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With the increasing usage of chloramines in drinking water treatment to control regulated disinfection byproducts, control of the formation of N-nitrosamines has now became problematic as N-nitrosamines are generally formed during chloramination, and in distribution systems using chloramine as a secondary disinfectant. The preferred way to minimize the N-nitrosamine formation is to remove N-nitrosamine formation precursors from the source water. This paper reports studies for the removal of seven N-nitrosamine precursors (i.e., dimethylamine, ethylmethylamine, diethylamine, dipropylamine, trimethylamine, 4-dimethylaminoantipyrine and 3-(dimethylaminomethyl)indole) using adsorption by zeolites and powdered activated carbons in both laboratory reagent water and untreated source water. Zeolites have showed promising removal for most of the secondary and tertiary amines precursors. Over 80% of ethylmethylamine, diethylamine, trimethylamine and 3-(dimethylaminomethyl)indole) were removed by Mordenite zeolite in laboratory reagent water at only 10 mg/L of adsorbents with a contact time of 4 h, while over 70% of diethylamine and 60% of dipropylamine were removed under the same condition. More than 90% of these precursors were removed by increasing the Mordenite zeolite concentration to 100 mg/L. The removal efficiencies were decreased in surface water sample. The effects of contact time and adsorbent dosage of Mordenite zeolite were also evaluated and adsorption isotherms were analyzed by using both Freundlich and Langmuir equations. The two powdered activated carbons were shown, however, to have higher removal efficiency for the two less hydrophilic tertiary amines. The combination of these two types of adsorbents for drinking water treatment may be an option for the control of N-nitrosamine precursors before chloramination, and merits further testing at pilot and full scale. |
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