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Alafifi, Fatima

University of British Columbia

The occurrence of cyanobacteria blooms is a growing environmental and human health concern, especially when blooms produce cyanotoxins. The use of different advanced oxidation processes (AOPs), such as ozone (O₃) and UV based treatments, is shown to be effective for degradation of these toxins. However, different water constituents such as natural organic matter (NOM) and halide salts are proven to have a significant impact on the performance of these AOPs. This research aimed to assess the performance of O₃ and vacuum UV (VUV) based AOPs in the presence of different water quality composition, and to explore any potential synergistic effects towards enhancing the degradation of microcystin-LR (MC-LR). Samples with a concentration of 0.2 mg Lˉ¹ of MC-LR and different concentrations of dissolved organic matter (DOC), chloride and bromide ions were treated with 0.025 – 0.1 mg Lˉ¹ of ozone and/or irradiated at fluence values ranging from 40 to 306 mJ cmˉ². The results showed that the presence of chloride and bromide ions enhanced MC-LR removal significantly under VUV. Direct photolysis of chloride ions led to the formation of chlorine radicals (Cl•). Direct photolysis of bromide ions led to formation of bromine radicals (Br•). These radicals were mainly responsible for the improvement of MC-LR removal. Kinetic modeling was used to estimate the second-order rate constants for the reaction of MC-LR with Br• and dibromide radical anions (Br₂•–). The second-order rate constants were estimated to be 1 x 10¹² 1 Mˉ¹ sˉ¹ and 1 x 10⁵ Mˉ¹ sˉ¹, respectively. When VUV was combined with O₃, the MC-LR degradation was higher than the degradation achieved by each of the individual processes. The addition of chloride ions to the VUV/O₃ process further enhanced MC-LR removal. Moreover, it was concluded that the presence of halide ions has potential to enhance the efficiency of the VUV process. Also, MC-LR removal by O₃ was found to be more efficient than the VUV/O₃ process in terms of energy requirements. However, investigation of the by-products formation and their toxicity is necessary in order to assess feasibility and practicality of the VUV/Chloride and VUV/Bromide processes for MC-LR degradation.

Text

2025-04-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/84525

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/