The action of chlorine dioxide on aquatic organic materials during the disinfection of drinking water

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Abstract
Measurements of the total organic halogens (TOX) producedin the National Water CArrier (NWC) of Israel after disinfection with ClO2 revealed that compared to Cl, ClO2 formed only a small amount of chlororganic compounds. Mixtures of Cl2 and ClO2 were reported to reduce the concentrations of both chlorinated organics and the chlorite ions produced by ClO2, were not useful because high bromide concentrations were present in the NWC. High ratios of ClO2/Cl2 were needed to reach a significant reduction in trihalomethanes (THM). The amount of THM was satisfactorily reduced when ClO2 was introduced a few hours before Cl. A comparison between Cl2 and ClO2 with regard to their reactions with a series of polycyclic aromatic hydrocarbons (PAH) showed that the ClO2 reactions were more unique. While the highly carcinogenic compounds, benz[a]pyrene and 1,2-benzanthracene reacted with ClO2 more rapidly than with Cl2, other PAH, such as naphthalene and fluoranthene, which reacted easily with Cl, reacted very slowly or not at all with ClO2. The differences between the physical factors influencing the reaction rates of Cl2 and ClO2, and the sequence of their reactions with various PAH indicated that in contrast to Cl which reacted by few possible pathways, ClO2 reacted mainly as an 1 electron acceptor. The main organic byproducts of Cl02 were aldehydes, ketones and quinones, beside low MW carboxylic acids. Although aldehydes and carboxylic acids are usually regarded as monotoxic materials, the toxicity of quinones and some keto-aldehydes were still largely unknown.