Optimal Treatment Strategies to Prevent and Manage Cyanobacteria and Cyanotoxins in Drinking Water Sludge

Health-related concerns on accumulation of cyanobacteria and cyanotoxins in the sludge of conventional treatment processes (coagulation, flocculation, sedimentation, and filtration) have been raised in drinking water treatment plants (DWTPs) in recent years. The fate of cyanobacteria and cyanotoxins in the sludge is complex due to the simultaneous impact of cyanobacterial composition in the intake water, environmental conditions, and various phenomena such as cell survival, growth, lysis, and cyanotoxin release during sludge storage. However, little information about the dynamics of cyanobacterial shifts from the intake water towards sludge and supernatant, the fate of cyanobacteria and cyanotoxins during sludge storage, and treatment of cyanobacteria-laden sludge is available. The general objective of this research study is to investigate the fate of cyanobacteria and cyanotoxins in the sludge of DWTPs during storage and handling. The specific objectives are to: i) Diagnose critical points of DWTPs where cyanobacteria cells and their associated cyanotoxins accumulate, ii) Determine the relationship between cyanobacterial communities in the intake water, sludge, and sludge supernatant; iii) Determine the impact of nutrients on cyanobacterial community shifts in the intake water, sludge, and sludge supernatant; iv) Compare taxonomic cell counts with shotgun metagenomic sequencing results; v) Validate cyanobacterial cell growth during sludge storage, vi) Study the dynamics of the cyanobacterial compositions in the stored sludge under controlled conditions, vii) Investigate the most resistant and susceptible cyanobacterial genus during sludge storage, viii) Study the potential health impact (i.e. cyanotoxin release) of the genera surviving sludge storage, ix) Investigate the impact of oxidation on cyanobacteria and cyanotoxins in both lab- and full- scales, x) Determine the efficiency of oxidation during sludge storage, xi) Evaluate the impact of oxidation and stagnation on microbial and cyanobacterial communities, xii) Conduct a critical review on the fate of cyanobacteria and cyanotoxins in conventional treatment plants' sludge and during sludge storage and, xiii) Develop an operational decision framework to determine the best practice to minimize risks associated with cyanobacteria and cyanotoxin presence in DWTPs.

Résumé

Ces dernières années, l'accumulation de cyanobactéries et leur cyanotoxines dans les boues générées par des procédés de traitement conventionnels (coagulation, floculation, décantation et filtration) ont suscité des inquiétudes liées à la santé dans les usines de filtration de l'eau potable. Le devenir des cyanobactéries et cyanotoxines dans les boues est complexe en raison de l'impact simultané de la composition des cyanobactéries de l'eau brute, des conditions environnementales et de divers phénomènes tels que la survie des cellules, la croissance, la lyse et le relâchement de cyanotoxines pendant le stockage des boues. Cependant, peu d'informations est disponible sur i) la dynamique des changements de la composition de la communauté cyanobactérienne entre l'eau brute et les boues stockées, ainsi que le surnageant associé, ii) le devenir des cyanobactéries et cyanotoxines lors du stockage de boues et iii) le traitement des boues contenant des cyanobactéries et cyanotoxines. L'objectif général de cette recherche est d'étudier le devenir des cyanobactéries et des cyanotoxines dans les usines de filtration de l'eau potable pendant le stockage et la manipulation.