摘要
Residual H_(2)O_(2)from UV/H_(2)O_(2)treatment can be quenched by thiosulfate,bisulfite,and chlorine,but the kinetics of these reactions have not been reported under the full range of practical conditions.In this study,the rates of H_(2)O_(2)quenching by these compounds were compared in different water matrices,temperatures,pH,and when using different forms of bisulfite and chlorine.In general,it was confirmed that thiosulfate would be too slow to serve as a quenching agent in most practical scenarios.At pH 7-8.5,chlorine tends to quench H_(2)O_(2)more than 20 times faster than bisulfite in the various conditions tested.An important observation was that in lightly-buffered water(e.g.,alkalinity of 20 mg/L as CaCO_(3)),the form of chlorine can have a large impact on quenching rate,with gaseous chlorine slowing the reaction due to its lowering of the pH,and hypochlorite having the opposite effect.These impacts will become less significant when water buffer capacity(i.e.,alkalinity)increases(e.g.,to 80 mg/L as CaCO_(3)).In addition,water temperature should be considered as the time required to quench H_(2)O_(2)by chlorine at 4℃is up to 3 times longer than at 20℃.
基金
supported through the Natural Sciences and Engineering Grant CRDPJ-542302-2019,by AECOM and by the City of Toronto.
