Chlorination of L-tyrosine and metal complex: degradation kinetics and disinfection by-products generation

Abstract

The presence of metal ions in drinking water treatment and distribution systems may affect the disinfection process of organic matter, which had aroused people's concern. L-tyrosine can complex with metal ions through carboxyl, carbonyl and amino groups and affected its chemical reactions. In this paper, the complexation of L-tyrosine with common metal ions was studied and the influence of complexation in chlorination with different experimental factors were investigated. It was inferred that L-tyrosine complexed with metal ions by single dentate ligand or double dentate chelation in a ratio of 2:1. The degradation of L-tyrosine-metal complex followed the pseudo-first-order reaction kinetic. TCM, DCAA and TCAA were the main species DBPs in chlorination of L-tyrosine. Compared with L-tyrosine, the reaction rate constants of complex increased by 5.6%, the formation of trihalomethane production decreased by 21.5% and the formation of haloacetic acids production increased by 26.9% at the state of metal complexation. The effect of metal complexation on chlorination was more obvious than that of metal coexistence. For different metal complexation, the order of inhibition on trihalomethane production was Ca2+> Fe3+> Mn2+ and the order of promotion on haloacetic acids production was Mn2+> Fe3+> Ca2+. Moreover, it was found that alkaline conditions were favorable to the formation of DBPs due to the hydroxyl radical. The combination of ultraviolet (UV) and chlorine disinfection promoted L-Tyr degradation and DBPs generation, and the promotion efficiency follow the order: UV/Cl2> UV-Cl2> Cl2.