| Environnement, ingénierie & développement |  |
N°74 - septembre 2017
1. Une méthodologie couplant mesures géophysiques et ponctuelles afin d'estimer la perméabilité d'un site destiné à l'infiltration d'eau usée traitée
When water cannot be discharged to superficial water body or the discharge volume needs to be limited, treated wastewater downstream a treatment plant can be infiltrated. Operational and environmental challenges emerge from this practice: how to size infiltration facilities and what will be the impact of the treated wastewater on groundwater quality? Preliminary studies are recommended for soil-based constructed wetlands and compulsory when permanent infiltration is needed. Unfortunately there is no guideline on how to deal with spatial heterogeneity of soil properties. They can greatly influence water pathway in the soil and the quantities of treated wastewater that can infiltrate. The aim of this article is to introduce a methodology that associates geophysical measurements and more localized ones in order to better described the near-surface with a particular focus on field saturated hydraulic conductivity. Starting from the fastest and coarsest method, the suggested hierarchical process allows optimizing the sampling strategies for longer and more accurate measurements. Therefore, such a methodology, while increasing the quality of results, may also reduce the time and cost of preliminary studies. Two applications are presented demonstrating the advantages of associating several methods. They also underline the input of using geophysical methods on soil that have been largely modified by human activity.
2. Assainissement par toilettes sèches à litière biomaîtrisée : premiers résultats d’une expérimentation menée en milieu rural (Grande Plaine, commune de Gros-Morne, Haïti)
This article presents an experiment on the management of a domestic sanitation device by dry litter toilets (TSLB), carried out in rural Haiti. This technology was chosen because of its affordability for the population concerned, in an area where the main practices are those of very simplified latrines (simple holes in the soil) and of defecation in open air. Several actions have been carried out: organization of hygiene awareness meetings, training workshops on the construction of toilets, consultation meetings to establish the needs of the populations in terms of domestic sanitation, their selection criteria, to discuss the availability and preparation of absorbent litter, the necessary equipment, the conditions for the management and treatment of liquid (direct individual use in personal gardens) and solid (choice of composting) residues. The experimentation began with the manufacture and delivery of 25 toilets modules to the pilot households, the selection of the collective composting site and its management conditions. Having opted for voluntary input and community-based management of residues, households bring their buckets there weekly. After one year of operation and monitoring, nearly 4 tons of solid residues were collected. Most of the households bring their residues very regularly and have completely adopted this method of sanitation. This encouraging result now justifies the implementation of an experimental program aimed to optimize the composting conditions to […]
3. Éditorial n°74 Déchets Sciences et Techniques
Dans la foulée du précédent, le numéro 74 est fidèle à la ligne éditoriale de la revue. Il publie en effet trois articles issus d’équipes du « Sud » (Haïti, Cameroun et Bénin) et deux articles provenant d’équipes du « Nord », en l’occurrence françaises. Certes, le distinguo « nord-sud » que je contribue ici à maintenir ne devrait avoir aucune justification, notamment dans le domaine scientifique dont le langage et les fondements sont universels. Mais dans la pratique et au quotidien, force est de constater que les travaux de recherche des collègues chercheurs et enseignants-chercheurs du « Sud » trouvent encore difficilement accès à la diffusion internationale à laquelle ils prétendent légitimement. C’est pourtant par cette diffusion que leur action trouvera la reconnaissance et les applications qu’elle mérite. Conduite avec souvent de nombreuses difficultés matérielles et financières, la recherche des collègues du « Sud » est nécessaire pour permettre le développement de solutions techniques et organisationnelles adaptées et durables dans le domaine de l’assainissement comme dans d’autres, pour nourrir l’innovation des acteurs locaux, pour capitaliser leur expérience unique qui trop souvent se perd faute d’avoir été décrite et diffusée alors qu’elle est potentiellement source de progrès, y compris pour les pays du « Nord » bien évidemment.La recherche en ingénierie environnementale a la spécificité de se […]
4. Evaluation des Risques Ecotoxicologiques liés à l’épandage de boues de STEP chaulées sur une parcelle agricole
Sewage sludge from urban wastewater plants can be applied on agricultural land in accordance to a regulatory framework established by a 1997 decree, under the responsibility of the producer of the sludge considered as waste. Under the impetus of the French Lime Association, a technical dossier for the creation of a new standard, based on the realization of an Ecotoxicological Risk Assessment (ERA) on limed sludge, was transmitted to ANSES, and led to the development of an AFNOR standard (NFU44-003) allowing the use of these sludge as soil improvers. The ERA, which typically involves four steps (problem formulation, characterization of exposure, characterization of effects, risk characterization), has been implemented using the "substances" approach to the terrestrial ecosystem, a typical scenario of spreading sludge on agricultural soil. Physicochemical analyzes were carried out on these sludges with regard to the following hazard tracers : 3 HAPs and 9 Trace Elements Metal. For each of these risk tracers, exposure (PEC) was characterized on the basis of a sludge dilution factor in agricultural soil, calculated for the so-called agricultural D1 (0.1 %) and a dose 5 times greater D5 (0.5 %), while ecotoxicological values (PNEC) were derived from international databases. For each substance, and for the exposure doses D1 and D5, the risk was characterized according to the quotient (PEC / PNEC) method of Technical Guidance Document (TGD). The results of the ERA suggest […]
5. Evolution des caractéristiques des déchets solides ménagers dans la ville de Yaoundé au Cameroun (1995-2015)
This study highlights the evolution of the characteristics of household waste at various stages of the value chain and for different periods. Four downstream characterization campaigns were done in 1995, 2006, 2011 and 2016 in the city of Yaoundé (3.1 million 'Inhabitants, tropical humid climate). It also determines the specific production of household waste, necessary for planning any collection and recovery operation.To assess the specific production of household waste, surveys were conducted with 440 households selected according to stratified method, followed by deposit trash bags in any household. The characterization of the upstream waste was made directly on all the bags collected from households, a total mass of about 1 800 kg of waste sorted by characterization campaign. The characterization of downstream waste was carried out on the waste arriving at the landfill. A mass of at least 2 000 kg of waste was sorted by country. The specific production of household waste in Yaoundé varies between 0.5 and 0.8 kg/capita/day as economic level of housing, with an average of 0.62. Compared to the 1995 campaign, this figure has remained virtually stable. The organic matter of household waste varies between 50 and 60 % of dry matter after production in the households and 45-65 % at the entrance of the landfill. The average volumic mass of household waste is 0.3. It is doubled during transport in the compaction trucks, but undergo a slight increase (10 to 20 %) in open […]
6. Caractérisation d’eaux usées des quartiers déshérités du sud du Bénin : cas du quartier Agla
The disadvantaged areas of South Benin and the Agla district of Cotonou are faced with problems of cyclical floods. These areas of swamps and water reservoirs favor the proliferation of water-borne diseases (diarrhea, cholera, dysentery, typhoid fever, etc.), especially in small children because of the 82.5% population.The aim of our study is to assess the pollution status of these waters in order to draw the attention of the population in general and of the communal officials in particular to the need to promote simple methods of reducing domestic wastewater pollutants.In order to achieve this objective, we collected and analyzed the waste water (EV water, gray water EG) and compared these results with those of the wastewater collector water (ECE) which crosses the Agla district. The physico-chemical parameters of the wastewater were determined in accordance with French standards.The results show that all waters are slightly alkaline and have a high content of organic pollutants (COD and BOD5). The waters of the collector (ECE) and the gray water (EG) have a COD content equal to 1 395 and 1 457 mg/L respectively. Valve water has a higher COD (3 077 mg/L) than the latter. Gray water has high conductivities (2 458 μS/cm). Finally, the presence of fecal enterococci (EV, ECE) which show fecal pollution. On the basis of these results, it can be concluded that the wastewater of the Agla district is polluted and that the waste water and the collector (EV; ECE) are out of class […]