| Environnement, ingénierie & développement |  |
N°11 - 3ème Trimestre 1998
1. Éditorial n°11 Déchets Sciences et Techniques
Les vacances d'été ne se sont pas achevées sans qu'un éclairage supplémentaire n'ait été apporté au problème des déchets et par la voix la plus officielle (ministère de l'Environnement). L'incinération « triomphante » ces dernières années, devrait dorénavant être freinée dans son développement pour faire plus de place à d'autres filières de traitement qui visent essentiellement la valorisation matière. Ce « ré-équilibrage », tout au moins du discours officiel, ne va pas sans nous interroger sur les besoins à satisfaire par la recherche dans ce domaine.En tout premier lieu, il apparaît que lorsqu'une technologie s'installe dans un développement conséquent il devient plus aisé d'en percevoir les insuffisances : on ne connaît bien que ce que l'on mesure et l'on mesure bien que ce qui existe ! Ceci est particulièrement vrai pour les impacts des fumées ou le devenir des résidus d'épuration des fumées (Refiom) ou des mâchefers (Miom), pour ce qui concerne plus spécifiquement les ordures ménagères. Ce constat devrait nous inciter à plus de curiosité, et donc à plus de travaux scientifiques relatifs aux impacts prévisibles de filières comme la thermolyse, les unités de tri, le recyclage des plastiques, etc. Par impact, nous entendons bien sûr les impacts sur l'environnement mais également, de plus en plus, les impacts toxicologiques et sanitaires.
2. Essai d'évaluation du potentiel de création d'emplois associés à la modernisation des systèmes de gestion des déchets ménagers
This article presents a methodology of employment accounting, related to territorial household refuse policies. The methodology is applied to a fictitious territory of one hundred thousand people. Its application is based on the distribution of employment by technical stages. Substitution effects of employment from a stage to another one are linked with the distribution of the flow-sheet. After that are presented the main results of a national extrapolation, once local contexts neutralized. Through the prevalence of sorting centers as a employment providing function, we can clearly conclude that the growth of the material valorization rate is the most important means towards benefits employment in waste management.
3. Application de l’oxydation, en voie humide au prétraitement de graisses résiduaires
Fatty emulsions (20-200 g/1) were treated on both a laboratory and pilot scale by wet air oxidation in order to improve their biodegradability. An 80% removal rate of the bioresistant fraction of COD was achieved after 1h at 240°C (500°F). The requiered costs of energy and chemicals were estimated at $ 100/ton of pure fat.
4. L’aluminium de récupération au service de l’alimentaire : fonderie et affinage (cas du Cameroun)
5. La formation des dioxines dans les incinérateurs: Quel mécanisme ?
This paper presents the new points of view concerning the mechanistic ways of formation of polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF) in municipal and hazardous waste incinerators. They are found in post-combustion zones at temperatures between 200 and 400 °C. PCDD/Fs are present in fly ash and their maximum concentrations are reached in the electrofilter chamber. Different ways of formation are possible in the plant with their own rate. The synthesis of PCDD/Fs in the gas phase from organic precursors like chlorobenzenes or chlorophenols cannot explain the concentrations of these molecules measured in fly ash. The « De Novo » synthesis is the dominant mechanism of dioxin and furan formation in actual combustion systems. The « De Novo » synthesis experiments indicate that carbon degenerated graphitic structures like soot, activated carbon are the essential carbon sources for dioxin and furan formation. This mechanism proceeding in three stages is an oxidative degradation of carbon graphitic structures where metals under chloride forms are essential. Metal chlorides and especially, copper chlorides, are the chlorinated agents in chlorination of the graphitic structure. They also catalyze the oxidative degration of the macromolecule of carbon. The major products of reaction are the carbon oxides. Formation of by-products like polychlorobenzenes, polychlorophenols, polychlorobiphenyls and PCDD/Fs is also noticeable.
6. Étude de la cinétique de décomposition d’acides sulfuriques résiduaires
Spent sulphuric acid (SSA) contaminated with organic or mineral impurities are valuable raw material resources for production of sulphuric acid. The oleum can be recovered by thermal decomposition of SSA in S02 followed by purification and conversion of S02 to S03. The impurities contained in the acid waste play an important role in decomposition of the spent sulphuric acid. In this work, we have studied the influence of a mineral (nitric acid) on the decomposition of sulphuric acid.
7. Le devenir des mâchefers d'incinération d'ordures ménagères: Partie 2 : traitement des mâchefers. Effet de la maturation, du tamisage, du déferraillage et du lavage à l’eau
According to the newsletter of 9 May 1994, municipal solid waste incinerator bottom ashes can be valorized as fill material if their polluting potential is low (V-class). In the opposite case, they have to be treated in a maturation center (M-class), or to be eliminated in a landfill center (S-class). The present study has allowed to show the beneficial effect of three treatments (maturation, sifting and water-washing) in the improvement of the environmental quality of bottom ashes. However, the separation of iron has no effect if it is carried out upstream the maturation, but this treatment has to be prescribed downstream of the maturation to allow an effective valorisation (this is a condition often demanded of a geotechnical viewpoint). ln general, if the maturation do not permit to obtain directly a V-class bottom ashes, it can be coupled to a 4 or 6 mm-sifting to convert bottom ashes of M or S-class to a V-class.
8. Les rejets industriels dans la zone portuaire du Havre
In order to put in a prominent position the influence of the basins in the purification of wastewater in industrial zone we try to land following points:- the impact of the fresh water supply by rivers leading in the stretch of water harbour.- the comparison of flow in and flow out in investigated zone with industrial waste.