In this paper, the biodegradability of estrogens; estrone (E1), 17β-estradiol (E2), and ethynylestradiol (EE2) ; was evaluated using a nitrifying activated sludge (NAS) . NAS could degrade E1, E2, EE2 with the biodegradation rate constants, i.e.0.035h^-1, 0.056h^-1, 1.3h^-1 respectively, indicating that E2 was the most biodegradable among the three estrogens.
It should be noted that biodegradation of E2 produced E1, which was confirmed by a spike test on a reversed phase high performance liquid chromatography equipped with an electrochemical detector (HPLC-ECD) . An sequential reaction analysis where it was assumed that E2 was biodegraded to an unknown compound via E1 showed that E1 was firstly produced by biodegradation of E2. As for the unknown intermediates of E1 and EE2 were detected by HPLC-ECD. Based on the result that these electrochemically detectable compounds were eluted faster than the parent compounds, i.e. E1 and EE2, On the HPLC-ECD, it was suggested that more polar compounds containing phenolic group than the three estrogens were produced by NAS. Because significant decrease of the peak area of these compounds on the HPLC-ECD chromatogram was observed during biodegradation of E1 and EE2, it was suggested that NAS could cleavage phenolic group of E1 and EE2.