AWWA WQTC58813

In order to comply with the maximum contaminant levels for trihalomethanes (THMs) and haloacetic acids (HAAs), many utilities are utilizing alternative disinfectants, such as chlorine dioxide (ClO₂) and chloramines (NH₂Cl). The use of ClO₂ in bench- and demonstration-scale tests was found to produce no THMs or trihalogenated HAAs, or only trace amounts, but it did form low levels of dihalogenated HAAs (DXAAs). In the presence of bromide, brominated DXAA species formed. Post-chloramination did not stop THM formation in waters high in total organic carbon and/or bromide. THM formation in the presence of NH₂Cl was of the order of 20 percent of the amount that would have formed in the presence of free chlorine. Because ClO₂ is a strong radical oxidant, it can form oxidation byproducts similar to those formed by ozone (carboxylic acids, aldoketoacids, aldehydes), but ClO₂ typically forms byproducts at lower levels (on a weight basis) than ozone. The formation of carboxylic acids, especially oxalate, increased with increasing ClO₂ demand. Secondary byproducts from postdisinfection (e.g., haloacetaldehydes) also formed. Includes 22 references, table, figures.