| Summary: | 碩士 === 輔英科技大學 === 環境工程與科學系碩士班 === 95 === This study is to investigate the Microcystin-LR (MC-LR) elimination in water treatment by means of pre-ozonation in waters with various hardness. After the water samples were treated with ozone, high performance liquid chromatography (HPLC) was used to determine the MC-LR concentration in samples, while the O3 residual concentration was measured on a UV/Vis spectrophotometer. Experiments were carried out in the laboratory with water samples synthetically-made from ultrapure water and taken from natural water body from Cheng Ching Lake Advanced Water Treatment Works (CCLAWTW), with or without MC-LR addition. Synthetic hard water samples were prepared by adding CaCl2‧H2O to simulate hard water with hardness of 180 and 300 mg/L as CaCO3. Samples were left to react with O3 within a specific time interval and MC-LR and O3 concentrations were measured before and after the tests. Meanwhile, total organic carbon (TOC) in samples was also measured to evaluate the MC-LR degradation in competition with other natural organic matters (NOMs) under O3 oxidation.
In the tests carried out with synthetically-made water samples, natural degradation of MC-LR was not observed while there was no hardness present in water. Nevertheless, the natural degradation increased when the hardness in water increased. With an O3 dose of 0.5 mg/L, MC-LR under 100 μg/L was completely removed from hard water with the hardness of 300 mg/L as CaCO3 or less by pre-ozonation. Results from the oxidation tests of samples taken from Cheng Ching Lake revealed there are other NOMs competing ozone with MC-LR—the consumption of O3 was rapid, while the MC-LR added in samples could not be removed successfully. When the ozone dosage was doubled from 50 to 100 mg/L, the removal of 100 μg/L MC-LR was slightly improved but not increased proportionally with ozone dosages. Analysis of TOC confirmed the other NOMs in natural water samples competed with MC-LR for O3 in the pre-ozonation step, while the NOMs appeared to react faster with O3 than MC-LR.
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