Research On Biotransformation Of Typical Estrogens In Shenzhen River And Related Waste Water Treatment Plants

This thesis focused on the transformation of typical estrogens in Shenzhen River and related wastewater treatment plants (WWTPs). Five steroid estrogens including estrone (E1), estradiol (E2), estriol (E3),17a-estradiol (17a-E2) and ethinylestradiol (EE2) were selected as target chemicals. The distribution and flux shift of estrogens in Shenzhen River and three related sewage treatment plants (STPs) were investigated using gas chromatography-mass spectrometry (GC-MS). Adsorption and biodegradation of estrogens were studied using activated sludge at designed conditions. The microbial community structure under the estrogen stress was analyzed with the method of16S rDNA polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Transformation of estrogens in river water under different dissolved oxygen conditions was explored. The dominant microbial populations were identified in detail. A quantum chemistry software of Gaussian03was applied to identify the intermediates and metabolic pathways of estrogens.It was found that five selected estrogens including E1, E2, E3,17a-E2and EE2were detected in Shenzhen River water. EE2was measured with concentrations as15.6～443.7ng·L-1, while other four estrogens with concentrations lower than80ng·L-It was showed that midstream was more polluted than upstream and downstream. In the effluents of three wastewater treatment plants (WWTPs), EE2was the predominant estrogen with high concentration reached853.0ng·L-1. Biological treatment processes in WWTPs were effective in removing E2, E3and EE2with mean removals of19.1%,71.7%and81.2%, respectively. However, E1and17α-E2were removed with negative removal ratios.Estrogen flux contributed by WWTP effluents were one of the main estrogen sources of Shenzhen River. In wet season, average fluxes of total estrogens discharged from two WWTPs were17.7g·d-1and17.8g·d-1, respectively, which took25%and12%proportions of Shenzhen River fluxes. In dry season, the average WWTPs effluent fluxes increased up to43.5g·d-1and69.7g·d-1with39%and52%contribution to Shenzhen River, respectively.The sorption equilibrium was attained in30min-lh and the biodegradation took relatively longer time. Under aerobic conditions, the average degrading rates of E1, E2, E3and17α-E2were347μg·L-1·d-1,252μg·L-1·d-1,405μg-L-1·d-1and268μg·L-1·d-1, respectively. However, the degradation rate of EE2was as low as14μg·L-1·d-1.16S rDNA analysis showed that E1and E3were able to increase the microbial diversity, while E2,17α-E2and EE2led to diversity decrease, γ-proteobacteria were identified as the dominant populations which were acclimatized under the estrogen stress in the long run. It was found that nitrifying bacteria was likely the significant functional population in EE2and E2transformation.Dissolved oxygen was a key factor for estrogen transformation in Shenzhen River. It was demonstrated that the average half-life time of EE2was12days under aerobic conditions and relatively long half-life time of20days under anaerobic conditions. However, the EE2half-life time under anoxic conditions was considerably short as3.5days. The average half-lives of E2under aerobic, anoxic and anaerobic conditions were <1day,<1day and3days, respectively. Estrone (E1) and estriol (E3) were detected as the intermediates in EE2and E2transformation. Bacterial communities in overlying water shifted gradually. Dominant populations included common biodegraders and typical oligotrophic microorganisms. There were also some pathogenic bacteria found in Shenzhen River.Molecular structural parameters including electron cloud, energy gap, dipole moment and bond order were demonstrated to be closely related to the reactivity and transformation properties of estrogens. Calculation results showed that the energy gaps of the frontier electron orbit were higher in E2,17α-E2and EE2than that in E1and E3, which increased the reactivity of E1and E3. It was demonstrated that hydroxyl oxidation on C16atom of E3occurred initially before further transformation. E1may be attacked at C13-C17bond due to the lowest bond order, which led to further epoxidation and cleavage of D ring on E1molecule.