BACKGROUND: The release of natural estrogen 17 beta-estradiol (E2) to the aquatic environment is a matter of concern. Batch experiments were conducted to study the adsorption of E2 by anaerobic granular sludge (AnGS) combined with zero-valent iron (ZVI). The enhancement mechanism of ZVI for E2 adsorption by AnGS was also analyzed. RESULTS: The E2 adsorption efficiency of AnGs with ZVI was 48% higher than that without ZVI. The optimal conditions for high E2 adsorption efficiency (92.21%) and high equilibrium adsorption capacity (4.92 mu g g(-1) VSS) were r(ZVI/AnGS) 1.33, pH 6, and temperature 25 degrees C. E2 adsorption by ZVI/AnGS was a spontaneous and exothermic process, well described by the Freundlich isotherm. CONCLUSION: The addition of a suitable amount of ZVI enhanced E2 adsorption by AnGS. (c) 2017 Society of Chemical Industry