Défluoruration des eaux d'exhaure de Youssoufia (Maroc) par percolation sur les cendres volantes de charbon

Dans cette étude, nous nous sommes intéressés à la défluoruration des eaux souterraines de Youssoufia (eaux d’exhaure) par percolation en colonne sur les cendres volantes de la centrale thermique d’El Jadida et à la désorption des fluorures par la suite. Les résultats obtenus ont montré que :- le rendement d'élimination du F- est d'environ 97 % dans nos conditions expérimentales avec un temps de séjour supérieur à 72 heures ;- la régénération des cendres est possible à l’aide de NaOH;- le nombre de cycles successifs tolérés par les cendres permettant d’atteindre des efficacités convenables est d’au moins huit.The layer of black phosphate in Youssoufia is characterized by the presence of underground water in the building sites. This drainage water must be removed to allow the exploitation of these layers. Observations of the tonnage/flow relationship during previous years allowed the prediction of more than 35000 m3 drainage water/day from the year 2000. This water has particularly high levels of fluorides, which represents a permanent risk for the rural population, which relies on groundwater (wells) for its daily consumption. To minimize adverse health affects and to build on earlier work, the current study was focussed on the sorption performances of coal fly ash in the dynamic mode and on regeneration tests of these ashes for possible revalorization. In this study, we were interested in both the defluoridation of subsoil waters in Youssoufia (drainage waters) by percolation through a column of fly-ash collected from the power station of El Jadida and in fluoride desorption from the ash.The first results from the characterization of this water showed that fluoride concentrations were elevated, exceeding the water quality standard established by the World Health Organization (WHO), 0.7 mg/L for a semi-arid climate. This abnormally elevated content in fluoride comes from the raw phosphates, which have a high fluoride content. Chemical analysis of the fly-ash, carried out by x-ray fluorescence, demonstrated that the principal components were silica, alumina, oxide iron (Fe2O3), and calcium oxide.With respect to the first objective of this study, the sorption experiments of water soluble F- ions from the drainage waters were carried out at 25 °C in a glass column (33 cm high, 2.2 cm in internal diameter) filled with a well-defined mass of fly-ash. The process involved: placing 250 mL of the solution in the higher tank (placed in top of the column) and the flows were adjusted to 4.6, 7.7 and 15.4 mL/h. The concentration of fluorides was measured in the effluent every 24 h, with a fluoride ion selective electrode, pH model Orion SA 520 according to a standardized method (AFNOR, T90-004). Each experiment was carried out twice. The drainage water used had a fluoride content of 2.50 mg/L.With respect to the second objective, the study of the desorption of fluorides from the fly-ash was carried out in a static reactor. The choice was related to chemical desorption with soda, and tests were carried out to evaluate the parameters likely to support desorption (concentration of soda, volume to be used, kinetics of desorption). The method used for desorption consisted of brewing the fly-ash in a basic solution (1g of ashes /100mL of soda) during one hour, at a stirring speed of 300 rpm. The concentration of fluorides was then measured in this solution by a potentiometric method following filtration. The fly-ash was removed and rinsed with distilled water and then re-used for a new sorption. The desorption tests were carried out on fly-ash that had been saturated by contact with the drainage waters from Youssoufia ([F] = 2.5 mg/L, pH=7.86). The sorption stage consisted of putting 10 g of ash in contact with 1 L of the drainage water with a stirring rate of 300 rpm and the tests were carried out at ambient temperature.The results of the defluoridation by percolation through the fly-ash showed that the concentration of fluorides in the effluent decreased to 0 mg/L « < 5 10-7 M », when the flow decreased from 15.4 mL/h (flow 1) to 7.7mL/h (flow 2) to 4.8 mL/h (flow 3), after 96 to 120 hours. Similar results were also obtained by Piekos et al (1998).The first regeneration results were encouraging for several reasons. First of all, the regeneration of support was possible and desorption was very important. This demonstrated that basic media are probably favorable for desorption. In parallel, the kinetics of desorption with soda were very fast and they did not exceed one hour for the various soda solution concentrations tested. Indeed, it was noted that at the end of one hour at least 90% of fluorides were desorbed. The optimum conditions for desorption were 60 min of contact and a soda concentration 6 M.Regenerated ashes were placed again in contact with drainage waters containing fluoride concentrations of 2.50 mg/L. A new sorption of fluorides was noted. This result led us to study the effect of cycle numbers on the adsorption-desorption of fluorides in relation to the effectiveness of regeneration. A histogram of the results demonstrated that the quantities adsorbed and desorbed for the same cycle were practically equal for the eight cycles carried out, thus the effectiveness of ash was practically the same

Desalination of brackish water and reverse osmotic retentate using nanofiltration membranes: effects of TMP and feed concentration on the treatment

This is an Accepted Manuscript of an article published by Taylor & Francis in Desalination and water treatment on 2017, available online: http://doi.org/10.5004/dwt.2017.20841[EN] Nanofiltration (NF) membrane with low-pressure operating conditions and high flux permeability seems to be an attractive alternative for water softening and desalination. In order to study the performance of NF membrane on treating real brackish water, with mixture of mono and divalent ions, two commercial flat sheet nanofiltration membranes (NF90 and NP030) were used. The experiments were carried out with transmembrane pressure from 4 to 12 bar with three brackish waters having different ions concentrations. The results obtained showed that the high hydrophilicity of NF90 and its small pore size were the main advantages that allow this membrane to have the highest permeability and salt rejection for both mono and divalent ions in comparison with NP030. The results also showed that the permeate flux and rejection increased linearly with increasing in TMP. NF90 membrane performance was assessed by studying the effect of feed ions concentration. It was observed that the permeate flux decreased with increasing in salts concentration due to concentration polarization. Additionally, the study of scaling problem showed that its contribution in permeate flux decreasing was not as much significant and that the membrane permeability, recovered after the cleaning step, was 90%. In the other hand, the salts rejection of NF90 remained high (more than 80%) for all the studied concentrations due to its separation mechanism.This work was carried out with the support of scholarship awarded by the National Center for Scientific and Technical Research (CNRST) - Morocco.Mountadar, S.; Carbonell Alcaina, C.; Lujan Facundo, MJ.; Ferrer-Polonio, E.; Soler Cabezas, JL.; Mendoza Roca, JA.; Tahiri, S. (2017). Desalination of brackish water and reverse osmotic retentate using nanofiltration membranes: effects of TMP and feed concentration on the treatment. Desalination and Water Treatment. 87:68-75. doi:10.5004/dwt.2017.21312S68758

Traitement d’un effluent industriel fluoré

The characterization of the industrial effluent has been carried out. This wastewater is strongly acid, salty, hard and concentrated mainly in fluorides, orthophosphates, sulfates and in metal compounds. The treatment of this effluent, mainly the defluoridation was realized by coagulation-decantation. This technique consists in precipitating fluorides, by using lime and calcite. The physico-chemical parameters that influence the treatment have been studied. The results show that it is possible to eliminate more than 85% of fluorides, 84% of orthophosphates, 45% of sulfates, 90% of Cd, 77% of the Co, 93% of Cu, 96% of Fe, 99% of Pb and 99% of Zn.La caractérisation de l’effluent industriel a été effectuée. Il en ressort que cette eau usée est très acide, saline, dure et chargée principalement en fluorures, orthophosphates, sulfates et en éléments métalliques. Le traitement de ce rejet concernant principalement la défluoruration a été réalisé par coagulation- décantation. Cette technique consiste à précipiter les fluorures, en utilisant la chaux et la calcite. Les paramètres physicochimiques qui influencent le traitement ont été étudiés. Les résultats montrent qu’il est possible d’éliminer plus de 85 % des fluorures, 84 % des orthophosphates, 45 % des sulfates, 90 % du Cd, 77 % du Co, 93 % du Cu, 96 % du Fe, 99 % du Pb et 99 % du Zn

Étude de la dénitratation par des adsorbats naturels (chitine et chitosane)

This study relates to the preparation of three natural adsorbent materials: rough chitin, chitin and chitosane extracted starting from shellfish shrimps, in order to study the elimination of nitrates from a synthetic effluent. The process of nitrates adsorption on these supports is described using the models of Freundlich and Langmuir in its linearized form. The study of the influence of some physicochemical parameters on the process of denitratation was undertaken. And in order to approach the operational conditions of denitratation water, we were also interested to study the influence of the presence of counter ions on the elimination capacity of the ions nitrate on the chitosane. Beside, we sought the optimum conditions for desorption by using a basic solution.Cette étude concerne la préparation des trois matériaux adsorbants naturels : chitine brute, chitine et chitosane extraites à partir de crustacés, en vue d’étudier l’élimination des nitrates à partir d’un effluent synthétique. Le processus d’adsorption des nitrates sur ces supports est décrit à l’aide des modèles de Freundlich et Langmuir dans leur forme linéarisée. L’étude de l’influence de certains paramètres physico-chimiques sur le processus de dénitratation a été entreprise. Et afin de s’approcher des conditions de dénitratation des eaux, nous nous sommes intéressés également à l’étude de l’influence de la présence des contre-ions sur la capacité d’élimination des ions nitrate sur le chitosane. Par ailleurs, nous avons cherché les conditions optimales de désorption en utilisant une solution basique

Desalination by cooling and freezing of seawater and groundwater: thermodynamic aspect of the liquid-solid equilibrium

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