A novel electrochemical oxidation-methanogenesis system for simultaneously degrading antibiotics and reducing CO2 to CH4 with low energy costs

A novel electrochemical oxidation-methanogenesis (EO-M) system was proposed for the first time to simultaneously achieve antibiotic degradation and a bioelectrochemical conversion of CO2 to CH4 with low energy costs. A dual-chamber system was installed with an antimony-doped tin oxide anode (Ti/SnO2-Sb) for the electrocatalytic generation of hydroxyl radicals to degrade ciprofloxacin (CIP), and a CO2-reducing methanogenic biocathode was enriched based on a three-dimensional (3D) graphitized granular activated carbon (GGAC) for microbial electromethanogenesis. The anode achieved removal efficiencies as high as 99.99% and 90.53% for CIP (14 mL, 50 mg L-1) and the chemical oxygen demand (COD, 89 mg L-1), respectively. The biocathode was rapidly enriched within 15 days and exhibited a methane production rate that stabilized at 15.12 +/- 1.82 m(3) m(-3) d(-1); additionally, the cathodic coulombic efficiency reached 71.76 +/- 17.24%. The energy consumption of CIP degradation was reduced by 3.03 Wh L-1 compared to that of a single electrochemical oxidation system due to the lower cathodic overpotential of CO2 bioelectrochemical reduction in the EO-M system. A detailed analysis of the biofilm evolution in the 3D biocathode during the start-up process demonstrated that the enhanced absorption of extracellular polymeric substances by the GGAC cathode accelerated the enrichment of methanogens and induced the formation of methanogens with a large number of flagella. An analysis of the microbial community showed that a high relative abundance of Methanobacterium movens could promote a flagella-mediated direct electron transfer of the biocathode, eventually reducing the cathodic overpotential and energy costs of the EO-M system. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

A novel EO-M system was proposed for simultaneous antibiotic degradation and bioelectrochemical conversion of CO2 to CH4, with a dual-chamber system comprising an anode for electrocatalytic generation of hydroxyl radicals and a CO2-reducing methanogenic biocathode. The system achieved high removal efficiencies for antibiotic and COD, and the enriched biocathode exhibited stable methane production and high coulombic efficiency. The energy consumption was reduced compared to a single electrochemical oxidation system, attributed to the lower cathodic overpotential in the EO-M system.