Utilisation de la coagulation - floculation pour la dépollution des eaux de surface au Liban

Ibrahim et Ghadir sont deux rivières côtières localisées aux environs de Beyrouth et exposées à des impacts anthropiques différents. L'élimination des Matières en Suspension MES des eaux de ces rivières a été étudiée par simple jar test couplé à des mesures de turbidité au niveau du surnageant, et à une mesure de volumes des sédiments. Les caractéristiques physico-chimiques des eaux avant et après traitement sont déterminées par absorption atomique et chromatographie ionique. Les jars tests montrent que la préhydrolyse des sels d'aluminium avant leur ajout dans l'eau permet l'utilisation de plus faibles quantités en Al pour la coagulation-floculation des eaux qui élimine préférentiellement les Matières en Suspension. Plus la turbidité initiale des eaux à traiter est faible, plus la concentration optimale en aluminium est moindre. L'élimination des MES par coagulation-floculation est plus efficace pour la rivière Ibrahim, où les rejets anthropiques directs dans son cours d'eau sont moindres que ceux dans la rivière Ghadir. La restabilisation dans les jars tests est marquée dans tous les essais de la rivière Ibrahim. Dans les deux cas, un échange cationique avec les polycations Al13 au niveau des sédiments marque la libération du calcium et l'augmentation de sa concentration dans le surnageant

Potential of Opuntia ficus-indica for air pollution biomonitoring : a lead isotopic study

Opuntia ficus-indica (Ofi) is a long-domesticated cactus that is widespread throughout arid and semiarid regions. Ofi is grown for both its fruits and edible cladodes, which are flattened photosynthetic stems. Young cladodes develop from mother cladodes, thus forming series of cladodes of different ages. Therefore, successive cladodes may hold some potential for biomonitoring over several years the local atmospheric pollution. In this study, cladodes, roots, dust deposited onto the cladodes, and soil samples were collected in the vicinity of three heavily polluted sites, i.e., a fertilizer industry, the road side of a highway, and mine tailings. The lead content was analyzed using atomic absorption spectroscopy (AAS) and inductively coupled plasma-mass spectrometry (ICP-MS). Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) was used to characterize the cladode surfaces and the nature of dust deposit, and the lead isotopes were analyzed to identify the origin of Pb. The results show that (i) Ofi readily bioaccumulates Pb, (ii) the lead isotopic composition of cladodes evidences a foliar pathway of lead into Ofi and identifies the relative contributions of local Pb sources, and (iii) an evolution of air quality is recorded with successive cladodes, which makes Ofi a potential biomonitor to be used in environmental and health studies

Trace element carriers in combined sewer during dry and wet weather: an electron microscope investigation

International audienceThe nature of trace element carriers contained in sewage and combined sewer overflow (CSO) was investigated by TEM-EDX-Electron diffraction and SEM-EDX. During dry weather, chalcophile elements were found to accumulate in sewer sediments as early diagenetic sulfide phases. The sulfurization of some metal alloys was also evidenced. Other heavy metal carriers detected in sewage include metal alloys, some iron oxihydroxide phases and neoformed phosphate minerals such as anapaite. During rain events, the detailed characterization of individual mineral species allowed to differentiate the contributions from various specific sources. Metal plating particles, barite from automobile brake, or rare earth oxides from catalytic exhaust pipes, originate from road runoff, whereas PbSn alloys and lead carbonates are attributed to zinc-works from roofs and paint from building siding. Soil contribution can be traced by the presence of clay minerals, iron oxihydroxides, zircons and rare earth phosphates. However, the most abundant heavy metal carriers in CSO samples were the sulfide particles eroded from sewer sediments. The evolution of relative abundances of trace element carriers during a single storm event, suggests that the pollution due to the “first flush” effect principally results from the sewer stock of sulfides and previously deposited metal alloys, rather than from urban surface runoff

Jurassic amber outcrops from Lebanon

International audienc

Speciation of Organic Matter and Heavy Metals in Urban Wastewaters from an Emerging Country

International audienc

Clarification of municipal sewage with ferric chloride: the nature of coagulant species

International audienceThe nature of coagulant species formed in the system ferric chloride/municipal sewage was explored with Transmission Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (TEM-EDXS) and Fe K-edge X-ray Absorption spectroscopy. Jar-test data combined with chemical analysis of supernatant (dissolved organic carbon, iron, and phosphorus) and Fourier-Transform-Infrared spectroscopy (FTIR) of freeze-dried sediment, provided a detailed description of sewage clarification. The results showed that the nature of coagulant species evolves with Fe concentration. Up to the optimum turbidity removal, mainly iron dimers linked with one phosphate anion are detected. At higher dosages, polymers of hydrolyzed Fe appear even though PO4 still participates in the formation of coagulant species. TEM observation of freeze-dried sediments corroborates such an evolution of Fe speciation. EDXS analyses reveal that minute amounts of sulfur, silicon, aluminum, and calcium, are associated with the coagulant species. Even though the coagulant species change with Fe concentration, the destabilization mechanism, inferred from electrophoretic mobility of aggregates and the evolution of floc size under cyclic changes of stirring conditions, is equivalent with a charge neutralization of sewage colloids in the whole range of coagulant concentration