FR :

Le chitosane est une substance biodégradable d’origine naturelle obtenue par la désacétylation de la chitine, qui se trouve dans l’exosquelette des crustacés. Une de leurs applications plus récentes est le traitement des eaux. Pour favoriser l’utilisation du chitosane des exosquelettes de crustacés (crevettes, crabes, etc.) dans le traitement des eaux usées, les procédés de transformation du chitosane ont été simplifiés et optimisés. Dans la présente étude, les crustacés de crevette grise (Palaemodiae) ont été utilisés pour extraire le chitosane. Les expériences ont porté sur les effets des interactions de la concentration de la solution alcaline, du temps et de la température de réaction sur le degré de désacétylation. En plus de simplifier le processus de transformation de trois à deux étapes, les résultats montrent l’influence de la concentration d’hydroxyde de sodium (7,5‑ 12,5 M), du temps de réaction (30 ‑ 180 min) et de la température (80 ‑ 120 ^oC) sur le degré de désacétylation. La méthode de la spectroscopie infrarouge en film mince a été utilisée pour analyser le degré de désacétylation du chitosane. Un degré de désacétylation de 90 % a été atteint avec une concentration de la solution alcaline de 12,5 M, un temps de réaction de 120 min et une température de 110 ^oC. Par ailleurs, en réduisant le nombre d’étapes de transformation et la consommation de réactifs, le procédé développé est plus économique et a une meilleure performance environnementale.

EN :

Chitosan is a natural biodegradable biopolymer produced from chitin, a polysaccharide derived from the shells of shrimp, crab and lobster. The development of commercial applications of chitin and chitosan in different fields such as biomedicine, nutrition, food processing, agriculture, cosmetics, and wastewater treatment has rapidly expanded in recent years. This paper investigates the hydrothermal production of chitosan from the carapace of gray shrimp (Palaemodiae) for use as a coagulant in wastewater treatment.

To obtain chitosan from shrimp exoskeletons, they were treated following two different steps. The first step was the demineralization of the shrimp’s exoskeleton, where calcium was removed using dilute HCl. The second deacetylation step completely dissolved the shrimp exoskeleton using a NaOH solution. In both steps, the ratio between solution digestive and exoskeleton was studied (1:10 (w:v)). For the demineralization process, the concentration of HCl was varied from 0.5 to 3.5 M in 0.5 M intervals at constant temperatures of 25^oC and 50^oC. The comparison of the results using these two temperatures indicated that the most favourable demineralization occurred after 6 h at 25^oC and after 2 h at 50^oC at a HCl concentration of 2 M. In this case, it was not necessary to use a HCl concentration greater than 2 M due to the fixed reaction time. When the HCl solution was heated, the reaction time of the demineralization process was reduced by a factor of three compared to that when room temperature HCl was used under the same conditions. Moreover, this reaction followed a pseudo-second-order equation with approximate rate constant of 2.38 L g^‑1 min^‑1 at 25^oC in 1.5 M HCl.

The effectiveness of the transformation to chitosan depends on the interaction among the sodium hydroxide concentration, the reaction time and the temperature at which the deacetylation process occurs. The influence of the concentration of the alkaline solution, the reaction temperature, and the reaction time on the degree of deacetylation (DD) was investigated. The DD obtained was quantitatively analyzed by thin film infrared spectroscopy (IR). Film thickness was measured by using a micrometer with the smallest possible unit measurement count of 0.01 mm. First, exoskeletons were exposed to NaOH concentrations of 7.5 M, 10 M and 12.5 M for 60 min at various temperatures ranging from 60^oC to 120^oC at intervals of 20^oC. Second, the reaction time was changed from 30 to 180 min at 100^oC at 30 min intervals using the same NaOH concentrations previously mentioned. The results show that the factors that influence the DD values were the reaction temperature and the concentration of NaOH. However, based on these experiments, the concentration of NaOH influences the DD values the most. The DD values of chitosan production began to reach a constant level when the reaction temperature was greater than 100^oC. As a result, after one hour at 110^oC, chitosan production was obtained with different DD values of 60%, 67%, and 78% at NaOH concentrations of 10 M, 11.25 M and 12.5 M respectively. Nevertheless, chitosan could not be formed at 7.5 M NaOH, even though the reaction time was 3 h. Furthermore, when the reaction time was longer than 120 min, the DD values of chitosan increased slowly.

Therefore, the optimum conditions required for the deacetylation production of chitosan from gray shrimp carapace (DD of 90%), to be applied in wastewater treatment, are as follows: the exoskeleton should be exposed to a solution of 12.5 M NaOH (45%) for 2 h at 110^oC. This product is generally termed chitosan when it has greater than 65% of the acetylic groups removed.

By diminishing the number of steps and reducing the chemical reagents needed, this study demonstrates the economical and environmental advantages of using chitosan as a coagulant to treat wastewater.

FR :

Le traitement à la pression atmosphérique de solutions aqueuses d’urée et de thiourée par plasma d’arc rampant en atmosphère d’air humide conduit à la dégradation totale de ces composés. Les cinétiques globales d’ordre nul ont des constantes voisines proches de 3•10^‑6 s^‑1. Le procédé met en jeu les espèces actives créées dans la décharge, les radicaux OH et NO, responsables des caractères chimiques principaux du plasma : oxydation du fait de la présence de OH (E°_OH H2O =  2,85 V/ENH) et acidification, provenant de la formation d’acides nitreux et nitrique en solution. Ces résultats sont relatifs à des molécules modèles, mais suggèrent l’extension du procédé à la dégradation de molécules toxiques et d’effluents industriels soufrés.

EN :

Electric discharges in humid air (i.e., a gliding arc discharge at atmospheric pressure and quasi-ambient temperature) are considered in the context of evaluating new techniques for pollution abatement. An electric discharge in a gas under specific conditions gives rise to a plasma, which involves activated gas species with enhanced reactivity. The main chemical properties of a discharge in humid air are attributed to NO and OH radicals formed in the discharge, which are able to react with solutes at the plasma/liquid interface. These activated species are formed in advanced oxidation processes and are respectively responsible for acid and oxidizing effects in the target solution: NO gives rise to nitrous and nitric acids, and OH is strongly oxidising [E°(OH/H₂O) =  2.85 V/NHE].

To examine the degradation power of the plasma treatment on molecules of the same family and to evaluate the ability of the gliding arc system to oxidize sulphur-containing solutes (2 x 10^‑3 M) in batch conditions, aqueous urea and thiourea were selected as suitable target solutions. The solutes were completely degraded within 180‑200 minutes of treatment and the concentrations decreased linearly with increasing exposure times in the discharge. This trend accounts for overall zero-order kinetic schemes with the relevant rate constants of k_urea = 5.28 x 10^‑6 s^‑1 and k_thiourea = 2.03 x 10^‑6 s^‑1.

The evolution of solutes with time was followed by total organic carbon (TOC) measurements for urea, and by the conductometric titration of the sulphate ions formed in the case of thiourea. Spectrophotometric measurements of the treated solutions at the solute absorption peaks were found to be unsuitable for analysis purposes due to the formation of nitrite/nitrate ions which absorb in the same wavelength range.

The extension of a gliding arc system from the laboratory level to an industrial scale for pollution abatement of industrial effluents is considered.

FR :

La spéciation physique des métaux rejetés par les effluents d’eaux usées municipales est fortement influencée par les conditions physico-chimiques des eaux réceptrices. Les zones de rejet d’effluents municipaux sont des milieux riches en matières organiques où les métaux sont susceptibles d’être fortement complexés et où la présence de colloïdes peut modifier la bioaccumulation et la biodisponibilité des métaux. La distribution de métaux (Al, Cd, Cu, Fe, Mn, Ag et Zn) a été déterminée dans les fractions dissoute (< 0,45 µm), colloïdale (< 0,45 µm et > 10 kDa) et perméable (ultrafiltrée < 10 kDa) à différents sites le long du panache de dispersion de l’effluent municipal majeur de la ville de Montréal. Les concentrations de métaux sous formes colloïdale et perméable sont généralement élevées près du point de rejet de l’effluent étudié. À cause du type de traitement des eaux usées utilisé par la ville de Montréal, ce rejet est une source importante de fer et plus de 70 % du fer dissous se retrouve sous forme colloïdale. Parmi les métaux traces étudiés, l’Ag, suivi du Cu, étaient les plus fortement associés aux colloïdes près du point de rejet de l’effluent. Les colloïdes, présents dans la phase dite dissoute ou filtrable, peuvent influencer différemment le transport et le devenir des métaux rejetés. La proportion colloïdale diminue toutefois rapidement comparativement à celle perméable lors du mélange des eaux usées avec les eaux réceptrices, ce qui semble indiquer que cette fraction a une importance limitée dans le transport à longue distance des métaux provenant de l’effluent. Les résultats de cette étude précisent le rôle des colloïdes dans le devenir géochimique des métaux lors du mélange des eaux usées de l’effluent avec les eaux réceptrices. L’étude souligne donc l’importance d’évaluer la spéciation physique des métaux dans une étude d’impact environnemental d’une zone de rejet urbain.

EN :

The physical speciation of metals contained in municipal effluents is significantly influenced by the physical and chemical conditions of the receiving water. Waters in the immediate area of an effluent outfall are rich in organic matter; metals are largely complexed and the abundance of colloids can modify metal bioavailability and bioaccumulation. The distributions of aluminum (Al), cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), silver (Ag) and zinc (Zn) were determined in the dissolved (< 0.45 µm), colloidal (< 0.45 µm and > 10 kDa) and permeable fractions (ultrafiltered < 10 kDa) at different points within the dispersion plume of the major effluent from the Montreal treatment plant. Concentrations of colloidal and permeable metals were typically high near the effluent outfall. Because of the treatment process used by the City of Montreal, this effluent is a major source of Fe and more than 70% of dissolved Fe is present in colloidal form. Of the metals studied, Ag was most associated with colloids near the outfall, followed by Cu. Colloids found in the so-called dissolved or filterable phase can influence the transport and fate of discharged metals in different ways. The colloidal proportion, however, declines rapidly during the mixing of wastewater with receiving water, which seems to suggest that this fraction, by its lower abundance, could have limited influence on the long-range transport of metals released by the effluent. Our results provide information on the role of colloids in determining the geochemical fate of metals contained in wastewater once they are released to the receiving environment. The study highlights the importance of physical speciation in the assessment of the environmental impact of urban effluents on discharge areas.

FR :

Cet article présente un débitmètre à ultrasons conçu en tant que capteur intelligent pour la mesure des écoulements en surface libre ou en conduites fermées. Ce type de débitmètre peut être utilisé pour des applications industrielles ou de gestion de l’eau. Il répond à la forte demande des autorités de supervision des ressources en eau dans les régions semi-arides d’agriculture irriguée. Un état de l’art et les principes généraux des mesures de débits de liquide par ultrasons sont donnés. Le débitmètre original proposé utilise le principe de la mesure des délais entre les impulsions envoyées vers l’amont et vers l’aval dans le fluide. L’approche repose sur la mesure de la différence du temps de transit des ondes acoustiques sur une ou plusieurs cordes de mesure, réparties sur un intervalle suffisant, de manière à assurer la précision requise. Cette méthode permet une véritable intégration du profil des vitesses, ce qui assure une meilleure précision. La vitesse du son dans le fluide est éliminée des calculs grâce à l’utilisation des temps de transmission réciproques. Les calculs de débit sont assurés par un micro-contrôleur. Les calculs théoriques et les technologies proposées ont donné lieu à la réalisation d’un prototype expérimental. Une première application de ce débitmètre à ultrason est réalisée en laboratoire en conduite fermée dans une installation d’essai comportant une seule paire de transducteurs à ultrason. Une seconde application expérimentale est menée sur un banc d’essai comprenant un canal artificiel de forme trapézoïdale de dimensions géométriques bien déterminées avec une pente variable. Ces tests ont permis de vérifier la précision de l’appareil et de valider les techniques et les principes mis en oeuvre dans la conception du débitmètre.

EN :

Measuring fluid flow is one of the most important measurements in the industrial fields of process control and water management. In fact, it may well be the most frequently measured process variable. Other measurements are water temperature, pressure and level. There are two types of ultrasonic flow meters used for discharge measurement: the Transit Time and Doppler flow meters. The first type is widely applied to fluid flows in pipes and open channels and is sensitive to suspended solids or air bubbles in the fluid. The second type is more popular and less expensive, but is not considered as accurate as the transit time flow meter. In this work, the Transit Time flow meter is discussed and applied, for the first time, to discharge measurements in pressurized conduits in a laboratory setting, and to open channel irrigation.

We used the Transit Time method, which is based on the dependence of the velocity of an ultrasonic signal in a given medium on the velocity at which this medium is itself flowing. Therefore, pressure disturbances of small magnitude are propagated through a fluid at velocity that is the sound velocity relative to the fluid. If the fluid also has a velocity, the absolute velocity of the pressure disturbance propagation is the algebraic sum of the two. This ultrasonic method uses measurements of the transit time of high frequency energy pulses between one or more pairs of transducers to determine the flow rate of the liquid. The relationship between the measured transit time of an ultrasonic pulse and the average velocity along the pulse path is well described in this paper.

This paper presents the state of the art of the general principle of liquid flow measurements by ultrasonic methods and the problems associated with such measurements. Using the ultrasonic transit time approach, we designed an ultrasonic flow meter according to a smart sensors concept, for the measurement of irrigation water flowing through pipelines or open channels. The new flow meter works on the principle of measuring time delay differences between sound pulses transmitted upstream and downstream in the flowing liquid. The speed of sound in the flowing medium is eliminated as a variable because the flow rate calculations are based on the reciprocals of the transmission times. The transit time difference is digitally measured by means of suitable microprocessor controlled logic.

We initially carried out experimental tests in closed conduits. The installation consisted of three tanks (storage tank, volumetric tank or etalon tank, and supply tank), a pipeline with the primary intelligent flow meter devices being tested, an ultrasonic level-meter and a volumetric flow meter for calibration. The secondary devices included a pump, valves for controlling the apparatus and a level gauge. This apparatus enabled the calibration of flow meters for various volumetric flows. The data can be gathered with a fixed sampling time and are stored and/or transmitted to the computer system, which enables not only data storage, but also the calculation of the time of measurement at a specified level of accuracy and volumetric flow rate.

The laboratory experiment was carried out to facilitate hydraulic studies with a flow rate ranging from 1.25 L/s to 50 L/s. The steel pipeline had a diameter of 100 mm. The flow rate is calculated and the characteristics of calibrated flow meter are plotted. The report from each measurement is shown on the monitor and may be printed. The flow meter is connected to a straight section of pipe that is run at least 15 pipe diameters upstream of the sensor without obstructions, and a minimum of 10 pipes diameters downstream without obstructions (locating a flow meter too close to a flow disturbance may cause a systematic error).

In addition to laboratory tests, the flow meter has also been evaluated in open channels.

Open channel flow is defined as flow in any channel where the liquid flows on a free surface, is not under pressure, gravity is the only force causing the flow and a continuous and progressive decline in water surface elevation occurs as the flow moves downstream. Examples of open channel flows are rivers, streams, creeks, and other uncovered conduits.

Open channel flow measurement is used in many applications: water supply networks, allocation of water for irrigation and agriculture, sewage treatment plants, etc. The discharge measurements in open channels may be computed by means of a rating curve, which is used to convert records of water level readings into flow rates. Because many phenomena can cause the rating curve to change, it must be checked periodically. In this context, the ultrasonic transit time technique is extremely useful in water management. By means of this technique, the flow rate is determined using single and multipath configurations. However, special attention must be paid to define the vertical velocity distribution and the suitable integration method.

The experiment was conducted in liquid (water) using a single path with two transducers (i.e., the velocity profile is sampled along a single line only), and a double path with four transducers; the liquid velocity was varied from 0.075 m/s to 2.4 m/s. The channel has a trapezoidal form (length: 4.2 m, width: 0.45 m, depth varying from 0.05 to 0.38 m) with channel slopes manually adjusted from 0.001 to 0.02, so as to produce variable flows.

In conclusion, the ultrasonic flow meters have the potential to significantly reduce the installation and operating costs of meter stations while providing accuracy levels consistent with, or better than, other traditional metering methods (vortex shedding, differential pressure, orifices, nozzles and venturi meters, Pitot-static-flow meters, magnetic flux, etc.). There may also be a substantial reduction in maintenance cost as the device utilizes digital measurement techniques and provides a wealth of diagnostic information on the status of the electronic measurement system.

The suggested ultrasonic flow meter designed according to a smart sensor concept constitutes a necessary link for the optimal water resources management of an irrigation system. It can be used with confidence and offers an economical and accurate means of measuring the flow of water in open channels. Typical uncertainties are of the order of 2% for single path and 1% for two paths and are attainable with careful application. In closed conduits, the results of the experiments demonstrate the validity and the performance of the laboratory ultrasonic flow meters. The application of the flow meters under favourable conditions produces a relative error that does not exceed 1%. This preliminary result shows the usefulness of these ultrasonic flow meters. Further investigations, however, are still needed in order to determine the overall performances of this instrument in terms of repeatability, linearity, reliability, and response time.

FR :

Les eaux résiduaires d’une usine agroalimentaire située à Abidjan, traitées par boues activées, ont été caractérisées en vue d’une réutilisation pour l’arrosage des espaces verts. L’effluent à la sortie de la STEP présente un taux d’abattement d’environ 96 % pour la DCO et la DBO₅. Le pH varie entre 6,5 et 8,5. Quant aux parasites (ankylostomes, anguillules, nématodes, helminthes), ils sont tous éliminés. Par contre, en moyenne 1,2•10⁶ coliformes totaux et 8,3•10³ coliformes thermotolérants pour 100 mL ont été dénombrés. En outre, la conductivité de l’effluent était en moyenne de 2 670 µmhos/cm avec un taux d’absorption de sodium (SAR) moyen de 23,92. Par conséquent, les effluents traités ne répondaient pas aux recommandations de l’O.M.S. quant à leur réutilisation pour l’arrosage d’espaces verts.

La mise en place d’ouvrages supplémentaires d’épuration des eaux pourrait contribuer à réduire les risques sanitaires et ceux liés à la salinité, susceptibles de compromettre la réutilisation des effluents traités pour l’arrosage.

EN :

The wastewater from an agro-food industrial factory, treated by an activated sludge process, was characterized for re-use in the watering of parklands. The factory was located in Abidjan, Ivory Coast. The effluent from the sewage treatment plant showed a reduction of the Chemical Oxygen Demand (COD) and five-day Biological Oxygen Demand (BOD₅ of approximately 96% and had a pH varying between 6.5 and 8.5. Parasites (ankylostomes, anguillules, nematodes, helminths) were also all eliminated. However, on average 1.2 x 10⁶ total coliforms and 8.3 x 10³ faecal coliforms per 100 mL were counted. Moreover, the average conductivity of the effluent was 2670 µmhos/cm with an average rate of sodium absorption (SAR) of 23.9. Consequently, the treated effluent did not meet the recommendations of the World Health Organization and was, therefore, not suitable for the watering of parklands. Additional water purification could reduce medical risks and those related to salinity, and allow the re-use of effluents for watering.

FR :

L’étude des caractéristiques physico-chimiques des eaux souterraines de la communauté Mzamza, soumises aux rejets liquides de la ville de Settat à partir de l’oued Boummoussa, montre que la qualité des eaux des différents puits est variable et dépend d’un certain nombre de facteurs tels que l’emplacement des puits par rapport aux eaux usées et l’activité agricole. L’interprétation des données d’analyse, la corrélation existante entre eaux usées et eaux de puits, et la répartition des eaux souterraines en groupes sont réalisées en utilisant l’Analyse en Composante Principale Normée. L’étude a révélé des origines différentes de la contamination des eaux souterraines, à savoir, la contamination par la matière organique due essentiellement à l’utilisation des eaux usées à des fins d’irrigation et à leur infiltration continue, et finalement le retour des eaux d’irrigation (chargées en engrais azotés) qui est considéré comme étant la principale origine de la minéralisation et de la pollution des eaux.

Plusieurs facteurs conditionnent la progression de cette pollution : les concentrations des polluants dans les eaux usées, la nature des sols, la lithologie, la perméabilité de l’aquifère exploité et la profondeur de la nappe.

Les résultats acquis dans cette étude font ressortir également l’influence primordiale des variations saisonnières, ainsi que le rôle bénéfique des précipitations.

EN :

The study of the physical-chemical characteristics of groundwater of the Mzamza community, subjected to domestic and industrial wastes from Settat City (Morocco) via the Boummoussa river, shows that the quality of water of the various wells is variable and depends on a certain number of factors such as the location of the wells in relation to waste water and agricultural activity. The interpretation of analyzed data, the correlation between waste water and well water, and the distribution of groundwater sites into groups was carried out using Normalized Principal Components Analysis. The study revealed several sources of groundwater contamination, namely, the contamination by organic matter due primarily to the infiltration of waste waters used for irrigation, and the return of irrigation water (loaded with nitrate fertilizers), which is regarded as being the principal source of dissolved solids and inorganic nitrogen in the groundwater. Several factors influence the progression of this pollution: the concentrations of the pollutants in the waste waters, the nature of the soil, the lithology, the permeability of the aquifer in use and the depth of the water table. The results achieved in this study also revealed the paramount influence of seasonal variability and the beneficial role of atmospheric precipitation.