饮用水新型含氮消毒副产物卤乙酰胺稳定性研究

Stability of Newfound Nitrogenous Disinfection By-products Haloacetamides in Drinking Water

饮用水氯化消毒工艺向氯胺消毒工艺的转变,降低了三卤甲烷(THM)和卤乙酸(HAA)等消毒副产物(DBP)的浓度,但增加了毒性更强的含氮消毒副产物(N-DBP)含量,卤乙酰胺(HAcAm)便是其中的代表.本研究结合线性自由能关系(LFER)理论,考察了HAcAm在不同pH条件下的水解特性,以及不同氯投加量条件下的氯化特性,并探讨了HAcAm的水解和氯化反应路径.结果表明,在较强的酸性条件下(pH=4)二氯乙酰胺(DCAcAm)将发生水解反应,pH=5时DCAcAm较为稳定,三氯乙酰胺(TCAcAm)在酸性条件下未产生明显的水解现象;碱性环境中TCAcAm和DCAcAm皆发生明显水解反应,反应符合一级动力学,保存DCAcAm和TCAcAm水样时需调pH至5左右.氯化消毒会产生较高浓度的THM和HAA,但可能会缩减毒性更强的HAcAm等N-DBP在饮用水中的含量.pH=10时TCAcAm水解后快速生成三氯乙酸(TCAA);而对于氯化反应,TCAcAm与HOCl反应生成较为稳定的中间产物Cl-N-TCAcAm,当HOCl浓度较高时,Cl-N-TCAcAm进一步与HOCl反应生成TCAA.

The conversion of drinking water disinfection process from free chlorine to mono-chloramine reduces the formation of trihalomethanes （THM）, but increases the concentration of nitrogenous disinfection by-products （N-DBP）, especially five new haloacetamides （HAcAm） including monochloroacetamide （MCAcAm）, dichloroacetamide （DCAcAm）, trichloroacetamide （TCAcAm）, monobromoacetamide （MBAcAm） and dibromoacetamide （DBAcAm）. Among these HAcAms, DCAcAm and TCAcAm are normally present in drinking water at a higher concentration. The hydrolysis characteristics with different pH values and chlorination characteristics under different chlorine dosages of HAcAm were studied by combination with linear free-energy relationship （LFER）. Based on the hydrolysis and chlorination characteristics of HAcAm, the reaction pathways of hydrolysis and chlorination for HAcAm were also investigated by detection of final product haloacetic acids （HAA）. The results indicated that DCAcAm reacted slowly with water in highly acidic condition （pH=4） but was stable at pH 5 within 7 d reaction time. Acid environment can not cause TCAcAm hydrolysis reaction. Obvious hydrolysis reactions of DCAcAm and TCAcAm were discovered in alkaline conditions, which followed the first order reaction. The water sample containing DCAcAm and TCAcAm could be preserved by adjusting pH to 5. The use of chlorine disinfection and increment of chlorine dosage caused the amount of THM and HAA to go up in drinking water, however, it maybe resulted in the decrease of N-DBP such as HAcAm. Trichloroacetic acid （TCAA） was produced rapidly by TCAcAm hydrolysis at pH 10. For chlorination of TCAcAm, relatively stable Cl-N-TCAcAm was produced from a reaction between TCAcAm and HOCl, then continued to generate TCAA and NHCl2 at a higher concentration of HOCl.