Étude expérimentale et modélisation de la désinfection par le chlore des eaux usées épurées

Pour étudier la désinfection d'une eau usée épurée au stade secondaire, traitée à l'hypochlorite de sodium, des essais en réacteur fermé ont été effectués en utilisant des doses variant entre 1 et 10 mg de chlore par litre. Les résultats obtenus montrent que la cinétique de désinfection est loin d'être uniforme. L'utilisation du modèle de Chick et Watson n'est en effet possible que si on l'adapte pour tenir compte de la modification de la vitesse de désinfection au cours du processus. Le modèle de Collins et Selleck permet de rendre compte de façon satisfaisante de l'évolution de la vitesse d'élimination des germes au cours du temps. La faible valeur du paramètre t trouvée (0.26 min.mg/l pour les coliformes totaux et 0.58 min.mg/l pour les coliformes fécaux) semble cependant démontrer que la période de latence est relativement peut importante surtout lorsqu'on utilise des dose de chlore élevées. Il s'avère d'autre part que la demande en chlore de ce type d'eau est très importante. La concentration en chlore résiduel dans le réacteur décroît très rapidement pour atteindre environs 10 % de la dose de chlore injectée et cela quelle que soit la dose utilisée (de 1 à 10 mg/l). Le dimensionnement des réacteurs de désinfection fonctionnant en continu nécessite de prendre en compte le comportement hydrodynamique de l'eau dans le réacteur. Sachant qu'un abattement de 3 U-Log est nécessaire, dans le cas de la réutilisation de l'eau pour l'irrigation, un modèle intégrant l'expression de la cinétique de désinfection et l'hydrodynamique du contacteur a été proposé. Les résultats mettent en évidence l'intérêt de concevoir des réacteurs se rapprochant le plus possible de l'écoulement piston.Secondary wastewater is considered as an important additional resource of water in a country, which has a semiarid climate as Tunisia. On quality basis, the use of water for irrigation is governed by chemical parameters of the water that affect plant, soils conditions and the underlying groundwater. Treated urban wastewater is susceptible to be used in irrigation without major risks (see table 1). However, the use of such a water can represent a risk of contamination of edible crops, pasture lands, and feed crops by direct contact with disease agent carried in reclaimed water or aerosols from spray irrigation. These sanitary risks can be considerably reduced with the practice of an efficient disinfection. Chlorinating is one of the simplest and less expensive disinfection processes. The objectives of this work are the study of the disinfection kinetics and the rate of exertion of chlorine demand of water, when the sodium hypochlorite is used for treating a secondary wastewater. for this, a batch reactor tests have been done. After applying a dose of chlorine (between 1 and 10 mg/l), we have determined the evolution with time of chlorine residual concentration and rate of inactivation of the total and fecal coliform. Chlorine demandTo describe chlorine decay in the complex milieu of water, like wastewater, Haas and Karra (1984) have developed followed equation:C=C0[XE-k1t+(1-X)e]-k2twhere:C : concentration of residual chlorine, mg/lC0 : dose of chlorine, mg/lX : empirical constantt : contact time, mink1and k2 : rate constants, min-1In the case of wastewater chlorinating, we can ascertain that the chlorine concentration in the batch reactor decrease rapidly, in the beginning of the reaction, and very moderately after satisfaction of the initial chlorine demand. This initial chlorine demand is very important. It represents near 90% of the dose injected in the reactor. The chlorine concentration decay can be described by Haas and Karra equation with X=0.9, k1=3 min-1 and k2=0.001 min-1. After some minutes of contact time, we can notes, see figure 2, that the chlorine concentration decay is susceptible to be approximate by a first order equation:t ≥ 2min ⇒ C ≅ 0.1e-0.001 tThe concentration of residual chlorine becomes practically constant in the reactor, once initial chlorine demand has been satisfied, with C ≅ 0.1 C0.Disinfection kineticsUsing a pseudo first order Chick and Watson model reveals that the rate of inactivation of coliform bacteria is not uniform. We can employ this model to fit experimental data only when we subdivide the process in two stages characterised by different kinetics. for example, the logarithm of fecal coliform survival rate can be expressed by the relationships:for C ∙ t ≤ 2.85 min ∙ mg/L Ln(N/N0)= -1.65C ∙ tfor C ∙ t ≥ 2.85 min ∙ mg/L Ln(N/N0)= -3.89-0.29C⋄tCollins and Selleck (1972) developed a general kinetic expression for the effect of combined chlorine residual on both total and fecal coliform. Combining the work of chick and Gard (Gard, 1957) they developed the following formula describing the survival of these bacteria:for C∙tτ (N/N0)=(τ/C∙t)nwhere C : the combined chlorine residual, mg/lt : contact time, minutet : an environmental coefficient or induction timen : Constant In this formula, we have assumed that the concentration of chlorine remains constant. We can apply this model when we consider that C is the chlorine concentration after the immediate wastewater demand had been satisfied. Using Collins and Selleck disinfection model to plot the survival rate of total and fecal coliform in chlorinated secondary effluent, we have obtained the coefficients below: for total coliform : n=1.94 t=0.26 min∙mg/lfor fecal coliform : n=3.1 t=0.58 min∙mg/lThe constant τ represents the time required for the disinfectant to diffuse through the cell wall and begin its disinfectant activity. we can see that this initial lag time is very short. The disinfectant becomes rapidly efficacious to inactivate coliform bacteria.Design of disinfectant contact facilitiesSo as to estimate the influence of the hydraulic efficiency of chlorine contact chambers on disinfection process performance, we have compared efficiency of two ideals reactors: the completely stirred tank reactor and plug flow reactor. The kinetic equations presented above had been established in a batch reactor. To obtain the mean conversion in the entire contactor, one has to apply the segregated flow model. Using the concept of segregated flow system, the survival ratio will be the sum of the batch reactions of all small aggregates, or:           ∞(N/N0)=∫(N/N0)batchE(Ɵ)dƟ           0Ɵ : normalized contact time (contact time/hydraulic residence time)E(Ɵ) : normalized frequency distribution of agesIn completely mixed regime, fluid particles are exponentially distributed throughout a tank until the fluid properties exhibited by the effluent leaving the unit are identical to those within the unit. Using Collins and Selleck model, the survival ratio corresponding to hydraulic residence time Ts and to the residual chlorine concentration C is expressed by equation:           ∞                      (τ/C∙Ts)           ∞(N/N0)=∫(N/N0)batche-ƟdƟ = ∫ e-ƟdƟ + ∫ (τ/C∙t)me-ƟdƟ           0                            0         (τ/C∙Ts)The survival ratio for a hydraulic residence times between 5 min and 60 min and a residual chlorine concentration between 0.2 mg/l and 1 mg/l are reported in table 3 and table 4.In a plug flow regime all particles entering in a basin have equal velocity values, travel on parallel flow paths, and remain in the unit for an identical period known as the hydraulic residence time. the performance of such a reactor is identical at the batch reactor performance. In table 5 and table 6 we have reported the survival ratio given by plug flow reactor with residence time until 60 min and residual chlorine concentration between 0.2 mg/l and 1 mg/l. Knowing that the secondary wastewater reuse necessitates a 3 U-Log fecal coliform inactivation, we can see clearly the importance of reactor design on his performance. Indeed, to reach a 3 U-log inactivation, it is sufficient (see table 6) to use a dose of 2 mg/l of chlorine and a hydraulic residence time of 30 minutes, in plug flow reactor. Such dose and the same residence time given only a 1 U -Log inactivation (see table 4) when the reactor is completely mixed

Purification of plasma membrane vesicles from Vitis vinifera cv. Gamay suspension cells by free electrophoresis

Research Not

Ethanol application at veraison decreases acidity in Cabernet Sauvignon grapes

Research NoteSpraying ethanol (5 % v/v in water) onto grape clusters at mid-veraison led to a 30 % drop in the malic acid concentration at harvest. As a consequence, titratable acidity also dropped by 10 %. The concentration of tartaric acid did not change significantly. The mode of action of ethanol on malic acid metabolism is discussed.

Technical Note: The air quality modeling system Polyphemus

International audiencePolyphemus is an air quality modeling platform which aims at covering the scope and the abilities of modern air quality systems. It deals with applications from local scale to continental scale, using two Gaussian models and two Eulerian models. It manages passive tracers, radioactive decay, photochemistry and aerosol dynamics. The structure of the system includes four independent levels with data management, physical parameterizations, numerical solvers and high-level methods such as data assimilation. This enables sensitivity and uncertainty analysis, primarily through multimodel approaches. On top of the models, drivers implement advanced methods such as model coupling or data assimilation

Characterization of the Tomato ARF Gene Family Uncovers a Multi-Levels Post-Transcriptional Regulation Including Alternative Splicing

Background: The phytohormone auxin is involved in a wide range of developmental processes and auxin signaling is known to modulate the expression of target genes via two types of transcriptional regulators, namely, Aux/IAA and Auxin Response Factors (ARF). ARFs play a major role in transcriptional activation or repression through direct binding to the promoter of auxin-responsive genes. The present study aims at gaining better insight on distinctive structural and functional features among ARF proteins. Results: Building on the most updated tomato (Solanum lycopersicon) reference genome sequence, a comprehensive set of ARF genes was identified, extending the total number of family members to 22. Upon correction of structural annotation inconsistencies, renaming the tomato ARF family members provided a consensus nomenclature for all ARF genes across plant species. In silico search predicted the presence of putative target site for small interfering RNAs within twelve Sl-ARFs while sequence analysis of the 59-leader sequences revealed the presence of potential small uORF regulatory elements. Functional characterization carried out by transactivation assay partitioned tomato ARFs into repressors and activators of auxin-dependent gene transcription. Expression studies identified tomato ARFs potentially involved in the fruit set process. Genome-wide expression profiling using RNA-seq revealed that at least one third of the gene family members display alternative splicing mode of regulation during the flower to fruit transition. Moreover, the regulation of several tomato ARF genes by both ethylene and auxin, suggests their potential contribution to the convergence mechanism between the signaling pathways of these two hormones. Conclusion: All together, the data bring new insight on the complexity of the expression control of Sl-ARF genes at the transcriptional and post-transcriptional levels supporting the hypothesis that these transcriptional mediators might represent one of the main components that enable auxin to regulate a wide range of physiological processes in a highly specific and coordinated manner

Preexisting and de novo humoral immunity to SARS-CoV-2 in humans

Zoonotic introduction of novel coronaviruses may encounter preexisting immunity in humans. Using diverse assays for antibodies recognizing SARS-CoV-2 proteins, we detect preexisting humoral immunity. SARS-CoV-2 spike glycoprotein (S)-reactive antibodies were detectable by a flow cytometry-based method in SARS-CoV-2-uninfected individuals and were particularly prevalent in children and adolescents. They were predominantly of the IgG class and targeted the S2 subunit. By contrast, SARS-CoV-2 infection induced higher titers of SARS-CoV-2 S-reactive IgG antibodies, targeting both the S1 and S2 subunits, and concomitant IgM and IgA antibodies, lasting throughout the observation period. Notably, SARS-CoV-2-uninfected donor sera exhibited specific neutralizing activity against SARS-CoV-2 and SARS-CoV-2 S pseudotypes. Distinguishing preexisting and de novo immunity will be critical for our understanding of susceptibility to and the natural course of SARS-CoV-2 infection

SARS-CoV-2 can recruit a haem metabolite to evade antibody immunity.

The coronaviral spike is the dominant viral antigen and the target of neutralizing antibodies. We show that SARS-CoV-2 spike binds biliverdin and bilirubin, the tetrapyrrole products of haem metabolism, with nanomolar affinity. Using cryo-electron microscopy and X-ray crystallography, we mapped the tetrapyrrole interaction pocket to a deep cleft on the spike N-terminal domain (NTD). At physiological concentrations, biliverdin significantly dampened the reactivity of SARS-CoV-2 spike with immune sera and inhibited a subset of neutralizing antibodies. Access to the tetrapyrrole-sensitive epitope is gated by a flexible loop on the distal face of the NTD. Accompanied by profound conformational changes in the NTD, antibody binding requires relocation of the gating loop, which folds into the cleft vacated by the metabolite. Our results indicate that SARS-CoV-2 spike NTD harbors a dominant epitope, access to which can be controlled by an allosteric mechanism that is regulated through the recruitment of a metabolite