Effect of surfactants on liquid side mass transfer coefficients

In the present paper, the effect of liquid properties (surfactants) on bubble generation phenomenon, interfacial area and liquid side mass transfer coefficient was investigated. The measurements of surface tension (static and dynamic methods), of Critical Micelle Concentration (CMC) and of characteristic adsorption parameters such as the surface coverage ratio at equilibrium (se) were performed to understand the effects of surfactants on the mass transfer efficiency. Tap water and aqueous solutions with surfactants (cationic and anionic) were used as liquid phases and an elastic membrane with a single orifice as gas sparger. The bubbles were generated into a small-scale bubble column. The local liquid side mass transfer coefficient (kL) was obtained from the volumetric mass transfer coefficient (kLa) and the interfacial area (a) was deduced from the bubble diameter (DB), the bubble frequency (fB) and the terminal bubble rising velocity (UB). Only the dynamic bubble regime was considered in this work (ReOR = 150 - 1000 and We = 0.002 - 4). This study has clearly shown that the presence of surfactants affects the bubble generation phenomenon and thus the interfacial area (a) and the different mass transfer parameters, such as the volumetric mass transfer coefficient (kLa) and the liquid-side mass transfer coefficient (kL). Whatever the operating conditions, the new kLa determination method has provided good accuracy without assuming that the liquid phase is perfectly mixed as in the classical method. The surface coverage ratio (se) proves to be crucial for predicting the changes of kL in aqueous solutions with surfactants

Analysis of membrane fouling during cross-flow microfiltration of wine

The aim of this study was to investigate the individual impact on wine molecules as tannins, pectins and mannoproteins on multichannel ceramic membrane fouling during wine cross-flow microfiltration. The characterization of fouling mechanisms involved in the previous filtrations was realized by using the classical fouling models and the analysis of the total resistance curves. It was shown that the obtained initial fluxes are dependant of the nature of the studied molecules and their concentration. According to their increasing effect on permeate flux decline, the studied wine components could be ranked as: mannoproteins < tannins < pectins. During the filtration of wine added with tannins, it was found that the filtrations were governed by the cake layer formation mechanism. The presence of pectins caused the formation of gel-type layer which is found to be compressible under high pressures. For wines added with mannoprotein filtrations, it was shown that there is a threshold concentration above which a plateau value of permeate flux is obtained. Industrial relevance: The cross-flow microfiltration applied to wine filtration has become a legitimate alternative to conventional filtration processes. However, membrane fouling which affects the operating costs and the plant maintenance, limits the widespread application of this technique. To avoid or reduce membrane fouling, it is extremely important to identify the fouling elements and the mechanisms that govern the process. A better understanding of the mechanisms whereby fouling is formed during wine microfiltration may lead to be in position to control fouling or reduce it, to improve cleaning procedures and to adapt the process to the product to be filtered. The results presented in this paper concern the investigation and the understanding of fouling mechanisms by wine colloids (tannins, pectins and mannoproteins). We found that wine colloids had a strong impact on membrane fouling. Independently of their concentrations found in wine, they can be ranked according to their increasing effect on permeate flux as: mannoproteins b tannins b pectins. Such result provides important information and a better vision on the methods which can be used to limit membrane fouling for example the use of pectinolytic enzymes before filtration in order to hydrolyze pectin chains or precipitation of unstable tannins by finning the wine with bentonite. By elucidating fouling mechanisms such as cake layer and gel type layer, we can adapt the hydrodynamic process to control membrane fouling

Cross-flow microfiltration applied to oenology: A review

The cross-flow microfiltration applied to wine filtration has become a legitimate alternative to conventional filtration processes. However, membrane fouling which affects the operating costs and the plant maintenance, limits the widespread application of this technique. The aim of this review is to provide a better understanding of the development of the cross-flow microfiltration in wine industry, as well as the complexity of wine composition and its consequences on membrane fouling. This review covers also the impact of the operating conditions and the membrane characteristics on fouling mechanisms. Strategies to limit fouling as well as the latest innovations and commercial proposal are discussed in this paper

Impact of the physico-chemistry of the wine on membrane filtration performance

During the process of wine making, operation of cross-flow microfiltration allows a one-step clarification and sterilization of wine, with lower waste compared to the conventional processes of clarification and sterilization. Indeed, these processes are sources of voluminous waste (earth, Kieselguhr, additives), when discharges are becoming more and more restricted by environmental and health rules. Nevertheless, cross-flow microfiltration of wine presents a major drawback: membrane fouling causes a significant decrease in the flow rates, due to excessive retention of some wine components which could lead ultimately to the alteration of the quality of wine. The aim of this work was to study the impact of some specific wine components (phenolic compounds and yeast extract), as well as some physico-chemical parameters (pH) in regard to membrane fouling. Studies were performed using one red wine and synthetic wines, using cellulose acetate membranes (0.2 μm) operated in the dead-end mode under 2 bar pressure. The simultaneous presence of the both species of phenolic compounds (anthocyanins and tannins) in the synthetic wine was shown to be the main cause of fouling, whereas the presence of one specie leads only to standard blocking type behavior. An important decrease in the flow rates was also observed when yeast extract was added to the liquid. This yeast extract was shown to contain 300 mg/g of proteins and to be free of mannoproteins. The influence of these proteins on fouling was demonstrated while pre-treating the synthetic wine with bentonite, which was able to adsorb proteins, and in this case, no fouling was observed. It was also shown that, when decreasing the pH, the flow rate was enhanced. For all experiments, a fouling index or cake specific resistance, according to the type of fouling, was calculated in order to be used as a reference to estimate the filterability of a given wine, according to its composition in some targeted molecules. Finally, the experiments of the actual red wine exhibited complete rapid fouling of the membrane, probably due to the presence of high concentration of phenolic compounds

The use of nanofiltration membranes for the fractionation of polyphenols from grape pomace extracts

Filtration experiments in batch concentration mode (with recycling of the retentate stream) of grape pomace extract were performed in laboratory filtration membrane equipment by using nine commercial nanofiltration (NF) membranes with an approximate molecular weight cut-off (MWCO) of 1000‒150 Da. The filtration experiments of the selected pomace extract were performed by modifying the most important operating variables: transmembrane pressure, tangential velocity, temperature, and the nature and MWCO of the membranes. The evolution of the cumulative permeate volumes and permeate fluxes with processing time was analyzed till a volume reduction factor (VRF) of 10 was reached. The effect of the mentioned operating conditions was discussed. The effectiveness of the filtration treatments was determined by the evaluation of the rejection coefficients for several families of polyphenols. Membranes possessing MWCO between 1000 and 500 Da were able to quantitatively recover polymeric proanthocyanidins in the concentrate stream and separate them from phenols that passed through the membrane into the permeate stream. On the other hand, the 600 to 300 Da membranes could also be used for the fractionation of monomeric phenolic families. The membranes were able to partially remove the anthocyanin fragments of phenolic acid derivatives and flavonols in the concentrate stream and at the same time

A New Test of Filterability for Unprocessed Wines Evaluation of the Enzyme Efficiency

A new Test of Filterability has been developed. Measurements carried out with different types of wines indicate that the new filterability index is a useful tool for understanding and predicting the propensity to fouling of treated or untreated wines, e.g. with or without enzyme addition. The measurement method used in the Test of Filterability, requires only one type of membrane for all types of wine, and uses the same equipment as the traditional Fouling Index. Numerous trials have demonstrated that the filtration of wines is governed by standard blocking law. The definition of the new Test of Filterability, based on this filtration law, is proposed. The choice of membrane and the selection of the optimal pore size were based on the results of the experiments. Current methods used for the determination of fouling properties in wine filtration have been developed for the membrane filtration of small quantities of suspended matter. Enzyme treatment is a process often used in wine clarification. The new Test of Filterability indicates the best conditions for the filtration of all types of wines. The test is easy to implement and has been validated with various wines. This new Test of Filterability is an important tool for winemakers as it constitutes a simplified test of a wine's filterability. The new test may also be used to determine the filtration process that is best adapted to each wine while reducing the number of operations. The same approach may be adopted for the filtration of other liquids.&nbsp

Étude des paramètres affectant le transfert d'oxygène dans les vins

La micro-oxygénation des vins, par la dispersion de bulles d oxygène, est une pratique de plus en plus utilisée dans le domaine de l œnologie. Cette technique n est pas toujours convenablement maitrisée par manque de connaissances scientifiques sur les paramètres régissant le transfert de l oxygène. La recherche s'est focalisée sur l'étude des coefficients de transfert en fonction des composés du vin (CO2, éthanol, sucrose, consommateurs d oxygène) et des conditions opératoires (type de diffuseur, température, rapport entre hauteur et diamètre du contenant de liquide). Les résultats montrent que lors de la micro-oxygénation, le dioxyde de carbone dissous et le sucrose ont une incidence négative sur le transfert alors que la présence d éthanol améliore le transfert. En ce qui concerne les conditions opératoires, l augmentation de débit de gaz et l augmentation de rapport entre la hauteur et le diamètre de la cuve de micro-oxygénation joue positivement sur le transfert d oxygène La surface spécifique des bulles et le coefficient de transfert de matière ont pu être dissociés pour les vins. La nature tensio-active des composés du vin semble être un élément important sur le transfert de matière. Les connaissances acquises ont été appliquées à la micro-oxygénation au cours de deux étapes de l'élaboration des vins : la fermentation alcoolique avec la maitrise de l apport d oxygène et la simulation de la technique d élevage en barrique par micro-oxygénation couplée à l ajout de copeaux de bois. Une nouvelle approche concerne l'étude d'un contacteur membranaire qui permet le transfert d oxygène par diffusion.Micro-oxygenation of the wines, by the dispersion of oxygen bubbles, is a practice increasingly used in oenology. This technique is not always suitably controlled for lack of scientific knowledge on the parameters governing the transfer of oxygen. Research was focused on the study of transfer coefficients in function of wine components (CO2, ethanol, sucrose, consuming oxygen) and of operating conditions (type of diffuser, temperature, relationship between height and diameter of the container of liquid). The results show that during micro-oxygenation, the dissolved carbon dioxide and the sucrose have a negative incidence on the transfer whereas the presence of ethanol improves the transfer. As operating conditions are concerned, the increase in gas output and the increase in micro-oxygenation tank height/diameter ratio positively influence oxygen transfer. For wines, the specific surface of the bubbles and the mass transfer coefficient could be dissociated. The surfactant nature of wine components seems to be the most important factor in mass transfer. The knowledge so acquired was applied to micro-oxygenation during two stages of wine making: alcoholic fermentation with the oxygen yield control and the simulation of ageing technique in barrels coupled with the wood chips addition. A new approach relates to the study of a membrane contactor application allowing the oxygen transfer by diffusion.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Modélisation du procédé bioréacteur à membranes immergées (calage et validation du modèle ASM1 sur un site réel)

Les bioréacteurs à membranes (BAM) sont de plus en plus utilisés dans le domaine du traitement des eaux résiduaires urbaines notamment lorsque le terrain est limité ou qu un traitement épuratoire poussé est requis. Néanmoins, la gestion de ces installations et plus particulièrement du colmatage des membranes reste difficile et constitue toujours une source de problèmes pour les exploitants. La modélisation est un outil efficace et déjà éprouvé sur les procédés conventionnels à boues activées pour l aide à la conduite et à la compréhension de procédé avec les modèles de boues activées de type ASM. Le traitement biologique donc, et aussi les capacités de filtration des membranes (colmatage) sont deux aspects qui peuvent être modélisés sur les BAM. Au cours de ce travail, trois installations réelles ont été étudiées et l une d entre elles a été choisie pour le calage du modèle ASM1. La méthodologie a été adaptée aux spécificités des bioréacteurs à membranes et de l installation modélisée en particulier (fractionnement des eaux usées, calage de l aération) et un nouveau jeu de paramètres de l ASM1 a pu être constitué. L influence des propriétés des boues activées et des conditions d opération sur les capacités de filtration des membranes reste encore l objet de nombreuses recherches, généralement sur installations pilotes, et la modélisation dans ce domaine n en est qu à ses débuts. L objectif de ce travail concernant la filtration membranaire a été de caractériser le système membrane/boues à travers l étude des interactions entre les propriétés des boues, les conditions d opération et les paramètres de la filtration (perméabilité membranaire et vitesse de colmatage) à comparer avec les résultats de la littérature scientifique. Les deux BAM étudiés ont montré des comportements et relations entre paramètres assez différents confirmant la complexité des interactions entre membrane, boues et conditions opératoires.Membrane bioreactors (MBRs) are becoming increasingly popular for the treatment of municipal wastewater especially when land is limited or when the treatment requirements are high. Nevertheless, the operation of these plants and in particular the fouling of the membrane are still difficult to manage for the operators. Modelling is an efficient tool, which has already been successfully used on conventional activated sludge processes, for the operation and the understanding of the process using Activated Sludge Models (ASM). Biological treatment and membranes filtration capacity (fouling) are two aspects that can be modeled on MBRs. In this work, three full-scale plants were investigated and one of them was chosen for the ASM1 calibration. The usual methodology was adapted to the MBR specificities and to the modeled wastewater treatment plant in particular (wastewater fractionation, oxygen calibration) and a new set of ASM1 parameters was estimated. The influence of the sludge properties and the operating conditions on the membrane filtration capacity is still the subject of numerous studies, generally on pilot-scale MBRs, and modelling is in its early stages. The objective of this work regarding membrane filtration was to characterize the membrane/sludge system by studying the interactions between the sludge properties, the operating conditions and the filtration parameters (membrane permeability and fouling rate) and to compare them with the results from the literature. The two studied MBRs showed quite different behaviors and correlations between parameters, validating the statement that the interactions between membranes, sludge and operating conditions are very complex.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Recherche de nouveaux média filtrants régénérables ou valorisables (application à la filtration du vin)

Les adjuvants de filtration, en particulier les diatomites, sont très utilisés lors de l'élaboration des vins durant la filtration sur précouche avec alluvionage. Ils retardent le colmatage du filtre, augmentant ainsi son efficacité. Cependant, ces particules ne sont pas régénérables. La loi européenne sur l'environnement de 2002 n'autorise plus le dépôt en décharge des diatomites usagées et contaminées. Le but de cette recherche est de proposer un média filtrant non polluant, c'est-à-dire régénérable et/ou valorisable, inerte vis-à-vis du vin et disponible en plusieurs granulométries afin d'être utilisé lors des différentes étapes de l'élaboration du vin. Dans un premier temps, divers matériaux de différentes granulométries, ont été caractérisés en tant qu'adjuvants de filtration.Puis, ces particules filtrantes sont testées en filtration sur précouche et en filtration dans la masse. Les résultats de filtration montrent que de nombreuses particules sont efficaces en tant qu'adjuvant de filtration (rilsan, celluloses...) sont valorisables (incinération, épandage, ...) et sont compatibles avec le vin. La filtration en profondeur du vin est possible sur sable ainsi que sur billes de polystyrène. Les billes de polystyrène semblent cependant plus adaptées pour la filtration de solutions moins colmatantes que les moûts et les lies. La filtration dans la masse sur un lit de sable de un mètre est particulièrement efficace. Des lavages à contre-courant ont été effectués, prouvant la régénérabilité de ces matériaux.The filter aids, especially the diatomites, are widely used during winemaking in precoat filtration process because they delay the fouling. These particles cannot be effectively regenerate. According to the European directive, since July 2002, the disposal of the spent diatomites used in precoat filtration is prohibited because they are not final wastes. The aim of the study is to propose regenerable filter aids having a high environmental acceptability and being compatible with wine. The new filtering particles must be inert regarding wine and available in different sizes for the various applications in wine production. Several particles have been tested in deep or precoat filtration. Some particles seem to be really effective as filter aids (celluloses, rilsan, etc...) and are able to be cleaned or up-graded. Sand filter is very effective too, especially when the filter bed depth is equal to 1 meter. EPS beads could be used for wine clarification. Moreover, these filtering particles are backwashable and they don't affect the wine quality.BORDEAUX2-BU Santé (330632101) / SudocBORDEAUX1-BU Sciences-Talence (335222101) / SudocVILLENAVE D'ORNON-Bib. ISVV (335502201) / SudocSudocFranceF

Crit Rev Food Sci Nutr

Membrane processes are increasingly reported for various applications in wine industry such as microfiltration, electrodialysis, and reverse osmosis, but also emerging processes as bipolar electrodialysis and membrane contactor. Membrane-based processes are playing a critical role in the field of separation/purification, clarification, stabilization, concentration, and de-alcoholization of wine products. They begin to be an integral part of the winemaking process. This review will provide an overview of recent developments, applications, and published literature in membrane technologies applied in wine industry