HAA formation during chloramination

Experiments were performed in the presence and absence of background ammonia to study the significance of the direct reaction(s) of monochloramine (NH₂Cl) with dissolved organic matter (DOM) in the haloacetic acid (HAA) formation during chloramination. Direct reactions were found to play a major role in the HAA formation compared to the reactions of NH₂Cl decomposition products (i.e., hypochlorous acid and dichloramine) with DOM. Dihalogenated HAAs (DXAA) constituted the major HAA₉ species formed during chloramination. The extent of DXAA formation decreased with increasing pH. Experiments conducted with sodium sulfite (Na₂SO₃) and ammonium chloride (NH₄Cl) showed that selection of quenching agent is important to obtain reliable results from chloramination kinetic experiments. When preformed chloramines are employed, the use of NH₄Cl, the quenching agent recommended by USEPA Method 552.3 for HAA samples, may result in false high HAA concentrations at early reaction periods. The type of quenching agent used in different studies appears to be the cause of different kinetic patterns reported for chloramination kinetics in the literature.