Municipal wastewater treatment and landfill leachate treatment are typical state-of-the-art applications of the membrane bioreactor technology. Therefore, in this study the possibilities of MBRs with regard to the elimination efficiency of estrogenic trace contaminants are considered for these two applications. Investigations of phase distributions of the trace contaminants were conducted. The membrane bioreactor process was considered with respect to possibilities of the membrane unit to enhance the rejection of selected estrogenic trace contaminants.