Background and purpose: Estrogen is a steroid hormone that enters water sources through urban and hospital waste water and is a serious threat to aquatic organisms, especially fish, and human health. The aim of this study was to evaluate the performance of municipal and hospital waste water treatment, especially biological treatment in removal of estrogenic compounds.

Materials and methods: Estrogens in aqueous samples were determined by tracking. Fifty six samples were obtained from various locations in Ahwaz municipal wastewater treatment plant and hospital waste water treatment facilities within 8 months. The samples were analyzed using Electrochemiluminescence (ECL). The results were reported in units of ng/L.

Results: The average influent and effluent hormone levels in municipal wastewater treatment plant were 58.8 ng/ L and 5.4 ng/L, respectively. In hospital treatment plant the average influent estrogen level was 61.8 ng/L and the average effluent level was 10.8 is ng/L. The results showed that biological treatment using activated sludge can remove significant amounts of estrogen and could reduce its level to a value lower than international standards.

Conclusion: The removal mechanism of estrogen in biological treatment system, especially activated sludge are adsorption and biological degradation. Secondary treatment of wastewater is effective in reducing hormones that could be due to wastewater biological treatment.