Degradation of estriol by chlorination in a pilot-scale water distribution system: Kinetics, pathway and DFT studies

Estriol (E3) is a potent intracellular estrogen and endocrine disruptor that has been frequently detected in surface water in recent years. We investigated the degradation kinetics of E3 during chlorination in a pilot-scale water distribution system (WDS), and found that its degradation followed second-order kinetics. Higher concentrations of bromide and neutral acids promoted the degradation of E3. In addition, the degradation of E3 was higher at higher water velocity in WDS. This study further compared the degradation of E3 in different pipe materials and the results indicated that the degradation of E3 was most efficient in stainless-steel pipe, followed by the polyethylene pipe and then ductile iron pipe. To gain more insights into the mechanisms of E3 degradation, intermediate products from E3 degradation were analyzed. Five intermediates were identified, and a possible pathway was proposed by combining the experimental observations with the density functional theory (DFT) calculation. Four types of disinfection byproducts (DBPs) in ductile iron pipe were detected from E3 degradation during chlorination, confirming that DBPs are generated by E3 during the free chlorine oxidation, which pose a greater safety threat to drinking water.