Capacités de traitement d'un effluent de synthèse en infiltration percolation

Dans cet article, nous présentons des travaux mettant en évidence les capacités de traitement biologique des eaux résiduaires urbaines au sein des milieux poreux de textures différentes. Une étude comparative du développement de la biomasse couplé aux mécanismes généraux de transferts gazeux à travers deux réacteurs biologiques est menée. Des lits d’infiltration percolation sont simulés par des colonnes garnies de sables d’origine et de structures différentes. Ils sont alimentés périodiquement via un automate de commande avec un influent d’une charge de 525 mgDCO/l et de 54 mgNK/l. Les résultats obtenus établissent le fait qu’un développement équilibré de la biomasse incluant les phases de croissance et de régression est intrinsèquement lié à la nature physique du matériau support. A l’aide des carottes prélevées sur les massifs filtrants et des sondes d’oxymétrie introduites à différentes hauteurs des lits d’infiltration, nous montrons que la répartition verticale du biofilm dans les colonnes ainsi que l’oxygénation des milieux poreux lors des périodes de repos sont également corrélées à la structure des supports pourtant de diamètres moyens similaires. L’efficacité de traitement biologique du carbone est supérieure pour un sable d’origine alluvionnaire comparativement à un sable concassé ; la tendance s’inversant significativement lorsqu’il s’agit de la diminution de l’azote.In this article, we present work highlighting the capacity of variously textured porous media to biologically process urban waste water. A comparative study was undertaken that coupled biomass development with general gas transfer mechanisms through two biological engines.Infiltration/percolation beds are biological systems that treat water using a purifying bacterial culture that develops on a mineral support. Used in domestic wastewater treatment, they are regarded as being well suited to rural areas. These infiltration/percolation beds are easy to use and attain a high quality in their output, two factors that constitute assets for small communities.Infiltration/percolation beds were simulated in the present work by columns lined with sands of varying origin and structure. They were fed automatically, at set intervals, with waste water containing 525 mg/L of dissolved organic carbon (DOC) and 54 mg/L of Kjeldahl nitrogen. A balanced development of the biomass, including the phases of growth and regression, was intrinsically related to the physical nature of the material used as a support. First, during the supply period, balanced growth of the biomass was quickly reached within the crushed sand. Secondly, within round sand, the regression of the biofilm was less significant and more regular over several weeks. In both supports, the regression was well correlated with an exponential decay. Lastly, the frequency of the supply periods, the organic loads involved, and the rest periods imposed are all factors that contribute to a lack of accumulation of living and/or inert organic matter in the columns.After obtaining a balanced development of the biomass, the abilities of the columns to reduce the concentrations of carbon, Kjeldahl nitrogen and ammonia were evaluated. Samples of effluent were taken downstream, both before the beginning of the supply period and as it came out of the column approximately thirty minutes after beginning the drainage period. The percentage of suspended matter coming out of the columns gave rather precise information on the scrubbing of the solid mass caused by various shearing speeds or by the structure of the base.Generally, it appeared that :- The reduction of the overall DOC was higher than 70%, regardless of which type of sand base was used.- In the water coming out of the column made up of round sand, the overall DOC content was without exception lower than 125 mg/L, as would be expected for an infiltration-percolation process.- The treatment of carbon in the columns based on stream sand was in general more effective than that obtained in columns with crushed sand.Concerning the treatment of nitrogen, crushed sand yielded outputs with a reduction in ammonia that was a lot higher than 80% (mean ± SD: 92 ± 4%) and was systematically higher than those obtained with stream sand (mean ± SD: 72 ± 7%). The suspended matter content was extremely low in the effluent; since no suspended matter was introduced into the effluent, the concentration coming out of the column was the direct result of the biofilm becoming detached and/or, to a lesser extent, of the transport of the biomass in the liquid phase. As could be expected, because of the roughness causing more shearing, more particles became detached when the interior solid mass was made up of crushed sand.Using core samples taken from the filter's solid mass, as well as oxygen probes inserted at various levels into the biological engines, we showed that the vertical distribution of the biofilm in the columns, as well as the oxygenation of the porous media during the rest periods, were all correlated with the structure of the solid supports (note that all sands had similar average diameters). Gaseous exchanges within the filter's solid mass were dependent on both the type of coating and the depth at which they took place. The oxygen probes were inserted at depths of 14 cm and 18 cm respectively, to determine the percentage of oxygen saturation in the liquid phase within the filter during one week while the columns were operating. Two phases were characteristic of the exchanges observed in the upper part of the filter's solid mass. First we noted an instantaneous reduction in the oxygen content of the liquid phase, linked to the arrival of a batch, followed by a reoxygenation of this portion. Next there was a long phase, lasting approximately 94% of the time between batches, during which time the oxygen content in the residual moisture remained constant. In the lower part of the solid mass, variation in oxygen content was different. Partial deoxygenation in the liquid phase of the porous media here was primarily due to the biochemical oxidation of the organic matter (i.e., consumption by the biomass). It was also due, to a lesser extent, to the augmentation in moisture content that occurs after each batch, and leads to a reduction in porosity and a decrease in oxygen transfer. During the final phase of drainage, a balance was created between the open porous space with air, and the space containing stagnant moisture. The diffusion of oxygen in the former and its transfer towards the latter thus compensated for this consumption, and it therefore remained constant. If the medium was left to dry out longer, the diffusion and transfer phenomena increased, and we observed an increase in oxygen content.With respect to the vertical distribution of biomass in the columns, we found that it was almost homogeneous inside the stream sand, up to a depth of 28 cm (total depth = 40 cm). Generally, the organic matter content at each point of measurement in the column was higher in the stream sand than in the crushed sand. The variation was greater around 28 cm, where there was a more significant quantity of moisture inside the sand

Dynamique du piégeage des micropolluants métalliques au sein des zones humides artificielles traitant des eaux pluviales urbaines strictes : Etude de cas à Strasbourg, Moulins-lès-Metz et Leuville-sur-Orge

Colloque avec actes et comité de lecture. internationale.International audienceStormwater constructed wetlands (SCW) in Strasbourg (Alsace, France), Moulin-lès-Metz (Lorraine, France), and Leuville-sur-Orge (Ile-de-France, France) receive and treat exclusively runoffs from urban catchments but with different soil uses. Made up of sedimentation ponds and a vertical subsurface flow constructed wetland, the treatment facilities lead to trap several trace metal pollution. Each site belongs to different hydroclimatic areas (modified oceanic, modified continental and semi-continental) and was designed for different purposes (watercourse protection in Strasbourg and in Leuville-sur-Orge, protection of drinking water wells in Moulins-lès-Metz). The aim of this study is to explore trace metals (Cd, Cu, Pb and Zn) behaviours in these SCW. We investigated trace metal trapping by determining concentrations in the systems compartments (filters media and plants). Then trace metal speciation was determined through sequencial extractions of the sediment and filter media. This allowed to determine their forms in soils and to anticipate their behaviour during physical and chemical condition changes. This study permits to obtain first results for the metals stability, to highlight a decrease of the concentrations through the SCW depth (from surficial sediment to clean filter media) and to observe a negligible metal trap in plants (mainly in roots)

Importance of electronic self-consistency in the TDDFT based treatment of nonadiabatic molecular dynamics

A mixed quantum-classical approach to simulate the coupled dynamics of electrons and nuclei in nanoscale molecular systems is presented. The method relies on a second order expansion of the Lagrangian in time-dependent density functional theory (TDDFT) around a suitable reference density. We show that the inclusion of the second order term renders the method a self-consistent scheme and improves the calculated optical spectra of molecules by a proper treatment of the coupled response. In the application to ion-fullerene collisions, the inclusion of self-consistency is found to be crucial for a correct description of the charge transfer between projectile and target. For a model of the photoreceptor in retinal proteins, nonadiabatic molecular dynamics simulations are performed and reveal problems of TDDFT in the prediction of intra-molecular charge transfer excitations.Comment: 9 pages, 8 figures. Minor changes in content wrt older versio

Polyyne electronic and vibrational properties under environmental interactions

Recently the novel system of linear carbon chains inside double-walled carbon nanotubes has extended the length of sp1 hybridized carbon chains from 44 to thousands of atoms [Shi, Nat. Mater. 15, 634 (2016)1476-112210.1038/nmat4617]. The optoelectronic properties of these ultralong chains are poorly described by current theoretical models, which are based on short chain experimental data and assume a constant environment. As such, a physical understanding of the system in terms of charge transfer and van der Waals interactions is widely missing. We provide a reference for the intrinsic Raman frequency of polyynes in vacuo and explicitly describe the interactions between polyynes and carbon nanotubes. We find that van der Waals interactions strongly shift this frequency, which has been neither expected nor described for other intramolecular C-C stretching vibrations. As a consequence of charge transfer from the tube to the chain, the Raman response of long chains is qualitatively different from the known phonon dispersion of polymers close to the Γ point. Based on these findings we show how to correctly interpret the Raman data, considering the nanotube's properties. This is essential for its use as an analytical tool to optimize the growth process for future applications. © 2016 American Physical Society

Confined linear carbon chains as a route to bulk carbyne

Strong chemical activity and extreme instability in ambient conditions characterize carbyne, an infinite sp1 hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for production, and even more so for application. We report a method for the bulk production of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk production of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbyne's bulk production. © 2016 Macmillan Publishers Limited

The Three-Dimensional Distribution of αA-Crystalline in Rat Lenses and Its Possible Relation to Transparency

Lens transparency depends on the accumulation of massive quantities (600–800 mg/ml) of twelve primary crystallines and two truncated crystallines in highly elongated “fiber” cells. Despite numerous studies, major unanswered questions are how this heterogeneous group of proteins becomes organized to bestow the lens with its unique optical properties and how it changes during cataract formation. Using novel methods based on conical tomography and labeling with antibody/gold conjugates, we have profiled the 3D-distribution of the αA-crystalline in rat lenses at ∼2 nm resolutions and three-dimensions. Analysis of tomograms calculated from lenses labeled with anti-αA-crystalline and gold particles (∼3 nm and ∼7 nm diameter) revealed geometric patterns shaped as lines, isosceles triangles and polyhedrons. A Gaussian distribution centered at ∼7.5 nm fitted the distances between the ∼3 nm diameter gold conjugates. A Gaussian distribution centered at ∼14 nm fitted the Euclidian distances between the smaller and the larger gold particles and another Gaussian at 21–24 nm the distances between the larger particles. Independent of their diameters, tethers of 14–17 nm in length connected files of gold particles to thin filaments or clusters to ∼15 nm diameter “beads.” We used the information gathered from tomograms of labeled lenses to determine the distribution of the αA-crystalline in unlabeled lenses. We found that αA-crystalline monomers spaced ∼7 nm or αA-crystalline dimers spaced ∼15 nm center-to-center apart decorated thin filaments of the lens cytoskeleton. It thus seems likely that lost or gain of long-range order determines the 3D-structure of the fiber cell and possible also cataract formation