Transformation of amines during water treatment with chlorine, ozone, chlorine/UV, and chlorine/ozone: kinetics, mechanisms, and implications for water quality change

Abstract

The widespread occurrence of organic nitrogen has been increasing in water sources. The organic nitrogen can exist in natural organic matter and micropollutants, which usually produce toxic nitrogenous disinfection byproducts during oxidative water treatments due to its reactive characteristic to oxidants by electron-rich nature of the neutral form. Among the various forms of organic nitrogen, amine moiety is a major reaction site during oxidative water treatments. Despite its prevalence in nature and high reactivity toward oxidants, the reaction chemistry of amine moiety during oxidative water treatments is still poorly understood. The aim of this thesis was to elucidate the reaction chemistry of aliphatic amine moiety with chlorine, ozone, and combined process of chlorine/UV and chlorine/ozone. With basis of reaction chemistry, it would be available to evaluate the removal efficiency of amines and its formation potential into toxic byproducts within each oxidative water treatment. The objectives of this thesis were (1) to determine the reaction kinetics, (2) to identify/quantify the transformation products, and (3) to propose reaction pathways and mechanisms during oxidative water treatments of aliphatic amines. For the water treatment with chlorine, chloramines were formed from the reaction between aliphatic amines and free chlorine. Once chloramines were decomposed, there can be full conversion of amine moiety into nitrile, which can be a potential threat to water safety. For ozonation, aliphatic amines were often converted into nitro-products that can be transformed into halonitroalkane in post chlorination, which is undesirable. For the combined use of chlorine and UV or ozone, halamine was the key intermediate to oxidation. Halamines get photolyzed into dealkylated amine and aldehyde, and ozonated to produce enhanced nitrate with reduced nitro-product formation. Overall, chlorine/UV was the most proper process to show significant abatement efficiency of amines and produce less toxic nitrogen-derived byproducts from the aliphatic amines. It warrants a further study relevant with the simultaneous formation of the other disinfection byproducts (e.g., THMs, HANs) during combined use of chlorine and UV to prove minimized formation potential of overall toxic disinfection byproducts.