HAA formation during chloramination—significance of monochloramine's direct reaction with DOM

Abstract

Three oxidants—monochloramine (NH 2 Cl) and its two decomposition products, free chlorine (HOCl) and dichloramine (NHCl 2 )—can be present in water during chloramination, potentially reacting with dissolved organic matter (DOM) to form haloacetic acids (HAAs). This study showed that the direct reaction between NH 2 Cl and DOM played a major role in the formation of HAAs, accounting for approximately 80% of HAA formation. The remaining HAA formation was attributed to HOCl that resulted from NH 2 Cl decomposition. No HAA formation was observed from preformed NHCl 2 . HAA formation was strongly dependent on pH and increased with decreasing pH. This research also found that the use of ammonium chloride, the quenching agent recommended by the US Environmental Protection Agency method 552.3 for disinfection by‐product samples, resulted in false high HAA determination at early reaction periods. This appears to be the cause of the significantly different kinetic patterns that the literature has reported for HAA formation during chloramination.