Composition organique de boues résiduaires de stations d'épuration lorraines : Caractérisation moléculaire et effets de la biodégradation

This study deals with the molecular characterisation of the organic content of sewage sludges from Lorraine (Northeast of France). The 48 samples collected come from domestic wastewater treatment plants of different capacities (rural, small urban and urban) and from depuration stations treating dairy, cheese dairy and paper-mill effluents. The first part of this study enabled to make the inventory of the compounds present in sewage sludges (i) under free form (soluble organic fraction – SOF), and (ii) linked to the macromolecular structure (insoluble organic fraction – IOF). To achieve that, the analytical tools used were respectively GC-MS on the one hand, and THM-GC-MS and Py-GC-AED on the other hand. The results of the analysis of the SOF and IOF provide equivalent information in that they enable the differentiation of sludges according to their origin (food-processing, paper-mill or domestic). A molecular fingerprint specific to each type of sludge was thus defined. Besides, all the domestic sludges are characterised by a geochemical petroleum background which testifies to a common diffuse pollution. Moreover, a variability in this geochemical background was observed for some domestic sludges, regardless of the size of the station, or of the degree of industrialisation of the region. These variations, which are essentially observed in the SOF, can be attributed to punctual or accidental pollution in the sewer system of domestic wastewater. The eventual goal of this work is to provide molecular parameters in order to improve the monitoring and the control of wastewater sewer systems. The second part of this project studies the effects of biodegradation on the organic content of sewage sludges. Four samples were incubated at 24°C during 140 days in order to simulate the processes of degradation. The simultaneous analysis of the SOF and IOF of the biodegraded samples enabled the determination of the great tendencies of the evolution of the organic content during the experiments. A global pattern of biodegradation reactions can thus be proposed: the chemical degradation of the macromolecular structure of the IOF produces extractable compounds which will be either degraded themselves into lower molecular weight compounds or mineralised. Besides, organic markers resistant to biodegradation could be determined and indexes of biodegradation proposedCette étude s'est intéressée à la caractérisation moléculaire du contenu organique de boues résiduaires de stations d'épuration de la région Lorraine. Les quarante huit échantillons collectés proviennent de stations domestiques de différentes tailles (rurales, petites urbaines et urbaines), de stations industrielles (papeteries) et de stations agro-alimentaires (laiteries et fromageries). Le premier volet développé au cours de cette étude a permis de dresser l'inventaire des composés présents dans les boues d'épuration (i) sous forme libre (fraction organique soluble- FOS) et (ii) sous forme liée à la structure macromoléculaire (fraction organique insoluble- FOI). A cette fin, les outils analytiques respectivement utilisés sont la GC-MS d'une part, et la THM-GC-MS et Py-GC-AED d'autre part. Les résultats de l'analyse de la FOS et de la FOI fournissent une information équivalente dans la mesure où ils permettent de différencier les boues selon leur origine (agro-alimentaire, industrielle ou domestique). Une empreinte moléculaire spécifique à chaque type de boues a ainsi pu être définie. Par ailleurs, l'ensemble des boues domestiques est caractérisé par un fonds géochimique pétrolier, témoignant d'une pollution diffuse commune. Une variabilité autour de ce fonds géochimique a également pu être identifiée pour certaines boues domestiques, sans relation avec la taille de la station, ni le degré d'industrialisation de la région. Ces variations, essentiellement observées au niveau de la FOS, peuvent par contre être imputées à des pollutions ponctuelles ou accidentelles dans le système de collecte des eaux usées domestiques. Ce travail a pour but de fournir, à terme, des paramètres moléculaires d'aide au suivi et au contrôle des réseaux de collecte des eaux usées. Le deuxième volet de ce projet s'est intéressé à l'étude des effets de la biodégradation sur le contenu organique des boues. Afin de simuler les processus de dégradation, quatre échantillons ont été incubés à 24°C pendant 140 jours. L'analyse couplée de la FOS et de la FOI des échantillons biodégradés a permis de déterminer les grandes tendances de l'évolution du contenu organique au cours des expérimentations. Un schéma réactionnel global de biodégradation peut ainsi être proposé : l'altération de la structure macromoléculaire de la FOI libère des composés extractibles, dégradés eux-mêmes en composés de plus bas poids moléculaire ou minéralisés. Par ailleurs, cette étude a permis de déterminer des indices de biodégradation ainsi que des marqueurs organiques résistants à cette biodégradation

Pollution des captages en rivière de Bretagne par les matières organiques. Facteurs de contrôle et évolution dans le temps

1 p.Sous l'impulsion de la DRASS Bretagne et de la Mission Bretagne Eau Pure, une étude a été lancée afin d'établir un tableau de bord de la pollution des captages en rivière de Bretagne par les matières organiques (MO) et d'en déterminer les causes, notamment le rôle des pratiques agricoles. Trois images ressortent du tableau de bord établi. La première est celle d'une forte variabilité spatiale des niveaux moyens de pollution, ceux-ci variant de 2.4 à 13.4 mg.L-1 d'oxydabilité suivant les rivières. La deuxième est celle d'une qualité d'eau relativement dégradée au plan régional du point de vue des MO avec plus de 30 captages sur 65 ayant dépassé au moins une fois la limite réglementaire des 10 mg.L-1 d'oxydabilité depuis 2005. Enfin, la troisième image est celle d'une distribution spatiale peut-être non totalement aléatoire de la pollution, les prises d'eau les plus "polluées" semblant se concentrer dans la partie nord, nord-est de la Région (Côtes d'Armor, notamment). Concernant les évolutions temporelles, plusieurs échelles de variation sont observées (journalière, saisonnière, inter-annuelles; pluri-annuelle). En particulier, les quelques séries longs termes disponibles montrent une échelle de variation étalées sur 25 ans et marquée par une augmentation continue de la teneur en MO des rivières caractérisées par un fort taux actuel de pollution. Ces mêmes quelques séries montrent que la dégradation de la qualité "organique" des eaux des rivières bretonnes actuellement fortement polluées par les MO est un phénomène toujours en cours, l'augmentation actuelle de la teneur en oxydabilité des eaux de ces rivières étant en base annuelle d'environ 0.2 mg.L-1 par an. Point important: une des séries long terme recueillies (BV de l'Elorn) montre une tendance à la diminution des concentrations en MO. Le croisement de ces données avec les facteurs propres au milieu breton (climat, topographie, pédogéologie,..) montrent que la variabilité morphologique et climatique de la Bretagne est susceptible de créer à elle seule des variations spatiales et temporelles de la concentration en MO des rivières bretonnes d'un facteur d'au moins 2 et 1.25, respectivement. Le climat pourrait être également à l'origine des évolutions à la hausse constatées depuis 25 ans. Relier directement la dégradation de la qualité "organique" des eaux des rivières de Bretagne du point de vue des MO aux changements climatiques en cours se heurte toutefois au fait que la dégradation n'a pas le caractère uniforme auquel on s'attendrait si un facteur global comme le climat devait être pris comme la cause principale des dégradations observées. Concernant le rôle des pratiques agricoles, l'analyse statistique n'a pas mis à jour de relation directe et globale entre la teneur en MO des eaux au droit des captages et des éléments comme le type d'assolement sur les BV, la pression d'épandage,... laissant plus de 50% de la variance observée dans les eaux inexpliquée. Des analyses moléculaires ont néanmoins permis de mettre en évidence qu'une partie des MO apportées par l'épandage des effluents d'élevage sur les BV se retrouvaient dans l'eau des rivières bretonnes. Le recoupement des données moléculaires avec les activités d'élevage sur les BV montrent que ce sont plutôt les activités d'élevage "bovin" et "volaille" qui pourraient être à l'origine de la dégradation de la qualité "organique" des rivières bretonnes, si tant est que l'on doive effectivement relier cette dégradation aux épandages d'effluents d'élevage pratiqués sur les BV, ce qui n'est pas encore totalement prouvé

Long-term trends in dissolved organic matter in French rivers

1 p.International audienceThis study presents long-term records of dissolved organic matter (DOM) as indicated by oxydability measurements that were constructed for four rivers in western France as back as 1979. Data show contrasted evolutions with three rivers exemplifying large increases in DOM concentrations over the period of study (a doubling of the mean annual concentration over a period of 25 years for one river), while the fourth shows decreasing DOM concentrations with time. All rivers show common inter-annual control on DOM concentration in response to a succession of dry and wet periods with a cyclicity of 5-7 years. The same cyclicity in DOM concentrations is apparent in the long-term records of DOM for rivers located in northern England. The evidence support the view that this cyclicity is climatic in origin being likely a consequence of the North Altantic Oscillation that controls the yearly amount of precipitation that falls over Europe. As regards the significance of long-term trends, we note that the onset of DOM increase in those rivers showing positive long- term DOM trends is in phase with an increase in average annual temperature. This might suggest that the change in temperature is the key mechanism that causes these trends, suggesting that the climate is also the driving force of long-term DOM trends in rivers. However, such an hypothesis is faced with the problem of explaining why one of the studied rivers shows a divergent evolution, i.e. a long-term DOM decrease. A change in hydrologic regimes must be also discarded. Alternative explanations other than climate change must thus be found. One such alternative explanation could include changes in land use and agricultural practices on river catchments. A survey of agricultural practices in the catchments drained by the four studied rivers reveals that the catchments of the river showing a long-term decrease of DOM receives massive pig manure spreading, a practice that does not occur in the other three catchments. Spreading of pig manure may acidify catchment soils, thereby promoting adsorption of organic matter on soil minerals which could ultimately limit the export of DOM by rivers. The evidence supports a view that DOM export by rivers is under the control of global, climatic factors mediated by local land use factors which can cause divergent long-term evolutions

Detection of manure-derived organic compounds in rivers draining agricultural areas of intensive manure spreading

1 p.International audienceThis study presents the potentiality of organic markers to trace the impact of animal manure in soils and rivers draining agricultural watersheds. As described by Gruau et al. (in this session), the analysis of long term records of dissolved organic matter (DOM) in five watersheds in Brittany (western of France) shows divergent trends which can not be explained solely by global changes. One alternative explanation could be that long- term records of DOM in rivers are controlled by human activities, and notably by agricultural practices. In Brittany, the agricultural intensification led to an over-application of animal manures to soils. This practice can strongly increase the amount of soil-water extractable organic matter, thereby leading to an increase of organic matter fluxes in agricultural landscapes and then to a contamination of river waters. Such an hypothesis deserves consideration in view of the massive manure fluxes that are disposed on agricultural land in many parts of the world. In this goal, our study aimed at determining potential sources of organic matter and molecular markers or specific distributions in rivers draining agricultural watersheds. In this study we focused on the analysis of pig slurries because of the importance of pig production in Brittany. The analysis of pig slurry evidenced the presence of coprostanol (5ß) as a specific marker, originating from the bio- hydrogenation of cholesterol by anaerobic bacteria. The difference with other animal or human wastes has been evidenced by two ratios: 5ß/C27 and C29/C27. After the validation of the ability of coprostanol to be a molecular marker of pig slurry, our analysis has been focused on the OM of watersheds in Brittany showing divergent evolutions. The results show a systematic relation between the C29/C27 and 5ß/C27 ratios and the type of animal breeding in each watershed. This study allows us to evidence the impact of animal breeding activities in the analysed rivers. Such a study supports the view that OM export by rivers is not solely under the control of global, climatic parameters, but also under the control of local land-use factors

Influence of natural organic matter on the solid-phase extraction of organic micropollutants: Application to the water-extract from highly contaminated river sediment

International audienceIn freshwater systems, organic micropollutants are bound to natural organic matter (NOM), which is responsible for a decrease in their recoveries by solid-phase extraction (SPE). This "negative effect" has been investigated for the SPE of polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs, nitrated PAHs and n-alkanes from salt water using Aldrich humic acid as a model of NOM. The effect has been partially obviated by the addition of isopropanol as a surfactant. The SPE protocol, developed with isopropanol, has been applied to the water-extract of a highly contaminated sediment. The water-extract has been size fractionated by cross-flow ultrafiltration into particulate (PM), colloidal (CM) and truly dissolved matter (tDM). Organic extracts from SPE experiments have been analyzed by gas chromatography­mass spectrometry. The major classes of molecules are heteroaromatic PAHs and PAHs. Those molecules are mainly bound to the tDM, which highlights: (1) the competition between organic micropollutants and natural organic molecules for available sorption sites and (2) the toxicological hazard linked to the mobilization of sediments highly contaminated by both industrial and urban activities

Nature and repartition of organic micropolluants during the mobilization of highly contaminates sediments

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Detection of manure-derived organic compounds in rivers draining agricultural areas of intensive manure spreading

International audienceIt is essential to have suitable tools able to trace the fate of manure organic matter in the environment to assess whether manure disposal on the soils of catchments could affect the organic quality of rivers. Sterol compounds ­ mainly expressed as C29 + 28/C27 and 5ß/C27 ratios ­ have been shown to be specific molecular tracers of pig, dairy and poultry manures in soils. The objective of this study was to measure C29 + 28/C27 and 5ß/C27 ratios in five Brittany rivers (Elorn, Yar, Léguer, Min Ran and Couesnon) draining agricultural catchments receiving massive annual inputs of pig, poultry and dairy manures and compare these ratios with ratios published for enriched soils and manure samples. The particulate organic fractions from the studied rivers yielded steroid signatures typical of animal manures. More specifically, a stanol compound diagnostic of pig slurry ­ the 5ß-stanol known as coprostanol ­ was found to be very widespread, with particularly high concentrations in one of the rivers (Elorn). The C29 + 28/C27 and 5ß/C27 ratios of the particulate fractions of the rivers were compared with ratios measured directly in pig, dairy and poultry manure samples, as well as with the breeding activities on river catchments. These comparisons show that the steroid profiles of the five investigated rivers correlate closely with the types of manure (i.e. pig, poultry or dairy) spread on soils in their catchments. For instance, the C29 + 28/C27 and 5ß/C27 ratios in the Elorn river are similar to the values typical of pig slurry (e.g. 5ß/C27 > 4); compared with other catchments, the soils in this area receive by far the largest amount of pig slurry. By contrast, the Yar river drains a catchment receiving only poultry and dairy manures, and its soils exhibit C29 + 28/C27 and 5ß/C27 ratios similar to those of dairy and poultry manures (e.g. 5ß/C27 1). Thus, this study indicates that the organic quality of rivers is modified in catchments where there is intense manure spreading on soils. It also provides evidence that rivers draining areas receiving different manure types may exhibit differences in the long-term evolution of their OM content. Indeed, two of the investigated river catchments receive dominantly dairy and poultry manure, and exhibit clear long-term upward trends in OM. On the other hand, one catchment receiving high proportions of pig slurry clearly shows a long-term downward trend in OM contents. A survey of the literature shows that the relative amount of OM and N received by soils in agricultural catchments could be the key parameter in determining the direction of the long-term OM trend of the river, rather than the absolute amount and/or type of manure that is applied to the soil. In any case, the present study suggests that sterol/stanol compounds may be of diagnostic value in determining whether a stream or a river is undergoing contamination by manure-derived organic matter