Ciprofloxacin degradation in photo-Fenton and photo-catalytic processes: Degradation mechanisms and iron chelation Ardhendu Sekhar Giri 1 , Animes Kumar Golder 2, ⁎ 1. Department of Chemical Engineering, Indian Institute of Science Education and Research Bhopal, MP, 462066, India 2. Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam, 781039, India ARTICLE INFO ABSTRACT Article history: Received 7 March 2018 Revised 21 August 2018 Accepted 12 September 2018 Available online 27 September 2018 Ciprofloxacin (CIP) is a broad spectrum synthetic antibiotic drug of fluoroquinolones class. CIP can act as a bidentate ligand forming iron complexes during its degradation in the photo- Fenton process (PFP). This work investigates on PFP for the degradation of CIP to understand the formation mechanism and stability of iron complexes under ultraviolet (UV)-light illumination. A comparison was made with the UV-photocatalysis (UV/TiO 2 ) process where CIP doesn't form a complex. In PFP, the optimal dose of Fe 2+ and H 2 O 2 were found to be 1.25 and 10 mmol/L with pH of 3.5. An optimal TiO 2 dose of 1.25 g/L was determined in the UV/TiO 2 process. Maximum CIP removal and mineralization efficiency of 93.1% and 47.3% were obtained in PFP against 69.7% and 27.6% in the UV/TiO 2 process. The mass spectra could identify seventeen intermediate products including iron-CIP complexes in PFP, and only seven intermediate products were found in the UV/TiO 2 process with a majority of common products in both the processes. The proposed mechanism supported by the mass spectra bridged the routes of CIP cleavage in the PFP and UV/TiO 2 process, and the decomposition pathway of Fe 3+ -CIP chelate complexes in PFP was also elucidated. Both in PFP and UV/TiO 2 processes, the target site of HO • radical attack was the secondary-N atom present in the piperazine ring of the CIP molecule. The death of Escherichia coli bacteria was 55.7% and 66.8% in comparison to the control media after 45 min of treatment in PFP and UV/TiO 2 process, respectively. © 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Keywords: Advanced oxidation processes Antibiotic decomposition Iron chelation Antimicrobial activity Introduction The occurrence of pharmaceutical discards in the environment is escalating since last few years. They are abundant in liquid and solid wastes in the vicinity of the production and bulk administration sites such as health centers (Ternes, 2003; Zhang et al., 2017; Rao and Golder, 2016). Ciprofloxacin (CIP) is a fluoroquinolone group broad-spectrum antibiotic drug. It works through the inhibition of protein synthesis of both gram-positive and gram-negative bacteria. CIP was globally prescribed in the order of 18.7 million defined daily doses in the year of 2010 (Schwabe and Paffrath, 2011). CIP could exist in target organisms even up to 72% of non-metabolized forms (Ternes, 2003). In a bulk drug production site in Patancheru, Hyderabad (India), the concentration of CIP obtained in disposed water was as high as the toxicity limit to some bacteria (Larsson et al., 2007). In fact, CIP residues are frequently found in hospital wastewater, sewage treatment plant effluent, and surface water (Li et al., JOURNAL OF ENVIRONMENTAL SCIENCES 80 (2019) 82 – 92 ⁎ Corresponding author. E-mail: animes@iitg.ernet.in. (Animes Kumar Golder). https://doi.org/10.1016/j.jes.2018.09.016 1001-0742 © 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Available online at www.sciencedirect.com ScienceDirect www.elsevier.com/locate/jes