Volume 2, numéro 1, 1989

FR :

L'eau interstitielle ou l'eau de lessivage d'un sédiment est mise en contact avec des lots de 50 femelles ovigères du copépode Tigriopus brevicornis. Notons que ce microcrustacé marin est sensible à la pollution mais résistant aux caractéristiques physico-chimiques des types d'eaux testés (salinité et température notamment). On évalue ensuite les effets de ces eaux sur la production larvaire en 10 jours et sur l'ingestion en 4 jours par les copépodes d'une suspension de Phaeodactylum tricornutum. Nous observons ici, pour des lots de sédiments provenant de la région de Marseille, des réductions de la production de larves variant de 61 % (Les Embiez) à 90 % (Vaine). Le test "consommation d'algues", bien moins sensible aboutit pour les mêmes stations à des réductions de 19 % à 35 %. Le test "production larvaire" du fait de sa plus grande sensibilité doit être préféré au test "consommation d'algues".

EN :

Most pollutants discharged into the sea are found in sediments, generally after temporary fixation in planktonic organisms. The slightest discharge leaves a trace in the soft bottoms. Thus, it may be said that these behave as good "data storage indicators" testifying to the degree of pollution present. Sediments therefore represent a privileged field in research on the state of pollution in the aquatic ecosystem. How can the degree of pollution in this field be evaluated?

A chemical analysis of pollutants in sediments is a good means of investigation to detect of degradation in the quality of waters. Most pollutants however are difficult to detect and dose. Moreover, in many cases dosage is tedious and costly. It is from this point of view that biological assays were considered essential.

Interstitial water or water used to wash a sediment was placed in contact with batches of 50 ovigerous females of the copepod Tigriopus brevicornis. This marine microcrustacean is known to be sensitive to pollution, though resisting the physical and chemical effects of the waters tested (salinity and temperature, in particular). An evaluation was the made on the effects of these waters; first on larval production during a period of ten days, and then on ingestion by copepeds of a suspension of Pheodactylum tricornutum for four days.

The results obtained here with batches of sediment from the Marseilles region show that the larval production test is the most sensitive one. Indeed, the inhibition percentages found by the larval production test range from 35 to 100 % (figure 1), whereas they vary from 5 to 55 % with the algae consumption test (figure 2). With the larval production test, it is possible to classify sediments according to their ecological quality.

From this test, moreover, the presence of harmful substances in the sediments can be rapidly detected. Being reproductible and not expensive, it supplements the far too restrictive traditional chemical analyses. When applied to estuarine sedimentary zones, combined with other tests, it should help establish a quality coefficient for sediments based on experimentation.

FR :

De 1947 à 1976, plusieurs dizaines de tonnes de mercure d'origine industrielle ont été déversées dans les eaux de la rivière Saguenay et une grande partie de ce métal toxique se retrouve aujourd'hui dans les sédiments du Fjord. Les sédiments de surface (0-2 cm) de 17 stations réparties sur tout le bassin intérieur du fjord ont été prélevés et analysés pour le mercure total. De plus, environ 150 crevettes (Pandalus borealis) ont été capturées à Sainte-Rose-du-Nord pour fins d'analyse du mercure et pour une expérience de bioaccumulation à partir d'une diète contaminée. L'analyse des données disponibles pour les sédiments de surface montre que les teneurs moyennes (0,93 ± 0,11 µg.g^-1 poids sec) en mercure n'ont pas varié de façon significative au cours des dix dernières années dans la région de Sainte-Rose-du-Nord, située dans la moitié amont du bassin intérieur. Les concentrations de mercure dans le muscle comestible des crevettes varient de 0,13 à 0,58 µg.g^-1 (poids humide) selon la taille avec une valeur moyenne de 0,36 ± 0,11 µg.g^-1. On trouve une concentration moyenne de 0,26 ± 0,09 µg.g^-1 dans le céphalothorax et la cuticule. Un accroissement rapide et important du mercure dans, l'appareil digestif a été observé chez tes crevettes adultes soumises à une diète de chair de moules préalablement contaminée (6,0 ± 1,0 µg.g^-1). Un taux de bioaccumulation de 0,09 µg.g^-1 par jour dans le muscle comestible a été estimé pour les 14 premiers jours de diète contaminée.

EN :

From 1947 to 1976, many tons of industrial mercury were tipped into the Saguenay River and a large amount of this toxic heavy metal is now in the sediments of the Saguenay Fjord. Surface sediments (0-2 cm) were collected at seventeen stations along the inner basin of the Saguenay Fjord and analysed for total mercury content. About 150 shrimps (Pandalus borealis) fished in the Sainte-Rose-du-Nord area were also used for mercury analyses and the determination of mercury uptake rate from contaminated food. The mercury concentrations in surface sediments ranged from 0.18 to 0.20 µg.g^-1 (dry weight) with a mean value of 0.63 µg.g^-1. This mean level is about one order of magnitude higher than the background level found in deep sediments. The examination of available data for surface sediments in the Sainte-Rose-du-Nord vicinity, located in the first half of the inner basin, shows the "steady state" of the mercury contamination over the last 10 years. Indeed, the mercury concentrations observed in surface sediments ranged from 0.75 to 1.20 µg.g^-1, with a mean value of 0.93 µg.g^-1 since 1976. The steady state of mercury contamination can be explained by two hypothesis : (1) an unexpected highly active bioturbation mechanism contributes to the mercury remobilisation from lower sediment layers (10-20 cm) and its vertical transportation up to the surface, or (2) the anthropogenic upstream discharge of mercury was not really stopped in 1976 and one or many unidentified sources are still active along the Saguenay River. The mercury concentrations in the edible part of shrimps (fished in November 1985) ranged from 0.13 to 0.58 µg.g-l (wet weight) with an average value of 0.36 ± 0.11 µg.g^-1. A positive and significative linear relationship (r = 0.786) is observed between the Hg concentration in the edible part and the total wet weight of the shrimp. The mean Hg in the edible part found in 1985 is not significantly different from the mean value reported in 1932. The mean concentration found in the cephalothorax and the cuticle (taken together) of shrimps was 0.26 ± 0.09 µg.g^-1. In order to estimate the mercury uptake rate by shrimps from contaminated food, a number of adult shrimps were fed with pre-contaminated mussel tissues (0.6 ± 1.0 µg.g^-1) for three weeks. A high and rapid increase of mercury concentration was observed in the digestive organs after only 24 hours. The uptake rate in the edible part was estimated at 0.09 µg.g^-1 per day during the first fourteen days of the bioassay. These findings clearly indicate the fragility of the balance between the biota and the physical environment and how fast major changes can occur when the level of contamination of the diet is modified.

FR :

Le présent article rapporte les résultats d'une investigation des facteurs géométriques applicables à des réacteurs annulaires à mélange axial complet et appliqués à la désinfection des eaux au moyen de lumière UV de 254 nm. La loi de Bunsen-Roscoe est suivie en prenant en compte la dose corrigée par un facteur géométrique m; dose=mI_ot. Le bactériophage f₂ ne montre pas de phase de latence de mortalité et constitue dès lors un modèle valable. La dose létale à 99 % mesurée est de 470 ± 30 J/m².

EN :

The f2-bacteriophage is chosen as a test organism to evaluate the geometrical factors which intervene in the disinfection of water by UV-light. This phage is an ARN and single strain cell which has the characteristic of being killed without a lethal lag phase being observed. It is also shown as a representative organism for the estimation of the virucidal action of UV-light.

In this work a cold cathode mercury lamp emitting the 254 nm photon at low intensity, th.e. 14.9 W/m² at the lamp surface, is used. The Lamp has the advantage that its photochemical yield does not depend on the temperature of the water investigated.

The geometrical factor of different annular reactors is investigated by submersing the lamp in water contained in vessels of different diameters. The introduction of an artificial competitor, that is para-hydroxybenzoïc acid, which absorbs part of the 254 nm-photons also allows the impact of the reactor geometry to be evaluated. All the experiments are carried out in batch-type conditions and the water is completely mixed during the experiments. These conditions applied in laboratory investigations are representative of those existing in plug-flow reactors with complete axial mixing of discrete portions of the liquid contained in the annular space between the lamp and the reactor.

In this work all data conform to the Bunsen-Roscoe Law relating the kinetics of first order decay to the irradiation dose : (I.t). No residual resisting organisms or "protected" organisms which could subsist at the end of exhaustive irradiation were observed.

The practical dose, that is the dose at any point of the reactors taking into account the absorption of the light and the increasing surface irradiated at increasing reactor diameter and also the finite dimension of the lamp diameter is accounted for by a single correction factor m : Dose (D) = m.I_o.t, in which, also according to the literature :

       2 r _o (1 - exp [- E (r^- - r_o) ] )

m = ______________________________

            E (r^-2 - r²_o)

where r_o and r^- are respectively the lamp radius and the reactor radius. E is the extinction coefficient (base e).

The data as a whole converge to a 99 % lethal dose of 470 ± 30 J/m² in clear water, either absorbing or not at 254 nm.

In the presence of turbidity, obtained by the introduction of 10 mgL^-1 koalin the efficiency is enhanced by 15 to 20 X, that is the apparent 99 % lethal dose is of 400 ± 30 J/m². By correcting the light intensity transmitted by reflection, this dose is about 420 J/m².

Turbidity in UV-disinfection is thus not necessarily a negative factor in disinfection of liquids with UV-light.

This investigation as a whole establishes an "economical space" between lamp surface and reactor wall of about 4 cm at which the energy consumption for a given level of disinfection attains a sufficiently tow value.

FR :

La qualité de l'effluent des systèmes de biotraitement par boues activées est souvent limitée par la performance de l'unité de décantation. Cette étude analyse les causes possibles des difficultés d'opération rencontrées dans la décantation des boues évacuées aux décanteurs secondaires d'une raffinerie de pétrole. Les objectifs visent à déterminer et à quantifier l'effet des paramètres d'opération qui affectent le fonctionnement du décanteur, en les reliant si possible à son mauvais fonctionnement, à évaluer de l'ajout d'alun et à proposer des méthodes correctives pour améliorer l'efficacité de décantation.

L'étude montre que :

- l'efficacité des décanteurs sera améliorée si le niveau d'oxygène dissous et la concentration en matières totales en suspension (MTS) dans le bassin d'aération sont respectivement maintenus entre 0,9 à 1,3 ppm et 4 300 à 4 800 mg/L;

- le pH de la liqueur mixte ne semble pas influencer la décantabitité;

- l'addition d'alun doit être évitée ou maintenue inférieure à 50 mg/L;

- l'agitation et les vitesses linéaires élevées dans les conduites d'alimentation des décanteurs doivent être évitées.

EN :

The wastewater treatment systems built in the seventies for treating the effluents from oil refineries often fail to comply with new environmental standards. The present study focuses mainly on the problem of sludge settling in the clarifiers. The purpose of this work was to determine the effect of various parameters on the settling characteristics of the activated sludge, to evaluate the rote of alun as a flocculating agent and to characterize the operation of the clarifiers primarily as it relates to the settling problem.

The influence of the quantity of the alun added and of the stirring speed on the settling characteristics of the sludge were determined in jar tests. The effects, on the performance of the clarifiers, of the level of dissolved oxygen in the bioreactor, of the pH and of the concentration in total suspended solids (TSS) maintained in the mixed liquor, were also investigated.

The studies on the sludge settleability led to the following conclusions :

- the concentration in dissolved oxygen and the concentration in TSS in the aeration tank are two parameters which have a critical effect on the effluent quality. The optimal operating intervals for these parameters are from 0.9 to 1.3 ppm for dissolved oxygen and from 4 300 to 4 800 mg/L for the TSS;

- the pH of the mixed liquor is not a main factor and does not seem to have any effect on the sludge settleability;

- the addition of alum in excess of 50 mg/L has an adverse effect on the sludge settling characteristics. Addition of alum below this level, however, improves the clarity of the residual liquor. Nevertheless, the addition of this flocculating agent is not recommended;

- the high flowrates and violent mixing in the piping system used to feed the mixed liquor from the aeration tank to the clarifiers adversely affects the solid-liquid separation in the clarifiers.

By simply stopping the addition of the flocculating agent, maintaining the dissolved oxygen concentration between 1 to 2 ppm and the TSS between 4 300 to 4 800 mg/L in the wastewater treatment unit, it was possible to improve substantially the quality of the effluent and thus meet the environmental standards.

FR :

10 paramètres physico-chimiques sont mesurés en surface dans 10 stations à 12 dates sur le lac réservoir de la Sorme (Saône-et-Loire). L'article montre comment une analyse multitableaux peut caractériser la structure spatiale et préciser sa stabilité. Les notions d'interstructure et de compromis sont accessibles par une procédure simple et efficace.

EN :

This paper is based on the observation that three-dimensional data matrices (sites x times x variables) often used in limnological investigations require statistical analyses fitted to experimental objectives. Many apparently different statistical tools (3-mode PCA of TUCKER, 1964; KROONENBERG, 1983; projection of variables WILLIAMS and STEPHENSON, 1973; DOLEDEC and CHESSEL, 1987) may be useful to clarify limnological problems such as : 1) the temporal variability of a pattern (elimination of spatial heterogenity) : 2) the spatial structure of a pattern (elimination of temporal effects, mapping of an average situation) : 3) the temporal variability of Lake stratification (stability, modification or inversion) : 4) the spatial structure of temporal variability, and 5) the between variables typology of a spatial and temporal structure. Our methodological approach allowed us to assess the temporal stability of the spatial structure of the Lake waters (question 3) using a multitable analysis known as triadic analysis (THIOULOUSE and CHESSEL, 1987).

As part of the limnological study of a reservoir Lake (Sorme reservoir Lake, Saône-et-Loire, France) 10 commonly used physical and chemical variables were studied from July 1980 to October 1931. During this period, 12 water samples were taken near the surface at each of the 10 stations scattered along the Sorme Lake (see figure 1). Main morphometric features of the Sorme Lake are : 1) a surface area equal to 230 ha, 2) a 25 km long perimeter and 3) a volume of 9.5 10⁶ m³ with a maximum depth of 13 meters upstream of the dam and an average depth of about 4 meters. Seasonal tidal range was only a few meters.

Only 2 of the 3 concepts of triadic analysis stated by THIOULOUSE and CHESSEL, 1987 are developed here : 1) for each of the 12 tables (stations x variables) coming from the 12 sampling dates, data are first centered (elimination of mean) and standardized (division by standard deviation) (see figure 2). The resulting table Y called interstructure matrix, i.e. interstructure between each of the sampling dates matrix, is organized to have sampling dates as columns and the ten physical and chemical variables at each station successively as fines. Principal Component Analysis (PCA on the variance-covariance matrix) is then applied to the interstructure matrix. In our case it is a one-dimensional matrix, i.e. according to physical and chemical variables, there is only one spatial structure common to each sampling date (figure 3 and 2) compromise matrix are associated with the successive PCA factors of the interstructure (figure 4). According to the previous remark, only the first factor is considered. Data are reorganized to have physical and chemical variables as columns, and stations as fines. This last table defines a compromise matrix labelled Z. The mapping of the numerical values of matrix Z renders a ten-dimensional description of the permanent spatial structure (figure 5). To summarize the multivariate description, matrix Z is processed with a PCA on the variance-covariance matrix producing a three-dimensional compromise (figure 6).

The interpretation of the compromise table by mapping the factorial scores of the PCA leads to a functional scheme of the reservoir Lake waters distinguishing five sectors (see figure 7) as a function of water depth, influence of tidal range, influence of tributaries and of the Sorme River. 3 stations are periodically isolated from the reservoir and produce 3 sectors with lower pH and temperature values and higher concentrations in ammonia and sulphate according to the influence of tributaries. The 4th sector is associated with the former submerged valley, i.e. main channel of the Sorme River prior to the dam closure, and demonstrated an ionic gradient concerning mainly nitrate and chloride-concentrations. The 5th sector, opposed to the latter, consists in the deeper area of the Sorme Lake which reveals rather homogeneous waters near the surface.

FR :

La retenue de Sainte-Croix sur te Verdon, mise en eau il y a dix ans, est un lac oligotrophe monomictique chaud de 2 200 ha de surface et de 80 m de profondeur maximum (profondeur moyenne 50 m). Une vidange hivernale partielle en abaisse le niveau de 8 à 16 m selon les années. La température dans l'épilimnion varie de 7 °C en février à 22 °C en juillet, avec une moyenne de plus de 900 degrés/jours au-dessus de 14 °C.

Les perches introduites depuis la mise en eau, se nourrissent des plus gros planctontes (Cladocères et Copépodes), des larves benthiques de divers insectes (Chironomides, Ephémères) ainsi que d'alevins. Malgré des conditions thermiques favorables, la croissance des perches est lente en raison de la faible densité des proies et de la concurrence avec des Cyprinidae planctonophages, ablettes et gardons, très bien représentés dans la retenue.

La maturité sexuelle est atteinte au terme de ta première année pour la majorité des mâles, la seconde année seulement pour 60 % des femelles. Mesurée sur 15 femelles de 14 à 40 cm, la fécondité variant de 2 500 à 50 000 ovules, est faible.

EN :

The large-scale hydro-electric reservoir of Lake Sainte-Croix fed by the Verdon river, was dammed in 1974 and holds 765 hm³, spreading over 2 200 ha at 477 meters above sea level. Its average and maximum depths-are 50 and 80 meters and the water level can fall 16 meters in Autumn and Winter, reducing the water cover by a maximum of 23 % during January and February. It is a warm monomictic lake where the hypolimnion is well oxygenated in all seasons. The water has an alkaline pH and is relatively poor in nutritional salts. Controlled by water temperature during the mixing period, the primary production, always tow, is limited by loss of nitrogen in the epilimnion and lack of light in the hypolimnion during the thermal stratified period.

The epilimnion temperature varies from 7 °C in February to 22 °C in July, with an average of more than 900 degrees per day per year above 14 °C. In addition to the various indigenous species, perch, roach and bleak are stocked, the latter two species being predominant now. The stomach contents of perch fished with nets and by electrical means during the Winter (December-March) and Summer (August) periods were examined and the animals' ages were determined using the opecularbone method. The scarcity of plankton compels the young as well as the adult perch to feed on macroinvertebrates of benthos. This trophic niche overlap between the two size groups creates intraspecific competition. The availability of benthic prey is conditioned to a great extent by the receeded water line in Winter (Winter tide) which leaves the essential feeding ground dry for several months and limits the development of aquatic vegetation. The existence of an interspecific roach-bleak competition, especially noticeable between the young planktivorous fry, accentuates the effects of the poor nutritional conditions on the rate of perch reproduction which is among the lowest on record. Sexual maturity is reached at the end of the first year for the males, and during the second year for only 50 % of the females. The absolute fertility measured on 15 females between 14 and 40 cm, varied from 2,500 to 50,000 eggs.

FR :

Ce travail décrit les caractéristiques hydrogéologiques et chimiques de deux lieux d'enfouissement de déchets municipaux localisés au Québec. Le site de Laterrière est en opération depuis 1971 dans une ancienne sablière. Sous les dépôts meubles, la topographie du sotte rocheux est marquée par une vallée qui forme une limite imperméable à l'aquifère de sable et impose un écoulement convergent de l'eau souterraine vers la rivière Chicoutimi. Le site de Ste-Sophie, en opération depuis 1976, repose sur une couche de 3,5 mètres de sables fins saturés recouvrant un lit d'argile marine. La surélévation de la nappe dans les déchets favorise un écoulement divergent vers le périmètre de la zone d'enfouissement.

Un réseau de piézomètres installé en bordure des deux sites a permis pendant trente mois de prélever des échantillons d'eau et de les analyser. Dans chaque panache de contamination, l'alcalinité, les ions majeurs Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl¯, le fer, le manganèse, l'azote total et ammoniacal, les DCO et DBO₅ montrent des concentrations généralement supérieures à celles de L'eau naturelle ambiante. A proximité des deux Lieux d'enfouissement, les teneurs en cadmium, chrome, nickel et plomb excèdent les normes québécoises de potabiLité de l'eau. Dans chaque cas, ta distribution des contaminants est surtout régie par le réseau d'écoulement. La dispersion hydrodynamique et les réactions géochimiques dans le sous-sol sont des processus importants d'atténuation des contaminants.

EN :

This paper describes the hydrogeological and geochemical features of two sanitary landfill sites located in the Province of Quebec : Laterriere and Ste-Sophie. The main objective is to evaluate the leachate attenuation performance of each site. For this project, the Quebec Ministry of the Environment chose two sites with contrasting hydrogeological settings.

The Laterriere landfill, in operation since 1971, covers an area of about 32 ha. The refuse is deposited in an old sandpit and the landfill boundary is located 400 meters away from the Chicoutimi River, 25 meters above the stream water level. The bedrock topography shows a valley under the landfill which acts an an impervious base for the sand aquifer and induces a convergent groundwater flow towards the river.

The Ste-Sophie landfill covers an area of 48 ha and began operating in 1976. The refuse zone is located on flat ground 350 meters away from the Ruisseau-aux-Castors. The refuse is deposited on a 3.5 meter layer of fine sands nearly saturated overlying a marine clay bed. A water table mound is observed beneath the landfill, resulting in diverging low lines outward from the center of the Landfill.

For each site, the occurence and migration of contaminants was investigated using networks of piezometers. Sampling was performed monthly over a period of thirty months and thirty parameters were analyzed on each sample. The analytical results were entered in a database and treated by statistical methods.

The shape of each contamination plume is controlled mainly by the groundwater flow system. At Laterriere, the plume is restricted to a narrow path between the landfill and the river and inside a bedrock valley. This flow net has been simulated by a two-dimensional finite elements model. At Ste-Sophie, the divergence of flow lines due to groundwater mounding beneath the site causes dispersion of contaminants around the landfill. The use of an analytical solution shows that longitudinal dispersivity is a major process of contaminant migration.

For the two landfills, the highest concentrations of contaminants occur directly beneath or close to the boundaries of the landfills. Total alkalinity, Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl¯, iron, manganèse, total and ammoniacal nitrogen, chemical and biological oxygen demand (COD and BOD) are much above background levels throughout the plume. Sulfate is also a major contaminant at Ste-Sophie with concentration of 1100/mg/l. The concentrations of cadmium, chrome, nickel and lead exceed the drinking water standards near the two landfill sites but they decline rapidly in the direction of flow. At Laterriere, the decline in chloride concentration measured at the discharge point S-23 is about 85 % while the decline of reactive contaminants, such as iron and COD, is respectively 98 and 99.7 %.

Finally, we discuss hydrogeological criteria for landfill site selection in Quebec.