Effects of Alum Coagulation on Speciation and Distribution of Trihalomethanes (THMs) and Haloacetic Acids (HAAs)

Abstract

The impacts of alum coagulation on the distribution of disinfection by-products (DBPs), trihalomethanes (THMs), and haloacetic acids (HAAs) were evaluated under controlled chlorination conditions using four surface waters. Among the nine HAAs found in waters, dihaloacetic acids (X₂AAs) have been found to be the dominant species in all of the raw and alum treated waters. Alum coagulation tends to remove more monohaloacetic acids (XAAs) and trihaloacetic acids (X₃AAs) precursors than that of dihaloacetic acids (X₂AAs). Alum coagulation treated water had a lower HAA₉/TTHM ratio compared with that of the raw water. The increase of THM bromine incorporation factors (BIF_α value of alum treated water was statistically significant in comparison with the raw water. On average, BIF_α increased by 54% after the alum coagulation process in these four different waters. This indicated that THM speciations shifted in favor of the more brominated compounds. However, alum coagulation treatment process had less effect on HAA bromine incorporation factors (BIF_βthan it did on BIF_α. Bromine incorporation factor (BIF) values decreased with time in the THM and HAA formation processes, especially within the first 10 h of the reaction time. This suggested that brominated THMs or HAAs formed faster than the chlorinated species in the initial period.

Keywords:

• Alum coagulation
• Bromine incorporation factor
• Disinfection by-products
• HAA₉/TTHM ratio
• Haloacetic acids; Trihalomethanes

ACKNOWLEDGMENTS

Although the research described in the article has been funded by the United States Environmental Protection Agency Office of Groundwater and Drinking Water, it has not been subjected to the agency's peer and administrative review and therefore may not reflect the views of the agency and no official endorsement should be inferred.