Insight into the degradation of ciprofloxacin by medium-pressure UV-activated monochloramine process

Zedong Lu; Yanchen Ling; Xuelin Wang; Simiao Li; Xiuwei Ao; Weibo Wang; Chen Li; Wenjun Sun; Tianyin Huang

doi:10.1016/j.scitotenv.2022.154850

Insight into the degradation of ciprofloxacin by medium-pressure UV-activated monochloramine process

Sci Total Environ. 2022 Aug 1:832:154850. doi: 10.1016/j.scitotenv.2022.154850. Epub 2022 Mar 26.

Authors

Zedong Lu¹, Yanchen Ling², Xuelin Wang¹, Simiao Li³, Xiuwei Ao¹, Weibo Wang¹, Chen Li¹, Wenjun Sun⁴, Tianyin Huang⁵

Affiliations

¹ School of Environment, Tsinghua University, Beijing 100084, China.
² School of Environment, Tsinghua University, Beijing 100084, China; Suzhou University of Science and Technology, Suzhou 215009, China.
³ Beijing General Municipal Engineering Design & Research Institute Co., Ltd, China.
⁴ School of Environment, Tsinghua University, Beijing 100084, China; Research Institute for Environmental Innovation (Suzhou) Tsinghua, Suzhou 215163, China. Electronic address: wsun@tsinghua.edu.cn.
⁵ Suzhou University of Science and Technology, Suzhou 215009, China.

PMID: 35351514
DOI: 10.1016/j.scitotenv.2022.154850

Abstract

The degradation efficiency and mechanisms of ciprofloxacin (CIP), a typical antibiotic, by a medium-pressure ultraviolet/chloramine (MPUV/NH₂Cl) treatment were investigated. The results showed that CIP degradation by MPUV/NH₂Cl was significantly higher than that by NH₂Cl oxidation and MPUV photolysis, and that this degradation processes were consistent with pseudo-first-order kinetics. The initial CIP concentration (7.5-30.2 μM) and the presence of HCO₃^- (0.5-10 mM) significantly inhibited CIP degradation with k_obs,CIP 0.0090-0.0069 and 0.0078-0.0048 cm²/mJ. In contrast, NO₃^- (50-500 μM) and Br^- (0.5-10 mM) significantly promoted the degradation with k_obs,CIP 0.0078-0.0102 and 0.0078-0.0124 cm²/mJ. The effect of Cl^- (0.5-10 mM) and natural organic matter (1-5 mg/L) were negligible. The NH₂Cl dosage (30-60 μM) presented a dual effect, in which its increase within the optimal concentration range (30-40 μM) accelerated CIP degradation due to the formation of reactive radicals, whereas an excessive increase (40-60 μM) quenched the free radicals, ultimately quenching the free radicals and inhibiting the degradation. The optimum pH for CIP degradation under MPUV/NH₂Cl treatment was 7.0. The contribution of reactive halogen species (i.e., reactive chlorine species and reactive nitrogen species) to CIP degradation was substantially greater than that of hydroxyl radicals under acidic or neutral conditions. We identified the degradation products of CIP and proposed degradation pathways, which included defluorination and cracking of the piperazine ring, with the latter being dominant. Compared to haloacetic acid (HAA) and nitrogenous disinfection byproducts (N-DBPs), MPUV/NH₂Cl significantly reduced trihalomethane (THM) production and theoretical cytotoxicity by 80.1% and 78.4% respectively, compared to the background experiment in natural water at a UV dose of 300 mJ/cm².

Keywords: Advanced oxidation process; Ciprofloxacin; MPUV/NH(2)Cl; Medium-pressure ultraviolet; Theoretical cytotoxicity; Trihalomethane.

MeSH terms

Chloramines
Chlorides
Chlorine
Ciprofloxacin
Disinfection
Kinetics
Oxidation-Reduction
Ultraviolet Rays
Water Pollutants, Chemical* / analysis
Water Purification*

Substances

Chloramines
Chlorides
Water Pollutants, Chemical
Chlorine
Ciprofloxacin
chloramine