Haloacetaldehydes (HAlds) are the third prevalent group of disinfection by-products and have been reported to be more cytotoxic and genotoxic than the regulate trihalomethanes and haloacetic acids. Previous researches mainly focused on chloral hydrate (CH), while there are very limited data on the formation and speciation of the nine chlorine- and bromine-containing HAlds. In this study, the formation and speciation of nine HAlds during ozonation-chlorination and chlorination were investigated for raw and treated water containing bromide. Formation potential tests showed that ozonation-chlorination produced much higher HAld yields than chlorination, and the total HAld yields were similar in raw and treated water whether under chlorination or ozonation-chlorination, which means the conventional treatment processes had little effect on the removal of HAld precursors. The major species of HAlds were CH and bromodichloroacetaldehyde, and CH contributed from 25% to 48% to the total HAlds formed in waters containing 100-150 μg/L bromide, indicating the wide existence of other HAlds after chlorination besides CH production.<br/>Based on this, a series of aliphatic and aromatic model compounds, which included ozonation by-products such as aldehydes and ketoacids, were selected to investigate the formation mechanism of HAlds during chlorination. The results showed that HAld molar yields of acetaldehyde were 1-2 magnitude larger than that of other model compounds. Chlorination conditions such as pH, chlorine dose, and react time had important effects on HAld yields during. With the increasing of pH, the yields of HAlds were firstly increased and then decreased because of the hydrolysis of HAlds under base condition. The HAlds yield increased as the chlorine dose increased. With the increasing of react time, the chloroacetaldehyde yield reached its maximum first, and then the dichloroacetaldehyde yield, and then the CH yield, while the chloroform yield kept increasing. Finally, the formation pathway of HAlds was proposed and verified by successfully establishing the kinetic model to predict the HAld yields during chlorination of acetaldehyde. When there is bromide in water, the bromine formed during chlorination will parallel competed with chlorine to substitute the α-H in acetaldehyde to form brominated HAlds. A series of sequential chlorine and bromine halogen incorporation steps occur to generate two mono-, tree di- and four trihalogenated acetaldehydes.

Charactrization of nine haloacetaldehyde formation during chlorination of bromide-containing water

255th National Meeting (2018)

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