Isotopic tracers and water quality indicators (TDS (Total Dissolved Solid), Cl -and NO 3 -contents) were used to characterize the recharge and control of the quality of groundwater in the alluvial aquifer beneath of the N'djamena city. For this study, a total of 92 waters samples were taken and this included 67 wells, 21 pumps and 4 surface waters. Some groundwater has δ 18 O and δ 2 H values close to those of the city of N'djamena and/or the Chari river rains. However, all sampled points are below the Global Meteoric Water Line reflecting their evaporated characters. The interpretation of the isotopic tracers highlights that the recharge of the analyzed ground waters may result from two major mechanisms: (1) direct infiltration of local precipitation; (2) lateral inflow of river waters. The upper aquifer is the most vulnerable to pollution, especially during the recharge period. This pollution is due to the leaching of soils during the rainy season and the rise of the groundwater level which accompanies the overflowing of the Chari and causes the leaching of the polluted horizons of the unsaturated zone. In contrast, the lower aquifer has acceptable concentrations of solutes.

The problem of access to water in quality and quantity is a major challenge, because it strongly influences the socio-economic conditions of populations in developing countries. The water of the basement of the city of N'Djamena is not sheltered from the risk of pollution. She disposes very little functional wastewater disposal system because the collection networks are almost non-existent, moreover there is a lack of infrastructures for evacuation of household waste, as well as the solid waste treatment units. In addition, under the town of N'Djamena there are two main aquifers located respectively at about 10 and 60 m depth, and the presence of an intermediate aquifer about 30 m deep was also noted. Like all urban cities, these aquifers are not immune to the risks associated with human activities. In order to highlight the influence of the hydrochemical process on the groundwater quality of the city of N'Djamena, a study was conducted on a sample of well water and borehole. In total, 20 open wells and 16 boreholes were sampled and analyzed. The pH and the temperature were measured in situ using the pH 323 / Set B mixed electrode and the conductivity using the Lf 318 / Set electrode. It is the same for the alkalinity which is determined by titrimetry, using a HACH / 16900 brand digital titrator. The analysis of major ions was carried out at the Laboratory of Hydrogeology of the University of Avignon. the anions (Cl - , SO42- , NO3 - ) were analyzed using a Dionex ion chromatograph, and the cations (Ca2+ , Mg2+ , Na+ , K + ) using an atomic absorption spectrometer for with a relative uncertainty of 5%. The results of the in-situ parameters have shown that the waters have a pH which is around 6.85 in the wells and 7.24 in the boreholes and the measured temperature is close to the ambient temperature of the air which is 28 ° C. The mineralization of the waters is sometimes high and this results in values of conductivities that can reach 1253 μS / cm), especially in the wells. This increase in conductivity is accompanied by an increase in Cl - and NO3 - ions in the water. Groundwater has a wide variety of chemical facies, among which mention may be made of calciumbicarbonate-type water, sometimes nitrated, sodium bicarbonate and potassium and nitrate, which may have high chloride contents and bicarbonate and chloride and nitrate calcium or sodium. Principal Component Analysis (PCA) has shown that the main processes influencing groundwater chemistry are hydrolysis of silicates, cation exchange between groundwater and clayey minerals, evaporation and the impact of human activities.

Our objective is to evaluate adequacy of water for consumption and irrigation. We collected nineteen water samples from 21 to 26, May 2017. Twenty-two physico-chemical and bacteriological parameters were taken into account, electrical conductivity, pH, total hardness, bicarbonate, nitrates, sulfates, chlorides, calcium, sodium, magnesium, potassium, dissolved oxygen and biochemical oxygen demand, chemical oxygen demand, total coliforms,

The purpose of this study is to determine the phase indicator functions (vacuum rate, velocity and bubble size) of the gas-liquid flow. The gas-liquid flows in these columns (aquarium) are intrinsically unstable and the dynamics of such flows influence the mixing and mass transfer performance. It is therefore important to characterize the dynamics of gas-liquid flow. Also, the complete knowledge of the global dynamics of the fluids of the bubble column is based on that of the bubble. The experimental analysis is carried out using a two-phase instrumentation consisting of an optical fiber bi-probe. The use of the experimental techniques has enabled a better understanding of the hydrodynamics of two-phase flow. In terms of results, intrusive techniques provide local measurements while non-intrusive techniques provide a distribution over a cross-section with different spatial and temporal resolutions. The optical fiber bi-probe placed between two column flanges permit to have a complete mapping of the dispersed phase flow. The use of a mass flow meter and an ultrasonic flow meter, in different flow configurations, made it possible to obtain data on the operation of the column. However, the analysis of granulometry of the bubbles in the columns is performed by intrusive, flow-disrupting and non-intrusive techniques. Knowledge of bubble size and vacuum rate is crucial for determining interfacial air.

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