Chloramination and Bromamination of Amino Acids

Monochloramine can be used instead of chlorine for disinfection of drinking water because monochloramine is more stable and produces less DBPs. Monochloramine can be formed also within swimming pools from the reaction of chlorine with ammonia. In the presence of bromide, other haloamines are produced such as bromochloramine and bromamines whose reactivity is even less known than for monochloramine. Haloamines can react with organic compounds and generate disinfection by-products like trihalomethanes and haloacetic acids. Unlike chlorine, few data are available on the chemistry of reactions between mineral haloamines and organic compounds. The aim of this study is to better understand the reactivity of haloamines with organic compounds by studying by-product formation from organic model molecules. Amino acids were chosen as model compounds because only scattered data are available in literature. The rate constants of the initial reaction of 12 amino acids with monochloramine at pH 8 and with monobromamine at pH 8.5 were determined in excess amino acid by using a continuous flow reactor and spectrophotometric determination of haloamines and the N-haloamino acids. Rate constants varied from 0.74 M−1 s−1 for alanine to 2.13 M−1 s−1 for histidine for chloramination experiments and from 132 M−1 s−1 for alanine to 704 M−1 s−1 for serine for bromamination experiments. Bromamination kinetic rate constants are 400 fold higher than chloramination rate constants. The formation potentials of trihalomethanes (THMs), and haloacetic acids (HAAs) were evaluated for a reaction time of 72 hours, a haloamine/amino acid ratio of 20 at pH 8 in phosphate buffer in the presence of monochloramine and bromochloramine, and at pH 8.5 in borate buffer in the presence of monobromamine. The formation potential of trihalomethanes and haloacetic acids were respectively up to 50 times and 3 times higher for bromamination compared to chloramination.