Study of the free residual chlorine concentration in drinking water in Benin: case of Cotonou municipality

The drinking water is very qualitatively monitored. Despite this monitoring, there is a deterioration in the Free Residual Chlorine Concentration (CCRL) along the drinking water distribution network of the commune of Cotonou. The objective of studying areas of consumer vulnerability where the CCRL reaches critical thresholds (<0.1 mg / l). To achieve this, water samples were taken from various locations in the supply network every day, from 04/30/2018. The assay method used is called N-Diethyl-P-phenylene Diamine (DPD) with the use of a DR / 890 colorimeter. This work reveal that the CCRL undergoes degradation during its delivery to the consumer's taps with average concentrations mainly above the standard in force [0.1; 0.8 mg / l] at the 5% threshold. The work made it possible to establish a linear model for predicting CCRL concentration as a function of distance and to identify areas of vulnerability in the study area. L’eau de consommation est très surveillée sur le plan qualitatif. En dépit de cette surveillance, on constate une dégradation de la Concentration en Chlore Résiduel Libre (CCRL) le long du réseau de distribution d’eau potable de la commune de Cotonou. L’objectif d’étudier les zones de vulnérabilité du consommateur où la CCRL atteint des seuils critiques (< à 0,1 mg /l). Pour y parvenir, des prélèvements d’échantillons d’eau ont été pris à divers endroits du réseau d’approvisionnement chaque jour, du 1er au 30/04/2018. La méthode de dosage utilisée est dénommée N-Diéthyl-P-phénylèneDiamine (DPD) avec usage d'un colorimètre DR/890. Ce travail à révéler, que la CCRL subi une dégradation lors de son acheminement vers les robinets du consommateur avec des concentrations moyennes majoritairement supérieures à la norme en vigueur [0,1 ; 0,8 mg/l] au seuil de 5%. Le travail a permis d’établir un modèle linéaire de prédiction de la concentration en CCRL en fonction de la distance et d’identifier les zones de vulnérabilité de la zone d’étude

Étude de l’activité floculante de la caséine acide extraite de la crème de Cocos nucifera dans la clarification des eaux de surface

La coagulation et la floculation sont deux étapes essentielles dans le traitement des eaux. Les graines de Moringa oleifera sont un floculant végétal qui introduisent des matières organiques dans les eaux clarifiées. C’est pour cela que nous avons testé le pouvoir floculant d’une caséine acide extraite de la crème de coco. Ce floculant comprend 83 % de matières organiques et 17 % de matières minérales. Les résultats des essais au jar-test effectués au laboratoire ont indiqué que son pouvoir floculant est supérieur à celui des graines de Moringa oleifera mais inférieur à celui du sulfate d’aluminium. Les concentrations des métaux usuels ont connu une réduction assez sensible au cours de la clarification soit 79 % pour l’aluminium, 54 % pour le cuivre, 58 % pour le fer et 80 % pour le zinc. Le pH a connu une légère baisse ce qui a entraîné une diminution du titre alcalimétrique complet (TAC). Les concentrations de la DCO et de la DBO ont légèrement augmenté.The clarification process is an important step during the treatment of raw waters. For this reason, under-developed countries have undertaken research on vegetable flocculants. In this context we determined the flocculation power of acidic casein from Cocos nucifera cream. This flocculant contains 83% organic matter and 17% mineral matter. The results of a clarification jar-test, carried out in the laboratory, indicated that the flocculant power is inferior to that of aluminium sulphate, but higher than Moringa oleifera seed powder. The metal concentrations present in raw water were significantly reduced by the treatment; 79% for aluminium, 54% for copper, 58% for iron and 80% for zinc. The pH and complete alkalimetric titer (CAT) values also slightly decreased. However, the Chemical Oxygen Demand and the Biochemical Oxygen Demand slightly increased

Environmental Geophysical Study of the Groundwater Mineralization in a Plot of the Cotonou Littoral Zone (South Benin)

Geophysical investigations comprising electrical resistivity and electromagnetic conductivities methods were deployed in a 350 m2 sector, strewn with 11 wells. Within the framework of an environmental study on a small scale in the south of Benin, the water conductivity of these wells was measured to determine in a direct way mineralization of the coastal water table in the littoral zone. This environmental study aimed to prospect by the geophysical methods the space extension of the water table mineralization obtained by direct measurements of water conductivity in the well and the depth of the fresh water/salted water interface in the coastal aquifer. Electromagnetic measurements of conductivities made it possible to chart a gradient of mineralization in the northwest direction. The logs of vertical electric soundings showed a deepening of the fresh water/salted water interface in the southern part and its rupture in the northern part. The electrical resistivities of the interface are sensitive to the degree of its mineralization. It has been observed that the geophysical methods in electrical and electromagnetic prospection are a great contribution to the environmental study of the water table mineralization in the littoral zone for a sustainable management of the water resource

South-West Benin Coastal Lagoon: Waters and sediments’ toxicity and contents in heavy metals during high water period (Togbin to the Mono Mouth)

The uncontrollable population growth is reaching Benin's rivers, especially the coastal lagoon, raising then the thorny problem of pollution, which is considerably accentuated by the malevolent behavior of the populations. The aim of this paper is to characterize the degree of contamination of the water and sediments of the lagoon in heavy metals (Cd, Cr, Zn, Cu, Pb and Fe) through the dosage with the molecular absorption spectrophotometer type DR 3900. At the same time, a cytotoxicity test with Allium cepa will be carried out in order to evaluate the toxic potential of the pollutants responsible for the degradation of the lagoon. The Cd, Cu and Zn contents in the water and sediments far exceed the accepted standards at almost all the stations. The Pollution Index (PI) and geo-accumulation index (Igeo) indicate the existence of polymetallic pollution in the sediments, which is extremely strong and dominated in order to decrease abundance by: Cd>Zn>Cu>Pb. The results of the cytotoxicity test highlight acute toxicity on 82% of the stations surveyed. The poor states of the coastal lagoon indexed by this study, impose the application of urgent measures of participative management, preservation and sanitation of the coastal zon

Dynamique hydrologique et évolution morpho sédimentaire du lac Ahémé au Sud-Ouest du Bénin

Le lac Ahémé dans le complexe estuarien sud-ouest béninois connait de nos jours, un véritable problème de dégradation dû à l’évolution naturelle et aux activités anthropiques ayant contribué à accélérer la vulnérabilité de l’hydrosystème. La présente étude, basée sur l’analyse de l’évolution bathymétrique et sédimentologique des fonds lagunaires vise à caractériser le rythme de comblement du lac Ahémé. La bathymétrie du lac Ahémé indique un plan d’eau encaissé, à fond plat, avec des profondeurs moyennes comprises entre 1,6 et 2,4 mètres. Les sédiments sont vaseux dans la partie centrale du Nord au centre du lac, sablo-vaseux au Sud et à l’Est puis sableux à l’Est et aux abords du lac en contact avec les plateaux de Terre de Barre. L’analyse comparative des cartes sédimentologiques et bathymétriques des années successives, a montré que le lac se comble au fil des ans, particulièrement dans sa partie sud. L’évolution des faciès sédimentaires du lac de 1999 à 2018 montre une plus large extension des vases et vases sableuses dans la partie sud du lac alors qu’elles se cantonnaient autrefois dans la moitié sud du lac. La répartition des vases n’est donc plus uniforme, comme c’était le cas il y a une vingtaine d’années. Une telle évolution bathymétrique est le signe tangible d’un comblement et cet état de chose est préjudiciable aux organismes vivants inféodés dans le milieu.   Lake Ahémé in the south-western Beninese estuary complex is nowadays experiencing a real problem of degradation due to natural evolution and anthropic activities that have contributed to accelerate the vulnerability of the hydro system. The present study, based on the analysis of the bathymetric and sedimentological evolution of the lagoon bottoms, aims at characterizing the filling rate of Lake Ahémé. The bathymetry of Lake Ahémé indicates an entrenched, flat-bottomed body of water with average depths between 1.6 and 2.4 meters. The sediments are muddy in the central northern part of the lake, sandy-muddy in the south and east, then sandy in the east, and on the edges of the lake in contact with the Terre de Barre plateaus. Comparative analysis of the sedimentological and bathymetric maps of successive years has shown that the lake fills up over the years, particularly in its southern part. The evolution of the sedimentary facies of the lake from 1999 to 2018 shows a wider extension of the mud and sandy mud in the southern part of the lake whereas they were formerly confined to the southern half of the lake. The distribution of mud is therefore no longer uniform, as was the case some twenty years ago. Such a bathymetric evolution is the tangible sign of a filling and this state of affairs is detrimental to the living organisms that are dependent on the environment

Caracterisation Hydrogeochimique Des Eaux Souterraines Des Aquiferes De Socle De La Commune De Natitingou Au Benin

L’objectif de cette étude est de préciser la nature hydrochimique des eaux souterraines de la commune de Natitingou et d’identifier les processus responsables de leur minéralisation, afin de contribuer à leur gestion durable. La méthodologie appliquée est basée sur une combinaison des techniques hydrochimiques et d’analyses statistiques (ACP et CHA). Les résultats issus des analyses physico-chimiques montrent une minéralisation comprise entre 40 et 3240 μS/cm pour une moyenne de 465,64 μS/cm. Les eaux souterraines étudiées sont généralement acides à neutres, avec un pH variant entre 4,1 et 7,3. Elles se classent, de par leurs anions, en deux principaux faciès hydrogéochimiques : celui bicarbonaté (75% des eaux) dont 45% de bicarbonaté calcique et 30% de bicarbonaté sodique et celui chloruré (25% des eaux) dont 17% de chloruré sodique et 8% de chloruré calcique. Les différentes corrélations entre les ions majeurs et les analyses statistiques ont permis d’identifier trois processus hydrogéochimiques qui participent à la minéralisation des eaux. Le processus dominant est l’hydrolyse des minéraux silicatés, suivi des échanges cationiques, puis l’apport anthropogénique qui influence la minéralisation en polluant les eaux. The aim of this study is to specify the hydrochemical nature of the groundwater in the commune of Natitingou and to identify the processes responsible for its mineralization, in order to contribute to its sustainable management. The methodology applied is based on a combination of hydrochemical techniques and statistical analysis (PCAand AHC). The results of the physico-chemical analyses show a mineralization between 40 and 3240 μS/cm for an average of 465.64 μS/cm. The groundwater studied is generally acidic to neutral, with a pH varying between 4.1 and 7.3. They are classified, by their anions, in two main hydrogeochemical facies: bicarbonate (75% of the waters) including 45% calcium bicarbonate and 30% sodium bicarbonate and chlorinated (25% of the waters) including 17% sodium chloride and 8% calcium chloride. The different correlations between the major ions and the statistical analyses made it possible to identify three hydrogeochemical processes that participate in the mineralization of the waters. The dominant process is the hydrolysis of silicate minerals, followed by cationic exchanges, then the anthropogenic contribution which influences the mineralization by polluting the waters

Evaluation de l’état trophique des eaux du complexe lagunaire côtier du Sud-Ouest Bénin en période de hautes eaux (de Togbin à l’Embouchure Mono)

Les lagunes servent de tanières pour un grand nombre d’espèces aquatiques et constituent de ce fait des richesses à entretenir. Malheureusement, la lagune côtière du Bénin fait face à un déséquilibre écologique qui se manifeste par une croissance excessive des végétaux aquatiques. En vue de caractériser l’état trophique de la lagune, une campagne d’échantillonnage a été effectuée en période de hautes eaux sur onze points représentatifs. La méthodologie de dosage au spectrophotomètre a été adoptée pour mettre en évidence les paramètres de diagnostic de pollution. Les analyses signalent de fortes concentrations en phosphore (28,75 mg/L) et en nitrites (10 mg/L) dans les eaux de la lagune. La lagune se trouve alors dans un état d’hyper-eutrophisation selon la grille de qualité établie par Ifremer. Le non-respect des mesures de protection des plans d’eau et la mauvaise gestion des déchets ménagers et des eaux usées entraînent la prolifération des nutriments responsables de l’eutrophisation de la lagune côtière. Vu l’ampleur de la pollution mise en relief par cette étude, l’institution d’un programme de surveillance s’avère indispensable afin de veiller au maintien de la qualité écologique des écosystèmes aquatiques en République du Bénin.Mots clés : Lagune côtière, eutrophisation, nutriments, pollution. English Title: Assessment of the trophic state of the waters of the coastal lagoon complex of Southwest Benin during high water periods (from Togbin to Mono Mouth)The lagoons serve as places of residence for several aquatic species and therefore constitute riches to be properly maintained. Unfortunately, the coastal lagoon of Benin faces an ecological imbalance visibly manifested by an excessive growth of aquatic plants. In order to characterize the trophic state of the lagoon, a sampling campaign was carried out during high water periods according to eleven representative points. The spectrophotometer assay methodology was adopted to highlight the pollution diagnostic parameters. Analyzes report high concentrations of phosphorus (28.75 mg/L) and nitrites (10 mg/L) in lagoon waters. The lagoon is then in an enlarged state according to the quality grid established by Ifremer. Failure to comply with measures to protect water bodies and poor management of household waste and wastewater lead to the proliferation of nutrients responsible for eutrophication within the coastal lagoon. Given the magnitude of the pollution highlighted by this study, the implementation of a monitoring program is essential in order to ensure the maintenance of the ecological quality of aquatic ecosystems in the Republic of Benin.Keywords: Coastal lagoon, eutrophication, nutrients, pollution

Caractérisation d'un Système Lagunaire en Zone Tropicale: Cas du lac Nokoué (Bénin)

This survey permitted to make hydrological balance of the lake Nokoué and to know quality physico-chemical of the waters of the lake in order to offer the basis elements for a future ecological modeling of the system. The results of hydrological balance show that the average of the flow of the soft waters received by the lake in period of high waters is 216m3/s essentially brought by the Ouémé stream, the longest stream of Benin that crosses the country from the north to the south. This value falls to 49m3/s in dry season with 86% of the flow brought by the Sô river in dry season. In dry season, the Sô at Ganvié has the most important rate of organic load (53% DBO). For the phosphorus in dry season, the highest rate is gotten at the level of strongest rate is gotten at the level of Ouémé stream at Totchè (42%). In the period of high waters (from August to October) a dilution effect of the contribution is observed. In term of nutrient loads brought by purification systems, the results obtained are 360kg/j-P and 840 kg/j - N for Cotonou and Calavi and 150 kg/j- P and 700 kg/j-N for Ganvié. The contributions of "Acadjas " give 2,3 - 2,9 kg/j P and 29 - 36 N kg/j. The main results obtained for the physico-chemical for characterization are presented as follows: * a very remarkable saline intrusion in dry season, Sô at Ganvié the value passes from 0g/L in period of high waters to 2,5g/L in dry season, * the average pH varies between 6,6 and 7,5 for the waters of the bottom and between 6,9 and 7,8 for the waters of surface of the lake. The pH varies very little between the bottom of the lake and its surface, * the values of nitrogen and phosphorus nutrients are extensively high than the limited values indicated by the system of classification by the Organization of Cooperation and Economic Development (OECD). The waters of the lake are therefore eutropheses. We notice a seasonal evolution of the system. According to the factors of control hyacinths of waters, it is concluded that nutrients control the development of hyacinths when the salinity doesn't inhibit the growth of hyacinths anymore; that means of July to January

Impacts des Hydrocarbures Aromatiques Polycycliques sur les poissons: Cas des Tilapias du lac Nokoué au Sud du Bénin (Afrique de l’Ouest)

Les résultats issus des analyses physico-chimiques et toxicologiques des eaux et des poissons du lac Nokoué nous ont permis de constater que les Hydrocarbures Aromatiques Polycycliques retrouvés dans le lac influencent sensiblement la qualité des poissons et que les valeurs limites sont dépassées pour certains paramètres. Les valeurs de conductivité moyenne (2752 μS/cm) et de concentration moyenne des nitrites (7,78 mg/L) ont montré que les échantillons d’eau prélevés sur le lac Nokoué sont pollués. Le dosage des polluants a permis de constater que les individus de Tilapia guineensis, Hemichromis fasciatus et de Sarotherodon melanotheron prélevés dans les eaux du lac sont respectivement contaminés à 10%, 18% et 10% au niveau de la rivière Sô à Dogodo, à 26%, 25% et 23% à Kétonou, 32%, 29% et 40% à 6 km de Domèguédji et 32%, 28%, 27% à l’embarcadère d’Abomey-Calavi. The results from physico-chemical and toxicological analyzes of the waters and fish of lake Nokoué have shown that the Polycyclic Aromatic Hydrocarbons found in the lake have a significant influence on the quality of the fish and that the limit values are exceeded for certain parameters. The mean conductivity and mean concentration values of the nitrites, estimated at 2752 μS / cm at 7.78 mg / L respectively, show that the water samples taken from lake Nokoué are polluted. The bioaccumulation factor revealed that individuals of Tilapia guineensis, Hemichromis fasciatus and Sarotherodon melanotheron taken from lake waters are respectively 10%, 18% and 10% contaminated at the Sô River level in Dogodo, at 26%, 25% and 23% at Kétonou, 32%, 29% and 40% at 6 km from Domèguédji and 32%, 28%, 27% at the Abomey-Calavi jetty

Physico- Chemical characteristics of compost (Cotonou, Benin, West Africa)

This work was led the town of Cotonou in Benin and particularly on the vegetable garden site of Hou\ue9yiho. It involved the valorization of the waste of this site by proceeding the aerobic composting of the biodegradable fraction of municipal solid waste collected in the markets. This consists among other rotten fruits of various plant debris and garbage obtained by initial sorting. After three months of biological decomposition, 48,531.78 kg of biodegradable waste was composted with a yield of 40,443.33 kg of fresh compost or approximately 83.33% compost. The moisture content of the biodegradable fraction is 65%. The physico-chemical characteristics of compost produced are as follow: 12.7594 \ub1 0.1006 mg / kg of heavy metals, the C / N ratio is 13% and the rate of total phosphorus is 0.34% and 61.18 meq/100 g of Dry Weight exchangeable bases. The humus of our compost has a high capacity of cationic exchange (CCE) and fixed mineral nutrient ions such as K+ and Ca2+ and phosphate in order to make them available for plant growth and development and proving the poverty of the soil of this site and their increased need of organic amendment