Aeration and hydrodynamics in submerged membrane bioreactors

Membrane bioreactor (MBR) is already a well-developed wastewater treatment process for both municipal and industrial applications. Nonetheless, membrane fouling remains a significant problem for its wider development. In the case of submerged membrane bioreactors (SMBRs), one of the most efficient strategies to limit fouling is the use of a gas/liquid two-phase flow to enhance the mass transfer. However, the effect of aeration still remains incompletely understood. The complexity of flows and of the nature of activated sludge makes a theoretical approach difficult. Aeration is the source of a large part of the operating costs in most industrial scale plants and its optimization is a necessity to make the process really efficient. This paper first deals with hydrodynamics in MBRs, then it reviews the parameters of aeration and their impact on filtration performance. Finally, the effects of aeration mechanisms on biological media are described

Rheological characterization of mixed liquor in a submerged membrane bioreactor: Interest for process management

Rheological analyses of a submerged membrane bioreactor mixed liquor were performed in the aim of characterizing the mixed liquor present in the bioreactor and thus proposing a process management. These analyses pointed out that the mixed liquor was characterized by its viscoplastic property, which leads to a possible restructuring ability when a shear stress lower than the yield stress is applied. As the shear stress in the bioreactor is essentially generated by coarse bubbles, specific experiments were carried out in which coarse bubbles were injected in an intermittent way. The results of these experiments showed that this method could avoid damage to the mixed liquor. So working with intermittent coarse bubbles is useful to prevent fouling, keep good flocculation and minimize the energy cost

Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy saving

Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy savin

CFD analysis of industrial multi-staged stirred vessels

This paper presents tools for analysis of CFD results adapted for flows in multi-stage stirred vessels through out two industrial cases. Those tanks fitted with double-flow impellers are used first to cool down highly viscous resins and subsequently for indirect emulsification. Since the simulation of these processes in their whole complexity would be unrealistic, it considers single-phase flows without heat transfer. The result analysis in order to prove that the mixing and the circulation are effective is not usual; in these cases, the circulation and impeller numbers are not adapted. The average axial flow numbers are relevant of the circulation in the whole tank and of the connection between the flows produced by the propellers in the given configuration. The velocity profiles give relevant results, but are not sufficient whereas the particle tracking validates that the propellers do not work together in one case and do work together in a second one

Submerged membrane bioreactor for waste water treatment: determination of the shear stresses produced by coarse bubbles

Submerged membrane bioreactor for waste water treatment: determination of the shear stresses produced by coarse bubble

Analyse morphologique des boues biologiques d'épuration. Descriptifs les plus pertinents et propriétés physico-chimiques des boues d’épuration

Analyse morphologique des boues biologiques d'épuration. Descriptifs les plus pertinents et propriétés physico-chimiques des boues d’épuratio

Modelling of submerged membrane bioreactor: Conceptual study about link between activated slugde biokinetics, aeration and fouling process

A mathematical model was developed to simulate filtration process and aeration influence on Submerged Membrane Bioreactor (SMBR) in aerobic conditions. The biological kinetics and the dynamic effect of the sludge attachment and detachment from the membrane, in relation to the filtration and a strong intermittent aeration, were included in the model. The model was established considering soluble microbial products (SMP) formation-degradation. The fouling components responsible of pore clogging, sludge cake growth, and temporal sludge film coverage were considered during calculation of the total membrane fouling resistance. The influence of SMP, trans-membrane pressure, and mixed liquor suspended solids on specific filtration resistance of the sludge cake was also included. With this model, the membrane fouling under different SMBR operational conditions can be simulated. The influence of a larger number of very important process variables on fouling development can be well quantified. The model was developed for evaluating the influence on fouling control of an intermittent aeration of bubbles synchronized or not with the filtration cycles, taking into account the effects of shear intensity on sludge cake removal

Aération pour le décolmatage dans les bioréacteurs à membranes immergées pour le traitement des eaux usées (impact sur le milieu biologique et la filtration)

Cette étude présente les travaux réalisés pour comprendre l'effet de l'aération sur le milieu biologique et sur la filtration dans les bioréacteurs à membranes immergées pour une gamme de paramètres opératoires proche de celles utilisées sur stations réelles. Notre démarche fait le lien entre paramètres opératoires (débit d'aération), hydrodynamique à l'échelle macroscopique (tailles et vitesses de bulles), hydrodynamique à l'échelle locale (contraintes de cisaillement) et propriétés du milieu biologique (taille de flocs et substances polymériques extracellulaires solubles). De moins bonnes performances de filtration à plus forte aération pourraient être expliquées par une plus grande déstructuration des boues sur le court terme. Par ailleurs tout effet d'évolution des boues sur le long terme en fonction des conditions d'aération a été écarté.This work contributes to the knowledge on aeration for fouling prevention in submerged membrane bioreactors, which represents a great part of energy consumption of the process. More precisely it aims at estimating the impact of aeration on mixed liquor properties for operational parameters range close to those used in full scale plants. Our study links operational parameters (airflow rate), hydrodynamics at macroscopic scale (bubble sizeand velocity), hydrodynamics at local scale (shear stresses), biological media properties (floc size and soluble extracellular polymeric substances), and filtration performance (transmembrane pressure variations). Hydrodynamics characterisation of two phase flow in membrane module enabled to highlight differences between air/water and air/sludge hydrodynamics with 15-25 % lower bubble velocities in sludge but one order of magnitude higher shear stress (maximal values of 10 Pa). Controlled breakdown of biological media was performed by imposing constant shear stress (range 0,1-10 Pa) to mixed liquor samples. Increase of shear induced a decrease of floc size, and soluble extracellular polymeric substances release. The comparison with shear value obtained by simulation showed that stresses induced by aeration were in the range of mixed liquor destructuration. A pilot campaign showed that wastewater had a stronger impact on the long term on mixed liquor properties, and thus filtration performances, than aeration. However higher transmembrane pressure increase rate observed on pilot for higher airflow at similar wastewater quality could be explained by stronger breakage of biological agregates on short termTOULOUSE-INP (315552154) / SudocSudocFranceF

Vinification continue avec levures immobilisées (analyse du système et conception du réacteur industriel)

Un nouveau procédé intensifié de vinification continue avec un mélange de levures S.cerevisiae et Sch.pombe immobilisées dans des billes d alginate est proposé. A l échelle laboratoire, l étude de la teneur en billes et de la configuration du réacteur conduit à l obtention d un réacteur de type lit fixe permettant une production de vin en 35 heures. Des validations du procédé aux échelles pilote (170 L) puis industrielle (120 hL) montrent que, en cave, du vin de qualité semblable au témoin est produit en 2 à 3 jours. Une analyse du comportement du réacteur a identifié des raisons de pertes de performances liées à l hydrodynamique lors du changement d échelle ainsi que des axes améliorations possibles. Ce procédé permet d obtenir un vin de qualité maitrisée et un gain de temps de plusieurs semainesFrom a batch to another, produced wines are usually different because of the different alcoholic and malolactic fermentation courses. To blend wines quality and continue wine production industrialization, a new continuous process, using Ca-alginate immobilized yeast cells, was developed for red wine-making. Working with a blending of S.cerevisiae and Sch.pombe allowed the regrouping of the alcoholic and malolactic fermentations in a unique step. After testing different reactor set-ups at lab scale, the selected process, a vertical bed reactor, was used in real wine-making conditions, firstly in a pilot reactor (170 L) and then in an industrial one (120 hL). The results showed that continuous wine-making was possible in 2 to 3 days. The wine presented nearly the same sensory profile compared to a classical one. Thanks to the analysis of the reactor behaviour, we were able to explain the efficiency losses linked to the hydrodynamic, observed during the scale-up. This new intensified process enables to obtain a wine with a controlled quality and to save several weeks of production timeTOULOUSE-ENSIACET (315552325) / SudocSudocFranceF

Weblab France-Brésil en génie des procédés

A Weblab is an experiment remotely operated via internet. A Weblab between the Chemical Engineering Department of the University of São Paulo Polytechnic School (EPUSP) and the Process Engineering Department of the Ecole Nationale Supérieurs d’Ingénieurs en Arts Chimiques et Technologiques (ENSIACET) is developed. The experiment consists of a tank level control. The main objective is to propose and test tunings for the system control loop. For this purpose, the students must work in synergy and propose models for the system in order to find the tuning parameters. Weblab is a showcase for new technologies and original experiences because it allows to perform a control action from anywhere in a supervision environment which is spreading out in the industry. The objectives and interests are mainly pedagogical as the Weblab favours the variety and diversity of intercultural experiences a student could experience during his undergraduate studies. Because of this, the Weblab perfectly integrates in an engineer curriculum that is open to international exchanges. Un WebLab est une installation commandée à distance via internet. Nous développons une expérience de Weblab entre le département de Génie Chimique de l’Ecole Polytechnique de l’Université de São Paulo (EPUSP) et le département Génie des Procédés et Informatique de l’Ecole Nationale Supérieurs d’Ingénieurs en Arts Chimiques et Technologiques (ENSIACET). L’expérience consiste en la régulation de niveau dans un bac. L’objectif de l’expérience est de proposer et de valider des réglages pour la boucle de commande du système. Pour cela, les étudiants de l’EPUSP et de l’ENSIACET doivent travailler en synergie et proposer des modélisations et un réglage du contrôleur. Le Weblab constitue une vitrine de technologies innovantes et d’expériences originales, car il permet, depuis n’importe où, d’effectuer une commande à distance dans un environnement de supervision qui est de plus en plus adopté dans l’industrie. Les objectifs et intérêts du WebLab se situent plutôt au niveau pédagogique car il peut être un facteur multiplicatif du nombre d’expériences interculturelles pouvant être vécues par un étudiant tout au long de son cursus. Pour ces raisons le Weblab s’intègre parfaitement dans une formation d’ingénieurs qui se doit d’être ouverte à l’international