Natural estrogens such as estrone, 17 beta-estradiol, estriol, and the synthetic component of contraceptive pills, 17 alpha-ethinylestradiol, enter the municipal wastewater treatment plant via human excretions. A significant portion of these substances is found to remain in reject water produced after anaerobic digestion of activated sludge. in this study, the effect of the oxidant, Fe(III), and facultative anaerobic strain of iron-reducing bacteria on the anaerobic degradation of estrogens in reject water was investigated. Synthetic 17 alpha-ethinylestradiol remained resistant to anaerobic biodegradation by iron-reducing bacteria, while natural estrogens such as 17 beta-estradiol, estriol, and estrone were removed by 92%,60% and 27%, respectively, after 15 days of batch cultivation of iron-reducing bacteria in reject water with the addition of all estrogens to concentrations 100 mu g l(-1) each. The ability of facultative anaerobic iron-reducing bacteria to degrade estrogens can be used for the anaerobic removal of trace organics from reject water in municipal wastewater treatment plant. (C) 2009 Elsevier Ltd. All rights reserved.