DBP formation during chlorination and chloramination: Effect of reaction time, pH, dosage, and temperature

Abstract

Despite extensive efforts in the identification of new disinfection by‐products (DBPs) by environmental scientists, a significant fraction of the total organic halogen (TOX) in drinking water still cannot be accounted for by known specific DBPs. The formation and control of these unknown DBPs have not been well established. The primary aim of this study was to evaluate the effect of reaction time, pH, dosage, and temperature on the formation of unknown TOX (UTOX) during chlorination and chloramination. Results showed that greater conversion of UTOX to measurable by‐products occurred with increasing reaction time, pH, dose, and temperature during chlorination. The UTOX‐to‐TOX ratio increased with reaction time but decreased with pH and dose during chloramination. The formation of unknown brominated and iodinated DBPs decreased as chlorination or chloramination pH increased. TOX formation was significantly reduced at high pH values during chloramination. For best control of DBPs, the authors recommend that water utilities using chloramines perform chloramination under alkaline conditions. Given that dihaloacetic acids and trihaloacetic acids exhibited distinct responses to the evaluated parameters, the authors also recommend that these be considered different classes of DBPs in future studies.