Performance and degradation mechanism of a sequencing batch biofilm reactor combined with an electrochemical process for the removal of low concentrations of cefuroxime

Abstract

A combination of biochemistry and electrochemistry was used as a strategy to remove antibiotics present in low concentrations at the laboratory scale. Experiments showed that the removal of antibiotics could be improved to 98% in the bio-electrochemical system (BES). The optimal operating conditions were a pH of 7, initial cefuroxime (CXM) concentration of 0.5mg·L−1, reaction period of 12h, aeration intensity of 15.8m3·m−2·h−1, and influent COD concentration of 1000mg·L−1. The chemical oxygen demand (COD) and ammonia-nitrogen (NH3-N) removals were also improved to above 90% and 80%, respectively. A conventional sequencing batch biofilm reactor (SBBR) process was simultaneously operated for comparison. Simulation results indicated that the degradation followed first-order kinetics in the SBBR, BES, and electrochemical system (ES). Through further studies and SEM observation, we found that a high current electric field would destroy microbes. Conversely, the degradation of CXM was promoted by a low current electric field. In addition, cyclic voltammetry (CV) analysis was performed and we found that the degradation contained two oxidation reactions and one reduction reaction. According to the intermediates identified by LC–MS, we inferred that the degradation pathway included breakage of β-lactam rings and organic oxidations. In conclusion, the integrated process considerably enhanced the synergistic effects of biochemistry and electrochemistry for the removal of specific contaminants.