Underlying mechanisms for natural organic matters mediated aerobic ciprofloxacin transformation by sulfide

Abstract

Natural organic matters (NOMs), sulfide and organic pollutants such as antibiotics might all coexist in natural water environments. However, the impact of NOMs on aerobic organic pollutants transformation by sulfide is still poor understood. In this study, it observed that 50 ppm (14.55–23.05 mg C L−1) of various NOMs could facilitate the aerobic transformation of antibiotic ciprofloxacin (CIP) by sulfide, and the pseudo first order reaction rate k ranged from 3.24 × 10−4 to 27.6 × 10−4 min−1 for different sources of NOMs compared with 1.36 × 10−4 min−1 for control one at pH 6.5. Moreover, sulfide oxidation process would play important roles for the aerobic CIP transformation, while transformation of other intermediate sulfur species did not directly promote CIP transformation. Electron paramagnetic resonance (EPR) and quenching experiments indicated that singlet oxygen (1O2) was the main active specie playing important roles in the process of aerobic CIP transformation with presence of sulfide and NOMs. Furthermore, carbonyl groups of the NOMs, especially the quinones, were demonstrated to play a critical role to promote the transformation of intermediate H2O2 to 1O2. This study provides a better understanding for the NOMs-mediated aerobic organic pollutants transformation by sulfide in aqueous environments.