Investigation on the estrogenicity of different processes in a sewage treatment plant

A solid phase extraction/yeast two-hybrid system was used to investigate the estrogenicity of wastewater in different seasons from each treatment unit of a sewage treatment plant located in the northeast part of China. Results showed that yeast two-hybrid system had a relatively high sensitivity with EC₅₀ value of 5.95 times; 10^-11 mol·L^-1. The estrogenic activities in raw sewage and the effluent of primary sedimentation were 16.13-21.65, 17.10-22.85 ng·L^-1 Estradiol Equivalents (EEQs), respectively, with the highest EEQs in summer and the lowest in winter. The estrogenic activity in the effluent of secondary sedimentation was reduced to 3.37-6.76 ng·L^-1 EEQs after the A/O process, with the higher level in spring and winter, the lower in summer and autumn. The total and average removal rates of the whole treatment process were 58.1%-84.3% and 75.2%, respectively, with the highest removal rate in summer, the lowest in winter. Additionally, it was shown that the secondary biotreatment process played a dominant role in the removal of estrogenic activity, whereas the primary treatment process had very limited removal efficiency such that the estrogenic level even increased compared with that in raw sewage.