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Understanding the Assisting Role of PMS in Low Current Electrochemical Processes for Degradation of Antibiotics

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Abstract

Electro-activated persulfate has displayed good performance in the oxidation of antibiotic pollutants in wastewater. However, high power consumption and the introduction of excessive sulfate ions hinder the application of this technology. This research provided a novel strategy for the applications of small power supply and simple devices in antibiotic pollutant treatment. It has been confirmed that sulfate radical (\({\mathrm{SO}}_4^{\bullet -}\)) could be generated at the boron-doped diamond (BDD) anode in both low and high current conditions. This study proposed a novel low current density electrochemical technology assisted by peroxymonosulfate (PMS) for the degradation of antibiotics. Adding 1 mg/L PMS at current density as low as 1.25 mA/cm2 increased the electro-oxidation rates of ciprofloxacin 5-fold from 1.92 ± 0.67 h−1to 9.70 ± 0.10 h−1. According to the Butler-Volmer equation, the introduction of PMS changed the mechanism of electrode reactions, thermodynamic properties of the system therefore changed. The electron spin resonance (ESR) test has confirmed that hydroxyl radical (•OH), \({\mathrm{SO}}_4^{\bullet -}\), and singlet oxygen (1O2) are all generated in low current electrochemical systems. Quenching experiments illustrate that both radical and non-radical ways play essential roles in electro-oxidation processes. The contribution rates of •OH, \({\mathrm{SO}}_4^{\bullet -}\), and 1O2 were 15.6%, 33.2%, and 40.5%, respectively. An oxidation peak was observed in cyclic voltammetry (CV) around +1.2 V, indicating that PMS electrolyte may drive oxidation at this potential. Besides, the reaction pathways of ciprofloxacin were speculated. Four transformation pathways including stepwise piperazine ring cleavage, OH/F substitution, cyclopropane ring cleavage, and decarboxylation were proposed for ciprofloxacin degradation.

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Data Availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

References

  • Aga, D. S., Lenczewski, M., Snow, D., Muurinen, J., Sallach, J. B., & Wallace, J. S. (2016). Challenges in the measurement of antibiotics and in evaluating their impacts in agroecosystems: A critical review. J. Environ. Qual., 45, 407–419. https://doi.org/10.2134/jeq2015.07.0393

    Article  CAS  Google Scholar 

  • Ajibola, A. S., & Zwiener, C. (2022). Occurrence and risk assessment of antibiotic residues in sewage sludge of two Nigerian hospital wastewater treatment plants. Water Air Soil Pollut., 233, 405. https://doi.org/10.1007/s11270-022-05875-4

    Article  CAS  Google Scholar 

  • Alsager, O. A., Alnajrani, M. N., Abuelizz, H. A., & Aldaghmani, I. A. (2018). Removal of antibiotics from water and waste milk by ozonation: Kinetics, byproducts, and antimicrobial activity. Ecotoxicol. Environ. Saf., 114–122.

  • An, T., Yang, H., Li, G., Song, W., Cooper, W. J., & Nie, X. (2010). Kinetics and mechanism of advanced oxidation processes (AOPs) in degradation of ciprofloxacin in water. Appl. Catal. B Environ., 94, 288–294 https://doi.org/10.1016/j.apcatb.2009.12.002

    Article  CAS  Google Scholar 

  • Anipsitakis, G. P. D., & D. D. (2004). Radical generation by the interaction of transition metals with common oxidants. Environ. Sci. Technol., 38, 3705.

    Article  CAS  Google Scholar 

  • Antonin, V. S., Santos, M. C., Garcia-Segura, S., & Brillas, E. (2015). Electrochemical incineration of the antibiotic ciprofloxacin in sulfate medium and synthetic urine matrix. Water Res., 83, 31–41. https://doi.org/10.1016/j.watres.2015.05.066

    Article  CAS  Google Scholar 

  • Antoniou, M. G., de la Cruz, A. A., & Dionysiou, D. D. (2010). Degradation of microcystin-LR using sulfate radicals generated through photolysis, thermolysis and e− transfer mechanisms. Appl. Catal. B Environ., 96, 290–298. https://doi.org/10.1016/j.apcatb.2010.02.013

    Article  CAS  Google Scholar 

  • Bard, A. J., & Faulkner, L. R. (2011). Electrochemical methods. Wiley.

    Google Scholar 

  • Can-Guven, E., Ilhan, F., Ulucan-Altuntas, K., Yazici Guvenc, S., & Varank, G. (2021). Electrochemically activated persulfate and peroxymonosulfate for furfural removal: Optimization using Box-Behnken design. Environ. Technol., 1-14. https://doi.org/10.1080/09593330.2021.2000037

  • Che, H., Che, G., Jiang, E., Liu, C., Dong, H., & Li, C. (2018). A novel Z-Scheme CdS/Bi3O4Cl heterostructure for photocatalytic degradation of antibiotics: Mineralization activity, degradation pathways and mechanism insight. J. Taiwan Inst. Chem. Eng., 91, 224–234.

    Article  CAS  Google Scholar 

  • Chen, M., & Chu, W. (2015). Photocatalytic degradation and decomposition mechanism of fluoroquinolones norfloxacin over bismuth tungstate: Experiment and mathematic model. Appl. Catal. B Environ., 168-169, 175–182. https://doi.org/10.1016/j.apcatb.2014.12.023

    Article  CAS  Google Scholar 

  • Davis, J., Baygents, J. C., & Farrell, J. (2014). Understanding persulfate production at boron doped diamond film anodes. Electrochim. Acta, 150, 68–74. https://doi.org/10.1016/j.electacta.2014.10.104

    Article  CAS  Google Scholar 

  • Dong, J., Yan, D., Mo, K., Chen, Q., Zhang, J., Chen, Y., & Wang, Z. (2022). Antibiotics along an alpine river and in the receiving lake with a catchment dominated by grazing husbandry. J. Environ. Sci. (China), 115, 374–382. https://doi.org/10.1016/j.jes.2021.08.007

    Article  CAS  Google Scholar 

  • Elmetwalli, A. (2022). Impact of antibiotic interactions with essential oils on bacterial growth. Journal of Complementary Medicine Research, 13. https://doi.org/10.5455/jcmr.2022.13.03.25

  • Farhat, A., Keller, J., Tait, S., & Radjenovic, J. (2015). Removal of persistent organic contaminants by electrochemically activated sulfate. Environ. Sci. Technol., 49, 14326–14333. https://doi.org/10.1021/acs.est.5b02705

    Article  CAS  Google Scholar 

  • Feng, Y., Wu, D., Deng, Y., Zhang, T., & Shih, K. (2016). Sulfate radical-mediated degradation of sulfadiazine by CuFeO2 rhombohedral crystal-catalyzed peroxymonosulfate: Synergistic effects and mechanisms. Environ. Sci. Technol., 50, 3119–3127. https://doi.org/10.1021/acs.est.5b05974

    Article  CAS  Google Scholar 

  • Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E., Robb, M. A., Cheeseman, J. R., Scalmani, G., Barone, V., Mennucci, B., Petersson, G. A., & Nakatsuji, H. (2013). Gaussian 09, Revision D.01. Wallingford CT.

    Google Scholar 

  • Ganiyu, S. O., & Gamal El-Din, M. (2020). Insight into in-situ radical and non-radical oxidative degradation of organic compounds in complex real matrix during electrooxidation with boron doped diamond electrode: A case study of oil sands process water treatment. Appl. Catal. B Environ., 279. https://doi.org/10.1016/j.apcatb.2020.119366

  • Ghanbari, F., & Moradi, M. (2017). Application of peroxymonosulfate and its activation methods for degradation of environmental organic pollutants: Review. Chem. Eng. J., 310, 41–62. https://doi.org/10.1016/j.cej.2016.10.064

    Article  CAS  Google Scholar 

  • Gothwal, R., & Shashidhar, T. (2015). Antibiotic pollution in the environment: A review. CLEAN - Soil, Air, Water, 43, 479–489. https://doi.org/10.1002/clen.201300989

    Article  CAS  Google Scholar 

  • Gwenzi, W., & Chaukura, N. (2018). Organic contaminants in African aquatic systems: Current knowledge, health risks, and future research directions. Sci. Total Environ., 619-620, 1493–1514. https://doi.org/10.1016/j.scitotenv.2017.11.121

    Article  CAS  Google Scholar 

  • He, Y., Lin, H., Guo, Z., Zhang, W., Li, H., & Huang, W. (2019a). Recent developments and advances in boron-doped diamond electrodes for electrochemical oxidation of organic pollutants. Sep. Purif. Technol., 212, 802–821. https://doi.org/10.1016/j.seppur.2018.11.056

    Article  CAS  Google Scholar 

  • Hong-Guang Guo, N.-Y. G., Chu, W.-H., Li, L., Zhang, Y.-J., Jin-Shan, G., & Yu-Liang, G. (2013). Photochemical degradation of ciprofloxacin in UV and UV/H2O2 process: Kinetics, parameters, and products. Environ. Sci. Pollut. Res., 20, 3202–3213.

    Article  Google Scholar 

  • Hori, H., Hayakawa, E., Einaga, H., Kutsuna, S., Koike, K., Ibusuki, T., Kiatagawa, H., & Arakawa, R. (2004). Decomposition of environmentally persistent perfluorooctanoic acid in water by photochemical approaches. Environ. Sci. Technol., 38, 6118–6124. https://doi.org/10.1021/es049719n

    Article  CAS  Google Scholar 

  • Huang, R., Ding, P., Huang, D., & Yang, F. (2015). Antibiotic pollution threatens public health in China. Lancet, 385, 773–774. https://doi.org/10.1016/s0140-6736(15)60437-8

    Article  Google Scholar 

  • Iniesta, J., Michaud, P. A., & Comninellis, C. (2002). Electrochemical oxidation of phenol at boron-doped diamond electrode. Electrochim. Acta, 46, 3573–3578.

    Article  Google Scholar 

  • Ji, Y., Ferronato, C., Salvador, A., Yang, X., & Chovelon, J.-M. (2014). Degradation of ciprofloxacin and sulfamethoxazole by ferrous-activated persulfate: Implications for remediation of groundwater contaminated by antibiotics. Sci. Total Environ., 472, 800–808. https://doi.org/10.1016/j.scitotenv.2013.11.008

    Article  CAS  Google Scholar 

  • Jiang, C., Ji, Y., Shi, Y., Chen, J., & Cai, T. (2016a). Sulfate radical-based oxidation of fluoroquinolone antibiotics: Kinetics, mechanisms and effects of natural water matrices. Water Res., 106, 507–517. https://doi.org/10.1016/j.watres.2016.10.025

    Article  CAS  Google Scholar 

  • Kumar, V., Bhatia, M., & Kumar, A. (2020). Microbes from mouth to gut impacting probiotics to antibiotics. Journal of Natural Science, Biology and Medicine, 11, 83–83.

    Google Scholar 

  • Kummerer, K. (2009a). Antibiotics in the aquatic environment--a review--part I. Chemosphere, 75, 417–434. https://doi.org/10.1016/j.chemosphere.2008.11.086

    Article  CAS  Google Scholar 

  • Kummerer, K. (2009b). Antibiotics in the aquatic environment--a review--part II. Chemosphere, 75, 435–441. https://doi.org/10.1016/j.chemosphere.2008.12.006

    Article  CAS  Google Scholar 

  • Liu, Z., Ding, H., Zhao, C., Wang, T., Wang, P., & Dionysiou, D. D. (2019). Electrochemical activation of peroxymonosulfate with ACF cathode: Kinetics, influencing factors, mechanism, and application potential. Water Res., 159, 111–121. https://doi.org/10.1016/j.watres.2019.04.052

    Article  CAS  Google Scholar 

  • Liu, H. P., Ma, S. L., Shao, L., Liu, H. T., Gao, Q. C., Li, B. J., Fu, H. C., Fu, S., Ye, H. G., Zhao, F. Y., & Zhou, J. G. (2020). Defective engineering in graphitic carbon nitride nanosheet for efficient photocatalytic pathogenic bacteria disinfection. APPLIED CATALYSIS B-ENVIRONMENTAL, 261. https://doi.org/10.1016/j.apcatb.2019.118201

  • Loos, G., Scheers, T., Van Eyck, K., Van Schepdael, A., Adams, E., Van der Bruggen, B., Cabooter, D., & Dewil, R. (2018). Electrochemical oxidation of key pharmaceuticals using a boron doped diamond electrode. Sep. Purif. Technol., 195, 184–191.

    Article  CAS  Google Scholar 

  • Luo, R., Li, M., Wang, C., Zhang, M., Nasir Khan, M. A., Sun, X., Shen, J., Han, W., Wang, L., & Li, J. (2019). Singlet oxygen-dominated non-radical oxidation process for efficient degradation of bisphenol A under high salinity condition. Water Res., 148, 416–424. https://doi.org/10.1016/j.watres.2018.10.087

    Article  CAS  Google Scholar 

  • Matta, R., Tlili, S., Chiron, S., & Barbati, S. (2010). Removal of carbamazepine from urban wastewater by sulfate radical oxidation. Environ. Chem. Lett., 9, 347–353.

    Article  Google Scholar 

  • Matzek, L. W., & Carter, K. E. (2016). Activated persulfate for organic chemical degradation: A review. Chemosphere, 151, 178–188. https://doi.org/10.1016/j.chemosphere.2016.02.055

    Article  CAS  Google Scholar 

  • Matzek, L. W., Tipton, M. J., Farmer, A. T., Steen, A. D., & Carter, K. E. (2018). Understanding electrochemically activated persulfate and its application to ciprofloxacin abatement. Environ. Sci. Technol., 52, 5875–5883. https://doi.org/10.1021/acs.est.8b00015

    Article  CAS  Google Scholar 

  • Michaud, P. A., Mahé, E., Haenni, W., Perret, A., & Comninellis, C. (2000). Preparation of peroxodisulfuric acid using boron-doped diamond thin film electrodes. Electrochem. Solid-State Lett., 3, 77–79.

    Article  CAS  Google Scholar 

  • Mojica, E. R. (2011). Antibiotics pollution in soil and water. Potential ecological and human health issues, 97-110.

  • Mutia, A. S., Ariyanto, T., & Prasetyo, I. (2022). Ciprofloxacin removal from simulated wastewater through a combined process of adsorption and oxidation processes using Fe/C adsorbent. Water Air Soil Pollut., 233, 146. https://doi.org/10.1007/s11270-022-05618-5

    Article  CAS  Google Scholar 

  • Nas, B., Dolu, T., & Koyuncu, S. (2021). Behavior and removal of ciprofloxacin and sulfamethoxazole antibiotics in three different types of full-scale wastewater treatment plants: A comparative study. Water Air Soil Pollut., 232, 127. https://doi.org/10.1007/s11270-021-05067-6

    Article  CAS  Google Scholar 

  • Nasseh, N., Taghavi, L., Barikbin, B., Nasseri, M. A., & Allahresani, A. (2019). FeNi3/SiO2 magnetic nanocomposite as an efficient and recyclable heterogeneous fenton-like catalyst for the oxidation of metronidazole in neutral environments: Adsorption and degradation studies. Compos. Part B, 166, 328–340.

    Article  CAS  Google Scholar 

  • Neta, P., Huie, R. E., & Ross, A. B. (1988). Rate constants for reactions of inorganic radicals in aqueous solution. J. Phys. Chem. Ref. Data, 17, 1027–1284.

    Article  CAS  Google Scholar 

  • Pan, F., Wang, R., & Englert, U. (2013). Competing protonation sites in sulfadiazine: Answers from chemistry and electron density. CrystEngComm, 15, 1164–1172. https://doi.org/10.1039/c2ce26633d

    Article  CAS  Google Scholar 

  • Panizza, M., & Cerisola, G. (2009). Direct and mediated anodic oxidation of organic pollutants. Chem. Rev., 109, 6541–6569.

    Article  CAS  Google Scholar 

  • Qi, C., Liu, X., Ma, J., Lin, C., Li, X., & Zhang, H. (2016). Activation of peroxymonosulfate by base: Implications for the degradation of organic pollutants. Chemosphere, 151, 280–288. https://doi.org/10.1016/j.chemosphere.2016.02.089

    Article  CAS  Google Scholar 

  • Rickman, K. A. M., & S. P. (2010). Kinetics and mechanisms of sulfate radical oxidation of β-lactam antibiotics in water. Chemosphere, 81, 359–365.

    Article  CAS  Google Scholar 

  • Rocha, J. B., Gomes, M. S., dos Santos, E. V., de Moura, E. M., da Silva, D. R., Quiroz, M. A., & Martínez-Huitle, C. A. (2014). Electrochemical degradation of Novacron Yellow C-RG using boron-doped diamond and platinum anodes: Direct and indirect oxidation. Electrochim. Acta, 419-426.

  • Schafhauser, B. H., Kristofco, L. A., de Oliveira, C. M. R., & Brooks, B. W. (2018). Global review and analysis of erythromycin in the environment: Occurrence, bioaccumulation and antibiotic resistance hazards. Environ. Pollut., 238, 440–451. https://doi.org/10.1016/j.envpol.2018.03.052

    Article  CAS  Google Scholar 

  • Septian, A., & Shin, W. S. (2021). Oxidative removal of sulfadiazine using synthetic and natural manganese dioxides. Environ. Technol., 42, 2254–2266. https://doi.org/10.1080/09593330.2019.1699963

    Article  CAS  Google Scholar 

  • Studer, A., & Curran, D. P. (2014). The electron is a catalyst. Nat. Chem., 6, 765–773. https://doi.org/10.1038/nchem.2031

    Article  CAS  Google Scholar 

  • Sun, J., Wang, Q., Zhang, J., Wang, Z., & Wu, Z. (2018). Degradation of sulfadiazine in drinking water by a cathodic electrochemical membrane filtration process. Electrochim. Acta, 277, 77–87.

    Article  CAS  Google Scholar 

  • Wang, J., & Wang, S. (2018). Activation of persulfate (PS) and peroxymonosulfate (PMS) and application for the degradation of emerging contaminants. Chem. Eng. J., 334, 1502–1517. https://doi.org/10.1016/j.cej.2017.11.059

    Article  CAS  Google Scholar 

  • Wang, Y., Zeng, X., & Meng, Y. (2021). Aqueous oxidation degradation of ciprofloxacin involving hydroxyl and sulfate radicals: A computational investigation. Computational and Theoretical Chemistry, 1204. https://doi.org/10.1016/j.comptc.2021.113427

  • Wu, S., Yang, C., Lin, Y., & Cheng, J. J. (2022). Efficient degradation of tetracycline by singlet oxygen-dominated peroxymonosulfate activation with magnetic nitrogen-doped porous carbon. J. Environ. Sci. (China), 115, 330–340. https://doi.org/10.1016/j.jes.2021.08.002

    Article  CAS  Google Scholar 

  • Xue, Y., Wang, Z. H., Bush, R., Yang, F., Yuan, R. X., Liu, J. S., Smith, N., Huang, M. H., Dharmarajan, R., & Annamalai, P. (2021). Resistance of alkyl chloride on chloramphenicol to oxidative degradation by sulfate radicals: Kinetics and mechanism. Chem. Eng. J., 415. https://doi.org/10.1016/j.cej.2021.129041

  • Yang, S.-Q., Cui, Y.-H., Liu, Y.-Y., Liu, Z.-Q., & Li, X.-Y. (2018). Electrochemical generation of persulfate and its performance on 4-bromophenol treatment. Sep. Purif. Technol., 207, 461–469. https://doi.org/10.1016/j.seppur.2018.06.071

    Article  CAS  Google Scholar 

  • Zhang, B.-T., Zhang, Y., Teng, Y., & Fan, M. (2014). Sulfate radical and its application in decontamination technologies. Crit. Rev. Environ. Sci. Technol., 45, 1756–1800. https://doi.org/10.1080/10643389.2014.970681

    Article  CAS  Google Scholar 

  • Zhang, Y., Kang, W., Yu, H., Chen, S., & Quan, X. (2020). Electrochemical activation of peroxymonosulfate in cathodic micro-channels for effective degradation of organic pollutants in wastewater. J. Hazard. Mater., 398, 122879. https://doi.org/10.1016/j.jhazmat.2020.122879

    Article  CAS  Google Scholar 

  • Zhou, Y., Jiang, J., Gao, Y., Ma, J., Pang, S. Y., Li, J., Lu, X. T., & Yuan, L. P. (2015). Activation of peroxymonosulfate by benzoquinone: A novel nonradical oxidation process. Environ. Sci. Technol., 49, 12941–12950. https://doi.org/10.1021/acs.est.5b03595

    Article  CAS  Google Scholar 

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Acknowledgement

Special thanks are due to the instrumental or data analysis from Analytical and Testing Center, Northeastern University, China.

Funding

This work was supported by the Fundamental Research Funds for the Central Universities (N2124007-1).

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Authors and Affiliations

  1. Department of Environmental Engineering, School of Resource & Civil Engineering, Northeastern University, Shenyang, 110819, China

    Dong Ma, Xupicheng Ren, Bo Zhang & Xiaomin Hu

  2. Institute for Frontier Technologies of Low-Carbon Steelmaking, Northeastern University, Shenyang, 110819, China

    Yan Zhao

  3. Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau, Macau, 999078, China

    Guangsheng Qian

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Contributions

Conceptualization and methodology: Dong Ma, Xiaomin Hu; material preparation, data collection, and analysis: Dong Ma, Xupicheng Ren, and Bo Zhang; writing - original draft preparation: Dong Ma; writing - review and editing: Guangsheng Qian; funding acquisition: Yan Zhao; resources: Xiaomin Hu; supervision: Xiaomin Hu. All authors read and approved the final manuscript.

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Highlights

• A novel strategy for the applications of small power supply in electro-oxidation

• CVs indicated that PMS electrolyte could depress the overpotential

• ESR tests confirmed that •OH, \({\mathrm{SO}}_4^{\bullet -}\), and 1O2 all generated in low current system

• Ciprofloxacin reaction pathways were speculated by MS spectra and DFT calculation

Supplementary Information

ESM 1:

Details of the ESR instrumental parameters, analytical methods of byproducts and HPLC-MS/MS spectra, Butler-Volmer equation, apparent rate constants for the oxidation of antibiotics, rate constants for the reaction of quenching agents with reactive oxygen species, diagram of experimental device, quenching experiments, effect of sulfate concentration and interelectrode distance on degradation rates, cyclic voltammetry. (DOCX 2407 kb)

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Ma, D., Ren, X., Zhang, B. et al. Understanding the Assisting Role of PMS in Low Current Electrochemical Processes for Degradation of Antibiotics. Water Air Soil Pollut 234, 253 (2023). https://doi.org/10.1007/s11270-023-06259-y

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