Étude du traitement et du recyclage des eaux issues des serres horticoles

La gestion de l'eau dans les systèmes de culture hors-sol fait apparaître deux problèmes distincts. D'une part, les ressources en eau doivent être de bonne qualité et ne pas contenir de pesticides ou de germes pathogènes. D'autre part, les rejets fortement " chargés " en nutriments (NO3-, PO43-) polluants pour l'environnement, doivent être limités par le biais de leur recyclage ce qui implique nécessairement la désinfection des effluents.La technique mise en œuvre pour obtenir cette maîtrise de la qualité tant chimique que microbiologique des solutions circulantes en culture hors-sol est celle d'une oxydation à l'ozone seul et couplé au peroxyde d'hydrogène dans des réacteurs constitués de mélangeurs statiques. Les conditions de traitement sont une dose d'oxydant de 10 g O3/m3 d'effluent à traiter, un rapport H2O2/O3 de 0,15 g/g pour un temps de contact dans le réacteur de l'ordre de la seconde. Etudié sur site dans le cadre du traitement de effluents de serre réels, le procédé s'est révélé tout à fait adapté pour abattre les pesticides (# 90 % pour l'atrazine), maîtriser la prolifération des micro-organismes (Flore aérobie mésophile, flore fongique) et en particulier des germes pathogènes (Clavibacter michiganensis, Fusarium, Pythium sp ).Le procédé novateur O3/H2O2 sur mélangeurs statiques constitue donc pour les serristes une réponse nouvelle dont l'un des intérêts est de combiner les effets " détoxiquant " et désinfectant.The management of water resources in soil-less cultures presents two difficulties. On one hand, the quality of these resources has to be good, that is to say without pesticides or pathogens. On the other hand, the effluents contain high concentrations of nutrients (NO3-, PO43-), damageable for the environment, and should be recycled. Thus, recycling has to include necessarily a disinfection step to satisfy the quality requirement. The main disinfection treatments used in soil-less cultures are slow sand filtration, ultraviolet treatment, heat treatment, nanofiltration, ozone or hydrogen peroxide oxidation, iodine or chlorine treatment.In order to control the chemical as well as the microbiological quality of the recycled nutrient solution, we suggest oxidation (O3) and advanced oxidation (O3/H2O2) processes, carried out in static mixers as chemical reactors instead of bubble columns. We have been studying this process in situ for the treatment of a 1-hectare greenhouse. The pilot plant unit can be configured under three setups (Figure 2) according to the aim to favor either the molecular action of ozone or the formation of very reactive radical species such as the hydroxyl radical. In this second case, the mechanism of ozone decomposition is given by Figure 1.The first step of the study was to measure the influence of the nutrient solution to be recycled on the efficiency of atrazine removal (Figures 3 and 4). In comparison with tap water, the percentage of pesticide removal is lower by about 10 to 20 %. Solutions with nutrients do not drastically change the process efficiency. The experiments were carried out with various ozone dosages and various ozone / hydrogen peroxide mass ratios, using the three configurations (Figures 5 and 6). With these results, the best operating conditions for micropollutant removal are a treatment rate of about 10 g O3 /m3 of treated solution, a H2O2/O3 ratio equal to 0.15 g/g and a contact time in the reactor in the range of 1 to 2 seconds. The influence of the configuration type is not really marked. The results show that, under these conditions, this technique leads to good pesticide removal efficiencies (about 90 % for atrazine).In a second step, experiments were carried out on real solutions containing microorganisms from the greenhouse, sometimes spiked with special bacteria (Clavibacter) or fungi (Fusarium). Some results are reported in Figures 7, 8 and 9. With the same oxidant dosage conditions, the role of the configuration is clearly demonstrated. The best results are obtained with a molecular action of ozone in the first static mixed reactor followed by a free-radical action within the second reactor. Thus, it is possible to prevent germ proliferation (aerobic mesophilic flora and fungi flora) and particularly pathogenic species. The abatement of Clavibacter michiganensis reaches 3.5 to 4 logarithmic units, 1 to 1.5 units for Pythium and 2 to 4 units for Fusarium. The treatment does not effect a complete sterilization, e.g., the beneficial bacterium Pseudomonas fluorescens survives. The global impact of the treatment on the nutritive quality of the treated solution is negligible. Nevertheless, we can note that the process induces a decrease of the ion concentrations of Fe (II) (- 5 to 30 %) and Mn (II) (-10 to 15 %) as a result of the oxidation of the EDTA chelate. In fact, this problem is observed with all oxidation and UV treatments. The residual oxidant (O3, H2O2) concentrations are low and do not induce obvious toxic effects on the cultures.Thus, the technique is consistent with a recycling of the treated effluents. The advantages of the process include very short contact times, compactness of the equipment, no need for pretreatment, reasonable investment and operating costs, an increase of the oxygen concentration in the treated effluent, and possible curative effects on the culture's germ contamination due to the residual concentration of hydrogen peroxide. The disinfection efficiency of this suggested process is similar to those obtained with more common techniques like UV irradiation. Moreover, the studied process can also reduce, for example, an eventual chemical pollution of the water resource. In conclusion, the O3, H2O2 process in static mixers appears to be a new solution for greenhouse farmers

Observation of individual molecules trapped on a nanostructured insulator

For the first time, ordered polar molecules confined in monolayer-deep rectangular pits produced on an alkali halide surface by electron irradiation have been resolved at room temperature by non-contact atomic force microscopy. Molecules self-assemble in a specific fashion inside pits of width smaller than 15 nm. By contrast no ordered aggregates of molecules are observed on flat terraces. Conclusions regarding nucleation and ordering mechanisms are drawn. Trapping in pits as small as 2 nm opens a route to address single molecules

Using exchange bias to extend the temperature range of square loop behavior in [Pt/Co] multilayers with perpendicular anisotropy

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The temperature dependence of the magnetic properties of [Pt/Co]multilayers (ML), exhibiting perpendicular anisotropy, with and without exchange biasing with an antiferromagnet(AFM) has been investigated. Upon heating, a loss of the out-of-plane anisotropy and, consequently, of the remanence to saturation ratio is observed in these systems. However, such effect occurs at higher temperatures in the [Pt/Co] ML exchange coupled to the AFM than for the unbiased ML. This is attributed to the additional anisotropy induced to the ML by the ferromagnetic-antiferromagnetic exchange coupling

Jets and Topography: Jet Transitions and the Impact on Transport in the Antarctic Circumpolar Current

The Southern Ocean’s Antarctic Circumpolar Current (ACC) naturally lends itself to interpretations using a zonally averaged framework. Yet, navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models. In this study, both observational and numerical results indicate that zonal asymmetries, in the form of topography, impact global flow structure and transport properties. The conclusions are based on a suite of more than 1.5 million virtual drifter trajectories advected using a satellite altimetry–derived surface velocity field spanning 17 years. The focus is on sites of “cross front” transport as defined by movement across selected sea surface height contours that correspond to jets along most of the ACC. Cross-front exchange is localized in the lee of bathymetric features with more than 75% of crossing events occurring in regions corresponding to only 20% of the ACC’s zonal extent. These observations motivate a series of numerical experiments using a two-layer quasigeostrophic model with simple, zonally asymmetric topography, which often produces transitions in the front structure along the channel. Significantly, regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic. Jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets. Eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering. The combination of high eddy kinetic energy and recirculation features enhances particle exchange. These results stress the complications in developing consistent circumpolar definitions of the ACC fronts

Obesity-induced insulin resistance in human skeletal muscle is characterised by defective activation of p42/p44 MAP kinase

Insulin resistance (IR), an impaired cellular, tissue and whole body response to insulin, is a major pathophysiological defect of type 2 diabetes mellitus. Although IR is closely associated with obesity, the identity of the molecular defect(s) underlying obesity-induced IR in skeletal muscle remains controversial; reduced post-receptor signalling of the insulin receptor substrate 1 (IRS1) adaptor protein and downstream effectors such as protein kinase B (PKB) have previously been implicated. We examined expression and/or activation of a number of components of the insulin-signalling cascade in skeletal muscle of 22 healthy young men (with body mass index (BMI) range, 20–37 kg/m2). Whole body insulin sensitivity (M value) and body composition was determined by the hyperinsulinaemic (40 mU. min−1.m−2.), euglycaemic clamp and by dual energy X-ray absorptiometry (DEXA) respectively. Skeletal muscle (vastus lateralis) biopsies were taken before and after one hour of hyperinsulinaemia and the muscle insulin signalling proteins examined by western blot and immunoprecipitation assay. There was a strong inverse relationship between M-value and BMI. The most striking abnormality was significantly reduced insulin-induced activation of p42/44 MAP kinase, measured by specific assay, in the volunteers with poor insulin sensitivity. However, there was no relationship between individuals' BMI or M-value and protein expression/phosphorylation of IRS1, PKB, or p42/44 MAP kinase protein, under basal or hyperinsulinaemic conditions. In the few individuals with poor insulin sensitivity but preserved p42/44 MAP kinase activation, other signalling defects were evident. These findings implicate defective p42/44 MAP kinase signalling as a potential contributor to obesity-related IR in a non-diabetic population, although clearly multiple signalling defects underlie obesity associated IR

RNA Oligomerisation without Added Catalyst from 2 ',3 '-Cyclic Nucleotides by Drying at Air-Water Interfaces

For the emergence of life, the abiotic synthesis of RNA from its monomers is a central step. We found that in alkaline, drying conditions in bulk and at heated air-water interfaces, 2 ',3 '-cyclic nucleotides oligomerised without additional catalyst, forming up to 10-mers within a day. The oligomerisation proceeded at a pH range of 7-12, at temperatures between 40-80 degrees C and was marginally enhanced by K+ ions. Among the canonical ribonucleotides, cGMP oligomerised most efficiently. Quantification was performed using HPLC coupled to ESI-TOF by fitting the isotope distribution to the mass spectra. Our study suggests a oligomerisation mechanism where cGMP aids the incorporation of the relatively unreactive nucleotides C, A and U. The 2 ',3 '-cyclic ribonucleotides are byproducts of prebiotic phosphorylation, nucleotide syntheses and RNA hydrolysis, indicating direct recycling pathways. The simple reaction condition offers a plausible entry point for RNA to the evolution of life on early Earth

Finite element analysis of the effect of cementing concepts on implant stability and cement fatigue failure

Background and purpose Two contradictory cementing techniques (using an undersized stem versus a canal-filling stem) can both lead to excellent survival rates, a phenomenon known as the “French paradox”. Furthermore, previous studies have indicated that the type of bone supporting the cement mantle may affect implant survival. To further evaluate the mechanical consequences of variations in cementing technique, we studied the effect of implant size and type of bone supporting the cement mantle on the mechanical performance of cemented total hip arthroplasty, using finite element analysis