The complex chlorine chemistry that involves interactions among chlorine, ammonia, bromide, and organics often plays important roles in the formation and control of disinfection byproducts (DBPs). This thesis work explored the chlorine chemistry that involved in the formation of organic DBPs and in the control of bromate during ozonation after bromide-containing waters are pretreated with control strategies using chlorine and/or ammonia. The chlorine chemistry that describes the step-wise chlorine substitution during chlorination of model organic nitrogen compounds was also explored, after the development of a collision-energy-dependent electrospray ionization-tandem mass spectrometry (ESI-tqMS) method.

The chlorine-ammonia (Cl₂-NH₃) and ammonia-chlorine (NH₃-Cl₂) pretreatmen...[ Read more ]

The complex chlorine chemistry that involves interactions among chlorine, ammonia, bromide, and organics often plays important roles in the formation and control of disinfection byproducts (DBPs). This thesis work explored the chlorine chemistry that involved in the formation of organic DBPs and in the control of bromate during ozonation after bromide-containing waters are pretreated with control strategies using chlorine and/or ammonia. The chlorine chemistry that describes the step-wise chlorine substitution during chlorination of model organic nitrogen compounds was also explored, after the development of a collision-energy-dependent electrospray ionization-tandem mass spectrometry (ESI-tqMS) method.

The chlorine-ammonia (Cl₂-NH₃) and ammonia-chlorine (NH₃-Cl₂) pretreatment processes were effective in bromate control during ozonation, compared to the ammonia addition strategies, but the involving chemistry was different. Bromide is primarily masked as bromochloramine in the NH₃-Cl₂ process, while monobromamine and dibromamine are the dominant masking haloamines in the Cl₂-NH₃ process. The bromate control by the NH₃-Cl₂ pretreatment is less pH-dependent but more sensitive to the initial bromide concentration than the Cl₂-NH₃ process. The Cl₂-NH₃ process, due to larger extent of free chlorine exposure, produced higher concentrations of the common organic DBPs.

An ESI-tqMS method based on investigation of the optimum collision energy was developed. This method differentiates chlorine attachment to the aliphatic part or the benzene ring of a molecule by the two distinct domains of their corresponding optimum collision energies in the precursor ion scan at m/z 35. This method is applied to predict the structures of intermediates and propose transformation pathways of chlorination of 4-amino-2-chlorobenzoic acid, adenine, cytosine and phenylalanine as a function of times, pH and chlorine to precursor ratios. Chlorine is found to replace first the hydrogen atom connected to the aliphatic nitrogen of phenylalanine, while hydrogen atoms attached to the aromatic rings of 4-amino-2-chlorobenzoic acid, adenine and cytosine were substituted first by chlorine.