Influence of the Method of Reagent Addition on Dichloroacetonitrile Formation during Chloramination

Abstract

Formation of dichloroacetonitrile (DCAN) in natural waters was evaluated for different disinfection scenarios, including application of free chlorine, preformed monochloramine or dichloramine, or formation of chloramines in situ by addition of free chlorine and ammonia in either order. Formation of DCAN was highest during free chlorination. Regardless of the order of ammonia or chlorine addition, DCAN formation was consistently higher over 1-2 day contact times when chloramines were formed in situ than when preformed chloramines were applied. During in situ chloramine formation, organic amine precursors effectively competed with ammonia to react with free chlorine, forming organic dichloramine intermediates to nitrile formation. Combined with previous research indicating that application of preformed monochloramine reduced nitrosamine formation, the results indicate that application of preformed monochloramine could provide an inexpensive alternative for chloraminating utilities to significantly reduce the exposure to DCAN and nitrosamines for consumers located within 1-2 days of water travel time from the treatment plant. This technique would be applicable in situations where chloramination is used alone (e.g., chlorination of non-nitrified secondary wastewater effluents during municipal wastewater recycling), or combined with primary disinfectants other than free chlorine (e.g., ozonation, chlorine dioxide, or ultraviolet light).