The fate and behavior of natural and synthetic estrogens in wastewater treatment processes is currently of increasing concern all over the world. In this study, the removal mechanisms of a natural estrogen, 17β-estradiol (E2), and a synthetic estrogen, 17α-ethinylestradiol (EE2) were investigated in membrane bioreactors (MBRs) with and without powdered activated carbon (PAC) addition. The experimental results showed that the average removal rates of E2 and EE2 by the MBR without PAC addition were 89.0 and 70.9%; PAC addition in the MBR increased the removal rate of E2 and EE2 by 3.4 and 15.8%, respectively. The greater impact of PAC dosing on EE2 removal was due to its greater hydrophobic property. Adsorption played a more important role in the removal mechanisms of EE2 than E2. Biodegradation was the dominant mechanism for the removal of E2 and EE2 in MBRs. Unlike their adsorption behavior, the biodegradation rates of both E2 and EE2 were not significantly different between the MBRs with and without PAC addition.

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