Mechanisms for simultaneous ozonation of sulfamethoxazole and natural organic matters in secondary effluent from sewage
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RESEARCH ARTICLE
Mechanisms for simultaneous ozonation of sulfamethoxazole and natural organic matters in secondary effluent from sewage treatment plant Xinshu Liu, Xiaoman Su, Sijie Tian, Yue Li, Rongfang Yuan (✉) Beijing Key Laboratory of Resource-oriented Treatment of Industrial Pollutants, Department of Environmental Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
HIGHLIGHTS
GRAPHIC ABSTRACT
• SMX was mainly degraded by hydrolysis, isoxazole oxidation and double-bond addition. • Isoxazole oxidation and bond addition products were formed by direct ozonation. • Hydroxylated products were produced by indirect oxidation. • NOM mainly affected the degradation of SMX by consuming OH rather than O3. • Inhibitory effect of NOM on SMX removal was related to the components’ aromaticity.
ABSTRACT ARTICLE INFO Article history:
Received 29 June 2020 Revised 29 September 2020 Accepted 5 October 2020 Available online 16 November 2020 Keywords: Sulfamethoxazole Ozonation Natural organic matters Secondary effluent Degradation mechanism
Sulfamethoxazole (SMX) is commonly detected in wastewater and cannot be completely decomposed during conventional treatment processes. Ozone (O3) is often used in water treatment. This study explored the influence of natural organic matters (NOM) in secondary effluent of a sewage treatment plant on the ozonation pathways of SMX. The changes in NOM components during ozonation were also analyzed. SMX was primarily degraded by hydrolysis, isoxazole-ring opening, and double-bond addition, whereas hydroxylation was not the principal route given the low maximum abundances of the hydroxylated products, with m/z of 269 and 287. The hydroxylation process occurred mainly through indirect oxidation because the maximum abundances of the products reduced by about 70% after the radical quencher was added, whereas isoxazole-ring opening and double-bond addition processes mainly depended on direct oxidation, which was unaffected by the quencher. NOM mainly affected the degradation of micropollutants by consuming OH rather than O3 molecules, resulting in the 63%– 85% decrease in indirect oxidation products. The NOM in the effluent were also degraded simultaneously during ozonation, and the components with larger aromaticity were more likely degraded through direct oxidation. The dependences of the three main components of NOM in the effluent on indirect oxidation followed the sequence: humic-like substances>fluvic-like substances>protein-like substances. This study reveals the ozonation mechanism of SMX in secondary effluent and provides a theoretical basis for the control of SMX and its degradation products in actual water treatment. © Higher Education Press 2020
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Introduction
The water pollution caused by antibiotics has aroused global concerns given the extensive production and
✉ Corresponding author E-mail: [email protected]
consumption of antibiotics, resulting in hazards to the aquatic environment and human health (Yuan et al., 2019; Li et al., 2020
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