High-level chloramphenicol degradation in mariculture wastewater via cathodic nitro-reduction in a single-chamber bioelectrochemical system.

The aim of this study was to investigate the mechanism of high-level chloramphenicol (CAP) degradation in mariculture wastewater using a single chamber bioelectrochemical system (BES). The reactor was assembled with carbon-brush electrodes and operated with sea mud as inoculum. Nearly complete removal of 200 mg/L CAP was achieved within 36 h when 2 g/L glucose was supplied as a co-substrate. With 200 mg/L CAP as the sole carbon source, BES at the close circuit achieved 28 ± 3% higher CAP removal than that at the open circuit within 72 h. CAP removal declined from 100 ± 5% to 45 ± 4% as the initial concentration increased from 200 to 600 mg/L within 36 h. High CAP concentration markedly inhibited sulfate-reducing bacteria (SRB), reducing the relative abundance of Desulfobulbus from 28.7% to < 0.5%, and decreasing sulfate removal from 90 ± 5% to < 56 ± 3% compared with the control. Nitro-reduction of CAP at the cathodic biofilm was determined as the predominant pathway among the three degradation routes in the BES. Metagenomic analysis revealed that 200 mg/L CAP significantly inhibited both multidrug efflux pump genes and key operons involved in dissimilatory sulfate reduction in the cathodic biofilm. Our results could be useful for eliminating high concentrations of antibiotic contaminants from seawater.