Flow-through reactors with manganese oxides were examined for their capacity to remove 17α-ethinylestradiol (EE2) at μg L −1 and ng L −1 range from synthetic wastewater treatment plant (WWTP) effluent. The mineral MnO 2 reactors removed 93% at a volumetric loading rate ( B V) of 5 μg EE2 L −1 d −1 and from a B V of 40 μg EE2 L −1 d −1 on, these reactors showed 75% EE2 removal. With the biologically produced manganese oxides, only 57% EE2 was removed at 40 μg EE2 L −1 d −1. EE2 removal in the ng L −1 range was 84%. The ammonium present in the influent (10 mg N L −1) was nitrified and ammonia-oxidizing bacteria (AOB) were found to be of prime importance for the degradation of EE2. Remarkably, EE2 removal by AOB continued for a period of 4 months after depleting NH 4 + in the influent. EE2 removal by manganese-oxidizing bacteria was inhibited by NH 4 +. These results indicate that the metabolic properties of nitrifiers can be employed to polish water containing EE2 based estrogenic activity.