Release of manganese and in situ regeneration of manganese dioxide during the degradation of ciprofloxacin

Abstract

Manganese ion, a by-product of the degradation of antibiotics by manganese dioxide (MnO2), may be released from the MnO2 surface into water; this loss of MnO2 is undesirable for its use. Therefore, the release behavior of manganese from MnO2 was investigated using ciprofloxacin (CIP) as a target antibiotic, and an effective way to regenerate the MnO2 was sought. It was found that the release of manganese under acidic conditions exhibited a negative correlation with pH and a positive linear relation with MnO2 dosage and CIP concentration. An exponential kinetic model accurately predicted the release behavior, even in the presence of Ca2+, Mg2+, Na+, and K+. The use of MnO2 in filters indicated that controlling the release of manganese was crucial for the regeneration of MnO2. Analyses by BET, SEM, XRD, and XPS revealed that both a chemical oxidizing agent (KMnO4) and bacteria could improve the surface area, change the surface morphology, weaken crystallinity, and maintain the distribution of manganese valence states, thereby favoring antibiotic degradation. However, the use of bacteria, which could continuously control the release of manganese in situ, was demonstrated to be convenient and cost-effective. It was found that the bacteria did not generate antibiotic-resistant genes.