Graduate Thesis Or Dissertation


Sunlight-induced Photochemical Processes in Natural and Wastewater Treatment Systems Public Deposited

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  • Photochemical processes initiated by sunlight irradiation in surface waters are known to influence a variety of environmentally-relevant processes by interacting with organic matter (OM), microorganisms, and other water constituents. An important role of OM in water bodies is that of a photosensitizer in the formation of reactive intermediates (RI), including excited states, hydroxyl radicals (HȮ) and singlet oxygen (¹O₂). Such RI are known to react at relatively high rates with various organic contaminants and microbes, thus affecting their fate in the environment as well as natural treatment systems (NTS). This work contributes to the understanding of these relevant photochemical processes by looking at both the underlying mechanisms affecting the formation of RI and the effects of such processes upon microbial populations. Concentrations of ¹O₂ ([¹O₂]ss) and quantum yields (Φso) were determined for OM present in or derived from wastewater (WWOM). Both size fractionation of WWOM and its chemical oxidation resulted in increases in Φso. The correlations between the photosensitizing properties of WWOM and optical characteristics (e.g., absorbance, E2:E3 ratio) are evaluated and a model for the prediction of [¹O₂]ss is proposed. Photophysical and photochemical processes of OM of distinct origins and molecular sizes were further evaluated through the analysis of absorbance, fluorescence, and the formation of various RI of interest. Larger size fractions displayed higher absorptivity that extends further into the visible region while smaller components displayed higher quantum yields for fluorescence and all RI measured. Possible explanations for the observed results are proposed based on the increased prevalence of non-radiative energy decay processes in larger OM molecules. The influence of OM on the photoinactivation of Enterococcus faecalis was evaluated under simulated sunlight due to their relevance for disinfection in NTS. The presence of OM resulted in increased inactivation rates compared to sensitizer-free experiments, suggesting that its role as a photosensitizer is greater than its impact in shielding microorganisms from light. Estimations of the endogenous and exogenous inactivation rates of E. faecalis as a function of depth in the presence of OM are presented and the implications of these results in the design of NTS are discussed.
Date Issued
  • 2015
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  • 2019-11-14
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