Kinetics and mechanism of 17β-estradiol chlorination in a pilot-scale water distribution systems

•17β-estradiol (E2) chlorination differed in a water distribution system (WDS) and deionized water.•Degradation of E2 by chlorine accelerated with an increase in pH and temperature in WDS and batch tests.•Degradation of E2 in WDS is faster than that in the batch test under the same pH and temperature.•Degradation mechanism of E2 by chlorine has three stages.•E2 chlorination in WDS greatly increase the formation of THMs and HAAs.

The kinetics and mechanisms of 17β-estradiol (E2) chlorination in water distribution systems (WDS) were studied. We examined the impacts of different factors, including pH, temperature, humic acid concentration and type, and flow velocity. The experimental results showed that the rate constants in beaker tests and WDS were described by a pseudo-first-order model. pH had the greatest impact on E2 chlorination in the beaker tests. However, temperature had the greatest impact on E2 chlorination in WDS. Mechanistic analysis of E2 chlorination showed that chlorine attacked E2 in three stages: 1) halogenation of the aromatic ring, 2) cleavage of the benzene moiety and chlorine or bromine substitution formation, and 3) formation of trihalomethanes (THMs) and halogenated acetic acids (HAAs) from phenolic intermediates through benzene ring opening with chlorine and/or bromine substitution of hydrogen on the carbon atoms. In the third stage, the concentrations of THMs and HAAs increased rapidly.

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