Cinétiques de biodégradation par boues activées de la matière organique soluble d'un effluent synthétique

L'approche expérimentale choisie pour cette étude a eu pour objet de mesurer en conditions batch, les cinétiques d'élimination de la demande chimique en oxygène soluble d'un effluent synthétique mis en contact avec des boues activées d'origine différente. Les essais conduits en laboratoire ont été réalisés en faisant varier le rapport So/Xo (mg de DCO initiale par mg de matières volatiles initiales) telles que les concentrations en So et en Xo correspondent aux concentrations en DCO soluble (DCOs) et en matières volatiles (MV) rencontrées sur les stations d'épuration. Les essais ont été effectués sous aération continue à 20 °C en mettant en contact l'effluent synthétique et de la boue activée prélevée depuis 24 h et stockée à 4 °C dans l'attente de l'essai. De ce fait, la valeur de So mesurée au début de l'essai représente la concentration en DCO amenée par l'effluent synthétique (Seff) et celle amenée par l'inoculum de boue activée (Sb) représentant selon les essais de 5 à 70 % de la DCO de l'essai. Les profils de cinétique d'élimination de la DCO soluble obtenus pour différentes conditions d'essai s'ajustent, selon les valeurs de So/Xo (So/Xo variant de 0,15 à 2,17 ) à une fonction du premier ordre par rapport au substrat ou à une fonction sigmoïde. Le type de fonction cinétique d'élimination est également contrôlé par la proportion de la DCO amenée par l'inoculum.The conventional activated sludge process used for wastewater treatment removes from 80 to 95% of the total organic matter. However, a quantity of "not well identified" (particular, colloidal and soluble) organic matter is always present in the treated effluent. Reducing this residual (and improving the treatment efficiency) requires knowledge of the origin of that organic matter and especially to determine the fraction originating from the influent and the fraction generated by the biomass.This research has been conducted in batch conditions and studies the soluble COD (CODs) removal kinetics of a synthetic effluent (casein + starch + acetate + mineral salts), in contact with different activated sludge originating from six different wastewater treatment plants (loads varying from 0.06 to 1.14 kg BOD[inf]5/kg VSS. d).Experiments have been conducted with different So/Xo values (ratio between CODs initial concentration and VSS initial concentration) in order that these values correspond to the CODs and VSS values found in the plants.In accordance with GRAU et al. (1975), CECH and CHUDOBA (1983), PITTER and CHUDOBA (1990), CHUDOBA et al (1992), the So/Xo ratio is a fundamental parameter governing the kinetics reactions.Experiments have been conducted under continuous aeration at 20°C where the synthetic wastewater (500 ml) is in contact with activated sludge (200 ml) collected 24 h before and stored at 4°C until the batch is started. In this manner, the initial So is due to the CODs of the synthetic effluent (So eff=197 mg/l) and to the CODs originating from the sludge (5 to 70% of the initial CODs). The initial VSS concentration (Xo) is between 0.6 and 2.5 g/l. Kinetics of CODs removal are simulated by two functions: the first order function, where the initial rate is the maximal, and the sigmoidal function where the maximal rate is reached after a lag time (3 to 8 h).Concerning the first order functions, the degradation rate is faster when the ratio is low (So/Xo lower than 0.44). This is not the case for the sigmoidal functions. In the results of this study, the residual of COD is always lower when the degradation kinetic follows the exponential model.Our experiments show that the type of degradation kinetics (first order or sigmoidal) is not only controlled by the So/Xo parameter but also by the proportion of CODs brought by the sludge and that parameter can play a determinant role.When the proportion of CODs brought by the sludge is very large (between 41% to 46%) the degradation reactions follow the sigmoidal type. These results can possibly be explained by the low biodegradability of the polymers or molecules originating from the inoculum which has been stored during 24 h, or by the low activity of the biomass after 24 h of storage on the biodegradation of the soluble organic matte

Dispersal by cattle of salt-marsh and dune species into salt-marsh and dune communities

Seed dispersal via ingestion and defecation by large herbivores (endozoochory) plays a potentially important role in structuring plant communities. In the present study we tested whether cattle disperse seeds between different plant communities in a heterogeneous coastal habitat. We surveyed the seed contents of cattle dung collected from two habitat types within a grazing system, one in dunes and the other in salt-marsh. The dunes are characterized by sandy soil, and infrequent inundation by the sea, whereas the salt-marsh features clay deposited during inundations. Seeds of both salt-marsh and dune species were dispersed into salt-marsh and dune habitats. The seed content of cattle dung collected in salt-marsh and dunes was similar with respect to species composition and seed density. However, dispersal of dune species into salt-marsh and vice-versa did not result in establishment in those communities. Seed traits per se did not differ between dune species and salt-marsh species. Species abundance in the established vegetation and seed density in dung were positively correlated. Seed abundance for most species found in dung was consistent with the availability of viable seeds during the growing season. Seed mass, seed 'roundness' and seed release height were all negatively correlated with seed numbers in dung. An indirect factor, namely, forage quality of the plant, and hence attractiveness for herbivores, could explain the higher likelihood of seed dispersal of salt-marsh species than of dune species. The salt-marsh harbours species with higher forage quality than the dune species, as derived from Ellenberg nitrogen indicator values

Dynamical Localization: Hydrogen Atoms in Magnetic and Microwave fields

We show that dynamical localization for excited hydrogen atoms in magnetic and microwave fields takes place at quite low microwave frequency much lower than the Kepler frequency. The estimates of localization length are given for different parameter regimes, showing that the quantum delocalization border drops significantly as compared to the case of zero magnetic field. This opens up broad possibilities for laboratory investigations.Comment: revtex, 11 pages, 3 figures, to appear in Phys. Rev. A, Feb (1997

Photons in polychromatic rotating modes

We propose a quantum theory of rotating light beams and study some of its properties. Such beams are polychromatic and have either a slowly rotating polarization or a slowly rotating transverse mode pattern. We show there are, for both cases, three different natural types of modes that qualify as rotating, one of which is a new type not previously considered. We discuss differences between these three types of rotating modes on the one hand and non-rotating modes as viewed from a rotating frame of reference on the other. We present various examples illustrating the possible use of rotating photons, mostly for quantum information processing purposes. We introduce in this context a rotating version of the two-photon singlet state.Comment: enormously expanded: 12 pages, 3 figures; a new, more informative, but less elegant title, especially designed for Phys. Rev.

Dynamic earthquake rupture modelled with an unstructured 3-D spectral element method applied to the 2011 M9 Tohoku earthquake

An important goal of computational seismology is to simulate dynamic earthquake rupture and strong ground motion in realistic models that include crustal heterogeneities and complex fault geometries. To accomplish this, we incorporate dynamic rupture modelling capabilities in a spectral element solver on unstructured meshes, the 3-D open source code SPECFEM3D, and employ state-of-the-art software for the generation of unstructured meshes of hexahedral elements. These tools provide high flexibility in representing fault systems with complex geometries, including faults with branches and non-planar faults. The domain size is extended with progressive mesh coarsening to maintain an accurate resolution of the static field. Our implementation of dynamic rupture does not affect the parallel scalability of the code. We verify our implementation by comparing our results to those of two finite element codes on benchmark problems including branched faults. Finally, we present a preliminary dynamic rupture model of the 2011 M_w 9.0 Tohoku earthquake including a non-planar plate interface with heterogeneous frictional properties and initial stresses. Our simulation reproduces qualitatively the depth-dependent frequency content of the source and the large slip close to the trench observed for this earthquake

Dynamic earthquake rupture modelled with an unstructured 3-D spectral element method applied to the 2011 M9 Tohoku earthquake

An important goal of computational seismology is to simulate dynamic earthquake rupture and strong ground motion in realistic models that include crustal heterogeneities and complex fault geometries. To accomplish this, we incorporate dynamic rupture modelling capabilities in a spectral element solver on unstructured meshes, the 3-D open source code SPECFEM3D, and employ state-of-the-art software for the generation of unstructured meshes of hexahedral elements. These tools provide high flexibility in representing fault systems with complex geometries, including faults with branches and non-planar faults. The domain size is extended with progressive mesh coarsening to maintain an accurate resolution of the static field. Our implementation of dynamic rupture does not affect the parallel scalability of the code. We verify our implementation by comparing our results to those of two finite element codes on benchmark problems including branched faults. Finally, we present a preliminary dynamic rupture model of the 2011 Mw 9.0 Tohoku earthquake including a non-planar plate interface with heterogeneous frictional properties and initial stresses. Our simulation reproduces qualitatively the depth-dependent frequency content of the source and the large slip close to the trench observed for this earthquak

J-band variability of M dwarfs in the WFCAM Transit Survey

We present an analysis of the photometric variability of M dwarfs in the Wide Field Camera (WFCAM) Transit Survey. Although periodic light-curve variability in low mass stars is generally dominated by photospheric star spot activity, M dwarf variability in the J band has not been as thoroughly investigated as at visible wavelengths. Spectral type estimates for a sample of over 200 000 objects are made using spectral type-colour relations, and over 9600 dwarfs (J 0.2 mag flaring event from an M4V star in our sample.Peer reviewe