Exploring HAA Formation Pathways During Chloramination

The use of chloramine for DBP control has received increasing attention in the U.S. water treatment industry since the first discovery of THM in drinking waters. Chloramination can almost completely suppress THM formation and reduce HAA concentration to 3-30 percent of the amounts formed during chlorination, making it a viable alternative to utilities for complying with the Stage 2 Disinfectants and Disinfection By-products Rule. This project investigated the routes of HAA formation during chloramination. The main objectives of this study were to investigate the pathways of dihalogenated acetic acids (DXAAs), the major class of haloacetic acids (HAAs) formed during chloramination, and to systematically examine the roles of important factors, namely dissolved organic matter (DOM) characteristics, pH and bromide, in DXAA formation and speciation. Understanding the pathways of DXAA formation and speciation during chloramination is critical for developing strategies toward their control and modeling of their formation through mechanistic or empirical models. Water utilities intending to decrease HAA formation should maintain pH above 7.5 and minimize the lag time between chlorine and ammonia addition or add ammonia before chlorine. This will also reduce the formation of brominated HAAs. The enhanced removal of the hydrophobic DOM components can assist with better control of HAA formation during chloramination. HAA formation kinetics during chloramination are not extremely fast, as has been previously reported in the literature. Since NH4Cl recommended by USEPA Method 552.3 does not quench residual chloramine, there is a possibility of overestimating HAA formation for distribution system samples close to a treatment plant. The magnitude of the error decreases with increasing distribution system residence time.