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

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

Characterization of the low-lying 0(+) and 2(+) states in Ni-68 via beta decay of the low-spin Co-68 isomer

The low-energy structure of the neutron-rich nucleus Ni-68 has been investigated by measuring the beta decay of the low-spin isomer in Co-68 selectively produced in the decay chain of Mn-68. A revised level scheme has been built based on the clear identification of beta-gamma-E0 delayed coincidences. Transitions between the three lowest-lying 0(+) and 2(+) states are discussed on the basis of measured intensities or their upper limits for unobserved branches and state-of-the-art shell model calculations

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

3D modelisation of snow slabs stability.

Snow slabs stability is a real problem to study in a mecanical point of view. A non exhaustive review of the different factors used to evaluate this stability or instability is done. All of them have been done in two dimensional cases, for an infinite constante slope and constant thickness of the snow cover. They are obtained by dividing a stress due to the snow pack weight by a snow hability. We present a numerical way for estimating the mecanical stability on any three dimensionnai slope. The mechanical stability factor is calculate with a stress strain 3D code using an elastoplastic behavior law for the snow. It considers a criteria of failure either in tension or in elasto-plasticity (Mohr Coulomb law) depending of the snow layer which fails. The application shown is a classic slab case and we are able to draw by the numerical calculation maps of a stability index in each layer, reproduces the phenomena generally observed in this case

A novel aerobic process for carbon and nitrogen removal from wastewater using a biofilm with passive aeration

Conventional municipal wastewater treatments use about 50 % of their energy for bulk liquid aeration to oxidise dissolved organic carbon (C) to CO2 and ammonium (NH4+) to nitrite (NO2-) and nitrate (NO3-). This thesis aims at reducing the energy requirement for bulk liquid aeration for the oxidation of dissolved carbon and ammonium in wastewater. This was done by developing two separate biofilm reactors that respectively oxidise C and NH4+ with passive aeration. Thereafter, the combination of the two processes was tested to achieve complete dissolved carbon and total Nitrogen (N) removal without aerating the bulk liquid. The first biofilm reactor removed dissolved carbon with a sequencing batch mode. The biofilm was flooded with wastewater, and dissolved C was biologically stored as Poly-Hydroxyalkanoates (PHAs) under anaerobic conditions, followed by the oxidation of PHAs to CO2, under aerobic conditions. The aeration was achieved by draining the wastewater, resulting in mere exposure of the biofilm to atmospheric oxygen partial pressure. The storing biomass was developed in 9 weeks from Activated Sludge (AS) and biomass of a storage driven denitrification biofilm, with a strict oscillation of: anaerobic conditions with acetate in solution, and exposure to the atmosphere (i.e. aerobic conditions) without dissolved carbon. The DNA analysis along with the testing of metabolites in biomass and solution demonstrated that the oscillating conditions enriched the biomass with Candidatus Accumulibacter, a known Glycogen Accumulating Organism (GAO). The process was operated over 9 months and repeatedly stored acetate as PHAs under anaerobic conditions and oxidised it during air exposure. Overall, > 80 % of the acetate added to the biofilm was removed at a rate of 4 Cmmol/L/h (128 g/m3/h BOD) and the reactor’s Hydraulic Retention Time (HRT) was 3 h. Both the rate and HRT were faster than conventional AS processes. The second reactor developed aimed at reducing the energy cost for oxygen supply for ammonium oxidation. To reduce the energy use for ammonium oxidation a two-step method was used. The first step was ammonia adsorption onto zeolite used as carrier for nitrifying biomass. The second step was the ammonia oxidation of the adsorbed ammonia using trickle method for oxygen transfer. The zeolite used in this study was an Australian Clinoptilolite zeolite (2 – 3.35 mm) with a maximum ammonium adsorption rate of 0.12 mmol-N/g/h (1.68 mg-N/g/h). Results showed that the nitrifying biomass was capable of oxidising 93 % of adsorbed ammonium on zeolite as nitrate when trickling the whole batch volume (1 bed volume) of wastewater, but the recovery reduced to < 34 % when only 20% of the liquid was recycled for reduced energy expense. To complete the total N removal, nitrate drained from this reactor was denitrified in the first reactor by GAO using PHA stored. The combination of the two reactors achieved 99 % of the acetate removal and 93 % of the nitrogen removal. However, liquid recirculation between two reactors was thought to be an energy cost that could be prevented. To reduce energy consumption, a single zeolite amended biofilm was synthesised by adding the GAO, nitrifiers and zeolite powder together, with the objective to remove dissolved C and total N within a single biofilm reactor. The operating principle was to simply fill the reactor and keep it anaerobic, so as to let the wastewater in contact with biofilm to biologically store dissolved acetate and adsorb ammonium on zeolite (Stage 1). Then aerobic conditions (Stage 2) were provided by draining the liquid. The liquid was recirculated for mass transfer at 0.4 m3/m2/d, which is a fraction of that used in trickle filter reactor. The zeolite amended biofilm reactor treated wastewater with a total treatment time of 19 h. Removal efficiencies were > 94 % for C and 80 % for total N. The production of dinitrogen gas under atmospheric oxygen partial pressure demonstrated that Simultaneous Nitrification and Denitrification (SND) occurred in air. SND in air can be explained to be due to an oxygen gradient formed in the biofilm. As the biofilm had been synthesised from different biomasses, it was tested for medium term sustainability. GAOs and nitrifiers were considered sustained in the synthesised biofilm over an operating period of 30 cycles (3 months), as their removal rates remained similar or improved over time. However, over this period the nitrite oxidizing bacteria (NOB) were washed out of the system, which is advantageous for effective nitrogen removal and known as SND over nitrite. It means that the zeolite amended biofilm reactor can effectively denitrify wastewater with low C/N ratio. On the contrary, conventional wastewater treatment plants are not effective at denitrifying low C/N wastewater. To optimise the zeolite amended biofilm reactor, its treatment time was shortened from 19 to 5 h and by omitting liquid recirculation in Stage 2. Under these short treatment times the removal efficiencies were > 83 % and 75 % for C and total N respectively over the tested period of 18 cycles. The system operating with 5 h treatment times is promising as a pre-treatment process for C and total N removal with a minimum of energy expense. This work does not propose a new process, it is the novel combination of the processes that achieve the novelty in this thesis. Overall, the system developed in this work is a novel combination of known biological and chemical steps for carbon and nitrogen removal from wastewater. In the first reactor, direct atmospheric contact between the carbon storage biomass and oxygen to oxidise PHAs was novel. In the zeolite amended biofilm reactor, the operation of SND in full atmospheric oxygen condition was novel and demonstrated zeolite bio-regeneration as well as PHAs oxidation. This novel biofilm reactor repeatedly removed soluble carbon and total nitrogen without liquid recirculation, over a medium term operation

Fast-timing study of the l -forbidden 12+→32+ M1 transition in Sn 129 FAST-TIMING STUDY of the l -FORBIDDEN ⋯ R. LICǎ et al.

© 2016 authors. Published by the American Physical Society.The levels in Sn129 populated from the β- decay of In129 isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station (IDS). The lowest 12+ state and the 32+ ground state in Sn129 are expected to have configurations dominated by the neutron s12 (l=0) and d32 (l=2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow l-forbidden M1 transition. Using fast-timing spectroscopy we have measured the half-life of the 12+ 315.3-keV state, T12= 19(10) ps, which corresponds to a moderately fast M1 transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and g factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured T12 value by the renormalization of the M1 effective operator for neutron holes

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