Removal of selected steroid estrogens in a sewage treatment plant with Unitank process in Nanjing, China

This study monitored estrone (E1), 17 beta-estradiol (E2) and 17 alpha-ethynylestradiol (EE2) concentrations monthly for one year in the influent, effluent and various unit processes of a Unitank-based sewage treatment plant in Nanjing, China. The results showed that the concentrations of E1, E2 and EE2 in influents were 32.4-89.0 ng(.)L(-1), 19.4-78.0 ng(.)L(-1) and 12.3-45.0 ng(.)L(-1), respectively. Estrogen concentrations in influents were significantly higher in summer than those in winter. The removal efficiencies of E1, E2 and EE2 varied from 21.3 to 77.0%, 23.4 to 73.5%, and 25.2 to 68.1%, respectively, depending on seasonal variation. Biodegradation contributed more to the removal of estrogens than the grit chamber. Higher temperature and enhanced nitrifying activity appeared to be conducive to estrogens removal, and the influent COD loading should be less than 0.11 kg COD kg MLSS-1 d(-1) to achieve optimal removal of estrogens.