Real-Time Cyanobacteria Monitoring in Water Supply Systems to Manage Risks to Drinking Water Quality

«RÉSUMÉ: Dans le monde entier, il y a eu une augmentation de la présence de proliférations des cyanobactéries (CB) potentiellement toxiques dans les sources d'eau potable et dans les usines de traitement de l'eau potable (UTEP). Les méthodes conventionnelles de surveillance de l'abondance de CB sont fastidieuses, chronophage et nécessitent des opérateurs hautement qualifiés et expérimentés. De plus, ces méthodes ne sont pas toujours efficaces à capturer les fluctuations de la densité de CB. Cela pourrait entraîner un délai entre l'échantillonnage ponctuel et les ajustements de traitement correspondants. Par conséquent, ce retard entrave la capacité des opérateurs à réagir à la formation et à l'atténuation des proliférations de CB. Des sondes de fluorescence in situ en temps quasi réel pour la détection rapide du phycocyanine (PC), un pigment spécifique aux cyanobactéries, ont été efficacement déployées comme moyen pour déterminer l'abondance de CB dans les sources d'eau potable. L'apparition d'efflorescences peut affecter l'efficacité à éliminer les CB, entraînant une accumulation des CB et des cyanotoxines dans divers processus de UTEP. Jusqu’ à présent l’adoption des sondes est relativement moins appliquée à l'intérieur des stations d'épuration à grande échelle. Cette recherche a étudié l'application de la sonde de fluorescence PC in situ comme outil de surveillance en temps réel du CB à la prise d'eau et dans les stations d'épuration. La recherche contient trois thèmes principaux: (1) les interférences associées aux lectures de la sonde; (2) l’interprétation du risque CB via l’utilisation des sondes in situ au sein des UTEP; et (3) la gestion des efflorescences à la source et dans UTEP. »

Abstract

«ABSTRACT: Worldwide, there has been an increase in the presence of potentially toxic cyanobacterial (CB) blooms in drinking water sources and within drinking water treatment plants (DWTPs). Conventional monitoring methods for CB abundance are tedious and time consuming and require highly trained and experienced operators. Moreover, such methods may not capture the fluctuations of CB density. This could result in the delay between discrete sampling and the corresponding treatment adjustments. Consequently, this delay impedes the ability of the plant operators to respond to the formation and mitigation of CB blooms. ear real time in situ fluorescence probes for rapid detection of the cyanobacteria-specific pigment, i.e. phycocyanin (PC), have been effectively deployed as a means to determine CB abundance in drinking water sources. The occurrence of bloom may affect the CB removal efficiency, leading to CB and cyanotoxins breakthrough into various processes of DWTPs. Yet, there is relatively less adoption of the probe applied inside the full-scale DWTPs. This research investigated the application of in situ PC fluorescence probe as a tool for real-time monitoring of CB at the water intake and within the DWTPs. The research contains three main themes: (1) interferences associated with probe readings; (2) CB risk interpretation by in situ probes within the DWTPs; and (3) management of blooms at the source and across the drinking water treatment plant. The first part of the study was to investigate the factors affecting the interpretation of in situ PC fluorescence readings. The interference of Suwannee River NOM (SRNOM) and the water temperature was conducted with laboratory-cultivated CB species and/or extracted PC pigment. The results showed that high SRNOM content in the water could lead to an underestimation of cell-bound CB PC readings. The fluorescence excitation-emission matrix (EEM) confirmed the decreased cell fluorescence intensity caused by the addition of SRNOM. We also found PC probe readings can be significantly affected by temperature in the range of their typical application (6–33 °C), and such interference could be reduced by applying the correction algorithms. Additionally, field samples from a water intake of a DWTP were also evaluated. We found the correlation between probe readings and taxonomic cell counts from the field samples is unreliable, and only biovolume-based estimations are a relevant option for management purposes. A simultaneous measurement of the other physical-chemical parameters by the probe may help increase the accuracy of PC readings.»