Chloramines in a pilot-scale water distribution system: Transformation of 17β-estradiol and formation of disinfection byproducts

Abstract

The degradation and transformation products of 17β-estradiol (E2) by chloramines in a pilot-scale water distribution system (WDS) were investigated using varying conditions including multiple mass ratios of chlorine to nitrogen (Cl/N), changing concentrations of chloramines, and different pH and pipe materials. The degradation of E2 was complete in ≤9 h in both deionized water (DW) and in the WDS under studied conditions. When the degradation rate of E2 was compared in WDS and DW, the degradation rate was appreciably greater in the WDS than in the DW at Cl/N mass ratios of 3, 4 and 6. However, at Cl/N mass ratios of 8 and 9, degradation was faster in the DW than in the WDS. The degradation rate of E2 was greatly affected by the initial total chloramine concentration, and the degradation of E2 in DW was consistent with second-order kinetics. The degradation rate of E2 in both the DW and the WDS increased with increasing pH. The order of degradation rate of E2in different pipes was: ductile iron loop (loop A) > polyethylene (PE) loop (loop B)> stainless steel loop (loop C). Ten specific degradation products of E2, produced by chloramination, were identified. Most of the degradation products of E2 chloramination were stable for more than 10 h. The degradation pathways of E2 in the WDS are proposed and briefly discussed. The concentrations of trihalomethanes (THMs), haloacetic acids (HAAs), and halogenated nitromethane (HNMs) during the degradation E2 in WDS were also determined.