The Influence of Operational Variables on the Formation of Dissolved Organic Halogen During Chloramination

The objective of this study was to extend previous work on disinfection by-product (DBP) formation during free chlorination to situations in which chloramines are used as the disinfectant. Although four trihalomethanes (THMs), two cyanogen halides (CNX), and the sum of six haloacetic acids (HAA6) were measured, the focus of this phase of the work was on the production of dissolved organic halogen (DOX), a group parameter that measures "all" of the halogen-substituted DBPs. Chloramination was carried out in three waters, at three pH levels, at three chlorine-to-nitrogen (Cl 2:N) ratios, at three total chlorine residual concentrations, and under a variety of mixing conditions. The results of all the DBP and DOX analyses on these samples showed that (1) in the range of 1-4 mg/L total residual (as used herein, total residual is the sum of the concentrations of monochloramine, dichloramine, and free chlorine), 2-d DOX production was not significantly influenced by disinfectant concentration; (2) usually, a small percentage of the measured DOX (typically 5-20 percent) could be identified when compared to the molar sum of the total THMs (TTHMs), CNX, and HAA6; (3) mixing techniques had little influence on DOX production; and (4) chloraminating at the highest possible pH and lowest possible Cl 2:N ratio typically minimized DOX formation.