Chloramination is a secondary disinfection process that is increasingly being used because it can provide a stable residual in the distribution system and it can produce lower levels of regulated disinfection by-products (DBPs) that are predominantly formed by free chlorine. However, chloramination can promote the formation of unregulated nitrogen-containing disinfection by-products (N-DBPs) such as haloacetonitriles and haloacetamides that have been found to be more cyto- and genotoxic than regulated DBPs.Previous studies have shown that monochloramine react with aldehydes, common ozone and chlorine DBPs, to form carbinolamines that can then slowly decompose to nitriles, with an imine as an intermediate compound. Additionally, carbinolamines can be oxidized to amides under mild conditions. In this research, the formation of chloroacetonitrile and N,2-dichloroacetamide from the reaction of monochloramine and chloroacetaldehyde is investigated. Chloroacetaldehyde and monochloramine react in a fast and reversible reaction to form carbinolamine 2-chloro-1-(chloroamino)ethanol. This carbinolamine then slowly dehydrates to 1-chloro-2-(chloroimino)ethane, which in turn decomposes quickly to chloroacetonitrile. Concurrently, 2-chloro-1-(chloroamino)ethanol is oxidized by monochloramine to form N,2-dichloroacetamide.   These reactions are acid/base catalyzed, and therefore, the rates of formation of chloroacetonitrile and N,2-dichloroacetamide are highly influenced by water quality conditions. A kinetic model is provided to predict N-DBP formation and aid in developing strategies for N-DBP control.

Haloacetamide and haloacetonitrile formation from the reaction of monochloramine and aldehydes in water

247th National Meeting (2014)

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