Fractionnement et caractérisation des lixiviats de centres d'enfouissement technique de déchets ménagers: intérêt de la chromatographie liquide haute performance sur le gel d'exclusion stérique

L'ultrafiltration et la chromatographie d'exclusion stérique haute performance sont utilisées pour la séparation et la caractérisation des composés organiques présents dans les lixiviats de centres d'enfouissement technique de déchets ménagers. Le fractionnement de la matière organique est obtenu sur des colonnes type TSK PW, en élution eau pH 4 et eau-méthanol. La spectroscopie en UV-visible et en fluorescence, un détecteur évaporatif à diffusion de lumière sont utilisés pour la caractérisation des fractions. Cette méthode rapide de séparation associée à une multidétection permet une mise en évidence, dans les fractions issues de l'ultrafiltration, de composés organiques caractéristiques. Dans la fraction de poids moléculaires inférieurs à 1000 Daltons, trois familles sont détectées. Les substances humiques et les protéines sont les principaux groupes présents dans la fraction de poids moléculaires supérieurs à 10000 Daltons.Landfill leachates represent a source of organic pollution characterized by an important organic load, with high chemical oxygen demand in recent sanitary landfills and some organic compounds refractory to biodegradation. Several researchers have examined the organic matter in these landfill leachates. In addition to measuring parameters such as chemical and biological oxygen demands (COD and BOD) and UV-absorbance, different analytical techniques were applied: gas chromatography with flame ionization or mass detection; high performance liquid chromatography; infrared spectroscopy; nuclear magnetic resonance spectrometry; and elementary analysis. Raw leachates or samples after fractionation on Sephadex gel were characterized by ultrafiltration or adsorption on XAD resins.Conclusions from these earlier studies were as follows:  - physico-chemical properties of leachates revealed not only a high organic pollution but also diversity and variability according to the age of the sanitary landfill and the climatic conditions; - gel permeation chromatography and ultrafiltration revealed two main fractions in the leachates: one with molecular weights below 1000 Daltons (Da), and another with molecular weights above 5000-10000 Da; - infrared spectroscopy and nuclear magnetic resonance spectrometry showed functional groups present in the humic and fulvic acid fractions of natural organic matter; - a varying number of peaks detected by gas chromatography with flame ionization or mass detection proved the complexity of the matrix. Few compounds were identified and quantified, with the exception of fatty acids. Moreover this technique was only applicable to molecules with low molecular weight.The purpose of the present work was to develop a new method of fractionation of organic matter in landfill leachates and to study their characterization and treatment biodegradation. Ultrafiltration, as a prefractionation step, divided the leachate into four fractions according to their molecular weight: above 10000 Da, from 10000 - 3000 Da, from 3000 - 1000 Da, and below 1000 Da. The second fractionation step was carried out using gel permeation chromatography. This technique has been was applied by earlier researchers for the characterization of landfill leachates, but at low pressure on Sephadex gels. In our study, we developed a high performance size-exclusion chromatography method using a polymer based TSK PW column, a hydrophilic cross-linked polyether. Three TSK G3000 PW columns and one G5000 PW column were tested with water at pH 4 with acetic acid and with a water/methanol mixture as mobile phases. This rapid method of separation, with short retention times, was coupled with on-line multidetection: UV-visible (254 nm - aromatic compounds), fluorescence spectroscopy (275/325 nm, protein-type molecules; 320/430 nm, humic-type molecules) and evaporative light scattering detection, ELSD. The ELSD allowed detection of all mineral and organic compounds that did not evaporate at the working temperature (45°C).The effect of the sodium chloride concentration on retention times was tested with eluants and columns. Secondary effects, often observed with size-exclusion chromatography, occurred with the gel chosen. The elution of sodium chloride solutions at different concentrations showed that the TSK PW gel bears electronegative charges, and that the density of these charges differs from one column to another. For the leachate we observed this influence: chromatograms obtained on two TSK G3000 columns were different for fractions with molecular weights below 1000 Da.The comparison of chromatograms obtained with the four detection methods provided information about the identity of the types of compounds present. For fractions with molecular weights below 1000 Da, separation was performed using a TSK G3000 PW column, with an eluant pH of 4 and a water-methanol mixture; three main families were detected. For fractions with molecular weights above 10000 Da, chromatographic separation was improved by elution with water/methanol (70/30) with TSK G5000 and G3000 columns in series; two main groups were identified, humic substances and protein-type compounds. The constituents of the two intermediate fractions with molecular weights between 10000 and 1000 Da were essentially humic substances, identified after separation on a TSK G3000 PW column with water-methanol (70/30) as the eluant

Mg and its alloys for biomedical applications: Exploring corrosion and its interplay with mechanical failure

The future of biomaterial design will rely on temporary implant materials that degrade while tissues grow, releasing no toxic species during degradation and no residue after full regeneration of the targeted anatomic site. In this aspect, Mg and its alloys are receiving increasing attention because they allow both mechanical strength and biodegradability. Yet their use as biomedical implants is limited due to their poor corrosion resistance and the consequential mechanical integrity problems leading to corrosion assisted cracking. This review provides the reader with an overview of current biomaterials, their stringent mechanical and chemical requirements and the potential of Mg alloys to fulfil them. We provide insight into corrosion mechanisms of Mg and its alloys, the fundamentals and established models behind stress corrosion cracking and corrosion fatigue. We explain Mgs unique negative differential effect and approaches to describe it. Finally, we go into depth on corrosion improvements, reviewing literature on high purity Mg, on the effect of alloying elements and their tolerance levels, as well as research on surface treatments that allow to tune degradation kinetics. Bridging fundamentals aspects with current research activities in the field, this review intends to give a substantial overview for all interested readers; potential and current researchers and practitioners of the future not yet familiar with this promising material. © 2017 by the authors. Licensee MDPI, Basel, Switzerland

In situ formation of low molecular weight organogelators for slick solidification

We have investigated the in situ formation of Low Molecular Weight Organogelator (LMWO) molecules in oil-on-water slicks through dual reactive precursor injection. This method alleviates the need for any carrier solvent or prior heating, therefore reducing the environmental impact of LMWOs, giving instantaneous gelation, even at low temperatures (−5 °C). We show minimal leaching from our gels into the water layer

Correlations between climate network and relief data

In the last few years, the scientific community has witnessed an ongoing trend of using ideas developed in the study of complex networks to analyze climate dynamics. This powerful combination, usually called climate networks, can be used to uncover non-trivial patterns of weather changes throughout the years. Here we investigate the temperature network of the North American region and show that two network characteristics, namely degree and clustering, have marked differences between the eastern and western regions. We show that such differences are a reflection of the presence of a large network community on the western side of the continent. Moreover, we provide evidence that this large community is a consequence of the peculiar characteristics of the western relief of North America

Accurate Measurement in the Field of the Earth of the General-Relativistic Precession of the LAGEOS II Pericenter and New Constraints on Non-Newtonian Gravity

The pericenter shift of a binary system represents a suitable observable to test for possible deviations from the Newtonian inverse-square law in favor of new weak interactions between macroscopic objects. We analyzed 13 years of tracking data of the LAGEOS satellites with GEODYN II software but with no models for general relativity. From the fit of LAGEOS II pericenter residuals we have been able to obtain a 99.8% agreement with the predictions of Einstein's theory. This result may be considered as a 99.8% measurement in the field of the Earth of the combination of the {\gamma} and {\beta} parameters of general relativity, and it may be used to constrain possible deviations from the inverse-square law in favor of new weak interactions parametrized by a Yukawa-like potential with strength {\alpha} and range {\lambda}. We obtained |{\alpha}|\lesssim1\times10-11, a huge improvement at a range of about 1 Earth radius

Hepatitis E Virus Antibodies in Patients with Chronic Liver Disease

In the United States, the seroprevalence rate for hepatitis E virus (HEV) is ≈20%. This study examined HEV seroprevalence in persons with and without chronic liver disease. Our data indicate that HEV seropositivity is high in patients with chronic liver disease and that HEV seroprevalence increases significantly with age