Effets differencies et confondus de la qualite de l'eau sur l'efficacite de la desinfection des eaux potables (French text)

The general objective of this thesis was to study inactivation of resistant organisms in natural waters in order to identify the origins of the observed lower inactivation in natural waters. More specifically, this project aimed at: (1) Comparing the effect of pH, temperature, natural organic matter and turbidity on the efficacy of free chlorine and chlorine dioxide, (2) Evaluate the interactions (synergies - antagonisms) existing among water quality variables. For example, is the pH effect influence by water temperature? (3) Study the conditions promoting microbial aggregation and evaluate the increase in resistance gained through this mechanism, (4) Compare inactivation data in synthetic waters and natural waters of various characteristics, (5) Confirm the adequacy of current safety factors employed during the design of disinfection processes. The initial phase of this project consisted in studying the role of turbidity, NOM, pH and temperature on the efficacy of free chlorine toward B. subtilis spores and MS2 coliphages. In order to reduce the number of assays to realise and increase the robustness of our demonstration, a partial half-factorial statistical design was used, which include eight water types (pH 6.5--8.5, T = 7--22°C, DOC = 0--5 mg/L, 0--5 NTU) for which three replicates were done. Temperature and pH were the most dominant variables, accounting for more than 78% of the variance of the doses requires to inactivate 99% (2-log) of MS2 coliphages or spores. The interaction of pH and temperature was statistically significant, being the 3rd most important factor to predict the variations in chlorine efficacy.; The second phase of this project consisted in studying the role of turbidity, NOM, pH and temperature on the efficacy of chlorine dioxide toward B. subtilis spores and MS2 coliphages. For this oxidant, a different modelling strategy had to be employed due to the presence of microbial aggregates, which caused a deviation from the traditional Chick-Watson kinetic (tailing).; The third part of this project validated the observed effects in synthetic waters using natural waters originating from three water treatment plants (WTP) in North America and one WTP located in the Caribbean (Atlanta, GA; Grand Rapids, MI; Montreal, PQ and San Juan, PR). These assays were conducted on raw waters spiked with B. subtilis spores and having undergone various treatment protocols (filtration, buffering, etc.). (Abstract shortened by UMI.)...