Ammonia recovery from wastewater using a Microbial Electrolysis Cell (MEC)

Wastewater contains ammonium that requires removal to prevent environmental degradation. The most common way of removing ammonium is by using nitrification and denitrification (i.e.: activated sludge), which requires energy (457 J/mmolNH4+ removed). Microbial Electrolysis Cell (MEC) is proposed, as a new process, to recover ammonium in the form of ammonia gas, from mild concentrated ammonium wastewater stream (50 mM). Such process has the advantage of removing organics and producing a current that enables the migration of ammonium against its concentration gradient to the cathode. The MEC also produces a high pH (>9.5) in the cathode, which favours ammonia gas production. It is demonstrated that the ammonium can accumulate against a maximum concentration gradient of 1 M ammonium in the catholyte. The ammonium migration from the anode to the cathode is caused by the electron flow (i.e.: current) due to bacteria biodegrading organics and donating electrons to the anode. The presence of current enables ammonium migration against its concentration, in a ratio of 0.47mmolNH4+/mmole-.The ammonium is accumulated in the cathode, and forms ammonia due to the high pH and dissociation constant (pKa = 9.2). The energy requirements for this novel process are similar to traditional activated sludge, and about five times less than electrodialysis. However these two processes are treating urban and high ammonium concentrated (up to 500 mM) wastewater, while the MEC proposed in this project treats wastewater with 50 mM ammonium concentration. The MEC is not proposed as a replacement for current technology but as an alternative to remove ammonium and organics from specific industrial wastewaters. Ammonia gas is used in large quantities to produce fertilisers. The MEC process recovers ammonia at half the cost of conventional technology. However there are limitations to the application of the system on a large scale, mainly because of the required membrane surface area

Caractérisation de l'endommagement d'une argile par mesures de la vitesse des ondes de cisaillement

International audienceLes glissements de terrain dans les argiles génèrent un endommagement interne du versant. Des essais de laboratoire et in situ ont montré que la mesure du paramètre sismique Vs (vitesse de propagation des ondes de cisaillement) permet de caractériser l'endommagement du matériau argileux et d'imager la zone affectée par le glissement de terrain

Organic carbon removal from wastewater by a PHA storing biofilm using direct atmospheric air contact as oxygen supply

The principal reason for the high energy costs for biological wastewater treatment is the poor transfer efficiency of oxygen to the bulk water phase. The current paper describes a biofilm reactor in which oxygen transfer to the bulk solution is avoided by alternating anaerobic submersed (2. h) and drained (1. h) operation of the biofilm. During the submersed phase the biofilm enriched for glycogen accumulating organism (GAO) stored the organic carbon (acetate) as poly-hydroxy-alkanoate (PHA). After draining the reactor, this carbon stored as PHA was biologically oxidised, using oxygen directly from the atmosphere. The 12. Cmmol/L (384. mg/L BOD) of acetate was completely removed during long term automated operation of the reactor for 9. months with a cycle length of 3.3. h. As the process specifically removes dissolved organic carbon but not N or P it could possibly be coupled with novel processes such as Anammox or nutrient recovery

Культурные последствия глобализации

Mitigation strategies against natural risks in mountainous areas often include protection works against torrential flooding, avalanches or falling rocks. These structures, which are submitted to specific phenomena as well as they are built in a difficult geotechnical context, must be designed in compliance with specific requirements. Torrent control dams based on an active protection concept are often built to limit the risks of bank slip in the upper part of the catchment area. Usually, design of such structures is based on a two-dimensional approach, allowing force reactions applied by the soil to the foundations of the structure to be assessed. Furthermore, the thrust of the bank is seldom taken into account, even if the loading is likely to be the cause of a lot of observed damages. This paper exposes a methodology whose purpose is to improve the modelling of interaction between soil and structure. After an original analytical approach is presented, the main basis of numerical simulation (Finite Element Code) are defined.Les barrages de consolidation visent à limiter l'érosion du chenal d'écoulement des torrents et sont souvent implantés dans des sites où les berges sont fortement instables. Ces zones constituent en effet d'importantes zones d'alimentation en matériaux solides. Les méthodes actuelles de dimensionnement de ces ouvrages restent basées sur une approche bidimensionnelle d'estimation des actions et des réactions du sol en fondation. De même, les actions dues aux poussées des berges instables, qui entraînent de nombreuses pathologies sur les ouvrages, restent mal connues et ne sont pas prises en compte dans les justifications de la stabilité externe et interne des ouvrages. Cet article présente la problématique et la démarche d'étude en vue d'améliorer la connaissance des interactions entre les barrages et le sol au niveau des fondations et des berges. Dans cette perspective, une approche analytique est proposée, puis les bases d'une simulation numérique introduisant la méthode des Eléments Finis sont définies

Modélisation constitutive du comportement cyclique des sables en condition drainée

Dans cette étude, une modélisation numérique simple du comportement des sables sous chargement cyclique est proposée ; la démarche proposée consiste, en condition drainée, à déterminer les paramètres caractérisant le chemin cyclique moyen du sol sous l’'effet de N cycles dûment caractérisés, et à traduire l'’effet cyclique par une déformation volumique cumulée ainsi que par une variation de module du sol. Dans cette étude on s’'intéresse à des essais triaxiaux cycliques simulés au moyen d’'un calcul en éléments finis utilisant le programme Plaxis. On détermine les paramètres d’'identification du premier cycle (charge-décharge) réalisé pas à pas en prenant, comme modèle de comportement du sol le modèle HSM. Puis le comportement après N cycles (N>1000) est simulé par la formulation proposée comme un pseudo-fluage. La comparaison de la méthode proposée à plusieurs essais triaxiaux cycliques confirme la bonne adaptation du modèle proposé à ce type de problème

3D failure of a scale-down dry stone retaining wall: a DEM modelling

International audienceDry stone retaining walls are vernacular structures that can be found in many places around the world and were mainly built to reduce slope erosion and to allow agricultural practices. Their stability is essentially warranted by the global wall weight and the capacity of individual blocks to develop friction at contact. The arrangement of these hand-placed blocks contributes also to the stability of the wall. A new interest arose in these structures in the last years, first due to the necessity to repair damages inherent to any built heritage, but also to their possible advantages regarding sustainability. Several studies have tried to address the behavior of slope dry stone retaining walls, whereas few conclusive studies have been performed concerning road dry stone retaining walls. In this latter case, the loading implies, apart from the backfill, the existence of a concentrated force on the backfill surface. The failure of such masonry work is accompanied by true three-dimensional deformations. This study is a first attempt to provide a better understanding of the mechanical behavior of road dry stone retaining walls. It involves a small-scale prototype with clay bricks for the wall, and steel blocks, acting as a concentrated loading on the backfill surface at a given distance from the inward wall face. Steel blocks have been superposed until wall failure. A numerical study based on these experiments is then performed by means of a mixed discrete-continuum approach. The numerical model was able to retrieve the average value of the concentrated force triggering failure found in the experiences, except when the concentrated loading is very close to the wall. Nevertheless, the results provided by this study are considered as encouraging even if further work is required to definitely state about the validity of such a numerical technique for the study of actual road dry stone retaining walls

First spectroscopy of 66^{66}Se and 65^{65}As: Investigating shape coexistence beyond the N = Z line

The experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL), at Michigan State University (USA).We report on the first γ spectroscopy of 66Se and 65As from two-neutron removal at intermediate beam energies. The deduced excitation energies for the first-excited states in 66Se and 65As are compared to mean-field-based predictions within a collective Hamiltonian formalism using the Gogny D1S effective interaction and to state-of-the-art shell-model calculations restricted to the pf5/2 g9/2 valence space. The obtained Coulomb-energy differences for the first excited states in 66Se and 65As are discussed within the shell-model formalism to assess the shape-coexistence picture for both nuclei. Our results support a favored oblate ground-state deformation in 66Se and 65As. A shape transition for the ground state of even-odd As isotopes from oblate in 65As to prolate in 67,69,71As is suggested