L'érosion hydrique des sols n'a pas été suffisamment étudiée dans la région de Bonoua au Sud-Est de la Côte d'Ivoire où l'activité économique dominante demeure l'agriculture. Par conséquent, des méthodes de contrôle s'avèrent nécessaires, afin d'assurer une gestion durable des sols et de sécuriser les productions agricoles. L'objectif de cette étude est de fournir des éléments pour cartographier la vulnérabilité multifactorielle à l'érosion hydrique. L'approche passe par une analyse des principaux facteurs de l'érosion : l'érosivité des pluies, l'érodabilité des sols, la pente et l'occupation des sols. Les cartes obtenues sont intégrées dans un Système d'Information Géographique (SIG) à l'aide d'une combinaison additive pour établir une carte de vulnérabilité à l'érosion hydrique. Cette carte est validée par des observations de terrain. Trois classes de vulnérabilité multifactorielle à l'érosion hydrique ont été distinguées : les zones à faible vulnérabilité (29 %) ; les zones à vulnérabilité moyenne (34 %) et les zones fortement vulnérables (37 %). Ainsi, dans la région de Bonoua, les classes à moyenne et forte vulnérabilité multifactorielle représentent 71 % de la superficie. Cette première ébauche cartographique est un outil devant aider les décideurs pour l'attribution des zones de cultures et des sites pouvant abriter des infrastructures socio-économiques.
Water soils erosion has not been studied enough in the region of Bonoua south-eastern Côte d'Ivoire where major economic activity remains the agriculture. Consequently, control methods are necessary in order to ensure sustainable management of soils and to secure agricultural productions. The objective of this study is to supply tools for mapping multifactorial vulnerability to water soil erosion. The method involves an analysis of the main factors of erosion: rainfall erosivity, soil erodibility, slope and land use. Obtained maps are integrated in Geographic Information System (GIS) throughout an additive combinaison to establish a vulnerability water soils erosion map. This map is validated after ground observations. Three classes of multifactorial vulnerability to water erosion have been distinguished: areas with low vulnerability (29 per cent); areas with middle vulnerability (34 per cent) and areas with high vulnerability (37 per cent). Thus, in the region of Bonoua, classes with a middle or high multifactorial vulnerability represent 71 per cent of the study area. This first map is a tool that would help decision makers in attribution of areas for agricultural activities and for socio-economic substructures
Recovering microalgae is one of the main technological and economic concerns in a high-rate algal pond (HRAP) because of their small size and their low density. This paper emphasizes the characterization (identification and assessment of potential flocculation) of chemical compounds involved in microalgae auto-flocculation in a HRAP. First, thermodynamic simulations were performed, using two models (i.e. Visual Minteq and a simplified thermodynamic model) in order to determine the chemical compounds of interest. Experimental tests were then carried out with these compounds for assessing their flocculation ability. Both models revealed that precipitates of calcium phosphates and their substituted forms were the compounds involved in the auto-flocculation. Moreover, experimental tests showed that the stoichiometric neutralization of algal charges by calcium phosphates (i.e. hydroxyapatite (Ca5(PO4)3OH), octacalcium phosphate (Ca4H(PO4)3) and amorphous calcium phosphate (Ca3(PO4)2)), at a pH within the range 7-10 yields 70-82% recovered algal biomass. The optimum ratio required for algae auto-flocculation was 0.33 Ca5(PO4)3OH/g DM(algae) at pH 10, 0.11 Ca4H(PO4)3/g DM(algae) at pH 7 and 0.23 g Ca3(PO4)2/g DM(algae) at pH 9. Auto-flocculation appears as a simple, sustainable and promising method for efficient harvesting of microalgae in a HRAP.
In this study, anionic surfactants concentrations and other physico-chemical parameters of surface water quality were assessed in the water of M'Koa Lake in the city of Jacqueville (Côte d'Ivoire). Three sampling campaigns were conducted at different seasons at six (6) sampling stations, identified in M'koa Lake by taking into account potential sources of pollution. The analyses of physico-chemical parameters were carried out using both the French AFNOR standard and the methods described by Rodier. The anionic surfactants concentrations were performed by using the methylene blue colorimetric method. The average concentrations of anionic surfactants in the water of M'koa Lake ranged from 0.23 ± 0.04 mg•L −1 to 1.43 ± 0.68 mg•L −1. They are high compared to both population density and socioeconomic activities of Jacqueville's town. These values can be explained by the characteristics of the studied Lake that do not allow enough dilution of the discharged effluent. The results indicate that M'koa Lake is subjected to harmful pollution by anionic surfactants. And among the physicochemical parameters studied, only turbidity and transparency values show water quality deterioration, favoured by wastewater discharge and direct human activities around the Lake.
The influence of the pollutants in surface water quality when used for drinking water is of great concern in many developing countries. This study seeks to characterize the types of pollution in Aghien lagoon and its tributaries. For the sampling, water was taken at a depth of 50 cm from the earth surface. Samples were analyzed by the spectrometric method of molecular absorption with sulfosalicylic acid for the nitrate, spectrophotometric method of molecular absorption for the nitrites, colorimetric determination with indophenol blue for the ammonium, colorimetric method for the orthophosphates and the phosphorus, filtration method on glass fiber (0.45 μm) for the Suspended Solids (SS), manometric method based on the respirometer principle for the Biochemical Oxygen Demand (BOD 5 ), Dichromate method for the Chemical Oxygen Demand (COD), inductively coupled plasma optical emission spectrometry (ICP-OES) technique for the heavy metals (iron, Manganese), on April and June 2015. The analysis of these physico-chemical parameters revealed that, all the year round, these waters contain real conductivity values comprised between 51 and 161.1 µS/cm, redox potential between 100.3 and 174.4 mV; nitrate between 0.23 and 6.72 mg/L. On the other hand, and over the same period, the waters of the Mé river and the channel had COD values comprised between 33 and 58.7 mg/L. Concerning the Djibi rivers SS were between 36.66 and 50 mg/L, dissolved oxygen between 1.46 and 1.59 mg/L; ammonium between 2.44 and 2.69 mg/L regardless the seasons. The results show that during the two seasons, the Aghien lagoon is the less polluted by the physico-chemical parameters, whereas for the same period, Mé and channel waters are the most charged with organic matters deriving from plants. As for the Djibi river, it remained the most polluted, as certified by the high values in SS and nutrient regardless of the seasons.
This work presents an approach to an anaerobic pond model by combining the stoichiometry of the hydrolysis and acidogenic processes of the main constituents of wastewater, i.e. carbohydrates, proteins, and lipids, grouped as a 'combined substrate' with a previously published settling model (see 'Suspended solids settling and half removal time in stabilization ponds (Tunisia)' by Effebi et al. (2011)). This approach includes biomass production. Coupling the kinetics and stoichiometry of the previous processes with the usual methanogenic model, we developed an anaerobic pond model. This paper gives the stoichiometry of the different chemical reactions that occur during the degradation of a conventional influent (corresponding to what we define as a 'combined substrate') of domestic wastewater and the model's first results.
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