Reaction patterns of NDMA precursors during the sequential chlorination process of short-term free chlorination and monochloramination

Abstract The sequential chlorination process of short-term free chlorination and monochloramination was designed to achieve the simultaneously control of pathogen, trihalomethanes and haloacetic acids. Its efficiency for N -nitrosodimethylamine (NDMA) control was tested with four model NDMA precursors, i.e. dimethylamine (DMA), chlordimeform, chlortoluron and pirimicarb as well as real water sample. The results showed that DMA or chlordimeform formed much less NDMA during the sequential chlorination process than during monochloramination. However, chlortoluron or pirimicarb formed more NDMA during the sequential chlorination process than during monochloramination. Seven sub-patterns were concluded for the reactions of NDMA precursors during the sequential chlorination process and some of them would lead to the decrease of NDMA. The mechanism of NDMA control during the sequential chlorination process was attributed to the quick oxidation of NDMA precursors by free chlorine, which products presented less or no yield of NDMA during the following monochloramination.