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 mgO 2 •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.

This study focused on the characterization of digestates resulting from anaerobic digestion of manioc effluents from attiéké factories. Two types of digestate were characterized, one consisting of manioc effluent + urine and another composed of manioc effluent + urine + cow dung. As a result, these residues of bio-digestion rich in nutrients (NPK) can be used as agricultural fertilizer. Moreover, the determination of some microorganisms and heavy metals digestates allowed to better appreciate its fertilizing quality. These parameters remained in accordance with the quality standards of a digestate prescribed. These results show that digestates from anaerobic co-digestion of manioc effluents, urine and cow dung can be used without fear as an agricultural biofertilizer.

The abiotic typology of the different sampling stations based on physico-chemical parameters and the assessment of the nutrient load and the relative contributions of the different nutrient sources to this surface water were analysed. Five physical and chemical parameters (temperature, dissolved oxygen, transparency, pH and conductivity) were measured in situ at each sampling campaign in Lake Dohou over a period of one year, once a month at seven (7) selected stations. Water samples were taken for subsequent determination of dissolved solids, biological oxygen demand for 5 days and nutrient salts (nitrite, nitrate, phosphate, ammonium).Thephysico-chemical characterisation revealed weakly mineralised water with average conductivities varying from 12.38 ±16.33 µS.cm-1 to 39.63 ±45.28 µS.cm-1 with high temperatures in the dry season. A hierarchical ascending classification (HAC) was used to group the stations into 3 groups. Group I (stations 6), due to its exposure to domestic discharges and leaching from agricultural land, is heavily loaded with organic matter and nutrients. The values of the pollution index express a high organic pollution at all the sampling stations. The water of Lake Dohou is highly loaded with organic matter and receives a very high amount of pollutant from the environment.

The aims of the work were to study the current quality of the water in Lake DOHOU used for drinking water supply through several physical, chemical analyses and using water quality indices (WQI). In addition, the question was whether the populations are at risk after drinking water of lake following a reduction of 50% and 75% in the median and maximum values of pesticides. Thus, the results of the pesticide monitoring program were incorporated into probabilistic human health risk assessment exercises. Water samples were collected over a period of one year. Pesticides were subjected to solid phase extraction and then analyzed using gas chromatography coupled to tandem mass spectroscopy. The other parameters were measured according to conventional methods. The results showed that the most frequently detected pesticides were aldicarb (79%), simazine (79%) and monolinuron (44%). They also showed the mean values of concentrations exceeding 1.5 μg/L. Metoxuron detected at a frequency of 29% showed the maximum average concentration (13.46 μg/L). Nearly 98% of the sampling points had at least one substance with an average concentration above the quality standard (0.1 μg/L) and 80% did not meet the total concentration standards. Cumulative risk quotient estimates after 50% or 75% abatement for frequently identified pesticides were greater than unity when extreme values for adults and children were considered. To determine the suitability of water for aquatic life, drinking water consumption and drinking water production, the water quality index (WQI), the heavy metal pollution (HPI) and the heavy metal evaluation (HEI) were calculated. The poor quality of the water was mainly related to pesticides, organic matter and microbiological parameters. Most of the nutrients and metals studied were often below the standards of drinking water

The objective is to study the phytoplankton community of Dohou Lake in order to contribute to the knowledge of its ecological quality. For this purpose, monthly samplings were carried out annually between October 2017 and September 2018. The studied physicochemical parameters (Temperature, Electrical conductivity, pH, Dissolved oxygen, Transparency, Depth, Total nitrogen, Nitrate, Nitrite, Total phosphorus) varied significantly over time. During the rainy season months, Dohou Lake is influenced by high values of total phosphorus, total nitrogen, conductivity, nitrate, pH, transparency and depth. However, in the dry season, the lake is characterized by high values of temperature, nitrite, dissolved oxygen and conductivity. For the phytoplankton community, 373 phytoplankton taxa divided into 111 genera, 51 families, 24 orders, 11 classes and 7 phyla (Chlorophyta, Euglenophyta, Cyanobacteria, Bacillariophyta, Pyrrophyta, Chrysophyta and Xanthophyta) have been identified. Chlorophyta with 50.67% is the most represented in the taxonomic richness of the environment. Total phytoplankton densities oscillate between 100 105 cells / L (August) and 321 105 cells / L (February) with high proportions of Cyanobacteria greater than 45% during each month of the rainy season. The highest values of Shannon and Equitability diversities are observed during the dry season months.