| Environnement, ingénierie & développement |  |
N°77 - septembre 2018
1. Vers une évaluation absolue de la durabilité écologique : quelle variabilité des valeurs de référence associées à l'écotoxicité aquatique ?
In LCA, some impact categories such as freshwater ecotoxicity represent local processes. Recent works about absolute environmental sustainability aims to develop LCA normalization references based on ecological carrying capacities. However, they does not always take into account the spatial extent of the local impacts and the ecological characteristics of the affected environments. The objective of this article is to estimate normalization references for the major French watersheds and the entire France mainland territory in order to test their sensitivity to different hypotheses. The spatial scale (river basin, France, Europe and World) and the demographic dynamics in the geographical entities prove to be sensitive parameters; the uncertainties due to this temporal and spatial variability must be taken into account during the normalization stage of the local impacts. Also, the lack of consideration of groundwater resources in the calculation of the normalization references has been identified as a strong hypothesis. Finally, the assessment and integration of the geochemical background in the calculation of carrying capacity-based normalization references could be the subject of future interdisciplinary investigations. Thus, this article pleads for the definition of the relevant spatial and temporal scale as an essential preliminary step in view of absolute environmental sustainability assessment.
2. Rôle de paramètres opérationnels et des substances organiques dans la structure physique des dépôts de surface des filtres plantés de roseaux à écoulement vertical
In the so-called "classical French system" of constructed wetlands, the percolation through the filter medium of untreated raw wastewater results in the accumulation of sludge deposits which gradually forms a sludge layer mainly on the surface of the first filter stage. The structure, composition and organization of the particulate matter of the deposits are determining factors of the macroscopic properties of the sludge layer, such as permeability, oxygen transfer, etc. In this study, representative samples of surface deposits were collected from 12 French vertical flow constructed wetlands (VFCW) in operation. The results of analyzes showed a remarkable similarity of their particle size distribution, and a relatively moderate but significant aggregation. The differences in operational conditions between the 12 selected treatment plants (age, implementation of additional treatments), did not have any observable effect on the particle size distribution in the sludge deposits. It was also observed that particle size and agregation were not related to the content of microbial exocellular polymeric substances (EPS). These substances were analyzed in surface deposits at much lower levels than in activated sludges for example, in which their role in the formation of microbial flocs is well documented in the scientific literature. On the other hand, humic substances were analyzed at much higher levels in sludge deposits, suggesting that the contribution of humic […]
3. Étude du potentiel de valorisation énergétique du biogaz de la décharge d’Akouédo (Abidjan, Côte d’Ivoire)
This study aims to evaluate the biogas production potential of the Akouédo landfill in Abidjan, Ivory Coast. Buried biodegradable organic waste generates biogas, which in particular contains methane, which is a greenhouse gas, but is also an alternative source of energy. An efficient capture of biogas thus makes it possible on the one hand to avoid diffuse emissions into the atmosphere and the associated impacts on the increase of the greenhouse effect, and on the other hand the energy recuperation of methane. Productivity measurements were made at the landfill site under static and intermittent pumping conditions. The results reveal a high biogas production potential composed of an average of 71.30 % v/v of methane and 27.10 % v/v of CO2. The monitoring carried out on the different wells of catchment suggests statistically a relatively uniform production on the whole of the site. However, many factors influence the production potential, including moisture and compaction of the waste mass, age and nature of waste, landfill methods, and so on. The valorization of methane must take into account these constraints for a faster amortization of the investment.
4. Mesure des tassements primaires et secondaires des déchets en décharge de classe II sous climat tropical humide
La présente étude a pour but de mesurer le tassement primaire et secondaire des déchets en décharge sous climat tropical humide. Une alvéole de 120 m3 a été remplie en quatre couches de 1 m sur un volume de 96 m3 de déchets ménagers (38,4 tonnes de déchets). À l’interface de chaque couche, nous avons disposé deux plaques reliées à une barre métallique graduée. Ce dispositif a permis de lire directement les tassements subis par chaque couche de déchets pendant le stockage. Les déchets ont été compactés en utilisant le godet de la pelle hydraulique (masse volumique de 0,42 tonnes/m3). Pendant le remplissage les déchets ont subi un tassement relatif de 14 % de la colonne des déchets, variable suivant les couches des déchets.Le tassement primaire est obtenu en 5 jours après couverture du casier. Il est évalué à 13 % de la colonne des déchets et varie en fonction de la position de la couche. La couche le plus profonde a le tassement le plus élevé.Après 7,5 mois de stockage, nous avons enregistré un début de tassement secondaire qui est évalué à 6,4 % de la colonne des déchets consolidés. Au bout de 2 ans et 1 mois, nous avons obtenu un tassement secondaire final de 15,14 %. Le tassement relatif total de la colonne des déchets est de 27,5 % et reste stable au bout de 2 ans. Pour le casier expérimental que nous avons mis en place, cela correspond à un tassement global de 104 cm hormis le tassement primaire instantané enregistré pendant […]
5. Retour d’expérience : programme de sélection d’équipements et infrastructures de gestion des déchets adaptés au contexte des villes secondaires d’Afrique de l’Ouest
With the support of CEAS Suisse, Ingénieurs sans frontières (ISF Belgium), and NGO Autre Terre (Belgium), CEAS Burkina is implementing since 2008 a Project which aim to support municipal solid wastes management in seven secondary towns in Burkina Faso. Municipal solid wastes management are indeed one of the major challenge municipalities of Burkina Faso which always do not have the human, technical and financial resources to correctly ensure this public service, transferred to them within the framework of decentralisation. CEAS Burkina’s challenges in supporting these five collectivities is to help set up and implement a waste management system that can be technically and financially assumed by the communes. In this process, the issue of equipments and infrastructures emerged as a preliminary.This article presents the challenges and the results reached by research/design of infrastructures and equipment adapted to secondary cities context. It highlights some difficulties, draws lessons learned from the implementation of the research activities and concludes with recommendations for wide diffusion of the innovations.