Re-assessing ICR GAC Treatment Study Database: Effect of Bromide on DBP Formation

While granular active carbon (GAC) can effectively remove disinfection byproduct (DBP) precursors, its use has raised concerns over increased formation of some brominated DBP species in treated water following postchlorination, especially for waters with high bromide concentrations. The Information Collection Rule Treatment Study Database contains results of the most extensive GAC studies ever conducted nationwide. Data were analyzed to assess the extent of DBP speciation changes and overall reduction of brominated DBPs by GAC to gain new insights of the bromide effect. Results showed that formation of three brominated trihalomethanes (collectively, Br-THM3) varied greatly depending on TOC removal and bromide concentrations. Low TOC concentrations in GAC effluents resulted in greatly reduced Br-THM3 formation, except for a few cases where Br-THM3 formation increased. GAC followed by chloramination were likely to better control Br-THM3 formation for waters with high TOC and high bromide. Lastly, the chlorine demand reduction by GAC was quantified.