State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China.
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China.
Water Res. 2022 Feb 15;210:117990. doi: 10.1016/j.watres.2021.117990. Epub 2021 Dec 21.
Amino acids (AAs) are a major group of odorous disinfection by-product (O-DBP) precursors. O-DBPs formations during free chlorine disinfection has been previously investigated. However, knowledge regarding the O-DBP formation mechanism and kinetics under chloramination of AAs is very limited. In this study, the generation of odorous isovaleraldehyde, isovaleronitrile and N-chloroisovaleraldimine from leucine (Leu), a typical and abundant AA in many drinking water sources, in its free and combined forms during chloramination under several typical addition schemes of disinfectants was investigated. Free Leu and glycylleucine (Gly-Leu) were chosen as model compounds since they have been indicated to be O-DBP precursors during chlorination. Intermediate product analysis and kinetics studies were conducted to study the reaction mechanisms. Impacts of disinfectants dosages and pH were also investigated in experiments and simulations. The results indicated that comparing with chlorination, chloramination of Leu has its uniqueness by participating in reacting with isovaleraldehyde to form N-chloroisovaleraldimine. And all the three O-DBPs formations from free Leu and Gly-Leu during chloramination (with preformed NHCl) were less than those during chlorination, indicating that using NHCl for disinfection ensures control over the off-flavor problems to some degree. When chloramination was realized by adding chlorine and ammonia separately, a longer pre-chlorination time led to greater yields of the O-DBPs from both precursors, whereas adding ammonia before chlorine promoted more isovaleraldehyde formation from free Leu. Under alkaline conditions, more isovaleronitrile and N-chloroisovaleraldimine were produced, and acidic conditions led to more isovaleraldehyde formation during chloramination. Notably, O-DBPs yields from free Leu were approximately 1000 times greater than those from Gly-Leu during chloramination under all the schemes. In addition, chlor(am)ination experiments with real water from Taihu Lake (the third largest freshwater lake and water source for twenty million people in China) indicated the formation of N-chloroisovaleraldimine and isovaleraldehyde was highly likely to cause odorous problems in drinking water. This study facilitates further understanding of the causes of off-flavor issues in drinking water and can help control the odorous problems by optimizing the operating parameters of drinking water treatment plants.
氨基酸（AAs）是一类主要的致嗅消毒副产物（O-DBP）前体。先前已经研究了游离氯消毒过程中 O-DBP 的形成。然而，关于氯胺条件下 AA 致嗅副产物的形成机制和动力学的知识非常有限。在这项研究中，研究了在几种典型消毒剂添加方案下，游离形式和结合形式的亮氨酸（Leu）（许多饮用水源中典型且丰富的 AA）在氯胺化过程中生成致嗅异戊醛、异戊腈和 N-氯代异戊二亚胺的情况。选择游离亮氨酸和甘氨酰亮氨酸（Gly-Leu）作为模型化合物，因为它们在氯化过程中已被表明是 O-DBP 前体。进行了中间产物分析和动力学研究以研究反应机制。实验和模拟还研究了消毒剂剂量和 pH 值的影响。结果表明，与氯化相比，亮氨酸的氯胺化具有独特性，因为它参与与异戊醛反应形成 N-氯代异戊二亚胺。并且，在氯胺化过程中（有预形成的 NHCl），游离亮氨酸和 Gly-Leu 生成的三种 O-DBP 均少于氯化过程，表明使用 NHCl 进行消毒在一定程度上可以控制异味问题。当通过分别添加氯和氨来实现氯胺化时，较长的预氯化时间会导致两种前体生成的 O-DBP 产量更大，而先加氨后加氯会促进更多的游离亮氨酸生成异戊醛。在碱性条件下，会生成更多的异戊腈和 N-氯代异戊二亚胺，而在氯胺化过程中，酸性条件会导致更多的异戊醛生成。值得注意的是，在所有方案下，游离亮氨酸生成的 O-DBP 产量均约为 Gly-Leu 的 1000 倍。此外，太湖（中国第三大淡水湖和 2000 万人的水源）实际水样的氯（氨）化实验表明，N-氯代异戊二亚胺和异戊醛的形成极有可能导致饮用水中的异味问题。这项研究有助于进一步了解饮用水异味问题的原因，并通过优化饮用水处理厂的运行参数来帮助控制异味问题。
