Oxydation d'un acide humique aquatique par le bioxyde de chlore. Incidences sur une post-chloration et sur un traitement au charbon actif

Cette étude de laboratoire a eu pour but d'examiner la réactivité du bioxyde de chlore sur un acide humique d'origine aquatique en solution aqueuse et en milieu neutre (pH = 7,5) et de préciser en particulier l'incidence d'une préoxydation chimique au CIO2 sur les potentiels de formation de composés organohalogénés (trihalométhanes, acides dicloroacétique et trichloroacétique, chlore organiquement lié) et sur l'adsorbabilité du carbone organique sur charbon actif.Les résultats obtenus montrent que radian du bioxyde de chlore sur racide humique Pinail à l'obscurité, conduit à des faibles abattements du carbone organique dissous (< 10 %) et de l'absorbance UV à 254 nm (de l'ordre de 30 %) et conduit à des productions potentiel es en composées organohalogénés très nettement inférieures à celles formées par chloration. De plus, une préoxydation chimique au bioxyde de chlore permet de diminuer d'une manière très significative la production de composés organohalogénés au cours d'une post-chloration et semble améliorer l'adsorbabllité du carbone organique sur charbon actif.L'oxydation de l'acide humique par le bioxyde de chlore s'accompagne, par ailleurs, de la formation de chlorites (0,65 mg/mg de CIO2 consommé) qui peuvent ensuite être oxydés en chlorates au cours d'une post-chloration ou réduits en chlorures par un traitement au charbon actif.Enfin, les résultats obtenus font apparaître que le mécanisme d'oxydation de composés organiques parle bioxyde de chlore en présence de la lumière ainsi que les interactions entre le bioxyde de chore, les chlorites, la matière organique et le charbon actif méritent d'être plus précisément étudiés.Chlorine dioxide has drawn much recent attention as an alternative disinfectant and oxidant for drinking water to replace chlorine because of its powerful disinfecting ability and its limited capacity to produce organohalogenated compounds. However, the use of chlorine dioxide leads to chlorite (ClO2-) and chlorate (ClO3-) as inorganic oxidation by-products which are reported to have toxic effects on humans. The reactions of ClO2 with simple organic compounds (phenols, aliphatic and aromatic amines...) produce polar compounds such as quinone, ketones, aldehydes and carboxylic acids while oxydation by-products of dissolved organic matter of surface waters (in particular humic substances) are largely unknown. Consequently, the aim of this work was to obtain a better understanding of the effects of the use of chlorine dioxide in drinking water treatment To this end, experiments were carried out with dilute aqueous solutions of an isolated aquatic humic acid (Pinail humic acid, PHA) and the objectives of this present study were :- To evaluate the ClO2 demand and to determine the productions of chlorite, chlorate and of organohalogenated compounds such as trihalomethanes (THMs), dichloroacetic and trichloroacetic acids (DCA, TCA) which are the main organohalogenated products formed by chlorination.- To show the effects of chlorine dioxide preoxidation on organic halide formation potentials (postchlorination) and on the removal of dissolved organic carbon (DOC) by activated carbon. In addition, reactions of chlorite with chlorine or with activated carbon were also examined.EXPERIMENTALPniail humic acid was dissolved in phosphate buffered ultra-pure water (pH = 7.5). Oxidation and adsorption experiments were carried out in headspace-free bottles, at 20 ± 1 °C and in the dark. Stock solutions of chlorine dioxide (4-6 g l-1) and of chlorine (6-10 g l-1) were prepared in the laboratory and titrated by iodometry. Residual chlorine dioxide concentration in PHA solutions was determined by spectrophotometric measurement at 360 nm and by two colorimetric methods : the chlorophenol red and the ACVK methods. Concentrations of DOC and of total organic chlorine or halogen (TOCI, TOX) were measured using a DOHRMANN DC 80 carbon analyser and a DOHRMANN DX 20 A TOX analyser equipped with a microcoulometric cell, respectively. THMs, DCA and TCA were determined by a gas chromatograph equipped with a 63 Ni electron capture detector after extraction by pentane for the THMs, and methylation in ether phase for DCA and TCA. Inorganic chlorine species were analysed by HPLC with a UV detector (ClO2-) or by chromatography (Cl-, ClO3-).RESULTS• Oxidation of PHA by ClO2The results showed that PHA consumed about 2 mg of ClO2/mg of DOC after a reaction time of 24 hours (fig. 1) and that there is a rapid consumption of ClO2 during the first 30 minutes of the reaction (fig. 2) Oxidation by ClO2 had no effect on DOC concentration (DOC removal : < 10 %) and led to a significant decrease (about 30 %) of the UV-absorbance at 254 or 270 nm (fig. 1 and 2), and to productions of ClO2- (0,65 mg of ClO2-/mg of ClO2 consumed) which were independant of the applied oxidant dose and of the reaction time.Furthermore, after a 72 hour reaction time in the dark, chlorine dioxide ([ClO2]0 = 5 mg l-1, [PHA]0 = 5 mg l-1, DOC = 2,6 mg l-1) produces very small amounts of chloroform (< 5 µg l-1), DCA (5 µg l-1) and TCA (5 µg l-1) and organochlorinated compounds (TOCl : 36 µg/mg DOC) compared to chlorine oxidation (tableau 1). However, in the presence of sunlight, ClO2 is rapidly photodecomposed (fig. 3) and the photodegradation products of ClO2 allow bromide oxidation (fig. 11) and lead to higher productions of organohalogenated compounds such as THMs (fig. 4).• Chlorine dioxide preoxidation followed by chlorinationAs shown in figure 5, chlorine dioxide preoxidation reduces the production of organohalogenated compounds and the chlorine demand during postchlorination. For a preoxidant dose corresponding to the ClO2 demand of PHA, the decrease in the formation potentials of CHCl3, DCA, TCA and TOCl was about 40-50 %. These results confirm the similarity of the action of chlorine dioxide and chlorine on aromatic structures which have high electron density carbons and which constitute probably the most reactive precursors of organohalogenated by-products.As far as chlorite concentration is concerned, the results showed that chlorite formed during the preoxidation step was completely oxidized to chlorate during postchlorination, under the experimental conditions used in this study (chlorine dose : 40 mg l-1; contact time : 24 or 72 hours). Because of the reactions of chlorine eh chlorine and with residual chlorine dioxide, a small increase in the chlorine demand was observed when PHA solutions were heavily preoxidized (fig. 5).• Chlorine dioxide preoxidation followed by activated carbon treatmentBatch experiments were carried out with a powdered activated carbon (PAC, granulometry : < 80 µm) which was obtained by crushing a commercial granular activated carbon (CECA 40,12 x 40 mesh). Once equilibrium was achieved (contact time : 10 days), adsorption isotherms indicated that chlorine dioxide preoxidation increases the absorbability of DOC on activated carbon (fig; 4tableau 2). Furthermore, chlorite in oxidized PHA solutions was reduced by PAC to chloride. The capacity of CECA 40 activated carbon for ClO2- reduction to Cl- was about 170 mg ClO2-/g of PAC (fig. 7). Other experiments showed that chlorite may react with specific surface groups on PAC to produce inorganic carbon (fig. 7) and with PHA only in the presence of PAC as shown the DOC and UV-absorbance curves in figure 8 and the increase of TOX concentration in the liquid phase in figure 9. Thus the observed increase in DOC absorbability on PAC after a chlorine dioxide preoxidation may be attributed to cheminal interactions between PAC, chlorite, residual chlorine dioxide and adsorbed organic matter and requires further study

L'inhibition de l'entartrage par les eaux géothermales du sud tunisien. Étude sur site

Une nappe d'eaux fossiles à grande profondeur (800 à 2 700 mètres) a été mise en exploitation dans le Sud-Tunisien pour alimenter une usine d'osmose inverse située à Gabès ayant une production de 15 000 m3 /jour, afin de lutter contre la désertification par irrigation et d'assurer le chauffage de serres pour la production de primeurs. La grande dureté (TH de l'ordre de 100 à 140 °F) de ces eaux géothermales a pour conséquence le colmatage rapide des conduites de distribution : 40 à 50 tonnes de tartre par forage, constitué essentiellement de carbonate de calcium, précipitent chaque année. Ce tartre est constitué d'aragonite comme le montrent la microscopie électronique à balayage et la diffraction des rayons X. Une technique électrochimique, la chronoélectrogravimétrie, permet d'étudier l'inhibition de l'entartrage par des composés de la famille des phosphates inorganiques, des phosphonates organiques et des polycarboxylates. La concentration efficace de chacun de ces inhibiteurs agissant par effet de seuil a été déterminée : elle est de l'ordre de 1,1 à 1,5 mg.l-1 pour l'eau du forage de EL HAMMA. Un essai sur le site de EL MANSOURA a été effectué en privilégiant un inhibiteur produit industriellement dans le Sud-Tunisien, le triphosphate de sodium. A la concentration de 1 mg.l-1 il évite l'entartrage du système de refroidissement de type cascade - piscines et des conduites de distribution.Deep fossil waters are used in Southern Tunisia (Gabès, Kébili, Tozeur) for the Gabès reverse osmosis plant, which delivers a flow rate of 15 000 m3 /day for irrigation and for heating greenhouses used for the production of early fruits and vegetables. Drilling depths vary between 800 and 2 700 meters. Water emerges under a pressure of ca. 20 bars and has a temperature between 50 and 73 °C. Mean flow rate is 7 800 m3 /day.Intake water at the Gabès plant has a salinity of 3.3 g.l-1 ; after reverse osmosis the salinity is less than 0.1 g.l-1. Water used for irrigation has to be cooled. Geothermal waters are characterized by high concentrations of calcium, magnesium, sulphate and chloride. Bicarbonate anions are present at limited concentrations (approx. 2.10-3 mol.l-1) that are, however, sufficient for the formation of large quantities of scale - 40 to 50 tons per year for each drilling. At the outlet of the drill hole, pressure decreases strongly, liberating carbon dioxide to the atmosphere. Water pH increases and the following equilibrium is displaced to the right, with scale precipitation : Ca2+ + 2HCO3-CO2 (g) + CaCO3(s) + H2OScale precipitation has two consequences :- the plugging of distribution pipes: a 85% reduction of the pipe has been observed, after four years, for an initial diameter of 15 cm; - water cooling installations such as cooling towers or pool systems are blocked by large quantities of scale, which have to be removed regularly. Scales have been analysed through inductively coupled plasma spectroscopy and thermogravimetry: calcium carbonate may represent, depending on the origin of the drilling water, 60 to 95% by weight of the solid. Iron oxides, silica, calcium phosphate and aluminum are present. Scanning electron microscopy and X-ray diffraction show that calcium carbonate precipitates in the form of aragonite. This is due to two reasons: the temperature at the drilling outlet is greater than 60 °C and the high magnesium concentration favours aragonite formation. Scale inhibition is possible through the use of certain chemicals such as phosphates, organic phosphonates and polycarboxylates.Chronoelectrogravimetry was used as the experimental method to determine the inhibitor concentration able to suppress scale precipitation. Dissolved oxygen is electrochemically reduced on a gold electrode; hydroxide anions are produced in the vicinity of the electrode and calcium carbonate precipitates according to:4Ca2+ + 4HCO3- + O2 + 4e -> 4CaCO3(s) + 2H2OThe gold electrode is deposited on the quartz disk of a recording microbalance. The electrode is polarized at - 1 V/SCE with a three-electrode potentiostatic device and the weight of CaCO3 deposited is recorded versus time.Four inhibitors have been studied :- PERMATREAT 191, which is the sodium salt of aminotris(methylenephosphonic) acid N(CH2COONa)3; - a proprietary organic phosphonate with high resistance to chlorine oxidation (DEQUEST 6004) ; - phosphonobutanetricarboxylic acid (DEQUEST 7000, BAYHIBIT-AM) ; - a copolymer of acrylic acid and acrylamidopropanesulfonic acid (FERROPHOS 5248). Breakthrough effects are obtained in the case of EL HAMMA water for the following concentrations: PERMATREAT 191: 1.1 mg.l-1 ; DEQUEST 6004: 1.5 mg.l-1 ; DEQUEST 7000: 1.3 mg.l-1 ; FERROPHOS 5248: 1.4 mg.l-1. These concentrations are low and, as a consequence, these inhibitors can be used for antiscale action even with high water flow rates.A field experiment was carried out on the EL MANSOURA drilling where water is cooled in three pools (input water: 5 184 m3 /day, temperature: 60 °C). For economical reasons the chosen inhibitor was sodium triphosphate Na5 P3 O10, which is produced industrially in Southern Tunisia. By chronoelectrogravimetry it has been shown that, with EL MANSOURA water, a breakthrough effect is obtained with a sodium triphosphate concentration of 0.75 mg.l-1.A dosing pump was used to inject sodium triphosphate in such a way that the inhibitor concentration would be 1 mg.l-1 in one of three pools, the two others not being treated. After four months a scale deposit of 23 cm was obtained in the untreated pools and the pipe diameter was reduced by 39%. In the treated pool scale deposit was not observed and the pipe diameter remained unchanged. In the untreated basins, examination of scale with electron scanning microscopy revealed that it was aragonite; in the treated basin, the precipitate was amorphous and an X-ray diffraction pattern with no characteristic bands was obtained.Some algal development was observed in the pool due to phosphate addition but this development was not a nuisance after the four month period. However, it could be suppressed by the use of an organic phosphonate or polycarboxylate as scale inhibitor

Les stenoses tracheales acquises: Experiencede l’hopitalhabibthameur

Introduction: Acquired tracheal stenoses represent rare but serious disease. They are often secondary to inappropriate management of patients under artificial ventilation. The goal of this study is to evaluate our results in the management of these stenoses and to assess the benefits and the limits different therapeutic means.Materials and methods : We carry a retrospective study about 18 cases of acquired tracheal stenoses treated and followed in our department between 1999 and 2006. Initial endoscopic and radiological explorations have been performed in all cases. Treatment of the stenoses was medical, endoscopic and/or surgical. Follow-up was clinical and endoscopicwith a mean period of 22 months.Results : All patients were victims of pathology needing intubation. Tracheotomy was performed after intubation in 50% of cases after a mean period of 12 days (5-20 days). Dyspnea and dysphonia were the major functional symptoms. Initial endoscopy showed a double tracheal stenosis in one case. Stenoses were initialy fibrous in 72.2% of cases and evolutivein 27.8% of cases. CT scan performed in 12 cases and MRI in 2 others allowed to better study stenosis characteristics. RFE was performed in 6 cases and showed an obstructive syndrome in all of them. All patients received medical treatment. Before a definitive treatment, dilatation was performed in 11 cases (61%) and stenting in one other (5.6%). Laser diode therapy was used in 11 patients including 2 cases having postoperative recurrence. Tracheal resection and reconstruction wasperformed in 11 cases (61%) having extensive and severe stenoses with involvement of tracheal cartilage.Conclusion : Acquired tracheal stenoses represent a serious complication with high morbidity. If tracheal resection and reconstruction remains the gold standard treatment, endoscopy represents now a major alternative in their management. Nevertheless, prevention should be considered, given that most stenoses are iatrogenic due to traumatic or prolongedintubations

Otospongiose : a propos de 149 cas

Introduction : L’otospongiose est une ostéodystrophie de la capsule otique se traduisant par une surdité de transmission ou plus rarement une surdité mixte d’apparition progressive. Le but de notre travail est d’analyser les caractéristiques épidémiologiques, cliniques, paracliniques et comparer les résultats en fonction de l’âge, du stade de l’ostéodystrophie, de la technique chirurgicale et de la prothèse.Patients et méthodes : notre étude est rétrospective portant sur 124 patients (149 oreilles) colligés sur une période de 9 ans (2000-2008).Résultats : notre population a comporté 86 femmes et 38 hommes. La moyenne d’âge à l’intervention était de 39,82 ans. La surdité était bilatérale dans 61,3% des cas et unilatérale dans 38,3%. Les seuils moyens préopératoires de la conduction osseuse et aérienne étaient respectivement de 17,33 dB et 52,52 dB, le rinne moyen était de 35,19 dB. La tomodensitométrie a été réalisée chez 63 patients. On a réalisé 21 platinectomie totale, 24 platinectomie partielle et 101 platinotomie calibrée. Selon la classification de Portmann, on a trouvé une répartition sensiblement égale entre les stades II, III et IV. On a utilisé un piston téflon 6/10 mm dans 119 cas et 4/10 mm dans 27 cas. Le rinne moyen postopératoire était de 15,95 dB. a 1 an, le rinne était de 14,81 dB avec un résultat satisfaisant de 94,2%.Conclusion : Il ressort de notre travail que certains facteurs semblent prédictifs de bons résultats et qui sont : le sexe féminin, l’âge &lt;50 ans, le stade chirurgical&lt; stade IV, la platinotomie, et le piston 0,4 mm.Mots clés : otospongiose, conduction osseuse, conduction aérienne, platinotomie, platinectomie.Objective : Otosclerosis is a common disorder of the otic capsule characterized by the presence of a progressive conductive or rarely mixed hearing loss. The aims of this study were to analyses the epidemiologic, clinical, paraclinical characteristic and compare our results according to age, stage, surgical technique and prosthesis. Patients et méthodes : Our study is retrospective about 124 patients (149 ears) in the period of 9 years (2000-2008).Results: Our population included 86 female and 38 male patients. mean age at intervention time was 39,82 years. The hearing loss was bilateral in 61,3% of cases and unilateral in 38,3%. The bone and air conduction threshold was 17.33 dB and 52,52 dB, the air-bone gap was 35,19 dB. The CT scan was realized in 63 patients. We have realized 21stapedectomy, 24 partial stapedectomy and 101 stapedotomy. In accordance with Portmann classification, the distribution between II, III and IV stages was almost equal. We used 6/10 mm Teflon piston prosthesis in 119 cases and 4/10 mm in 27 cases. The postoperative air-bone gap was 15,95 dB. after 1 year, the air-bone gap was 14,81 dB with a satisfying results in 94,2%.Conclusion: it seems that some factors are predictive for good results like a female sex, age&lt;50 years, stage&lt; stage IV, platinotomy and piston 4/10 mm.Keyswords : otosclerosis, bone conduction, air conduction, stapedectomy, stapedotom

Maladie De Forestier Revelee Par Une Dysphagie A Propos De Deux Cas

La maladie de Forestier ou hyperostose ankylosante vertébrale engainante est un désordre musculo-squelettique non inflammatoire responsable d\'une ossification ligamentaire essentiellement du ligament longitudinal antérieur. Elle touche de préférence l\'homme de plus de 50 ans. La dysphagie est un symptôme rarement observé dans l\'évolution de la maladie de Forestier. Nous rapportons deux cas révélés par une dysphagie isolée. Il s\'agit de deux hommes âgés de 50 et 56 ans. Le diagnostic était radiologique. La radiographie standard du rachis a objectivé des ostéophytes du rachis cervical. Le transit oesogastroduodénal a montré une compression modérée de l\'oesophage cervical. Le traitement était médical reposant sur les anti inflammatoires non stéroïdiens et les antalgiques. Le traitement chirurgical est indiqué dans les cas de dysphagie sévère. Keywords: maladie de Forestier, hyperostose vertébrale, dysphagie. Journal Tunisien d\'ORL et de chirurgie cervico-faciale Vol. 18 2007: pp. 55-5