Enhanced Removal of Metronidazole from Aqueous Solutions via Bioelectrochemical Systems

Abstract

Metronidazole (MNZ) is a typical nitroimidazole antibiotic that often enters the environment via wastewater, and the demand for its degradation in wastewater is increasing in view of the potential environmental risks. Bioelectrochemical systems can effectively improve the degradation of refractory pollutants and are environmentally acceptable. In this study, the MNZ degradation performance of a bioelectrochemical system was investigated. The majority of MNZ in aqueous solutions could be degraded rapidly (within 180 min) at a current of 1 mA in the bioelectrochemical system, and its removal followed the pseudo–first-order kinetic model. The MNZ degradation rate constant in the bioelectrochemical system was nearly eight and two times higher than those in open circuit and nonbiological cathode systems, respectively. Increasing the electric current within a certain range could accelerate the degradation of MNZ, and increasing the initial MNZ concentration led to a slight reduction of the degradation efficiency. Furthermore, the activity of the electrode biofilm was examined, and the microbes were found to be in an active state. High-throughput sequencing analysis revealed that the microbial community structure varied greatly among the tested systems. Finally, the possible degradation mechanism of MNZ in bioelectrochemical systems with the stimulation of electric current was proposed. The synergetic biodegradation of the biofilm and electrochemistry may be responsible for MNZ degradation. These results indicate that bioelectrochemical systems have significant potential for the efficient treatment of wastewater contaminated with antibiotics, which would facilitate a more comprehensive understanding of the contaminant removal process.