Complete Degradation and Detoxification of Ciprofloxacin by a Micro-/Nanostructured Biogenic Mn Oxide Composite from a Highly Active Mn2+-Oxidizing Pseudomonas Strain

Abstract

Ciprofloxacin (CIP), as a representative broad-spectrum antibiotic, poses a major threat to human health and the ecological environment as a result of its abuse and emissions. In this study, a highly active Mn2+-oxidizing bacterium, Pseudomonas sp. CCTCC M2014168, was induced to form micro-/nanostructured biogenic Mn oxide (BMO) aggregates through continuous culturing with 1 mmoL−1 Mn2+. Following the characterization of Mn4+ oxides and the micro-/nanostructures by scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction assays, the BMO composites were subjected to CIP degradation and detoxification in laboratory trials. High-performance liquid chromatograph (HPLC) analysis identified that the BMO composites were capable of completely degrading CIP, and HPLC with a mass spectrometer (LC/MS) assays identified three intermediates in the degradation pathway. The reaction temperature, pH and initial ciprofloxacin concentration substantially affected the degradation efficiency of CIP to a certain extent, and the metal ions Mg2+, Cu2+, Ni2+ and Co2+ exerted significant inhibitory effects on CIP degradation. A toxicity test of the degradation products showed that CIP was completely detoxified by degradation. Moreover, the prepared BMO composite exhibited a high capacity for repeated degradation and good performance in continuous degradation cycles, as well as a high capacity to degrade CIP in real natural water.