Study on the formation of nitrogenous disinfection by products from the reaction between dichloroacetaldehyde and monochloramine

Nitrogenous Disinfection By-products, aldehyde pathway, kinetic rate constants

Vu, Trang Nha

关键词: Nitrogenous Disinfection By-products, aldehyde pathway, kinetic rate constants;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/100980/VU-DISSERTATION-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Disinfection is a mandatory step in drinking water treatment to inactivate harmful pathogens found in source waters and minimize health risks for human consumers. Among many powerful oxidants commonly used as disinfectants, chlorine has been widely utilized at many water treatment facilities due to low cost and high efficiency in reducing waterborne diseases such as cholera and typhoid. However, the major downside of this process is the formation of a group of compounds known as disinfection by-products (DBPs) when chlorine unintentionally reacts with some constituents naturally occurring in source water. To prevent the negative health effects of chlorinated DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs), regulations that stipulate their maximum contaminant levels have been established since 1970s and gradually become more stringent. For this reason, switching to alternative disinfectants (i.e. ozone, UV or chloramine) helps to significantly reduce the concentration of chlorinated DBPs in finished water. Although this strategy allows water utilities to comply the stricter regulation recently proposed, the alternative disinfectants introduce new DBP classes that are not well studied and can also cause severe human health effects. Among newly found DBPs which are introduced to disinfected water by using alternative disinfectant, nitrogen containing DBPs (N-DBPs) are of growing concern to human consumers due to their relatively high toxicity compared to regulated DBPs mostly produced by chlorination. Occurrence studies have shown that haloacetonitriles (HANs) and haloacetamides (HAMs), two unregulated N-DBP groups, were commonly found in drinking water with chloramine disinfection. Although these N-DBP groups occur at lower levels than chlorinated DBPs, they are shown to be more toxic and can significantly contribute to the overall toxicity of disinfected drinking water. In addition, haloaldehydes were also observed in the finished water from several water facilities and they are identified as the third largest DBP group by weight, only behind THMs and HAAs.For the first time, this study confirms the predominant formation of HAN and HAM dominant species, dichloroacetonitrile (DCAN) and dichloroacetamide (DCAM), from the reaction between monochloramine and dichloroacetaldehyde via the aldehyde reaction pathway. Initial reactants reacted quickly and reached equilibrium with carbinolamine 2,2-dichloro-1-(chloroamino)ethanol. Then, the carbinolamine underwent two parallel reactions where, (1) it slowly dehydrated to 1,1-dichloro-2-(chloroimino)ethane and further decomposed to dichloroacetonitrile and (2) it was oxidized by monochloramine to form a newly discovered N-haloacetamide N,2,2-trichloroacetamide. Additionally, labelled 15N-monochloramine experiments with natural water reveals the prevalence of the aldehyde pathway in real drinking water conditions as 60-70% DCAN and DCAM contain 15N atom which was contributed by 15N-monochloramine. Furthermore, free chlorine pretreatment followed by chloramination was shown to enhance the formation of 15N-DBPs. A kinetic model was developed that predicted up to 90% of N-DBPs in natural waters.