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The presence of natural estrogens, a class of endocrine disrupting compounds, in water has caused increasing concerns over their adverse impacts on the health of aquatic eco-systems and human beings. In this study, adsorption characteristics of two natural estrogens, 17β-estradiol (E2) and estrone (E1), on granular activated carbon (GAC) were investigated in isotherm tests and in a GAC column. The GAC column was then converted to a biologically active carbon (BAC) column and the removal efficiency of E2 and its primary biodegradation intermediate E1 were monitored. During BAC operation, the impacts of various reactor operation parameters, such as the carbon (i.e., acetic acid vs. humic acid) and nitrogen sources (i.e., ammonium vs. nitrate) in reactor influent and empty bed contact times (i.e., 20 – 48 minutes), were systematically studied. Corresponding to each reactor operation, the structure of the bacterial community, particularly the E2 and E1 degrading bacterial populations, in the BAC reactor was monitored using the pyrosequencing technology. Finally, metabolic pathways involved in E2 biodegradation in an E1 degrading bacterial isolate, Stenotrophomonas maltophilia strain ZL1, were investigated using a quantitative proteomic approach.
The following conclusions were drawn from this study:
- The adsorption isotherm experiment showed that the F400 GAC had a higher adsorption capacity for E1 than for E2, and revealed mild competitive adsorption between E1 and E2.
- The GAC column cannot effectively remove E2 due to the long mass transfer zone. The microbial activities in the BAC column enhanced E2 removal. Highest removal of E2 and its primary degradation product E1 occurred when the BAC column was operated with long EBCTs and fed acetic acid as the energy source and ammonium as the nitrogen source.
- Microbial community analysis showed that E2 degrading bacteria were accumulated in the BAC reactor and E1 degrading bacteria were the most abundant when ammonium was used as the nitrogen source.
- Enzymes associated with fatty acid biosynthesis, protein biosynthesis and oxidative phosphorylation were up-regulated during the biodegradation of E2 and E1 in Stenotrophomonas maltophilia strain ZL1. An E2 assimilation pathway through aromatic amino acid biosynthesis was proposed.
Advisor: Xu Li