Ultraviolet (UV) irradiation has been an alternative disinfection technology for water treatment in recent decades. Compared with conventional free chlorine sanitizer, a combined process of chlorine and UV can improve the disinfection efficiency of chlorination and reduce the demand of chlorine dose applied in water treatment. It has been reported that UV disinfection followed by chlorination is applied in more than 28 drinking water treatment plants in the United States. UV treatment is also increasingly being applied to chlorinated swimming pool water as a secondary disinfection process and chloramine control strategy.
Halobenzoquinones (HBQs), as new emerging disinfection by-products (DPBs), are frequently detected in drinking and swimming pool waters. In fact, HBQs are also precursors to other DBPs such as currently regulated trihalomethanes (THMs), which pose a high risk to public health and the environment. When UV is applied during the chlorination process, DBP formation can be quite different from that under chlorine alone or UV alone. However, there are still many questions that require further investigation. For example, does combined UV/chlorine disinfection promote or limit the transformation of HBQ into SPD compared to disinfection with chlorine alone? In particular, does UV play a significant role in the transformation of organic precursors and the formation of DBPs during chlorine disinfection?
To answer these questions, Professor Ching-Hua Huang from the Georgia Institute of Technology, Dr. He Zhao from the Institute of Process Engineering, Chinese Academy of Sciences, and their team members worked together and systematically revealed the molecular mechanism of THMs produced from HBQ. in chlorination or combined UV/chlorine. Their work identified the promoter effect of UV on HBQs in the formation of THMs, which provided valuable information on the potential risk when applying combined UV/chlorine in water treatment. This study titled “Enhanced formation of trihalomethane disinfection byproducts from halobenzoquinones under combination UV/chlorine conditions” is published online in Frontiers of Environmental Science & Engineering in 2022.
In this study, the research team found that UV was increased nearly 10 times CHCl3 yield of formation of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ, one of the most frequently detected HBQs in drinking water). They also thoroughly investigated the reaction mechanism using complementary experimental measurements and Density Functional Theory (DFT) calculations, and revealed different patterns of THM formation from four HBQ species. during chlorine-only and UV/chlorine processes. Their investigation showed that UV had a great influence depending on the chemical structure of HBQs, directly affecting the rate of hydrolysis, transformation pathways, intermediates and subsequent production of THMs. Their results also revealed that HBQ hydroxylation was a key intermediate pathway in promoting THM formation.
This study comprehensively and systematically investigated the formation of THMs from HBQ during chlorination or combined UV/chlorine processes for the first time, which should be considered in the application of combined UV and chlorine processes in water treatment. It has deepened our understanding of the promoting roles of UV irradiation and HBQ hydroxylation in THM formation, providing new insight into potential risks for UV disinfection of drinking water treatment.
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Founded in May 1954, Higher Education Press Limited Company (HEP), affiliated with the Ministry of Education, is one of the earliest institutions engaged in educational publishing after the establishment of PR China in 1949. After six decades of efforts, HEP has grown into a large comprehensive publisher, with products in various forms and at different levels. Both for import and export, HEP strives to fill the gap in domestic and overseas markets and meet the demand of global customers by cooperating with more than 200 partners around the world and selling products and services in 32 languages worldwide. Today, HEP ranks among the top Chinese publishers in terms of copyright export volume and among the top 50 publishing companies in the world in terms of overall strength.
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About the Frontiers of Environmental Science and Engineering
Frontiers of Environmental Science & Engineering (FESE) is the leading forum for original peer-reviewed submissions in English on all major branches of environmental disciplines. FESE welcomes original research papers, review articles, short communications, viewpoints and commentaries. All articles will be published within 6 months of submission. The editors are Academician Jiuhui Qu of Tsinghua University and Professor John C. Crittenden of the Georgia Institute of Technology, USA. The journal has been indexed by almost all authoritative databases such as SCI, Ei, INSPEC, SCOPUS, CSCD, etc.