Fractionnement et caractérisation de la matière organique des lixiviats de décharges d'ordures ménagères

Les lixiviats de décharge constituent une source de nuisance qui vient s'ajouter aux nombreux problèmes de contamination du milieu environnant s'ils ne sont pas traités avant leur rejet. La matière organique, principale composante de ces effluents, doit retenir une grande attention dans la mesure où il est difficile d'éviter la propagation et la diffusion de cette pollution dans les sols et vers les nappes phréatiques. Cette étude vise à fractionner et à caractériser la matière organique présente dans des lixiviats de décharges d'ordures ménagères afin de prévoir et d'orienter le choix des traitements les plus adaptés compte tenu de leur biodégradabilité.La méthode de fractionnement utilisée comprend une adsorption spécifique sur résines macroporeuses Amberlite XAD (combinaison de XAD-7 et XAD-4) pour séparer les composés hydrophobes et hydrophiles qui sont ensuite extraits à la soude (composés acides) et au dichlorométhane (composés neutres). Le fractionnement de la matière organique par filtration sur résines XAD-7 et XAD-4, après une première étape de précipitation en milieu acide (pH=1), a permis de répartir l'ensemble des composés organiques du lixiviat dans six fractions de spécificités différentes fonction de la taille et/ou du caractère hydrophile ou hydrophobe des molécules. Les résultats montrent que ce protocole expérimental permet d'extraire au moins 98 % de la matière organique totale (pourcentage relatif aux teneurs de la demande chimique en oxygène ou DCO), dont la plus grande proportion est constituée des substances humiques (76 % à 90 % en DCO). Diverses méthodes analytiques ont été proposées en vue de caractériser les fractions isolées telles que l'analyse élémentaire, la spectrophotométrie infrarouge, la résonanoe magnétique nucléaire C13 (RMN Cl3) et la chromatographie CG/FID et CG/SM.Landfill leachates represent an obvious source of pollution for the environment and many studies have attempted to analyze organic pollutants found in leachates. A number of methods have been described in the literature for the isolation and concentration of dissolved organic matter from landfill leachate samples. Membrane ultrafiltration, gel permeation and high performance liquid chromatography are commonly used because these techniques can be easily adapted to separate soluble organic substances from large volumes of leachate. The objective of this study was to fractionate and characterize dissolved organic matter found in leachates collected from sanitary landfills.The discharges are defined with regard to the geological context from which they are situated and the nature of the waste. The discharges are classified in three categories, based upon the value of the permeability coefficient K, the substratum and its continuity.- class 1; impermeable site (K 10-[sup]6 ms-¹). The studied leachates come from landfill of class 2:- Crézin (Haute-Vienne) of compacted type: it was used for household rubbish and assimilated ordinary wastes. - Foussais-Payre (Vendée): leachate coming from the fermentation area of a composting plant and from the compost refuse. Fractionation of dissolved organic matter was applied on three leachates samples. The first sample was the raw leachate collected from the Crézin landfill and the two others came from Foussais-Payre (a raw sample and a sample treated in an aerated lagoon for 52 days). Because of the wide variety of organic compounds that can be found in such leachates, we classified and isolated the different groups of organic constituents using an XAD resin adsorption procedure. The experimental method consisted of acidifying samples to pH 1 to isolate the first fraction (fig. 1) and then treating the remaining supernatant with XAD-7 and XAD-4 resins. The adsorption on XAD resins allowed the isolation of the other organic fractions (figs. 2 to 6). Various analytical techniques were applied to characterize the isolated fractions such as elementary analysis infrared spectroscopy, ¹3C nuclear magnetic resonance (¹3C CP/MAS NMR), gas chromatography (GC/FID), and gas chromatography coupled to mass spectrometry (GC/MS). Results showed that more then 90% of the total organic carbon (TOC) in leachates can he recovered by the isolation procedure. Most of the isolated compounds corresponded to humic substances (76% to 90% of the chemical oxygen demand). Hydrophobic and hydrophilic neutral compounds were found only in small concentrations

La mise à l'équilibre des eaux tropicales : conséquences sur la déferrisation

L'étude de l'équilibre calco-carbonique d'une eau souterraine de l'Afrique de l'Ouest par la méthode de LEGRAND et POIRIER, a conduit à la détermination des conditions de traitement pour neutraliser l'agressivité naturelle de l'eau, due essentiellement à une forte teneur en acide carbonique et réduire ainsi son caractère corrosif. le problème de l'évolution du fer présent en relation avec la mise à l'équilibre a été également étudiée.L'application réalisée sur un pilote de laboratoire a permis d'optimiser les principales étapes du traitement, c'est-à-dire l'addition d'une base forte, la précipitation et la filtration des hydroxydes ferriques qui se forment à la suite de la neutralisation de l'acide carbonique.Studies on calcium carbonate equilibrium of West African ground water, a sample of potable water distributed in Lomé (Togo), were carried out using the method described by LEGRAND and POIRIER. It is a standard graphic method in which calculations include all basic (Ca++, HCO3-, CO3--, CO2, H2O+, OH-), and characteristic (Mg++, Na+, K+, SO4--, Cl- ...) chemical parameters of natural water. Processing of a computer program for calculations enabled the equilibrium and saturation curve [CO2] = f[Ca++], to be obtained. The aggressivity to the lime deposit character, different conditions of treatment, aeration, and addition of an appropriate base to neutralise the nature aggressivity of water due to its high dissolved carbon dioxide content could also be defined.The problem of the presence of iron was studied; high concentration of iron in natural ground water lead to various problems : developing of tastes, staining and discoloration of clothes, and growth of iron bacteria in the distribution system. Its removal from water is accomplished by means of the oxidation of iron (II) to iron (III) followed by the precipitation of relatively insoluble ferric hydroxide. The oxidation rate is highly dependent on pH. Thus, the process of removal of carbon dioxide by stripping or neutralisation raises the pH of the water. If the pH is raised high enough, an insoluble form of iron will precipitate. Another important aspect of the chemical behaviour of iron is the formation of complex ions with inorganic as well as organic ligands; silica in water forms a relatively stable complex with iron (III). The difficulty in removing iron from water is often associated with this phenomenon.Continuous flow studies were carried out to improve important steps of treatment such as addition of a strong base, and precipitation and filtration of ferric hydroxide produced during carbonic acid neutralization. They show the weak stability of silicato-iron (III) complex at high pH value and prove that practically complete iron removal may be obtained

Social class, parents' education and dental caries in 3- to 5-year-old children

KIMThe caries prevalence of 1273-, 4- and 5-y-old white children was determined with mirror and probe under natural light at mother and child clinics. The social class of the family, the educational level of the mother and that of the father were determined from a questionnaire filled in by the accompanying adult at the time of examination. Both social class and parent's education had a statistically significant influence on the caries prevalence: those in the lower social classes and with parents without tertiary education had a much higher prevalence of carie

Permanent denition caries in KwaZulu and Namibia 11-year-olds

KIMThe permanent dentitions of 11-year-old children in Namibia (n = 295) and KwaZulu (n = 308) living in rural and urban areas were examined using WHO caries diagnostic criteria. In low fluoride areas (less than 0.15 ppmF) significantly more caries was present in rural compared to urban KwaZulu but the prevalences in rural and urban Namibia were similar although significantly higher than in an area with 1.56ppmF in the drinking water. There was significantly more caries in rural Namibia than KwaZulu but the urban prevalences in both regions were similar. It is suggested that the urban findings are useful predictors for the needs of 11-year-old black children but local baseline surveys should be undertaken before considering dental programmes, treatment or preventive, for different rural communities in South Africa

Inequivalent representations of commutator or anticommutator rings of field operators and their applications

Hamiltonian of a system in quantum field theory can give rise to infinitely many partition functions which correspond to infinitely many inequivalent representations of the canonical commutator or anticommutator rings of field operators. This implies that the system can theoretically exist in infinitely many Gibbs states. The system resides in the Gibbs state which corresponds to its minimal Helmholtz free energy at a given range of the thermodynamic variables. Individual inequivalent representations are associated with different thermodynamic phases of the system. The BCS Hamiltonian of superconductivity is chosen to be an explicit example for the demonstration of the important role of inequivalent representations in practical applications. Its analysis from the inequivalent representations' point of view has led to a recognition of a novel type of the superconducting phase transition.Comment: 25 pages, 6 figure