Nouveaux procédés d'oxydation chimique pour l'élimination des rejets aqueux phénolés

Pour faire face au problème posé par les rejets aqueux chargés en phénol, deux procédés d'épuration par voie chimique sont proposés. Les deux méthodes font appel au peroxyde d'hydrogène. Celui-ci joue le rôle de promoteur de radicaux lors de l'oxydation de la charge organique par l'oxygène moléculaire dans le premier procédé qui s'inspire de la technique « Wet Air Oxidation » et constitue l'agent oxydant dans le second procédé intitulé « Wet Peroxide Oxidation ».L'introduction en continu de peroxyde d'hydrogène permet d'initier la réaction d'oxydation du phénol par l'oxygène moléculaire et de réduire considérable-ment les conditions de température et de pression de fonctionnement de la technique WAO classique. La réduction de la Demande Chimique en Oxygène de l'effluent dépasse 95 % à 160 °C en introduisant du peroxyde d'hydrogène à raison de 10 % de la quantité stoechiométrique nécessaire pour l'oxydation complète du phénol. Le second procédé consiste à utiliser l'oxydation par le peroxyde d'hydrogène en présence de fer ferreux (réactif de Fenton) dans des conditions de température (environ 120 °C) conduisant à un abattement important de la charge organique de l'effluent. A température élevée, la compétition entre la réaction de décomposition du peroxyde en oxygène moléculaire inactif et celle de décomposition en radicaux qui développent le processus d'oxydation engendre des conditions opératoires optimales pour lesquelles l'efficacité du procédé est maximale.Ces deux procédés apportent une solution technique satisfaisante pour traiter, avec un abattement important de la demande chimique en oxygène et du carbone organique, les effluents aqueux assez fortement chargés en composés phénolés.Despite of a growing concern about the problems of wastes elimination during the previous years, there is still a lack of processes in order to treat industrial aqueous wastes. Organic aqueous wastes and specially phenolic wastes, that can be either nonbiodegradable or toxic, give rise to one of the main problems. Landfilling disposal and related methods are a priori rejected as they appear to leaving the legacy of a problem we have net been able to solve rather than to considering our environment as being borrowed from the future mankind. Various oxidation techniques are suited for the elimination of this class of wastes. But, because of the environmental and economical drawbacks of incineration, it seems that liquid phase oxidation techniques should be preferred.The paper reviews : two liquid phase purification techniques using the chemical oxidation route; phenol being used as a test compound. The first technique is adapted from the wet air oxidation (WAO) process and uses molecular oxygen as the oxidizing agent. In the meantime, hydrogen peroxide is added at a low dosage and promotes the radicle reactions. Thus, the reaction temperature and pressure can be set at lower values (typically 160 °C, 25 bar) than usually. In this way, the conventional WAO process, which is very capital intensive because of temperature and pressure constraints is turned into a more affordable process. The second technique uses hydrogen peroxide as the oxidizer. it is associated to a ferrous salt as in the Fenton's reagent but it is run out under temperature (about 120 °C) so that a very important total organic carbon (TOC) removal efficiency con be obtained. This technique was named wet peroxide oxidation (WPO) process. As opposed to WAO, WPO needs only limited capital but generates higher running colts. Yet, both techniques can be regarded as efficient and economically satisfying in order to treat organic aqueous wastes containing fair amounts of phenol or phenolic compounds.The test compound was selected considering the frequent occurrence of phenol within the wastewaters of refineries, steel works and chemical industries. Their biological treatment is still very difficult for high concentrations despite of an important research activity. Treatment times and efficiencies of physicochemical methods are not but seldom satisfactory. Then, liquid phase oxidation methods have their whole interest. As it was reported that phenolic compounds (methylphenols, chloro-phenols) oxidation proceeds in a similar way than for phenol, the last molecule was considered for assessing the efficiency of both oxidation methods.The first method (WAO) was tested using a completely mixed batch reactor (stirred autoclave): The cold reactor was loaded with a phenol (2100 mg. 1-1) and ferrous sulfate (10 mg. l-11) solution al the convenient pH value (3.5). After heating at the rated temperature, the run was started by injecting instantaneously a large amount of oxygen (10 times the amount necessary). At the same time, a dosing pump was started and fed continuously hydrogen peroxide within the reactor all along the run (90 minutes). The total amount injected was usually 10 % of the amount necessary for a stoechiometric oxidation. The promoting effect of hydrogen peroxide on molecular oxygen is evidenced on figure 2 where the initiating period is shortened and on figure 3 where the oxidation efficiency actually obtained (curve 3) is greater than expected by adding the efficiencies of molecular oxygen and hydrogen peroxide oxidations if separated (curve 2). WAO promoted with hydrogen peroxide gave after 90 minutes better oxidation efficiencies at 160 °C than conventional WAO at 220 °C, then turning into a medium pressure process a high pressure one. The promoting effect of the peroxide is more marked at 160 °C than above 200 °C where a rapid decomposition occurs; dosages greater 15 % do not significantly increase the efficiency and dosages as small as 0,2 % have already a significant affect (see figure 5). Various compounds have been identified and the oxidation sequence is as follows : phenol -> dihydroxy-benzenes -> maleic acid -> oxalic, formic, acetic acids. Most of the remaining chemical oxygen demand (COD) of the oxidized solutions is acetic acid. Only more drastic experimental conditions allow its total removal.The WPO runs (second oxidation method) were conducted into a similar reactor. It was batch loaded with the phenol (2300 mg. 1-1) and ferrous sulfate (30 mg. l-1) solution at pH 3.5. After heating at 120 °C, the run was started and hydrogen peroxide was continuously fed using a dosing pump. The total amount injected all along the run (60 minutes) was the amount necessary for a stoechiometric oxidation. A similar oxidation sequence than reported hereon was observed; pyrocatechol, bydroquinone and oxalic acid were evidenced (figure 9) but, in this case, only very limited amounts of formic and acetic acids were detected. For the two processes, tables 2 and 3 summarize the material balances of the various products as a function of the oxidation time. A 90 % COD removal efficiency and a 70 % total organic carbon (TOC) removal efficiency is reported on figure 10. This result has to be compared with the TOC removal efficiencies (< 25 %) reported for the usual Fenton’s reagent at room temperature. The changes of the pH value and of the COD/TOC ratio (figure 11) during the run are easily explained by considering that oxalic acid is quite the sole product remaining after oxidation contrarily to promoted WAO where acetic acid is the major remaining product. Besides the production of radicles that bring on the oxidation process, a side-reaction decomposes hydrogen peroxide into molecular oxygen which is net active at such a low temperature. The competition between the two reactions makes optimum operating conditions to exist and to lead to a maximum efficiency of the process.Both processes bring on new methods in order to treat fairly concentrated phenolic solutions with a typical 90 % COD removal efficiency. The products remaining after oxidation (mainly acetic acid or oxalic acid) should not be regarded as a drawback of these processes. In actual fact, such compounds can be easily treated by adding a biological post-treatment unit to the chemical oxidation

Non-Linear Elasticity of Extracellular Matrices Enables Contractile Cells to Communicate Local Position and Orientation

Most tissue cells grown in sparse cultures on linearly elastic substrates typically display a small, round phenotype on soft substrates and become increasingly spread as the modulus of the substrate increases until their spread area reaches a maximum value. As cell density increases, individual cells retain the same stiffness-dependent differences unless they are very close or in molecular contact. On nonlinear strain-stiffening fibrin gels, the same cell types become maximally spread even when the low strain elastic modulus would predict a round morphology, and cells are influenced by the presence of neighbors hundreds of microns away. Time lapse microscopy reveals that fibroblasts and human mesenchymal stem cells on fibrin deform the substrate by several microns up to five cell lengths away from their plasma membrane through a force limited mechanism. Atomic force microscopy and rheology confirm that these strains locally and globally stiffen the gel, depending on cell density, and this effect leads to long distance cell-cell communication and alignment. Thus cells are acutely responsive to the nonlinear elasticity of their substrates and can manipulate this rheological property to induce patterning

ENDOGLIN is dispensable for vasculogenesis, but required for vascular endothelial growth factor-induced angiogenesis

ENDOGLIN (ENG) is a co-receptor for transforming growth factor-β (TGF-β) family members that is highly expressed in endothelial cells and has a critical function in the development of the vascular system. Mutations in Eng are associated with the vascular disease known as hereditary hemorrhagic telangiectasia type l. Using mouse embryonic stem cells we observed that angiogenic factors, including vascular endothelial growth factor (VEGF), induce vasculogenesis in embryoid bodies even when Eng deficient cells or cells depleted of Eng using shRNA are used. However, ENG is required for the stem cell-derived endothelial cells to organize effectively into tubular structures. Consistent with this finding, fetal metatarsals isolated from E17.5 Eng heterozygous mouse embryos showed reduced VEGF-induced vascular network formation. Moreover, shRNA-mediated depletion and pharmacological inhibition of ENG in human umbilical vein cells mitigated VEGF-induced angiogenesis. In summary, we demonstrate that ENG is required for efficient VEGF-induced angiogenesis

Selección de líneas de garbanzo tolerantes a la salinidad empleando caracteres de producción de biomasa y funcionamiento nodular como indicadores

Se estudió la tolerancia a la salinidad de 30 líneas cultivadas en solución nutritiva, evaluando nodulación, conductancia nodular al O2 y biomasa. En condiciones no salinas las plantas mostraron alta nodulación y crecimiento, mientras que la salinidad (25 mM NaCl), disminuyó significativamente estos parámetros. La sensibilidad a la sal determinada como crecimiento foliar, y nodular relativo y eficiencia de uso de la simbiosis con Mesorhizobium mostró importantes diferencias entre líneas, las que se agruparon en 4 clases. Se concluyó que la tolerancia a la salinidad está relacionada con alto potencial simbiótico y elevada y estable conductancia nodular al O2

Genotypic variation for N2-fixation in Voandzou (<em>Vigna subterranea</em>) under P deficiency and O sufficiency

International audienc

Genotypic variability in P use efficiency for symbiotic nitrogen fixation is associated with variation of proton efflux in cowpea rhizosphere

Correspondance auteurs: Alkama N. [email protected] Drevon J.J. [email protected] audienceVigna unguiculata sp., or cowpea, varieties vary in their adaptation to low-P soils. In order to investigate to what extent this variation may be related to P use efficiency and proton efflux by nodulated roots, three genotypes, 26-73, Danila and Melakh, inoculated with Brodyrhizobium sp. Vigna CB756 were grown in hydroaeroponic culture in a glasshouse at two levels of phosphorus supply corresponding to P sufficiency or P deficiency. After 4 weeks, individual symbiotic-plants were transferred to a reference-soil layer in a rhizotron, and harvested after 2 further weeks. Nodule and shoot biomass were less when P was deficient The effect of P deficiency on biomass production followed the trend Danila > 26-73 > Melakh. Under P deficiency, the proton efflux for the P-efficient genotype 26-73 was 43% and 60% greater than for the P-inefficient Danila in hydroaeroponics and in soil, respectively. This increase in proton efflux was associated with an increase in nodule specific respiration that was 115% greater for Danila than for 26-73. It is concluded that the genotypic variability in P use efficiency for symbiotic nitrogen fixation is associated with a variation in nodulated-root proton efflux and respiration in cowpea rhizosphere, and that these parameters should be measured for more contrasting genotypes in order to test whether they correlate with the adaptation of N-2-dependent legumes to low-P soil