in term of permeate quality. Two influents were selected: a synthetic complex influent (acetate/Viandox®, MBR1) and a real seafood processing wastewater (surimi product, MBR2). The MBR systems were operated for long periods without any sludge extraction except for sampling. Organic matter removal, sludge production and quality of the treated wastewater were analysed and studied. COD removal efficiencies after a period of biomass adaptation were higher than 97% and 95% for the synthetic and real wastewater respectively. In both cases, the COD of the treated wastewater was lower than 50 mg.L−1. In spite of salt concentration in the real wastewater a biomass adaptation process occurs. In the overall operational period, a 0.058 gCODP.gCODT−1 and a 0.12 gCODP.gCODT−1 observed sludge yields were obtained for the MBR1 and MBR2 respectively. These values are approximately 5 to 10 times lower than those measured in conventional activated sludge process. These results showed that the presence of particular and some of non-easily degradable compounds in the influent of MBR2 didn't limit the performance of MBR in term of COD removal achieved. The results have also confirmed the excellent permeate quality for water reuse from MBRs systems.

This work focuses on the performances of two immersed membrane bioreactors used for the treatment of easily biodegradable organic matter present in food industry effluents, for the purpose of water reuse. Two reactor functioning modes (continuous and sequencing) were compared in terms of organic carbon removal and of membrane permeability. For each working mode, pollutant removal was very high, treated water quality presented a low COD concentration (

This study shows the changes in transmembrane pressure in a membrane bioreactor (MBR) operating at a constant flux and in well-defined biological conditions. Despite the initial choice of filtration conditions at sub-critical flux, gradual fouling is seen to develop in membrane material which, after long periods of experimentation without intermediary membrane regeneration, proves to be hydraulically irreversible. Thus a single parameter model was set up, whose value could be derived from monitoring the changes in transmembrane pressure. It works on the hypothesis that the open surface is reduced due to a successive blocking of membrane pores. The development of this model has shown that, despite operating conditions held at constant flux, an increase occurs in the rate of circulation in the pores which remain open, which may reach critical local filtration conditions, resulting in the formation of deposits which are reversible but induce an abrupt change in transmembrane pressure.

The aim of this study was to quantify the specific effect of adsorption on membrane fouling during filtration of a membrane bioreactor (MBR) mixed liquor suspension. Adsorption experiments were performed on well-defined protein solutions (β-lactoglobulin solutions) to provide reference results and compare them to those obtained during the filtration of MBR suspensions (raw suspension and settled suspension). Two different methods were used to quantify the role of adsorption in membrane fouling: a “static” method in which membranes were immersed in the biological suspension and a “dynamic” method supposing that the resistance due to adsorption is an irreversible phenomenon that remains after filtration and back-washing. It was shown for the two types of suspensions that (i) due to limited diffusion, the dynamic method appears to be more adapted than the static method; (ii) adsorption is a rapid fouling phenomenon that induces irreversible resistance and that, in frontal mode takes place at the beginning of the operation; (iii) the adsorption phenomenon shows specific hydraulic resistance of the same order of magnitude as the clean membrane resistance; (iv) other phenomena, i.e. progressive pore clogging, can also take place though subcritical hydrodynamic conditions.

The behaviour of an activated sludge system in starvation conditions was examined in batch according to substrate impulses defined by different S0/X0 ratio. The answer was characterised by an exogenous phase followed by a starvation one. If at high S0/X0 ratio, bacterial cell multiplication was the main synthesis process during exogenous phase, at low S0/X0 ratio the observed phenomenon was compound storage. In starvation conditions, for the lowest S0/X0 ratio, a rapid decrease in the MLVSS without soluble proteins production was observed. No bacterial lysis occurred and this phenomenon was due to consumption of the storage compounds with a decrease rate equal to 0.74 d−1. For high S0/X0 ratio, as soon as the exogenous phase was completed, a decrease of the MLVSS simultaneously to a soluble protein production was observed. An immediate bacterial lysis occurred with a decay rate equal to 0.53 d−1. Because MBR systems work generally in low F/M conditions, the activity of the present microbial population is close to the one observed in starvation phase. This work points out that these conditions do not allow net bacterial growth and cells just use lysis products to satisfy their maintenance requirements. These assumptions confirm the feasibility of a decrease of the net biomass production in a MBR when high sludge retention time is operated.

The aim of this work was to quantify the activity of autotrophic and heterotrophic populations present in a submerged membrane bioreactor submitted to a sequenced aeration, ensuring alternate nitrification and denitrification (BIOSEP® process). Specific nitrification and denitrification rates were determined over a fifteen-month running period, with and without physico-chemical phosphorus removal. The results show (i) zero-order kinetics; (ii) a specific activity independent of MLVSS concentration; and (iii) an evolution of the nitrification kinetics directly linked to an evolution of the nitrifying population within the unit. The study confirmed that denitrification kinetics depend on the concentration and on the nature of wastewater organic matter. L'objectif de ce travail a ete de quantifier l'activite biologique de populations autotrophes et heterotrophes presentes dans un bioreacteur a membrane soumis a une aeration sequencee, permettant alternativement nitrification et denitrification (procede BIOSEP®). Les vitesses specifiques de nitrification et denitrification ont ete determinees durant une periode de fonctionnement de 15 mois, avec et sans dephosphatation physico-chimique. Les resultats montrent (i) des cinetiques d'ordre nul, (ii) une activite specifique independante de la concentration en biomasse, (iii) une evolution de la vitesse de nitrification directement liee a l'evolution des populations nitrifiantes. L'eude a confirme que les cinetiques de denitrification dependent de la concentration et de la nature de la matiere organique des eaux usees.

The aim of this work was to present results from filtration of biological suspensions which had been subjected to defined hydrodynamic and biological conditions in a membrane bioreactor. In the context of our experiment, the granulometric distribution of particles and that of the soluble organic matter show that most of the suspension consists mainly of the particles with a radius of around 1 μm. The filterability tests demonstrate the positive effect of the crossflow velocity and the possible presence of a particle layer close to the membrane surface. Reference models (Brownian diffusion model, Shear-induced diffusion model and Inertial lift model) are used to identify the size of those particles that were responsible for the major clogging phenomenon according to the experimental results. The theory according to which back-transport of particles is favoured by a sideways migration of particles due to inertial lift would appear to be better adapted, as the calculations lead us to particle radius values of around those measured. However, certain essential points and certain experimental findings demonstrate the necessity to take into account elements that have often been neglected or forgotten so far in the formalism of models, such as biological growth conditions.

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.; 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.