BACKGROUNDAs the strongest natural estrogen, 17-estradiol (E2) which occurs in water through drainage of municipal and industrial wastewater treatment plants, may represent a serious health risk to humans, even at extremely low concentrations (ngL(-1)). To reduce the amount of E2 in an aqueous system, KMnO4-assisted ultrasound was adopted and compared with ultrasound and KMnO4, each alone, and the influencing factors were determined. RESULTSThe efficiency of removal of E2 was low under single ultrasound irradiation alone, but was enhanced from14.6% to 85.5% when assisted by the addition of 3mgL(-1) KMnO4 after 30min contact. Degradation of E2 could be described by first-order kinetics models. The degradation rates were proportional to the dosage of KMnO4 in the range from 0 to 5mgL(-1). The optimal pH for the processes was alkaline (for the ultrasound) and strong acidic (for the combined ultrasound/KMnO4). The common cation Na+ initially inhibited and then promoted degradation of E2 in both processes, and anionic surfactant was a favourable factor in the degradation of E2. CONCLUSIONKMnO4-oxidatively enhanced ultrasound effectively removed E2 from an aqueous system. Since pH, cation and existing chemicals such as surfactant can affect the degradation of E2, these factors should be taken into consideration to obtain satisfactory results. (c) 2013 Society of Chemical Industry