Human beings discharge substantial amount of estrogens into water receiving bodies, which threatens the safety of water supply sources. Removal of estrogens from sewage effluent is desired. Membrane bioreactor (MBR) is an ideal candidate to achieve this goal due to its long sludge retention time (SRT), excellent effluent quality and reactor compactness. Information on biological removal of estrogens in MBR is limited. This research is therefore focused on biological estrogen removal in MBR through studies of three lab-scale MBRs under different SRTs which lasted for more than three years. The research included background investigation of estrogen concentrations in surface waters, estrogens removal in pilot-scale and full-scale sewage treatment works, studies of the selected process affe...[ Read more ]

Human beings discharge substantial amount of estrogens into water receiving bodies, which threatens the safety of water supply sources. Removal of estrogens from sewage effluent is desired. Membrane bioreactor (MBR) is an ideal candidate to achieve this goal due to its long sludge retention time (SRT), excellent effluent quality and reactor compactness. Information on biological removal of estrogens in MBR is limited. This research is therefore focused on biological estrogen removal in MBR through studies of three lab-scale MBRs under different SRTs which lasted for more than three years. The research included background investigation of estrogen concentrations in surface waters, estrogens removal in pilot-scale and full-scale sewage treatment works, studies of the selected process affecting factors and the sludge characteristics as well as the effects of the microbial populations on the estrogen removal.

Serious estrogenic pollution was found in the surface waters and the sewage effluents with respective maximum estrogens concentrations up to 300 and 68 ng/L, respectively. The average estrogens removal efficiency of conventional sewage treatment works ranged from 61 to 73%, depending on the treatment processes. Comparatively, higher estrogens removal efficiencies of 80, 84 and 94% were achieved in the three MBRs with respective SRTs of 40, 52 and 96 days. Such higher removal efficiencies were attributed to the higher biomass concentrations and greater bioactivities in these MBRs.

The microbial community structures of the MBRs were analyzed both qualitatively and quantitatively using Terminal Restriction Fragment Length Polymorphism (T-RFLP) and 16S rDNA gene cloning methods. Proteobacteria was identified to be the dominant bacterial species in both the suspended growth in the bioreactors and the attached growth (biofilm) on the membranes. Ten estrogen-degrading bacteria were successfully isolated from the MBRs. All isolates showed the ability to degrade estradiol, with only two Alphaproteobacteria sub-groups degraded estrone in the presence of estradiol.