Comparative Evaluation of Photo-Chemical AOPs for Ciprofoxacin Degradation: Elimination in Natural Waters and Analysis of pH Effect, Primary Degradation By-Products, and the Relationship with the Antibiotic Activity

Abstract

In this work, ciprofloxacin (CIP) degradation is investigated using different photo-chemical advanced oxidation processes (AOPs): Fe2+/H2O2/UV, TiO2/UV, and H2O2/UV. At natural pH, direct oxidation at the photo-generated holes showed to be the main pathway during TiO2/UV process, while H2O2/UV and Fe2+/H2O2/UV degradation mainly occurred by hydroxyl radical attack. The identification of degradation by-products confirmed the differences in the degradation pathways. Water matrix effects were also investigated by evaluating the influence of the initial pH and testing CIP degradation in mineral natural water and distilled water. Significant differences were observed associated to the pH, the H2O2/UV system being the less affected process. Natural water showed to be an inhibitor medium for the tested photo-chemical processes. Interestingly, H2O2/UV system showed again to be not considerably affected by the natural water matrix. Additionally, degradation extent of treated solutions was determined by the mineralization level (TOC removal) and the antimicrobial activity (AA) elimination using Staphylococcus aureus and Escherichia coli as probe microorganisms. Despite mineralization was no reached in any case, AA elimination was promoted by all processes suggesting the formation of by-products with non-antibiotic character. However, due to the particular degradation pathway, interesting differences were observed according to the type of bacteria when TiO2 photo-catalysis was used.