Factors affecting disinfection by-product formation during chloramination of drinking water

This study examined the impact of the pH, chlorine to ammonia—nitrogen ratio (Cl₂:N ratio), total chlorine residual, bromide concentration and water source on the formation of dissolved organic halides (DOX), total trihalomethanes (TTHM), haloacetic acids (group of six) (HAA6), and cyanogen halides (CNX) in the context of drinking water treatment of three natural waters with chloramines, under two-day simulated distribution system and pilot conditions. Generally, DBP formation and the degree of bromination of DBPs increased with decreasing pH, increasing Cl₂:N ratio, and increasing bromide concentration. Increasing the total chlorine residual increased DBP formation only slightly. Under many conditions, chloramination produced HAA6 concentrations in excess of the TTHM concentration. Only 10 to 30 percent of the DOX formed through chloramination was represented by TTHM, HAA6, and CNX. Some anomalies were observed at the mid-range pH condition—pH 8. Utilities should do batch testing to develop profiles like those presented in this work to determine where anomalies may exist for the specific water they treat.