AWWA JAW18891

This article discusses the factors that contribute to the formation of trihalomethanes (THMs) and total organic halogen (TOX) in drinking water. Oxidation and substitution are important mechanisms in the interaction between disinfectants and naturally occurring organics in water. Oxidation processes are responsible for the removal of organic compounds and precursors of THMs and TOX. Substitution reactions are the source of chlorine incorporation into the organic matter. This incorporation manifests itself in the TOX measurement, part of which is due to THMs. Disinfectants differ in their abilities to carry out oxidation and substitution reactions. Chlorine, a strong disinfectant, is also a strong oxidant, whereas chloramines (weak disinfectants) are nearly as likely as chlorine to add to organic materials by substitution. Thus, both chlorine and chloramines produce TOX and may impart adverse health effects from the chloro-organic compounds they produce. Before a decision is made to change disinfectants, operating parameters such as pH and chlorine dose must be taken into account to achieve the best quality drinking water. Includes 62 references, tables, figures.