Évolution de la qualité de l'eau dans le réseau de distribution de la ville de Montréal

Dans la présente étude, nous montrons l'évolution de l'eau dans un réseau de distribution. Ce réseau a été construit dans les années 70 à l'aide de conduites d'acier ou de fonte ductile munies d'un revêtement intérieur de ciment. Il est alimenté par des eaux de très bonne qualité qui circulent d'abord dans une suite de conduites maîtresses (de 2 700 mm à 900 mm) jusqu'à un secteur de petites conduites maillées (200 et 300 mm). Des échantillons d'eau ont été prélevés à 14 reprises durant une année, le long de la conduite maîtresse (le temps de séjour y varie de 0 h à 13,6 h) et dans le secteur de petites conduites (de 13,6 h à 18,4 h). Nous avons mesuré la température, le pH, plusieurs sous-produits de désinfection dont les trihalométhanes et les aldéhydes, le carbone organique total et biodégradable ainsi que les concentrations de bactéries hétérotrophes aérobies et anaérobies facultatives (BHA) et les comptes directs totaux mesurés en épifluorescence. Le réseau a très peu d'effet sur l'évolution des sous-produits de désinfection. En effet, les résultats obtenus à partir des échantillons témoins (eaux traitées conservées dans un flacon propre à la même température que dans le réseau) sont semblables à ceux obtenus à partir des eaux prélevées dans le réseau de distribution.Les concentrations de bactéries ainsi que les concentrations de CODB sont assez stables dans le réseau. Il est intéressant de noter qu'il y a de 0,2 à 0,45 mg/l de CODB, ce qui est supérieur à la concentration minimale de 0,15 mg/l requise pour la croissance des bactéries. Par contre, le chlore résiduel libre est toujours supérieur à 0,20 mg/l. Une seule exception, le 11 juillet 1994, dans le secteur de petites conduites, le chlore résiduel a baissé jusqu'à 0,16 mg/l. Durant cette journée, nous avons observé une légère augmentation des comptes directs totaux mesurés en épifluorescence.Studies were performed to follow the changes in water quality along a distribution system. The distribution system under study is divided into two parts: main pipes starting from the plant (from 2 700 mm to 900 mm diameter) feeding a small pipes sector (200 mm and 300 mm diameter). Residence times range from 0 to 13.6 hours in main pipes and from 13.6 h to 18.4 h in small pipes. All pipes are made of steel or ductile iron and their interior is lined with concrete; there is therefore little corrosion. Since the raw water is of such high quality, the treatment plant is very simple: a direct filtration on sand followed by ozonation and chlorine disinfection. Samples were taken on 14 occasions, during a full year period, in the distribution system and in the treatment plant after chlorination. These last samples were incubated in clean flasks at the network temperature. Measurements of temperature, pH, disinfection by-products (trihalomethanes, aldehydes, haloacetonitriles, haloacetones and chloropicrine), total organic carbon (TOC), biodegradable dissolved organic carbon (BDOC) and number of bacteria (heterotrophic plate count and total direct count by epifluorescence) were completed.The distribution network seems to have very little effect on chlorine demand and disinfection by-products. Results from water incubated in flasks are similar to those from distribution network. After more than 18 hours contact time, the chlorine residual is still higher than 0.2 mg/l in most of the samples taken in the distribution network and in the flask. It should be noted that the initial chlorine concentrations range from 0.65 mg/l (cold water) to 1.00 mg/l (warm water). Chlorine demand and trihalomethane (THM) curves are typical, a rapid increase with time followed by a relatively stable level. THM concentrations in the distribution network are low: a typical value of 14 µg/l after 13.6 hours contact time is detected. The maximum concentration of 43 µg/l of total THM was measured in a dead end. In this latter sample, 42 % of the THM was present as bromodichloromethane and 39 % as chloroform. Other by-products such as haloacetonitrile, haloacetone and chloropicrine were always detected in very small concentrations.Aldehyde concentrations in treated water were low, between 21 and 42 µg/l. These concentrations were stable throughout the distribution system. Fixed and free biomass seems to have very little effect on these biodegradable compounds. These results were confirmed by BDOC results. BDOC in treated water ranges from 0.2 to 0.45 mg/l and remains stable in the distribution system. These low BDOC concentrations and the chlorine residual of approximately 0.2 mg/l seem to be sufficient to prevent regrowth in the distribution system. Total direct counts by epifluorescence showed almost no increase of bacterial density except for the July 11th sample. This is the only day where the free chlorine residual dropped below 0.2 mg/l, with values of free chlorine residual dropping as low as 0.16 mg/l

Étude de l'évolution des acides aminés totaux dans deux filières de traitement d'eau potable

Cette étude présente un suivi de l'élimination des acides aminés totaux par les différentes étapes de traitement de deux usines canadiennes de Ville de Laval (Québec, Canada). L'influence des saisons sur l'efficacité de l'abattement ainsi que le devenir des acides aminés dans les réseaux de distribution de ces usines ont aussi été étudiés.D'une manière générale, l'étape de coagulation-floculation-décantation permet une élimination important d'acides aminés totaux (34-72%), l'effet de la filtration sur sable et anthracite est peu prononcé et varie avec les saisons, l'ozonation provoque une augmentation (20-100%) et la filtration sur charbon actif biologique (CAB) permet un abattement en eau tiède (25-34%), mais semble relarguer en eaux froides (35%). Finalement, la post-désinfection au chlore permet une élimination supplémentaire (47%) à cause de la réactivité de cet oxydant envers les acides aminés. La post-désinfection au bioxyde de chlore permet elle aussi d'abattre les teneurs en acides aminés (12-39%) et ce, malgré le fait que cet oxydant soit moins réactif envers les acides aminés. L'élimination des acides aminés totaux avant la chloration est préférable afin de limiter la formation de sous-produits de chloration.Low concentrations of free and combined amino acids are found at every stage of water treatment (LE CLOIREC and RENAUD, 1984; SCULLY et al., 1988; BERNE et al., 1994). A decrease in amino acid concentrations has been observed after settling (LE CLOIREC et al., 1983; LE CLOIREC and RENAUD, 1984), while ozonation has been shown to increase free amino acid concentrations. Biological activated carbon (BAC) filtration may also decrease the concentration of total amino acids (JADAS-HÉCART, 1989; BERNE, 1994). Total amino acids represent a small fraction of dissolved organic matter (1 to 3% of DOC), but account for an important part of the chlorine demand of treated water (JADAS-HÉCART, 1989; HUREIKI et al., 1994). Moreover, recent work by HUREIKI and GAUTHIER (1994) has suggested that some amino acids found in surface waters may represent a significant fraction of the precursors of some organohalogenated disinfection by- products (DBP). It is also possible that total amino acids amount to an important fraction of biodegradable organic carbon (BOC). These characteristics of amino acids suggest that removing them by treatment will improve water quality, both from a biological and a chemical (DBP) stability standpoint.The objectives of the research described in this paper were to:1. assess the seasonal variability of the removal of free and combined amino acids by different treatment processes in two Canadian water treatment plants located in the city of Laval (Québec, Canada); 2. monitor the fate of total amino acids in the distribution systems of these two plants with the objective of correlating total amino acids with biodegradable dissolved organic carbon (BDOC) and fixed bacterial density. Sampling was conducted in two water treatment plants. The Ste-Rose water treatment plant (100,000 m3/d) uses conventional treatment (dynamic settling and dual-media filtration on sand and anthracite) followed by ozonation, pH adjustment, and post-chlorination using either chlorine of chlorine dioxide. The second plant studied is the Chomedey water treatment plant (180,000 m3/d) in which the following processes are used: conventional treatment (dynamic settling and dual-media filtration on sand and anthracite) followed by ozonation, second stage filtration on biological activated carbon (BAC), pH adjustment, and post-chlorination using chlorine dioxide. Samples were collected in the two distribution systems according to the residence time of the water calculated by a hydraulic model. Samples were taken directly from small diameter (15 cm internal diameter) ductile iron pipes. Results of the monitoring of the treatment plants show a very strong decrease of total amino acids by coagulation-flocculation-settling (34-72%). First stage dual-media filtration may increase or decrease the concentrations of total amino acids present, depending on the time of the year. In all but one case ozonation increases the concentration of total amino acids (20-100%). To document the source of this increase, we verified the yields of hydrolysis of amino acids found in natural matrices under different hydrolysis conditions. The objective of this experiment was to verify if more drastic hydrolysis conditions would free some amino acids linked to more complex structures found in natural waters. If such were the case, this would explain why higher concentrations of total amino acids were obtained after ozonation. Results showed that the hydrolysis conditions used by BERNE (1994) are optimal for recovery of amino acids in the natural water studied (sand and anthracite filter effluent). Total amino acids were decreased by BAC filtration in warm water (24 to 34%) but increased in cold water (+35%). This could either be related to the slower kinetics of the hydrolysis of combined amino acids by the fixed biomass or by the form in which amino acids were present in the winter matrix. The expected effect of chlorination on total amino acids was observed with a decrease of 47% at the post-chlorination step. Some impact of chlorine dioxide was noted although it is believed that chlorine dioxide will not readily react with free and combined amino acids. This effect was more pronounced in cold water and could be related to the fact that chlorine dioxide in full-scale plants is produced in the presence of excess chlorine (less than 10%).The analysis of the composition of total amino acids present in the Mille-Îles River showed that the amino acids most commonly found were glycine, serine, alanine, leucine, lysine, aspartic acid and glutamic acid. We observed that the trends of major amino acids present followed the trends observed for total amino acids. This concordance of trends does not reflect the individual characteristics of each amino acid or the ability of a treatment process to remove or transform them. It most probably reflects the ability of each treatment process to remove or transform complex bound forms of amino acids. In the Ste-Rose distribution system (DS), we observed stable concentrations of total amino acids regardless of the residence time. In the case of the Chomedey distribution system, concentrations decreased slightly with residence time, suggesting a greater stability of amino acids in the DS fed by biologically treated water. In both cases, levels of amino acids were very low close to the detection limit. In the case of the Ste-Rose DS, these low levels were attributed to biological removal, whereas in the case of the Chomedey DS this was associated with post-chlorination.No direct correlation between biodegradable organic carbon (BDOC) and total amino acids was observed. This may reflect the fact that total amino acids represent a variable fraction of the total pool of biodegradable organic carbon depending on the source water composition and on the treatment process applied. In the case of the source water studied, total amino acids represented a major fraction of the biodegradable organic carbon pool: more than 42% in raw water and more than 45% in BAC filter effluent. These high proportions may partially be explained by the eutrophic state of our source water and by the method of BDOC measurement used.In conclusion, amino acids represent an important fraction of biodegradable organic carbon which can be removed most efficiently by optimized coagulation-flocculation and settling, biological treatment and chlorination. It is preferable to remove total amino acids before chlorination in order to limit the formation of undesirable DBPs

Evidence for spin liquid ground state in SrDy2_2O4_4 frustrated magnet probed by muSR

Muon spin relaxation ($\mu$SR) measurements were carried out on SrDy$_2$O$_4$, a frustrated magnet featuring short range magnetic correlations at low temperatures. Zero-field muon spin depolarization measurements demonstrate that fast magnetic fluctuations are present from $T=300$ K down to 20 mK. The coexistence of short range magnetic correlations and fluctuations at $T=20$ mK indicates that SrDy$_2$O$_4$ features a spin liquid ground state. Large longitudinal fields affect weakly the muon spin depolarization, also suggesting the presence of fast fluctuations. For a longitudinal field of $\mu_0H=2$ T, a non-relaxing asymmetry contribution appears below $T=6$ K, indicating considerable slowing down of the magnetic fluctuations as field-induced magnetically-ordered phases are approached.Comment: 6 pages, 4 figures, to be published as a proceeding of HFM2016 in Journal of Physics: Conference Series (JPCS

γ-Hemolysin oligomeric structure and effect of its formation on supported lipid bilayers: An AFM Investigation.

γ-Hemolysins are bicomponent β-barrel pore forming toxins produced by Staphylococcus aureus as water-soluble monomers, which assemble into oligomeric pores on the surface of lipid bilayers. Here, after investigating the oligomeric structure of γ-hemolysins on supported lipid bilayers (SLBs) by atomic force microscopy (AFM), we studied the effect produced by this toxin on the structure of SLBs. We found that oligomeric structures with different number of monomers can assemble on the lipid bilayer being the octameric form the most stable one. Moreover, in this membrane model we found that γ-hemolysins can form clusters of oligomers inducing a curvature in the lipid bilayer, which could probably enhance the aggressiveness of these toxins at high concentrations

Absence of correlation between nitrate reductase and symbiotic nitrogen fixation efficiency in rhizobium meliloti

Les activités spécifiques des nitrates réductases assimilatoires et "régulatoires" ont été étudiées chez 41 souches de Rhizobium meliloti ayant des activités différentes de fixation symbiotique d’azote. Les deux nitrates réductases ont été retrouvées chez les souches très efficaces ainsi que chez les souches inefficaces et aucune corrélation significative n’a été trouvée entre les activités spécifiques et le rendement de la matière sèche de la luzerne obtenu avec les 41 souches à l’essai. La détermination des activités spécifiques de ces deux nitrates réductases chez les bactéries végétatives ne peut donc pas être utilisée comme un test physiologique rapide pour la sélection de souches très efficaces de R. meliloti.Specific activities of the assimilatory and "regulatory" types of nitrate reductase were studied in 41 strains of Rhizobium m,eliloti naving ditierent symbiotic nitrogen fixation activities. Both nitrate reductase enzymes were present in very effective ind ineffective strains and no significant correlation was iound between the specific activities of the two enzymes and the dry matter yields of alfalfa obtained with the 41 strains. Measurements of the specific activities of the two nitrate reductase enzymes in the vegetative bacteria cannot be used as a rapid physiological test for the seiection of very effective strains of R. meliloti

Partial Purification and Characterization of the Mode of Action of Enterocin S37: A Bacteriocin Produced by Enterococcus faecalis S37 Isolated from Poultry Feces

The aim of this research was to purify and characterize the mode of action of enterocin S37, a bacteriocin produced by Enterococcus faecalis S37, a strain recently isolated from the chicken feces. Enterocin S37 has a molecular weight comprised between 4 and 5 kDa. It remained active after 1 h at 80oC and at pH values ranging from 4.0 to 9.0. Furthermore, cell-free supernatant of Enterococcus faecalis S37 and purified enterocin S37 were active against Gram-positive bacteria including Listeria monocytogenes EGDe, L. innocua F, Enterococcus faecalis JH2-2, and Lactobacillus brevis F145. The purification of enterocin S37 was performed by ammonium sulfate precipitation followed up by hydrophobic-interaction chromatography procedures. Treatment of enterocin S37 with proteinase K, α-chymotrypsin, and papain confirmed its proteinaceous nature, while its treatment with lysozyme and lipase resulted in no alteration of activity. Enterocin S37 is hydrophobic, anti-Listeria and likely acting by depletion of intracellular K+ ions upon action on KATP channels. This study contributed to gain more insights into the mode of action of enterocins

Fermi-surface topology of the iron pnictide LaFe2_2P2_2

We report on a comprehensive de Haas--van Alphen (dHvA) study of the iron pnictide LaFe$_2$P$_2$. Our extensive density-functional band-structure calculations can well explain the measured angular-dependent dHvA frequencies. As salient feature, we observe only one quasi-two-dimensional Fermi-surface sheet, i.e., a hole-like Fermi-surface cylinder around $\Gamma$, essential for $s_\pm$ pairing, is missing. In spite of considerable mass enhancements due to many-body effects, LaFe$_2$P$_2$ shows no superconductivity. This is likely caused by the absence of any nesting between electron and hole bands.Comment: 5 pages, 4 figure

Evolution of shell structure in neutron-rich calcium isotopes

We employ interactions from chiral effective field theory and compute the binding energies and low-lying excitations of calcium isotopes with the coupled-cluster method. Effects of three-nucleon forces are included phenomenologically as in-medium two-nucleon interactions, and the coupling to the particle continuum is taken into account using a Berggren basis. The computed ground-state energies and the low-lying 2+ states for the isotopes 42,48,50,52Ca are in good agreement with data, and we predict the excitation energy of the first 2+ state in 54Ca at 1.9 MeV, displaying only a weak sub-shell closure. In the odd-mass nuclei 53,55,61Ca we find that the positive parity states deviate strongly from the naive shell model.Comment: 5 pages, 4 figures; small correction of effective 3NF and slight change of the corresponding parameters; updated figures and tables; main results and conclusions unchange