Degradation of chloramphenicol by chlorine and chlorine dioxide in a pilot-scale water distribution system

This paper presents the degradation of chloramphenicol (CAP) by chlorine and chlorine dioxide (ClO 2 ) in tap water in a pilot-scale water distribution system (WDS) containing loops of three different pipe materials (stainless steel, ductile iron , and polyethylene). Greater degradation of CAP was seen with chlorine than with chlorine dioxide. After 180 min in the ductile iron loop of the WDS, the percent degradation of CAP by 2.0 mg/L of chlorine or ClO 2 was 76% and 52%, respectively. The degradation of CAP by chlorine in the WDS was investigated under various conditions, including chlorine concentrations of 1.0–4.0 mg/L, and varying pipe materials, flow velocity, and temperature. Degradation of CAP under different conditions could be fitted by first-order kinetics, and the determined first-order rate constants ( k , min −1 ) increased with an increase in chlorine concentration, flow velocity, and temperature. The degradation of CAP in different pipes followed the order stainless steel loop > ductile iron loop >  polyethylene loop. Identified oxidized products of the chlorination of CAP were in agreement with proposed reaction pathways, which were also theoretically confirmed by quantum chemical calculations. Formation of three disinfection byproducts (chloroform, bromodichloromethane, and dibromochloromethane) was observed, with increases of 7.7, 0.76, and 0.39 µg/L, respectively, after 160 min.