Cathodic degradation of antibiotics: Characterization and pathway analysis

Abstract

Antibacterial activity elimination a b s t r a c tAntibiotics in wastewaters must be degraded to eliminate their antibacterial activity before discharging into the environment. A cathode can provide continuous electrons for the degradation of refractory pollutants, however the cathodic degradation feasibility, efficiency and pathway for different kinds of antibiotics is poorly understood. Here, we investigated the degradation of four antibiotics, namely nitrofurazone (NFZ), metronidazole (MNZ), chloramphenicol (CAP), and florfenicol (FLO) by a poised cathode in a dual chamber electrochemical reactor. The cyclic voltammetry preliminarily proved the feasibility of the cathodic degradation of these antibiotics. The cathodic reducibility of these antibiotics followed the order of NFZ > MNZ > CAP > FLO. A decreased phosphate buffered solution (PBS) concentration as low as 2 mM or utilization of NaCl buffer solution as catholyte had significant influence on antibiotics degradation rate and efficiency for CAP and FLO but not for NFZ and MNZ. PBS could be replaced by Na 2 CO 3 eNaHCO 3 buffer solution as catholyte for the degradation of these antibiotics. Reductive dechlorination of CAP proceeded only after the reduction of the nitro group to aromatic amine. The composition of the degradation products depended on the cathode potential except for MNZ. The cathodic degradation process could eliminate the antibacterial activity of these antibiotics. The current study suggests that the electrochemical reduction could serve as a potential pretreatment or advanced treatment unit for the treatment of antibiotics containing wastewaters.© 2015 Elsevier Ltd. All rights reserved. IntroductionPharmaceuticals and personal care products (PPCPs), as emerging contaminants, have attracted growing attention worldwide in recent years, which would pose potential threats to aquatic life and even human health (Liu and Wong, 2013 w a t e r r e s e a r c h 7 2 ( 2 0 1 5 ) 2 8 1 e2 9 2http://dx

Response of antimicrobial nitrofurazone-degrading biocathode communities to different cathode potentials

“…CV analysis preliminarily indicated that almost no reductive current was recorded for the enrichment within 72 h, which was quite close to the cyclic voltammogram of PBS control. In contrast, NFZ containing medium (50 mg/L) showed three obvious reduction peaks those were consistent with our previous study (Kong et al, 2015a). CV result indirectly showed the added NFZ could be efficiently reduced by the acclimated NFZ-reducing consortium (Fig.…”

“…Though the degradation rate, efficiency and degree of NFZ were obviously affected by different cathode potentials, three mainly identified degradation products including AMH, AMN and NFF were consistent (Kong et al, 2015a). In this study, the three products of both the biocathode and open circuit biofilms were the same as previously identified based on the HPLC peak sequence and retention time.…”

“…Interestingly, these three main products (retention time at 3.2 min, 3.5 min and 3.6 min respectively) were the same as the NFZ reduction products from the pure electrochemical process. They were preliminarily identified as NFF, AMN and AMH (Kong et al, 2015a). These results suggest that microbial nitroreductase and N-N bond reductase catalyze the reduction of NFZ.…”

“…The concentrations of NFZ and its three main products, [(5-hydroxyamino-2-furyl)-methyl]-hydrazinecarboxa mide (AMH), [(5-amino-2-furyl)-methylene]-hydrazinecarboxa mide (AMN) and N-N fraction product (5-nitro-2-furyl) methanamine (NFF) were measured using a reverse-phase HPLC system with a UV detector (model e2695, Waters Co., Milford, MA, USA) (Kong et al, 2015a). The NFZ reduction products were identified by a HPLC-QTOFMS as described recently (Kong et al, 2015a). …”

“…The BES reactors were constructed by assembling two equalsized Lexan plates (4 Â 4 Â 3 cm 3 ) with a cylindrical cavity (3 cm in diameter and 4 cm in length) and two equal-sized Lexan plates (4 Â 4 Â 1 cm 3 ) as outside baffles and separated by a cation exchange membrane (Ultrex CMI-7000, Membranes International, Ringwood, NJ, U.S.) as described elsewhere (Kong et al, 2015a). The internal volume of each chamber was 28 mL.…”