Exploration des séries chronologiques d’analyse de la qualité des eaux de surface dans le bassin de la Tafna (Algérie)

La qualité des eaux de surface est sujette à de nombreuses fluctuations et par conséquence les gestionnaires sont souvent confrontés à des pics de pollution problématiques. À cet effet, nous présentons dans cette étude les résultats d’une exploration des séries d’analyses de la qualité des eaux de surface dans le bassin de la Tafna (Algérie). Nous avons retenu trois descripteurs de la qualité des eaux; la matière en suspension (MES), la conductivité et la demande chimique en oxygène (DCO). On dispose pour cette étude de séries de prélèvements instantanés d’une fréquence au moins mensuelle, couvrant une période de sept ans (avril 1995-mars 2002). Les stations de prélèvements choisies se situent sur les principaux cours d’eau du bassin de la Tafna (Mouillah, Isser et Tafna) de manière à couvrir l’ensemble du bassin versant.Afin d’aboutir à des conclusions exploitables, nous avons commencé, dans une première étape, par une vérification de la cohérence des résultats d’analyse, suivie d’une analyse conjointe de tous les paramètres pour explorer la structure globale des données et appréhender les principaux facteurs qui contrôlent l’évolution de la qualité physico-chimique des eaux.Nous proposons dans cette étude deux modèles mathématiques prévisionnels : le premier est un modèle de simulation du comportement de la qualité des eaux basé sur les relations concentration-débit. Le second est une approche prédictive qui permet de mettre en évidence les saisonnalités et les tendances d’évolution des paramètres étudiés.A river is a complex system in interaction with the whole of its catchment area. River water acquires its physicochemical composition under the combined action of several factors: weathering of rocks, decomposition of terrestrial organic matter, diffuse and point-source pollution, and atmospheric precipitation.The large catchment area of Tafna (7,245 km2 surface area), located at the extreme northwest sector of Algeria and extending into Moroccan territory (23%), is subdivided into four sub-basins. However, the downstream portion of the basin, which represents the sub-basin of maritime Tafna, was not retained in this study; its principal river Tafna is often dry because several hydraulic constructions have been installed in the upstream part of the basin. The three sub-basins concerned then with this study are the upper Tafna, the Mouillah and the Isser.In the basin of Tafna, surface water quality is being continually degraded. In addition to the phenomenon of erosion, which has been estimated to be 400 t/km2/year in the Mouillah sub-basin and 1,000 t/km2/year in the Isser and upper Tafna sub-basins, domestic and industrial wastes increasingly threaten the quality of the surface water.The basin of Tafna has a surface water quality network composed of 41 sampling stations. Three stations have been selected for this study. They are distributed in the three sub-basins studied, and are located upstream of dams, so as to cover the whole of the basin: Station ST160202 in the Mouillah sub-basin, ST160426 in the upper Tafna sub-basin and ST160614 in the Isser sub-basin. This work presents the results of an exploration of a series of instantaneous samples collected with at least monthly frequency over a period of seven years (April 1995-March 2002). The descriptors used in this study are the total concentrations: suspended matter concentration (SS), conductivity, which expresses the dissolved matter concentration, and the organic matter concentration as estimated with the chemical oxygen demand (COD).To be able to interpret the influence of the characteristics of the catchment area on the physicochemical quality of surface water, we started by describing the principal characteristics of the sub-basins studied. Given the great variability of the results of the analysis, we considered it to be useful and necessary to evaluate the coherence of the measurements with ion balance and statistical analysis (Box and Whisker plots). A joint analysis of all parameters was then applied to explore the total structure of the data in order to understand the principal factors that control the evolution of the physicochemical water quality.This study proposes two models. The first model is a simulation of the behaviour of surface water quality based on concentration-flow relations. The second is a predictive approach that makes it possible to highlight the seasonal effects and the temporal trends of the studied parameters.Based on this modelling, it appears that the concentration variance explained by the concentration-flow models varies between 50% and 72%, which means that the reconstitution of the concentrations is only approximate. To improve the reliability of these models, we propose several solutions.As for the forecasting models, a comparison of the values calculated to those measured shows that the results for conductivity and the COD are close to the measured values, with average relative variations of the order of 15%, but the forecasts of SS are considered to be less precise because they produce greater average relative variations. This is explained by the fact that the suspended matter concentrations do not follow a seasonal trend but are strongly related to flow variations.Finally, it should be noted that the reliability of the established models remains very sensitive to the size of the measurement series one has. Better information contained in longer series of analyses would undoubtedly make it possible to reduce this uncertainty.The methodology has been suggested on a purely exploratory basis and was limited to the three descriptors of the surface water quality: SS, conductivity and COD. The work will be extended by applying it to other parameters, which should make it possible to establish a complete model for the behaviour of surface water quality in the catchment area of the Tafna

Étude corrélative des paramètres physico-chimiques et des données satellites IRS1C pour caractériser la pollution aquatique. Application à la baie d’Oran, Algérie

Le contrôle de la qualité de l'eau est fondé naturellement et traditionnellement sur des mesures et des prélèvements in situ. Des images satellites étalonnées à partir des données mesurées in situ fournissent une information quantitative et continue sur le milieu aquatique et peuvent être employées pour estimer, avec une approximation raisonnable, les facteurs affectant la qualité de l’eauL’objectif de cet article consiste à établir des corrélations entre les propriétés optiques de l’eau de mer et les paramètres physico-chimiques. Nous présentons des relations exprimant les variables indicatrices de la qualité des eaux du littoral d’Oran et la réflectance calculée de chaque pixel à partir d’un modèle physique de correction radiométrique. Les mesures in- situ sont effectuées pour des zones de différentes qualités d’eaux et leurs réflectances sont calculées à partir d’une image satellite à haute résolution IRS1-C.Les meilleures corrélations sont obtenues sur le deuxième et le troisième canal visible. Pour la demande chimique en oxygène, le coefficient de corrélation atteint 0.84, pour les matières en suspension r2 = 0.88, pour la demande biochimique de l’oxygène pendant cinq jours r2 = 0.62, pour l’oxygène dissous r2 = 0.77 et pour la turbidité r2 = 0.90.Finalement, des relations linéaires sont établies avec les réflectances. L’inversion de ces relations permet d’obtenir des images transformées à partir du logiciel de traitement d’image afin d’estimer pour chaque pixel le degré de pollution du milieu.Population growth in developing countries has led to a rapid expansion of primary urban areas. Solid and liquid wastes coming from domestic consumption and industrial activities are discharged into potential water sources such as seas, lakes and other natural areas. In order to protect these areas and to control the pollution caused by such waste, it is necessary to continuously monitor these zones. Satellite imagery, such as that obtained with the IRS1C satellite, can be used to estimate, with reasonable accuracy, the factors affecting water quality. This technique allows for the necessary continuous monitoring of impacted areas and affords an overall analysis of their degree of pollution.Waste disposal affects and alters the chemical and physical characteristics of water. Moreover, water quality could be altered by the decay products of extracellular release and death of aquatic organisms. In turn, these changes can cause an alteration in the appearance of water. It is therefore reasonable to look for relations linking variations in chemical and physical properties to variations in the spectral properties of water, or more precisely, to its reflecting power. The aim of the present study was to:1. relate the reflectance of polluted water to its physico-chemical parameters;2. show the significance of such relationships.Water samples were collected from different sites:1. two outlets where sewage of Oran City is being emptied into the sea;2. far from these outlets;3. far from the port;4. far from two sites in a lake known to be subjected to both urban and industrial waste.From each site, water samples were taken at the source and from different places far from the coast. The following water quality parameters were analyzed: temperature, acidity, turbidity, suspended material, dissolved oxygen, electrical conductivity, chemical oxygen demand and 5-day biological oxygen demand. The reflectance coefficient of water in each of the studied areas was calculated using the IRS1C image at four bands. The satellite observes the earth in four spectral channels: C1 (0.45- 0.52 m); C2 (0.52 - 0.59 m); C3 (0.62 - 0.68 m) and C4 (0.77 - 0.86 m) with a spatial resolution of 6 m. The radiance measured by the satellite sensor results from solar radiation affected by several processes including absorption and diffusion on both downward and upward paths by the atmospheric components, and reflection at the ground surface.We first simulated the measurement achieved by the captor of our reference water (from the sea far from any pollution). Secondly, we used imagery treatment to determine the real value evaluated by the satellite for deep-sea water. We used both a simulated value and the real value to calculate the calibration factor for each channel. We took the image and transformed the digital account into radiance by linear relationships. For each channel, we use the reverse model to calculate the reflectance for each pixel. The substances that determine the optical properties of water surfaces, and thus influence their reflectivity, may be classified into three categories:1. living phytoplankton and the associated detritus;2. suspended particles;3. dissolved organic matter.The phytoplankton and the associated biogenic detritus generally have the same colour. In most oceanic waters, and in some coastal waters where terrigenous supplies are unimportant, the influence of phytoplankton is dominant. In natural conditions, it is very difficult to dissociate the influences of phytoplankton and those of biogenic detritus on the coefficient of absorption, for which only global estimations are made. The phytoplankton cells and the particles corresponding to biogenic detritus cause a Mie diffusion of light, which is relatively independent of the wavelength. Therefore, the colour of water gradually turns green with increasing phytoplankton concentration.As expected, our results demonstrated that for polluted waters there was a good correlation between turbidity and concentrations of suspended material. Turbidity and suspended solids have a common effect in reducing light penetration, thereby suppressing primary production in the form of algae and macrophytes. This decrease, in turn, affects the available dissolved oxygen. Our results confirmed this situation by showing a highly negative correlation between turbidity and dissolved oxygen. The oxygen needed for chemical oxidation of organic matter and the accompanied minerals is expressed as COD. Therefore, higher values of this parameter means more organic pollution. BOD5 estimates the oxygen needed for biological oxidation of organic and inorganic matter by organisms that are actually present in the polluted water. Therefore, the DCO/DBO5 ratio refers to the capacity of organisms found in the water to oxidize the organic matter found in the medium. Our results showed that this ratio increased with increasing pollution and with reflectance in the different channels. For easier water quality monitoring we could use the satellite imagery to estimate, with excellent validity, the capability of the water to reduce organic pollution resulting from urban discharge. Moreover, biological parameters could be calculated from each other since there was a high correlation found among them.The correlation between reflectance and the biochemical parameters was higher for channels C2 and C3 than for the other two channels. The following correlations between reflectance and the measured parameters chemical were obtained: oxygen demand, r = 0.84; suspended matter, r = 0.88; 5-day biological oxygen demand, r = 0.62; dissolved oxygen, r = 0.77; turbidity, r = 0.90. Finally, linear relationships were established between physico-chemical parameters and reflectance values. The inversion of these relationships offered the possibility to estimate for each pixel the degree of water quality. Figures showed clearly different distinct colour sub-areas in each of the studied areas. Each colour indicated a different degree of water quality or pollution. With this technique it was possible to construct, relatively rapidly, a global picture describing the degree of unknown pollution spread over a wide water surface

Cationic Dye Removal from Aqueous Solutions Using Ionic Liquid and Nonionic Surfactant-Ionic Liquid Systems: A Comparative Study Based upon Experimental Design

In order to separate methylene blue from aqueous solution, a novel method based upon liquid-liquid extraction, using a nonionic surfactant-ionic liquid system as extracting phase, was investigated. A comparative study was carried out with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, known as [C4mim]PF6. By using the nonionic surfactant-ionic liquid system, the extraction efficiency could reach 97.8%, indicating that the addition of nonionic surfactant (Triton X-114) significantly improves the extraction of methylene blue. Under optimal conditions, the dye concentration in the effluent showed an almost 50-fold reduction. However, the extraction extent of methylene blue was found to be low at low pH values, and in the presence of K2CO3, which may be useful for surfactant-ionic liquid system regeneration

Détermination des enthalpies de fusion et des courbes de solubilité des acides 2,3- et 3,5-diméthylbenzoïques dans le n-hexane. Comparaison avec les résultats obtenus par la méthode d’UNIFAC

Nous avons déterminé:a

Microstructure et potentiel de gonflement d’une argile du Sahara algérien

Durant les années 80, une raffinerie de pétrole et des bâtiments résidentiels divers, construits dans la région d’In-Aménas (au sud-est de l’Algérie), ont subi des dommages sévères dus au gonflement du sol. Quelques années seulement après sa réception, la raffinerie a dû être fermée et les constructions touchées sont tombées en ruine et ont dû être déblayées. Des études réalisées sur le sol de la région ont montré qu’il s’agit d’une argile de type kaolinite contenant des interstratifiés : illite-vermiculite. Ces argiles présentent habituellement un potentiel de gonflement relativement faible. Dans le but de comprendre pourquoi les argiles d’In-Aménas ont développé un gonflement aussi dévastateur, les résultats d’une campagne d’essais de gonflement ont été analysés. Des investigations expérimentales complémentaires portant sur la microstructure et les propriétés de rétention d’eau du sol ont été effectuées. A la lumière de ces derniers résultats, l’importance de la microstructure du sol sur son comportement au gonflement est mise en évidence

Metal partitioning in calcerous sediment of the Tafna river and its estuary (Algeria)

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Comportement des ouvrages dans les argiles expansives d’In-Aménas

La présence d’argile gonflante cause de sérieux problèmes dans les régions à climat aride. Dans ces régions l’argile se trouve dans un état de dessiccation tellement poussé que l’apport d’une infime quantité d’eau peut libérer une énergie faramineuse capable de provoquer des sinistres importants dans les constructions.En Algérie les argiles gonflantes constituent un handicap majeur pour le développement des régions du Sud, d’autant plus que ces dernières renferment l’essentiel des ressources pétrolières du pays. On rapporte dans cet article l’expérience de désordres du gonflement vécue dans la région d’In-Aménas. On présente la région dans ses contextes environnemental et géomorphologique puis on analyse le comportement de quelques ouvrages affectés par le gonflement du sol. On termine en inférant quelques recommandations relatives à la réalisation de constructions dans la région

Microstructure and swell behaviour of a clay from the Argelian Sahara

Durant les années 80, une raffinerie de pétrole et des bâtiments résidentiels divers, construits dans la région d’In-Áménas (au sud-est de l’Algérie), ont subi des dommages sévères dus au gonflement du sol. Quelques années seulement après sa réception, la raffinerie a du être fermée et les constructions touchés sont tombées en ruine et on dû être déblayées. Des études réalisées sur le sol de la région ont montré qu’il s’agit d’une argile de type kaolinite contenant des inter stratifiés : illite vermiculite. Ces argiles présentent habituellement un potentiel de gonflement relativement faible. Dans le but de comprendre pourquoi les argiles d’In-Aménas ont développe un gonflement aussi dévastateur, les résultats d’une campagne d’essais de gonflement on été analysées. Des investigations expérimentales complémentaires portant sur la microstructure et les propriétés de rétention d’eau du sol on été effectuées. A la lumière de ces derniers résultats, l’importance de la microstructure du sol sur le comportement au gonflement est mise en évidence.Peer Reviewe