Isolation and Characterization of Microbes Degrading Octachlorodibenzofuran under Aerobic Conditions
| Autor: | Yang-YuLin, 林洋宇 |
|---|---|
| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 Highly chlorinated dioxins contribute mainly to total toxicity and mass concentration of dioxin congeners emitted to the environments. These persistent organic pollutants are chemically stable, low soluble, high hydrophobic, and recalcitrant to microbial degradations, so as to be easily accumulated in higher organisms via food chains, which in turn greatly affect health and ecology. Octachlorodibenzofuran (OCDF) fully substituted with chlorine as a model congener was studied. The aims of this study are to develop the bacteria agents capable of degrading OCDF aerobically and apply them to effectively remedy dioxin-contaminated soil. The contaminated soil, in which more than 90% of total toxic dioxins (toxicity level, 6.4 µg I-TEQ/kg) were octa-chlorinated dioxins was used for isolating potential OCDF degraders. Totally, 40 aerobic cultures from 102 bacterial colonies were obtained with OCDF as the substrate, and phylogenetically classified over three phyla and thirteen genera. This result demonstrated that the diversified functional microbes can tolerate the high concentrations of dioxin in soil. With high potential of those isolates capable of dioxin degradation, six cultures from the genera Bacillus, Rhodococcus, Micrococcus and Mesorhizobium and from Sphingomonadaceae were demonstrated with excellent degradation capacities of OCDF. The average degradation efficiency were 26%-43% within a 21-d incubation. This is the first report, showing diversified bacteria for aerobic degradation of OCDF. Further, the specialists of Bacillus, Rhodococcus, Micrococcus and Pseudomonas were applied to actual dioxin-contaminated soil to study the effectiveness of dioxin degradations. After 21 days of incubation, the total toxicity level was decreased by 17%, 15%, 17% and 42%, respectively. The result showed that the soil dioxins can be detoxified by these bacteria under aerobic conditions. The mixed bacterial agents were then used for degradation of soil dioxins under various conditions. The results suggested that with the conditions at pH 8.1 and soil size of 93.5 µm, the removal of soil dioxins achieved the highest, with average toxicity loss of 34% and 26%. By measuring the amount of bacterial DNA in soil, it was suggested that microbial quantity can substantially increase at the conditions of soil size at 31µm and pH 6.3. In conclusion, this study uncovered that the OCDF degraders could be developed within complex microbial community in the contaminated soil. The factors such as bioavailable mercury, pH and size of soil particle (or organic matter) were determinant for the microbial growth of OCDF degraders in soil and hence the degradation efficiency. The overall results will be valuable for operating bioremediation and bioaugmentation on soil dioxins. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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