Mélange diffusif et réactif dans des réacteurs tubulaires à trajectoires complexes.

Ce mémoire a pour objectif l'étude des mécanismes de mélange diffusif et réactif au sein de réacteurs tubulaires dont l'écoulement peut conduire à des trajectoires chaotiques, même à très faible vitesse. Dans une première partie, un réacteur fermé composé de six coudes agencés dans les trois directions de l'espace a été comparé expérimentalement à un réacteur torique plat de même volume. Pour les conditions expérimentales étudiées, l'agencement tridimensionnel des coudes n'apporte pas de gain significatif pour le mélange par rapport à un agencement dans le même plan. Ensuite, deux types de réacteurs ouverts sont comparés. L'efficacité du mélange dans un réacteur en écoulement de Dean alterné et dans un réacteur hélicoïdal est étudié expérimentalement et numériquement. Il est ainsi montré que dans le réacteur en écoulement de Dean alterné, le mélange par advection est plus efficace que dans le réacteur hélicoïdal.The PhD presents the study of the mixing of diffusing and reacting fluids in tubular reactors. The flow can lead to chaotic trajectories, even to very small speeds. First of all, a batch reactor compound of six elbows ordered in the three directions of the space was experimentally compared with a flat toroidal reactor of the same volume. For the studied experimental conditions, the three-dimensional structure of elbows does not bring significant earning for the mixing with regard to a structure in the same plan. Then, two types of opened reactors are compared. The efficiency of mixing in a reactor in alternative Dean flow and in a helical reactor is studied in experiments and numerically. It is demonstrated that the mixing by advection in the reactor in alternative Dean flow is more efficient than is the helical reactor.PAU-BU Sciences (644452103) / SudocSudocFranceF

New Bio-Indicators for Long Term Natural Attenuation of Monoaromatic Compounds in Deep Terrestrial Aquifers

International audienceDeep subsurface aquifers despite difficult access, represent important water resources and, at the same time, are key locations for subsurface engineering activities for the oil and gas industries, geothermal energy, and CO 2 or energy storage. Formation water originating from a 760 m-deep geological gas storage aquifer was sampled and microcosms were set up to test the biodegradation potential of BTEX by indigenous microorganisms. The microbial community diversity was studied using molecular approaches based on 16S rRNA genes. After a long incubation period, with several subcultures, a sulfate-reducing consortium composed of only two Desulfotomaculum populations was observed able to degrade benzene, toluene, and ethylbenzene, extending the number of hydrocarbonoclastic-related species among the Desulfotomaculum genus. Furthermore, we were able to couple specific carbon and hydrogen isotopic fractionation during benzene removal and the results obtained by dual compound specific isotope analysis (ε C = −2.4 ± 0.3 ; ε H = −57 ± 0.98 ; AKIE C : 1.0146 ± 0.0009, and AKIE H : 1.5184 ± 0.0283) were close to those obtained previously in sulfate-reducing conditions: this finding could confirm the existence of a common enzymatic reaction involving sulfate-reducers to activate benzene anaerobically. Although we cannot assign the role of each population of Desulfotomaculum in the mono-aromatic hydrocarbon degradation, this study suggests an important role of the genus Desulfotomaculum as potential biodegrader among indigenous populations in subsurface habitats. This community represents the simplest model of benzene-degrading anaerobes originating from the deepest subterranean settings ever described. As Desulfotomaculum species are often encountered in subsurface environments, this study provides some interesting results for assessing the natural response of these specific hydrologic systems in response to BTEX contamination during remediation projects