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Bori Akadar A.,University of Franche Comte | Bourioug M.,French National Center for Scientific Research | Mohamed N.,Center Detude Et Of Recherche Of Djibouti Cerd | Alaoui-Sosse B.,French National Center for Scientific Research | Cavalli E.,University of Franche Comte
International Journal of Environmental Research | Year: 2014

The purpose of this work was to test the efficiency of the treatment of wastewater by infiltration under laboratory conditions, to remove bacterial and organic load and to convert it to available nutrient for crop plants. In order to achieve this objective, polyvinyl chloride (PVC) columns of 133 cm of height were used. The columns were filled with sand and/or pozzolana and loaded with municipal wastewaters. Various parameters were measured at the inlet and outlet of these columns: chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonium (NH4 +), nitrate (NO3 -), Total Kjeldahl Nitrogen (TKN), total phosphorus (pt), pH and Escherichia coli (E. coli). With an average charge in chemical oxygen demand (COD) of 601.5 mg/L O2 at the input, A better reduction by sand (S) followed by mixing sand-pozzolana (SP) and finally by pozzolana (P) were observed. Good bacterial removal was also achieved with S. Indeed, after 49 days of experiment, the output effluent treated by S showed only 2.4×104 CFU/100 mL of Escherichia coli, against 108 CFU/100 mL in the output effluent treated by P. Moreover the almost total conversions of the nitrogen to nitrate makes the water treated by sand filter suitable for irrigation, because it is rich in nutrients and enables the conservation of conventional water stocks thereby protecting human life and environmental quality. Source

Abdoulkader B.A.,Office National des Eaux et dAssainissement de Djibouti ONEAD | Mohamed B.,Jean-Francois Champollion University Center for Teaching and Research | Nabil M.,Center Detude Et Of Recherche Of Djibouti Cerd | Alaoui-Sosse B.,University of Burgundy | And 2 more authors.
Ecological Engineering | Year: 2015

In the arid climate of Djibouti, salt concentrations of up to 1200mgL-1 have been recorded in well water, attributed to the overexploitation of aquifers. Farmers are therefore turning to untreated wastewater as a source of water for crop irrigation. The authors undertook a study in two phases. In the first phase they tested the field transposition of an experimental water treatment method previously laboratory-tested on a small scale. The pilot device was composed of an adaptor basin for the wastewater, a filter basin filled with sand and a storage basin to collect and hold the treated water. Transfer of waters from basin to basin was gravitational. The physicochemical and microbiological sleek raw water parameters were determined weekly for 7 weeks. Monitoring of chemical oxygen demand concentrations decreased from 445±5.76mgL-1 O2 on the first day of the experiment to 101±1.34mgL-1 O2 on the 21st day. The removal of total coliforms attained more than 99.6% as of day 21. The performance of the microbiological treatment of waters obtained through sand filtration is therefore of definite interest in agriculture. In the second phase the effect of different irrigation waters (untreated wastewater (WW), treated wastewater (TW), saline well water (SW), mixed water (MW) and potable water (PW)) on growth and yield of the grass Panicum maximum were also compared. The use of WW and TW in irrigation effectively increased stem height and aerial part dry matter compared to other treatments, while irrigation with SW and PW showed the lowest measured values. Depending on their performance, the effectiveness of the treated waters can be ranked in the following increasing order: TW; WW>MW>PW; SW. The performance of the TW treatment can be explained by its higher nutritive content, especially in N. © 2015 Elsevier B.V. Source

Dekov V.M.,French Research Institute for Exploitation of the Sea | Egueh N.M.,French Research Institute for Exploitation of the Sea | Egueh N.M.,CNRS Oceanic Domains Laboratory | Egueh N.M.,Center Detude Et Of Recherche Of Djibouti Cerd | And 11 more authors.
Chemical Geology | Year: 2014

Carbonate chimney-like deposits up to 60m high are scattered or arranged in rows at the shores of a desiccating hypersaline and alkaline lake from a continental rift setting (Lake Abhé, Afar Rift, Djibouti). The chimneys formed sub-aqueously in the lake water body at a higher water level than observed today. Alternating calcite and low-Mg calcite+silica concentric layers compose the chimney structures. Mineralogical and geochemical investigations of the chimneys, lake water, and hot spring (hydrothermal) fluids suggest that the chimneys are a result of rapid carbonate precipitation during the mixing of hydrothermal fluids with lake water. In contrast to the hot spring fluid, lake water is enriched in HREE and possesses a pronounced positive Ce anomaly, features that are preserved in the carbonate chimney layers. Mixing calculations based on Sr-isotope and concentration data indicate a hydrothermal fluid contribution of ~45% in the chimney interior, which decreases to ~4% in the external chimney layer. Sr in the hydrothermal fluids is predominantly leached from the underlying volcanic rocks, whereas the lake's Sr budget is dominated by riverine input. Considering the fluid mixing ratios calculated by Sr-data, the measured C and O isotope compositions indicate that chimney carbonates precipitated at temperatures between 14°C (internal part) and 22°C (external part) with δ13C-carbonate mainly controlled by isotope equilibrium exchange of lake water with atmospheric CO2. The low-Mg calcite layers, including the outermost layer, have enhanced signals of lake water inheritance based on elevated concentrations of immobile elements, σREE, and Sr and Ca isotope compositions. Ca-isotope data reveal that internal chimney layers formed by non-equilibrium calcite precipitation with a predominantly hydrothermal Ca source. The external low-Mg calcite layer received Ca contributions from both hydrothermal fluid and lake water, with the latter being the dominant Ca source. Highly positive δ44/40Ca of lake water likely reflects non-equilibrium Ca-carbonate precipitation during lake water evaporation with resulting 44Ca enrichment of residual lake water. The strong degree of 44Ca enrichment may point towards multiple lake drying and Ca-reservoir depletion events. Coupled C-O-Ca-isotope data of the sampled carbonate chimney suggest late-stage (low-temperature) hydrothermal carbonate chimney formation during strongly evaporative lake conditions at the time of low-Mg calcite precipitation. U-Th age dating suggests that the chimneys formed no earlier than 0.82kyrBP (0.28±0.54). © 2014 Elsevier B.V. Source

Moussa N.,French Research Institute for Exploitation of the Sea | Moussa N.,CNRS Oceanic Domains Laboratory | Moussa N.,Center Detude Et Of Recherche Of Djibouti Cerd | Fouquet Y.,French Research Institute for Exploitation of the Sea | And 7 more authors.
Mineralium Deposita | Year: 2012

The geology of the Republic of Djibouti, in the SE Afar Triangle, is characterized by intense tectonic and bimodal volcanic activity that began as early as 25-30 Ma. Each magmatic event was accompanied by hydrothermal activity. Mineralization generally occurs as gold-silver bearing chalcedony veins and is associated with felsic volcanism. Eighty samples from mineralized hydrothermal chalcedony, quartz ± carbonate veins and breccias were studied from ten sites representing four major volcanic events that range in age from early Miocene to the present. The most recent veins are controlled by fractures at the edges of grabens established during the last 4 Myr. Gold in excess of 200 ppb is present in 30% of the samples, with values up to 16 ppm. Mineralogical compositions allowed us to identify different types of mineralization corresponding to different depths in the hydrothermal system: (1) surface and subsurface mineralization characterized by carbonate chimneys, gypsum, silica cap and quartz ± carbonate veins that are depleted in metals and Au; (2) shallow banded chalcedony ± adularia veins related to boiling that contain up to 16 ppm Au, occurring as native gold and electrum with pyrite, and tetradymite; (3) quartz veins with sulfides, and (4) epidote alteration in the deepest hydrothermal zones. Samples in which pyrite is enriched in As tend to have a high Au content. The association with bimodal volcanism, the occurrence of adularia and the native Au and electrum in banded chalcedony veins are typical of epithermal systems and confirm that this type of mineralization can occur in a young intracontinental rift system. © 2012 Springer-Verlag. Source

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