Impacts de l’utilisation des eaux polluées en agriculture urbaine sur la qualité de la nappe de Dakar (Sénégal)

L’agriculture urbaine de la région de Dakar est un secteur en plein essor. À cause de la salinisation progressive des eaux de la nappe peu profonde (eaux de Céanes ), des eaux usées brutes sont utilisées pour irriguer les champs. L’objectif de notre étude est d’évaluer la qualité chimique et microbiologique des eaux de la nappe sous-jacentes aux champs irrigués et d’identifier les sources de pollution. Notre travail a été effectué dans les sites de Pikine et de Patte d’Oie.L’analyse de la qualité chimique des eaux d’arrosage a montré qu’à Pikine, la conductivité des eaux de Céanes est plus élevée (4822±2411 µS cm-1) par rapport à celle des eaux usées (3579±1242 µS cm-1 ; p<0.04). Par contre à Patte d’Oie, les eaux d’arrosage sont moins salées (<3000 µS cm-1). La quantité d’azote total de tous les types d’eaux d’arrosage est supérieure à la valeur guide de l’OMS (5-30 mg l-1).Salmonella spp. a été isolée dans 35 % des eaux d’arrosage. Un échantillon d’eaux usées a été positif pour Vibrio cholerae.L’impact des eaux d’irrigation sur la qualité chimique et microbiologique de la nappe d’eau souterraine est fortement influencé par la pluviométrie et est différent selon le site considéré.Ce travail a montré que l’irrigation avec les eaux polluées et l’usage de fumiers organiques peut altérer la qualité de la nappe et constituer des risques pour la santé.In Dakar capital city of Senegal, the urban agriculture is in high expansion. Since the progressive increase of salinity in the local groundwater (Céanes water), raw wastewater is used to water the crops. The objective of this study is to assess chemical and microbiological quality of the groundwater underlying the irrigated plots and to identify the sources of pollution. This work was carried out in the sites of Pikine and Patte d’Oie in Dakar Senegal.Chemical analysis of irrigation water showed that in Pikine, the conductivity of Céanes water was higher (4822±2411 µS cm-1) than those of the wastewater (3579±1242 µS cm-1 ; p<0.04), while at Patte d’Oie it was less salted (<3000 µS cm-1). The quantity of total nitrogen of irrigation water in both sites was higher than the WHO’s threshold (5-30 mg l-1).Salmonella spp. was isolated in 35 % of the irrigation water. One wastewater sample was Vibrio cholerae positive.The impact of irrigation water on the chemical and microbiological quality of the groundwater is strongly influenced by precipitations and is different according to the site considered.This work showed that the use of polluted water and organic manures can spoil the quality of the groundwater and constitute a health threat.Urban agricultur

Analyse Par Approche Hydrogeochimique De La Distribution Spatiale De La Salinite Des Eaux De La Nappe Et Des Sables Quaternaires Du Secteur Des Niayes Du Gandiolais (Littoral Nord Senegalais)

Dans le Gandiolais, la nappe des sables quaternaires, fortement salée sur la majeure partie de la zone, est utilisée pour irriguer les cultures et pose de véritables difficultés pour la durabilité du système maraicher. La salinisation secondaire du sol irrigué et la réaction du complexe absorbant dépendent principalement des paramètres intrinsèques, particulièrement la texture du sol. L’objet de cet article est d’analyser la distribution spatiale de la salinité en tenant en compte les caractéristiques granulométriques du complexe absorbant. L'approche hydrogéochimique basée sur les relations de concentration permet d'apprécier les modalités de conservation in situ entre les eaux d'irrigation et le sol exploité. Les résultats obtenus ont confirmé que la texture grossière de type sables moyens à fins permet un lessivage rapide des sels solubles sur tout le profil. Les sols restent globalement calcimagnésiens même si les eaux d'irrigation sont globalement chlorurées sodiques et potassiques ou sulfatées sodiques. Cependant, cette forte perméabilité du complexe constitue un risque de surconcentration ionique dans la nappe. Les retours d'irrigation associés aux engrais accentuent la minéralisation de la nappe des sables quaternaires. In the Gandiolais, the groundwater of the quaternary sands, heavily salted over most of the area, is used to irrigate crops and poses real difficulties for the sustainability of the market gardening system. Secondary salinization of the irrigated soil and the reaction of the absorbing complex depend mainly on the intrinsic parameters, particularly the texture of the soil. The purpose of this article is to analyze the spatial distribution of salinity taking into account the particle size characteristics of the absorbent complex.The hydrogeochemical approach based on the relations of concentration makes it possible to appreciate the process of conservation in situ between the irrigation water and the exploited soil. The results obtained confirmed that the coarse texture of medium-to-fine sand type allows rapid leaching of soluble salts over the entire profile. Soils remain globally calcimagnesian although the irrigation water is globally sodium chloride and potassium or sodium sulphated. However, this high permeability of the complex constitutes a risk of ionic overconcentration in the aquifer. Irrigation returns associated with fertilizers accentuate the mineralization of the groundwater of the quaternary sands

Results from FaME (Faecal Management Enterprises) - can dried faecal sludge fuel the sanitation service chain?

In Sub-Saharan Africa, sanitation needs for the majority of the urban population are met by onsite sanitation technologies. Cities grapple with management of faecal sludge (FS) once these technologies become full, while at the same time the urban economy is resource intensive. The FaME (Faecal Management Enterprises) project addressed both of these issues by identifying untapped markets for FS treatment products. Industries have a high fuel demand and FaME demonstrated that dried FS could be used as a solid combustible in industrial kilns. Existing treatment technologies were adapted for fuel production, and its application was demonstrated in two pilot kilns. Historically used as a soil conditioner, processing of FS to a solid biofuel could provide higher revenues, thereby providing a financial incentive for stakeholders to enhance FS management service along the entire sanitation chain

Pharmaceutical pollution of the world's rivers

Environmental exposure to active pharmaceutical ingredients (APIs) can have negative effects on the health of ecosystems and humans. While numerous studies have monitored APIs in rivers, these employ different analytical methods, measure different APIs, and have ignored many of the countries of the world. This makes it difficult to quantify the scale of the problem from a global perspective. Furthermore, comparison of the existing data, generated for different studies/regions/continents, is challenging due to the vast differences between the analytical methodologies employed. Here, we present a global-scale study of API pollution in 258 of the world's rivers, representing the environmental influence of 471.4 million people across 137 geographic regions. Samples were obtained from 1,052 locations in 104 countries (representing all continents and 36 countries not previously studied for API contamination) and analyzed for 61 APIs. Highest cumulative API concentrations were observed in sub-Saharan Africa, south Asia, and South America. The most contaminated sites were in low- to middle-income countries and were associated with areas with poor wastewater and waste management infrastructure and pharmaceutical manufacturing. The most frequently detected APIs were carbamazepine, metformin, and caffeine (a compound also arising from lifestyle use), which were detected at over half of the sites monitored. Concentrations of at least one API at 25.7% of the sampling sites were greater than concentrations considered safe for aquatic organisms, or which are of concern in terms of selection for antimicrobial resistance. Therefore, pharmaceutical pollution poses a global threat to environmental and human health, as well as to delivery of the United Nations Sustainable Development Goals