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

Accumulation et fonte de la neige en milieux boisé et déboisé

Les auteurs présentent une étude des caractéristiques physiques du couvert de neige en relation avec l'altitude, l'exposition et le couvert forestier. L'expérience s'est déroulée à la forêt Montmorency, sise à 80 km au nord de Québec. Au cours des hivers 1981 et 1982, l'équivalent en eau maximal de la neige, pour l'ensemble du bassin du lac Laflamme, a été de 28 et 29 cm, respectivement. Durant cette période, les mesures effectuées n'ont pas permis de détecter l'effet des faibles différences d'altitude (50 m) sur l'accumulation de la neige. L'équivalent en eau de la neige était maximal dans les milieux découverts et apparaissait plus important sous les jeunes peuplements que sous les vieux. Les jeunes sapinières, entourées d'arbres plus hauts, agissent comme des pièges à neige. L'influence de l'exposition ne ressort que durant la période de fonte, accélérée d'une semaine sur les flancs sud. La fonte en sous-bois dure un mois et demi en moyenne et est écourtée d'une à deux semaines dans les sites découverts. Un modèle de fonte, basé sur les degrés-jours, est finalement adapté. Le coefficient de fonte est rajusté en fonction de deux périodes distinctes par la densité du manteau nival ou les degrés-jours cumulés.A study of physical characteristics of the snow cover in relation to altitude, aspect and forest cover, is presented in this paper. The experimental site is located at Montmorency forest, 80 km north of Québec City. During the winters of 1981 and 1982, the snow water equivalent for the lake Laflamme watershed reached a maximum of 28 and 29 cm, respectively. The effect on snow accumulation by the small elevation range (50 m) was not detectable by our measurements. The snow water equivalent was greatest in open areas and appeared greater under the young than the older stands. The young fir associations, surrounded by higher trees, act as snow traps. The aspect plays a role during the melting period only, which is shortened by one week on south exposures. Snowmeit lasts one and a half month in average under the cover and is shortened by one to two weeks in the open. A snowmeit model, based on degree-days, is finally calibrated. The melt coefficient is readjusted for two periods separated by snow density or cumulative degree-days.Die Autoren legen eine Studie vor, die die Beziehung der physischen Merkmale der Schneedecke zu Hôhe, Himmelsrichtung und Bewaldung untersucht. Der Versuch wurde im WaId Montmorency, der 80 km nôrdlich von Québec liegt, durchgefùhrt. Wàhrend der Winter 1981 und 1982 war das maximale Wasserâquivalent der Schneemenge 28 cm bzw. 29 cm fur das gesamte Becken des Laflamme-Sees. Wahrend dieser Période konnten die durchgefuhrten Messungen keinerlei Einflup der schwachen Hôhenunterschiede (50 m) auf die Menge des angesammelten Schnees feststellen. Das der Schneemenge entsprechende Wasserâquivalent war maximal in den freien Gebieten und schien grosser unter den jungen Baumbestanden als unter den alten. Die jungen Tannenwâlder, die von hôheren Baurnen umgeben sind, wirken wie Schneefallen. Der EinfluB der Himmelsrichtung wird erst wâhrend der Zeit der Schneeschmelze spurbar, die auf den Sudflanken urn eine Woche kùrzer ist. Die Schneeschmelze im WaId dauert im Durchschnitt eineinhalb Monate und ist ein bis zwei Wochen kurzer in den offenen Gelànden. Ein Schneeschmelze-Modell auf der Basis Grade-Tage wird schlieplich geeicht. Der Schmelzkoeffizient wird zwei Perioden angepaBt, die sich durch die Dichte der Schneedecke oder die kumulierten Grade-Tage unterscheiden

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

Evidence for Model-based Computations in the Human Amygdala during Pavlovian Conditioning

Contemporary computational accounts of instrumental conditioning have emphasized a role for a model-based system in which values are computed with reference to a rich model of the structure of the world, and a model-free system in which values are updated without encoding such structure. Much less studied is the possibility of a similar distinction operating at the level of Pavlovian conditioning. In the present study, we scanned human participants while they participated in a Pavlovian conditioning task with a simple structure while measuring activity in the human amygdala using a high-resolution fMRI protocol. After fitting a model-based algorithm and a variety of model-free algorithms to the fMRI data, we found evidence for the superiority of a model-based algorithm in accounting for activity in the amygdala compared to the model-free counterparts. These findings support an important role for model-based algorithms in describing the processes underpinning Pavlovian conditioning, as well as providing evidence of a role for the human amygdala in model-based inference

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

Analysis of steroid hormones and their conjugated forms in water and urine by on-line solid-phase extraction coupled to liquid chromatography tandem mass spectrometry

Background: In recent years, endocrine disrupting compounds (EDCs) have been found in rivers that receive significant inputs of wastewater. Among EDCs, natural and synthetic steroid hormones are recognized for their potential to mimic or interfere with normal hormonal functions (development, growth and reproduction), even at ultratrace levels (ng L-1). Although conjugated hormones are less active than free hormones, they can be cleaved and release the unconjugated estrogens through microbial processes before or during the treatment of wastewater. Due to the need to identify and quantify these compounds, a new fully automated method was developed for the simultaneous determination of the two forms of several steroid hormones (free and conjugated) in different water matrixes and in urine.Results: The method is based on online solid phase extraction coupled with liquid chromatography and tandem mass spectrometry (SPE-LC-MS/MS). Several parameters were assessed in order to optimize the efficiency of the method, such as the type and flow rate of the mobile phase, the various SPE columns, chromatography as well as different sources and ionization modes for MS. The method demonstrated good linearity (R-2 > 0.993) and precision with a coefficient of variance of less than 10 %. The quantification limits vary from a minimum of 3-15 ng L-1 for an injection volume of 1 and 5 mL, respectively, with the recovery values of the compounds varying from 72 to 117 %.Conclusion: The suggested method has been validated and successfully applied for the simultaneous analysis of several steroid hormones in different water matrixes and in urine

Liposome Co-sedimentation and Co-flotation Assays to Study Lipid-Protein Interactions

A large proportion of proteins are expected to interact with cellular membranes to carry out their physiological functions in processes such as membrane transport, morphogenesis, cytoskeletal organization, and signal transduction. The recruitment of proteins at the membrane-cytoplasm interface and their activities are precisely regulated by phosphoinositides, which are negatively charged phospholipids found on the cytoplasmic leaflet of cellular membranes and play critical roles in membrane homeostasis and cellular signaling. Thus, it is important to reveal which proteins interact with phosphoinositides and to elucidate the underlying mechanisms. Here, we present two standard in vitro methods, liposome co-sedimentation and co-flotation assays, to study lipid-protein interactions. Liposomes can mimic various biological membranes in these assays because their lipid compositions and concentrations can be varied. Thus, in addition to mechanisms of lipid-protein interactions, these methods provide information on the possible specificities of proteins toward certain lipids such as specific phosphoinositide species and can hence shed light on the roles of membrane interactions on the functions of membrane-associated proteins.Peer reviewe