[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Jun 2008 · Journal of Membrane Science
[Show abstract][Hide abstract] ABSTRACT: A novel heterogeneous extractive distillation process is considered for separating the azeotropic mixture chloroform – methanol in a batch rectifying column, including for the first time an experimental validation of the process. Heterogeneous heavy entrainer water is selected inducing an unstable ternary heteroazeotrope and a saddle binary heteroazeotrope with chloroform (ternary diagram class 2.1-2b). Unlike to well-known heterogeneous azeotropic distillation process and thanks to continuous water feeding at the column top, the saddle binary heteroazeotrope chloroform – water is obtained at the column top, condensed and further split into the liquid – liquid decanter where the chloroform-rich phase is drawn as distillate. First, feasibility analysis is carried out by using a simplified differential model in the extractive section for determining the proper range of the entrainer flowrate and the reflux ratio. The operating conditions and reflux policy are validated by rigorous simulation with ProSim Batch Column® where technical features of a bench scale distillation column have been described. Six reproducible experiments are run in the bench scale column matching the simulated operating conditions with two sequentially increasing reflux ratio values. Simulation and experiments agree well. With an average molar purity higher than 99%, more than 85% of recovery yield was obtained for chloroform and methanol.
Full-text · Article · Jan 2008 · Chemical Engineering Science
[Show abstract][Hide abstract] ABSTRACT: Membrane Bioreactors (MBR) are advantageous processes allowing guaranteeing a rejection of treated effluent respecting both reliability and recent sanitary rules. However main drawback for these processes remains the fouling of the membrane which depends in particular on the flocculation state of the sludge. Roughly, it can be take as assessment that the more the sludge is flocculated the weaker the fouling becomes. This work intends to show how a precise characterization of this state is thus of primary importance in order to optimize the choice of the operating conditions of the bioreactor.
In the case of immersed membrane bioreactors, the mixed liquor flocculation can be altered by the shearing generated by the aeration used to limit the fouling. The goal of our work is thus to study the potential of shearing generated by the system of aeration on the sludge flocculation. Rheological analyses are a possible key of explanation and lead to a process control proposal.
[Show abstract][Hide abstract] ABSTRACT: Le travail présenté dans ce mémoire est focalisé sur la compréhension de l’action des paramètres de filtration (temps de filtration, de non filtration, de rétrolavage, mode et débit d’aération) dans un BAMI pour le traitement d’eaux usées domestiques. La partie expérimentale a été conduite en deux temps. Tout d’abord sur effluent synthétique pour tester différentes conditions opératoires de filtration dans des conditions biologiques maîtrisées puis sur effluent domestique afin de valider les expériences précédentes. Les résultats de ces expérimentations ont mis en évidence que : - Le temps de non filtration pouvait être optimisé à partir de valeurs seuil de la perméabilité de la membrane et de la résistance spécifique de la liqueur mixte. - l’antagonisme dans le rôle de l’aération. D’une part un train de grosses bulles vient classiquement limiter l’apport de matière à la membrane (décolmatage) et d’autre part cette aération induit un cisaillement déstructurant les flocs (colmatage). Une caractérisation hydrodynamique et rhéologique du système a montré le caractère viscoplastique de la boue de BAMI et la pertinence de l’aération syncopé lors de la filtration d’un tel fluide. - L’ensemble des expériences menées sur l’effluent réel a confirmé d’une part les conditions opératoires choisies, d’autre part les caractéristiques de la boue sous contrainte de cisaillement. - L’analyse technico-économique, qui tient compte du « remplacement » des membranes pour lavage montre que l’on a mis en évidence des plages de paramètres opératoires conduisant à un fonctionnement rentable du procédé de traitement d’eau résiduaire urbaine. ABSTRACT : The aim of this work is the study of a waste water treatment operation using a submerged membrane bioreactor. The study was focused on the influence of operating parameter (filtration time, non filtration time, backflushing, aeration mode and aeration flow rate) in the prevention of membrane fouling. The first part of the study was made with synthetic effluent in order to test several filtration operating conditions in a well known biological environment. The second part consisted in the test of the system with municipal wastewater in order to validate the previous experiments. The main results are that : - Non filtration time can be optimized according to threshold value for membrane permeability and mixed liquor specific resistance. - Aeration has an opposite influence. On one hand, coarse bubbles are useful to prevent membrane fouling but on the other hand aeration can disturb sludge flocculation. Rheological and hydrodynamic analyses points out the viscoplasticity of the mixed liquor, which increases the interest in injecting coarse bubbles in an intermittent way. - Experiments realized with domestic effluent confirm on one hand the operating parameter choice and on the other hand sludge rheological characteristics. - Energetic analysis have pointed out that the operating parameters fixed in this study leads to an economically viable process for domestic wastewater.
[Show abstract][Hide abstract] ABSTRACT: Many studies have been performed to analyze the influence of extracellular polymeric substances (EPS) in membrane fouling. Most of these works deal with the impact of solid contents in the fouling, and some of them have studied the role of supernatant compounds. The aim of this work was to clarify the role of the different sludge fractions in the context of membrane bioreactor fouling. The laboratory-scale reactor used for experiments consists of a submerged membrane bioreactor for the treatment of synthetic wastewater. For the same organic load (0.4 g COD/g MLSS.d), several samples of sludge were taken off and divided intohree fractions (solid contents, soluble and colloids). COD and extractable EPS were quantified (carbohydrates and proteins). Dead-end filtration tests for each fraction were also carried out. According to these experiments, no correlation between EPS concentration in the solid part of the sludge and filtration resistance was found. Instead, a change of the filtration resistance was explained as a function of COD in the supernatant, and more especially as a function of proteins concentration. Indeed, when the value of proteins concentration in the supernatant changes from 30 to 100 mg/l, the value of specific resistance increased by a factor of 10. Finally, the characterization of the supernatant was shown as a key parameter for the MBR operating control. When the COD and proteins concentration in the supernatant remained low, the transmembrane pressure in the reactor remained even lower. Moreover, with the biomass growth rate analysis, our results suggest that the EPS production was linked to growth of microorganisms. The faster he growth, the less EPS production.
[Show abstract][Hide abstract] ABSTRACT: A systematic study of the separation of the azeotropic mixture chloroform – methanol by heterogeneous extractive distillation process is addressed in this work by using a batch rectifying column. Water was selected as an effective heavy entrainer adding to the resulting ternary system one unstable heterogeneous ternary azeotrope and one saddle heterogeneous binary azeotrope with chloroform. Unlike to well-known heteroazeotropic distillation process, the saddle binary heteroazeotrope chloroform – water can be drawn as a top condensed vapour thanks to the feeding of water at the first tray of the column. Therefore, the splitting of two liquid phases occurs into the top decanter and the chloroform-rich phase can be drawn as distillate product. The zeotropic mixture methanol – water left in the still can be separated in a further conventional batch distillation step. First, the process performance was determined by using rigorous simulation with the batch process simulator ProSim Batch taking into the technical features of the real bench batch distillation column. Experimental validation of the computed operating conditions for the extractive distillation step (reflux ratio and entrainer flowrate) was performed in the bench rectifying distillation column. One litre of the organic waste mainly composed by chloroform and methanol was separated adding continuously 20 mol/h of water at 25°C in the column top. Two constant reflux ratios, R=1.4 and R=10, was kept in the extractive distillation step during 1h and 20 minutes, respectively. Good agreement was obtained between simulation and experimental results. More than 85% of recovery yield can be obtained of each original component with a molar purity higher than 0.99 by using the proposed heterogeneous extractive distillation processes. This novel technology can be implemented at industrial scale for treatment of this organic waste and both azeotropic components can be reused in the genuine process.
[Show abstract][Hide abstract] ABSTRACT: Feasibility study of the separation of azeotropic mixture chloroform – methanol by heterogeneous batch extractive distillation is checked for water as a heavy heterogeneous entrainer in a batch rectifier. The main peculiarity of this process compared with the well known heterogeneous azeotropic distillation process is the withdrawal of the saddle binary heteroazeotrope chloroform – water thanks to the continuous feeding of the entrainer at the column top. First, the feasibility study of heterogeneous extractive distillation is carried out for determining essential operating conditions such as minimum entrainer flowrate and the proper range of reflux ratio, which provide the expected top and bottom product composition in a batch rectifying column. Finally, these results were validated via rigorous simulation with ProSim Batch. More than 85% of recovery yield of each original component can be obtained with a molar purity higher than 99% by using the proposed heterogeneous extractive distillation processes.