Abstract
The objective of this study was to evaluate the typology of water through physicochemical and bacteriological characterization with the aim of highlighting its vulnerability as a drinking water resource. The methodology adopted was to evaluate the level of pollution by monitoring the spatiotemporal variation of the water pollution indicator levels of Lake Dohou. The sampling frequency is monthly for one year, from November 2017 to October 2018, in order to obtain a fairly representative image of water quality and its seasonal evolution in eight (8) well-defined stations. The parameters were determined using the standard methods defined by the French Association for Standardization (AFNOR). This study shows that the waters are acidic, with an average pH of 5.81 and a low electrical conductivity of between 42.67 ± 4.30 and 59.62 ± 21.84 μS.cm-1. At all stations, seasonal mean water transparencies are low (<1 m). It is also noted that 99.7% of the water samples collected had total nitrogen (TN) levels above the limit of 4 mg.L-1. All of the lake’s waters have non-compliant BOD5 (<3 mgO2.L-1) for raw water intended for the production of drinking water. Sites D6 and D7 have COD/BOD5 ratio greater than 3, which indicates the presence of non-biodegradable organic matter in these areas. Total coliforms, Escherichia coli and Enterococci were present in 100% (28/28) water samples at concentrations ranging from 2300 to 173,000 CFU/100 mL, from 100 to 1650 CFU/100 mL and from 20 to 1140 CFU 1/100 mL respectively. For Salmonella pathogens, they were detected in 50% of the dry season samples and in 100% of the rainy season samples. This almost permanent presence of this pathogenic germ denotes a poor quality of water with reference to this parameter. The presence of total coliform and other microbial contaminants suggests that supplied water is highly contaminated with pathogens and great reservoirs for them. Principal component analysis (PCA) of the physicochemical data set allowed defining three different classes of water on the Dohou Lake. Outside the upstream zone (D6 and D8), water could continue to be used for the production of drinking water.
Highlights
The use of water in many areas of human activity, the ever-increasing population and climatic variations are all factors that affect the water resource, in terms of quantity and quality, and constitute a major global concern in recent years
In Duékoué, a city located in the west of Côte d’Ivoire, the production of drinking water is in a special situation because of the vulnerability of the resource used
Maximum temperatures were recorded during the dry season and low during the rainy season
Summary
The use of water in many areas of human activity, the ever-increasing population and climatic variations are all factors that affect the water resource, in terms of quantity and quality, and constitute a major global concern in recent years. In Duékoué, a city located in the west of Côte d’Ivoire, the production of drinking water is in a special situation because of the vulnerability of the resource used (distributed water is produced from superficial resources) This situation is linked to agricultural pressures, climatic hazards, urbanization, geological and topographical factors that favor the leaching of pollutants (nitrogen, phosphorus, organic matter and pesticides) to these resources. Heavy rains can lead to sewer overflows and heavy urban runoff leading to a surge of contamination in surface water These changes in the quality of the raw water can pose several problems for water treatment, such as fouling and blockage of membranes, an increase in the dosage of the chemical and a decrease in
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