BTX biodegradation rates, biochemical expression patterns and microbial ecology were studied under anoxic (denitrifying), anoxic/microaerobic/aerobic, and anoxic/microaerobic conditions in activated sludge sequencing batch reactors. The studies showed that toluene and m-xylene were denitrified via benzoyl-CoA reductase. Although benzene, o-, and p-xylene were recalcitrant under denitrifying conditions, they were biodegraded under microaerobic (< 0.2 mg/L dissolved oxygen) and nitrate or nitrite (NOx)-supplemented microaerobic conditions. The patterns of the specific enzymes associated with BTX biodegradation under microaerobic conditions indicated that the three compounds were metabolized by oxygen-dependent pathways. The expression levels of catechol 1, 2-dioxygenase and catechol 2, 3-dioxygenase under microaerobic conditions were induced to levels as high as under aerobic conditions (> 4 mg/L dissolved oxygen). Benzene, o-, and p-xylene biodegradation rates were twice as fast under NO<sub>x</sub>-supplemented compared to NO<sub>x</sub>-free microaerobic conditions, and the specific biodegradation rates under aerobic and NO<sub>x</sub>-supplemented microaerobic conditions were comparable.
16S rRNA probes targeting representative toluene-degraders were used to investigate the microbial communities in the three sequencing batch reactors by using a dot blot hybridization technique. The hybridization results suggest that multiple redox environments fostered a more diverse microbial community and the activities of the target organisms in the reactors with multiple redox environments were higher than in the single redox reactor. Additionally, facultative toluene-degraders appeared to play a less significant role than the strict anoxic and aerobic toluene-degraders in all three SBRs. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/28883 |
| Date | 08 September 1999 |
| Creators | Ma, Guihua |
| Contributors | Civil Engineering, Love, Nancy G., Novak, John T., Dietrich, Andrea M., Stevens, Ann M., Terlesky, Kathy C., Benoit, Robert E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | vita.pdf, appendix.pdf, dissertation.pdf |
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