Characterization of enoxacin (ENO) during ClO2 disinfection in water distribution system: Kinetics, byproducts, toxicity evaluation and halogenated disinfection byproducts (DBPs) formation potential
Graphical abstract
Introduction
Chlorination is the most commonly used disinfection technique for water treatment to prevent the spread of pathogenic microorganisms and bacteria (Gao et al., 2018; Zhang et al., 2019). However, a large amount of chlorine produces undesirable halogenated disinfection byproducts (DBPs), which are potentially carcinogenic, cytotoxic, genotoxic, and developmentally toxic (Richardson and Kimura, 2016; Sharma et al., 2014; Yang and Zhang, 2013; Wagner and Plewa, 2017). As an alternative disinfectant, chlorine dioxide (ClO2) is widely applied to reduce DBP formation (He et al., 2019; Hua and Reckhow, 2007; Shah et al., 2012; Han and Zhang, 2018; Han et al., 2021). ClO2 is sometimes utilized as a secondary disinfection approach to protect the water distribution system (WDS) from microbiological recontamination and fouling (Lv et al., 2021; Lu et al., 2012; Tao et al., 2018). The ClO2 concentrations in the finished water of the treatment plant are lower than 0.8 mg/L (USEPA, 1999). Therefore, ClO2 prevents the recontamination of microbes and reacts with organic matter to form DBPs when finished water is transferred to the WDS, and some of these DBPs can substantially affect human health (Volk et al., 2002).
Numerous studies have been carried out to evaluate the effect of ClO2 on disinfecting organic matter, particularly emerging contaminants that are not encompassed by legislation (Jia et al., 2018a; Navalon et al., 2008). However, most previous studies have been based on laboratory-scale experiments (e.g., ultrapure water, buffered water, or deionized water (DI water)), and the results deviate from those observed for actual WDS wherein changes in pH value, flow rate, or pipe material may affect the disinfection of ClO2 in WDS. Unfortunately, to the best of our knowledge, minimal investigations on ClO2 disinfection of emergent pollutants within the WDS have been carried out in published studies. Therefore, disinfection using ClO2 for removing fluoroquinolones (FQs, a typical type of emergent pollutant) in WDS, its related intermediates, and halogenated DBPs was first evaluated in this study.
As a class of synthetic broad-spectrum antibacterial pharmaceuticals, FQs are commonly used in many human and veterinary applications (Ling et al., 2017; Yassine et al., 2017). However, not all FQs can be metabolized adequately in human and animal bodies, and more than 70% of these compounds are excreted into municipal wastewater systems through feces and urine (Pan et al., 2021). Since FQs cannot be removed completely in conventional wastewater treatment processes, they are frequently measured within the water environment, with a range of concentrations in the ng/L-mg/L scale (Nasuhoglu et al., 2012; Speltini et al., 2010; Sturini et al., 2012; Yahya et al., 2014). FQs are prevalent in the water environment, which raises the possibility of bacterial drug resistance (Jia et al., 2018b; Johnson et al., 2015). The World Health Organization (WHO) reports that bacterial resistance to antibiotics poses a significant threat to human health (Pruden et al., 2013).
FQs are usually discovered in sources of drinking water (Annabi et al., 2016; Riaz et al., 2017; Yahya et al., 2014). When water containing FQs is handled using the traditional management system in water treatment plants, only approximately 15.5–73.6% of FQs are removed (Lia et al., 2018). Even though advanced treatment processes have been applied in some water treatment plants, FQs cannot be removed entirely. According to a study by Vieno, when ozonation was applied to water treatment plants, approximately 16% ciprofloxacin (CIP) was removed (Vieno et al., 2007). In addition, most of the FQs could be removed effectively when activated carbon filtration was used; however, the removal ratio of enrofloxacin was lower than 10% (Xu et al., 2015). This suggests that the FQs could not be eradicated from the finished water. A previous investigation reported that FQs concentrations in finished water ranged between 0 and 126.43 ng/L (Zhang et al., 2018). Therefore, the ClO2 contained within the finished water may react with the remaining FQs after it is delivered into the WDS. As a result, we must pay particular attention to the final FQ state during ClO2 disinfection to ensure drinking water safety.
Enoxacin (ENO) is a third-generation FQs, containing a naphthyridine ring in its structure (Sortino et al., 1998). Owing to its good absorption and low efficiency of adverse reactions (Liu et al., 2010), ENO is commonly used as a human and veterinary antibiotic to treat respiratory, urinary, skin, and gastrointestinal systems by inhibiting bacterial DNA-rotase in cells (Tong and Xiang, 2007). ENO cannot be adequately metabolized by humans and animals, resulting in its widespread disposal in water (Mabel et al., 2018; Tong and Xiang, 2007). In China, the concentration of ENO in water bodies can reach up to 448 μg/L (Bu et al., 2013). However, there is a lack of knowledge on the effectiveness of ClO2 in removing ENO, especially in WDS. Therefore, the removal ratio of ENO oxidation, formation of intermediates and halogenated DBPs, and potential toxicity risks associated with ENO destruction by ClO2 in WDS were first assessed in this study.
The specific aims of this study were to (i) examine ENO destruction in WDS as a function of varying ClO2 concentration, pH, flow velocity, and pipe material; (ii) explore the possible transformation products formed during the ENO destruction and identify the proposed reaction pathways; (iii) evaluate the formation of halogenated DBPs and chlorite during the oxidation of ENO by ClO2; and (iv) assess the toxicity variation during ENO destruction.
Section snippets
Reagents and materials
All chemicals were obtained from various manufacturers and were used directly without further purification. ENO (purity > 98%), 6 %–14% sodium hypochlorite (NaClO) solution, methyl tertiary butyl ether (MTBE), acetonitrile, and methanol of HPLC grade were purchased from Aladdin (Shanghai, China). Five halogenated DBP standards (three THMs, four HAAs, two HKs, one halogenated aldehyde, and nine HANs) with gas chromatographically pure mixture were provided by Cansyn (Toronto, Canada). The
ClO2 concentration
ENO destruction by ClO2 was investigated in DI water and a pilot-scale PE pipe at ClO2 concentrations ranging from 0.3 mg/L to 1.3 mg/L. Fig. 1 shows that the ENO degradation efficiency increased monotonically as the ClO2 concentration increased in both DI water and the pilot-scale PE pipe. When ClO2 concentration elevated in the range of 0.3–1.3 mg/L, ENO removal efficiency after 180 min increased from 38.0% to 64.3% in the pilot-scale PE pipe and from 45.7% to 68.4% in the DI water
Conclusions
This study elucidated the ENO destruction using ClO2 in both DI water and a pilot-scale PE pipe. Under the experimental conditions used in this experiment, the removal ratio of ENO by ClO2 in DI water was higher than that in the pilot-scale PE pipe, and the reactions between ENO and ClO2 in DI water followed the second-order kinetic model. The destruction of ENO using ClO2 showed a strong pH dependence as the destruction efficiency increased with a rise in pH. Additionally, pipe material and
Credit author statement
Guilin He: Methodology, Formal analysis, Writing – original draft, Funding acquisition. Tuqiao Zhang: Supervision, Funding acquisition, Conceptualization, Qingzhou Zhang: Investigation, Writing – review & editing, Feilong Dong, Methodology, Formal analysis, Yonglei Wang, Project administration, Supervision, Resources.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work has been funded by the Doctoral Research Fund of Shandong Jianzhu University (X20038Z0101); the China Postdoctoral Science Foundation (No. 2018M632465) and the Funds for International Cooperation and Exchange of the National Natural Science Foundation of China (51761145022).
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2023, Chemical Engineering JournalCitation Excerpt :Furthermore, the DCAcAm yields from these tetracyclines were 0.43 %–54.26 % during chlorination and 0.65 %–44.57 % during chloramination, indicating that tetracyclines were the precursors of DCAcAm. He et al. [10] reported that five types of halogenated DBPs (i.e., HAAs, HANs, THMs, HKs, and HALs) and ClO2− formed during enoxacin (ENO) destruction when using ClO2 as the disinfectant in the water distribution system. Furthermore, during chlor(am)ination, EOMPs with higher aromaticity and more phenyl or heterocyclic (e.g., some PPCPs and EDCs) may easily convert to aromatic DBPs, then they go through side chain cleavage and ring opening reactions to form aliphatic DBPs, like THMs and HAAs [22].
Coprecipitation of ferrihydrite, enoxacin, and citrate for their transformation
2022, Journal of Cleaner ProductionCitation Excerpt :Forming radical attacks caused C-hydroxylation to form subsequent byproducts (Zhang and Huang. 2007). The intermediate product TP-352-2 was also found in previous studies in the degradation of ENO (He et al., 2021). Subsequently, TP-352-2 underwent successive quinolone ring opening and dihydroxylation to form TP-336 and TP-283, respectively.