Degradation of metronidazole by UV/chlorine treatment: Efficiency, mechanism, pathways and DBPs formation

Yishuai Pan; Xuchun Li; Kun Fu; Huiping Deng; Jun Shi

doi:10.1016/j.chemosphere.2019.02.081

Degradation of metronidazole by UV/chlorine treatment: Efficiency, mechanism, pathways and DBPs formation

Chemosphere. 2019 Jun:224:228-236. doi: 10.1016/j.chemosphere.2019.02.081. Epub 2019 Feb 15.

Authors

Yishuai Pan¹, Xuchun Li², Kun Fu¹, Huiping Deng³, Jun Shi⁴

Affiliations

¹ Key Laboratory of Yangtze River Water Environment, Ministry of Education, Shanghai Institute of Pollution Control and Ecological Security, College of Environmental Science and Engineering, Tongji University, Shanghai, 20092, China.
² School of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou, 310018, China.
³ Key Laboratory of Yangtze River Water Environment, Ministry of Education, Shanghai Institute of Pollution Control and Ecological Security, College of Environmental Science and Engineering, Tongji University, Shanghai, 20092, China. Electronic address: denghuiping@tongji.edu.cn.
⁴ Key Laboratory of Yangtze River Water Environment, Ministry of Education, Shanghai Institute of Pollution Control and Ecological Security, College of Environmental Science and Engineering, Tongji University, Shanghai, 20092, China. Electronic address: shijun215@tongji.edu.cn.

PMID: 30822729
DOI: 10.1016/j.chemosphere.2019.02.081

Abstract

Metronidazole (MET) is a widely used antibiotic but is recalcitrant in aquatic environment. This study investigated elimination of MET by UV/chlorine process systematically. The degradation of MET in the process well fitted pseudo first-order kinetics. Decreasing pH from 9 to 5 raised the rate constant from 0.0199 min^-1 to 0.1485 min^-1, possibly ascribed to change in species distribution and apparent quantum yields of radicals. Scavenging experiments indicated that both HO and Cl contributed to the degradation of MET, and that HO was the dominant species in the pH range studied. The second-order rate constant between Cl and MET was determined to be (5.64 ± 0.1) × 10⁹ M^-1 s^-1. Three products were identified by UPLC-Q-TOF MS and degradation pathway was thus proposed. Significant amounts of chlorinated disinfection by-products (DBPs) were produced and 1,1,1-TCP was the dominant (83.6%-92.3%) in the UV/chlorine process. The kinetic model developed fitted well with experimental results, and was used to examine the effects of typical water parameters, such as chorine dosage, pH, inorganic anions, NOM and real water matrix. Furthermore, removal efficiency of MET by the UV/chlorine process were assessed in terms of electrical energy per order (EE/O). The efficiency was about 0.43 kWh m^-3 order^-1, 0.54 kWh m^-3 order^-1, 0.57 kWh m^-3 order^-1, respectively, for the removal of MET in ultrapure water (UPW) and two types of real water samples, indicating that UV/chorine was a practical method for authentic drinking water treatment practices.

Keywords: Disinfection byproducts; EE/O; Metronidazole; UV/chlorine AOP.

MeSH terms

Chlorine / chemistry*
Disinfection
Halogenation
Kinetics
Metronidazole / analysis*
Metronidazole / radiation effects
Models, Theoretical
Oxidation-Reduction
Ultraviolet Rays*
Water Pollutants, Chemical / analysis*
Water Pollutants, Chemical / radiation effects
Water Purification / methods*

Substances

Water Pollutants, Chemical
Metronidazole
Chlorine