«Amer M.», de Joséphine Serre, ou l’amertume de la mémoire

MEMOIRS - Children of Empires and European Postmemories (648624

Migrations, exclusions et post mémoires de la guerre d'Algérie (1945-1989)

Actes du colloque scientifique «Nations, nationalismes, minorités et migrations dans l'espace euro-méditerranéen, 1945-1989» les 6-7 octobre 2016, Université de Szeged

Description of the topographical changes associated to the different stages of the DsbA catalytic cycle.

This paper provides a description of the surface topography of DsbA, the bacterial disulfide-bond forming enzyme, in the different phases of its catalytic cycle. Three representative states, that is, oxidized and reduced protein and a covalent complex mimicking the DsbA-substrate disulfide intermediate, have been investigated by a combination of limited proteolysis experiments and mass spectrometry methodologies. Protease-accessible sites are largely distributed in the oxidized form with a small predominance inside the thioredoxin domain. Proteolysis occurs even in secondary structure elements, revealing a significant mobility of the protein. Many cleavage sites disappear in the reduced form and most of the remaining ones appear with strongly reduced kinetics. The protein within the complex shows an intermediate behavior. This variation of flexibility in DsbA is probably the determining factor for the course of its catalytic cycle. In particular, the great mobility of the oxidized protein might facilitate the accommodation of its various substrates, whereas the increasing rigidity from the complexed to the reduced form could help the release of oxidized products. The formation of the complex between PID peptide and DsbA does not significantly protect the enzyme against proteolysis, reinforcing the results previously obtained by calorimetry concerning the weakness of their interaction. The few cleavage sites observed, however, are in favor of the presence of the peptide in the binding site postulated from crystallographic studies. As for the peptide itself, the proteolytic pattern and the protection effect exerted by DsbA could be explained by a preferential orientation within the binding site

Traitement de lixiviats stabilisés de décharge par des membranes de nanofiltration

Le terme "lixiviat" ou "jus de décharge", désigne l'eau qui a percolé à travers les déchets en se chargeant de polluants. Ces effluents pollués doivent être traités.En raison des exigences croissantes des normes de rejet et de la stabilisation des lixiviats au cours du temps, de nouvelles techniques ont fait leur apparition dans ce domaine. La technologie de l'osmose inverse s'est développée dans de nombreux pays européens. Cependant cette technique sélective et coûteuse, se justifie seulement quand les normes sont drastiques. C'est pourquoi la nanofiltration pourrait constituer une solution intermédiaire.L'objectif de ce travail est de contribuer à mieux maîtriser cette technique pour l'élimination de la Demande Chimique en Oxygène (DCO) récalcitrante, subsistant après les traitements biologiques classiques.Nous avons évalué les performances de trois membranes (organiques et minérales) pour l'abaissement de la charge organique, en fonction des conditions hydrodynamiques (vitesse et pression).Chacune de ces membranes possède un comportement spécifique vis à vis de ces lixiviats stabilisés (adsorption, polarisation de concentration, obstruction des pores).L'influence d'une coagulation préalable sur les performances d'épuration a également été examinée pour l'une des membranes.Cette étude constitue une étape préliminaire au dimensionnement d'une installation.Landfill leachate is the name given to water that has passed through solid waste and contains organic and mineral contaminants. Therefore this effluent must be treated before discharge to the environment. Because of new norms and the stabilization of leachates with time, new treatment methods have been designed. Thus, reverse osmosis is used in many European countries. But the use of reverse osmosis is only justified when norms are severe, because the treatment is highly selective (salt rejection >99%) and very expensive. In other cases, nanofiltration may be an interesting alternative.The purpose of the present work is to propose a process for recalcitrant organic matter in order to optimize the technique. Thus, three membranes (organic and mineral) have been used to evaluate their ability to decrease the Chemical Oxygen Demand (COD) of the leachate. This study helps to determine the size of the device. First, physical parameters were investigated. Each time, the hydraulic regime was turbulent (Re > 2500). Higher permeation fluxes were obtained with organic membranes than with the mineral one (80 L·h-1·m-2 compared to 25 L·h-1·m-2) under the same experimental conditions (10 bar and 3.4 m·s-1). Tangential flow rates higher than 2.5 m·s-1 do not influence COD retention; at lower flow rates polarisation concentration may occur. The removal of COD is achieved in the three cases. At 10 bar an acceptable value of less than 120 mg O2·L-1 (norm) is obtained. The inorganic membrane (Tech-Sep) gives the best results (COD rejection: 70 % at 10 bar).Membranes behave differently toward landfill. The organic membrane MP 20 (Weizmann membrane, cut-off 450 Dalton (Da), polyacrylonitrile) shows low adsorption with landfill leachate. The organic membrane MP 31 (Weizmann membrane, cut off 450 Da, polysulfone) gave a high COD retention ratio; the values for irreversible fouling and static adsorption are of the same order ofmagnitude; a strong membrane-foulant interaction must occur, which improves membrane selectivity. The mineral membrane N01A (Tech-Sep membrane, cut off 1000 Da, zirconium oxide), like MP-31, gives high static adsorption with leachate and irreversible fouling as well. The latter phenomenon can be explained by the obstruction of membrane pores by leachate particles, the size of which is near the membrane cut-off point. Fouling and static adsorption contribute to the increase in the membrane rejection rate. We studied coagulation as a pretreatment to improve performances of the N01A membrane. Experiments have been carried out with Jar-Test and FeCl3-like coagulants. The optimal amount of coagulant was 1.4 g Fe·L-1; 60% COD reduction was achieved. The results obtained with the N01A membrane are improved: reduction of COD rises from 78% to 92 %, concentration polarisation is lower, and therefore the flux increases up to 53 L·h-1·m-2. This value still remains lower than the organic membrane fluxes (respectively 80 L·h-1·m-2 for organic membranes and 25 L·h-1·m-2 for N01A). However, coagulation may not be the appropriate pretreatment because the fouling index of the supernatant after coagulation was similar to that of the raw leachate. Permeability measurements after treatment show that internal fouling is still important (25%). In fact, coagulation does not remove molecules with molecular weights around 500 Daltons, and consequently these particles still obstruct the membrane pores. The phenomenon limits the performance (flux) of this membrane

Étude préliminaire du traitement d’effluents contenant de l’encre de seiche par centrifugation et procédés à membranes

Il s’agit d’une étude préliminaire sur le traitement d’effluents de conditionnement de la seiche avant congélation en vue de réduire la charge polluante des rejets et de valoriser l’encre qu’ils contiennent. Deux types de procédés ont été mis en oeuvre : d’une part, la centrifugation, qui permet de fractionner la suspension d’encre de seiche entre un culot noir à DCO (Demande Chimique en Oxygène) élevée et un surnageant limpide et, d’autre part, l’ultrafiltration (UF) et la microfiltration (MF). Les flux de perméat obtenus par les deux procédés à membranes sont du même ordre de grandeur (25 à 30 L·h‑1·m‑2 sous 1,5 bar). La rétention moyenne en DCO est de 65 % et la rétention en COT (Carbone Organique Total) et azote protéique (NTK) de plus de 95 %. Cependant le colmatage irréversible de la membrane de MF conduit à préférer l’UF, plus facilement régénérable.Industries that condition fish products have to cope with the problem of processing their usually protein-rich wastewaters. An example of such an industry that discards a large amount of wastewater is the CALEMBO Company (Sfax-Tunisia), which uses 50 m3 per metric ton a day to condition cuttlefish for freezing. In order to conserve water, high-salinity bore water is sometimes used. This high salinity water is responsible for the difficulties encountered during the biological treatment of wastewaters and the recovery of valuable by-products. In this respect, membrane processes, used in the treatment and exploitation of effluents from industries that process sea products, are very attractive. The first membrane filtration trials on sea-product effluents date back to the 1980’s, but they did not result in major developments. Legislative pressures and the increasing costs of water and effluent-processing, as well as the improvement of membrane efficiencies, have made membrane treatment processes much more interesting for wastewater treatment processes. The GEPEA Laboratory at Nantes University has carried out research on membrane technologies to clean up polluted process waters, enhance substances such as soluble fish proteins, and to recover substances responsible for the flavour of bivalves and shellfish.This paper presents preliminary research on the treatment and exploitation of water used in cuttlefish conditioning. Treatment processes used include centrifugation, microfiltration and ultrafiltration. Centrifugation is used to determine the distribution of the effluent between the black residue and the clear supernatant, whereas membrane processing is used to reduce wastewater pollution and concentrate pigments.The effluent studied was reconstituted from pure cuttlefish-ink samples taken directly from the animal and salt waters of the same salinity as the bore water used by the CALEMBO Company (Table 1). The samples were reconstituted in ratios of 1 to 50 for centrifugation and 1 to 100 for membrane filtration. Centrifugation trials were carried out using a KR 22i type JOUAN centrifuge, whereas ultrafiltration and microfiltration trials were carried out using the laboratory apparatus represented in figure 1. The main characteristics of membranes used are indicated in table 2. Operating conditions were determined according to the capacities of the feed pump: transmembrane pressure Ptm = 1.5 bar, circulation velocity U = 1.5 m·s‑1 and temperature T = 25°C. The parameters measured on initial feed solutions and the fractions obtained were COD (Chemical Oxygen Demand), TOC (Total Organic Carbon) and nitrogen content (NTK). Filtration trials were carried out according to two different procedures, either with constant feed composition to determine the best operating conditions, or with increasing effluent concentration together with monitoring of the Volumetric Reduction Factor (VRF).Centrifugation of the cuttlefish-ink suspension produced two phases: a very dense black residue and relatively clear supernatant. The volumetric distribution and the COD and TOC contents of the different fractions are presented in table 3. The supernatant represented about 75% of crude effluent volume. Organic matter was concentrated in the residue and consisted primarily of suspended particles.At a constant concentration, the ultrafiltration (UF) and microfiltration (MF) processes behaved differently. A rapid drop in flux in the first minutes followed by stabilization at 30 L·h‑1·m‑2 after 30 min was observed for the MF process, whereas a rapid stabilization at approximately 25 L·h‑1·m‑2 was observed for the UF process. The drop in flux at the beginning of MF process may be due to the partial fouling of the membrane pores by melanin particles ranging in sizes from 55 to 160 nm, which are of the same order of magnitude as the membrane pores of 100 nm. On the other hand, the small decrease in flux in the case of ultrafiltration resulted essentially from the formation of a polarization layer and possible interactions between the membrane material and the solution.Batch-concentration trials were carried out for 5 and 4 h using UF and MF respectively, the operating time being dictated by the dead volume of the equipment (0.75 L). The permeate flux variation as a function of the volumetric reduction factor (VRF) is illustrated in figure 3. The MF flux was slightly higher despite the higher initial concentration of organic substances. For a VRF of 2.64 (final concentration), J = 2.8 L·h‑1·m‑2 for MF and 15.2 L·h‑1·m‑2 for UF. Despite the significantly different permeabilities of the MR and UF membranes to pure water (2690 against 34 L·h‑1·m‑2·bar‑1), their very similar J values are a consequence of the internal pore fouling of the MF membranes.Analyses performed on the initial feed samples, and on the different fractions of ink suspensions obtained by MF and UF following concentration, are presented in table 5. Retention ratios for UF were very slightly higher than those found for MF, about 65% for COD, 98% for TOC and 95% for NTK. From the point of view of pollution remediation, and considering permeate COD values, the efficiency of the membrane technique does not seem sufficient.Following ultrafiltration, membrane regeneration was possible by simply rinsing the membrane with water. On the other hand, the same procedure proved inefficient for the microfiltration (PVDF) membrane. The black pigment remained stuck to the membrane surface and most likely inside the pores as well. Furthermore, chemical regeneration (NaOH 0.1 M, 20 min, 25°C) was not enough to recover the membrane’s initial permeability.To conclude, the ultrafiltration process is better adapted to the treatment of cuttlefish washing wastewater. However, considering the level of residual COD in the ultrafiltration permeate, more efficient post-treatment techniques must be developed

Réduction de la DCO dure des lisiers de porc et lixiviats par nanofiltration

Malgré un traitement biologique préalable, les lisiers et les lixiviats de décharge ont en commun de conserver une Demande Chimique en Oxygène (DCO) résiduelle supérieure à 500 mg O2.l-1 : valeur 4 à 5 fois trop élevée pour un rejet direct dans le milieu naturel. La nanofiltration pourrait constituer une solution comme traitement de finition. Dans le cadre de cette étude expérimentale, deux membranes de nanofiltration sont mises en œuvre à l'échelle pilote afin de comparer leur efficacité pour réduire la DCO non biodégradable des deux effluents précités. Dans un premier temps, l'étude menée à concentration constante, montre que les performances (flux de perméation et DCO dans le perméat) dépendent principalement du couple membrane - effluent. Dans le cas du lisier, la couche de colmatants formée à la surface de la membrane a un caractère compressible et peu structuré ce qui entraîne une plus grande sensibilité aux variations de conditions hydrodynamiques. Dans le cas des lixiviats, la couche formée est moins dépendante des conditions opératoires. Après avoir sélectionné les meilleures conditions opératoires pour réduire la DCO des deux effluents étudiés, les essais de nanofiltration sont ensuite menés en mode "concentration" en fixant la pression à 15 bar et la vitesse de recirculation à 1,5 m.s-1. L'obtention d'un facteur de réduction volumique de 4 entraîne, d'une part, une diminution plus accentuée des flux de perméation dans le cas du lisier que dans celui du lixiviat et, d'autre part, une augmentation plus importante de la DCO du perméat pour le lisier. La valeur de la DCO devient alors supérieure, en fin de concentration, à celle requise pour un rejet en milieu naturel (120 mg O2.l-1).Pig manure and landfill leachate cannot be treated only by conventional biological treatment because a "refractory" COD persists, superior to 500 mg O2.l-1 : four times too high for a direct discharge in the environment. Nanofiltration, an intermediate process between reverse osmosis and ultrafiltration, may be an interesting alternative as a final treatment. In nanofiltration, lower pressure can be used and fluxes are higher than for reverse osmosis. The present study compared the treatability of pig manure and landfill leachate after biological treatment using a pilot-scale nanofiltration plant. Performances were evaluated in terms of permeate COD and permeate flux versus operating conditions (applied pressure, crossflow velocity and recovery rate). Two tubular organic nanofiltration membranes with 450 diameter cut-offs were used for pilot-scale testing: MPT-20 (polyacrylonitrile) and MPT-31 (polysulfone). Preliminary experiments carried out at constant concentrations show that performance (permeation flux and permeate COD) depends mainly on the nanofiltration membrane/effluent coupling. Permeate fluxes obtained with the MPT-20 membrane were higher than those obtained with the MPT-31. The increased crossflow velocity produced a particularly marked flux increase for pig manure. Moreover, the flux obtained with pig manure decreased at pressures superior to 15 bars whereas for the landfill leachate it became constant regardless of the pressure applied. COD retention was better in the case of pig manure and increased with pressure. On the other hand, high crossflow velocity helped reduce the COD retention, particularly for pig manure. The difference stems mainly from the foulant layer on the membrane surface. This layer is compressible and not organised; in the case of pig manure, it may explain the influence of hydrodynamic parameters: crossflow velocity favours the back migration of potential foulant such as colloids from the membrane surface to the bulk liquid phase. This may explain an increased mass transfer and consequent reduction of COD retention at high tangential velocities. Moreover, higher pressure generates a dense layer, which leads to a reduction of mass transfer. The influence of operating conditions was less important for the leachate, as the foulant layer may be more organised and have better cohesion.In the second part of this study, the nanofiltration pilot plant was operated in concentration mode in order to evaluate the influence of recovery rate on flux and retention. Since COD retention is better with the MPT-31 membrane, the latter was used for concentration experiments. The applied pressure was fixed at 15 bar and crossflow velocity at 1.5 m.s-1. Both effluents were concentrated with a volume reduction factor of 4. However this reduction of retentate volume led to both a drop in permeation flux and a rise of permeate COD, to a value above to the environmental norm of 120 mg O2.l-1