| Environnement, ingénierie & développement |  |
N°32 - 4ème Trimestre 2003
1. Éditorial n°32 Déchets Sciences et Techniques: Quelles recherches pour les déchets ? Une vieille question, des réponses nouvelles ?
Le réseau Ecrin est une association (loi de 1901) qui a pour ambition de créer et faciliter le rapprochement recherche-entreprise pour le développement et l’innovation. Son fonctionnement est organisé autour de clubs qui concrétisent la volonté de plusieurs partenaires d’approfondir une problématique d’intérêt général, en structurant des réseaux d’experts, en animant et organisant des travaux sur des thématiques qui apparaissent comme prioritaires. Le rapprochement entre recherche publique et industrielle et l’expression des besoins en matière d’enjeux sociétaux et économiques doit permettre de définir des stratégies et de mobiliser les compétences des chercheurs. Le club « Environnement et Société », crée en 2000, s’est fixé comme objectif de mieux prendre en compte les préoccupations du citoyen et les aspects socio-économiques dans les questions liées à l’environnement, en visant à fournir aux décideurs les éléments les plus rationnels possibles pour la prise de décision.
2. Pourquoi les boues ne tiennent pas en tas
Sewage sludge is the residue of wastewater treatment, which must be stored before reused in agricultural or incineration. But storage areas appear often under-dimensioned due to creep flow of sludge. In this paper, we intend to demonstrate that a sludge can't be stored in heap because its flowing structure. Using rheometric experiments with pasty sludge and the pressure filtration with non-limed solid sludge, we demonstrate that a sludge is deformed as long as an external stress is applied, whichever its structure. Moreover, we show that fermentation affects the heap behavior : the sludge is more fluid during aging, but paradoxically, solid-liquid interactions are stronger. Finally, we highlight that leaching is a consequence of the creep flow of sludge in storage areas.
3. Effet des acides organiques sur l’indice écotoxique des mâchefers d’incinération d’ordures ménagères (Miom)
In France, incineration, with or without heat recovery, handles about 50% of municipal waste. The main by-product of the process is the bottom ash. Bottom ash disposal is regulated by a directive that allows or not the disposal. The bottom ash must undergo physico- chemical tests and depending on the results are sorted into different classes allowing the re-use or not. This study shows that it is difficult to find a directcorrelation between the well studied leaching and physico- chemical tests and the biotest response. However, we find a correlation between the carboxylic acids amount and the ecotoxicologic index for the bottom ash. These results demonstrate that organic carbon caracterisation in the bottom ash is needed if one wants to have a coherent sorting procedure for the bottom ashes.
4. Caractérisation des flux de gaz émis par un sol pollué
Inhalation of volatile chemicals emitted from a contaminated soil might form a major exposure way for people living on site and in the surroundings. It is essential then to quantify ambient air concentrations for characterizing such exposure and assessing the risks for human health.Two approaches are commonly used :Direct ambient air monitoring only supplies punctual information which is strongly dependent on the prevailing meteorological conditions. Furthermore, concentrations lying below the analytical detection limits cannot be measured whereas they may be harmful to health, especially in the case of a long term exposure.Some exposure models include transfer functions which derive concentrations in the atmosphere from those measured in soil or in the soil pore-air. Such functions are based on simplified hypothesis and can ignore site characteristics likely to influence atmospheric dispersion.To overcome the limitations of both methods INERIS has examined the possibility of using atmospheric dispersion models. According to a preliminary modelling study, they might be useful tools to produce quantitative maps of short term worst case or long term concentrations, making it possible to delimit the impact area of the emissions from the soil. However, the reliability of the model predictions largely depend on the precision of the input data. In particular the pollution source should be defined very carefully. This is why INERIS has devised a strategy for getting a quantitative […]
5. Diagnostic et caractérisation d'un site pollué : comparaison de techniques d'échantillonnage des sols
The choice of a suitable soil sampling strategy plays an important role in the characterization of contaminated land. In order to achieve representative sampling it is necessary to minimize errors due to field investigation, i.e. soil sampling, tool sampling, soil types and land uses.The main objective of this work was a comparison of sampling strategies for mapping trace element concentrations at a given site. The studied area is a former arsenical pesticide manufactory site. Sampling area is approximately 5000 m2. Soil samples were collected during 1999 and 2001, on a regular grid of 10 x 10 m and 20 x 20 m. Additional sampling was also carried out on the basis of a regular grid of 5 x 5 m on two particular zones. At each sampling point two different tools were used (power shovel and hand auger). Random sampling was also used and compared to regular soil sampling.A total of 121 soil samples were collected. Arsenic concentration was analysed on each sample. Arsenic concentrations ranged from 100 mg·kg-1 to 14 000 mg·kg-1. The topsoil (0 to -20 cm) has a higher arsenic content than the lower layers (-20 to -40 cm and –40 to –60 cm). The regular sampling appears to be the better strategy to achieve representative soil sampling. On the other hand, an increase of the number of sampling points does not necessarily improve soil sampling representativity. The use of the two tools provides similar arsenic concentrations. This paper argues for more research on sampling […]
6. Mise en évidence du transport de polluants métalliques facilité par les bactéries dans les sols
Many cases of groundwater contamination by immobile pollutants have been described in the last years. These phenomena are hardly predictable if mechanisms inducing leaching of high amounts of contaminant within short periods are not taken into account. This is the case of particulate transport of pollutants, although only few experimental evidence is available to date. Especially, the effect of bacterial cells on the facilitated transport of heavy metals is not yet well characterised, although micro-organisms, as colloidal particles, can be found every where in soil and water and present very specific mobility and pollutant mobilization potential. The objective of the present work was to show the capability of two well known bacterial strains: Ralstonia metallidurans CH34 and Escherichia coli, to accelerate the transport of mercury, zinc and cadmium in a simple model soil: the Fontainebleau sand. The results showed that under certain conditions, bio-sorbed heavy metals were transported from 1.2 to 3.5 times faster than metals in solution and that this last transport mechanism becomes negligible (5 to 7 times lower). Furthermore, the main factors controlling accelerated pollutant transport by bacterial colloids were identified and quantified. Soil solution ionic strength and velocity control the mobility of the colloids, so do their own concentration. Hydrophobicity and cell surface charge control both adhesion to the matrix i.e. cell mobility, and heavy metal adsorption, i.e. […]
7. Étude de la biodisponibilité des métaux lourds dans des sols agricoles irrigués par des eaux polluées
The sequential extraction procedure proposed by the Standard, Measurements and Testing program “SM&T” of the European Union has been applied to evaluate the amounts of Cr, Cu, Ni, Pb and Zn, extracted at each stage of the procedure and indirectly their mobility and bioavailability in agricultural soils irrigated by a polluted water.Analysis of the extracts was carried out by flame atomic absorption spectrometry (FAAS). No significant matrix interferences were found except for Cr in the acetic acid and hydroxylammonium chloride extracts, which required determination by the standard additions method.The results obtained by sequential extraction showed that all the studied elements present a great affinity towards the organic fraction whereas the acido-soluble fraction was dominated by nickel and lead. The extractability with the EDTA showed that lead, copper and zinc are potentially bioavailable (≅ 30 %). Chromium seems to require more aggressive conditions to presents a risk of contamination. The results of the analysis of some crop plants on this soil confirm partly the results obtained. Indeed, Cu and Zn are mobilised by the plants whereas Pb, Cr and Ni do not exceed 3 % of their total content in the soil.