Etude par capteur optique du dépôt formé lors de la filtration d'une suspension de bentonite sur fibre creuse

Lors de la filtration sur fibres creuses de suspensions de bentonite, il a été mis en évidence que le facteur limitant est la formation d'un dépôt à la surface de la fibre.Parlant de ces considérations, un dispositif optique a été mis au point pour suivre l'évolution spatio-temporelle du dépôt en cours de filtration sur fibre creuse à peau externe.Ainsi, il a pu être mis en évidence que l'influence de la vitesse d'écoulement n'est sensible qu'après un certain temps de filtration ou un certain volume filtré.Dans le domaine testé des faibles vitesses d'écoulement, il existe une période initiale où la loi de filtration sur gâteau est applicable.Dans le cas de fibres creuses à peau externe, l'optimum technique (productivité maximale) ou économique (coût minimal du m3 traité) serait donc plus à rechercher dans une optimisation de la séquence filtration-lavage que dans une augmentation de la vitesse d'écoulement.L'efficacité du réentraînement du dépôt lors du lavage peut être suivie grâce à l'équipement et au capteur développés.Use of membranes (MF or UF) for water treatment is now developed at an industrial scale. This approach is considered as a good solution to deal with the periodic strong increases in suspended solids contents which occur in karstic aquifers.Under these conditions, the main contribution to the growth of hydraulic resistance is related to the formation of a deposit on the membrane surface.Thus, an experimental study was performed at the laboratory scale in order to perform on line characterization of deposit formation during the filtration of a bentonite suspension through a hollow fiber.The filtration module is transparent and contains only one hollow fiber with its external skin.An optical device formerly developed was used as a sensor : a horizontal laser beam is focussed at the surface of the hollow fiber which is held perpendicular to the beam and can be moved step by step in the micrometric range.Experiments were performed with a bentonite suspension (concentration 0.375 kg/m3) and under different operating conditions :- dead end filtration and crossflow filtration with velocities up to 0,30 m/s in the annular space (which means Re ≈ 2000, velocity gradient ≈ 1000 S-1, shear stress ≈ 1 Pa) ;-transmembrane pressure between 85 and 185 Kpa.One of the main conclusions of this study is that influence of the velocity appears only after an initial period during which the growth of the deposit and the filtrate flowrate variation with time are in agreement with the equations of dead end filtration at constant pressure.Thus a combination of dead end filtration and periodic backwash for removing the deposit might be the best solution for getting the highest productivity with minimal energy consumption.These optimal conditions may be simulated using the equations of dead end filtration at constant pressure and making the assumption that the backwashing is fully efficicent.The experimental study of backwashing, using the optical sensor for measuring the diameter of the fiber after each backwashing, proves that this assumption is correct and that it is possible to get a steady mean filtrate flux by periodic backwashing.From the theoretical study, the optimal duration of the filtration period is rather short (about 10 minutes) but the decline after the maximum is very malt, which means that the fiitration period may be longer without significative variation of the productivity.Thus the method presented here is able, if applied to actual raw water, to give technical and economical elements of comparison between dead end filtration with periodic backwashing and crossflow filtration

Modélisation d'un bioréacteur à membrane vraie grandeur avec le modèle boues activées ASM1 : défis et solutions

International audienceA full-scale membrane bioreactor (1600 m3.d-1) was monitored for modelling purposes during the summer of 2006. A complete calibration of the ASM1 model is presented, in which the key points were the wastewater characterisation, the oxygen transfer and the biomass kinetics. Total BOD tests were not able to correctly estimate the biodegradable fraction of the wastewater. Therefore the wastewater fractionation was identified by adjusting the simulated sludge production rate to the measured value. MLVSS and MLSS were accurately predicted during both calibration and validation periods (20 and 30 days). Because the membranes were immerged in the aeration tank, the coarse bubble and fine bubble diffusion systems coexisted in the same tank. This allowed five different aeration combinations, depending whether the 2 systems were operating separately or simultaneously, and at low speed or high speed. The aeration control maintained low DO concentrations, allowing simultaneous nitrification and denitrification. This made it difficult to calibrate the oxygen transfer. The nitrogen removal kinetics were determined using maximum nitrification rate tests and an 8-hour intensive sampling campaign. Despite the challenges encountered, a calibrated set of parameters was identified for ASM1 that gave very satisfactory results for the calibration period. Matching simulated and measured data became more difficult during the validation period, mainly because the dominant aeration configuration had changed. However, the merit of this study is to be the first effort to simulate a full-scale MBR plant

Extraction and purification of high added value compounds from by-products of the winemaking chain using alternative/nonconventional processes/technologies

Grape byproducts are today considered as a cheap source of valuable compounds since existent technologies allow the recovery of target compounds and their recycling. The goal of the current article is to explore the different recovery stages used by both conventional and alternative techniques and processes. Alternative pre-treatments techniques reviewed are: ultrasounds, pulsed electric fields and high voltage discharges. In addition, nonconventional solvent extraction under high pressure, specifically, supercritical fluid extraction and subcritical water extraction are discussed. Finally alternative purification technologies, for example membrane processing were also examined. The intent is to describe the mechanisms involved by these alternative technologies and to summarize the work done on the improvement of the extraction process of phenolic compounds from winery by-products. With a focus on the developmental stage of each technology, highlighting the research need and challenges to be overcome for an industrial implementation of these unitary operations in the overall extraction process. A critical comparison of conventional and alternative techniques will be reviewed for ethe pre-treatment of raw material, the diffusion of polyphenols and the purification of these high added value compounds. This review intends to give the reader some key answers (costs, advantages, drawbacks) to help in the choice of alternative technologies for extraction purposes

Comparison of the effect of pulsed electric field or high voltage electrical discharge for the control of sweet white must fermentation process with the conventional addition of sulfur dioxide

International audienceThe present work discusses the efficiency of pulsed electrical treatments for the inactivation of yeasts. The application of pulsed electric fields (PEFs) and high voltage electrical discharges (HVEDs) as alternatives to sulfites, which are used as anti-microbial to stop the fermentation of sweet white wine, was investigated. The influence of sulfite concentration (from 0 mg.L-1 to 500 mg.L-1), PEF (from 4 kV.cm(-1) to 20 kV.cm(-1); from 0.25 ms to 6 ms) and HVED (40 kV/cm; 1 ms or 4 ms) treatments on the inactivation of total yeasts and non-Saccharomyces yeasts was determined. The addition of SO2 (250 mg.L-1) resulted in 8 log total yeast reduction. The maximum yeast inactivation obtained with PEF and HVED was respectively 3 and 4 logs. The use of SO2, HVED and PEF allows decreasing the non-Saccharomyces yeast level by 7, 5 and 4 logs respectively. However, the wine browning was less pronounced for the samples treated by PEF in comparison with HVED and SO2 treatments. PEF seems to be the most suitable alternative technique to sulfite addition

Performance evaluation of microfiltration with electrocoagulation and chemical coagulation pretreatment

ne of the significant parameters to be considered for evaluating the process and economic viability of crosssflow microfiltration (MF) is flux stability. The MF economics are dependent on the flux decay through the membrane caused by membrane fouling. This work aims to evaluate the performance of MF by electro and chemical coagulation as pretreatments. The performance of MF was found to be sensitive to pH of feed solution, coagulant dosing and generation time. Acrylonitrile butadiene styrene (ABS) MF membrane of pore size 0.4 μm was used in this study. Without pretreatment normalised flux declined by 94% after 160 min of MF operation using model wastewater. However with pretreatments, the MF flux was significantly improved. The optimum performance for MF with both electro and chemical coagulation pretreatments occurred at isoelectric point where the highest removal of organic and turbidity was observed. With chemical coagulation under optimum conditions (30 mg/l alum dose and pH 6.5), MF did not experience any flux decline. MF performed better with chemical coagulation compared to electrocoagulation (EC). Also organic matter removal was found to be more for chemical coagulation than for EC