Title page for ETD etd-090699-164851


Type of Document Dissertation
Author Ma, Guihua
Author's Email Address guma@vt.edu
URN etd-090699-164851
Title The Kinetics, Biochemical Patterns, and Microbial Ecology in Multiredox (Anoxic, Microaerobic, Aerobic) Activated Sludge Systems Treating btx Containing Wastewater
Degree PhD
Department Civil Engineering
Advisory Committee
Advisor Name Title
Love, Nancy G. Committee Chair
Benoit, Robert E. Committee Member
Dietrich, Andrea M. Committee Member
Novak, John T. Committee Member
Stevens, Ann M. Committee Member
Terlesky, Kathy C. Committee Member
Keywords
  • 16S rRNA
  • BTX
  • microbial activity
  • anoxic
  • enzymes
  • dot blot hybridization
  • standard blots
  • energy balance
  • redox
  • aerobic
  • microaerobic
  • probe
Date of Defense 1999-09-02
Availability unrestricted
Abstract
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 NOx-supplemented compared to NOx-free microaerobic conditions, and the specific biodegradation rates under aerobic and NOx-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.

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