Revue sur l’état actuel des connaissances des procédés utilisés pour l’élimination des cyanobactéries et cyanotoxines lors de la potabilisation des eaux

Les toxines cyanobactériennes sont des contaminants importants des écosystèmes aquatiques et constituent un risque pour la santé humaine. Les cyanobactéries peuvent libérer des toxines dans l’eau, particulièrement lors de la lyse des cellules qui se produit souvent au moment de leur passage à travers la filière conventionnelle de potabilisation des eaux. Dans cet article de revue de la littérature, les normes sur la qualité de l’eau concernant les toxines ainsi que les principales méthodes de détection des toxines sont d’abord présentées. Les méthodes d’élimination des cyanobactéries et des cyanotoxines sont ensuite décrites et leur performance discutée. Les procédés conventionnels présentés sont la coagulation/floculation, la clarification, la filtration sur sable, l’utilisation du charbon actif ainsi que l’oxydation chimique par chloration ou par le permanganate de potassium. Les méthodes alternatives présentement en développement pour optimiser les systèmes actuels de potabilisation des eaux ou remplacer les technologies conventionnelles trop peu efficaces pour l’élimination des polluants émergents (par ex., les procédés d’oxydation avancée et la filtration membranaire) sont également présentées. Des procédés conventionnels tels que la chloration peuvent s’avérer inadéquats, notamment par leur manque de fiabilité pour l’oxydation des cyanotoxines et par le risque encouru suite à la formation de sous-produits toxiques (par ex., les organochlorés). Des méthodes alternatives telles que la combinaison d’ozone et de peroxyde d’hydrogène permettent une oxydation fiable des cyanotoxines en assurant un effet rémanent à la sortie du contacteur. Ce type de traitement peut être facilement mis en oeuvre dans les usines de potabilisation des eaux possédant déjà une unité d’ozonation. L’utilisation du charbon actif, notamment sous forme de poudre, peut être efficace lors de contaminations ponctuelles par les fleurs d’eau de cyanobactéries. Ce document fait ainsi une synthèse de ces procédés chimiques, physiques ou physico-chimiques contribuant à l’élimination des cyanotoxines et des cyanobactéries lors de la potabilisation des eaux.Cyanobacterial toxins are important contaminants of aquatic ecosystems and present a risk for human health. Cyanobacteria can release toxins in water, particularly following cell lysis, which often happens during their passage through a conventional water treatment plant. In this literature review, water quality guidelines for the elimination of cyanotoxins and major detection methods of cyanotoxins are briefly presented. The processes used for cyanobacteria and cyanotoxin removal from drinking water are then reviewed and their performance discussed. The conventional methods presented are: coagulation/flocculation, clarification, sand filtration, activated carbon and chemical oxidation with chlorination or potassium permanganate. Alternative methods that are presently developed to enhance existing treatment plants or to replace conventional technologies that are less effective in removing emergent pollutants (e.g., advanced oxidation processes and membrane filtration) are also presented. Conventional methods such as chlorination can be inappropriate, notably because of their inability to fully oxidize cyanotoxins and the associated risk of formation of toxic by-products (e.g., organochlorinated compounds). Alternative methods such as the combination of ozone and hydrogen peroxide are more reliable to eliminate cyanotoxins, with a residual effect downstream from the treatment contactor. In addition, this type of treatment can be easily implemented in water treatment plants that are already using ozonation. The use of activated carbon, notably in the form of powder, can be efficient in the case of point contamination by cyanobacterial blooms. This document aims to synthesize these chemical, physical and physico-chemical methods to eliminate cyanotoxins and cyanobacteria during the treatment of drinking water

Winter accumulation of methane and its variable timing of release from thermokarst lakes in subarctic peatlands.

Previous studies of thermokarst lakes have drawn attention to the potential for accumulationof CH4under the ice and its subsequent release in spring; however, such observations have not beenavailable for thermokarst waters in carbon‐rich peatlands. Here we undertook a winter profiling of fiveblack‐water lakes located on eroding permafrost peatlands in subarctic Quebec for comparison with summerprofiles and used a 2‐year data set of automated water temperature, conductivity, and oxygenmeasurements to evaluate how the annual mixing dynamics may affect the venting of greenhouse gases tothe atmosphere. All of the sampled lakes contained large amounts of dissolved CH4under their winter icecover. These sub‐ice concentrations were up to 5 orders of magnitude above air equilibrium (i.e., theexpected concentration in lake water equilibrated with the atmosphere), resulting in calculated emissionrates at ice breakup that would be 1–2 orders of magnitude higher than midsummer averages. The amount ofCO2dissolved in the water column was reduced in winter, and the estimated ratio of potential diffusive CO2to CH4emission in spring was half the measured summer ratio, suggesting a seasonal shift inmethanogenesis and bacterial activity. All surface lake ice contained bubbles of CH4and CO2, but thisamounted to <5% of the total amount of the dissolved CH4and CO2in the corresponding lake water column.The continuous logging records suggested that lake morphometry may play a role in controlling the timingand extent of CH4and CO2release from the water column to the atmosphere

Développement d’outils de détection des fleurs d’eau d’algues sur les lacs du Québec méridional.

L’occurrence des fleurs d’eau d’algues (FEA) est devenue une préoccupation croissante pour la société, surtout lorsqu'elles sont dominées par les cyanobactéries toxiques. Notre groupe développe une méthode pour étudier la dynamique spatio-temporelle des FEA et identifier les facteurs environnementaux et météorologiques qui les régissent. La télédétection est déjà utilisée pour générer une cartographie des FEA sur les lacs du Québec méridional à l'aide du satellite MODIS, qui fournit des images quotidiennes et gratuites permettant de représenter la distribution et l'intensité des FEA sur un plan d'eau avec une résolution de 250 m2. La nouvelle technologie des drones hyperspectraux sera utilisée pour définir spatialement les FEA et distinguer les différents groupes d'algues incluant les cyanobactéries. Une banque de signatures spectrales sera générée à l'aide de cultures d'algues. Nous ferons ensuite le quadrillage de quelques lacs touchés par différentes intensités et compositions de FEA à l'aide du senseur installé sur le drone. Pour valider ces résultats, en plus de l'échantillonnage d'eau conventionnel (chlorophylle-a, taxonomie), des sondes de fluorescence EXO de YSI sont utilisées pour estimer la biomasse du phytoplancton et des cyanobactéries. Ces sondes multiparamétriques mesurent également la turbidité et la matière organique dissoute pouvant interférer sur les estimations de la biomasse. Les données recueillies par une sonde mobile servent à calibrer un algorithme d’estimation utilisant les données du drone avec une haute résolution spatiale et spectrale. Une sonde stationnaire fixée à une bouée permet de recueillir des données à haute fréquence temporelle et suivre les variations saisonnières au lac StCharles, réservoir d'eau potable pour la Ville de Québec et subissant une eutrophisation. Une fois calibré, cet algorithme permettra la validation des images satellitaires et ainsi combler l’écart qui existe actuellement entre les données satellitaires de résolution spatiale moyenne (par ex. MODIS) et les données in situ, conduisant à une estimation biaisée, en particulier dans la phase d'initiation des FEA où les densités sont encore faibles. À terme, les outils optiques développés permettront d’identifier la dynamique spatio-temporelle d’une FEA à haute résolution spatiale et spectrale de manière plus précise et rapide, et comprendre les facteurs environnementaux modulant leurs apparitions

Spatiotemporal Variability in Phytoplankton Bloom Phenology in Eastern Canadian Lakes Related to Physiographic, Morphologic, and Climatic Drivers.

Phytoplankton bloom monitoring in freshwaters is a challenging task, particularly when biomass is dominated by buoyant cyanobacterial communities that present complex spatiotemporal patterns. Increases in bloom frequency or intensity and their earlier onset in spring were shown to be linked to multiple anthropogenic disturbances, including climate change. The aim of the present study was to describe the phenology of phytoplankton blooms and its potential link with morphological, physiographic, anthropogenic, and climatic characteristics of the lakes and their watershed. The spatiotemporal dynamics of near-surface blooms were studied on 580 lakes in southern Quebec (Eastern Canada) over a 17-year period by analyzing chlorophyll-a concentrations gathered from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite images. Results show a significant increase by 23% in bloom frequency across all studied lakes between 2000 and 2016. The first blooms of the year appeared increasingly early over this period but only by 3 days (median date changing from 6 June to 3 June). Results also indicate that high biomass values are often reached, but the problem is seldom extended to the entire lake surface. The canonical correlation analysis between phenological variables and environmental variables shows that higher frequency and intensity of phytoplankton blooms and earlier onset date occurred for smaller watersheds and higher degree-days, lake surface area, and proportion of urban zones. This study provides a regional picture of lake trophic state over a wide variety of lacustrine environments in Quebec, a detailed phenology allowing to go beyond local biomass assessments, and the first steps on the development of an approach exploiting regional trends for local pattern assessments

Abiotic control of underwater light in a drinking water reservoir: Photon budget analysis and implications for water quality monitoring.

In optically complex inland waters, the underwater attenuation of photosynthetically active radiation (PAR) is controlled by a variable combination of absorption and scattering components of the lake or river water. Here we applied a photon budget approach to identify the main optical components affecting PAR attenuation in Lake St. Charles, a drinking water reservoir for Quebec City, Canada. This analysis showed the dominant role of colored dissolved organic matter (CDOM) absorption (average of 44% of total absorption during the sampling period), but with large changes over depth in the absolute and relative contribution of the individual absorption components (water, non-algal particulates, phytoplankton and CDOM) to PAR attenuation. This pronounced vertical variation occurred because of the large spectral changes in the light field with depth, and it strongly affected the average in situ diffuse absorption coefficients in the water column. For example the diffuse absorption coefficient for pure-water in the ambient light field was ten-fold higher than the value previously measured in the blue open ocean and erroneously applied to lakes and coastal waters. Photon absorption budget calculations for a range of limnological conditions confirmed that phytoplankton had little direct influence on underwater light, even at chlorophyll a values above those observed during harmful algal blooms in the lake. These results imply that traditional measures of water quality such as Secchi depth and radiometric transparency do not provide a meaningful estimate of the biological state of the water column in CDOM-colored lakes and reservoirs

Effects of phytoplankton blooms on fluxes and emissions of greenhouse gases in a eutrophic lake.

Lakes are important sources of greenhouse gases (GHGs) to the atmosphere. Factors controlling CO₂, CH₄ and N₂O fluxes include eutrophication and warming, but the integrated influence of climate-warming-driven stratification, oxygen loss and resultant changes in bloom characteristics on GHGs are not well understood. Here we assessed the influence of contrasting meteorological conditions on stratification and phytoplankton bloom composition in a eutrophic lake, and tested for associated changes in GHGs inventories in both the shallow and deep waters, over three seasons (2010-2012). Atmospheric heatwaves had one of the most dramatic effects on GHGs. Indeed, cyanobacterial blooms that developed in response to heatwave events in 2012 enhanced both sedimentary CH₄ concentrations (reaching up to 1mM) and emissions to the atmosphere (up to 8 mmol m⁻² d⁻¹). That summer, CH₄ contributed 52% of the integrated warming potential of GHGs produced in the lake (in CO₂ equivalents) as compared to between 34 and 39% in years without cyanobacterial blooms. High CH₄ accumulation and subsequent emission in 2012 were preceded by CO₂ and N2O consumption and under-saturation at the lake surface (uptakes at -30 mmol m⁻² d⁻¹ and -1.6 µmol m⁻² d⁻¹, respectively). Fall overturn presented a large efflux of N₂O and CH₄, particularly from the littoral zone after the cyanobacterial bloom. We provide evidence that, despite cooling observed at depth during hot summers, CH₄ emissions increased via stronger stratification and surface warming, resulting in enhanced cyanobacterial biomass deposition and intensified bottom water anoxia. Our results, supported by recent literature reports, suggests a novel interplay between climate change effects on lake hydrodynamics that impacts both bloom characteristics and GHGs production in shallow eutrophic lakes. Given global trends of warming and enrichment, these interactive effects should be considered to more accurately predict the future global role of lakes in GHG emissions

Arctic microbial ecosystems and impacts of extreme warming during the International Polar Year

As a contribution to the International Polar Year program MERGE (Microbiological and Ecological Responses to Global Environmental change in polar regions), studies were conducted on the terrestrial and aquatic microbial ecosystems of northern Canada (details at: http://www.cen.ulaval.ca/merge/). The habitats included permafrost soils, saline coldwater springs, supraglacial lakes on ice shelves, epishelf lakes in fjords, deep meromictic lakes, and shallow lakes, ponds and streams. Microbiological samples from each habitat were analysed by HPLC pigment assays, light and fluorescence microscopy, and DNA sequencing. The results show a remarkably diverse microflora of viruses, Archaea (including ammonium oxidisers and methanotrophs), Bacteria (including filamentous sulfur-oxidisers in a saline spring and benthic mats of Cyanobacteria in many waterbodies), and protists (including microbial eukaryotes in snowbanks and ciliates in ice-dammed lakes). In summer 2008, we recorded extreme warming at Ward Hunt Island and vicinity, the northern limit of the Canadian high Arctic, with air temperatures up to 20.5 \ub0C. This was accompanied by pronounced changes in microbial habitats: deepening of the permafrost active layer; loss of perennial lake ice and sea ice; loss of ice-dammed freshwater lakes; and 23% loss of total ice shelf area, including complete break-up and loss of the Markham Ice Shelf cryo-ecosystem. These observations underscore the vulnerability of Arctic microbial ecosystems to ongoing climate change.Peer reviewed: YesNRC publication: Ye

Arctic microbial ecosystems and impacts of extreme warming during the International Polar Year

As a contribution to the International Polar Year program MERGE (Microbiological and Ecological Responses to Global Environmental change in polar regions), studies were conducted on the terrestrial and aquatic microbial ecosystems of northern Canada (details at: http://www.cen.ulaval.ca/merge/). The habitats included permafrost soils, saline coldwater springs, supraglacial lakes on ice shelves, epishelf lakes in fjords, deep meromictic lakes, and shallow lakes, ponds and streams. Microbiological samples from each habitat were analysed by HPLC pigment assays, light and fluorescence microscopy, and DNA sequencing. The results show a remarkably diverse microflora of viruses, Archaea (including ammonium oxidisers and methanotrophs), Bacteria (including filamentous sulfur-oxidisers in a saline spring and benthic mats of Cyanobacteria in many waterbodies), and protists (including microbial eukaryotes in snowbanks and ciliates in ice-dammed lakes). In summer 2008, we recorded extreme warming at Ward Hunt Island and vicinity, the northern limit of the Canadian high Arctic, with air temperatures up to 20.5 \ub0C. This was accompanied by pronounced changes in microbial habitats: deepening of the permafrost active layer; loss of perennial lake ice and sea ice; loss of ice-dammed freshwater lakes; and 23% loss of total ice shelf area, including complete break-up and loss of the Markham Ice Shelf cryo-ecosystem. These observations underscore the vulnerability of Arctic microbial ecosystems to ongoing climate change.Peer reviewed: YesNRC publication: Ye